Dynamic viscoelasticities for short fiber-thermoplastic elastomer composites

Dynamic moduli, E′ and E″, and loss tangent tan δ were investigated for thermoplastic elastomers (TPEs), styrene-isoprene-styrene copolymers (SISs), styrene-butadiene-styrene copolymer (SBS), and Hytrel and composites reinforced by poly(ethylene terephthalate) (PET) short fibers. The styrenic TPEs have a typical rubbery behavior and the Hytrel TPE has medial characteristics between rubber and plastic. Both E′ and E″ of the composites depended on the matrix as well as the fiber loading and fiber length. Based on the viewpoint of different extensibility between the fiber and the matrix elastomer, a triblock model was considered for estimating the storage modulus of the short fiber-TPE composites as follows: E_c = αV_fE_f + β (1 ? V_f) E_m, where α and β are the effective deformation coefficients for the fiber and the matrix elastomer, respectively. They can be quantitatively represented by modulus ratio M (= E_m/E_f) and fiber length L: α = ( Lⁿ + k) M/ ( LⁿM + k), β = (1 ? α V_f)/ (1 ? V_f), where the constants n and k are obtained experimentally. When k = 0.022 and n = 0.45, E_c of the TPE composites agreed well with the prediction of the proposed model. The relaxation spectrum of the composites showed a distinct main peak ascribed to the matrix elastomer, but no peak to the PET fiber. The relative damping of main relaxation, (tan δ_max)_c/(tan δ_max)_m, decreased monotonously with increasing fiber loading and fiber length and with decreasing modulus of matrix elastomer. Thus, the relative damping may be attributed not only to the volume effect of matrix, but also to the unevenness of the strain distribution in the matrix phase, which depends on the fiber length and the matrix's modulus. The findings prove that the different extensibility between fiber and matrix and the uneven distribution of strain in matrix were important for the short-fiber reinforcement of the TPE composites. © 1993 John Wiley & Sons, Inc.     

Stress-Strain and stress relaxation in oxidated short carbon fiber-thermoplastic elastomer composites

Stress-strain and stress relaxation properties are studied in composites consisting of a thermoplastic elastomer butadiene styrene copolymer (SBS) matrix and oxidated carbon fiber. The results obtained from samples at different degrees of oxidation are contrasted with those obtained from SBS filled with commercial carbon fiber. Carbon fiber oxidation with nitric acid gives rise to an increase in functional surface groups, which in turn enhance the capacity in the fiber to interact with the matrix. In the experimental composites, the increase in fiber-matrix interactions translates into proportionally greater strain necessary to reach the yield point, as well as into an increase in stress at the yield point. In addition, at initial strain below the strain at yield point, a slower stress relaxation rate is observed in oxidated fiber composites, as compared with those recorded for the matrix filled with commercial fiber. In the oxidated fiber composites, stress relaxation occurs in three stages, the first two of which may be associated to the fiber-matrix interface. © 1996 John Wiley & Sons, Inc.     

SBS and SEBS block copolymers as impact modifiers for polypropylene compounds

Blends of polypropylene (PP) and thermoplastic elastomers (TPE), namely SBS (styrene‐butadiene‐styrene) and SEBS (styrene‐ethylene/1‐butene‐styrene) block copolymers, were prepared to evaluate the effectiveness of the TPE type as an impact modifier for PP and influence of the concentration of elastomer on the polymer properties. Polypropylene homopolymer (PP‐H) and ethylene–propylene random copolymer (PP‐R) were evaluated as the PP matrix. Results showed that TPEs had a nucleating effect that caused the PP crystallization temperature to increase, with SBS being more effective than SEBS. Microstructure characterization tests showed that in most cases PP/SEBS blends showed the smallest rubber droplets regardless of the matrix used. It was seen that SEBS is a more effective toughening agent for PP than SBS. At 0°C the Izod impact strength of the PP‐H/SEBS 30% b/w blend was twofold higher than the SBS strength, with the PP‐R/SEBS 30% b/w blend showing no break. A similar behavior on tensile properties and flexural modulus were observed in both PP/TPE blends. Yield stress and tensile strength decreased and elongation at break increased by expanding the dispersed elastomeric phase in the PP matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 254–263, 2005     

Characterization of defatted soy flour and elastomer composites

Defatted soy flour (DSF) is an abundant renewable commodity and is more economically favorable then soy protein isolate or soy protein concentrate. DSF contains soy protein, soy carbohydrate, and soy whey. The aqueous dispersion of DSF was blended with styrene‐butadiene latex to form elastomer composites. The inclusion of soy carbohydrate increased the tensile stress in the small strain region, but reduced the elongation at break. The shear elastic modulus of the composites showed an increase in the small strain region, consistent with its stress‐strain behavior. The inclusion of soy carbohydrate and soy whey also improved the recovery behavior in the nonlinear region. At small strain, the shear elastic modulus of 30% filled composites at 140°C was about 500 times higher than that of the unfilled elastomer, indicating a significant reinforcement effect generated by DSF. Compared with soy protein isolate (SPI), the stress softening effect and recovery behavior under dynamic strain indicate the addition of soy carbohydrate and soy whey may have increased the filler‐rubber interaction. In general, the DSF composites gave better mechanical properties compared with the protein composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 353–361, 2005     

Effect of absorbed water on dynamic modulus for short fiber–CR composites

Short fiber–elastomer composites with 10 vol % fiber, nylon 6–CR and PET–CR composites, absorbed water either in the moisture atmosphere or in water. The effect of absorbed water on the viscoelastic properties for these composites was investigated. The temperature dependence of tan σ for the nylon–CR composite showed that the α-dispersion peak of nylon shifted to lower temperatures with increasing absorbed water content and that after displacement of the α-dispersion peak the additional small hump appeared at about 90°C. For the PET composite, the α-dispersion peak of PET shifted slightly to lower temperatures and the small shoulder at 90°C diminished with increasing absorbed water. The additional dispersion probably was caused by the interface between fiber and CR matrix and was independent of fiber orientation. The results suggested that nylon fiber absorbed a larger amount of water than CR matrix, while the water absorption for PET fiber was considerably less than for nylon fiber. The absorbed water in nylon fiber bonded stronger than that in CR matrix and was only slightly diminished by heat treatment under 100°C.     

Investigation on stress-crack opening relationship of engineered cementitious composites using inverse approach

The stress-crack opening relationship of engineered cementitious composites was determined with an inverse method. Four cement matrixes with water to cement ratio of 0.55, 0.45, 0.35, 0.25 and fiber contents of 0.5%, 1.0% in volume were selected to form different series of composites. The results show that the σ–w relationship of the cement matrix is instant strain softening after the cracking strength. After adding polyvinyl alcohol fibers, the stress-crack opening relationship of the composites changes to a double peak mode behavior as the crack bridging first decreases from cracking strength, then increases to the second peak. After that the tensile softening is displayed again with increase of crack opening. The cracking strength is governed by the cement matrix and the second peak stress is controlled by the fibers and fiber/matrix interface. The second peak is greatly increased with increase of fiber content. The second peak stress larger than the cracking strength means strain-hardening and multiple cracking performances can be expected under tension.     

Fiber length distribution and thermal,mechanical and morphological properties of thermally conductive polycarbonate/chopped carbon fiber composites

Chopped carbon fibers (CCFs) coated by poly(ethylene terephthalate) (PET) were treated using 3‐aminopropyltriethoxysilane (Si), and then used for fabricating thermally conductive polycarbonate/CCF (PC/(Si + PET)@CCFi) composites with various filler contents. Optical microscopy measurements indicated that CCF fillers in the composites had a wide length distribution and, with CCF content increasing, the mean fiber length and mean fiber aspect ratio steadily decreased. Compared to PC/(Si + PET)@CCF0, the molten flowability of composites declined. Thermogravimetric analysis and pyrolysis–gas chromatography–mass spectrometry characterizations showed that introducing CCFs could enhance the thermal stability of the composites and restrict the pyrolytic degradation of the polymer matrix. Moreover, both in‐plane and through‐thickness thermal conductivities increased with increasing CCF content. These conductivities at 50% CCF content reached 2.45 and 0.59 W m^?1 K^?1, and were improved by 11.25 and 1.95, respectively. Furthermore, the tensile and flexural properties of the composites continuously enhanced, accompanying decreased impact strength and elongation at break. Fractography revealed that fillers dispersed in matrix uniformly and a great many fiber cross‐sections and circular cavities coexisted in fracture surface, besides a clear interface and reduced long fibers. And the fracture behavior was mainly the breaking and peeling of fibers from matrix. © 2018 Society of Chemical Industry     

碳纤维/聚氨酯复合材料的制备与性能研究

以聚酯二元醇、异氰酸酯、碳纤维为主要原料,采用预聚体法制备了一系列碳纤维/聚氨酯复合材料,并对该复合材料进行了性能测试和结构表征。研究表明,复合材料的机械性能随着碳纤维长度和含量的增加出现先升高后降低的趋势。当碳纤维长度为3 mm、质量分数为1.0%时,复合材料的机械性能达到最佳值,此时其拉伸强度增加22.7%,撕裂强度增加48.1%,扯断伸长率增加5.9%。热力学分析和动态力学性能研究表明,复合材料的热分解温度提高,质量保留率提高,失重率降低,材料的玻璃化转变温度和软化温度提高,引入碳纤维后材料的耐热性提高。     

RFL coated aramid short fiber reinforced thermoplastic elastomer: Mechanical, rheological and morphological characteristics

Composite based on a new generation metallocene catalyzed thermoplastic elastomer ethylene-octene copolymer (EOC) and resorcinol formaldehyde latex (RFL) coated aramid short fiber was prepared by varying the short fiber loading from 1 to 10 phr. The mechanical, morphological and rheological characterizations were carried out. The impact of a low molecular weight maleic anhydride grafted 1, 2 polybutadiene (MA-g-PB) on various properties was also investigated. It has been observed that with increasing the short fiber content both the low strain modulus and modulus at 100% increase but the tensile strength and elongation at break decrease. The improvements in tensile strength coupled with elongation at break and good fiber dispersion particularly at high fiber loaded composite were achieved with the incorporation of MA-g-PB, which indicates that it acts as an interface modifier through compatibilization between the fiber and the EOC matrix as well as a good dispersing agent. The understanding of adhesion between the fiber and the polymer and the sticking of polymer traces on the tensile fractured fiber surface of the composite by scanning electron microscopic analyses further support the compatibilizing action of MA-g-PB. The melt rheological behavior such as storage modulus, loss modulus, complex viscosity and storage viscosity of the composites were investigated using a Rubber Process Analyser (RPA) under strain and frequency sweep mode.     

Mechanical and morphological properties of white rice husk ash filled polypropylene/ethylene‐propylene‐diene terpolymer thermoplastic elastomer composites

The performance of white rice husk ash (WRHA) as filler for polypropylene (PP)/ethylene‐propylene‐diene terpolymer (EPDM) thermoplastic elastomer (TPE) composites was investigated. The composites with different filler loadings were prepared in a Brabender plasticorder internal mixer. Both unvulcanized and dynamically vulcanized composites were prepared. Mixing and vulcanization processes of the composites were monitored through the typical Brabender torque‐time curves. The mechanical properties and morphology of the composites were also studied. The Brabender torque curves revealed that the dynamic vulcanization process employed was successful and incorporation of filler has no adverse effect on the processibility of the composites. Incorporation of WRHA improves the tensile modulus and flexural modulus and lowers tensile strength, elongation at break, tear strength, and toughness of both types of composites. Dynamic vulcanization significantly enhances the mechanical and TPE properties of the composites. Dynamic mechanical analysis (DMA) study revealed the existence of two phases in both types of composites. It further shows that neither dynamic vulcanization nor filler agglomeration has played a prominent role in the compatibility of the composites. Thermogravimetric investigation shows that dynamic vulcanization or WRHA loading has not adversely affected the thermal stability of the composites. The scanning electron micrographs provide evidence for the tendency to form filler agglomerates with increasing filler loading, better filler dispersion of dynamically vulcanized composites over unvulcanized composites, and effective vulcanization of elastomer phase of the composites in the presence of filler. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 438–453, 2002     

The moisture and temperature effect on mechanical performance of flax/starch composites in quasi‐static tension

The effect of temperature and moisture on mechanical behavior of flax fiber/starch based composites was investigated experimentally. Elastic modulus, the nonlinear tensile loading curves, and failure strain were analyzed. Neat matrix and composites with 20 and 40% weight content of fibers were tested. It was found, performing tests with different amplitudes, that microdamage development with stress is rather limited and the related elastic modulus reduction in this type of composites is not significant. It was shown that the composite elastic modulus and failure stress are linearly related to the maximum tensile stress in resin. The sensitivity of the maximum stress of the resin with respect to temperature and moisture is the source of composites sensitivity to these parameters. Constant interface stress shear lag model for stress transfer assuming matrix yielding at the fiber/matrix interface has been successfully used to explain the tensile test data. It indicates that the sensitivity of the used composite with respect to the matrix properties change could be significantly reduced by increasing the average fiber length from 0.9 mm to 1.5 mm. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Mechanical Properties of Thermoplastic Butadiene–Styrene (SBS) and Oxidized Short Carbon Fibre Composites

This work reports on some results of research conducted on composite materials consisting of a butadiene–styrene (SBS) thermoplastic elastomer matrix filled with short carbon fibres previously subjected to oxidative treatment to increase the surface functionality. Scanning electron microscopy confirms the existence of interactions between the matrix and the fibre, which are not observed for commercial fibre fillers and which translate into mechanical strength increments, in terms of the Young’s modulus, tensile and tear strengths for the oxidized fibre composites. The stress–strain curves of the composites show yield point phenomena as strain is applied longitudinally to the main fibre orientation. In oxidized fibre composites the stress and strain coordinates are a function of the degree of oxidation (greater strain for more strongly oxidized fibre) and fibre strength (lower stress for longer treatment times). © 1997 SCI.     

Plasticization of nano‐CaCO3 in polystyrene/nano‐CaCO3 composites

The shear rheological properties of polystyrene (PS)/nano‐CaCO₃ composites were studied to determine the plasticization of nano‐CaCO₃ to PS. The composites were prepared by melt extrusion. A poly(styrene–butadiene–styrene) triblock copolymer (SBS), a poly(styrene–isoprene–styrene) triblock copolymer (SIS), SBS‐grafted maleic anhydride (SBS–MAH), and SIS‐grafted maleic anhydride were used as modifiers or compatibilizers. Because of the weak interaction between CaCO₃ and the PS matrix, the composites with 1 and 3 phr CaCO₃ loadings exhibited apparently higher melt shear rates under the same shear stress with respect to the matrix polymer. The storage moduli for the composites increased with low CaCO₃ concentrations. The results showed that CaCO₃ had some effects on the compatibility of PS/SBS (or SBS–MAH)/CaCO₃ composites, in which SBS could effectively retard the movement of PS chain segments. The improvement of compatibility, due to the chemical interaction between CaCO₃ and the grafted maleic anhydride, had obvious effects on the rheological behavior of the composites, the melt shear rate of the composites decreased greatly, and the results showed that nano‐CaCO₃ could plasticize the PS matrix to some extent. Rheological methods provided an indirect but useful characterization of the composite structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Effect of short polyethylene terephthalate fibers on properties of ethylene-propylene diene rubber composites

The alteration in some properties of electron beam (EB) cured ethylene-propylene diene rubber (EPDM) reinforced by polyethylene terephthalate (PET) fiber was investigated in this study. Bonding system Resorcinol/Hexamethylenetetramine/Silica (RHS) was used to enhance the fiber/EPDM adhesion and to maintain optimum composite strength properties. Mechanical properties of composites namely; tensile strength, hardness and modulus at 100 % elongation have been enhanced by adding PET fibers and increasing irradiation dose. Moreover, the effect of fiber loading and irradiation dose on the soluble fraction behavior of the composite in benzene was also investigated. The soluble fraction of the composites decreased with increasing the fiber loading and irradiation dose. The extent of fiber alignment and strength of fiber-rubber interface adhesion were analyzed from the anisotropic swelling measurements. In addition, thermal stability of the composites was increased. Besides, the mechanical properties like tensile strength and stiffness were improved by thermal ageing. Scanning electron microscopy (SEM) for the fractured surfaces and Wide- angle X- ray diffraction (WAXD) of the investigated samples confirmed that the adhesion occurred between fibers and EPDM.     

Deformation and fracture of Mg(OH)2‐filled polyolefin composites under tensile stress

The tensile behavior of high‐density polyethylene (HDPE), polypropylene (PP), and linear low‐density polyethylene composites containing a titanate coupling agent and silicone‐oil‐treated magnesium hydroxide [Mg(OH)₂] was studied. The increase in the extent of the ultimate elongation of the composites was affected by the yield stress and the strain‐hardening tendency of the polymer matrix in the composites. Ethylene–propylene–diene rubber and octane–ethylene copolymer were introduced to adjust the yield stress of PP and HDPE. Although the ultimate elongation of PP/elastomer and HDPE/elastomer blends was higher than that of virgin PP or HDPE, the ultimate elongation of the filled composites dropped at a high content of Mg(OH)₂. Scanning electron microscopy showed that the difference in the uniformity of the interface exfoliation decreased with the yield stress of the matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3248–3255, 2003     

Effect of multiple loading sequence on time-dependent stress rupture of fiber-reinforced ceramic-matrix composites

In this paper, the effect of multiple loading sequence on time-dependent stress rupture of fiber-reinforced ceramic-matrix composites (CMCs) at intermediate temperatures in oxidative environment is investigated. Considering multiple damage mechanisms, a micromechanical constitutive model for time-dependent stress rupture is developed to determine damage evolution of matrix crack spacing, interface debonding and oxidation length, and fiber failure probability under single and multiple loading sequences. The relationships between multiple loading sequence, composite strain evolution, time, matrix cracking, interface debonding and oxidation, and fiber fracture are established. The effects of fiber volume, matrix crack spacing, interface shear stress in the slip and oxidation region, and environment temperature on the stress/time-dependent strain, interface debonding and oxidation fraction, and fiber broken fraction of SiC/SiC composite are analyzed. The experimental stress rupture of SiC/SiC composite under single and multiple loading sequences at 950°C in air atmosphere is predicted. Compared with single loading stress, multiple loading sequence affects the interface debonding and oxidation fraction in the debonding region, leading to the higher fiber broken fraction and shorter stress-rupture lifetime.     

Short fiber reinforced thermoplastic polyurethane elastomer composites

Mechanical properties of thermoplastic polyurethane elastomer (TPE) reinforced with short fibers were studied. Two types of fibers were used as the discontinuous phase: an aromatic polyamide (Twaron, diameter: 12 μm) and carbon fiber (FCI 140/90-R33—diameter: 8–10 μm). Because of processing limitations, the maximum length of both fibers, after incorporation in the composites, was reduced to 3 mm. The TPE (continuous phase) was a polyol-polyester type [Elastollan—glass transition of short fiber segments: −42°C (1)]. Both types of composites had fiber concentration of 10, 20, and 30 phr. Component interaction is discussed, as well as the application of a third power polynomial to establish a relationship between the amount of fiber added and stress at break data. Stress-strength, tear resistance, shore A and B hardness, abrasion resistance, and compression set tests were performed. Composites reinforced with aromatic polyamides showed higher values in most of the tests, except in the abrasion resistance test, in which a smaller material loss was observed.     

Polypropylene Hybrid Composites: A Preliminary Study on the use of Glass and Coconut Fiber as Reinforcements in Polypropylene Composites

Polypropylene hybrid composites were made using coconut and glass fibers as reinforcing agents in the polypropylene matrix. The incorporation of both fibers into the PP matrix has resulted in the reduction of flex-ural, tensile, and impact strengths and elongation at break. The reduction has been attributed to the increased incompatibility between the fibers and the PP matrix, and the irregularity in fiber size, especially for biofibers as shown by scanning electron micrographs. Both the flexural and tensile moduli have been improved with the increasing level of fiber loading. Most of the properties tested for Composites with high glass fibers/low biofiber loading are comparable with the ones with low glass fiber/high biofiber loading. The results show that more biofibers could be incorporated in hybrid composites which would give the same range of properties as the composites with higher loading of glass fibers.     

Mechanical properties of surface‐modified ultra‐high molecular weight polyethylene fiber reinforced natural rubber composites

The mechanical properties of ultra‐high molecular weight polyethylene (UHMWPE) fibers reinforced natural rubber (NR) composites were determined, and the effects of fiber surface treatment and fiber mass fraction on the mechanical properties of the composites were investigated. Chromic acid was used to modify the UHMWPE fibers, and the results showed that the surface roughness and the oxygen‐containing groups on the surface of the fibers could be effectively increased. The NR matrix composites were prepared with as‐received and chromic acid treated UHMWPE fibers added 0–6 wt%. The treated UHMWPE fibers increased the elongation at break, tear strength, and hardness of the NR composites, especially the tensile stress at a given elongation, but reduced the tensile strength. The elongation at break increased markedly with increasing fiber mass fraction, attained maximum values at 3.0 wt%, and then decreased. The tear strength and hardness exhibited continuous increase with increasing the fiber content. Several microfibrillations between the fiber and NR matrix were observed from SEM images of the fractured surfaces of the treated UHMWPE fibers/NR composites, which meant that the interfacial adhesion strength was improved. POLYM. COMPOS., 38:1215–1220, 2017. © 2015 Society of Plastics Engineers     

短纤维对橡胶发泡复合材料增强机理的细观分析

分别制备未增强的橡胶发泡体、未处理短纤维增强的橡胶发泡体和预处理短纤维增强的橡胶发泡体,考察气体泡孔和短纤维在橡胶发泡复合体中的微观形态,细观分析短纤维对橡胶发泡复合材料拉伸行为和压缩行为过程各阶段的增强机理。结果表明:气体泡孔在3种发泡复合材料基体中分布均匀,模压工艺使得短纤维在基体中呈现为平面分布,未处理短纤维周围有气泡包围,而预处理短纤维与橡胶间粘合良好;短纤维能有效地提高发泡复合材料在初始阶段的拉伸模量和100%定伸应力,特别是预处理短纤维表面与橡胶之间具有良好的粘合,有利于传递应力,限制橡胶基体的变形,而对拉伸强度却影响不大。在压缩弹性阶段,由于主要承载的泡壁中纤维呈平面取向,短纤维对压缩模量影响不大,但能有效地限制橡胶发泡复合材料在后屈曲阶段的压缩变形,提高其在高应变下的压缩强度,预处理短纤维增强效果明显高于未处理短纤维。