Composites from poly (lactic acid) and bleached chemical fibres: Thermal properties

• Poly (lactic acid) (PLA) reinforced with bleached kraft soft wood (BKSW) biocomposites with fibre content up to 35% were processed by kinetic mixing and injection moulding. The cellulosic filler was a commercial chemical bleached kraft soft wood pulps composed of well individualized fibres free from lignin with diameter about 20 μm and length within micron scale. The effect of fibre addition on the thermal properties of composites was investigated using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermal gravimetric analysis (TGA) and thermo-mechanical analysis (TMA). In a previous work, it was demonstrated that fibre inclusion on PLA enhanced the modulus as well as the strength. Fibre addition promoted the crystallization of PLA by favouring the heterogeneous nucleation and accelerating the crystallization kinetic, without adversely altering the thermal stability. The DMA analysis confirmed the strong stiffening effect brought by the addition of fibres at the glassy as well as the rubbery domains. The presence of fibres had also a beneficial effect on the dimension stability by lowering the thermal expansion coefficient of composites.

Recycled fibers for fluting production: The role of lignocellulosic micro/nanofibers of banana leaves

• Recycling is becoming one of the main activities of the papermaking industry to palliate the consumption of natural resources. However, with the recycling process, the fibers experience structural damages due to the hornification phenomena and the mechanical refining. The present work aims to compare the effect of mechanical refining during recycling cycles, to recover the original mechanical properties of paper with the incorporation of lignocellulosic micro/nanofibers (LCMNF) from banana leaf residue. For that, industrial fluting paper was submitted to a recycling cycle and the effect of the increasing intensity of PFI-refining was compared versus the incorporation of LCMNF additions ranging from 1.5 to 4.5 wt%. In addition, with the objective of demonstrating that the proposed process could be plausible at a large scale, process water with high conductivity and charge density was used for comparison with tap water, usually used at laboratory scale. Results showed that the incorporation of 1.5 wt% of LCMNF was enough to recover the original properties of fluting paper (a breaking length value greater than 3443 m) with a low impact in pulp drainability (54 ºSR). At the same time, no structural damages were caused to the fibrous compounds, implying that the life span of paper products can be successfully increased. Higher dosages lead to papers with significantly improved mechanical properties, opening the opportunity to adopt environmental friendly strategies such as decreasing basis weight or, on the other hand, to reach new market niches by maintaining the basis weight.

Approaching a new generation of fiberboards taking advantage of self lignin as green adhesive

• This study describes the use of lignin as natural adhesive for the production high density fiberboards (HDF) made from wheat straw. In the present work, this agricultural residue was used to produce thermomechanical pulp and the used lignin was obtained from the spent liquors generated in the same process. A hot pressing process was conducted to manufacture these fiberboards and different percentages of this green adhesive were targeted. The wheat straw raw material and its pulp were characterized. Apart from that, the chemical composition and the thermal properties of the lignin sample were evaluated. Physical and mechanical properties were assessed and the results revealed that the panels made only with wheat straw fibers had a flexural strength value (52.79 MPa) even above the value corresponding to the commercial HDF (41.70 MPa). Also, results showed that the incorporation of soda-lignin lead to lignocellulosic composites that, as lignin content was increased (from 0 to 15%), mechanical properties were enhanced. The highest mechanical performance was reached for fiberboards at 15% of lignin with a flexural strength of 96.81 MPa, a flexural modulus of 3.55 GPa, and finally an internal bond of 1.46 MPa.

Key role of anionic trash catching system on the efficiency of lignocellulose nanofibers in industrial recycled slurries

• The processing of recycled paper into packaging materials is becoming one of the most important activities of paper mills. However, the use of recycled paper as a raw material causes an important increase of dissolved colloidal substances in industrial waters, known as anionic trash, which greatly increases water conductivity and cationic demand disturbing the function of commonly used retention agents (cationic starch, cationic polyacrylamides). On the other hand, several investigators showed that lignocellulosic nanofibers (LCNF) can be used as reinforcement in papermaking, but their retention can be affected by anionic trash. This work aims to study the technical viability of the application of triticale straw lignocellulose nanofibers in recycled fiber suspensions at industrial scale. For this purpose, a complex retention system of LCNF was proposed to improve the reinforcement efficiency of LCNF. Results show that, with the addition of only 1.5% (w/w) of LCNF, it is possible to fulfill the physical–mechanical requirements of the commercial test liner, and the addition of 4.5% of LCNF would allow the reduction of basis weight and additives or the development of applications with higher mechanical requirements.

Mechanical and chemical dispersion of nanocelluloses to improve their reinforcing effect on recycled paper

• The use of nanocelluloses as strength-enhancing additives in papermaking is widely known since both cellulose nanofibers (CNF) and nanocrystals (CNC) present similar composition than paper but their exceptional properties in the nanometer scale confers a paper quality enhancement. However, some agglomeration problems in CNF and CNC through hydrogen bonding cause a lower improvement of mechanical properties of paper. Therefore, a better dispersion of both nanocelluloses can maximize their effect on paper properties, thus reducing the needed dose to get the same increment in tensile strength and then reducing material costs. To ease the implementation of these nanocelluloses in the production process of recycled paper, typically used operations of these industries have been used. Among them, those devoted to improve the homogeneous mixture of nanocellulose in the pulp suspension have been assessed. Firstly, pulping conditions were studied, including pulping time, temperature and need for soaking as variables. Secondly, some dispersing agents used in papermaking were considered, studying the effect of different types and doses. The highest tensile strength of paper was achieved by applying long pulping times (60 min), getting increments up to 30% with the use of soaking and polyacrylamide as retention system. However, with the use of a low dose of a dispersing agent (0.003%), tensile index can be still increased up to 20.6% avoiding these long times. This study can be of great interest of those researchers trying to implement the use of nanocelluloses as strength additive in papermaking.

Towards a new generation of functional fiber-based packaging: cellulose nanofibers for improved barrier, mechanical and surface properties

• The present work shows the suitability of using industrial fluting papers as raw material for the development of four different substrates, enzymatically refined and/or containing cellulose nanofibers (CNF) in bulk. These four substrates were deeply studied and treated with different coating formulations, containing CNF, polyvinyl alcohol (PVA), native starch and alkyl ketene dimer, with the purpose of evaluating the benefits of using fiber-based packaging paper with improved mechanical, physical and barrier properties. The results showed that if CNF are coated in combination with PVA the tensile properties of paper can be significantly improved, as well as the grease resistance, whereas the air permeability and water vapor transmission rate decrease. The obtained papers present interesting vapor and air barrier properties, at the same time that unconceivable limits of breaking length are achieved (6.44 km). In addition, when a second layer of alkyl ketene dimer was coated on both sides of paper, the water contact angle was significantly improved, being higher than 115°. Overall, the present work shows the feasibility of recycled fibers for the production of high value-added papers that can be used for packaging purposes due to their improved barrier and mechanical properties, and contributes therefore for the bio-based circular economy.

Combined effect of sodium carboxymethyl cellulose, cellulose nanofibers and drainage aids in recycled paper production process

• The present work shows the suitability of using recovered cardboard boxes for the development of high-performance papers through the use of cellulose nanofibers (CNF) and sodium carboxymethyl cellulose (CMC-Na). CNF were prepared by enzymatic hydrolysis using bleached kraft hardwood pulp, while a commercial grade of CMC-Na was used. Both were added in bulk together with polyethylenimine (PEI) as wet-end additive to improve pulp drainability. The combination of 3 wt% CNF and 7.5 wt% CMC-Na double the breaking length of paper. In addition, the use of 0.4 wt% of PEI significantly decreased the Schopper – Riegler degree, while mechanical properties remained almost at the same level. It was found that it is possible to recover and even increase the properties of recycled papers, with the added advantage that no structural damages were caused on the fibres, increasing the life span and recyclability of paper products.

Cellulose nanofibers from residues to improve linting and mechanical properties of recycled paper

• The production of high filler-loaded recycled papers is often affected by high values of linting and low values of strength. In the first case, the accumulation of lint particles from paper’s surface on the printing blanket affects the quality of the printed paper and the pressroom’s productivity. In the second case, increasing the use of fillers and recycling cycles lead to poor paper strength. Cellulose nanofibers (CNFs) are receiving a great deal of attention due to their potential as a reinforcement aid for high filler-loaded papers through filler–fiber interaction and interfiber bonding. It is already proven that high quality CNFs can reduce linting, although their industrial application is limited by their high production cost. The objective of this research is, therefore, to quantify the effect of applying lower grade, more sustainable CNFs on linting phenomena and on the mechanical properties of recycled papers. Eucalyptus, pine and triticale residues were used as cellulose sources, and the CNFs were produced minimizing the chemical pretreatment before homogenization. Addition of 3 wt% of CNFs from pine residues into the recycled paper with 15.7 wt% of total filler reduced linting by 40% and increased tensile strength by 15.1%; further improvements on linting and mechanical properties were achieved at 5 wt%. Moreover, the increase in drainage time can be overcome by the addition of a retention aid, in this case a coagulant-cationic polyacrylamide-bentonite system, commonly used in paper mills.

Extending the value chain of corn agricultura by evaluating technical feasibility and the quality of the interphase of chemo-termomechanical fiber from corn stover reinforced polypropylene biocomposites

• With the increasing concerns towards the environment, industries are interested in substituting glass fibers by natural fiber. Nonetheless, filaments or strands from jute, hemp or abaca, are mainly used as reinforcement. Such fibers are, in some cases, more expensive than the glass fibers that are replacing. Grain corn harvest creates a huge amount of by-products in the shape of corn stover. These stover usually remains in the field to be incinerated, or recovered to prepare feedstuff, or bedding for livestock. Besides, corn is a globally spread crop, and consequently, corn stover becomes available as renewable source for reinforcing fibers. The aim and main novelty of the research is transforming a by-product as corn stover into a cheap source of reinforcing fibers to obtain competitive biocomposites. To do so, such biocomposites must show mechanical properties comparable to those materials currently present in the market. In this work, biocomposites reinforced with natural fibers from corn stover are used as reinforcement of polypropylene; their mechanical properties are investigated and compared. Moreover, the interphase between the reinforcement and the matrix is also modelled by means of the Kelly and Tyson equation to assess its quality.

Macro and micromechanical preliminary assessment of the tensile strength of particulate rapeseed sawdust reinforced polypropylene copolymer biocomposites for its use as building material

• The growing environmental awareness promotes the research of greener and more sustainable materials for their use in building materials. Polyolefin-based wood plastic composites (WPCs) have attracted the attention of researchers in the last decades mainly due to their improved mechanical properties, low weight and low cost. On the other hand, rapeseed is one of the most extended harvests in the world and their production is expected to increase in the next years, according to FAO (Food and Agriculture Organization). Rapeseed is mainly used for the production of biodiesel, and moving from an oil-based economy to a bio-based economy will presumably involve increases of rapeseed production. Its harvest produces high amount of agroforestry residue in the shape of integral stems which can be exploited as polymer reinforcing element, although very little information is found in the literature in this respect. In this work, the viability of rapeseed sawdust reinforced polypropylene copolymer composites was analysed regarding its mechanical tensile strength. Besides, the coupling agent percentage to ensure the best performance was also studied. The tensile strength of the produced composites has been modelled using well-known micromechanical models which allow the determination of the fibre and matrix contributions to the composite strength. The results showed that competitive green composite materials can be obtained using a byproduct of rapeseed harvesting.

Macro and micro-mechanics behavior of stiffness in alkaline treated hemp core fibres polypropylene-based composites

• Traditionally, glass fibre has been used as plastic reinforcement whenever mechanical properties of a matrix, like stiffness, do not meet the specifications. However, current tendencies try to replace glass fibres by more sustainable fibres to obtain eco-friendlier products. Natural fibres show comparatively good physical and mechanical properties and, unlike glass fibres, come from renewable resources and are recyclable and sustainable. In this work, hemp straw discarded from hemp manufacturing was used as reinforcement in polypropylene composites. One drawback associated to hemp straw is its high lignin content that reduces its reinforcing potential. Therefore, a soft alkaline treatment was employed to adjust the lignin contents. In this work, the evolution of the Young's modulus with the NaOH treatment is assessed and discussed. Intrinsic Young's moduli of hemp straw fibres at different alkaline conditions were determined by Hirsch model. Finally, Tsai-Pagano and Halpin-Tsai equations allowed the prediction of the theoretical Young's modulus of the composites. The results showed the competitiveness of a by-product reinforced composite in front of commodity materials.

High electrical and electrochemical properties in bacterial cellulose/polypyrrole membranes

• The purpose of the current work was to produce conducting electroactive membranes from bacterial cellulose (BC) coated with polypyrrole (PPy) via in situ chemical polymerization of pyrrole at 4 °C using FeCl3 as oxidant agent. The electrical conductivity, tensile, thermal and electrochemical properties of BC-PPy membranes were investigated. The results revealed that the uniformly coating of PPy nanoparticles on the surface of BC template achieved high electrical conductivity of 3.39 S cm−1 and a specific capacitance of 191.94 F g−1 at 5 mv s−1 scan rate. The high conductivity and specific capacitance of the present BC-PPy membranes opens new potential applications for BC in various fields as biosensors, flexible electronics, or energy storage devices.

Smart nanopaper based on cellulose nanofibers with hybrid PEDOT: PSS/polypyrrole for energy storage devices

• In the current work, flexible, lightweight, and strong conductive nanopapers based on cellulose nanofibers (CNFs) with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and/or polypyrrole (PPy) were prepared by following a mixing and in situ chemical polymerization method. A successful homogeneous coating of PEDOT:PSS on cellulose nanofibers occurred by means hydrogen-bonding interactions between the hydroxyl functionalized CNF and the electronically charged PEDOT:PSS, as shown by FTIR spectra. The electrical conductivity and the specific capacitance of CNF-PEDOT:PSS nanopapers were 2.58 S cm−1 and 6.21 F g−1, respectively. Further coating of PPy produced a substantial improvement on the electrical conductivity (10.55 S cm−1) and the specific capacitance (315.5 F g−1) of the resulting CNF-PEDOT:PSS-PPy nanopaper. A synergistic phenomenon between both conductive polymers supported the high electrical conductivity and specific capacitance of the ternary formulation. Moreover, CNF-PEDOT:PSS-PPy nanopaper showed higher mechanical properties and it was more flexible than the nanopaper containing only polypyrrole conducting polymer (CNF-PPy). It is concluded that the good mechanical, electrical and electrochemical properties of the ternary formulation can apply for smart nanopaper in flexible electronics and energy storage devices.

The effect of pre-treatment on the production of lignocellulosic nanofibers and their application as a reinforcing agent in paper

• In this work, three different lignocellulosic nanofibers (LCNF) were produced from unbleached wheat straw soda pulp by using different pre-treatments: mechanical, enzymatic, and TEMPO [(2,2,6,6-tetramethylpiperidin-1-yl) oxy radical]-mediated oxidation processes. The different LCNF were characterized and studied by their chemical composition (FTIR), crystal structure (XRD), thermal degradation behaviour (TGA), morphological (TEM), and their reinforcement effect on papermaking slurries. The pre-treatment used to obtain LCNF showed significant differences on the nanofibrillation yield (37–95%), carboxyl content (74–362 µmol g−1), cationic demand (428–1116 µeq g−1), and on its dimensions (7–14 nm), thermal stability, and structure. Regarding application as reinforcement on papermaking slurries, LCNF obtained by TEMPO-mediated oxidation produced a greater reinforcing effect than the other LCNF. Nevertheless, the obtained LCNF from mechanical process produce a similar increase in the mechanical properties of the papersheets due to its high length, compared with LCNF obtained by TEMPO-mediated oxidation.

Cardboard boxes as raw material for high-performance papers through the implementation of alternative technologies: more than closing the loop

• The aim of this work is to develop high-performance papers from recovered cardboard boxes. To tackle this objective, cardboard boxes were enzymatically refined and subsequently reinforced with CNF. Results revealed that although cardboard boxes are usually used for test-liner paper production, they could be used for high-performance applications. In this sense, stronger papers than common test-liner were produced through the use of harmless techniques for fibers. In terms of circular economy, the proposed combined approach goes further than closing the loop: new markets can be achieved or lighter papers could be used, leading to significant resources savings.

Mechanical and micromechanical tensile strength of eucalyptus bleached fibers reinforced polyoxymethylene composites

• Composite materials search a combination of the properties of the phases that compose such materials. In the case of natural fiber composites, as an alternative to mineral fiber reinforced composites, the matrices are limited to those with processing temperatures under 200 °C. Actually, the most commonly reinforced polyolefin are polypropylene and polyethylene, but the literature shows that the tensile properties of such composites had almost reached their ultimate values. Then, the use of matrices with higher tensile strengths opens the field to develop stronger composite materials. Polyoxymethylene has been used with success with mineral reinforcements or man-made cellulose, but has showed poor results with natural fiber based reinforcements. In this work, natural fiber polyoxymethylene composites have been prepared and tested, showing tensile strengths higher to that of natural fiber reinforced polypropylene, and comparable to uncoupled fiberglass polypropylene composites. The interphase of the composites, as a main factor to the performance of the composites was also studied. The research also works on the micromechanics aspects of the tensile strength of such composites.

Influence of TEMPO-oxidised cellulose nanofibrils on the properties of filler-containing papers

• In this work, cellulose nanofibrils (CNF) were produced from a Eucalyptus globulus bleached kraft pulp by TEMPO-mediated oxidation and mechanical homogenisation, and their effects in papermaking, namely filler flocculation and retention, dry and wet-web strength and structural properties, were studied in detail. Cellulose nanofibrils possessing 0.6 mmol/g carboxyl groups and a degree of polymerisation (DP) of ca. 550 were found to promote filler flocculation and retention in the fibre mat, whereas the same amount (3 wt%) of CNF having 1.5 mmol/g of carboxyl groups, a DP of ca. 200 and a similar mean diameter exhibited the opposite effect. These results were interpreted with the help of flocculation studies of precipitated calcium carbonate (PCC) in the presence of CNF carried out by laser diffraction spectrometry. In addition, the mechanical and structural properties of the handsheets were analysed, revealing that the less charged CNF led to more closed matrices and, even increasing the filler retention, had a positive role on the tensile strength. A bonding mechanism among eucalypt fibres, PCC, CNF and a linear cationic polyacrylamide is proposed, consistent with the flocculation, retention and paper strength and structural property results. It is concluded that, to be used in papermaking, the CNF must not have a high charge (or a small length) to be able to flocculate the filler particles and, at the same time, to increase the filler-to-cellulosic fibres bonding. A complementary study on the wet-web resistance of handsheets produced with the less charged CNF was conducted for moisture contents between 10 and 70%, showing that these CNF can significantly improve the handsheet wet tensile strength (nearly 100%) even for water contents above 50%. The use of CNF in the paper machine may thus contribute, through the higher wet-web tensile resistance, to reducing breaks and increasing the operating speeds and, through the higher filler retention, to important fibre and cost savings.

Enzymatically hydrolyzed and TEMPO-oxidized cellulose nanofibers for the production of nanopapers: morphological, optical, thermal and mechanical properties

• In the present study, CNF prepared by TEMPO-mediated oxidation and enzymatic hydrolysis were used for the production of nanopapers using a papermaking-like route. Nanopapers were characterized in terms of tensile, thermal, optical and morphological properties. Those prepared from enzymatically hydrolyzed CNF were found to be weaker at tensile than those resulting from TEMPO-mediated oxidation, but with similar level of stiffness. Enzymatically obtained CNF presented lower transparency due to their higher diameter and lower fibrillation yield. Moreover, TEMPO-oxidized CNF presented lower onset of the thermal degradation temperature (230 °C) due to the presence of carboxylic groups. Overall, the influence of increasing the amount of enzyme during enzymatic hydrolysis and the amount of sodium hypochlorite during TEMPO-mediated oxidation was assessed as function of the ultimate properties of nanopapers.

Fiberboards made from corn stalk thermomechanical pulp and kraft lignin as a green adhesive

• The feasibility of incorporating purified kraft lignin, at different concentrations ranging from 5 to 29%, into fiberboards made from corn residues was studied. The lignin was obtained from black liquor, which is a residue of the paper industry. Corn stalk raw material and its thermomechanically produced fiber were characterized in terms of their chemical composition. The physical and mechanical properties of the resulting fiberboards were evaluated. The fiberboards produced following a wet process had good mechanical and water resistance properties that satisfied the requirements of the relevant standards. In addition, a Life Cycle Thinking (LCT) approach suggested that lignin-based fiberboards are environmentally preferable than those based on thermosetting resins.

High-yield pulp from Brassica napus to manufacture packaging paper

• The stalks that are left on the field after harvesting rapeseed crops could be used to make packaging grade paper. This work evaluates the suitability of mechanical and thermomechanical pulps from rapeseed stalks for papermaking, with a view to alleviating the limitations of recycled fluting. Their performance was compared to that of commercial fluting (recycled fluting) of the same basis weight, 100 g/m2, and to that of virgin pulps from pine wood. The thermomechanical pulp was refined to improve key mechanical properties. Its drainability was found to be very low, even before refining, and its breaking length after beating to 1200 PFI revolutions, 4 km, surpassed that of sheets of recycled fluting that were obtained under similar conditions. These findings support the hypothesis that high-yield pulps from rapeseed stalks are a strong choice of virgin fibres to produce fluting and, generally speaking, packaging paper.

Sugarcane Bagasse Reinforced Composites: Studies on the Young’s Modulus and Macro and Micro-Mechanics

• The stiffness of a material greatly influences its possible use as an engineering material. Thus, despite the theoretical environmental advantages of natural fiber reinforced composites, or fully biodegradable composites, if certain mechanical properties are not achieved, a material can have fewer engineering uses. In this work, sugarcane bagasse fibers, a by-product of the sugarcane-juice extraction process, were used to obtain reinforcing fibers. Two polyolefins, a polypropylene and a high-density polyethylene, and a starch-based polymer were used as matrices. The composite materials were prepared and tested to obtain their tensile properties such as the Young’s moduli. Some micromechanical models were used to obtain the intrinsic Young’s moduli of the fibers and the efficiency factors. The dependence of such parameters on the matrix and fibers characteristics was studied. The fiber orientation efficiency factor was used to compute the orientation angle of the fibers inside the composite under three different distributions. Finally, the Tsai and Pagano models, and the Halpin and Tsai equations were used to compute the theoretical values of the Young’s moduli of the composites.

Lignocellulosic nanofibers from triticale straw: the influence of hemicelluloses and lignin in their production and properties

• The present work aims to determine the influence of hemicellulose and lignin content in the production of lignocellulosic nanofibers (LCNF) from triticale straws. Triticale straws were digested and then gradually delignified, preserving as much hemicelluloses as possible. The obtained LCNF was characterized and used as paper strength additive, observing that hemicellulose and lignin have a key role on the final properties thereof, as well as on their reinforcing potential as paper additive, obtaining LCNF with the same paper reinforcing potential than CNF obtained by TEMPO ((2,2,6,6-Tetramethyl-piperidin-1-yl)oxyl) mediated oxidation.

The suitability of banana leaf residue as raw material for the production of high lignin content micro/nano fibers: from residue to value-added products

• Each year the agri-food industry produces millions of tonnes of lignocellulosic residue, which could be valorized for its composition. Taking into account the economic cycle, this valorization is increasingly necessary and important. The Canary Islands’ banana (Musa acuminate var. Dwarf Cavenish) is an example of this. Its annual production is around 400,000 tons, which translates into 320,000–400,000 tons of banana leaf waste or residue. This residue can represent an important source of raw material for the production of value-added products, such as lignocellulosic micro/nanofibers (LCMNF) for different applications. However, when using a residue as raw material for value-added products, the maximum exploitation rate has to be achieved in terms of producing the minimum amount of sub-residue. In this sense, the present work aims to produce LCMNF from pulp made of banana leaf residue and to assess their reinforcement potential and production costs for the papermaking sector. For the first time, high-lignin content LCMNF will be produced with the same reinforcing capacity than CMNF prepared from woody and bleached pulp, using methodologies under the umbrella of bioeconomy, waste valorization and sustainable growth. The obtained results showed that the presence of high contents of lignin and hemicelluloses promotes the fibrillation, leading to LCMNF with the same reinforcing potential than those obtained from wood and oxidative methods. In addition, the obtained LCMNF had lower production costs that the aforementioned and presented higher yield in terms of raw material utilization. However, further research must be still developed on decreasing production costs thereof.

Magnetic bionanocomposites from cellulose nanofibers: Fast, simple and effective production method

• Nanocellulose is becoming a topic of great interest due to its lightweight, huge availability and its interesting properties. Among these properties, it is worthy to distinguish its specific surface and its strength. Both properties allow producing films with great mechanical properties able to retain nanoparticles which can provide the nanopaper of much functionality. Many applications for nanocellulose nanocomposites have been reported, demonstrating the interesting opportunities that this product has in a near future. In this sense, the present work attempts to produce membranes based on cellulose nanofibers (CNF) filled with magnetite nanoparticles with the purpose of developing membranes for loudspeakers. The main advantage of this is the avoiding of the iron core that one can find in any loudspeaker, since the membrane itself acts as that core. Bionanocomposites ranging from 10 to 70% of magnetite nanoparticles were produced by filtration in a nitrocellulose membrane with a pore size of 0,22 μm. Tensile tests showed that mechanical properties were decreased as the amount of magnetite was increased. They were observed by FE-SEM to see the interactions between nanoparticles and CNF. Finally, a loudspeaker prototype was developed in order to evaluate the sonorous efficiency of the resulting membranes.

Effect of Sodium Hydroxide Treatments on the Tensile Strength and the Interphase Quality of Hemp Core Fiber-Reinforced Polypropylene Composites

• The formulation of greener composite materials by substituting glass fibers with natural fibers is a current field of research. If such natural fiber reinforcements come from industrial side streams, as hemp core fibers (HCFs) come from the extraction of hemp strands for the textile industry, an additional advantage can be identified. Nonetheless, such by-product fibers show some drawbacks, such as high lignin contents, which can make it difficult to obtain a good interphase between the fibers and the matrix and to obtain a good fiber individualization. A digestion treatment at different NaOH contents is proposed to eliminate soluble lignin and extractives from the surface of the fibers. At the same time, the use of a coupling agent solves incompatibilities between the fibers and the matrix. The composites were tensile tested and the impact of the proposed treatments is evaluated and discussed. Later, the Kelly-Tyson modified equation and a modified rule of mixtures—the micro-mechanic models—is used to study the impact of such treatments on the quality of the interphase between the polymer and the reinforcement. Both treatments showed a high impact on the tensile strength and the quality of the interphase, obtaining competitive composite materials reinforced with HCFs derived from a by-product.

Bio composite from bleached pine fibers reinforced polylactic acid as a replacement of glass fiber reinforced polypropylene, macro and micro-mechanics of the Young’s modulus

• The search of more environmentally friendly material is not an end in itself. Such materials must also show competitive mechanical properties, comparative prices and a good adaptation to the manufacture processes. Nowadays, Glass fibers had been traditionally used as reinforcement of polyolefin for mold injected products. Natural fibers and non-oil-based polymers are seen as possible replacements. Nonetheless, the substitution of a mineral reinforcement or an oil-based matrix by renewable alternatives is not enough. From an engineering point of view, stiffness is one of the most relevant properties of composite materials. In this work, commercial Kraft Bleached pine fibers were used as reinforcement for a polylactic acid-based thermoplastic. Composite materials with 15–35% w/w of reinforcing fibers were prepared, mechanically characterized, and compared with polypropylene-based composites. A fiber tensile modulus factor was defined in order to characterize the net contribution of the fibers to the Young's moduli of the composites. The intrinsic Young's modulus of the fibers was back calculated by means of the Hirsch model, and its matrix dependence or independence was examined. The moduli were also obtained by Halpin-Tsai equations with Tsai-Pagano methods and then compared to establish the influence of the aspect ratio.

Evaluation of thermal and thermomechanical behaviour of bio-based polyamide 11 based composites reinforced with lignocellulosic fibres

• In this work, polyamide 11 (PA11) and stone ground wood fibres (SGW) were used, as an alternative to non-bio-based polymer matrices and reinforcements, to obtain short fibre reinforced composites. The impact of the reinforcement on the thermal degradation, thermal transitions and microstructure of PA11-based composites were studied. Natural fibres have lower degradation temperatures than PA11, thus, composites showed lower onset degradation temperatures than PA11, as well. The thermal transition and the semi-crystalline structure of the composites were similar to PA11. On the other hand, when SGW was submitted to an annealing treatment, the composites prepared with these fibres increased its crystallinity, with increasing fibre contents, compared to PA11. The differences between the glass transition temperatures of annealed and untreated composites decreased with the fibre contents. Thus, the fibres had a higher impact in the composites mechanical behaviour than on the mobility of the amorphous phase. The crystalline structure of PA11 and PA11-SGW composites, after annealing, was transformed to α’ more stable phase, without any negative impact on the properties of the fibres.

Reducing the Amount of Catalyst in TEMPO-Oxidized Cellulose Nanofibers: Effect on Properties and Cost

• Cellulose nanofibers (CNF) are interesting biopolymers that find numerous applications in different scientific and technological fields. However, manufacturing costs are still one of the main drawbacks for the industrial production of highly fibrillated, transparent CNF suspensions. In the present study, cellulose nanofibers were produced from bleached eucalyptus pulp via TEMPO-mediated oxidation with varying amounts of NaClO and passed through a high-pressure homogenizer. The CNFs were chemically and physically characterized; cellulose nanopapers were also produced to study tensile properties. Production costs were also calculated. Results indicated that CNF properties are strongly dependent on the carboxyl content. Manufacturing costs showed that chemicals, in particular TEMPO catalyst, represent a large part of the final cost of CNFs. In order to solve this problem, a set of samples were prepared where the amount of TEMPO was gradually reduced. Characterization of samples prepared in this way showed that not only were the costs reduced, but also that the final properties of the CNFs were not significantly affected when the amount of TEMPO was reduced to half.

Behavior of the interphase of dyed cotton residue flocks reinforced polypropylene composites

• Textile industry produces a high amount of residues that, nowadays, are poorly managed. The majority of such wastes are dumped and landfilled. Among all the textile value chain, cotton yarning factories produce wastes in the shape of fiber flocks, with lengths smaller than 10 mm that prevent their reintroduction in the textiles manufacturing process. Nonetheless, such waste cotton flocks could be used as reinforcement for short fiber mould injected composites. This paper reports on the behavior of the interphase between the cotton flocks and a polypropylene matrix. It was found that the organic dyes present on the cotton flocks seem to affect the quality of the interphase in two ways: on the one hand by increasing the affinity between the cotton fibers and the matrix, and on the other hand by limiting the effect of the coupling agents. Micromechanic models are used to further research the quality of the interphase and the intrinsic properties of the composites.

Comparison between two different pretreatment technologies of rice straw fibers prior to fiberboard manufacturing: Twin-screw extrusion and digestion plus defibration

• The present work compares two different pretreatment technologies, i.e. twin-screw extrusion, and steaming digestion plus defibration, for producing a thermo-mechanical pulp from rice straw for fiberboard manufacturing. Five liquid/solid ratios from 0.43 to 1.02 were tested for twin-screw extrusion pretreatment, while liquid/solid ratios from 4 to 6 were used for digestion pretreatment. Energy consumption, and characteristics of the extrudates (twin-screw extrusion) and pulps (digestion) (including fiber morphology, chemical composition, thermal properties, apparent and tapped densities, as well as color) were the analyzed parameters for the resulting lignocellulosic fibers. The results showed that liquid/solid ratio had influence on energy consumption of the equipment for both defibrating methods For the twin-screw extrusion method, a lower liquid/solid ratio required more energy while for the digestion plus defibration the effect was the opposite. The corresponding total specific energy consumption ranged from 0.668 kW h/kg to 0.946 kW h/kg dry matter for twin-screw extrusion, and from 6.176 kW h/kg to 8.52 kW h/kg dry matter for digestion plus defibration. Thus, the pulping method consumed about nine times more energy than that of the twin-screw extrusion. In addition, for twin-screw extrusion, the liquid/solid ratio did not have a substantial effect on fiber characteristics with similar chemical compositions and thermal properties. For twin-screw extrusion, the energy consumption was 37% reduced when the liquid/solid ratio was increased from 0.43 to 1.02. Instead, for digestion plus defibration, the energy increase was 38% when the liquid/solid ratio increased from 4 to 6.

Immobilization of antimicrobial peptides onto cellulose nanopaper

• In this work we report the production of cellulose nanopapers modified with alkyl ketene dimer (AKD) in order to allow the immobilization of antimicrobial peptides (AMPs) to produce surfaces with antimicrobial properties. Cellulose nanofibers (CNF) were prepared from softwood bleached pulp via high pressure homogenization after chemical pretreatment of fibers via TEMPO oxidation. Nanopapers were then prepared after a casting technique and functionalized with alkyl ketene dimer before AMPs were immobilized. The immobilization process was performed by submerging the samples into AMP aqueous solutions and then dried at room temperature. Antimicrobial activity was tested against B. subtilis. Results indicated that AMPs were bound onto the nanopaper surface and released when the nanopaper was put in contact with the culture medium, which effectively demonstrates the viability of the immobilization process.

Lignocellulosic micro/nanofibers from wood sawdust applied to recycled fibers for the production of paper bags

• In the present work, lignocellulosic micro/nanofibers (LCMNF) were produced from pine sawdust. For that, pine sawdust was submitted to alkali treatment and subsequent bleaching stages, tailoring its chemical composition with the purpose of obtaining effective LCMNF. The obtained LCMNF were characterized and incorporated to recycled cardboard boxes with the purpose of producing recycled paper. The obtained results showed that it was possible to obtain LCMNF with the same reinforcing potential than those cellulose nanofibers (CNF) prepared by oxidative or other chemical methods In fact, the obtained papers increased the breaking length of recycled cardboard from 3338 m to 5347 m, being a value significantly higher than the requirements to produce paper bags. Overall, the studied strategies could allow a significant reduction of paper basis weight, with the consequent material saving and, thus, contribution to the environment.

Suitability of wheat straw semichemical pulp for the fabrication of lignocellulosic nanofibres and their application to papermaking slurries

• The present work studies the feasibility of wheat soda pulp as a raw material for the fabrication of cellulose nanofibres and their application as an additive in papermaking. Wheat straws were cooked under alkaline conditions and the resulting pulp was used as a raw material for the production of lignocellulosic nanofibres (LCNF). Nanofibres were fabricated by intense mechanical beating followed by high-pressure homogenization. The produced LCNF were characterized and applied to papermaking slurry based also on wheat straw soda pulp. Paper sheets made thereof were analysed for their physical and mechanical properties. The results indicated that paper strength was improved after addition of LCNF, whereas density increased and porosity was reduced. These improvements in properties (except the Tear Index) are significant because they were achieved using LCNF with lower fibrillation degree compared to previous works where chemically pre-treated LCNF were used as reinforcement.

Semichemical fibres of Leucaena collinsii reinforced polypropylene: Macromechanical and micromechanical analysis

• Leucaena collinsii (LCN) is a fast growing legume. Due to the ability of legumes to fix nitrogen in the ground and the wide range of soils where they can grow up, Leucaena genus has been proposed for recovering deserted soils. Furthermore, the incorporation of fibres into the bosom of a polymeric matrix increases the tensile strength. This study examines the options of a treated fibre of L. collinsii to be added as reinforcement to a polypropylene matrix. The influence on the tensile properties of different percentages of coupling agent and reinforcement were studied. A local maximum for the tensile strength was noticed when increasing the amount of coupling agent up to 6% for 30% w/w LCN contents. Afterwards, a tensile strength characterisation for 20–50% w/w LCN contents with the same amount of coupling agent was performed. The fibres from the composite reinforced with a 30% of LCN were recovered by extraction. The theoretical tensile strengths for composites from 20 to 50% w/w LCN content were modelled using the fibre distribution of the 30% composite material and compared with the experimental results. A good correlation between experimental and theoretical values was confirmed.

Valorization of Corn Stalk by the Production of Cellulose Nanofibers to Improve Recycled Paper Properties

• Corn stalk, an agricultural waste, was valorized by the production of cellulose nanofibers (CNF), which were tested for improving recycled paper properties. CNF from eucalyptus kraft pulp (E-CNF) was used as a reference. Addition of 0.5% wt. CNF produced from corn organosolv pulp (C-CNF) to recycled paper increased the tensile index by 20%, whereas the same improvement with E-CNF was achieved at 1.5% wt. Tensile index was further enhanced by increasing the E-CNF, whereas C-CNF achieved its maximum effect at this dose. Different recycled furnish compositions were studied to evaluate C-CNF as a product additive. CCNF improved tensile strength in all the different recycled furnishes studied. The tensile index improvement caused by C-CNF did not depend on the proportions of old newspaper and old magazine paper used. Addition of C-CNF to recycled corrugated board fluting increased the tensile strength, but to a slightly lower extent than in the case of recycled newsprint paper.

Polypropylene reinforced with semi-chemical fibres of Leucaena collinsii: Thermal properties

• The incorporation of reinforcements with lower thermal stability than the matrix is one of the main handicaps of wood fibre composites. This work studies the influence of the incorporation of increasing quantities of semichemical Leucaena collinsii derived fibres on thermal properties, such as degradation temperature, glass transition, crystallization and melting temperatures, thermal conductivity and thermal expansion coefficient. With that aim, materials were tested by means of differential scanning calorimetry, thermogravimetric analysis, thermal conductivity analysis, thermomechanical analysis and dynamic mechanical analysis. It has been established that the thermal degradation occurs in two different phases, corresponding to the reinforcement around 260 °C and the matrix at 350 °C. It has not been observed any influence on thermal transitions by the addition of reinforcement. The crystalline phase of the polymer enhances from 56 to 63% when a 50%w/w of fibres was added. Thermal conductivity increased by 44% when the fibre content was enhanced from 0 to 50%w/w. The thermal expansion coefficient evolution establishes that the conductivity drops when increasing the reinforcement composition.

The key role of lignin in the production of low-cost lignocellulosic nanofibres for papermaking applications

• The use of cellulose nanofibres (CNF) for the enhancement of paper’s mechanical properties has been reported by many authors. Concretely, the available literature is mainly focused on TEMPO-oxidized cellulose nanofibres. However, recent industrial research projects, in which LEPAMAP group has been involved, have demonstrated that this type of nanocellulose has unaffordable production costs for the papermaking industry. In this sense, the present work aims to produce low-cost lignocellulosic nanofibres (LCNF), finding some strong alternatives to TEMPO-mediated oxidation. For that, lignocellulosic nanofibres (LCNF) were produced from stone groundwood pulp (SGW) from pine after a chemical pulping process (sodium hydroxide and antraquinone). The effect of lignin content was studied and controlled through bleaching steps and quantified. It was found that high lignin content makes nanofibrillation difficult. The reinforcing effect of CNF was mechanically characterized by the addition of 3 wt% of CNF into different papermaking pulps. The results showed that it is possible to obtain low-cost LCNF that provide the same increase in mechanical properties than TEMPO-oxidized CNF when they are used for paper reinforcement. It was also found that lignin plays an important role in the obtaining of LCNF by fully mechanical treatments, where lower lignin contents expedite the nanofibrillation.

The feasibility of incorporating cellulose micro/nanofibers in papermaking processes: the relevance of enzymatic hydrolysis

• Cellulose nanofiber (CNF) is becoming a topic of great interest among the industrial and academic communities, mainly due to their potential applications in very well-differentiated industrial sectors. Among this wide range of applications, papermaking is one of the most accepted and studied. However, it is widely known that the papermaking sector is forced to compete in markets where products do not have huge added value and production margins are very low. Therefore, papermakers are constantly looking for new technologies that balance efficiency and production costs. In line with this, the present work attempts to assay the enzymatic hydrolysis of cellulose fibers to obtain CNFs. Accordingly, pH, pulp consistency, treatment time, enzyme dosage and temperature were varied to find a combination of parameters that could lead to highly efficient CNF in terms of the mechanical properties of paper enhancement and production costs. For this, CNFs were applied to unrefined and refined bleached kraft pulps and their properties were assessed. The obtained results demonstrated that it is possible to obtain highly efficient CNFs from bleached pulp at affordable costs for papermakers. Moreover, it was found that the treatment time has a key role during the production of this CNF but at low enzyme dosages since the obtained results, in terms of intrinsic properties and reinforcing potential, for high enzyme charges did not vary significantly as time was increased. In sum, the present work offers a cost-efficient solution for the application of CNF in the production of paper from bleached pulp as well as a promising alternative to those conventional processes from a technical point of view.

Semichemical fibres of Leucaena collinsii reinforced polypropylene composites: flexural characterisation, impact behaviour and water uptake properties

• Leucaena collinsii is a legume genus with interesting properties for soil recovering. This study uses it as reinforcement in polypropylene reinforced composites. Composites from 20 to 50% w/w composites with a 6% of coupling agent (over the weight of fibre) were produced and injected. Flexural, impact and water uptake behaviour was studied. The flexural strength and stiffness increased as the reinforcement was increased. The impact strength decreased for un-notched samples, but increased for notched samples. The sample's fracture was observed by SEM. Both fibrilar and granular fibre fractures could be recognized. Regarding the water uptake, despite observing no influence on the diffusion coefficient, the maximum water uptake capacity enhanced when the L. collinsii was increased.

Towards a good interphase between bleached kraft softwood fibers and poly(lactic) acid

• An increasing environmental consciousness on society led to the development of materials with a lower environmental impact. In this sense, in the recent years, the substitution of synthetic or mineral fibers by natural fibers, as polyolefin matrices reinforcement, has been an active and interesting topic of research, as well as the development of competitive matrices based on renewable resources. PLA is a biodegradable polymer with higher mechanical properties than polypropylene (PP). Moreover, the interphase between polylactic acid (PLA) and natural fibers, in order to obtain relevant mechanical properties, is still unsolved. Nowadays, and to the best knowledge of the authors, there are few relevant works published about these biodegradable material reinforced showing satisfactory mechanical properties. The present work pretends to obtain PLA biocomposites with a good interphase that allow a relevant improvement on mechanical properties when reinforced. Thus, different amounts of diglyme were added to bleached kraft softwood fibers with the purpose of avoiding fiber agglomeration during compounding. Moreover, stone groundwood (SGW) and fluff pulps were also used as reinforcements. Then, and the results were compared to the previous ones in order to determine the influence both of the lignin on fiber surface, via XPS analysis, and the dispersion within the matrix. The fiber treated with 2/3 of diglyme followed a lineal and positive progression of the tensile strength when increasing reinforcement contents were added. Moreover, the 30 wt% reinforced PLA biocomposite exhibited a tensile strength of the same magnitude than 20 wt% of glass fibers reinforced PP composites, bringing to light the feasibility of substituting the synthetic matrix commodities and obtaining new and biodegradable generation of composites.

Cu-coated cellulose nanopaper for green and low-cost electronics

• In this work we have developed low-cost, renewable and sustainable materials based on cellulose for electronic applications. The UV–Vis spectroscopy, water contact angle and differential scanning calorimetry results reveal a marked effect of absorbed water on the physical properties of cellulose nanopaper. Morphological observations reveal that the TEMPO oxidized cellulose-based foils were successfully covered by a 200-nm-thick copper layer by DC sputtering. The obtained low surface roughness, porosity and hydrophilicity of the nanopaper allow an efficient deposition of Cu on synthesized nanopaper. The thermal stability of cellulose nanopaper is markedly increased from 240 to 324 °C after Cu sputtering, results that are especially interesting for applications in which devices should withstand high temperatures. Dynamic mechanical analysis shows that the Cu-covered nanopaper maintains its mechanical stiffness up to ~180 °C. Finally, dielectric spectroscopy measurements reveal that developed Cu-coated nanopaper could emerge as a suitable bio-based material for radiofrequency applications. In this work we explore sputter coating as an alternative method to reduce the intrinsic hydrophilicity of synthesized nanopaper instead of including a polymer in the nanocellulose or functionalizing its surface chemically. The obtained findings highlight the potential application of transparent and mechanically robust cellulose nanopaper in the field of electronics and communication engineering.

New strategy for the production of packaging from recycled fibers

• The paper industry needs to implement several concurrent strategies. In particular, the industry can be expected to view recycling as a central part of its activities. These activities will be focused on the intense demand of chemical and biochemical strategies to enhance bonding within paper and paperboard. Nowadays, on average, 55% of fibrous compositions for papermaking are made of recycled fibers. In this field, about 65-70% are fibrous compositions intended to be used for packaging papermaking. Corrugated cardboard is one of the most significant examples, since it is made of fluting (internal part) and test liner (external part). In test liner mills, fibrous compositions are made of 50% paper cuts from the cardboard industry and the rest of other types of paper and cardboard. Some test liner papers have low content of mineral fillers. While recycling, fibers get damaged due to the hornification phenomena and mechanical refining of the pulp (with the purpose of enhancing the mechanical properties). The producer does not have many alternatives to address this situation: to increase the quality of the pulp, to slightly refine the pulp or to add some chemical additives that enhance mechanical properties. One strategy or alternative to this situation could be biorefining processes of the pulp. The present work aims to biorefine a pulp made of recycled fibers with the purpose of restoring the mechanical properties of the industrial test liner or improving them and making possible the addition of mineral fillers in order to decrease the production costs. It was observed that, at best, the tensile strength improved by 55% with regard to the original breaking length of the industrial test liner.

From pine sawdust to cellulose nanofibers

• Biorefinery technology is a current alternative to petroleum based industry to produce energy, chemicals and materials. The use of forest and agricultural lignocellulosic residues as raw materials to generate value-added products has become a topic of great interestdue to their renewability and availability. Pine sawdust is a promising candidate as raw material for biorefinery. This waste, which comes from the primary industrialization of wood, is available in large quantities, at low cost, and is currently open-airburned. The aim of this study was to obtain cellulose nanofiber (CNF) from pine sawdust. Delignification methods were applied to pulp until a kappa number lower than 1was achieved. CNF was produced by the combination of chemical (TEMPO-oxidation) pretreatment and mechanical destructuration in a homogenizer. Once CNF was produced at different oxidation degrees, the degree of polymerization, cationic demand, carboxyl rate, and the yield of fibrillation were determined with the purpose of assessing the effect of the oxidation degree on the final properties thereof.Finally, the suitability of using the obtained CNF as paper strength additive was studied through the assessment of the mechanical properties increase of paper.

Tensile properties and micromechanical analysis of stone groundwood from softwood reinforced bio-based polyamide11 composites

• Bio-polyamides (BioPA) reinforced with natural fibres are one of the most promising bio-based composites. However the principal challenge of polyamides (PA) is their high melting temperature close to the degradation temperature of the natural fibres. Polyamide 11 (PA11) is a 100% BioPA with a melting point lower than cellulose temperature degradation. Nonetheless, few researches about PA11 reinforced with natural fibres composites had been performed. In this work, PA11 was reinforced with stone groundwood fibres (SGW) ranging 20% up to 60% of fibre contents. The composites were prepared, extruded, injected moulded and their tensile properties were characterised. An enhancement of 66.8% was obtained for the tensile strength of the composites, besides the strain and the toughness decreased as expected. The significant enhancement of the tensile strength leads to consider a relatively good interface between the fibre and the polymer matrix which was determined in the micromechanical studies. Moreover a morphology analysis of the fibre and its chemical composition study at surface were carried on, in order to discuss the micromechanical analysis results. The average orientation factor and intrinsic tensile strength of the fibres were also determined in the micromechanical analysis.

Cellulose nanofibers modified with alkyl ketene dimer for oil absorbent aerogels

• Nanofibrillated cellulose consists of interconnected cellulose nanofibers, isolated from wood or agricultural byproducts, which leads to a three dimensional, porous and flexible structure. In this sense, the present work aims to develop hydrophobic aerogels for oil absorbing. Different percentages of alkyl ketene dimer (AKD) were added to the cellulose nanofiber (CNF) gel in order to partially hydrophobize the surface thereof. After mechanical stirring in an Ultraturrax and two cycles of sonication at 80 watts for 2 minutes, the CNF gel was poured into aluminum dishes and frozen at - 80ºC for two hours. Then, the samples were freeze-dried for 48 hours. Water and oil absorption capacity was determined both under static and dynamic conditions in an oil-water mixture.

Comparasion of the soundproofing characteristics of olive stone filled polypropylene, gypsum boards and wood fiber reinforced polypropylene

• Noise, caused by the society and technical progress, is nowadays considered a pollutant. Noise pollution affects or could affect a great number of people. One the most concerned fields, in part by a growing law framework and by the quality expectations of the clients, is architecture. The solution to sound pollution involves eliminating it or reducing it to acceptable levels. Nowadays, one of the most recurred solutions is the use of lightweight materials such as gypsum boards, to create acoustic insulation elements. On the other hand, the environmental awareness has increased the attention towards recycled materials. In the case of composite materials, major attention has been devoted to the substitution of mineral reinforcements, such as glass fibers, by more sustainable reinforcements, as wood fibers or agroforestry wastes. In this sense, olive stones, which are a byproduct of olive oil extraction, could be used. In the present work, olive stone filled polypropylene composites were prepared. Different percentages of filler were used. The soundproofing properties of the composites were tested by means of an impedance tube. Then, the results were compared with those for gypsum boards, wood veneer and wood fiber reinforced polypropylene.

Fully biodegradable polylactic composites reinforced with bleached softwood fibers

• The increasing environmental awareness of the society has led to the development of materials with a lower environmental impact. Polylactic acid (PLA) is a biodegradable polymer with higher mechanical properties than PP. The scientific literature shows some interest in PLA reinforced biocomposites, but the published mechanical properties of such materials are comparatively low. In fact, the generation of a good interface, when the reinforcement contents are higher than 30%, is nowadays unsolved. The main objective of this study is to obtain PLA biocomposites with a good interface and with satisfactory improvements in their mechanical properties against reinforcement contents. Bleached pine fibers, used as reinforcement, were prepared and shred with 1/3 and 2/3 of diglyme, in order to avoid the formation of hydrogen bonds among the cellulose fibers. Then, composite materials were obtained through kinetic mixing. The composites were injection molded to make standard specimens and were submitted to tensile tests. The results showed that the addition of diglyme favored the formation of hydrogen bonds between the reinforcement and the PLA. Only the fibers treated with 2/3 diglyme followed a linear positive progression of its tensile strength when increasing reinforcement contents were added. Although suitable results were obtained, it seems that these composites allow further improvement.

Fast and simple method for prediction of the micromechanical parameters and macromechanical properties of composite materials

• The method described in the present work was assessed through the production of composite materials made of polypropylene reinforced with chemical thermomechanical pulp of hemp core fibers. Composite materials were obtained by extrusion and injection molding, and by the addition of a coupling agent to ensure a good interphase between fiber and matrix. In all cases, the composite materials were considered as semi-aligned reinforced. Tensile strength was selected as a representative parameter and was studied by the Kelly-Tyson model.1 Since the original Kelly-Tyson equation was formulated for fully aligned reinforced composite materials, the present work uses a modified one, where the orientation factor is included. The fiber length and diameter distribution were determined by the extraction of the fibers from the composite materials and analyzed in a MorFi equipment. The orientation factor was calculated taking into account the predicted tensile strength for fully aligned composites and the experimental value from the semi-aligned ones. The interfacial shear strength was estimated through Tresca and Von Mises criteria. The values obtained through the simulation were compared to the experimental ones, showing a good correlation between the mathematical model and the experimental part.

Effective and simple methodology to produce nanocellulose-based aerogels for selective oil removal

• Spilled oil in seas has a direct impact on the environment and biodiversity. Moreover, there is no clear relationship between the amount of oil in the aquatic environment and its impact, since it mainly depends on the time and season that the oil is spilled. Nowadays, there are several techniques to clean up and recover oil from the sea, including the use of microorganisms, chemicals, controlled burning, dispersants and solidifiers, among others. Sometimes, unfortunately, the best option is to watch and wait for natural attenuation. Cellulose nanofibers have potential environmental applications due to their availability, light weight, mechanical and optical properties, and renewability. Several studies have dealt with modification of their hydrophilic character through silanation and acetylation. Both treatments, despite having a significant impact on the environment, are not plausible on a large scale because of the cost of chemicals and complexity of the modification. In this sense, the present work aims to develop hydrophobic nanocellulose-based aerogels from bleached kraft eucalyptus fibers modified with alkyl ketene dimers. For this, an experimental batch of 24 aerogels was prepared, including three types of CNF (TEMPO-oxidized, enzymatically hydrolyzed and mechanical) and eight modification degrees. The obtained aerogels were characterized in terms of morphology, hydrophilicity and water–oil absorption capacity under static and dynamic conditions, as well as their suitability for recycling and reuse for selective oil removal. The results showed that it is possible to obtain 3D-structured aerogels with a high oil absorption capacity by a simple and presumably low-cost methodology.

Nanofibrillated Cellulose as an additive in Papermaking Process: A review

• During the last two decades, cellulose nanofibres (CNF) have emerged as a promising, sustainable reinforcement with outstanding potential in material sciences. Though application of CNF in papermaking is recent, it is expected to find implementation in the near future to give a broader commercial market to this type of cellulose. The present review highlights recent progress in the field of the application of cellulose nanofibres as additives in papermaking. The effect of CNF addition on the wet end process is analysed according to the type of pulp used for papermaking. According to the literature consulted, improvement in paper’s overall properties after CNF addition depended not only on the type and amount of CNF applied, but also in the pulp’s origin and treatment. Bulk and surface application of CNF also presented significant differences regarding paper’s final properties. This review also revises the mechanisms behind CNF reinforcing effect on paper and the effect of chemically modified CNF as additives.

Fully biodegradable polylactic composites reinforced with bleached softwood fibers

• The increasing environmental awareness of the society has led to the development of materials with a lower environmental impact. Polylactic acid (PLA) is a biodegradable polymer with higher mechanical properties than PP. The scientific literature shows some interest in PLA reinforced biocomposites, but the published mechanical properties of such materials are comparatively low. In fact, the generation of a good interface, when the reinforcement contents are higher than 30%, is nowadays unsolved. The main objective of this study is to obtain PLA biocomposites with a good interface and with satisfactory improvements in their mechanical properties against reinforcement contents. Bleached pine fibers, used as reinforcement, were prepared and shred with 1/3 and 2/3 of diglyme, in order to avoid the formation of hydrogen bonds among the cellulose fibers. Then, composite materials were obtained through kinetic mixing. The composites were injection molded to make standard specimens and were submitted to tensile tests. The results showed that the addition of diglyme favored the formation of hydrogen bonds between the reinforcement and the PLA. Only the fibers treated with 2/3 diglyme followed a linear positive progression of its tensile strength when increasing reinforcement contents were added. Although suitable results were obtained, it seems that these composites.

New strategy for the production of packaging from recycled fibers

• The paper industry needs to implement several concurrent strategies. In particular, the industry can be expected to view recycling as a central part of its activities. These activities will be focused on the intense demand of chemical and biochemical strategies to enhance bonding within paper and paperboard. Nowadays, on average, 55% of fibrous compositions for papermaking are made of recycled fibers. In this field, about 65-70% are fibrous compositions intended to be used for packaging papermaking. Corrugated cardboard is one of the most significant examples, since it is made of fluting (internal part) and test liner (external part). In test liner mills, fibrous compositions are made of 50% paper cuts from the cardboard industry and the rest of other types of paper and cardboard. Some test liner papers have low content of mineral fillers. While recycling, fibers get damaged due to the hornification phenomena and mechanical refining of the pulp (with the purpose of enhancing the mechanical properties). The producer does not have many alternatives to address this situation: to increase the quality of the pulp, to slightly refine the pulp or to add some chemical additives that enhance mechanical properties. One strategy or alternative to this situation could be biorefining processes of the pulp. The present work aims to biorefine a pulp made of recycled fibers with the purpose of restoring the mechanical properties of the industrial test liner or improving them and making possible the addition of mineral fillers in order to decrease the production costs. It was observed that, at best, the tensile strength improved by 55% with regard to the original breaking length of the industrial test liner.

Papermaking potential of Citrus sinensis trimmings using organosolv pulping, chlorine-free bleaching and refining

• One of the most popular ways to carry out the re-use of wastes from agriculture is the pulping, refining and bleaching of those residues for papermaking. Spain annually produces more than 300 thousand tonnes of Citrus sinensis (orange tree) trimmings, crops being concentrated in the East and the South of the country. Their chemical composition is similar to that of common hardwoods.
  This work aims to show the suitability of ethanolamine cooking when applied to orange tree trimmings, and to study the effect of peroxide bleaching and refining on some key properties. As for bleaching, we used a design of experiments to discuss the influence of peroxide concentration, time and temperature on the yield, brightness, viscosity, kappa number of pulps and mechanical properties of paper sheets. Refining was studied by analysing the diminishment in freeness and the mechanical properties of paper sheets formed. Results showed that even a mild bleaching process gives out a high relative brightness gain, but a multiple-step process is necessary to achieve enough brightness for printing paper. Mechanical properties of non-refined pulps were found to be too low for paper of any grade, but they were greatly improved by refining.

Semichemical fibres of Leucaena Collinsii reinforced polypropylene composites: Young’s Modulus analysis and fibre diameter effect on the stiffness

• Leucaena genus offers environmental benefits related with soil recovering. The use of natural fibres as reinforcement in composites materials is a current technology for strengthening and stiffening polymeric materials. Besides, some authors suggest the idea that the diameter has a strong influence on the material stiffness. The material's stiffness is one of the most important design parameters. This work studies the Leucaena collinsii influence on the polypropylene composite materials stiffness. A tensile test was performed for measuring the Young's moduli from composite materials reinforced with 20–50% of fibre. Furthermore, the diameter influence on that property has been studied through modelling. The mechanical results show a high L. collinsii stiffness contribution, increasing its stiffness a 400%. The fibre intrinsic Young modulus was located in the high range of natural fibre's intrinsic Young's modulus. The fibre diameter rendered little influence on the fibre intrinsic stiffness.

Nanofibrillated cellulose (CNF) from eucalyptus sawdust as a dry strength agent of unrefined eucalyptus handsheets

• Nanofibrillated cellulose has been obtained from the cellulosic fraction of eucalyptus sawdust. The fractionation process involved the partial removal of hemicelluloses and lignin. CNF was obtained using TEMPO oxidation with NaOCl in basic medium followed by mechanical homogenization. The obtained CNF was subsequently used as a dry strength agent on unbleached unrefined eucalyptus pulp. The addition of 3, 6 and 9 wt.% of CNF increased lineally the tensile index of handsheets to about 55 N m g−1 at 35°SR, compatible with papermachine runnability. The other mechanical properties also increased substantially, and porosity decreased moderately. The estimated specific surface and average diameter of these CNF were 60 m2 g−1, and of 41.0 nm, respectively. The addition of 9 wt.% of CNF produced an increase in mechanical strength, equivalent to that produced by PFI refining at 1600 revolutions.

Tensile Strength Assessment of Injection-Molded High Yield Sugarcane Bagasse-Reinforced Polypropylene

• Sugarcane bagasse was treated to obtain sawdust, in addition to mechanical, thermomechanical, and chemical-thermomechanical pulps. The obtained fibers were used to obtain reinforced polypropylene composites prepared by injection molding. Coupling agent contents ranging from 2 to 10% w/w were added to the composite to obtain the highest tensile strength. All the composites included 30% w/w of reinforcing fibers. The tensile strength of the different sugarcane bagasse fiber composites were tested and discussed. The results were compared with that of other natural fiber- or glass fiber-reinforced polypropylene composites. Pulp-based composites showed higher tensile strength than sawdust-based composites. A micromechanical analysis showed the relationship of some micromechanical properties to the orientation angle, critical length, the intrinsic tensile strength, and the interfacial shear strength. The pulps showed similar intrinsic tensile strengths and were higher than that of sawdust. The properties of the sugarcane bagasse composites compared well with other natural fiber-reinforced composites.

Starch-based biopolymer reinforced with high yield fibers from sugarcane bagasse as a technical and environmentally friendly alternative to high density polyethylene

• Greener composites, as alternatives to more common materials, should also achieve technical and economic feasibility to be commercially competitive. This study presents the results obtained from using a biodegradable starch-based matrix, and a natural fiber reinforcement coming from sugarcane bagasse, currently an agro-waste. The sugarcane bagasse biomass was treated to obtain four kinds of fibers with different morphological and chemical properties. The fibers were used to obtain composite materials, which were then tested for tensile properties. The results showed that some of the composites were suitable to replace high density polyethylene, from a technical and environmental point of view. The comparatively higher cost of the biobased matrices hinders the substitution, but the higher the fiber content, the lower the economic disadvantage. A micromechanical test and a sensitivity analysis showed that the fiber orientation had the highest impact on the tensile strength, followed by the fibers mean length and the quality of the interphase between the fibers and the matrix.

Morphological analysis of pulps from orange tree trimmings and its relation to mechanical properties

• To optimize the pulping and refining processes of new alternative raw materials for papermaking, researchers generally perform tests that consume considerable time and large amounts of sample. We propose measuring the morphological properties of pulps from orange tree trimmings by image analysis systems, which are fast and user-friendly, to develop models relating key mechanical properties to the dimensions, the deformation and the population of fibers. Data modeling involves multiple linear regression, as used in other studies, and support vector regression, not used before for this purpose, achieving higher R2 values (up to 0.90). Although tensile, tear and burst tests are still required to obtain accurate values, a quick morphological characterization allows for a rough but satisfactory prediction of paper strength. In this case, chemical pulping and moderate refining are shown to be necessary to obtain pulps of acceptable quality from orange tree trimmings.

Stiffness of bio-based polyamide 11 reinforced with softwood stone ground-wood fibres as an alternative to polypropylene-glass fibre composites

• Polyolefin had been successfully reinforced with glass fibres and applied in the industry during the last decades. However there are unsolved processability and recyclability problems due to its fragility. There are also concerns related with the human health. This had promoted the interest towards more environmentally friendly and healthier reinforcements such as natural fibres. In addition, the oil origin of polyolefin increases the interest in researching greener polymer alternatives. This work proposes polyamide 11 (PA11) as a promising alternative to polypropylene or other commodity polyolefin. This paper studies the behaviour of the Young’s modulus of natural fibre reinforced PA11 composites at different fibre contents. The composites were prepared, injection molded and characterized to tensile modulus. Afterwards a micromechanical modelling was performed using two models: Hirsch’s and Tsai-Pagano’s. The results allow proposing natural fibre reinforced PA11 composites as a suitable replacement to glass fibre reinforced polypropylene composites.

Remarkable increase of paper strength by combining enzymatic cellulose nanofibers in bulk and TEMPO-oxidized nanofibers as coating

• Cellulose nanofibers (CNF) have been proposed by several authors as a reinforcing additive for papermaking pulps; their use allows one to avoid mechanical refining of pulp fibers, which damages the fibers and reduces their lifespan and consequently recycling cycles. In the present work, use of CNF obtained through enzymatic pretreatment as a bulk pulp additive is studied versus traditional (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized CNF. Results indicate that enzymatic CNF improves the overall paper properties in a similar way to TEMPO-oxidized CNF; however, the enzymatic pretreatment is supposed to be significantly cheaper and environmentally friendly compared with the chemical treatment. Paper reinforced with enzymatic CNF was later surface-coated with solution containing TEMPO nanofibers oxidized with 15 mmol NaClO to further promote the mechanical strength. The results indicate that the combination of bulk addition of enzymatic CNF to the papermaking pulp followed by surface application of TEMPO-oxidized CNF induced significant improvement in the mechanical properties of the paper at lower cost than sole use of TEMPO-oxidized CNF as bulk additive. To the best of our knowledge, this is the first work in which enzymatic and TEMPO-oxidized CNF are combined as paper additives for bulk and surface application to improve overall paper properties.

Polypropylene composites based on lignocellulosic fillers: how the filler morphology affects the composite properties

• In this research, composite materials were made from wood flour (WF) or olive stone flour (OSF) as reinforcement, polypropylene (PP) as polymer matrix, and maleated polypropylene (MAPP) as coupling agent, by using injection molding. The effects of the filler loading and coupling agent on the physical properties of the composites, in terms of tensile and impact strength, water absorption and wear resistance were studied. The macromechanical properties were explained by the morphological features of the reinforcements. Composites containing coupling agents exhibited the best mechanical properties, and reduced the negative impacts of water absorption. The difference in the morphology of the two lignocellulosic fillers was found to be a key factor controlling the properties of the composites and the evolution of their properties against water absorption.

Improvement of deinked old newspaper/old magazine pulp suspensions by means of nanofibrillated cellulose addition

• During their recycling, cellulosic fibres suffer irreversible damage caused by repeated wetting and drying cycles, beating stages and bleaching reactions. This damage decreases the mechanical properties of the paper prepared from recycled pulp. Soft beating of the pulp is a simple way to partially recover the original mechanical properties, but it is limited by the high degradation of fibres, fines generation and decrease in drainage rate that recycled fibres already present. The present research studies the use of nanofibrillated cellulose (CNF) as an alternative to mechanical beating to improve the strength properties of paper produced from a deinked recycled pulp obtained by disintegration and flotation of a mixture of old newspapers and magazines. Different percentages of CNF were added to this mixture with a retention aid. A fraction of the same pulp without CNF was also beaten at different intensities in a PFI mill. Morphological properties of both beaten and CNF-reinforced pulp suspensions, as well as structural and mechanical properties of handsheets made thereof, were analysed and their results compared. Paper containing 1.5 % of CNF presented a higher tensile strength and stiffness than paper from beaten pulp with similar freeness and water retention values. A higher amount of CNF further improved the mechanical properties, up to double the tensile index, which opens new possibilities of use for recycled paper.

Olive stones flour as reinforcement in polypropylene composites: A step forward in the valorization of the solid waste from the olive oil industry

• The usefulness of olive stone flour (OSF) from the solid residue of the olive oil extraction as a reinforcement for the preparation of a cost-effective polypropylene-based composite was investigated. The lignocellulosic filler consisted of acicular particles with a broad size distribution ranging from about 50 to 400 μm, and is composed of lignin, hemicelluloses, and cellulose. Composites with filler loading up to 70 wt% were prepared using a melt processing and injection molding. The evolution of the mechanical performance, impact properties, and water absorbance of the composites as a function of the filler content were investigated. The addition of a maleated polypropylene (MAPP) coupling agent at a level of 5%, with respect to the filler, was shown to be essential in bringing about a reinforcing effect. A steady increase in the modulus along with a preservation in the tensile strength was observed up to a content of 60% OSF. The obtained results have confirmed the viability of OSF as cheap reinforcing filler for the PP matrix; thus, opening new perspectives for the use of this agricultural by-product.

On the morphology of cellulose nanofibrils obtained by TEMPO-mediated oxidation and mechanical treatment

• The morphological properties of cellulose nanofibrils obtained from eucalyptus pulp fibres were assessed. Two samples were produced with the same chemical treatment (NaClO/NaBr/TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidation), but distinct mechanical treatment intensities during homogenization. It was shown that the nanofibrils production yield increases with the mechanical energy. The effect of mechanical treatment on the yield was confirmed by laser profilometry of air-dried nanocellulose films. However, no significant differences were detected regarding the nanofibrils width as measured by atomic force microscopy (AFM) of air-dried films. On the other hand, differences in size were found either by laser diffraction spectroscopy or by dynamic light scattering (DLS) of the cellulose nanofibrils suspensions as a consequence of the differences in the length distribution of both samples. The nanofibrils length of the more nanofibrillated sample was calculated based on the width measured by AFM and the hydrodynamic diameter obtained by DLS. A length value of ca. 600 nm was estimated. The DLS hydrodynamic diameter, as an equivalent spherical diameter, was used to estimate the nanofibrils length assuming a cylinder with the same volume and with the diameter (width) assessed by AFM. A simple method is thus proposed to evaluate the cellulose nanofibrils length combining microscopy and light scattering methods.

Approaching a low-cost production of cellulose nanofibers for papermaking applications

• The use of cellulose nanofibers (CNF) as an additive in papermaking is an attractive alternative to improve paper's strength. However, the costs of CNF production need to be competitive compared to other approaches aimed at reducing mechanical beating. Five different types of CNFs were prepared following different pretreatments: TEMPO-mediated oxidation at basic and neutral conditions, soft acid hydrolysis, enzymatic treatment, and mechanical beating. All of the pretreated fibers were later passed through a high-pressure homogenizer. The resulting CNFs were each applied to a papermaking pulp to investigate their reinforcing ability. Results indicated that the TEMPO-oxidized CNFs offered the highest increase at the same nanofiber content compared to the other types of CNFs. However, an analysis of the cost of increasing paper's breaking length by 75% indicated that TEMPO-oxidized CNFs were more expensive than the other CNF grades, whereas CNFs from mechanical and acid pretreatment offered similar increases at lower prices. The results indicated that CNFs of high fibrillation degree were not necessary to induce dramatic increases in paper strength. This finding offers a new possibility for the escalation of CNF production to industrial levels with competitive prices.

Enzymatic refining and cellulose nanofiber addition in papermaking processes from recycled and deinked slurries

• Recycling and deinking processes cause fiber damage because of hornification phenomena and increased external fibrillation. Mechanical refining has been used for many years to enhance the mechanical properties of paper. Biorefining of pulp using enzymes is receiving increasing interest for energy reduction at the refining step of the papermaking process. Moreover, enzymes have also been used for the enhancement of mechanical properties without affecting the drainage rate. As an alternative to mechanical refining treatment, a combination of an enzymatic treatment and cellulose nanofibril (CNF) addition was explored to enhance the mechanical properties of paper. The tests were carried out on a deinked pulp (DIP) suspension made of 50% old newspapers (ONP) and 50% old magazines (OMG). Various enzyme charges and CNF amounts were added to the mixture of ONP and OMG. All pulps (treated and untreated) were characterized from a morphological point of view, and the paper sheets made thereof were mechanically characterized. The combination of the enzymatic treatment with the addition of 3% CNF provided sufficient tensile strength for the paper to be used in high-performance applications.

Rapeseed stalks for papermaking: studies on pulping, refining and dewatering

• Cereal straw, bamboo and bagasse are the most widely used non-wood raw materials, but work is being done towards other interesting sources of fibres, such as rapeseed stalks and straw. Rapeseed oil production for energetic purposes is increasing, and so are wastes. In this work, pulps from Brassica napus (rapeseed) stalks were obtained by soda-anthraquinone and Organosolv cooking. They were refined in a PFI mill. Handsheets made from those pulps were tested. Drainage rate and retention of fillers were also evaluated. We address the capabilities of rapeseed stalks and stems for papermaking and the influence of refining on the mechanical properties, the morphology of fibres and the amount of fines. This material was found to be suitable for papermaking and, as an advantage, a small number of PFI revolutions resulted in a substantial gain in mechanical properties.

Orange Wood Fiber Reinforced Polypropylene Composites: Thermal Properties

• A major drawback of natural-based composites is the incorporation of reinforcements that are less thermally stable than the matrix; therefore, the thermal properties of the resultant composite material needs to be studied. In this work, orange wood fibers were used to reinforce polypropylene. The effects on the thermal properties of the polymeric matrix were analyzed. To this end, differential scanning calorimetry (DSC), thermogravimetry (TGA), thermomechanical analysis (TMA), and dynamic-mechanical analysis (DMA) were performed. It was found that the degradation of the material took place in two distinct phases: the reinforcement, close to 250 °C, and the matrix, above 340 °C. DSC results showed that fiber reinforcement did not influence the transition temperatures of the materials, although it did affect the polymer crystallinity value, increasing by 7% when the composite is reinforced with 50% of the lignocellulosic reinforcement. The coefficient of expansion obtained by TMA indicated that thermal expansion decreased as the amount of reinforcement increased. DMA assays showed that the reinforcement did not modify the glass transition (20 to 25 °C) temperature and confirmed that the addition of reinforcement increased the crystallinity of the product.

Tensile Properties of Polypropylene Composites Reinforced with Mechanical, Thermomechanical, and Chemi-Thermomechanical Pulps from Orange Pruning

• This paper explores the evolution in the tensile strength of orange pruning fiber-reinforced polypropylene composites. The exploitation of these pruning's can effectively avoid incineration, with the consequence of CO2 emissions and fire risk, while extending the value chain of the agricultural industry. This biomass was subjected to three different treatments yielding mechanical, thermomechanical, and chemi-thermomechanical pulps. It was found that 20 to 50% of these pulps, together with a coupling agent, were used as polypropylene reinforcement. The evolution in the tensile strength and morphological properties of the fibers, and the effect of treatments on these properties were analyzed. A modified rule of mixtures (mROM) was used to analyze the micromechanical properties of the interface. In addition, the mechanical properties were weighted against the fiber treatment yields. Finally, factors to compute the net contribution of the fibers to the final strength of the composite materials were proposed.

Acoustic properties of agroforestry waste orange pruning fibers reinforced polypropylene composites as an alternative to laminated gypsum boards

• The present paper investigates the acoustic properties of natural fiber reinforced composites. Fibers from orange tree pruning were obtained and subject to different treatments in order to obtain mechanical, thermomechanical and chemi-thermomechanical pulps. These pulps were used as reinforcement for a polypropylene matrix. The obtained composite materials were submitted to acoustical tests in an impedance tubes device. The transmission losses obtained against the fiber content were obtained and discussed. Latter it was researched the influence of the fiber treatments on the soundproof characteristics. A numerical method was used to preview the acoustic insulation of the materials against the sound frequency. Finally the results were compared with that of the most usual lightweight soundproof solutions.

Are cellulose nanofibers a solution for a more circular economy of paper products?

• This paper presents the study of the feasibility of incorporating lignocellulosic nanofibers (LCNF) to paper in order to maintain the relevant physical properties and increase the number of cycles that paper can be recycled in the technosphere in a more circular economy. For that purpose, the effect of mechanical refining in recycling processes was compared with that of the novel LCNF addition. In this sense, the behavior of a bleached kraft hardwood pulp when recycled was investigated, as well as the effects of each methodology. Since there are many issues to be considered when trying to replace a technology, the present paper analyses its feasibility from a technical and environmental point of view. Technically, LCNF present greater advantages against mechanical refining, such as higher mechanical properties and longer durability of the fibers. A preliminary life cycle assessment showed that the environmental impacts of both systems are very similar; however, changing the boundary conditions to some feasible future scenarios, led to demonstrate that the CNF technology may improve significantly those impacts.

Flexural properties of fully biodegradable alpha-grass fibers reinforced starch-based thermoplastics

• This work has the aim of study the flexural properties of alpha-grass reinforced starch-based composites. The composite materials contain alpha-fibers in the range from 5 to 35 wt%. The reinforcing fibers were submitted to an alkali treatment to create a good interphase between the fibers and the matrix. It was observed that a mild 2.5 h cooking process was enough to create a good interphase, while longer periods rendered lesser improvements. The surface charges of the fibers and the matrix were determined by polyelectrolyte titration, and it was found that after the alkaline treatment both were similar. The composite materials were injection molded and tested under flexural conditions. All the flexural properties of the studies composites increased linearly with the reinforcement contents. The micromechanics of the flexural modulus and strength were studied and compared with that of tensile modulus and strength. It was established that the efficiency factors for the tensile and flexural properties were statistically similar. Three different methods were used to compute the intrinsic flexural strength from the available data. Finally the Weibull theory was used to study the best prediction of the standard deviation of the intrinsic flexural modulus.

All-lignocellulosic fiberboard from corn biomass and cellulose nanofibers

• In general, fiberboards are made of lignocellulosic fibers with synthetic adhesive to connect between fibers. Synthetic adhesives are usually non-biodegradable constituents and they cause health and environmental troubles. The present study aims to develop fiberboards from corn thermomechanical fibers reinforced with cellulose nanofibers. In this work, corn stalk biomass was used to produce high yield thermomechanical pulp (TMP) that was converted into binderless fiberboards. Cellulose nanofibers (CNF) were also added as reinforcing agent. The mechanical and physical properties of the resulting fiberboards were characterized and compared with commercial high density fiberboard (HDF) containing synthetic adhesives. Fiberboards with 0.5 wt% CNF showed modulus of rupture of 43 MPa, similar to that of commercial HDF. The highest mechanical performance was reached for fiberboards at 2 wt% of CNF, with modulus of rupture of 52 MPa. CNF was found to increase the resistance of the new all-lignocellulosic fiberboards when compared to the products made only with corn stalk fiber, and also when compared with commercial HDF.