Thermoset phenolic matrices reinforced with unmodified and surface-grafted furfuryl alcohol sugar cane bagasse and curaua fibers: properties of fibers and composites

Composites based on phenolic matrices and unmodified and chemically modified sugar cane bagasse and curaua fibers were prepared. The fibers were oxidized by chlorine dioxide, mainly phenolic syringyl and guaiacyl units of the lignin polymer, followed by grafting furfuryl alcohol (FA), which is a chemical obtained from a renewable source. The fibers were widely characterized by chemical composition analysis, crystallinity, UV-vis diffuse reflectance spectroscopy, SEM, DSC, TG, tensile strength, and 13C CP-MAS NMR. The composites were analyzed by SEM, impact strength, and DMA. The SEM images and DMA results showed that the oxidation of sugar cane bagasse fibers followed by reaction with FA favored the fiber/matrix interaction at the interface. The same chemical modification was less effective for curaua fibers, probably due to its lower lignin content, since the reaction considered touches mainly the lignin moiety. The tensile strength results obtained showed that the fibers were partially degraded by the chemical treatment, decreasing then the impact strength of the composites reinforced with them. In the continuity of the present project, efforts has been addressed to the optimization of fiber surface modification, looking for reagents preferably obtained from renewable resources and for chemical modifications that intensify the fiber/matrix interaction without loss of mechanical properties.     

The Effect of Surface Modification of Aligned Poly-L-Lactic Acid Electrospun Fibers on Fiber Degradation and Neurite Extension

The surface of aligned, electrospun poly-L-lactic acid (PLLA) fibers was chemically modified to determine if surface chemistry and hydrophilicity could improve neurite extension from chick dorsal root ganglia. Specifically, diethylenetriamine (DTA, for amine functionalization), 2-(2-aminoethoxy)ethanol (AEO, for alcohol functionalization), or GRGDS (cell adhesion peptide) were covalently attached to the surface of electrospun fibers. Water contact angle measurements revealed that surface modification of electrospun fibers significantly improved fiber hydrophilicity compared to unmodified fibers (p < 0.05). Scanning electron microscopy (SEM) of fibers revealed that surface modification changed fiber topography modestly, with DTA modified fibers displaying the roughest surface structure. Degradation of chemically modified fibers revealed no change in fiber diameter in any group over a period of seven days. Unexpectedly, neurites from chick DRG were longest on fibers without surface modification (1651 ± 488 μm) and fibers containing GRGDS (1560 ± 107 μm). Fibers modified with oxygen plasma (1240 ± 143 μm) or DTA (1118 ± 82 μm) produced shorter neurites than the GRGDS or unmodified fibers, but were not statistically shorter than unmodified and GRGDS modified fibers. Fibers modified with AEO (844 ± 151 μm) were significantly shorter than unmodified and GRGDS modified fibers (p<0.05). Based on these results, we conclude that fiber hydrophilic enhancement alone on electrospun PLLA fibers does not enhance neurite outgrowth. Further work must be conducted to better understand why neurite extension was not improved on more hydrophilic fibers, but the results presented here do not recommend hydrophilic surface modification for the purpose of improving neurite extension unless a bioactive ligand is used.     

Properties and potential applications of natural cellulose fibers from the bark of cotton stalks

Natural cellulose fibers have been obtained from the bark of cotton stalks and the fibers have been used to develop composites. Cotton stalks are rich in cellulose and account for up to 3 times the quantity of cotton fiber produced per acre. Currently, cotton stalks have limited use and are mostly burned on the ground. Natural cellulose fibers obtained from cotton stalks are composed of approximately 79% cellulose and 13.7% lignin. The fibers have breaking tenacity of 2.9 g per denier and breaking elongation of 3% and modulus of 144 g per denier, between that of cotton and linen. Polypropylene composites reinforced with cotton stalk fibers have flexural, tensile and impact resistance properties similar to jute fiber reinforced polypropylene composites. Utilizing cotton stalks as a source for natural cellulose fibers provides an opportunity to increase the income from cotton crops and make cotton crops more competitive to the biofuel crops.     

Investigation on the surface properties of chemically modified natural fibers using inverse gas chromatography

This paper presents the application of inverse gas chromatography (IGC) technique for characterization and comparison of the surface properties of the natural fibers as reinforcement fillers in wood plastic composites. The effects of chemical modification using 1% NaOH were also studied. The fibers used for this work were Iranian cultivated eucalyptus, spruce, bagasse, and wheat straw. Chemical composition of fibers was found to be modified after treatment as characterized by Fourier transform infrared spectroscopy (FTIR). The crystallinity of fibers and the specific interaction was improved by the alkaline treatment, with more relevance to the agro-fibers. The IGC shows also a general increase in the wettability of the modified fiber when compared with the raw (unmodified) samples. Alkaline treatment achieves the best overall improvement in the properties evaluated of the agro-fibers when compared to the wood fibers.     

Preparation and properties of HDPE/sugarcane bagasse cellulose composites obtained for thermokinetic mixer

The use of natural fibers as reinforcement for thermoplastics has generated much interest due to their low cost, possibility of environmental protection and use of locally available renewable resources. In this work the mechanical and morphological properties of high density polyethylene/pre-treated and modified residues from sugarcane bagasse cellulose composites were analyzed. Composites were produced by a thermokinetic mixer. The microstructural analyses of fracture surface from composites can be easily evaluated by microscopic techniques. Results showed that the modification of sugarcane bagasse cellulose with zirconium oxychloride was successfully accomplished and that this reinforcement material with high density polyethylene showed tensile strength higher than non-modified sugarcane bagasse cellulose. Modification in the sugarcane bagasse cellulose influenced directly in mechanical properties of the composite material. This can be observed by the fracture surface, which showed that modified cellulose sugarcane bagasse improved interfacial adhesion between fiber and matrix.     

Influence of silicone oil modification on properties of ramie fiber reinforced polypropylene composites

This paper focused on the analyses of the composition, microstructure, thermal stability and mechanical behavior of modified ramie fiber and its reinforced polypropylene composites. Ramie fiber (RF) was treated with epoxy-silicone oil (ESO) at 160 °C in argon gas. The FTIR and XRD analyses indicated that some silicone molecular chains were bonded on the surface of modified RF, which decreased the crystallinity of the fiber without changing the crystalline type of cellulose. The SEM results of fracture surface showed that the modified RF/PP composite had better interfacial bonding between RF and PP. The mechanical tests showed that the impact strength and the elongation at break of RF/PP were increased by 17.0% and 196% after modification, respectively. The tensile strength of 30RF/PP was improved from 18.95 MPa to 25.96 MPa compared to pure PP. The results of TGA showed that fiber treatment could improve the degradation temperature of RF/PP composites.     

Contributions of polystyrene to the mechanical properties of blended mixture of old newspaper and wood pulp

Composites from recycled newspaper would result in the effective use of the waste product which is currently burned or land-filled, as well as potential reduction in the cost of manufactured composite. In this work, old newspaper (ONP) together with yellowish wood pulp and waste polystyrene from packaging were used to produce composite. The technique studied in this work is an alternative to the conventional melt compounding and was expected to provide efficient wetting of fibers by the polymer. Polystyrene was grafted with acrylonitrile, ethylmethacrylate and butylmethacrylate, respectively, using benzoyl peroxide as an initiator. The amount of polystyrene to monomer is 1:0.75 and to initiator is 1:1. The grafted copolymers were characterized using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Different ratios of waste polystyrene or grafted waste polystyrene were mixed with a blend of old newsprint and wood pulp to form composites. The mechanical properties of these composites as well as water uptake were studied. The tensile properties of the prepared composites did not show essential improvement, except for the modulus of elasticity. Scanning electron microscopy indicate that composites with grafted polystyrene showed more homogeneity than the composite with polystyrene and also than blank, so the grafted polymer is distributed very well improving the mechanical properties of the composites. Strong adhesion between the fiber and grafted polymer was found.     

Effect of fiber treatments on tensile and thermal properties of starch/ethylene vinyl alcohol copolymers/coir biocomposites

Coir fibers received three treatments, namely washing with water, alkali treatment (mercerization) and bleaching. Treated fibers were incorporated in starch/ethylene vinyl alcohol copolymers (EVOH) blends. Mechanical and thermal properties of starch/EVOH/coir biocomposites were evaluated. Fiber morphology and the fiber/matrix interface were further characterized by scanning electron microscopy (SEM). All treatments produced surface modifications and improved the thermal stability of the fibers and consequently of the composites. The best results were obtained for mercerized fibers where the tensile strength was increased by about 53% as compared to the composites with untreated fibers, and about 33.3% as compared to the composites without fibers. The mercerization improved fiber–matrix adhesion, allowing an efficient stress transfer from the matrix to the fibers. The increased adhesion between fiber and matrix was also observed by SEM. Treatment with water also improved values of Young’s modulus which were increased by about 75% as compared to the blends without the fibers. Thus, starch/EVOH blends reinforced with the treated fibers exhibited superior properties than neat starch/EVOH.     

Surface modification of natural fibers using bacteria: depositing bacterial cellulose onto natural fibers to create hierarchical fiber reinforced nanocomposites

Triggered biodegradable composites made entirely from renewable resources are urgently sought after to improve material recyclability or be able to divert materials from waste streams. Many biobased polymers and natural fibers usually display poor interfacial adhesion when combined in a composite material. Here we propose a way to modify the surfaces of natural fibers by utilizing bacteria ( Acetobacter xylinum) to deposit nanosized bacterial cellulose around natural fibers, which enhances their adhesion to renewable polymers. This paper describes the process of modifying large quantities of natural fibers with bacterial cellulose through their use as substrates for bacteria during fermentation. The modified fibers were characterized by scanning electron microscopy, single fiber tensile tests, X-ray photoelectron spectroscopy, and inverse gas chromatography to determine their surface and mechanical properties. The practical adhesion between the modified fibers and the renewable polymers cellulose acetate butyrate and poly(L-lactic acid) was quantified using the single fiber pullout test.     

Immobilization of cellulases on the reversibly soluble polymer Eudragit S‐100 for cotton treatment

Cellulases can penetrate into the fiber, causing tensile strength loss of the cellulosic fibers or fabrics. To minimize the tensile strength loss, we have immobilized cellulases on Eudragit S‐100. The characteristics of covalent Eudragit cellulase were evaluated using gel filtration analysis and UV spectra. Gel filtration analysis revealed that the cellulases were covalently bound to the polymer. Covalent Eudragit cellulase was loaded with the enzyme of about 40% and had a relative activity about 80% at a Eudragit S‐100 concentration of 15 g/L. When cellulase is bound to the polymer, the solubility profile becomes similar to the one of Eudragit. In addition, the effects of the enzyme on the cotton yarns and fabric using cellulases have been investigated. Native and immobilized cellulases caused improvements in whiteness and wrinkle recovery angle of the fabric in comparison to the control samples. The bending stiffness results show that native and immobilized cellulase treated cotton fabric has an improved softness than the control samples. It was found that using the immobilized cellulase reduced the weight and tensile strength, because the hydrolytic attack is only limited to the surfaces of cotton fibers.     

Renewable resource-based green composites from recycled cellulose fiber and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) bioplastic

Novel "green" composites were successfully fabricated from recycled cellulose fibers (RCF) and a bacterial polyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) by melt mixing technique. Various weight contents (15%, 30%, and 40%) of the fibers were incorporated in the PHBV matrix. The effect of the fiber weight contents on the thermal, mechanical, and dynamic-mechanical thermal properties of PHBV was investigated and a comparative property analysis was performed with RCF-reinforced polypropylene (PP) composites. The tensile and storage moduli of the PHBV-based composites were improved by 220% and 190%, respectively, by reinforcement with 40 wt % RCF. Halpin-Tsai and Tsai-Pagano's equations were applied for the theoretical modeling of the tensile modulus of PHBV-based composites. The heat deflection temperature (HDT) of the PHBV-based composites was increased from 105 to 131 degrees C, while the coefficient of linear thermal expansion (CLTE) value was reduced by 70% upon reinforcement with 40 wt % RCF. The PHBV-based composites had also shown better tensile and storage moduli and lower CLTE values than PP-based composites. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were used to study the melting behavior, thermal stability, and morphology of the composite systems, respectively.     

Quality of chemically modified hemp fibers

Hemp fibers are very interesting natural material for textile and technical applications now. Applying hemp fibers to the apparel sector requires improved quality fibers. In this paper, hemp fibers were modified with sodium hydroxide solutions (5% and 18% w/v), at room and boiling temperature, for different periods of time, and both under tension and slack, in order to partially extract noncellulosic substances, and separate the fiber bundles. The quality of hemp fibers was characterised by determining their chemical composition, fineness, mechanical and sorption properties. The modified hemp fibers were finer, with lower content of lignin, increased flexibility, and in some cases tensile properties were improved. An original method for evaluation of tensile properties of hemp fibers was developed.     

Modification of high lignin content kraft pulps with laccase to improve paper strength properties. 1. Laccase treatment in the presence of gallic acid

Laccase was reacted with gallic acid in the presence of a high-kappa (91) kraft pulp. The result was a modified pulp with 34%, 20%, and 72% improvements in burst, tensile, and wet tensile strength compared to untreated control samples. Fully bleached pulps were not responsive to the laccase treatment, indicating lignin was the major target for the fiber modification. The results indicate that the strength increases were a combined effect of improvements of hydrogen bonding between fibers and creation of phenoxy radical cross-links within the sheet.     

Nutritional characteristics of a neoglycoprotein, casein modified covalently by glucose

Glucose was combined covalently with the epsilon-amino groups of lysyl residues of bovine casein in the presence of sodium cyanoborohydride as a reducing reagent by reductive alkylation, forming stable secondary amine linkages. Solubility characteristics and nutritional values of the neoglycoprotein were examined. The degree of modification (%) of the glucosylated casein was 82.5. Solubility of the modified casein was increased by the attachment of glucose. The modification did not disturb the digestion of casein by pepsin or trypsin. Rat feeding experiments using 10% protein diets demonstrated that the protein efficiency ratio (PER) of the modified casein was 0.35 +/- 0.33 compared with 2.99 +/- 0.29 for the unmodified casein. When the modified casein was supplemented with L-lysine to equal the level of total lysine of unmodified casein, the PER value was increased to 2.21 +/- 0.29. Nitrogen balance experiments showed that the modified casein was digested completely. On the other hand, biological value and net protein utilization of the modified protein were shown to be considerably lower than those of the unmodified casein.     

Protein adsorption and leakage in carrier-enzyme systems

The capability of binding enzymes adsorptively to unmodified and silanized silica and glass as well as modified polystyrene carriers was studied for alpha-amylase, beta-amylase, and alpha-chymotrypsin. In most cases a high percentage of protein was bound very firmly under considerable loss of activity. The leakage of protein from the carriers was studied by measuring the intrinsic protein fluorescence on beta-amylase adsorptively bound to aminopropyl silica, aminomethyl, and hexadecylaminomethyl polystyrene. It was compared with the leakage of beta-amylase covalently bound to the same carriers via glutaraldehyde, trichloro-triazine, or benzoquinone. In the absence and in the presence of substrate, at 25 and at 60 degrees C, the leakage rates of the adsorptively bound enzymes were not higher than in the covalently bound systems. The poorest binding stability was found in benzoquinone-coupled beta-amylase derivatives. It is even reduced at higher temperatures, whereas the temperature did not show any remarkable influence on the leakage of the other derivatives. In adsorptively as well as in all the covalently bound systems, the presence of substrate did not promote the protein leakage.     

ATRP grafting from cellulose fibers to create block-copolymer grafts

Cellulose fibers, in the form of a conventional filter paper, have been modified by reacting the hydroxyl groups on the fiber surface with 2-bromoisobutyryl bromide, followed by grafting using ATRP conditions. The papers were first grafted with methyl acrylate (MA), rendering the paper very hydrophobic as reported in an earlier work. The papers were analyzed by gravimetry, FT-IR, ESCA, and AFM. To verify that the polymerization from the surface was "living", a second layer of another, hydrophilic, polymer, 2-hydroxyethyl methacrylate (HEMA), was grafted upon the PMA layer, creating a block-copolymer graft from the fibers. After the layer of PHEMA had been attached, contact angle measurements were no longer possible, because of the absorbing nature of PHEMA-grafted layer. This indicates that a copolymer had indeed been formed on the surface. FT-IR showed a large increase in carbonyl content after the PHEMA-grafting, which further proves that a layer of PHEMA was attached to the PMA layer. This goes to show that the hydrophilic/hydrophobic behavior of a cellulose surface can be tailored by the use of "living"/controlled radical polymerization methods such as ATRP.     

Grafting of cellulose fibers with poly(epsilon-caprolactone) and poly(L-lactic acid) via ring-opening polymerization

In this study, ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) and L-lactide (L-LA) has been performed from cellulose fibers. The hydroxyl groups on cellulose act as initiators in the polymerization, and the polymers are covalently bonded to the cellulose fiber. As an attempt to introduce more available hydroxyl groups on the surface, and thereby obtain higher grafting efficiency in the ROP of epsilon-CL and L-LA, unmodified paper was modified with xyloglucan-bis(methylol)-2-methylpropanamide (XG-bis-MPA) and 2,2-bis(methylol)propionic acid (bis-MPA), respectively. The grafted substrates were characterized via Fourier transform infrared spectroscopy (FTIR), contact angle measurement, atomic force microscopy, and enzymatic degradation. The results showed a successful grafting of poly(epsilon-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) from the cellulose fiber surfaces. Furthermore, the results showed an improved grafting efficiency after activation of the cellulose surface with bis-MPA, and showed that the amount of grafted polymer could be controlled by the ratio of added free initiator to monomer.     

A Comprehensive Study of the Polypropylene Fiber Reinforced Fly Ash Based Geopolymer

As a cementitious material, geopolymers show a high quasi-brittle behavior and a relatively low fracture energy. To overcome such a weakness, incorporation of fibers to a brittle matrix is a well-known technique to enhance the flexural properties. This study comprehensively evaluates the short and long term impacts of different volume percentages of polypropylene fiber (PPF) reinforcement on fly ash based geopolymer composites. Different characteristics of the composite were compared at fresh state by flow measurement and hardened state by variation of shrinkage over time to assess the response of composites under flexural and compressive load conditions. The fiber-matrix interface, fiber surface and toughening mechanisms were assessed using field emission scan electron microscopy (FESEM) and atomic force microscopy (AFM). The results show that incorporation of PPF up to 3 wt % into the geopolymer paste reduces the shrinkage and enhances the energy absorption of the composites. While, it might reduce the ultimate flexural and compressive strength of the material depending on fiber content.     

A novel and efficient approach for imparting magnetic susceptibility to lignocellulosic fibers

We have imparted magnetic susceptibility to lignocellulosic fibers by adding iron powder in a heterogeneous manner to the fibers during hydrogen peroxide bleaching chemistry. We have therefore generated carboxylic acid groups in the fibers by deliberately inducing cellulose degradation through Fenton catalysis of the hydrogen peroxide during the chemical oxidation process at a specified level of iron. The iron particles consequently have an exposed layer of iron oxide that allows ionic neutralization of the negatively charged fiber acid groups. After removal of non-attached, excess iron, these fibers have been cast into two-dimensional sheets with two different original iron concentrations and tested for physical and chemical properties. Physical tests included tensile, zero-span tensile, caliper, and surface resistivity. Chemical tests included surface charge, lignin content (kappa) and viscosity. SEM and ICP were also conducted. Remarkably, the magnetically susceptible sheets with incorporated iron were able to retain a tensile strength similar to the unbleached sheets despite attenuation in fiber strength. This is likely due to a chemical refining phenomenon which allowed for increased fiber–fiber bonding. The introduction of the retained iron also significantly alters the surface resistivity of the paper sheets. Such fibers may have a use in applications where charge conduction or dispersion is necessary.     

Gamma-radiation induced changes in the physical and chemical properties of lignocellulose

gamma-radiation induced effects on the physical and chemical properties of natural lignocellulose (jute) polymer were investigated. Samples were irradiated to required total doses at a particular dose rate. The changes in the parameters such as the tensile strength, elongation at break, and work done at rupture for the lignocellulose samples on irradiation with the gamma-rays from a cobalt-60 source were measured. The mechanical properties were found to have nonlinear relations with the radiation doses. The chemical stability of irradiated fibers was found to degrade progressively with the increase of radiation dose. Additionally, other chemical changes of the samples due to exposure to high-energy radiation were also investigated using fluorescence and infrared spectroscopic analysis. Differential scanning calorimetry and thermogravimetric studies showed a significant reduction in thermal stability. The wide-angle X-ray diffraction study showed that structural changes of cellulose appeared due to the radiation-induced chemical reaction of lignocellulose.