Mechanical and viscoelastic properties of short fiber reinforced natural rubber composites: effects of interfacial adhesion,fiber loading,and orientation

The effect of a two-component dry bonding system consisting of resorcinol and hexamethylene tetramine on the mechanical and viscoelastic properties of short sisal fiber reinforced natural rubber composites has been studied. The studies were conducted with chemically treated and untreated short sisal fibers. Treated fibers impart better mechanical properties to the composites. By mixing with short fibers, the dynamic storage modulus (E') of natural rubber composites was improved. The effects of fiber-matrix adhesion on the mechanical and viscoelastic properties of the composites were investigated. The storage moduli and mechanical loss increased continuously with an increase in fiber loading but decreased with an increase of temperature. The influence of the fiber orientation on the mechanical and viscoelastic properties is discussed.     

PTFE基复合材料动态力学性能的研究

将聚四氟乙烯(PTFE)和几种添加物采用机械共混、冷压、烧结成型的方法制备了PTFE基复合材料。用粘弹分析仪测试了复合材料的动态力学性能,得到了损耗因子、储能模量及损耗模量随温度变化的曲线,用扫描电子显微镜观察了PTFE与添加物的结合状况。结果表明,PTFE基复合材料的储能模量随添加物含量的增加而增大：加入聚苯硫醚(PPS)的PTFE基复合材料的损耗因子曲线只出现一个明显的峰,峰值变大;而加入聚苯酯、聚全氟(乙烯／丙烯)共聚物、聚醚醚酮后可使PTFE基复合材料的损耗因子峰值变小,当含量在某一范围时,复合材料的损耗因子曲线出现双峰,此时可拓宽复合材料的有效阻尼温域;随着石墨、MoS2含量的增加,PTFE基复合材料的储能模量提高,损耗因子峰值变小。     

Physico-mechanical and dynamic mechanical studies of nanographite reinforced chlorobutyl nanocomposites

Abstract

Nanographite reinforced chlorobutyl elastomer (CIIR) nanocomposites were prepared. The dispersion of the nanographite in the CIIR matrix has been investigated by scanning electron microscopy. The effect of increasing nanographite loadings (2, 4, 6 and 8 phr) on mechanical properties like tensile strength, hardness, elongation at break and modulus (100, 200 and 300%) has been studied. The study shows increase in tensile strength, hardness and modulus and decrease in elongation at break with nanographite loading, which can be attributed towards better CIIR–nanographite interaction. The above explanation was again verified from bound rubber measurements. It shows increase in bound rubber contents with nanographite loading. Dynamic mechanical analysis was used to study their relaxation behaviour as a function of temperature (?100 to 100°C) at frequency 1 Hz and 1% strain. The effect of increasing nanographite loadings on glass transition temperature was marginal in all the composites, and Tg value was in the range of ?10 to 10°C, which has been explained on the basis of relaxation dynamics of polymer chains in the vicinity of fillers. The effects of variation in nanographite loading and temperature on dynamic mechanical properties like loss tangent, storage and loss modulus have been reported. The effect of solvent (chloroform, benzene and tri-chloroethylene) on swelling properties at different periods of time (15, 30, 45 and 60 min) shows that the degree of swelling increases with time and decreases with concentration of nanographite loading.     

Dynamic mechanical properties of sisal fiber reinforced polyester composites fabricated by resin transfer molding

The dynamic mechanical properties of sisal fiber reinforced polyester composites fabricated by resin transfer molding (RTM) were investigated as a function of fiber content, frequency, and temperature. Investigation proved that at all temperature range the storage modulus (E′) value is maximum for the composites having fiber loading of 40 vol%. The loss modulus (E″) and damping peaks (tan δ) were lowered with increasing fiber content. The height of the damping peaks depends upon the fiber content and the fiber/matrix adhesion. The extent of the reinforcement was estimated from the experimental storage modulus, and it has been found that the effect of reinforcement is maximum at 40 vol% fiber content. As the fiber content increases the T_g from tan δ curve showed a positive shift. The loss modulus, storage modulus, and damping peaks were evaluated as a function of frequency. The activation energy for the glass transition increases upon the fiber content. Cole–Cole analysis was made to understand the phase behavior of the fiber reinforced composites. Finally, attempts were made to correlate the experimental dynamic properties with theoretical predictions. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Mechanical Properties of Mullite–Corundum Composites Prepared from Bauxite

Mullite–corundum composites have been prepared by reaction sintering of Indian bauxite having considerable amount of impurities and silica sol. The effect of changing mullite phase proportion on the mechanical properties (i.e., flexural strength, elastic modulus, hot modulus of rupture, thermal shock resistance) of prepared composites has been studied. Flexural strength and elastic modulus increase with increasing free corundum phase content in the composites. Hot modulus of rupture for the sample containing only mullite phase increases with increasing test temperature over entire temperature range. Theoretical thermal shock resistance parameters R and R? are well supported by experimental thermal shock data.     

Dynamic mechanical properties of oil palm fiber/phenol formaldehyde and oil palm fiber/glass hybrid phenol formaldehyde composites

The dynamic mechanical properties of oil palm fiber reinforced phenol formaldehyde (PF) composites and oil palm/glass hybrid fiber reinforced PF composites were investigated as a function of fiber content and hybrid fiber ratio. The dynamic modulus of the neat PF sample decreases with decrease in frequency. Glass transition attributed with the α relaxation of the neat PF sample was observed around 140°C. Tanδ values and storage modulus show great enhancement upon fiber addition. The value increases with increase in fiber content. The loss modulus shows a reverse trend with increase in fiber loading. Incorporation of oil palm fiber shifts the glass transition towards lower temperature value. The glass transition temperature of the hybrid composites is lower than that of the unhybridized composites. The highest value of mechanical damping is observed in hybrid composites. Storage modulus of the hybrid composites is lower than unhybridized oil palm fiber/PF composite. A similar trend is observed for loss modulus. Activation energies for the relaxation processes in different composites were calculated. Activation energy is increased upon fibrous reinforcement. Complex modulus variations and phase behavior of the composites were studied from Cole‐Cole plots. Finally, master curves for the viscoelastic properties of the composites were constructed on the basis of time‐temperature superposition principle. POLYM. COMPOS., 26:388–400, 2005. © 2005 Society of Plastics Engineers     

碳纳米纤维增强聚甲醛复合材料制备及性能

通过纳米碳纤维(CNFs)在聚甲醛(POM)基体中的均匀分散以及取向,制备了具有优异力学性能和热性能的POM/CNFs复合材料。利用扫描电子显微镜、透射电子显微镜、拉伸性能测试、热重分析、动态热机械分析测试表征了POM/CNFs复合材料的结构和力学、热学性能。结果表明,CNFs与POM分子链形成氢键相互作用,促进了CNFs在POM基体内分散,同时使POM/CNFs复合材料的结晶度显著提高。随着CNFs含量增加,POM/CNFs复合材料的拉伸强度、储能模量和损耗模量均得到提高。当添加0.5%的CNFs时,拉伸强度、储能模量及损耗模量分别提高了20.5%,127%和58%。进一步研究了高温拉伸对POM/CNFs复合材料性能的影响。结果表明,CNFs沿拉伸方向定向排列,同时复合材料拉伸后结晶度提高,拉伸强度显著增加。     

Thermoplastic biopolyester natural fiber composites

Natural fiber–biopolymer composites have been prepared using flax and poly(3‐hydroxylbutyrate) bipolyesters (PHB). The biopolyesters consist of the homopolyester PHB and its copolymers with 5 and 12% 3‐hydroxyvalerate (PHV). These biopolymer–natural fiber composites provide structures totally composed of biodegradable and renewable resources. The adhesion between the fibers and the polyesters was better than for analogous polypropylene composites. Wetting of the fibers by the polyesters was observed using scanning electron microscopy. The composites were limited by the properties of the polyesters. PHB is a brittle polymer though flexibility is improved in its copolymers with PHV, but at the expense of crystallization rate. Nucleation was increased by the fibers and silane coupling agent used as adhesion promoter. The melting temperature was influenced by the promoted adhesion and copolymerization. The bending modulus was increased in the composites and dynamic mechanical analysis provided storage modulus of as much as 4 GPa at 25°C with a smaller component as the loss modulus. The maximum in the loss modulus curve was taken as the glass transition temperature, and this increased in the composites. The influence of silane coupling agent was found beneficial for the material properties of the biopolyester–flax composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2114–2121, 2004     

Dynamic mechanical analysis of polypropylene composites based on surface-treated sepiolite

The dynamic mechanical properties in terms of the storage modulus G′, loss modulus G″, and loss tangent δ have been studied for polypropylene-sepiolite composites. The effect of surface treatment on the relaxation spectra has been elucidated, and quantitative values indicating the extent of polymer-filler interaction have been given. Analysis of the results show that the addition of sepiolite leads to an increase in the values of the modulus, a value of the glass transition temperature lower than that of unfilled polypropylene, and displacement towards higher temperatures of the α_c relaxation associated with the crystalline regions. Surface treatment of the sepiolite, by esterification with organic acids of different chain length, does not have a marked effect on the relaxation spectra of the composites, even though the polymer-filler interaction parameter decreases with respect to untreated sepiolite.     

The comparison of properties of (rubber tree seed shell flour)‐filled polypropylene and high‐density polyethylene composites

The effect of varied rubber tree seed shell flour (RSSF) filler loadings on processing torque, mechanical, thermal, water absorption, and morphological properties of polypropylene (PP) and high‐density polyethylene (HDPE) composites has been studied. The addition of RSSF in the composites increased the stabilization torque in both PP‐ and HDPE‐based composites. Tensile strength, elongation at break, flexural strength, and impact strength show significant reduction when higher loading of RSSF was incorporated, while tensile modulus and flexural modulus were improved. The phenomenon was noted for both matrices, PP and HDPE, but HDPE‐based composites showed clear effects on the reduction of the mechanical properties compared with RSSF‐filled PP. Scanning electron microscopy of tensile fracture specimens revealed the degree of dispersion of RSSF filler in the matrices. At higher filler loadings, agglomerations and poor dispersion of RSSF particles were spotted, which induce the debonding mechanism of the system. Thermogravimetric analysis thermograms showed that both PP‐ and HDPE‐based composite systems with higher RSSF content have higher thermal stability, initial degradation temperature, degradation temperature, and total weight loss. Water absorption ability of the composites increases as the filler loading increases for both matrices. J. VINYL ADDIT. TECHNOL., 22:91–99, 2016. © 2014 Society of Plastics Engineers     

Application of dynamic mechanical analysis for the study of the interfacial region in carbon fiber/epoxy composite materials

The application of dynamic mechanical analysis (DMA) for quantifying interfacial interactions in composites is briefly reviewed. Carbon fiber/epoxy composites with fiber volume fractions of 12, 17, 38 and 61 vol% were subjected to flexural deformation on a Dupont DMA 983 instrument. The dependencies of dynamic mechanical properties of the composites on experimental parameters such as oscillation mode, amplitude, frequency, and temperature were investigate. As opposed to the storage modulus, the loss modulus is found to be sensitive to all parameters. In a fixed multiple frequency mode, the loss modulus of the composites increases with oscillation amplitude and decreases with frequency and the number of tests. The information produced in the resonant mode is more reproducible. An additional damping at the interfaces, apart from those of the constituents, suggests a poor interface adhesion in these composites. A linear relationship between the excess damping at the interfaces and the fiber volume fraction shows a similar interface quality for these composites having different fiber volume fractions. The detection of interfacial properities was found to be more sensitive in the flexural deformation mode than in the torsional mode. At temperatures higher than the glass transition temperature of the matrix, the effective volume fraction of the matrix is reduced. Such a reduction can be interpreted from the mismatch of thermal expansion of the matrix and the fibers.     

Highly filled thermoplastic composites. II: Effects of particle size distribution on some properties

The effect of irregularly shaped glass particle size and size distribution on the packing density and flexural mechanical properties of highly-filled composites with a rubbery thermoplastic matrix was studied. Increasing the particle's median size and size distribution width significantly increases the packing density of the composites. Compression molding causes the glass particles to fracture at a decreasing level with an increasing distribution width. Particle median size, rather than size distribution, affects the mechanical properties; The flexural modulus and strength increase and the ultimate deflection in flexure decreases with a decreasing median size. A “glass network” is formed in the compression molded composites because of the mechanical interlocking of particles. The nature of this continuous glass phase predominates the composites mechanical behavior. The particle's size and shape determine the nature of the glass network and, thus, have a dominating effect on the mechanical properties. The latter are significantly affected by the particle's surface properties. A specific silane treatment of the glass particles acts to reduce the particle/particle friction, resulting in a higher packing density. The treatment also acts as a cohesive liquid to increase the strength of the glass network, and to increase the particle/polymer adhesion, increasing the composites' strength and ductility.     

CNT基木塑复合材料的力学性能、电磁屏蔽性能

采用碳纤维(CF)和碳纳米管(CNT)通过模压工艺制备出具有电磁屏蔽功能的丙烯酸酯木塑复合材料。借助材料试验机、动态热机械分析仪、微欧计和电磁屏蔽测量仪等详细研究CNT质量分数对丙烯酸酯木塑复合材料弯曲性能、动态力学性能、电阻率和电磁屏蔽效能的影响。结果表明,添加质量分数为2%的CNT,使得复合材料的弯曲强度和弯曲弹性模量分别增加了10%和16%。复合材料的储能模量也在CNT质量分数为2%时达到最大值,之后储能模量随着CNT的增加而逐渐下降,损耗因子在CNT质量分数多于2%时也逐渐增加。复合材料的吸水率和导电性能随着CNT含量的增加而增加。同时复合材料的电磁屏蔽效能也随着CNT含量增加而递增。在30~1 500 MHz范围内,电磁屏蔽效能从27 d B增加到40 d B。结果证明,当CNT质量分数在2%时,丙烯酸酯木塑复合材料具有较佳的力学性能和较好的电磁屏蔽效能(30 d B),能满足商业要求。     

Influence of fiber treatment on the performance of sisal–polypropylene composites

This article concerns the effectiveness of MAPP as a coupling agent in sisal–polypropylene composites. The fiber loading, MAPP concentration, and fiber treatment time influenced the mechanical properties of the composites. It was observed that the composites prepared at 21 volume percent of fibers with 1% MAPP concentration exhibits optimum mechanical strength. SEM investigations confirmed that the increase in properties is caused by improved fiber‐matrix adhesion. The viscoelastic properties of the treated and untreated composites were also studied. From the storage modulus versus temperature plots, an increase in the magnitude of the peaks was observed with the addition of MAPP and fiber reinforcement, thus showing an improvement in stiffness of the treated composites. The damping properties of the composites, however, decreased with the addition of the fibers and MAPP. The thermal properties of the composites were analyzed through DSC and TGA measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1336–1345, 2004     

Characterization of highly filled wood flour–polyvinyl chloride composites: Dynamic mechanical and dielectric analysis

Viscoelastic and dielectric properties of composites with polyvinyl chloride as major matrix constituent, ethylene vinyl acetate (EVA) as polymeric plasticizer, and wood flour (WF) and fly ash (FA) as filler have been studied. The effect of variation of WF, FA, and EVA on storage modulus E′, loss modulus E″, and glass transition temperature, T_g has been evaluated using dynamic mechanical analysis (DMA). Effect on permittivity ε′ and conductivity is evaluated using dielectric analysis. The results show considerable influence of constituents of the composite on the properties evaluated. DMA shows that WF contributes to an increase in T_g, E′, and E″ and a decrease in loss tangent, tan δ. The FA content has insignificant effect on these properties. Increasing WF content increases ε′. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Dynamic mechanical analysis of adhesion between poly(vinyl chloride) and nitrile rubber

The degree of adhesion between poly(vinyl chloride) and nitrile rubber sheets depends on the contact time and temperature. Good adhesion is attributed to the compatibility of the two polymers which allows interdiffusion of the chains across the interface. The dynamic mechanical properties of the composites are found to vary according to the moulding conditions. The changes in the storage modulus and the loss tangent values of the composites with contact time and temperature are explained on the basis of the extent of adhesion and the molecular dynamics of the chains at the interface.     

Polyphenylene sulphide/carbon fiber composites: study on their thermal,mechanical and microscopic properties

The present study investigates the thermal, mechanical and microscopic properties of polyphenylene sulphide/carbon fiber (PPS/CF) composites by incremental number of fiber layers. The composites were prepared by hand lay-up technique followed by compression molding. A superior matrix-reinforcement adhesion was attained without the use of coupling agent and mechanical stability of the composites improved with increasing fiber layers. Transverse rupture strength and bending modulus were improved by 59.84 and 125.21 %, respectively, without loss in toughness. Impact strength and hardness values were enhanced while storage modulus, loss modulus and damping factor were dropped by increases in fiber layers. Thermogravimetric analysis (TGA) indicated a gradual rise in thermal stability (16.84 %) of the composite as compared to pure matrix. Surface morphology and crack propagation were studied by optical microscopy. It was found that crack was propagated in a linear plane by applying load. In addition, scanning electron microscopy (SEM) illustrated steady alignment of fibers and uniform distribution of the matrix around reinforcement. Based on the obtained results, fiber layers showed great potential for enhancement of thermal and mechanical properties of the composites.     

Studies on the dynamic mechanical and vibration damping properties of polyether urethane and epoxy composites

The dynamic mechanical and vibration damping properties of polyether urethane and epoxy composites have been studied. The experiment results show: the crosslink density is an important factor that influences the loss factor of polyether urethane damping materials; increasing the amount of pendant methyl of the backbone contributes to raising the value of the loss factor (tan δ) and broadens the damping temperature range; adding the planar filler can increase the shear motion and the internal dissipation in polyurethane materials. As the thickness ratio and the Young's modulus of the constraining layer increase, the composite loss factor (η) increases significantly. © 1993 John Wiley & Sons, Inc.     

Mechanical and dynamic mechanical analysis of hybrid composites molded by resin transfer molding

This work aims to evaluate the performance of glass/sisal hybrid composites focusing on mechanical (flexural and impact) and dynamic mechanical analyses (DMTA). Hybrid composites with different fiber loadings and different volume ratios between glass and sisal were studied. The effect of the fiber length has also been investigated. The densities of the composites were compared with the theoretical values, showing agreement with the rule of mixtures. The results obtained in the flexural and impact analysis revealed that, in general, the properties were always higher for higher overall reinforcement content. By DMTA, an increase in the storage and loss modulus was found, as well as a shift to higher values for higher glass loading and overall fiber volume. It was also noticed an increase in the efficiency of the filler and the calculated activation energy for the relaxation process in the glass transition region. The fiber length did not significantly change the results observed in all analyses carried out in this work. The calculated adhesion factor increased for higher glass loadings, meaning the equation may not be applied for the system studied and there are other factors, besides adhesion influencing energy dissipation of the composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of mesogenic organic salts on vulcanization and physical properties of rubber compounds

The effect of mesogenic organic salts as reinforcing fillers for non‐ionic elastomers such as natural rubber and styrene–butadiene rubber has been investigated. The influence of cation size (thallium and sodium) and organic chain length (thallium(I) pentanoate and thallium(I) dodecanoate) on vulcanization parameters, physical and mechanical characteristics and rheological behaviour has also been analysed. In general, the maximum torque of the vulcanizates increases in the presence of the salts and is clearly manifested in a noticeable increase in tensile modulus and strength of the composites. The thallium(I) salts are more effective reinforcements than the sodium salt, and the length of the organic chain has hardly any influence on the mechanical properties. The composites based on the thallium(I) dodecanoate salt show a very peculiar rheological behaviour with a ‘plateau’ in the elastic modulus and loss modulus versus temperature plots which is related to solid phase I, existing between 83.5 and 127 °C, characterized as a plastic condis phase. This issue is especially interesting for the fabrication of devices such as sensors to control, for instance, the security (resistance of a material) as a function of temperature. © 2013 Society of Chemical Industry