Measurement of rubber particle fraction in high-impact polystyrene

The rubber particle fraction in high-impact polystyrene (HIPS) can be separated efficiently from the polystyrene matrix if the rubber phase is cross-linked using heat-treatment. A conventional gel test to measure the rubber particle weight fraction has been used on HIPS, which has been heat-treated to cross-link the rubber phase. The rubber particle fraction results obtained by the gel test method are shown to agree with results from an alternative method where the rubber particle fraction is calculated using measurements taken directly from transmission electron photomicrographs.     

Computer modelling of rubber-toughened plastics

Coarse models of high-impact polystyrene (HIPS) have been created by computer simulation of the rubber particle spacing in the resin. Interparticle surface-surface distance parameters can be calculated from the models to help explain properties of real materials and predict the properties of hypothetical impact-polystyrene resins. Calculations of the geometric spacing of rubber particles in a group of hypothetical HIPS resins show that a narrow rubber-particle size distribution gives smaller interparticle distance and more reinforcing particles compared to broad distributions for a given average particle size.     

Rubber toughening of plastics

Electron microscopy of a high-impact polystyrene (HIPS) polymer, containing 8.5 wt% polybutadiene, shows that the volume fraction, , of composite rubber particles is 35%. The rubber particle size distribution has 8 median diameter of 1.6 µm. By making a series of blends between this HIPS and polystyrene, it is shown that Young's modulus decreases linearly with . Dilution with polystyrene results in a sharp drop in notched Charpy impact strength. The relevance of these data to the interpretation of structure-property relationships for a wide range of HIPS morphologies is discussed.     

Rubber toughening of plastics

Measurements of particle size distribution, particle volume fraction?/, Young's modulus, tensile and compressive yield stress and Charpy impact strength were made on a series of 14 high-impact polystyrene (HIPS) polymers of widely varying structure. In materials throughout the series containing 8.5 wt % polybutadiene, it was found that?/ varied between 0.17 and 0.44 as the mean particle size increased from 0.2 to 1.8 μm. Modulus and yield stresses depended principally upon particle volume fraction but the ratio of polybutadiene to polystyrene within the particles also appeared to have some influence upon properties. By contrast, variations in ? provided only a partial explanation for the observed differences in Charpy impact strength. It is concluded that impact strength is affected by rubber particle size to a much greater extent than properties measured at low strain rates.     

Role of the rubber particle and polybutadiene cis content on the toughness of high impact polystyrene

High impact polystyrene (HIPS) is a classical reactor polymer blend produced by in situ polymerization of styrene in solution with polybutadiene rubber. The importance of the particle size and rubber crosslink density on the particle cavitation capability and the controlling of toughening mechanisms in the styrenic matrix is well established in current literature. In the present work, the role of the rubber particle on the HIPS toughness has been investigated for two commercial grades with low and high cis polybutadiene. Transmission electron microscopy (TEM) was employed for observation of particle size distribution and digital imaging applied for quantitative analysis of the micrographs. Measurements of apparent volume fraction and average particle size were determined in TEM images for both grades, while the gel content and swelling index were employed to evaluate the effect of the polybutadiene cis isomer on the rubber crosslink density. Grade morphology and crosslink effects on mechanical properties were assessed by slow three-point bending and uniaxial tensile testing. The results illustrate that polybutadiene cis content in HIPS grades has strong influence on the mechanical properties, particularly affecting yielding and energy to failure. Accordingly, it was observed that HIPS grades with equivalent average particle size and apparent volume fractions present a much higher energy to failure and a lower yield stress with high cis content polybutadiene when compared to their lower cis polybutadiene counterparts.     

Rubber particle size and cavitation process in high impact polystyrene blends

The rubber particle size and its volume fraction are recognised as being important factors in determining the yield and fracture behaviour of high impact polystyrene (HIPS). However, correlations between the average particle size and cavitation in the rubber with toughening efficiency have only recently been established theoretically. This work provides further evidence on how the deformation kinetics in HIPS are affected by variations in the average rubber particle size highlighting along the way the role of rubber cavitation in the process. Variations in the average particle size were achieved by melt blending different proportions of two commercial grades of HIPS that had the traditional multiple inclusion particle morphology. Tensile and impact properties of the blends were measured and correlated to morphological parameters determined by quantitative image analysis. It was found that yield and fracture behaviour in tensile and impact test were strongly dependent on the amount of sub-micron particles in the blend. At high rates, toughness drops steeply with particle size. It was proposed that stress at yield and post yield strain hardening are controlled by particle size and rubber stretching respectively. Microfracture analysis by transmission electron microscopy lent support to the arguments presented. This revised version was published online in November 2006 with corrections to the Cover Date.     

Rubber-toughening of plastics

The effects of matrix ductility upon mechanisms of rubber toughening have been studied in a set of materials having identical rubber contents, but differing in matrix composition. The materials were made by solution blending 50% of HIPS (high-impact polystyrene) with polystyrene and PPO^® poly-(2, 6-dimethyl-1, 4-phenylene oxide) in varying proportions. Crazing was studied quantitatively by measuring volume changes during creep. Analysis showed that in blends of HIPS with polystyrene, crazing is the only significant mechanism of tensile creep, whereas in blends containing polyphenylene oxide, shearing mechanisms are also important, and the contribution of crazing to creep deformation can be as low as 30%, depending upon matrix composition. Scanning electron microscopy showed that both crazes and shear bands were present in strained HIPS/PPO blends. Shear band formation appears to be responsible for the increased fracture resistance of blends containing a high proportion of polyphenylene oxide. A theory of toughening is proposed for these blends.     

Internal structure of rubber particles and craze break-down in high-impact polystyrene (HIPS)

Polystyrene can be substantially toughened by the addition of rubber particles, their role being to act as craze initiators permitting substantial plastic deformation to occur prior to fracture. The internal structure of these particles is variable: typically the smaller (1 m) particles are solid rubber and the larger particles contain sub-inclusions of polystyrene. Thin films of a toughened high-impact polystyrene (HIPS) suitable for optical and transmission electron microscopy (TEM) have been prepared, and the interplay between the internal structure of the particles and the crazes they generate has been examined by TEM. It is found that as crazes form around the solid rubber particles, significant lateral contraction occurs accompanying their elongation in the tensile direction. As this contraction proceeds, decohesion occurs just beneath the particlecraze interface, resulting in the formation of a void. This void will grow under increasing stress, leading to premature failure of the craze. In contrast to this behaviour, occluded particles can accommodate the displacements due to crazing by local fibrillation of the rubber shell which surrounds each sub-inclusion, without the formation of large voids. Consequently, the occluded particles do not act as sites for early craze break-down. These results suggest that the optimum morphology for rubber particles in HIPS will consist of a large number of small PS occlusions, each surrounded by a thin layer of rubber, in which case the size of the inherent flaws introduced during crazing will be minimized.     

不同冲击断裂方式下橡胶粒子形态对HIPS脆韧转变的影响

核-壳型/蜂窝型高抗冲聚苯乙烯(HIPS)树脂在Izod冲击和落锤冲击断裂过程中的脆-韧转变行为不同。透射电镜(TEM)对亚断裂形变区的观察表明,蜂窝型HIPS对落锤冲击作用下的脆韧转变敏感,应力集中能有效引发基体的塑性形变,呈韧性断裂,但在v-notched Izod冲击断裂过程中,却呈脆性;而核-壳型HIPS的冲击断裂性能与之相反。将LDO假说引入冲击破坏研究并结合损伤竞争准数Da和Vincent图探讨了分散相特性及冲击方式对脆韧转变行为的影响。     

高抗冲聚苯乙烯的断裂韧性

综述了高抗冲聚苯乙烯断裂韧性方面工作的进展。评述了高聚物的脆性断裂－韧性断裂转变、分散相粒子大小及其分布、基材与分散相间的界面粘结等因素对高抗冲聚苯乙烯冲击韧性的影响。     

Stabilization of high-impact polystyrene/ polyethylene blends

Commercial poly(styrene-b-butadiene) copolymers (SBS) can act as effective compatibilizers in blends between high-impact polystyrene (HIPS) and polyethylene (PE), allowing a fine dispersion of PE in the polystyrene matrix, with a good balance of stiffness and impact strength. However, when processed under more severe conditions (e.g. in multiple extrusions, which simulate customer's product scrap recovery), the above blends show rather poor stability and their useful properties are rapidly lost. That undesirable effect is mainly due to cross-linking of SBS, which thus looses its compatibilizing activity. A correlation has been found between the time-to-cross-linking of SBS rubber in a Brabender mixer and the rapid decay of mechanical properties. The analysis of the mixing process and the morphology examinations of the final blend sample by TEM seem to support the above hypothesis. A significant reduction of block copolymer degradation has been achieved by means of a suitable stabilization.     

Toughening of polystyrene by natural rubber-based composite particles: Part III Fracture mechanisms

Impact testing has allowed the toughness of PS blends to be correlated with the morphology of the dispersed rubber phase, which was a natural rubber (NR) in particle form, coated with a shell of polystyrene (PS) or polymethylmethacrylate (PMMA). PS subinclusions were also introduced into the NR core. The impact resistance of the prepared PS blends began to rise steeply at a particle content of about 18 wt %. Transmission electron microscopy (TEM) in combination with osmium tetroxide staining techniques, allowed direct analysis of the crazing and cavitation processes in the composite natural rubber particle-toughened PS blends. Bulk samples were studied at high and slow deformation speeds. Different deformation mechanisms were effective, depending on the location of the observed stress-whitened zone relative to the notch tip. The apparent fracture mechanisms in rubber-toughened PS blends were also studied by scanning electron microscopy. PS blends containing polydisperse natural rubber-based particles or monodisperse poly(n-butylacrylate)-based particles, and commercial high-impact polystyrene, were compared. This revised version was published online in November 2006 with corrections to the Cover Date.     

Sensors for chemicals based on electrically conductive immiscible HIPS/TPU blends containing carbon black

Carbon Black (CB)-containing immiscible polymer blends based on high-impact polystyrene/thermoplastic polyurethane (HIPS/TPU) were studied as sensing materials for an homologous series of alcohols, including, methanol, ethanol and 1-propanol. The studied immiscible blend was designed to exhibit a double-continuity structure i.e., the CB particles form chain-like network structures within the TPU phase, which forms a continuous phase within the HIPS matrix. Extruded HIPS/TPU/CB filaments produced by a capillary rheometer process at various shear rate levels were used for the sensing experiments. All filaments displayed a selective resistance changes upon exposure to the various alcohols combined with reproducibility and recovery behaviour. An attempt is made to identify the dominant mechanisms controlling the sensing process in a CB-containing immiscible polymer blend characterized by a double-continuity structure. The distinct structure and composition of the HIPS/TPU interphase region were found to have a crucial role in the sensing mechanism, determining the selectivity of the filaments toward the studied alcohols. Additionally, the sensing performance of HIPS/TPU/CB system is compared to recent results for TPU/CB compounds, polypropylene/TPU/CB and HIPS/ethylene vinyl acetate/CB immiscible polymer blends.     

Second phase volume fraction and rubber particle size determinations in rubber-toughened polymers: A simple stereological approach and its application to the case of high impact polystyrene

The determination of the volume fraction and of the particle size distributionF(R) of the rubbery phase is necessary in many rubber-toughened polymers. High impact polystyrene is a good model system in which such a determination has to be performeda posteriori. The more commonly used procedures, i.e. phase-separation methods, analysis of micrographs and indirect mechanical measurements, all present drawbacks and difficulties. A simple stereological method, in which some of these difficulties are avoided, is proposed for the determination of and of some features ofF(R) from the analysis of micrographs. The validity of the method is tested by means of a wide numerical simulation. The proposed method, together with a standard phase-separation procedure and with indirect, mechanical measurements, is tested experimentally on two series of high impact polystyrene and the collected data are compared and discussed. The results of this investigation suggest that approximate views relating elastic properties of rubber-toughened materials only to the rubber particle volume fraction, however this parameter has been measured, not considering the size, the morphology and/or the structure of the rubber particles, are possibly questionable.     

Effect of lognormal particle size distributions on particle spreading in additive manufacturing

Additive manufacturing (AM) has attracted much attention worldwide in various applications due to its convenience and flexibility to rapidly fabricate products, which is a key advantage compared to the traditional subtractive manufacturing. This discrete element method (DEM) study focusses on the impact of particle polydispersity during the particle spreading process on parameters that affect the quality of the final product, like packing and bed surface roughness. The particle systems include four lognormal particle size distribution (PSD) widths, which are benchmarked against the monodisperse system with the same mean particle diameter. The results reveal that: (i) the solid volume fraction of the initial packed particle bed in the delivery chamber increases then plateaus as the PSD width increases; (ii) regardless of PSD width, the solid volume fraction of the particle bed increases with spreading layer height before compression, but decreases with layer height after compression; (iii) the bed surface roughness increases with PSD width or layer height both before and after the compression of the spreading layer; (iv) the extent of increase in solid volume fraction during compression is correlated with the extent of decrease in bed surface roughness; and (v) the broader PSDs exhibit larger fluctuations of solid volume fraction of the particle bed and bed surface roughness due to greater variability in the arrangement of particles of different sizes. The results here have important implications on the design and operation of particle-based AM systems.     

Sub critical crack advance vs. impact fracture on high impact polystyrene with different second phase volume contents and structures

Also for polymers, many fractures in service occurs after a period in which an existing crack has propagated in a sub-critical manner, while the laboratory tests are mainly concentrated on impact fractures. Aim of this paper is then to investigate the sub critical fracture in some high impact polystyrene (HIPS) materials with different second phase volume fraction and particle size and to compare it with the outcomes of impact Fracture Mechanics experiments. Large differences in the results of the two mechanical test procedures are evidenced: the materials behaviour is then examined from the structural point of view and an interesting case of interfacial failure, which disappears at high strain rate, is attested on some HIPSs by means of different techniques, i.e. electron microscopy, nuclear magnetic resonance spectroscopy and dynamic mechanical spectroscopy, indicating that the slow crack fracture behaviour can be influenced by parameters that do not affect ordinary mechanical tests.     

HIPS性能与橡胶粒子结构的关联及落锤冲击断裂的增韧机理

研究了橡胶粒子的结构对高抗冲聚苯乙烯(HIPS)性能及落锤冲击断裂的影响。结果表明,屈服强度随着橡胶体积分数的增加而线性递减;材料的落锤冲击韧性主要由分散相粒子的形态及粒子-界面间的粘接强度决定。透射电子显微镜(TEM)和扫描电镜(SEM)对落锤冲击断裂下的微观形变机理研究显示:(1)塑性形变或多重银纹是落锤冲击断裂过程中主要的能量耗散形式;(2)落锤冲击增韧机理可以通过橡胶粒子的形态设计及组成进行调控。另外,采用热重分析法(TGA)研究了HIPS中基质和凝胶的热稳定性。     

Characterization of filled rubbers using small-angle X-ray scattering

It is demonstrated how small-angle X-ray scattering (SAXS) can be used to characterize the structure of fillers such as carbon black and silica both before and after their incorporation into natural rubber. It is found that SAXS has significant advantages over conventional techniques such as gas adsorption or electron microscopy in determining both the size and distribution of sizes of the filler particles. The results are shown to be in good agreement with those obtained using conventional techniques. In addition it is demonstrated that SAXS can be used to characterize the filler particlesin situ enabling the volume fraction, particle size and particle surface area to be determined for a filled rubber and factors such as aggregation to be examined.     

Combined modelling and experimental studies of rubber toughening in polymers

When researching the effect of rubber toughening in acrylonitrile-butadiene-styrene (ABS) copolymer and high-impact polystyrene (HIPS) and also toughening methods used in other materials, then, often comparisons are needed between materials with and without the toughening agents over the full crack velocity range. This is from the threshold stress to just maintain crack propagation up to the limiting crack velocity conditions. However, the toughening of materials can change other material properties including, for example, the onset of yield in the material under static stress. The result can be that a crack velocity versus stress curve cannot be obtained by experiment over the full crack velocity range for some toughened materials. However, as used in this study, combined experimental and computer simulations can provide for a meaningful and informative comparison between crack velocity versus stress curves for materials with and without toughening agents over the full crack velocity range.     

弹性体改性高抗冲聚苯乙烯的力学行为：Ⅰ.拉伸和动态力学性能

研究了高抗冲聚苯乙烯（ＨＩＰＳ）同苯乙烯－丁二烯－苯乙烯热塑性弹性体（ＳＢＳ）、丁苯橡胶（ＳＢＲ）、高顺式聚丁二烯橡胶（ＰＢＲ）共混物的拉伸性能及动态力学性质。ＳＢＳ改性的ＨＩＰＳ试样具有最大的断裂能，最大的断裂伸长率，较高的拉伸杨氏模量、屈服强度，屈服点过后有明显的应变硬化现象。ＳＢＲ改性的ＨＩＰＳ也呈现韧性断裂，拉伸过程中有明显的应力发白现象。ＲＢＲ改改ＨＩＰＳ试样表现为脆性断裂，力学性能变劣