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International audience; The rheological properties of a dispersion of cellulose nanocrystals (CNCs) in an aqueous solution of polyoxyethylene (PEO) have been investigated. A peculiar behavior is reported. Upon adding CNC, the viscosity of the suspension first decreases and then increases. Adsorption of PEO chains on the surface of the nanoparticles has been suspected. Freeze-drying of this PEO-adsorbed CNC dispersion was performed, and the ensuing lyophilizate was extruded with low density polyethylene. Compared to neat CNC-based nanocomposites, both improved dispersibility and thermal stability were observed. This simple and physical method constitutes an approach of choice for the melt processing of CNC-based nanocomposites with a hydrophobic polymeric matrix applicable at the industrial scale.

Cellulose nanocrystals (CNC) exhibit remarkable properties such as being lightweight, renewability, nanoscale dimension, raw material availability, and a unique morphology. They have been widely used in film-forming composites, but the literature is scarce concerning bulky-composites (i.e., non-filmogenic). Microcrystalline cellulose (MCC) is widely available and has emerged as an important material for the reinforcement of composites. This investigation focuses on the preparation of non-filmogenic composites prepared from a polyurethane-type matrix, based on modified lignosulfonate and castor oil, reinforced with CNC or MCC, aiming to compare their reinforcing capacity. CNC was obtained through the acid hydrolysis of MCC. Sodium lignosulfonate was chemically modified using glutaraldehyde to increase its reactivity towards isocyanate groups in the synthesis of lignopolyurethane. The results show that adding CNC or MCC led to materials with improved impact strength, flexural properties, and storage modulus compared to pristine lignopolyurethane. With the exception of the flexural modulus, which was higher for the CNC-reinforced composite compared to the MCC-reinforced composite, all other properties were similar. The set of results indicates that CNC and MCC are promising for the reinforcement of polyurethane-type matrices. Bulky materials with good properties and prepared from high renewable raw material contents were obtained, meeting current expectations concerning sustainable development.

The rational valorization of lignin and its derivatives is a challenge in biorefinery because this biopolymer is one of the major source of aromatic moieties. Lignosulfonates are used to a lesser extent than lignin to prepare macromolecular materials. In the current study, sodium lignosulfonate (NaLS), which was either blended or not blended with OH-containing vegetable oil (i.e., castor oil (CO)), was reacted with diphenylmethane diisocyanate (MDI) to prepare polyurethane-type materials, such as lignopolyurethanes (i.e., CO/NaLS/MDI and NaLS/MDI, respectively). NaLS was oxypropylated (LS-Oxy) to increase its reactivity towards MDI. LS-Oxy was characterized and then used after being blended or not blended with CO to prepare lignopolyurethanes CO/LS-Oxy/MDI and LS-Oxy/MDI, respectively. These materials were characterized by infrared spectroscopy, thermogravimetry (TG), and dynamic mechanical thermoanalysis (DMA). The Tg values obtained from DMA (loss modulus peak) indicated that the lignopolyurethanes with an intermediate degree of cross-linking were obtained. In a final set of experiments and due to their potential application, the obtained lignopolyurethanes were reinforced with sisal fibers, and the impact strength, flexural properties and scanning electron microscopy (SEM) images of the materials were obtained. The results indicated that the presence of sisal fibers led to a significant improvement in the impact strength of the lignopolyurethanes, especially in those prepared from LS-Oxy [CO/LS-Oxy/MDI: approximately from 40 J m −1 (without sisal) to 370 J m −1 (with sisal); LS-Oxy/MDI: from 15 J m −1 (without sisal) to 459 J m −1 (with sisal)]. The flexural properties of CO/LS-Oxy/MDI (with or without sisal) corresponded to a less rigid material compared to the other material. The results indicated that the characteristics of the lignopolyurethanes could be tuned by oxypropylation of NaLS and/or blending with CO as well as by the addition of sisal fibers, which enables the production of materials with a wide range of properties.

The use of products and byproducts from the agro-industry and forest biorefinery is essential for the development of value-added and low environmental-impact materials. In this study, polyurethanes were prepared using sodium lignosulfonate (NaLS) and castor oil (CO) as reagents and were used to prepare composites reinforced with lignocellulosic fibers, namely, curaua and coir fibers (30 wt %, 3 cm length, and randomly oriented). The SEM images of fractured surfaces of the composites revealed excellent adhesion at the fiber/matrix interface of both coir and curaua composites, which probably resulted from the favorable interactions between polar groups, as well as amid low polarity domains that are present in both the matrix and the reinforcements. The composites exhibited different impact/flexural and strength/flexural moduli (NaLS/CO/Curaua = 465 Jm−1/44 MPa/2 GPa; NaLS/CO/Coir = 180 Jm−1/25 MPa/1 GPa). The higher tensile strength/aspect ratio of the curaua fibers (485 MPa/259) compared with that of the coir fibers (120 MPa/130) most likely contributes to the enhanced performance of its composite. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A tannin–phenolic resin (40 wt% of tannin, characterized by 1 H nuclear magnetic resonance (NMR) and 13 C NMR, Fourier transform infrared, thermogravimetry, differential scanning calorimetry) was used to prepare composites reinforced with sisal fibers (30–70 wt%). Inverse gas chromatography results showed that the sisal fibers and the tannin–phenolic thermoset have close values of the dispersive component and also have predominance of acid sites (acid character) at the surface, confirming the favoring of interaction between the sisal fibers and the tannin–phenolic matrix at the interface. The Izod impact strength increased up to 50 wt% of sisal fibers. This composite also showed high storage modulus, and the lower loss modulus, confirming its good fiber/matrix interface, also observed by SEM images. A composite with good properties was prepared from high content of raw material obtained from renewable sources (40 wt% of tannin substituted the phenol in the preparation of the matrix and 50 wt% of matrix was replaced by sisal fibers).

Aqueous suspensions of cellulose nanocrystals can be obtained by acid hydrolysis of lignocellulosic fibers. Cellulose nanocrystals correspond to defect-free rod-like nanoparticles that present remarkable properties such as light weight, low cost, availability of raw material, renewability, nanoscale dimension, and unique morphology. Because of these properties, cellulose nanocrystals have been largely applied as reinforcing fillers in nanocomposites materials. This paper discusses the preparation, morphological features, and physical properties of cellulose nanocrystals, as well as their incorporation in nanocomposite materials.

Tannin–phenolic polymers prepared using tannin, a macromolecule obtained from natural sources, were used in the preparation of composites reinforced with coir fibers. The composites based on tannin–phenolic polymers (50% (w/w) of tannin as substitute of the phenol) were prepared using the coir fibers as reinforcement (30–70% (w/w), 3.0–6.0 cm, randomly distributed). The Izod impact strength of the composites showed an improvement in this property due to the incorporation of coir fibers in the tannin–phenolic matrices. The SEM images showed excellent adhesion at the fiber/matrix interface. The coir fiber had bundles regularly spaced, which enhanced the diffusion of the resin into the fiber. In addition, the high lignin content of this fiber results in a high concentration of aromatic rings, which increased the compatibility with the matrix. The values of the diffusion coefficient of water, determined using Fick's laws, show that there was no correlation between the fiber percentage and the water diffusion. The DMTA curves showed that the storage moduli of the composites reinforced with coir fibers were considerably higher than that of the thermoset, and the increase in the proportion of fibers led to a proportional increase in the storage moduli of these materials. The biobased composites obtained have potential for non-structural applications, such as in the internal parts of automotives vehicles. To our knowledge, this is the first study on this kind of biobased composites.

The aim of the present work was to investigate the toughening of phenolic thermoset and its composites reinforced with sisal fibers, using hydroxyl-terminated polybutadiene rubber (HTPB) as both impact modifier and coupling agent. Substantial increase in the impact strength of the thermoset was achieved by the addition 10% of HTPB. Scanning electron microscopy (SEM) images of the material with 15% HTPB content revealed the formation of some rubber aggregates that reduced the efficiency of the toughening mechanism. In composites, the toughening effect was observed only when 2.5% of HTPB was added. The rubber aggregates were found located mainly at the matrix–fiber interface suggesting that HTPB could be used as coupling agent between the sisal fibers and the phenolic matrix. A composite reinforced with sisal fibers pre-impregnated with HTPB was then prepared; its SEM images showed the formation of a thin coating of HTPB on the surface of the fibers. The ability of HTBP as coupling agent between sisal fibers and phenolic matrix was then investigated by preparing a composite reinforced with sisal fibers pre-treated with HTPB. As revealed by its SEM images, the HTPB pre-treatment of the fibers resulted on the formation of a thin coating of HTPB on the surface of the fibers, which provided better compatibility between the fibers and the matrix at their interface, resulting in a material with low water absorption capacity and no loss of impact strength.

The (bio)degradation of polyolefins can be accelerated by modifying the level of crystallinity or by incorporation of carbonyl groups by adding pro-oxidants to masterbatches or through exposure to ultraviolet irradiation. In this work, we sought to improve the degradation of PP by adding cobalt, calcium or magnesium stearate to Ecoflex ® , PP or Ecoflex ® /PP blends. The effect of the pro-oxidants on biodegradability was assessed by examining the mechanical properties and fluidity of the polymers. PP had higher values for tensile strength at break and Young's modulus than Ecoflex ® , and the latter had little influence on the properties of PP in Ecoflex ® /PP blends. However, the presence of pro-oxidants (except for calcium) reduced these properties. All of the pro-oxidants enhanced the fluidity of PP, a phenomenon that facilitated polymer degradation at high temperatures.

Thermoset phenolic composites reinforced with sisal fibers were prepared to optimize the cure step. In the present study, processing parameters such as pressure, temperature, and time interval were varied to control the vaporization of the water generated as a byproduct during the crosslinking reaction. These molecules can vaporize forming voids, which in turn affect the final material properties. The set of results on impact strength revealed that the application of higher pressure before the gel point of the phenolic matrix produced composites with better properties. The SEM images showed that the cure cycle corresponding to the application of higher values of molding pressure at the gel point of the phenolic resin led to the reduction of voids in the matrix. In addition, the increase in the molding pressure during the cure step increased the resin interdiffusion. Better filling of the fiber channels decreased the possibility of water molecules diffusing through the internal spaces of the fibers. These molecules then diffused mainly through the bulk of the thermoset matrix, which led to a decrease in the water diffusion coefficient (D) at all three temperatures (25, 55 and 70 °C) considered in the experiments.

The goals of our studies have been the use of renewable raw materials in the preparation of polymeric materials with diversified properties. In this context, lignosulfonate, which is produced in large scale around the world, but not widely used in the production of polymeric materials, was used to replace phenol and polyols in the preparation of phenolic- (Ligno-PH) and polyurethane-type (Ligno-PU) polymers, respectively. These polymers were used to prepare composites reinforced with sisal lignocellulosic fibers. The use of lignosulfonate in the formulation of both types of polymers was beneficial, because in general composites with improved properties, specially impact strength, were obtained. Composites were also prepared from the so called “biopolyethylene” (HDPE), curaua lignocellulosic fiber, and castor oil (CO). All composites HDBPE/CO/Fiber exhibited higher impact strength, when compared to those of the corresponding HDBPE/Fiber. These results, combined with others (eg SEM images of the fractured s...

Lignocellulosic sisal fiber (LSF) and sisal pulp (SP) were electrospun at room temperature from solutions in trifluoroacetic acid (TFA) prepared at concentrations of 2 × 10−2 g mL−1 and 3 × 10−2 g mL−1, respectively. Scanning electron microscopy images of the electrospun LSF showed fibers with diameters ranging from 120 to 510 nm. The presence of defects decreased along with increasing the flow rate of the SP solution, which generated nanofibers and ultrathin fibers with diameters in the range of 40–60 (at 5.5 µL min−1) up to 90–200 nm (at 65.5 µL min−1). Despite the known ability of TFA to esterify the hydroxyl groups present in the starting materials, the Fourier transform infrared spectra indicated the absence of trifluoroacetyl groups in the electrospun samples. The thermal stability of the final materials proved suitable for many applications even though some differences were observed relative to the starting materials. This study demonstrated a feasible novel approach for producing nano/ultrathin fibers from lignocellulosic biomass or its main component, which allows for a wide range of applications for these materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41826.

Mats of ultrathin and nanoscale fibers were prepared via room temperature electrospinning of lignocellulosic sisal fibers (S) and recycled PET trifluoroacetic acid solutions. The properties of the resulting mats (S/PET ratios from 0.1 to 0.4) were examined by infrared spectroscopy, scanning electronic microscopy (SEM), contact angle measurements (CA), thermogravimetry and dynamic mechanical analysis (DMA). SEM images confirmed that the electrospinning led to ultrathin and nanofibers. The CA results revealed that the hydrophilicity of the mats could be tuned by controlling the S/PET ratio. The DMA results showed that the addition of sisal led to stiffer mats and higher Tg values relative to a PETneat mat, indicating interactions between the components of the lignocellulosic fibers and the PET chains at a molecular level. The present study may contribute to the development of cellulosic nanocomposites via a one-pot process, which may be an alternative to processes that require cellulose nanofibers or nanocrystals to be prepared before hand as well as optimal conditions for subsequent dispersion in mats based on thermoplastic polymers.

Thermosets such as phenolic thermosets are brittle at room temperature. Thus, in applications where good mechanical properties are required thermosets must be combined with reinforcements to improve these properties. Composites based on thermoset matrices can substitute for steel and concrete in some applications of civil construction structures because of their higher resistance to oxidation than steel and better freeze–thaw resistance than concrete. Furthermore, phenolic composites can be produced with complex shapes, and with careful design, materials can be obtained with high strength and stiffness and excellent impact strength, making these materials alternatives to metals. Construction materials require fire- and high-temperature-resistant components, and moldings and laminates based on phenolics can be utilized due to their resistance to burning and minimal smoke and toxic fumes production. Phenolic composites can positively impact the building and construction industry by improving safety and reducing cost.

This chapter describes the preparation, morphological features, and physical properties of cellulose nanocrystals and nanofibrillated cellulose and their incorporation in nanocomposite materials, including processing methods and ensuing properties. Cellulose nanoparticles have remarkable properties such as light weight, low cost, and availability of the raw material, renewability, nanoscale dimension, and unique morphology. Because of these properties, cellulose nanoparticles have been largely applied as reinforcing fillers in nanocomposite materials.

International audience; 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

Glyoxal, which can be obtained from biomass (as by lipids oxidation), is non-toxic and non-volatile. It was used as a substitute of formaldehyde, which does not have these properties, in the synthesis of a novolac-type phenolic resin, using oxalic acid as a catalyst, which can also be obtained from renewable sources. The glyoxal-phenol resin was used in the preparation of composites reinforced with microcrystalline cellulose (MCC 30, 50, and 70% w/w). Scanning electron microscopy (SEM) images of the fractured surfaces showed that the composites presented a good reinforcement/matrix interface. This can be attributed to the high surface area of the MCC and also to the presence of polar groups (hydroxyl) in both cellulose and matrix, which allowed the formation of hydrogen bonds, leading to a good adhesion between the components present at the interface. Dynamic mechanical thermoanalysis (DMTA) showed that all of the obtained composites have high storage modulus at room temperature. Moreover, the composite reinforced with 30% of MCC showed the lowest water absorption, almost the same as that of the phenolic thermoset, which is used in industrial applications. The results showed that composites with good properties can be prepared using high proportions of materials obtained from biomass., Glioxal pode ser obtido a partir de biomassa (como da oxidação de lipídeos) e não é tóxico ou volátil, tendo sido por isso utilizado no presente trabalho como substituto de formaldeído na preparação de resina fenólica do tipo novolaca, sendo usado como catalisador o ácido oxálico, que também pode ser obtido de fontes renováveis. A resina glioxal-fenol foi utilizada na preparação de compósitos reforçados com celulose microcristalina (CM, 30, 50 e 70% em massa), uma celulose com elevada área superficial. As imagens de microscopia eletrônica de varredura (MEV) das superfícies fraturadas demonstraram que os compósitos apresentaram boa interface reforço/matriz, consequência da elevada área superficial da CM e presença de grupos polares (hidroxilas) tanto na matriz como na celulose, o que permitiu a formação de ligações hidrogênio, favorecendo a compatibilidade entre ambas. A análise térmica dinâmico-mecânica (DMTA) demonstrou que todos os compósitos apresentaram elevado módulo de armazenamento à temperatura ambiente. Além disso, o compósito reforçado com 30% de CM apresentou baixa absorção de água, comparável à do termorrígido fenólico, que é utilizado em escala industrial. Os resultados demonstraram que compósitos com boas propriedades podem ser preparados usando elevada proporção de materiais obtidos de biomassa.

International audience; 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, (2)D, 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.