Viscose fiber/polyamide 12 composites: Novel gas‐phase method for the modification of cellulose fibers with an aminosilane coupling agent

The objective of this study was to improve the adhesion between viscose fibers and polyamide 12 and, thereby, the mechanical properties of the corresponding composites. The cellulose fiber surface was chemically modified in the vapor phase with a silyl coupling agent, aminosilane [(3‐aminopropyl) triethoxysilane]. This new gas‐phase treatment for cellulose fibers proved to be highly effective. Relative to composites without the coupling‐agent treatment, the tensile strength of the composites (40/60 wt % fiber/polymer) increased from 49.3 to 87.4 MPa; the improved adhesion between the fibers and matrix induced by the coupling agent was observed under a scanning electron microscope. The presence and bonding of the coupling agent on the fibers after the reaction was confirmed by solid‐state ²⁹Si‐NMR. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4478–4483, 2006     

Location of some typical vinyl polymers within radiation-grafted cotton fibers: An electron microscopical survey

Electron microscopical observations of radiation-induced rayon–styrene graft copolymers were published by Kaeppner and Huang in 1965. The present paper reports electron microscopical investigations on the relationship of the structure of vinyl–cotton graft polymers to the original morphology of the cotton fiber and into the distribution of the grafted vinyl polymer in the cotton fiber structure. The grafted vinyl monomers investigated in this study were acrylonitrile, styrene, methyl methacrylate, and vinyl acetate. Two radiation-induced procedures were used: simultaneous irradiation grafting and post-irradiation grafting. Ceric ion grafting of acrylonitrile to cotton was included for purposes of comparison. Distribution of the vinyl polymer within the cotton fiber is illustrated by a series of electron micrographs, selected as typical of the particular grafted species under consideration. Results indicate that the diffusion rate of monomer into the cellulose fiber plays an important role in the final distribution of polyacrylonitrile grafts within the fiber. Uniform distribution of polyacrylonitrile in the fiber was achieved by simultaneous irradiation grafting of acrylonitrile on a highly substituted cyanoethylated cotton. In samples of low degree of cyanoethylation the distribution of graft polymer was non-uniform. In grafting initiated by ceric ion the acrylonitrile graft polymer was evenly distributed. Polystyrene–cotton copolymers from grafts, made by simultaneous irradiation of cotton in methanol solutions of the styrene monomer, were uniform throughout the fiber but showed opening of structure associated with the amount of graft formed. Grafting of methyl methacrylate occurred only in the peripheral regions of the fiber; by contrast, grafting of vinyl acetate was uniform throughout the fiber wall. Important factors governing the successful irradiation grafting in cotton fibers are choice of solvent, ratio of monomer to cellulose, nature of prior chemical modification of the cellulose, and total irradiation dosage.     

Crystallization of poly(hydroxybutrate-co-hydroxyvalerate) in wood fiber-reinforced composites

Wood fiber-reinforced composites were prepared from poly(hydroxybutyrate) (PHB) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHB/HV) copolymers containing 9 and 24% valerate. The effects of fibers on crystallization were investigated. Thermomechanical pulp, bleached Kraft fibers, and microcrystalline cellulose filler were used as the reinforcing phase. The crystallization of PHB/HV in composite materials was examined using Modulated Differential Scanning Calorimetry (MDSC) and hot-stage microscopy. Hot-stage microscopy showed that polymer crystallites are nucleated on the fiber surface and that the density of nuclei was greater in fiber-reinforced composites than in unfilled material. Dynamic crystallization experiments showed that bleached Kraft, thermomechanical pulp, and microcrystalline cellulose increased the crystallization rate of PHB and PHB/HV both from the glass and melt. However, ultimate crystallinity determined from the heat of crystallization was the same in unreinforced and reinforced materials. The kinetics of PHB/HV crystallization were examined using nonisothermal Avrami-type analysis. Unreinforced and Kraft-reinforced PHB were characterized and compared with unreinforced PHB/9%HV. The Avrami exponent of crystallization, related to nucleation mechanism and growth morphology, is 2.0 for unreinforced PHB, 2.8 for kraft-reinforced PHB, and 3.0 for unreinforced PHB/9%HV. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1785–1796, 1997     

Diffuse reflectance Fourier transform infrared spectra of wood fibers treated with maleated polypropylenes

The esterification reaction between wood fibers and maleated polypropylenes was investigated. The reaction was conducted in a reactor in the presence of xylene used as a solvent and sodium hypophosphite as catalyst. The reaction between wood fibers and pure maleic anhydride was also investigated. The appearance of an infrared absorption band near 1730 cm⁻¹ indicated that maleated polypropylene chemically reacted by esterification with bleached Kraft cellulose. However, no direct evidence of an esterification reaction was obtained between thermomechanical pulp and maleated polypropylene. The Fourier transform infrared (FTIR) studies showed also that both bleached Kraft cellulose and thermomechanical pulp reacted with maleic anhydride with the formation of ester links. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1163–1173, 1997     

Effect of Kraft Cooking Conditions on the Chemical Composition of the Surface and Bulk of Spruce Fibers

By varying cooking temperature, alkali charge, ionic strength, and cooking time in Kraft pulping of spruce chips, pulps ranging between kappa numbers 20–80 were obtained. The unbleached Kraft pulp fibers were subjected to mechanical peeling in order to separate the surface material from the bulk of the fibers and the carbohydrate composition and lignin content of the two fractions were analyzed. As expected, the lignin and xylan contents were higher on the fiber surface than in the fiber wall. The percentage of xylan on the fiber surface was fairly constant, independent of different pulping conditions or degree of delignification. The lignin proportion on the fiber surface gradually decreased with decreasing kappa number. At a given kappa number, pulping at a higher temperature resulted in less lignin on the fiber surface, probably because of the higher solubility of lignin at higher temperature. Cooking at lower alkali charge also resulted in lower lignin content on the fiber surface at a given kappa number. In this case, there was more time available for degradation of the surface lignin since the lower alkali charge resulted in longer cooking time needed to reach a certain kappa number.     

Microscopical study of carbon/carbon composites obtained by chemical vapor infiltration of 0°/0°/90°/90° carbon fiber preforms

The microstructure of carbon/carbon composites obtained by isothermal, isobaric chemical vapor infiltration (CVI) of carbon fiber preforms consisting of aligned fiber bundles separated by fiber fleeces was studied comparatively by polarized light microscopy (PLM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED). Deposition rate as well as matrix microstructure do not differ in the aligned fiber bundles and fiber fleeces exhibiting different local surface area/volume ratios. The matrices which are homogeneously textured according to PLM exhibit pronounced spatial texture gradients at the sub-μm-scale if investigated by SAED. The texture gradients appear to be independent on the infiltration time, distance between fibers but evidently depend on the total methane pressure. TEM and SEM observations show a thin high-textured layer between the fiber and the medium-textured transitional layer below the high-textured matrix layer containing columnar grains. This thin layer replicates the surface unevenness of the fiber surface while it is absent at the initial carbon fiber surface before infiltration.     

Grafting of poly (methyl acrylate) onto sulfite pulp fibers and its effect on water absorbance

To prepare super water absorbent hydrogels of wood cellulose fibers, poly (methyl acrylate) (PMA) was copolymerized onto softwood sulfite pulp fibers using free radical initiator followed by alkaline hydrolysis. Ceric ammonium nitrate (CAN) was used as the free radical initiator. Effects of various parameters such as fiber concentration, monomer/pulp (M/pulp) ratio, CAN concentration, and reaction time on the grafting yield and on other grafting parameters were investigated. The graft conversion was the same from low to medium fiber concentration. The amount of initiator required was found to be independent of fiber concentration to achieve maximum grafting yield. Different fiber fractions (classified based on their length) have no effect on the grafting yield. The evidence of graft copolymerization was determined by using ATR‐IR spectroscopy. The X‐ray diffraction (XRD) analysis shows that grafting takes place both in amorphous and crystalline regions of cellulose fibers and the decrease in crystallinity of the grafted fibers with an increase in grafting yield was confirmed. The surface morphology of the PMA‐g‐cellulose was characterized by scanning electron microscopy (SEM). The water retention value of the hydrolyzed grafted pulp was determined based on a centrifugation technique. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of sterilization techniques on the physicochemical properties of polysulfone hollow fibers

Sterilized hollow‐fiber membranes are used in hemodialysis, ultrafiltration, bioprocessing, and tissue engineering applications that require a stable and biocompatible surface. In this study, we demonstrated significant changes in the fiber physicochemical properties with different methods of sterilization. Commercial polysulfone (PS) hollow fibers containing poly(vinyl pyrrolidone) were subjected to standard ethylene oxide (ETO), sodium hypochlorite (bleach), and electron‐beam (e‐beam) sterilization techniques followed by analysis of the surface hydrophilicity, morphology, and water‐retention ability. E‐beam sterilization rendered more hydrophilic fibers with water contact angles near 47° compared to the ETO‐ and bleach‐treated fibers, which were each near 56°. Atomic force microscopy revealed lumen root mean square (rms) roughness values near 19 nm for all three sterilization methods; however, e‐beam‐sterilized and bleach‐treated fibers had significantly higher (～ 106 nm) rms values for the outer wall compared to the ETO‐sterilized fibers (～ 39 nm). The increased hydrophilicity and surface area of the e‐beam‐sterilized fiber were reflected by a greater water evaporation rate than that of the ETO‐treated fiber. These results demonstrate that common sterilization methods may significantly and distinctly alter the polymer membrane physicochemical properties, which may, in turn, impact the performance and, in particular, surface fouling. For tissue engineering and bioprocessing applications, these changes may be leveraged to promote cell adhesion and spreading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A new and simple way of preparing polycation‐grafted fibrous cellulose

A new way of producing polycation‐grafted fibrous cellulose for its use as a retention aid in the papermaking process was conceived. It consists of adding, under intense stirring, to a cellulose fibers suspension at a basic pH a cationic polyacrylamide dissolved in water. As the cellulose fiber's surface is negatively charged because of its more or less acid groups, the cationic polymer adsorbs on it. The cationic‐grafted cellulose fibers are very similar to the cellulose fibers used in papermaking, since the polymer is (on a micrometer scale) homogeneously grafted on them as a film. It could so be used to increase the retention of the negatively charged fillers, fibers, and pigments during the process, without altering the properties of the resulting sheet of paper. The amount of polymeric grafts depends on the quantity of anionic groups on fiber's surface and varies monotonically with the grafting temperature and polyacrylamide's concentration in the blend. The grafted fibrous cellulose is well stable, even in drastic media and for lower M_w grafts, and the amount of grafted polymer also depends on the concentration and characteristics of fiber's suspension. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3149–3157, 2006     

Photoinitiated polymerization of glycidyl methacrylate with cotton cellulose

Unsensitized, photoinitiated polymerization reactions of glycidyl methacrylate from solutions of water and water–methanol with cotton cellulose fabrics were investigated. When several layers of cotton fabrics were immersed in solutions of glycidyl methacrylate and only the surface layer was exposed to light, polymerization reactions were initiated in this layer and also initiated in inner layers of fabrics, probably by chain transfer reactions. Photoinitiated (350 nm, 24 W, 34 min) polymerizations of glycidyl methacrylate (7.5 vol-%) from water (43 vol-%)–methanol (57 vol-%) with cotton fabrics in one-, three-, and six-layered configurations were: one-layered, 32% polymer; three-layered, 30%, 27%, and 25% polymer; and six-layered, 29%, 25%, 22%, 20%, 14%, and 11% polymer. Electron-microscopic examination of the distribution of poly(glycidyl methacrylate) within the cotton fibrous structure showed that polymer was distributed throughout the cross section of the fiber. At the surface of the fibers, the polymer tended to be more concentrated than within the cross section of the fibers and to encapsulate them. Photoinitiated polymerization reactivities of several vinyl monomers from solution with cotton cellulose fabrics were compared with those of glycidyl methacrylate as follows: methyl methacrylate > glycidyl methacrylate > diacetone acrylamide > 1,3-butylene dimethacrylate > methacrylic acid > acrylonitrile > divinylbenzene.     

Surface modification of natural substrates by atom transfer radical polymerization

Surface modification of various solid polysaccharide substrates was conducted by grafting methyl acrylate (MA) and styrene via atom transfer radical polymerization (ATRP) to produce well‐defined polymer grafts. The hydroxyl groups on the surfaces of the substrates were reacted with 2‐bromoisobutyryl bromide followed by graft copolymerization under ATRP conditions. The studied substrates were filter paper, microcrystalline cellulose, Lyocell fibers, dialysis tubing, and chitosan films. The modified substrates were analyzed by FT‐IR, water contact angle measurements, TGA, and SEM. FT‐IR characterization of the grafted substrates showed significant differences between the different substrates in the amount of grafted polymer. Higher amounts of polymer seem to be possible to graft from native cellulose substrates than from regenerated cellulose substrates. To investigate whether the grafted polymers were “living” after a longer time period, a second layer of polystyrene was grafted from a filter paper modified with PMA one year ago. FT‐IR characterization of the filter paper showed a peak corresponding to styrene, indicating that a block copolymer had been formed on the surface. Graft copolymerization can be used to change and tailor the surface properties of the polysaccharide substrates. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4155–4162, 2006     

The sorption of poly(vinyl acetate) on cellulose. I. The nature and extent of the sorbed layer

The sorption of poly(vinyl acetate) from benzene solution onto cellulose fibers has been investigated with particular attention to the nature and extent of the sorbed layer of polymer. The cellulose substrate has been varied by swelling pretreatments with water, ethylenediamine, and 18% sodium hydroxide. The density of the sorbed polymer after drying was found to be similar to that of the bulk polymer (1.19–1.20 g/cm³). Water vapor sorption isotherms were used to evaluate the internal surface of cellulose and the decrease in the surface area accessible to water after sorption of the polymer. This decrease was considered equivalent to the area covered by sorbed polymer. The amount of polymer sorbed per unit area (5.0–5.5 mg PVAc sorbed from benzene per 1 m² of cellulose surface) was found to be substantially independent of the amount of sorbed polymer and of the swelling pretreatment, indicating that the thickness of the sorbed layer was quite uniform (40–50 Å). A comparison of the thickness of the sorbed layer in the dry state with the thickness of a monolayer with polymer molecules lying flat on the solid surface indicated that the fraction of the polymer segments attached directly to the surface was about 0.10. The amount of polymer sorbed per unit area of cellulose and consequently the thickness of the sorbed layer and the fraction of attachment can be affected by the nature of the solvent from which the polymer is sorbed.     

Electrospinning of Technical Lignins for the Production of Fibrous Networks

Abstract

Electrospinning is an effective strategy to produce micron and sub-micron diameter fibrous networks from a variety of polymeric systems. Using seven different technical lignins the effect of lignin structure on fiber formation by electrospinning was studied. Surprisingly, none of the technical lignins could be electrospun into continuous fibers, although beaded fiber formation was observed for the softwood Kraft lignin system at high concentration (>50 wt%). However, the addition of poly(ethylene oxide) dramatically affected the electrospinning behavior and fiber formation. For all of the technical lignins a clear transition from electrospray or beaded fibers to uniform fibers was observed upon addition of poly(ethylene oxide); the lignin concentration dependent on poly(ethylene oxide) content. In all of the systems a linear increase in fiber diameter with increasing lignin concentration was observed. At the same concentration, the various lignin solutions had varying viscosities and different electrospinning behavior, that is, fiber diameter and ability to form uniform fibers, suggesting lignin specific structures and intermolecular interactions are influencing solution properties and electrospinning behavior. In fact, specific viscosity versus concentration plots reveal scaling exponents’, η ～ c^7.4–7.8 consistent with a branched polymer participating in intermolecular interactions such as hydrogen bonding or association complexes.     

Eucalyptus Kraft pulp fibers as an alternative reinforcement of silicone composites. I. Characterization and chemical modification of Eucalyptus fibers with organosilane coupling agent

In this study, bleached Eucalyptus fibers obtained by a Kraft pulping process were characterized prior to and after chemical modification with a silane coupling agent, vinyltriethoxysilane, for use as an alternative additive in composites based on silicone. The presence of a silane coating on the fiber surface was observed by infrared, energy dispersive, and X‐ray photoelectron spectroscopies. The morphology of the fibers was investigated by field emission scanning electron microscopy. The untreated fibers were ribbon‐shaped and had a rough surface, due to the presence of fibrils. The coating reaction conducted in ethanol gave rise to loose fibrils and a more rough surface compared with those of untreated fibers. A smoother surface was observed when fibers were modified in tetrahydrofuran. The surface topography of the fibers was also examined by atomic force microscopy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2573–2579, 2002     

Interfacial properties of polyelectrolyte–cellulose systems. II. Electrokinetic properties of cellulose fibers with adsorbed monolayers of cationic polyelectrolyte

Zeta potential measurements by the streaming current method were performed on pulp (DP) fibers with or without irreversibly adsorbed monolayers of cationic polyelectrolyte. Factors affecting the electrokinetic properties of these fibers, such as the amount of adsorbed polymer, the polymer molecular weight (M_n 50,000 and 200,000), ionic strength (10^?5 ～ 10^?2M KCl), and the pH of the streaming medium (KCl solution), were examined. As the amount of adsorbed polymer increased, the negative zeta potential of the fibers decreased until the polarity of the zeta potential was reversed to the positive side. A marked change in the value of zeta potential was not observed when the formation of the saturated monolayer was completed. The zeta potential also varied in proportion to an increase in the amount of polymer adsorbed. Experimental results are interpreted with reference to the origin of the surface charge, the amphoteric nature of the surface, the modes of adsorption, and the adsorbed polymer chain configuration. Possible effects of the adsorbed monolayer formation on the structural change of the electric double layer at the fiber surface are discussed. It is concluded that the formation of a monolayer of cationic polyelectrolytes on the negatively charged cellulose fibers under the condition of k₁ > k₂ (part I) provides a means to arbitrarily control the charge of the fibers until formation of a saturated monolayer.     

高压静电场纺丝法制备羟丙基甲基纤维素邻苯二甲酸酯超细纤维

通过高压静电场纺丝法制备了羟丙基甲基纤维素邻苯二甲酸酯(HPMCP)的超细纤维,并详细研究了溶液浓度、纺丝电压及混合溶剂的配比对纤维形态和直径的影响。当混合溶剂中的无水乙醇与二氯甲烷为1∶1(V/V)时,在纺丝电压为30kV的条件下,HPMCP可纺丝的浓度范围为7%～16%(wt)。溶液浓度为7%时,电纺得到珠状纤维;浓度大于8%时,得到表面光滑的圆柱状纤维。随着纺丝溶液浓度的增大,所得纤维的平均直径逐渐增大。在HPMCP溶液浓度(8%)和溶剂组成(无水乙醇/二氯甲烷=1∶1)保持一定时,随着纺丝电压的增大,所得纤维的平均直径呈下降的趋势。而在纺丝浓度和电压一定的情况下,随着混合溶剂中二氯甲烷体积分数的增大,所得纤维的平均直径先增大后减小,无水乙醇与二氯甲烷体积比为1∶1和1∶2时,所得纤维的直径分布相对集中。     

Controlled interactions in cellulose-polymer composites. 1: Effect on mechanical properties

The surface properties of cellulose fibers have been modified by heat treatment, by silane coupling agents, and by maleated polypropylene grafts. The effectiveness of these methods has been evaluated by electron spectroscopy (ESCA), by contact angle measurements, and by inverse gas chromatography. The latter analyses yielded information on the fibers' acid/base interaction potential. Cellulose was found to be amphoteric, with prevalent acidic properties. Heat and chloro-silane treatments accentuated acidity, while amino-silane treatment produced net basicity in the fiber surface. Modification with maleated polypropylene reduced specific interactions and converted the fiber to a predominantly dispersion-force solid. The modified fibers were used in composites with polypropylene (neutral), polystyrene (base), and chlorinated polyethylene (acid) as matrix. Stress/strain and dynamic mechanical parameters were found to vary with acid/base interactions between polymer and fiber, significant improvements being noted in elastic and storage moduli, in tensile strength and elongation. In polypropylene, properties were unaffected by acid/base considerations. Acid/base forces, not necessarily dominant, merit consideration in the design of surface modification strategies intended to optimize composite mechanical properties.     

Surface and pore structure modification of cellulose fibers through cellulase treatment

The surface and pore structure of cellulose fibers have a significant impact on the properties and performance in applications. Cellulase enzymatic hydrolysis of cellulose fibers can result in changes to the surface and pore structure, thus providing a useful tool for fiber modification. This research characterizes these changes using various test methods such as fiber dimension, water retention value (WRV), hard‐to‐remove (HR) water content, freezing and nonfreezing bound water content, polymer adsorption, and crystallinity index. For a high‐dosage cellulase treatment (600 U/g dry solid), the fiber length was significantly decreased and the fibers were “cut” in the cross direction, not in the axial direction. The swelling capacities as measured by the WRV and HR water content increased for the high‐dosage treatment. Three independent measurements (nonfreezing bound water, polymer adsorption, and crystallinity index) are in good agreement with the statement that the amorphous regions of cellulose fibers are a more readily available substrate relative to crystalline regions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3833–3839, 2007     

Characterization of Poly (Methyl Acrylate) Grafted Bleached Sulfite Pulp Fibers using AFM,AEM, EDS and STEM

Abstract

Sulfite pulp fibers were grafted by poly (methyl acrylate) at a low‐consistency (1% pulp consistency) and medium‐consistency (10% pulp consistency). It is of fundamental interest to determine the distribution of the polymer chains obtained at different fiber concentrations during grafting. In this study, modern analytical tools such as atomic force microscope (AFM), energy dispersive spectrometer (EDS), and scanning transmission electron microscope (STEM) were used for investigating the distribution of the polymer chains in the fiber matrix. AFM images in tapping mode showed that the fiber surface was covered with in‐situ generated polymers. The X‐ray mapping of Na in the cross‐section of the hydrolyzed grafted fibers by using EDS in combination with Na line scans by STEM showed that the distribution of poly (methyl acrylate) was affected by the pulp consistency during grafting; at a medium‐consistency condition the outer region of the fiber structure had a higher polymer concentration than the inner region. On the other hand, at a low‐consistency condition, grafting occurred uniformly across the fiber wall structure.     

Polymer deposition in sisal fibers: A structural investigation

Sisal (Agave sisalana) fibers were graft copolymerized with certain vinyl monomers (methyl acrylate, ethyl acrylate and methyl methacrylate) using gamma irradiation and ceric ammonium nitrate as initiation techniques. Examinations of the surface topology and the internal structure of the grafted fibers made by scanning electron microscopy. The results derived from the SEM observations on transverse sections of the grafted fibers were supplemented by information obtained by polarized light microscopy. Polymer was deposited not only on the surface of the fiber substrate, but also in the lumen, the middle lamellae, and throughout the cell wall network of the multicellular aggregates. The degree of polymer inclusion in the lumen (which is the most conspicuous of all the available internal sites) was found to depend on the percentage graft copolymer add-on, as well as on the previous history of the fiber (natural or chemically modified). The mechanical properties of the grafted fibers were investigated (by means of an Instron tensile tester).