Fracture mechanisms of poly(ethylene terephthalate) and blends with styrene-butadiene-styrene elastomers

Poly(ethylene terephthalate) (PET) was blended with 5 wt % of an elastomeric block copolymer. The hydrogenated styrene-butadiene-styrene (SEBS) elastomers were functionalized with 0–4.5 wt % maleic anhydride grafted on the midblock. Notched tensile tests in the temperature range − 40–55 °C differentiated among the blends in terms of their toughness. The least effective elastomer was the unfunctionalized SEBS; all the functionalized SEBS elastomers effectively increased the toughness of PET. Fractographic analysis indicated that PET and the blend with unfunctionalized SEBS fractured through a pre-existing craze. Although adhesion of the unfunctionalized SEBS to the matrix was poor, the elastomer strengthened the craze somewhat, as indicated by an increase in length of the pre-existing craze when final separation occurred. A functionalized SEBS caused the fracture mechanism to change from crazing to ductile yielding. Graft copolymer formed by reaction of PET hydroxyl end groups with the anhydride in situ was thought to act as an emulsifier to decrease particle size and improve adhesion. These factors promoted cavitation, which relieved the triaxiality at the notch root and permitted the matrix to shear yield. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of morphology on the behaviour of ternary composites of polypropylene with inorganic fillers and elastomer inclusions

The effects of phase morphology, interfacial adhesion, rigid filler particle shape and elastomer volume fraction on the tensile yield strength of polypropylene (PP) filled with inorganic filler (CaCO₃ or Mg(OH)₂) and ethylene-propylene elastomer (EPR) were investigated. Separation of the filler and elastomer particles was achieved using maleic-anhydride-grafted PP (MPP) to enhance the filler-matrix adhesion. Encapsulation of the rigid filler by the elastomer was achieved using maleic-anhydride-grafted EPR (MEPR) to increase the filler-elastomer adhesion. The two limiting morphologies differ significantly in mechanical properties under tensile loading at the same material composition. Elastomer particles separately dispersed in the matrix enhance the shear banding in the bulk matrix which prevents the crazes growing from the filler surface from becoming unstable and, thus, increases the ductility of the material. Encapsulation by an elastomer layer on the filler surface relieves triaxial stresses at the filler surface, changing the major local failure mechanism from crazing to shear yielding and, hence, increasing the ductility of the material. Increase of the elastomer volume fraction also causes, in both cases, an increase in matrix ductility. Composite models are used to predict upper and lower limits of yield strength (_y) for the two limiting morphologies over an interval of elastomer volume fractions (V _e) from 0 to 0.2 at a constant filler loading of 30 vol.% and over a filler volume fraction from 0 to 0.4 at a constant EPR content in the matrix. Satisfactory agreement was found between the experimental data and theoretical predictions.     

Yield behaviour of renewable biocomposites of dimer fatty acid-based polyamides with cellulose fibres

The yield behaviour of dimer acid-based polyamides (DAPA) and DAPA reinforced with cellulose fibres (CF) was examined in this study. Both dynamic mechanical analysis (DMA) and tensile tests were used to follow the effect of strain rate or frequency, temperature and filler content on the transitions temperatures, the storage modulus and the yield stresses. The DMA results show that the storage modulus increases with increasing CF concentration. The tensile tests reveal that the yield stress is strain rate, temperature and CF concentration sensitive. Both activation enthalpy and activation volume calculated by the Eyring’s model reveal a slight increase of activation energy with increasing filler content and a decrease of the activation volume. A micromechanically-model was used to predict the yield stress of both DAPA and DAPA/cellulose composites. The model predictions of the yield stress are in good agreement with the experimental data.     

Fracture behaviour of polypropylene/glass bead elastomer composites by using the essential work-of-fracture method

The plane-stress static fracture response of blends composed of isotactic polypropylene glass beads (GBs) and an elastomer of styrene/ethylene–butylene/styrene type (SEBS) in both the ungrafted state and the grafted state with maleic acid anhydride (SEBS-g-MA) was studied at room temperature and v=1 mm min-1 cross-head speed. The volume fraction of GBs was kept constant (10 vol%) whereas that of the elastomer was set for 5 and 20 vol%, respectively. Deeply double edge-notched specimens of different ligaments were cut from pressed sheets of about 1 mm thickness and subjected to tensile tests at ambient temperature. The development of the plastic and process zone was studied in situ, i.e., during loading of the specimens, by light microscopy and infrared thermography. From the specific work of fracture versus ligament length plots, the essential and non-essential work of fracture components were determined. It was established that the essential work-of-fracture approach works well for these hybrid composites. The specific essential work of fracture, we, increased with increasing amount of the rubbery modifier but depended on its type. Grafting changed the morphology of the composites (SEBS-g-MA covered the GBs, whereas SEBS was present as an additional dispersed phase) and affected both the essential (slightly) and the non-essential or plastic work (considerably) terms. It was established that SEBS-g-MA is a less efficient toughener than SEBS because of the substantial differences in the related failure modes. © 1998 Chapman & Hall     

Polymer-filler interactions in rubber reinforcement

The reinforcement of elastomers by finely divided fillers, particularly carbon black and silica, is fundamental to the rubber industry. Optimal reinforcement appears to involve both physical and chemical interactions. From a consideration of the effects of particle size as such, it appears that reinforcement, in the sense of tensile enhancement, will occur with any very finely divided filler. Physical factors prevent escape of the polymer from the filler surface (vacuole formation) but allow stress delocalization through interfacial slippage. Occasional stronger bonds may be introduced advantageously to facilitate dispersion, reduce particle/ particle interactions, and optimize practical properties relating to resilience and durability. Several lines of evidence suggest that only a minor amount of strong bonding is necessary or desirable, such that polymer/filler slippage can occur, under stress, over most of the interfacial area.     

形状记忆合金的力学及界面参数和体积分数对大块金属玻璃基复合材料增韧的影响

采用考虑塑性的超弹性材料模型和基于损伤塑性的准脆性材料模型,建立了三维单胞有限元模型,模拟了形状记忆合金颗粒增韧大块金属玻璃基复合材料的单调拉伸行为。讨论了形状记忆合金的力学参数、体积分数、界面厚度和界面材料参数对金属玻璃增韧效果的影响。结果表明:提高形状记忆合金的相变应变和马氏体塑性屈服应力将显著提高形状记忆合金颗粒增韧大块金属玻璃基复合材料的拉伸失效应变;形状记忆合金弹性模量超过50.0GPa、马氏体塑性屈服应力超过1.8GPa后,复合材料的拉伸失效应变变化不大。能同时兼顾失效应变和失效应力的形状记忆合金体积分数为15%左右。复合材料界面弹性模量和界面屈服应力的增加将提高复合材料的失效应力,但对失效应变影响不大;复合材料界面厚度的增加在提高失效应变的同时,也降低了复合材料的失效应力。     

Failure mechanics in ternary composites of polypropylene with inorganic fillers and elastomer inclusions

The effects of phase morphology, interfacial adhesion and filler particle shape and volume fraction on the fracture toughness of polypropylene (PP) filled with CaCO₃ or Mg(OH)₂ and ethylene-propylene elastomer (EPR) were investigated. Separation of the inorganic filler and elastomer particles was achieved using maleic-anhydride-grafted PP (MPP) to enhance the inorganic filler-matrix adhesion. Encapsulation of the rigid filler by the elastomer was achieved by using maleic-anhydride-grafted EPR (MEPR) to increase the inorganic filler-elastomer adhesion. The two limiting morphologies differed significantly in fracture toughness under impact loading at the same material composition. A model for a mixed mode of failure, accounting for the plane strain and plane stress contributions to the strain energy release rate,G _c, was used to predict the upper and lower limits forG _c for the two limiting morphologies over an interval of elastomer volume fractions,v _e, from 0–0.2 at a constant filler volume fraction,V _f = 0.3, and over the filler volume fraction from 0–0.4 at constant EPR content. The role of material yield strength in controlling fracture toughness has been described successfully using Irwin's analysis of plastic zone size. The presence of elastomer enhances both the critical strain energy release rate for crack initiation,G _c, and the resistance to crack propagation as expressed by Charpy notched impact strength for the two limiting morphologies. Satisfactory agreement was found between the experimental data and predictions of upper and lowerG _c limits.     

Dielectric constant enhancement in a silicone elastomer filled with lead magnesium niobate–lead titanate

Lead magnesium niobate–lead titanate (PMN–PT) ferroelectric powder was used to develop a particulated composite based on a silicone elastomer matrix, with improved dielectric permittivity. The filler was characterised by X-ray diffraction and scanning electron microscopy. Complex dielectric permittivity (10–10⁸ Hz) and tensile mechanical properties (elastic modulus and ultimate stress) of composites at various filler contents (up to 30% by vol.) were compared with those of the neat silicone elastomer. Both the dielectric constant and loss factor regularly increased with the filler content. The elastic modulus increased with a lower rate than that of the dielectric constant. Even though the addition of filler resulted in a detriment of both toughness, ultimate stress and elongation at break, a good stretchability was still retained, as elongation ratios greater than 3 were possible at the highest filler content. Several dielectric models were compared to the experimental data and the best match was achieved by the Bruggeman model, which can be used as a predictive rule for different volume contents of filler.     

The effect of dispersed paint particles on the mechanical properties of rubber toughened polypropylene composites

The influence of dispersed paint particles on the mechanical properties of rubber toughened PP was investigated. The matrix was basically a hybrid of PP, rubber and talc. Model systems with spherical glass bead filled matrix were also studied to examine the effect of filler shape and size. Properties like tensile strength, strain at break, impact strength, and fracture toughness were influenced by the dispersed inclusions. Tensile strength at yield decreased linearly according to Piggott and Leinder's equation. Strain at break decreased more drastically with paint particles than glass beads, revealing that irregularly shaped particles offered greater stress concentrations. The tensile strength and strain at break were less influenced by the size of paint particles whereas a slight decrease in the modulus values was observed with decreasing particle size. Impact strength and fracture toughness also decreased with increasing filler fraction. Lack of stress transfer between filler and matrix aided in reduction of impact strength. Decrease in fracture toughness was influenced by volume replacement and constraints posed by fillers. The size of paint particles had little effect on the impact strength and fracture properties at the filler concentration levels used in this investigation.     

Structure, thermal properties and mechanical properties of sPS-based nanocomposites with and without styrenic elastomer inclusions

Syndiotactic polystyrene (sPS)-based nanocomposites with and without toughener inclusions were successfully prepared. One organo-montmorillonite (20A) and two styrenic elastomers (SBS and SEBS) served as the reinforcing filler and as tougheners, respectively. XRD and TEM results confirmed the achievement of intercalated and partially exfoliated sPS/20A nanocomposites. The presence of SBS or SEBS slightly depressed the dispersibility of 20A. DSC results indicated that 20A inhibited the crystallization of sPS. The presence of SBS or SEBS further retarded the crystallization of sPS; this effect was more apparent with SEBS. The presences of 20A and SBS/SEBS facilitated the formation of α-form sPS crystals. The thermal stability enhancement of sPS/20A nanocomposites was confirmed, and was further improved with the inclusion of SBS or SEBS. The stiffness of sPS increased with the sole addition of 20A. The addition of SBS or SEBS greatly increased the impact strength of the composites, especially with the addition of SEBS. The achievement of toughened sPS-based nanocomposites was confirmed.     

Magnetoactive elastomeric composites: Cure, tensile, electrical and magnetic properties

Magnetically active elastomer materials were prepared by incorporating nickel powder in synthetic elastomeric matrices, polychloroprene and nitrile rubber. Cure characteristics, mechanical, electrical and magnetic properties were experimentally determined for different volume fractions of magnetoactive filler. The cure time decreases sharply for initial filler loading and the decrease is marginal for additional loading of filler. The tensile strength and modulus at 100% strain was found to increase with increase in the volume fraction of nickel due to reinforcement action. The magnetic impedance and a.c. conductivity are found to increase with increase in volume fraction of nickel as well as frequency.     

Effect of polar modification on morphology and properties of styrene-(ethylene-co-butylene)-styrene triblock copolymer and its montmorillonite clay-based nanocomposites

This article deals with the functionalization of a triblock copolymer, poly-(styrene-ethylene-co-butylene)-styrene (SEBS), at the mid-block by means of chemical grafting by two polar moieties—acrylic acid and maleic anhydride and subsequent novel synthesis of nanocomposites based on hydrophilic montmorillonite clay (MT) at very low loadings. The mid-block was grafted with 3 and 6 wt% acrylic acid through solution grafting and 2 and 4 wt% maleic anhydride through melt grafting reactions which were confirmed by spectroscopic techniques. The nanocomposites derived from the grafted SEBS and hydrophilic MT clay conferred dramatically better mechanical, dynamic mechanical, and thermal properties as compared to those of the original SEBS and its clay-based nanocomposites. Different phase separated morphologies could be observed from transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies for grafted SEBS. X-ray diffraction (XRD), AFM, and TEM studies revealed better interaction and dispersion of MT clays with the grafted SEBS matrix, resulting in better transparency of these nanocomposite films. Superlative enhancement of thermal degradation properties was achieved with maleated and acrylated SEBS–MT nanocomposites. Thermodynamic calculations and interfacial tension measurements indicated possible ways of favorable intercalation-exfoliation mechanism of maleated and acrylated SEBS–MT nanocomposites.     

Gas-induced damage in elastomeric composites

Gases may induce extensive and irreversible damage in elastomers when they are allowed to escape from the polymeric matrix. The damage is most evident as internal lacerations and also as an overall change in certain mechanical properties. The damage process, commonly termed explosive decompression failure, is really confined to gas-polymer systems which are initially equilibrated at high pneumatic stresses; greater than 10⁷ Pa. Two interrelated facets of this phenomenon are described in the context of elastomeric composites with particular emphasis on the role of interfacial quality. The results of an optical examination of the internal cracks found during a typical gas-induced rupture cycle are described. The system is a commercial silicone elastomer-glass filler composite where the fillers have been surface modified in order to alter the adhesive strength of the interface. The data indicate that the filler particles significantly modify the stress fields in the elastomer during gas-induced rupture. Essentially, the fillers suppress the development of the characteristic large scale axially symmetrical stress fields in the composites. This visual assessment of the damage is then related to the deterioration in certain mechanical properties of this current system.     

反应挤出法制备PPO/PA6/SEBS共混物的研究EI

研究了 PPO- g- MA对 PPO/PA6 /SEBS共混体系的原位增容作用和 SEBS对 PPO/PA6的增韧作用。 PPO/PA6 /SEBS共混物的 TEM结果表明 ,SEBS分散在 PPO中 ,而 PPO又分散在 PA6基体中。 TEM和 SEM的结果均表明 ,PPO- g- MA细化了分散相的相畴 ,增加了界面强度 ;冲击实验的结果表明 ,PPO- g- MA和 SEBS的用量分别为 2 0 %～ 2 5 %和 10 %～ 15 %时 。     

HDPE/E-TMB共混物和HDPE/弹性体共混物的脆韧转变和断面形态

用材料力学性能测试方法和扫描电镜研究了HDPE/E-TMB共混物和HDPE/弹性体共混物的脆韧转变行为和冲击断面形态。结果表明,HDPE/E-TMB共混物的脆韧转变可在弹性体含量较低的情况下发生;弹性体含量相同时,HDPE/E-TMB共混物有更高的冲击强度和拉伸屈服应力;冲击强度相同时,HDPE/E-TMB共混物有更高的拉伸屈服应力和弯曲弹性模量。弹性体含量为8%的两种共混物的冲击断面形态属于不同的断裂机理,这种机理的不同揭示了HDPE/E-TMB共混物具有特殊的结构特征。     

Numerical analysis of the stress–strain distributions in the particle reinforced metal matrix composite SiC/6064Al

The axisymmetric cell model consisting of interface, matrix and reinforced particle is used to simulate the tensile test of particle reinforced metal matrix composite for predicting the micro stress/strain field and macro tensile stress/strain curve. In simulation of the tensile test, the cohesive element model is selected to model interfacial crack growth. It mainly analyzed the effects of interfacial properties, reinforcement volume fractions and aspect ratios on the stress–strain states of particle reinforced metal matrix composite. The results show that the peak micro stress and plastic strain occur at the interface in which it is a certain angle from the tensile stress direction; with the interfacial fracture toughness and reinforcement volume fraction increasing, the flow stress increases firstly and then decreases. The tensile stress–strain properties of SiC/6064Al are good when the interfacial fracture toughness is equal to 60 J/m and the reinforcement fraction volume is equal to 20%. Smaller reinforcement aspect ratio leads to smaller micro stress in composites.     

Studies on polypropylene composites filled with talc particles

Tensile and impact properties of talc-filled isotactic polypropylene composites are investigated at 0–60 wt% filler contents. Tensile modulus registered an increase whereas tensile yield strength and strain-at-break decreased with increasing filler content. Mechanical restraint imposed by the talc particles on the molecular mobility or deformability of polypropylene explained the increase in modulus and decrease in strain-at-break while decrease in tensile yield strength was attributed to decreased crystallinity and formation of stress concentration points around the filler particles. Izod impact strength decreased with increased talc content. Surface modification of talc with a titanate coupling agent LICA 38 enhanced the filler-polymer interaction, further modifying the composite properties consequent upon significant decrease in the stress concentration. Scanning electron microscopic studies revealed better dispersion of surface-modified filler particles in the polymer matrix.     

催化剂对异佛尔酮二异氰酸酯制备的脂肪族聚氨酯弹性体结构和性能的影响

采用一步法通过异佛尔酮二异氰酸酯与聚丙二醇和1,4-丁二醇反应合成了脂肪族聚氨酯（PU）弹性体。考察了催化剂的种类和含量对PU弹性体结构和性能的影响。结果表明,以辛酸亚锡为催化剂时,PU弹性体的软段相和硬段相间的相分离程度最明显且分子量最低,导致其力学性能最差;以辛酸铋为催化剂时,PU弹性体软段相和硬段相的相容性较好且...     

Interfacial stress distribution between bovine dentine and resin composite in dentine bonding systems

In finite element stress analysis, the principal interfacial stress at a tensile bond strength of 10 MPa during tensile loading was estimated for the resin composite/dentine material including the bonding area with elastic moduli of 0.03, 0.3, 3.0 and 12.0 GPa assumed in this study. Interfacial stress along the resin composite/bonding area interface or bonding area/dentine interface increased with increasing elastic modulus. The interfacial stress distributed non-uniformly and locally at the most sensitive sites, that is, the edge of the resin composite/bonding area interface with the lowest elastic modulus (0.03 GPa) and the edge of bonding area/dentine interfaces with other elastic modulus values (0.3, 3.0 and 12.0 GPa). The maximum value of interfacial stress increased linearly with increasing elastic modulus of bonding area from 0.03 to 12.0 GPa. This study showed that the distribution of interfacial stress was highly non-uniform along the interfaces of the bonded areas in dentinal adhesives.     

Poly(ethylene terephalate) prepolymer graft modification of nano-TiO2 and its effect on mechanical property of polycarbonate nanocomposites

Abstract

Nano-TiO₂ particles were modified by the poly(ethylene terephalate) prepolymer (pre-PET) via polycondensation. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy results showed that pre-PET was successfully grafted on the surface of the nano-TiO₂ particles. Thermogravimetric analysis results indicated that the grafting efficiency depended on the vacuum degree. Compared to the original nano-TiO₂, the grafted nano-TiO₂ had better compatibility with the polycarbonate (PC) matrix and could be dispersed more homogeneously in PC. Hence, interfacial adhesion between TiO₂ and PC was enhanced. The mechanical properties of the resultant PC/nano-TiO₂ composites like tensile strength and notched impact strength were greatly improved. Calculated respectively from tensile yield stress PC/nano-TiO₂ composites, the interfacial interaction parameter B was employed to quantitatively characterise the effective interfacial interaction between the nano-TiO₂ and PC matrix. It demonstrated that the nano-TiO₂ grafted with pre-PET had stronger effective interfacial interaction with PC matrix than original nano-TiO₂.