Banana fiber-reinforced biodegradable soy protein composites

Banana fiber, a waste product of banana cultivation, has been used to prepare banana fiber reinforced soy protein composites. Alkali modified banana fibers were characterized in terms of density, denier and crystallinity index. Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were also performed on the fibers. Soy protein composites were prepared by incorporating different volume fractions of alkali-treated and untreated fibers into soy protein isolate (SPI) with different amounts of glycerol (25%–50%) as plasticizer. Composites thus prepared were characterized in terms of mechanical properties, SEM and water resistance. The results indicate that at 0.3 volume fraction, tensile strength and modulus of alkali treated fiber reinforced soy protein composites increased to 82% and 963%, respectively, compared to soy protein film without fibers. Water resistance of the composites increased significantly with the addition of glutaraldehyde which acts as cross-linking agent. Biodegradability of the composites has also been tested in the contaminated environment and the composites were found to be 100% biodegradable.     

大豆蛋白接枝苯乙烯的合成及膜性能

大豆蛋白膜是无污染的包装涂布材料.但目前大豆蛋白膜尚不能取代合成高分子薄膜。其原因是亲水性使得它对水蒸气的阻隔有限,且它的力学性能无法达到要求。将苯乙烯接枝到大豆蛋白上,将有望提高大豆蛋白膜的力学性能。本文采用大豆分离蛋白和苯乙烯合成了接枝共聚物（SPI-g-PSt）。用流涎法分别制成SPI膜和SPI-g-PSt膜,并研究了它们的力学性能。     

Viscoelastic properties of nanosilica‐filled epoxy composites investigated by dynamic nanoindentation

The viscoelastic properties of the epoxy filled with silica nanoparicles have been investigated by dynamic nanoindentation and characterized by the storage modulus and loss tangent. The materials studied are neat epoxy and silica/epoxy composites with silica volume fraction of 1, 3, 6, 10, and 14 vol %, respectively. The silica nanoparticles with an average diameter of 25 nm are found to disperse homogeneously in the epoxy matrix. The effect of the particle content, force frequency, and penetration load on the viscoelastic behavior is studied and discussed. The comparison with traditional testing methods such as tension, bending, and DMTA is made. Besides, theoretical results by using micromechanics models are also obtained and compared with the experimental results. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1030–1038, 2009     

Influence of the crosslink network structure on stress‐relaxation behavior: Viscoelastic modeling of the compression set experiment

A viscoelastic approach of the compression set test is addressed in this work. This test measures the ability of rubber compounds to retain elastic properties after prolonged action of compressive stresses. Elastic properties were tested by recording the normal stress under a constant deformation of 25% with a laboratory rheometer. Considering the Boltzmann superposition principle, compression set data were modeled from the relaxation of Young's modulus, described by a Maxwell spectrum plus a constant E_∞ defining the elastic properties at the long times. This approach was developed with the copolymer of ethylene and vinyl acetate (EVA) networks crosslinked by radical chemistry and by an exchange reaction between acetate groups and silane compounds as crosslinking agents. Regarding the recovery of the elastic properties, radical chemistry provided better results than the exchange reaction for the identical crosslinking density of the network. Then, the Curro–Pincus molecular approach was developed to understand the influence of the microstructure of the EVA network on the elastic properties. The difference of the elastic properties between the two networks crosslinked by two different chemistry means was accounted for by considering the probability of having a dangling end of n units for a random crosslinking process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1779–1790, 2003     

Anisotropic mechanical properties of thermoplastic elastomers in situ reinforced with thermotropic liquid‐crystalline polymer fibers revealed by biaxial deformations

The anisotropic mechanical properties of the thermoplastic elastomer (TPE) in situ reinforced with thermotropic liquid‐crystalline polymer (TLCP) fibers were investigated by uniaxial, strip‐biaxial, and equibiaxial tensile measurements. The in situ composite sheets were prepared from an immiscible blend of a TLCP, Rodrun LC3000, and a TPE, styrene‐(ethylene butylene)‐styrene (SEBS) triblock copolymer, by a melt extrusion process. The uniaxial orientation of the TLCP fibers in the TPE matrix generated during processing yielded a significant mechanical anisotropy in the composites. The biaxial tensile measurements clearly demonstrated the anisotropic mechanical properties of the composites: The modulus in the direction parallel to the machine direction (MD) was considerably higher than that in the transverse direction (TD), even at large deformations; in equibiaxial stretching, the yield strain in the MD was smaller than that in the TD; the composite containing 10 wt % of TLCP exhibited the highest mechanical anisotropy among the composites, with 0–30 wt % TLCP. The latter result was in accord with the SEM observation that the composite with 10 wt % of TLCP possessed the best fibrillar morphology and the highest degree of uniaxial orientation of the TLCP fibers. The yield strains in uni‐ and biaxial elongation for the composite containing 10 wt % of TLCP were almost the same as those for the neat styrene‐ethylene butylene‐styrene. The TLCP phase with good fibrillation did not appreciably alter the original yielding characteristics of the elastomer matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 135–144, 2005     

Electrical properties of conductive polymer composites prepared by an innovational method

<正>An innovational method that poly(styrene-co-maleic anhydride)(SMA),a compatibilizer of immiscible nylon6/polystyrene(PA6/PS) blends,was first reacted with carbon black(CB) and then blended with PA6/PS,has been employed to prepare the PA6/PS/(SMA-CB) composites of which CB localized at the interface.In PA6/PS/CB blends,CB was found to preferentially localize in the PA6 phase.However,in the PA6/PS/(SMA-CB) blends,it was found that CB particles can be induced by SMA to localize at the interface.The electrical porperties of PA6/PS/(SMA-CB) composites were investigated.The results showed that the composites exhibited distinct triple percolation behavior,i.e.the percolation is governed by the percolation of CB in SMA phase,the continuity of SMA-CB at the interface and the continuity of PA6/PS interface.The percolation threshold of PA6/PS/(SMA-CB) was only 0.15 wt%,which is much lower than that of PA6/PS/CB.Moreover,the PTC(positive temperature coefficient) intensity of PA6/PS/(SMA-CB) composites was stronger than that of PA6/PS/CB and the negative temperature coefficient(NTC) effect was eliminated.The electrical properties of PA6/PS/(SMA-CB) were explained in terms of its special interface morphology:SMA and CB localize at interphase to form the conductive pathways.     

Crystallization,mechanical, thermal and rheological properties of polypropylene composites reinforced by magnesium oxysulfate whisker

Polypropylene(PP) composites containing magnesium oxysulfate whisker(MOSw) or lauric acid(LA) modified MOSw(LAMOSw) were prepared via melt mixing in a torque rheometer. The heterogeneous nucleating effect of LAMOSw was clearly observed in polarized light microscopy(PLM) pictures with the presence of an abundance of small spherulites. MOSw exhibited no nucleation effect and formed a few spherulites with large size. Compared with PP/MOSw composites, PP/LAMOSw exhibited better impact strength, tensile strength and nominal strain at break, ascribing to three possible reasons:(i) more β-crystal PP formed,(ii) better dispersity of LAMOSw in PP matrix and(iii) the plasticizing effect of LA. The results of dynamic mechanical thermal analysis(DMTA) indicated that brittleness of the PP matrix at low temperature was improved by the addition of LAMOSw, while the interfacial interactions between MOSw and PP matrix were actually weakened by LA, as evidenced by the higher tanδ values over the entire range of test temperatures. In terms of the rheological properties of the composites, both the η* and G′ at low frequencies increase with the addition of MOSw or LAMOSw, indicating that the PP matrix was transformed from liquid-like to solid-like. However, a network of whiskers did not form because no plateau was found in the G′ at low frequencies. With low filler content, LAMOSw produced a stronger solid-like behavior than MOSw mainly due to the better dispersion of the LAMOSw in PP matrix. However, for highly-filled composites, the η* of PP/LAMOSw at low frequencies was smaller than that of PP/MOSw composite, since the particleparticle contact effect played a major role.     

Application of vibrational spectroscopy for the analysis of polymer composites

Various examples of filled elastomeric networks will illustrate the potential of Fourier-transform infrared spectroscopy for a better understanding of the properties of elastomeric composite materials which are two-phase materials. The addition of an inorganic component to polymers leads to improvements in various physical and mechanical properties. These improvements are the result of a complex interplay between the properties of the individual constituent phases : the polymer, the filler and the interfacial region. Infrared spectroscopy has been used to characterize the interface in the isotropic state and also under uniaxial extension.     

Rheological properties of wood polymer composites at high shear rates

This paper presents the rheological properties of wood-polymer composites (WPC) with a polypropylene (PP) matrix in the corrected shear rate range from approx. 20 s⁻¹ to 150 000 s⁻¹. Tests were conducted using a capillary rheometer and a rheological head of the author's construction, for which the working element is a thermoplastic injection moulding machine. The constructed tool was found to be very useful, especially for the determination of the processing characteristics of WPC composites containing a large particle-size filler. It was observed that the rheological properties of wood-polymer composites in the shear rate range of up to several thousand s⁻¹ significantly depended on the filler content of the polymer matrix; at the same time, at higher shear rate, a clear decrease in the effect of the wood filler content on the viscosity of the composites and on the flow behaviour, as described by the power law, took place.     

Viscoelastic properties of sterically stabilized nonaqueous dispersions

The viscoelastic properties of a dispersion of poly(vinyl acetate) particles sterically stabilized by poly(2-ethyl hexyl methacrylate) and dispersed in Isopar G have been measured as a function of particle concentration and frequency at ambient temperature.At low particle concentrations, it was found that the loss modulus was larger than the storage modulus, while at high particle concentrations, i.e.,w>0.40, the storage modulus was found to be larger than the loss modulus. This inversion from a viscous to an elastic response as a function of particle concentration is attributable to the change in the configurational entropy of the steric barrier as a result of increasing the concentration of particles in the dispersion.     

Mechanical properties and frictional resistance of Al composites reinforced with Ti_3C_2T_x MXene

Two-dimensional(2D) Ti_3C_2T_x MXene is an attractive additive not only used in base oil due to its low friction coefficient,but also used in composites due to its high aspect ratio and rich surface functional groups.So far there has been intense research into polymer matrix composites reinforced with Ti_3C_2T_x,Here we report on the use of 2D Ti_3C_2T_x to enhance the mechanical and frictional properties of Al matrix composites.Ti_3C_2T_x/Al composites were designed and prepared by pre s sureless sintering followed by hot extrusion technique.The prepared composites exhibit a homogeneous distribution of Ti_3C_2T_x.The Vickers hardness and the tensile strength continuously increase with increasing Ti_3C_2T_x content.A hardness of 0.52 GPa and a tensile strength of 148 MPa were achieved in the 3 wt% Ti_3C_2T_x/Al composite.The frictional properties of pure Al and the Ti_3C_2T_x/Al composite were comparably studied under dry sliding.A low friction coefficient of 0.2,twice lower than that of pure Al,was achieved in the 3 wt%Ti_3C_2T_x/Al composite.Ti_3C_2T_x acting as a solid lubricant reduces the abrasive wear in the composite,improving the frictional properties of Al matrix composites.     

Viscoelastic properties of chitosan with different hydration degrees as studied by dynamic mechanical analysis

Dynamic mechanical analysis, DMA, is an adequate technique for characterizing the mechanical features of biomaterials, as one can use test conditions that can more closely simulate the physiological environments in which they are going to be applied. In this work it was possible to perform different tests on chitosan membranes using low/moderate hydration levels, as well in completely wet conditions. In the first case the data obtained at different relative humidity environments were rationalized under a time-humidity superposition principle, where a master curve for the storage modulus could be obtained along a wide range of frequencies. The temperature dependence of the shift factors exhibited a curvature opposite to that expected by the WLF equation, and is consistent with relaxation dynamics behavior below the glass transition. Temperature scans above room temperature in both dry and wet conditions did not reveal strong variations in the viscoelastic properties. It was possible to follow in real time the water uptake in an initially-dry membrane. During the initial strong and fast decrease of the storage modulus the loss factor exhibited a peak that should correspond to the occurrence of the glass transition resulting from the plasticization effect of water. Upon equilibration the loss factor reached similar values as for the dry material (tandelta approximately equal to 0.5). The viscoelastic characterization reported in this work for chitosan may be useful in the use of such material for a variety of biomedical applications.     

Effect of side groups of polymer glycol on microphase‐separated structure and mechanical properties of polyurethane elastomers

The effect of side methyl and dimethyl groups of the soft segment component on the microphase‐separated structure and mechanical properties of polyurethane elastomers (PUEs) was investigated. Poly(oxytetramethylene) glycol (PTMG), and PTMG incorporating dimethyl groups (PTG‐X) and methyl side groups (PTG‐L) were used as a polymer glycol, which forms a soft segment in the PUEs. The PUEs were synthesized with 4,4′‐dipheylmethane diisocyanate [1,1′‐methylenebis(4‐isocyanatobenzene)], 1,4‐butane diol, and 1,1,1‐trimethylol propane by a prepolymer method. The degree of microphase separation of the PUEs became weaker with increasing side group content in polymer glycols. Dynamic viscoelastic properties measurement showed reorganized‐crystallization and melting of the soft segment for the PUEs based on PTMG, PTG‐L, and PTG‐X with a lower content of the side groups, but not for a PTG‐L and PTG‐X with higher content of the side groups. Tensile testing revealed that increasing methyl group concentration made the PUEs soften and weaken. The PTMG‐based PUEs obviously exhibited strain‐induced crystallization of the soft segment chains during elongation process. In contrast, for the PTG‐L and PTG‐X‐based PUEs, crystallinity decreased with increasing side group content, and the PUEs with PTG‐L and PTG‐X with highest methyl group content did not crystallize even at a large strain. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2054–2063, 2008     

Mechanical properties of rigid polyurethane composites reinforced with surface treated ultrahigh molecular weight polyethylene fibers

The mechanical properties of ultrahigh molecular weight polyethylene (UHMWPE) fibers reinforced rigid polyurethane (PU) composites were studied, and the effects of the fiber surface treatment and the mass fraction were discussed. Chromic acid was used to treat the UHMWPE fibers, and polyurethane composites were prepared with 0.1 to 0.6 wt% as‐received and treated UHMWPE fibers. Attenuated total reflection Fourier transform infrared demonstrated that oxygen‐containing functional groups were efficiently grafted to the fiber surface. The mechanical performance tests of the UHMWPE fibers/PU composites were conducted, and the results revealed that the treated UHMWPE fibers/PU composites had better tensile, compression, and bending properties than as‐received UHMWPE fibers/PU composites. Thermal gravimetric analyzer showed that the thermal stability of the treated fiber composites were improved. The interface bonding of PU composites were investigated by scanning electron microscopy and dynamic mechanical analysis, and the results indicated that the surface modification of UHMWPE fiber could improve the interaction between fiber and PU, which played a positive role in mechanical properties of composites.     

Improved mechanical properties of epoxy composites reinforced with surface‐treated UHMWPE fibers

The surface treatment of ultra‐high molecular weight polyethylene fiber using potassium permanganate and the mechanical properties of its epoxy composites were studied. After treatment, many changes were happened in the fiber surface: more O‐containing groups (―OH, ―C═O, and ―C―O groups), drastically decreased contact angles with water and ethylene glycol, slightly increased melting point and crystallinity, and formed cracks. Different contents (0.1–0.5 wt%) ultra‐high molecular weight polyethylene fibers/epoxy composites were prepared. The results indicated that the surface treatment decreased the tensile strength of epoxy composites, but increased the bending strength. When the fiber content was 0.3 wt%, the above properties reached the maximum. At the same fiber content, the interlaminar shear strength of the composites was increased by 26.6% up to the as‐received fiber composites. Dynamic mechanical analysis of the composites suggested the storage modulus and tanδ were decreased due to the surface treatment. Fractured surface analysis confirmed that the potassium permanganate treatment was effective in improving the interface interaction.     

A review on potential development of flame retardant kenaf fibers reinforced polymer composites

Kenaf fibers have been extensively explored from the past few decades in polymer composites industries owing to its extensive adaptations, excellent properties together with its comparable mechanical properties to traditional glass fibers polymer composites. The combustibility or lowered flame retardancy hampered the diverse applications of kenaf fibers reinforced polymer composites, as it affects the mechanical strength and stiffness of composites during fire. Current review article intended to be a comprehensive source of published literature involving the flame retardants (FRs), types and applications of FRs and the fabrication of kenaf fibers reinforced polymer composites. This article will also provide a perfect data on the recent development of the FR kenaf fibers polymer composites with different FRs and explored its structural and semi‐structural industrial application for performing further research in this topic. Copyright © 2016 John Wiley & Sons, Ltd.     

Viscoelastic phase diagram of fluorinated and grafted polymer films and proton‐exchange membranes for fuel cell applications

The influence of temperature and moisture activity on the viscoelastic behavior of fluorinated membranes for fuel cell applications was investigated. Uncrosslinked and crosslinked ethylene tetrafluoroethylene (ETFE)‐based proton‐conducting membranes were prepared by radiation grafting and subsequent sulfonation and their behavior was compared with ETFE base film and commercial Nafion^® NR212 membrane. Uniaxial tensile tests and stress relaxation tests at controlled temperature and relative humidity (RH) were carried out at 30 and 50 °C for 10% < RH < 90%. Grafted films were stiffer and exhibited stronger strain hardening when compared with ETFE. Similarly, both uncrosslinked and crosslinked membranes were stiffer and stronger than Nafion^®. Yield stress was found to decrease and moisture sensitivity to increase on sulfonation. The viscoelastic relaxation of the grafted films was found to obey a power‐law behavior with exponent equal to ?0.04 ± 0.01, a factor of almost 2 lower than ETFE, weakly influenced by moisture and temperature. Moreover, the grafted films presented a higher hygrothermal stability when compared with their membranes counterparts. In the case of membranes, a power‐law behavior at RH < 60% was also observed. However, a markedly different behavior was evident at RH > 60%, with an almost single relaxation time exponential. An exponential decrease of relaxation time with RH from 60 s to 10 s was obtained at RH ≥ 70% and 30 °C. The general behavior of grafted films observed at 30 °C was also obtained at 50 °C. However, an anomalous result was noticed for the membranes, with a higher modulus at 50 °C when compared with 30 °C. This behavior was explained by solvation of the sulfonic acid groups by water absorption creating hydrogen bonding within the clusters. A viscoelastic phase diagram was elaborated to map critical conditions (temperature and RH) for transitions in time‐dependent behavior, from power‐law scaling to exponential scaling. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1139–1148     

Dielectric properties and molecular mobility of organic/inorganic polymer composites

Microstructure-dielectric properties relationship and molecular mobility of organic/inorganic polymer composites (OIPCs), consisting of polyurethane (PU) and sodium silicate (NaSi), were investigated in this work. Broadband dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization current (TSDC) techniques were employed. Our interest was focused on the study of the glass transition mechanism and conductivity relaxation. The influence of the molecular weight of PU and inorganic phase content on the dielectric properties of the composites was of particular interest. Glass transition temperature shifts to higher temperatures with the addition of NaSi. The overall molecular mobility was found to increase in the composites, compared to the pure PU matrix. The results are more intense for the composites based on the PU with low molecular weight.     

Viscoelastic properties and residual stresses in polyhedral oligomeric silsesquioxane-reinforced epoxy matrices

Fiber-filled thermosetting polymer composites are extensively used in aerospace industries. One disadvantage of these materials is cure induced or thermally induced residual stresses in the matrix, which may result in deteriorated performance and premature failure. This article explores the use of epoxy/multifunctional polyhedral oligomeric silsesquioxane (POSS) nanocomposites as resins with reduced thermal stress coefficients that result in mitigated residual stresses. The effect of POSS loading on the thermal stress coefficient of the epoxy/POSS nanocomposite resins was investigated from below the β-relaxation to the α-relaxation, or glass transition temperature, (i.e., from −100 to 180 °C) by measuring the shear modulus and linear thermal expansion coefficient. The thermal stress coefficient of the epoxy/POSS nanocomposites is found to be a strong function of temperature, decreasing rapidly with decreasing temperature through the α-relaxation region, increasing in the vicinity of the β-relaxation, and then decreasing below the temperature associated with the peak in the β-relaxation. With increasing POSS content, the thermal stress coefficient is reduced compared with the neat resin in the vicinity of the α-relaxation; however, the thermal stress coefficient increases with increasing POSS content below the temperature of the β-relaxation peak. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2719–2732, 2008