Effects of polar groups of polymer matrix on reinforcement-matrix interaction in kevlar fiber-reinforced composites

In order to investigate the interaction between the polar groups of reinforcement and matrix in polymer composite, mechanical properties were studied for the Kevlar fiber-reinforced composites (Kevlar is a registered trademark of E. I. duPont de Nemours Co. Inc.), in which the kind and fraction of polar components in matrix were varied using blended polymers. For the composites comprised of polymethyl methacrylate and poly(hydroxypropyl ether of bisphenol A) as the matrix, a subtransition, which can be ascribed to the interphase formed on the reinforcement surface by a strong interaction between reinforcement and matrix, appears at a temperature above the primary transition on the E″ versus temperature curves. Such a subtransition is obscured or diminished accompanying the decrease in fraction of the polar components in the matrix. The fiber efficiency factors for strength are also decreased with a decrease in the fraction of the polar components. These results imply that the reinforcement-matrix interaction is affected depending on the fraction of the polar components in matrix. For the composite comprised of blending the two polar components as the matrix, each component can contribute to the interaction with the reinforcement. The results obtained from the Fourier transform infrared spectroscopy on the matrix polymer-coated Kevlar cloth do not contradict those obtained by studying the mechanical properties.     

Hybrid polymer networks of unsaturated polyester–urethane as composite matrices for jute reinforcement

Reactions of unsaturated polyester resin and 4,4′ diphenyl methane diisocyanate were carried out at different NCO/OH ratios in presence of catalysts to form the hybrid polymer networks. Chain extender (1,4 butanediol) added in the hybrid network (NCO/OH ratio: 0.76) was optimized at a level of ～ 3 wt % only of the polyester resin. The curing of these networks was studied by a rigid body pendulum type (RPT) method in terms of reduced damping ratio and increased frequency. Lack of multiple glass transition temperatures, sharp Tan delta peak, and particulate composite type morphology clearly demonstrated the formation of phase mixed domains in the hybrid networks. The storage modulus and loss modulus master curves obtained by dynamic mechanical analysis indicate that hybrid polymer networks retained higher modulus at lower and intermediate frequencies over the polyester resin showing their superior time‐dependent response. Efficacy of these hybrid network resins was examined as matrices in the jute composites and compared with those of polyester resin and unsaturated polyester–polyurethane interpenetrating network matrices. It is found that the hybrid polymer network matrix composites exhibited superior physicomechanical properties under both dry and boiling water age test. Fractographic evidences such as fiber–matrix adhesion, hackle markings, and fiber breakage also supported their superior behavior over other composite matrices. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of nanofillers as reinforcement agents for lignin composite fibers

Biobased nanocomposites and composite fibers were prepared from organosolv lignin/organoclay mixtures by mechanical mixing and subsequent melt intercalation. Two organically‐modified montmorillonite (MMT) clays with different ammonium cations were used. The effect of organoclay varying from 1 to 10 wt % on the mechanical and thermal properties of the nanocomposites was studied. Thermal analysis revealed an increased in T_g for the nanocomposites as compared with the original organosolv lignin. For both organoclays, lignin intercalation into the silicate layers was observed using X‐ray diffraction (XRD). The intercalated hybrids exhibited a substantial increase in tensile strength and melt processability. In the case of organoclay Cloisite 30B, X‐ray analysis indicates the possibility of complete exfoliation at 1 wt % organoclay loading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Alkali–methanol–anthraquinone pulping of Miscanthus x giganteus for thermoplastic composite reinforcement

The potential of pulp fiber–reinforced thermoplastics is currently not fully explored in composites. One of the main reasons is that pulp fibers are extracted for the use in papermaking and are thus not optimized for use as reinforcements in thermoplastics. Furthermore, currently used processing methods constitute several severe thermomechanical steps inducing premature degradation of the fibers. A systematic development of these composite materials requires the study of both these aspects. The goal of this work was to optimize fiber extraction against properties relevant to the reinforcement of thermoplastics. To this end, thick‐walled Miscanthus x giganteus pulp fibers were selected. The fibers were pulped by the alkaline–methanol–anthraquinone process. An unreplicated factorial design was applied to determine the effect of key operating variables on fiber thermal stability and mechanical properties. The thermomechanical properties of pulp fibers depend primarily on the morphology and chemical composition of the fiber resource in terms of the respective amounts of lignin, hemicellulose, and cellulose, all strongly influenced by the choice of pulping conditions. Optimal pulping parameters were identified, allowing production of fibers thermally stable up to 255°C with an aspect ratio of 40, a straightness of 95%, and tensile strength as high as 890 MPa. Specific stiffness and strength values with respect to density and material cost of 56 GPa m^?3 $^?1 and 820 MPa m^?3 $^?1 were highly competitive with glass fibers, with corresponding values of 15 GPa m^?3$^?1 and 270–490 MPa m^?3 $^?1, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2132–2143, 2004     

Biocomposites developed using water‐plasticized wheat gluten as matrix and jute fibers as reinforcement

Biocomposites developed from wheat gluten using water without any chemicals as plasticizer and jute fibers as reinforcement have much better flexural and tensile properties than similar polypropylene composites reinforced with jute fibers. Wheat gluten is an inexpensive and abundant co‐product derived from renewable resources and is biodegradable but non‐thermoplastic. Previous attempts at developing biocomposites from wheat gluten have used plasticizers such as glycerol or chemical modifications to make gluten thermoplastic. However, plasticizers have a considerably negative effect on the mechanical properties of the composites and chemical modifications make wheat gluten less biodegradable, expensive and/or environmentally unfriendly. In the research reported, we developed composites from wheat gluten using water as a plasticizer without any chemicals. Water plasticizes wheat gluten but evaporates during compression molding and therefore does not affect the mechanical properties of the composites. The effect of composite fabrication conditions on the flexural, tensile and acoustic properties was studied in comparison to polypropylene composites reinforced with jute fibers. Wheat gluten composites had flexural strength (20 MPa), tensile strength (69 MPa) and tensile modulus (7.7 GPa) values approximately twice those of polypropylene composites. Water is an effective plasticizer for wheat gluten and could be used to develop various types of inexpensive and biodegradable wheat gluten‐based thermoplastics. Copyright © 2011 Society of Chemical Industry     

Natural rubber and butadiene rubber blend using diblock copolymer of isoprene–butadiene as compatibilizer

Blends of natural rubber (NR) and butadiene rubber (BR) have been studied with or without diblock copolymers of isoprene–butadiene (BIR). It was found that NR/BR blends displayed the optimal properties at about 4 wt % of BIR from the tensile measurements of NR/BR blends. Increase of molecular weight of BIR resulted in the decrease of tensile properties, but had no significant effect on their hardness. Abrasion resistance of rubber blends containing BIR was about 30% higher than that without BIR. The molecular weight of BIR did not show a remarkable effect on the abrasion index. Differential scanning calorimetry and dynamic mechanical analyses of rubber blends suggested a two-phase structure even in the presence of BIR. © 1993 John Wiley & Sons, Inc.     

Effect of meta‐dihydroxy benzene as a surface modifier on filler–filler and filler–polymer interaction of carbon black polymer composite

In the present context an attempt was made to use polyhydroxybenzene on rubber‐grade carbon black to suitably modify the surface morphology and hence to achieve improved thermomechanical and mechanical dynamic properties. FTIR studies clearly point out the presence of excess hydroxyl group in the modified black. The improvement in mechanical properties is attributed to higher crosslink density through hydrogen bonding and oxygen bridge participation during the covulcanization reaction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2025–2033, 2002     

Modeling of the relationship between morphology and viscoelastic behavior of unidirectional fiber-reinforced polymers

A new approach is proposed to predict the relationship between geometric arrangement of fibers within the polymer matrix and viscoelastic behavior displayed by unidirectional fiber-reinforced polymers. Based on a quantitative morphology analysis of epoxy/glass fibers composites, a four-phase model taking into account the fiber spatial distribution is developed to rigorously express the reinforcement effect of the polymer matrix over a wide range of fibers and temperatures. Comparisons with other modelings and experiment illustrate the validity of the proposed approach. In addition, changes in the viscoelastic behavior of the epoxy matrix in composite materials resulting from a decrease in the crosslinking degree of such a kind of polymer are, subsequently, assessed through such an approach.     

Interaction between the reinforcement and matrix in carbon-fiber-reinforced composite: Effect of forming the thin layer of polyimide resin on carbon fiber by in situ polymerization

For the purpose of enhancing the reinforcement–matrix interaction in carbon-fiber-reinforced polymer composite, mechanical and spectroscopic studies were made on the epoxy resin composite reinforced with the carbon fiber coated with thin Layer of polyimide resin. On the loss modulus and loss tangent vs. temperature curves, a subtransition appears at a temperature above the primary transition. The T-peel strength of a laminated specimen and the fiber efficiency factors for modulus and strength are larger than those of the composite reinforced with nonpolyimide treated fiber. These results show the increased interaction between the epoxy resin and the carbon fiber coated with polyimide resin. The occurrence of specific interaction between an epoxy resin and the polyimide resin are recognized on fourier transform infrared spectra.     

Relationship between interchain spacing of amorphous polymers and blend miscibility as determined by wide-angle X-ray scattering

The average molecular interchain spacing (〈R〉) in Angstroms for amorphous polymers was calculated from the strong maximum in the wide-angle X-ray scattering (WAXS) diffraction scan using established equations. The half-width (HW) of the maximum was used to qualitatively describe the distribution of 〈R〉. 〈R〉 and HW for immiscible blends corresponded to the weighted average of 〈R〉 and HW of the homopolymers in the blend. 〈R〉 for a miscible blend (natural rubber and high-vinyl PBd) was much larger than the weighted average of 〈R〉 of the component homopolymers, indicating that a new amorphous molecular structure had developed. The larger 〈R〉 for the miscible blend indicates that the molecular chains are spread further apart, resulting in an increase in free volume to accommodate the new packing order. The single T_g of this blend was lower than predicated by the Gordon-Taylor equation.     

Tire rubber–sisal composites: Effect of mercerization and acetylation on reinforcement

Tire rubber particles were mixed randomly with short sisal fibers and hot pressed. Sisal fibers were used as received, mercerized, and mercerized/acetylated. The fibers were characterized by scanning electron microscopy (SEM), thermal gravimetry analysis (TGA), infrared spectroscopy (FTIR), water sorption, and mechanical properties. Thermal stability of the mercerized/acetylated fibers improves (from 200 to 300°C) with respect to the raw fibers, and water sorption is ～ 20% smaller than for the raw and the mercerized fibers. Tensile strength is unchanged after the chemical treatments. Water sorption, mechanical properties, and SEM evaluated the performance of the tire rubber composites. All composites showed enhanced elastic modulus; increase is dependent on fiber load. Smallest water sorption was obtained in composites with the mercerized/acetylated fibers. With these fibers at 10% load, the best results were obtained with the smaller tire rubber particles (320 μm) and at 5% load with the bigger (740 μm) tire rubber particles. Both composites showed ～ 50% increase in tensile strength when compared to similar composites with raw fibers. SEM of the surface of fracture showed that the adhesion between fiber and rubber was enhanced after both chemical treatments. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2507–2515, 2003     

FT–NIR as a determination method for reinforcement of polymer nanocomposites

Layered silicates as nanoscale fillers have a great potential in improving polymer material properties. Depending on the composite structure (agglomerated, intercalated, or exfoliated) a significantly higher level of reinforcement of the virgin polymer can be achieved with a very small amount of filler. The morphology of the composites is usually characterized by XRD and microscopic methods (e.g., transmission electron microscopy). But the level of reinforcement of nanocomposites is not always proportional to morphology (delamination level of the silicate layers). A new approach for characterizing the material reinforcement level as a consequence of melt quality is to correlate the results of extensional rheometry (level of melt strength) with those of near infrared (NIR) spectroscopy. The advantage of the NIR technique is the suitability for in‐line implementation by using quartz based optics and optical fibers for the signal transfer from the measuring probe to the NIR spectrometer. The presented results show a direct correlation between the reinforcement level determined by rheotens measurements and the data analyzed from off‐line NIR measurements. The results of the chemometric analysis of the NIR data shows that this in‐line capable optical method provides quantitative information on the quality of the nanocomposite. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polymer blend: A novel method for the preparation of a natural rubber–carboxylated nitrile rubber blend

Bis(diisopropyl)thiophosphoryl disfulfide (DIPDIS) can be successfully used to form a blend comprising polar carboxylated nitrile rubber (XNBR) and nonpolar NR through a chemical link between the two. It is revealed from the study that the physical properties of the vulcanizates obtained from the NR-XNBR blend could be significantly improved by the judicious selection of the NR:XNBR ratio. These properties can further be improved by two-stage vulcanization as described in the procedure. The SEM study reveals that it is possible to form a coherent blend of NR and XNBR in the presence of DIPDIS. © 1994 John Wiley & Sons, Inc.     

Thermal behavior and morphological properties of novel magnesium salt–polyacrylamide composite polymers

Magnesium salt–polyacrylamide composite polymers have been prepared by blending magnesium chloride and magnesium hydroxide, respectively, with polyacrylamide aqueous solution. The thermal behavior of the dried magnesium salt–polyacrylamide composite polymers has been studied. Differential scanning calorimetric (DSC) analysis and thermal gravimetric analysis (TGA) were carried out to investigate the changes of the composite polymers' behavior with temperature. The kinetics of the thermal decomposition of magnesium salt–polyacrylamide composite polymers was investigated over temperature range of 35–800°C with three heating rates of 10, 20, and 40°C/min under nitrogen atmosphere. Flynn and Wall's model was usedto determine the activation energies of thermal decomposition for magnesium salt–polyacrylamide composite polymers. The activation energies needed to decompose 50 wt% of magnesium hydroxide‐polyacrylamide (MHPAM) composite polymer ranged from of 28.993–174.307 kJ/mol which are higher than the values for magnesium chloride–polyacrylamide (MCPAM) composite polymer (21.069–39.412 kJ/mol). Therefore, MHPAM composite polymer has a better thermal stability compared with MCPAM composite polymer. The morphological properties of magnesium salt–polyacrylamide composite polymers were studied using scanning electron microscopy (SEM). Energy‐dispersive X‐ray (EDX) spectroscopy was used to determine the composition of the chemical elements. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Quinone amine polymers. IX. Attempts to synthesize polyamine–benzoquinone polymers using air and oxygen as oxidizing agents

Attempts to synthesize Jeffamine D-400 : p-benzoquinone = 1 : 1 and later Jeffamine D-400 : hydroquinone = 1 : 1 oligomers, using air or oxygen as the oxidizing agent, have been only partially successful. Although oligomers that yield nontacky coatings are completely precipitable in water, only about 25% of these products are precipitable in water while 75% remains in suspension. These polymers yield tacky coatings, which suggests that neither air nor oxygen is capable of oxidizing hydroquinone to benzoquinone, which is necessary for the formation of the polymer. Hence, most of the oligomer chains are too short to precipitate in water.     

Effect of ultrasound on extrusion of polypropylene/ethylene–propylene–diene terpolymer blend: Processing and mechanical properties

The effects of ultrasonic irradiation on extrusion processing and mechanical properties of polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM) blends are examined. Results show that appropriate irradiation intensity can prominently decrease die pressure and apparent viscosity of the melt, increase output, as well as increase toughness of PP/EPDM blends without harming rigidity. In case the blends are extruded with ultrasonic irradiation twice, the impact strength of the blend rises sharply at 50–100 W ultrasonic intensity, and amounts to more than 900 J/m, 1.5 times as high as that of blend without ultrasonic irradiation. Scanning electron microscopy observation shows that with ultrasonic irradiation, morphology of uniform dispersed EPDM phase and good adhesion between EPDM and PP matrix was formed in PP/EPDM blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3519–3525, 2003     

Selective solid‐phase extraction of naphazoline using imprinted polymers as matrix prepared by precipitation polymerization

The molecularly imprinted polymers (MIP) for drug naphazoline (NAZ) have been synthesized by precipitation polymerization. The effect of the dispersive solvents dichloromethane (DCM), acetonitrile (ACN), and Methanol (MeOH) on particle size and morphology of MIP (P1, P2, and P3) was investigated by scanning electron microscopy (SEM). The selectivity of P1, compared with nonimprinted polymer (NIP), C₈ and C₁₈ were evaluated via static adsorption using UV spectrophotometer. The result showed that the bond amount of P1 for NAZ was significantly higher than other sorbents. The P1 were applied as a solid‐phase extraction (SPE) stationary phase to extract the NAZ from nasal drops and recoveries of more than 89% (relative standard deviations, RSD <5%) were obtained by high performance liquid chromatograph (HPLC) analyses. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Electrical behavior of carbon black-filled polymer composites: Effect of interaction between filler and matrix

The effect of interaction between carbon black and polymer on electrical behavior was studied using the ESR method. The polymer matrices used were HDPE, LDPE, and ethylene/vinyl acetate (EVA). Two kinds of carbon blacks (CB), high structure CSF-III and low structure FEF, were used as a conductive filler. Compared to that of the HDPE/FEF compound, the positive temperature coefficient (PTC) intensity is lower and electrical reproducibility is worse for the HDPE/CSF-III compound; however, it can be improved significantly by radiation cross-linking. On the other hand, the cross-linking has no practical effect on the PTC intensity of the LDPE/CSF-III compound while it can be achieved by mixing the compound for a longer time. The great PTC intensity was obtained in the HDPE/EVA/CSF-III compound, and it is greater than that of HDPE/CSF-III or EVA/CSF-III. We explain these results using the concept of interaction between the filler and matrix. The absorption of the polymer on the carbon black surface may be physical or chemical; the latter is caused by the free-radical reaction between the polymer and carbon black, and it can occur during the radiation or preparation process of the compound. These “bound polymers” are essentially important for materials to have a great PTC intensity and good reproducibility. © 1994 John Wiley & Sons, Inc.     

An approximate method for the determination of polymer–polymer interaction parameters of incompatible polymers in solution

A method is developed, based on Scott's equations for ternary systems of two polymers and a mutual solvent, for the calculation of values of the polymer–polymer interaction parameter, χ₂₃, for systems in which both polymer–solvent interaction parameters χ₁₂ and χ₁₃ are not known a priori. Equilibrium phase studies were carried out on ternary systems of polystyrene, polybutadiene, and tetrahydrofuran or toluene at 23°C and 1 atm. Typical interaction parameter values (χ₂₃) calculated by this new method were compared with the values of χ₂₃ determined earlier using standard equations and known χ₁₂ values for these systems, and were found to agree very well. It is concluded that the technique presented in this article can be used for mixed polymer systems in good mutual solvents where neither polymer–solvent interaction parameter is known, for determining an approximate value of the χ₂₃ parameter alone.