Synthesis, Characterization, and Evaluation of the Antimicrobial Effects and Cytotoxicity of a Novel Nanocomposite Based on Polyamide 6 and Trimetaphosphate Nanoparticles Decorated with Silver Nanoparticles.

This study aimed to develop a polymeric matrix of polyamide-6 (P6) impregnated with trimetaphosphate (TMP) nanoparticles and silver nanoparticles (AgNPs), and to evaluate its antimicrobial activity, surface free energy, TMP and Ag+ release, and cytotoxicity for use as a support in dental tissue. The data were subjected to statistical analysis (p < 0.05). P6 can be incorporated into TMP without altering its properties. In the first three hours, Ag+ was released for all groups decorated with AgNPs, and for TMP, the release only occurred for the P6-TMP-5% and P6-TMP-10% groups. In the inhibition zones, the AgNPs showed activity against both microorganisms. The P6-TMP-2.5%-Ag and P6-TMP-5%-Ag groups with AgNPs showed a greater reduction in CFU for S. mutans. For C. albicans, all groups showed a reduction in CFU. The P6-TMP groups showed higher cell viability, regardless of time (p < 0.05). The developed P6 polymeric matrix impregnated with TMP and AgNPs demonstrated promising antimicrobial properties against the tested microorganisms, making it a potential material for applications in scaffolds in dental tissues.

Cellulose esters: Synthesis for further formation of films with magnetite nanoparticles incorporated.

This study investigated the homogeneous synthesis of cellulose acetate (CA) and propionate (CP) with varying degrees of substitution (DS) from sisal cellulose in a N, N-dimethylacetamide/lithium chloride (DMAc/LiCl) solvent system. These esters were used to prepare neat (CADSF/CPDSF) and nanocomposite films (CADSFFe/CPDSFFe) from prior synthesized magnetite nanoparticles (NPs, Fe3O4, 5.1 ± 0.5 nm). Among the CA and CP series, the composite CA0.7FFe and the neat CP0.7F films exhibited the highest modulus of elasticity, 2105 MPa and 2768 MPa, respectively, probably a consequence of the continuous fibrous structures present on the surface of these films. Microsphere formation on the film's surface was observed in scanning electron microscopy micrographs. This points to applications in the controlled release of targeted substances. The VSM analysis showed that the cellulosic matrices preserved the superparamagnetic characteristics of the NPs. This study suggested a reduced coupling effect between nanoparticles inside polymeric films due to magnetic saturation at low fields. CA0.7FFe and CA1.3FFe composite films reached a saturation magnetization (MSAT) of 46 emu/g around 7 kOe field. Hosting magnetite nanoparticles in cellulose ester matrices may be an interesting way to develop new functional cellulose-based materials, which have the potential for diverse applications, including microelectromechanical systems and microsensors.

Cellulose acylation in homogeneous and heterogeneous media: Optimization of reactions conditions.

The dependence of the DS on the acid anhydride/anhydroglucose unit ((RCO)2O/AGU) molar ratio was correlated using second-order polynomials. The regression coefficients of the (RCO)2O/AGU terms showed that increasing the length of the RCO group of the anhydride led to lower values of DS. For acylation under heterogeneous reaction conditions, the following were employed: acid anhydrides and butyryl chloride as acylating agents; iodine as a catalyst; N,N-dimethylformamide (DMF) as a solvent, pyridine, and triethylamine as solvents and catalysts. For acylation using acetic anhydride plus iodine, the values of DS correlate with reaction time by a second-order polynomial. Due to its role as a polar solvent and a nucleophilic catalyst, pyridine was the most effective base catalyst, independent of the acylating agent (butyric anhydride and butyryl chloride).

Polyurethane films formation from microcrystalline cellulose as a polyol and cellulose nanocrystals as additive: Reactions favored by the low viscosity of the source of isocyanate groups used.

To simultaneously form films while synthesizing solvent-free and catalyst-free bio-based polyurethanes, hexamethylene diisocyanate trimer was selected as an isocyanate group source to produce a low-viscosity reaction medium for dispersing high contents of microcrystalline cellulose (MCC, polyol) and cellulose nanocrystals (CNC). Castor oil was used as an additional polyol source. Up to 80 % of the MCC was dispersed, producing a film exhibiting the highest Tg (72 °C), tensile strength (18 MPa), and Young's modulus (522.4 MPa). 12.5 % (30 % MCC) and 7.5 % (50 % MCC) of CNC dispersed in the reaction medium formed films stiffer than their counterparts. All the films exhibited transparency and high crystallinity. The contact angle/zeta potential (ζ) indicated hydrophobic film surfaces. At pH 7.4, ζ suggested that the films interacted with physiological fluids favorably. The films were non-cytotoxic, and the composites exhibited cell growth compared with the control. The reported results, as far as it is known, are unprecedented.

Cross-Linked and Surface-Modified Cellulose Acetate as a Cover Layer for Paper-Based Electrochromic Devices.

We studied the surface and microstructure of cellulose acetate (CA) films to tailor their barrier and mechanical properties for application in electrochromic devices (ECDs). Cross-linking of CA was carried out with pyromellitic dianhydride to enhance the properties relative to unmodified CA: solvent resistance (by 43% in acetone and 37% in DMSO), strength (by 91% for tensile at break), and barrier (by 65% to oxygen and 92% to water vapor). Surface modification via tetraethyl orthosilicate and octyltrichlorosilane endowed the films with hydrophobicity, stiffness, and further enhanced solvent resistance. A detailed comparison of structural, chemical, surface, and thermal properties was performed by using X-ray diffraction, dynamic mechanical analyses, Fourier-transform infrared spectroscopy, and atomic force microscopy. Coplanar ECDs were synthesized by incorporating a hydrogel electrolyte comprising TEMPO-oxidized cellulose nanofibrils and an ionic liquid. When applied as the top layer in the ECDs, cross-linked and hydrophobized CA films extended the functionality of the assembled displays. The results indicate excellent prospects for CA films in achieving environmental-friendly ECDs that can replace poly(ethylene terephthalate)-based counterparts.

Cellulose nanocrystals: Pretreatments, preparation strategies, and surface functionalization.

Cellulose nanocrystals (CNCs) have attracted great interest from researchers from academic and industrial areas because of their interesting structural features and unique physicochemical properties, such as magnificent mechanical strength, high surface area, and many hydroxyl groups for chemical modification, low density, and biodegradability. CNCs are an outstanding contender for applications in assorted fields comprehensive of, e.g., biomedical, electronic gadgets, water purifications, nanocomposites, membranes. Additionally, a persistent progression is going on in the extraction and surface modification of cellulose nanocrystals to fulfill the expanding need of producers to fabricate cellulose nanocrystals-based materials. In this review, the foundation of nanocellulose that emerged from lignocellulosic biomass and recent development in extraction/preparation of cellulose nanocrystals and different types of cellulose nanocrystal surface modification techniques are summed up. The different sorts of cellulose modification reactions that have been discussed are acetylation, oxidations, esterifications, etherifications, ion-pair formation, hydrogen bonding, silanization, nucleophilic substitution reactions, and so forth. The mechanisms of surface functionalization reactions are also introduced and considered concerning the impact on the reactions. Moreover, the primary association of cellulose and different forms of nanocellulose has likewise been examined for beginners in this field.

Hydrogel from all in all lignocellulosic sisal fibers macromolecular components.

The heterogeneous structure of lignocellulosic biomass makes it difficult to dissolve its main components (cellulose, hemicelluloses, and lignin) by solvent action with the aim of further applying the mixture of the biological macromolecules generated in the solvent medium. In the present study, the dissolution efficiency (DE) of lignocellulosic sisal fibers in the lithium chloride/dimethylacetamide solvent system (LiCl/DMAc) was evaluated for further application in the formation of hydrogels. Catalytic amounts of trifluoroacetic acid (TFA) were used in some experiments, which increased the DE from 40% to 90%. The regeneration of the solutions, either previously filtered or not, led to hydrogels based on sisal lignocellulosic biomass. In brief, the properties of the hydrogels were influenced by the content of the lignocellulosic components in the hydrogels, present both in the dissolved fraction and in the incorporated undissolved fraction (when nonfiltered solutions were used). Hydrogels presented water absorption up to 7479% and resorption content in the lyophilized hydrogel up to 2133%. Extracts obtained from preselected hydrogels exhibited cell viability up to 127% compared to the control group when in contact with fibroblast cultures, exhibiting their noncytotoxic properties. This attribute increased the range of possible applications of these hydrogels, ranging from agriculture to biocompatible materials.

Bio-based electrospun mats composed of aligned and nonaligned fibers from cellulose nanocrystals, castor oil, and recycled PET.

Cellulose nanocrystals (CNCs), castor oil (CO), and recycled poly(ethylene terephthalate) (rPET), were used to add value to renewable raw materials and to a recycled polymer produced worldwide, producing mats composed of fibers on the nano- and submicrometric (ultrathin) scales through a sustainable process. Bio-based electrospun mats composed of aligned (rotary collector) and nonaligned (static collector) nanofibers/ultrathin fibers were produced from the electrospinning of solutions prepared from rPET (mixed with CO, CNCs, or CNCs/CO). The contact angle results showed that the CNC mat surfaces composed of nonaligned fibers were hydrophilic, and in contrast, these surfaces were hydrophobic when composed of aligned fibers. Among the mats composed of nonaligned fibers, PET/CO/CNC exhibited storage and Young's moduli approximately eleven and ten times, respectively, better than those of neat rPET. The PET/CO/CNC mat showed both modulus and tensile strength values higher than those of PET/CNC, when characterized in the preferential direction of fiber alignment. Electrospun mats were obtained from environmentally sound raw materials with diversified properties, which were modulated by the type of collector used, as well as whether CO and CNC were mixed with rPET, and have the potential for use in applications such as membrane separation processes and biomedical applications.

Synthesis of bio-based polyurethanes from Kraft lignin and castor oil with simultaneous film formation.

Kraft lignin (KL) and castor oil (CO) were used as polyols in the synthesis of bio-based polyurethanes (PUs) in the absence of both solvents and catalysts at room temperature with simultaneous film formation. KL was purified (PKL), and both KL and PKL were fully characterized. CO was mixed with different percentages of PKL (0%, 10%, 30%, and 50%), as well as with polymeric methyl phenyl diisocyanate. After degassing, the reaction mixture was stirred; when the medium viscosity was suitable for spreading, it was poured onto a glass plate, and the thickness was adjusted using an extender. The storage modulus (E', 25 °C) and tensile strength of the lignopolyurethane films (LignoPUCOPKL) were higher than those of the control film (PUCO). LignoPUCOPKL30 and LignoPUCOPKL50 did not break under the conditions that the other films broke under. It was noted phase segregation (rigid and flexible domains) for LignoPUCOPKL30 and LignoPUCOPKL50, and the glass transition temperature (Tg) of the flexible domains (96.2 °C and 52.3 °C, respectively) was higher than that of PUCO (8.4 °C). The formed films were also characterized by scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, contact angles, and swelling tests. To our knowledge, the approach of this study is unprecedented.

Investigating effects of high cellulase concentration on the enzymatic hydrolysis of the sisal cellulosic pulp.

The goal of this study was to investigate how the use of high concentration of cellulase may impact the properties of the substrate and the reaction medium during the enzymatic hydrolysis of the sisal pulp. Enzyme concentration of 0.9 mL g-1 was considered for hydrolysis of a sisal cellulosic substrate, and the results were compared with previous ones using 0.5 mL g-1 as cellulase concentration. Nonhydrolyzed pulps and the liquors were withdrawn from the reaction medium and characterized by scanning electron microscopy, crystallinity index, average molar mass, length/thickness, and high-performance liquid chromatography (HPLC). The results indicated that the enzyme/substrate ratio impacted crystallinity variations during the reaction and the induction period for exoglucanase action. The concentration of 0.9 mL g-1 led to a glucose yield (98%, an almost quantitative conversion) higher than 0.5 mL g-1 (89%). Aiming to gain information on the post-burst phase (after 15 h), 1 g of sisal pulp was added, and the results demonstrated that the enzymes remained active, which can counterbalance the higher cost due to the use of high enzymes concentrations. This study deepened the understanding of the enzymatic hydrolysis of sisal cellulosic pulp, and the findings may also benefit investigations on other pulps.

Nanostructured electrospun nonwovens of poly(ε-caprolactone)/quaternized chitosan for potential biomedical applications.

Blend solutions of poly(ε-caprolactone) (PCL) and N-(2-hydroxy)-propyl-3-trimethylammonium chitosan chloride (QCh) were successfully electrospun. The weight ratio PCL/QCh ranged in the interval 95/5-70/30 while two QCh samples were used, namely QCh1 (DQ¯â€¯= 47.3%; DPv¯â€¯= 2218) and QCh2 (DQ¯â€¯= 71.1%; DPv¯â€¯= 1427). According to the characteristics of QCh derivative and to the QCh content on the resulting PCL/QCh nonwoven, the nanofibers displayed different average diameter (175 nm-415 nm), and the nonwovens exhibited variable porosity (57.0%-81.6%), swelling capacity (175%-425%) and water vapor transmission rate (1600 g m-2 24 h-2500 g m-2 24 h). The surface hydrophilicity of nonwovens increases with increasing QCh content, favoring fibroblast (HDFn) adhesion and spreading. Tensile tests revealed that the nonwovens present a good balance between elasticity and strength under both dry and hydrated state. Results indicate that the PCL/QCh electrospun nonwovens are new nanofibers-based biomaterials potentially useful as wound dressings.

Renewable Resources and a Recycled Polymer as Raw Materials: Mats from Electrospinning of Lignocellulosic Biomass and PET Solutions.

Interest in the use of renewable raw materials in the preparation of materials has been growing uninterruptedly in recent decades. The aim of this strategy is to offer alternatives to the use of fossil fuel-based raw materials and to meet the demand for materials that are less detrimental to the environment after disposal. In this context, several studies have been carried out on the use of lignocellulosic biomass and its main components (cellulose, hemicelluloses, and lignin) as raw materials for polymeric materials. Lignocellulosic fibers have a high content of cellulose, but there has been a notable lack of investigations on application of the electrospinning technique for solutions prepared from raw lignocellulosic biomass, even though the presence of cellulose favors the alignment of the fiber chains during electrospinning. In this investigation, ultrathin (submicrometric) and nanoscale aligned fibers were successfully prepared via electrospinning (room temperature) of solutions prepared with different contents of lignocellulosic sisal fibers combined with recycled poly(ethylene terephthalate) (PET) using trifluoroacetic acid (TFA) as solvent. The "macro" fibers were deconstructed by the action of TFA, resulting in solutions containing their constituents, i.e., cellulose, hemicelluloses, and lignin, in addition to PET. The "macro" sisal fibers were reconstructed at the nanometer and submicrometric scale from these solutions. The SEM micrographs of the mats containing the components of sisal showed distinct fiber networks, likely due to differences in the solubility of these components in TFA and in their dielectric constants. The mechanical properties of the mats (dynamic mechanical analysis, DMA, and tensile properties) were evaluated with the samples positioned both in the direction (dir) of and in opposition (op) to the alignment of the nano and ultrathin fibers, which can be considered a novelty in the analysis of this type of material. DMA showed superior values of storage modulus (E' at 30 °C) for the mats characterized in the preferential direction of fiber alignment. For example, for mats obtained from solutions prepared from a 0.4 ratio of sisal fibers/PET, Sisal/PET0.40dir presented a high E' value of 765 MPa compared to Sisal/PET0.40op that presented an E' value of 88.4 MPa. The fiber alignment did not influence the Tg values (from tan δ peak) of electrospun mats with the same compositions, as they presented similar values for this property. The tensile properties of the electrospun mats were significantly impacted by the alignment of the fibers: e.g., Sisal/PET0.40dir presented a high tensile strength value of 15.72 MPa, and Sisal/PET0.40op presented a value of approximately 2.5 MPa. An opposite trend was observed regarding the values of elongation at break for these materials. Other properties of the mats are also discussed; such as the index of fiber alignment, average porosity, and surface contact angle. To our knowledge, this is the first time that the influence of fiber alignment on the properties of electrospun mats based on untreated lignocellulosic biomass combined with a recycled polymer, such as PET, has been evaluated. The mats obtained in this study have potential for diversified applications, such as reinforcement for polymeric matrices in nanocomposites, membranes for filtration, and support for enzymes, wherein the fiber alignment, together with other evaluated properties, can impact their effectiveness in these applications.

Sodium lignosulfonate as a renewable stabilizing agent for aqueous alumina suspensions.

The macromolecule sodium lignosulfonate (SL) has been investigated as dispersing agent for aqueous alumina colloids as a renewable alternative to usual petrochemical stabilizing agents. Optimization of the SL concentration necessary to stabilize the alumina suspension at different pH values was determined by viscometer. The results showed that addition of 250 ppm of the total suspension mass led to about 70% viscosity reduction of the suspension, whereas zeta potential analysis revealed negative values for the SL suspensions throughout the pH range investigated, suggesting that the alumina particles were covered by negatively charged SL molecules. Particle size investigation informed that the average particle diameter of the SL suspensions was smaller compared to that of the pristine particles. Sedimentation time for the SL suspensions was dramatically longer than that for the pristine one. The reported data strongly corroborated that SL is a suitable renewable dispersing agent for aqueous alumina colloids.

Dynamic mechanical thermal analysis of composite resins with CQ and PPD as photo-initiators photoactivated by QTH and LED units.

OBJECTIVES: The aim of this study was to evaluate the thermal and mechanical properties of the composite resins containing the photo-initiators camphorquinone (CQ) and/or phenyl-propanodione (PPD) when photoactivated with halogen lamp (XL2500/3M-ESPE), monowave (UltraBlueIS/DMC) and polywave (UltraLume5/Ultradent) LED units. MATERIALS AND METHODS: A blend of BisGMA, UDMA, BisEMA and TEGDMA was prepared with the same wt% of photo-initiators CQ and/or PPD and 65wt% of silaneted filler particles. Compression strength (CS), diametral tensile strength (DTS) and diametral modulus (DM) were tested. Thermogravimetric analysis (TGA) was made and the lost residual monomer were verified. Dynamic mechanical thermal analysis (DMTA) was used for to analyze the glass transition temperature (Tg) and the storage modulus in 37°C. Degree of conversion (DC) was accomplished in the same samples of DMA using middle-infrared spectroscopy (mid-IR). RESULTS: CQ, CQ/PPD and PPD obtained the same results for all mechanical properties (CS, DTS and DM), lost residual monomer and storage modulus in 37°C, regardless LCU used. The results of Tg showed that the combination PPD-UltraLume5 produced the highest values. DC showed that the combination CQ-UltraLume5 resulted in the highest values and PPD-XL2500 in the lowest DC values. CONCLUSION: The study shows that PPD is not only effective photosensitizers, but also photocrosslinking agents for dental composite resins with a similar efficiency to CQ.

Effect of acid concentration and pulp properties on hydrolysis reactions of mercerized sisal.

The influence of sulfuric acid concentration (H2SO4 5-25%, 100°C), crystallinity and fibers size on the hydrolysis reaction of sisal pulps were investigated, with the goal of evaluating both the liquor composition, as an important step in the production of bioethanol, and the residual non-hydrolyzed pulp, to determine its potential application as materials. Aliquots were withdrawn from the reaction media, and the liquor composition was analyzed by HPLC. The residual non-hydrolyzed pulps were characterized by SEM, their average molar mass and crystallinity index, and their size distribution was determined using a fiber analyzer. Sulfuric acid 25% led to the highest glucose content (approximately 10gL(-1)), and this acid concentration was chosen to evaluate the influence of both the fiber size and crystallinity of the starting pulp on hydrolysis. The results showed that fibers with higher length and lower crystallinity favored glucose production in approximately 12%, with respect to the highly crystalline shorter fibers.

Bio-based Films from Linter Cellulose and Its Acetates: Formation and Properties.

This paper describes the results obtained on the preparation of films composed of linter cellulose and the corresponding acetates. The acetylation was carried out in the LiCl/DMAc solvent system. Films were prepared from a LiCl/DMAc solution of cellulose acetates (degree of substitution, DS 0.8-2.9) mixed with linter cellulose (5, 10 and 15 wt %). Detailed characterization of the films revealed the following: (i) they exhibited fibrous structures on their surfaces. The strong tendency of the linter cellulose chains to aggregate in LiCl/DMAc suggests that these fibrous elements consist of cellulose chains, as can be deduced from SEM images of the film of cellulose proper; (ii) the cellulose acetate films obtained from samples with DS 2.1 and 2.9 exhibited microspheres on the surface, whose formation seems to be favored for acetates with higher DS; (iii) AFM analysis showed that, in general, the presence of cellulose increased both the asperity thickness and the surface roughness of the analyzed films, indicating that cellulose chains are at least partially organized in domains and not molecularly dispersed between acetate chains; and (iv) the films prepared from cellulose and acetates exhibited lower hygroscopicity than the acetate films, also suggesting that the cellulose chains are organized into domains, probably due to strong intermolecular interactions. The linter and sisal acetates (the latter from a prior study), and their respective films, were prepared using the same processes; however, the two sets of films presented more differences (as in humidity absorption, optical, and tensile properties) than similarities (as in some morphological aspects), most likely due to the different properties of the starting materials. Potential applications of the films prepared in tissue engineering scaffold coatings and/or drug delivery are mentioned.

Effect of different photo-initiators and light curing units on degree of conversion of composites.

The aim of this study was to evaluate: (i) the absorption of photo-initiators and emission spectra of light curing units (LCUs); and (ii) the degree of conversion (DC) of experimental composites formulated with different photo-initiators when activated by different LCUs. Blends of BisGMA, UDMA, BisEMA and TEGDMA with camphorquinone (CQ) and/ or 1-phenyl-1,2-propanedione (PPD) were prepared. Dimethylaminoethyl methacrylate (DMAEMA) was used as co-initiator. Each mixture was loaded with 65 wt% of silanated filler particles. One quartz-tungsten-halogen - QTH (XL 2500, 3M/ESPE) and two lightemitting diode (LED) LCUs (UltraBlue IS, DMC and UltraLume LED 5, Ultradent) were used for activation procedures. Irradiance (mW/cm²) was calculated by the ratio of the output power by the area of the tip, and spectral distribution with a spectrometer (USB 2000). The absorption curve of each photo-initiator was determined using a spectrophotometer (Varian Cary 5G). DC was assessed by Fourier transformed infrared spectroscopy. Data were submitted to two-way ANOVA and Tukey's test (5%). No significant difference was found for DC values when using LED LCUs regardless of the photo-initiator type. However, PPD showed significantly lower DC values than composites with CQ when irradiated with QTH. PPD produced DC values similar to those of CQ, but it was dependent on the LCU type.

Effect of different photo-initiators and light curing units on degree of conversion of composites

The aim of this study was to evaluate: (i) the absorption of photo-initiators and emission spectra of light curing units (LCUs); and (ii) the degree of conversion (DC) of experimental composites formulated with different photo-initiators when activated by different LCUs. Blends of BisGMA, UDMA, BisEMA and TEGDMA with camphorquinone (CQ) and/ or 1-phenyl-1,2-propanedione (PPD) were prepared. Dimethylaminoethyl methacrylate (DMAEMA) was used as co-initiator. Each mixture was loaded with 65 wt percent of silanated filler particles. One quartz-tungsten-halogen - QTH (XL 2500, 3M/ESPE) and two lightemitting diode (LED) LCUs (UltraBlue IS, DMC and UltraLume LED 5, Ultradent) were used for activation procedures. Irradiance (mW/cm²) was calculated by the ratio of the output power by the area of the tip, and spectral distribution with a spectrometer (USB 2000). The absorption curve of each photo-initiator was determined using a spectrophotometer (Varian Cary 5G). DC was assessed by Fourier transformed infrared spectroscopy. Data were submitted to two-way ANOVA and Tukey's test (5 percent). No significant difference was found for DC values when using LED LCUs regardless of the photo-initiator type. However, PPD showed significantly lower DC values than composites with CQ when irradiated with QTH. PPD produced DC values similar to those of CQ, but it was dependent on the LCU type.

Valorization of an industrial organosolv-sugarcane bagasse lignin: Characterization and use as a matrix in biobased composites reinforced with sisal fibers.

In the present study, the main focus was the characterization and application of the by-product lignin isolated through an industrial organosolv acid hydrolysis process from sugarcane bagasse, aiming at the production of bioethanol. The sugarcane lignin was characterized and used to prepare phenolic-type resins. The analysis confirmed that the industrial sugarcane lignin is of HGS type, with a high proportion of the less substituted aromatic ring p-hydroxyphenyl units, which favors further reaction with formaldehyde. The lignin-formaldehyde resins were used to produce biobased composites reinforced with different proportions of randomly distributed sisal fibers. The presence of lignin moieties in both the fiber and matrix increases their mutual affinity, as confirmed by SEM images, which showed good adhesion at the biocomposite fiber/matrix interface. This in turn allowed good load transference from the matrix to the fiber, leading to biobased composites with good impact strength (near 500 J m(-1) for a 40 wt% sisal fiber-reinforced composite). The study demonstrates that sugarcane bagasse lignin obtained from a bioethanol plant can be used without excessive purification in the preparation of lignocellulosic fiber-reinforced biobased composites displaying high mechanical properties.

Biobased composites from glyoxal-phenolic resins and sisal fibers.

Lignocellulosic materials can significantly contribute to the development of biobased composites. In this work, glyoxal-phenolic resins for composites were prepared using glyoxal, which is a dialdehyde obtained from several natural resources. The resins were characterized by (1)H, (13)C, 2D, and (31)P NMR spectroscopies. Resorcinol (10%) was used as an accelerator for curing the glyoxal-phenol resins in order to obtain the thermosets. The impact-strength measurement showed that regardless of the cure cycle used, the reinforcement of thermosets by 30% (w/w) sisal fibers improved the impact strength by one order of magnitude. Curing with cycle 1 (150 degrees C) induced a high diffusion coefficient for water absorption in composites, due to less interaction between the sisal fibers and water. The composites cured with cycle 2 (180 degrees C) had less glyoxal resin coverage of the cellulosic fibers, as observed by images of the fractured interface observed by SEM. This study shows that biobased composites with good properties can be prepared using a high proportion of materials obtained from natural resources.