Effect of Poly(butyl acrylate)-g-poly(styrene-co-acrylonitrile)’s Core/shell Ratio on Mechanical and Thermal Properties of Poly(butyl acrylate)-g-poly(styrene-co-acrylonitrile)/α-methylstyrene-acrylonitrile Binary Blends

Poly(butyl acrylate)-g-poly(styrene-co-acrylonitrile) terpolymer (PBA-g-SAN) with different core/shell ratios and α-methylstyrene-acrylonitrile (α-MSAN) were mixed via melt blending (25/75, W/W). It was found that the core/shell ratio of PBA-g-SAN played an important role in the toughening of rigid α-MSAN. According to an analysis of the impact strength and the morphologies of the impact fractured surfaces, the optimum core/shell ratio with the highest toughening efficiency was 60/40. Considering the results of dynamic mechanical thermal analysis (DMTA), the blends retained the high glass transition temperature (T_g) of α-MSAN because of the immiscibility between the two components. Moreover, increasing the core/shell ratio did not result in sacrificing the heat distortion temperature of the blends, which was attributed to the almost unchanged high temperature T_g of α-MSAN. The tensile strength, flexural strength, and modulus declined slightly with the increasing core content of PBA-g-SAN, which suggested that the stiffness of the blends decreased with the increasing core/shell ratio. This study showed that 60/40 was the optimum core/shell ratio used for toughening modification; it achieved a good balance between mechanical and heat resistance performance.     

Research progress in toughening modification of poly(lactic acid)

Renewable poly(lactic acid) (PLA) exhibits high strength and stiffness. PLA is fully biodegradable and has received great interest. However, the inherent brittleness of PLA largely impedes its wide applications. In this article, the recent progress in PLA toughening using various routes including plasticization, copolymerization, and melt blending with flexible polymers, was reviewed in detail. PLA toughening, particularly modification of impact toughness through melt blending, was emphasized in this review. Reactive blending was shown to be especially effective in achieving high impact strength. The relationship between composition, morphology, and mechanical properties were summarized. Toughening mechanisms were also discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011.     

碳酸钙粒子增韧高密度聚乙烯的脆韧转变-Wu氏增韧理论聚合物共混物脆韧转变判据的适用条件

采用不同尺寸的碳酸钙粒子增韧高密度聚乙烯,研究了不同温度下共混体系的临界粒子间距与碳酸钙粒子尺寸和含量之间的关系,确定了温度是Wu氏增韧理论临界粒子间判据适用性的重要影响因素。 结果表明,在17 ℃下,临界粒子间距与碳酸钙粒子的尺寸和含量无关,该条件下Wu氏增韧理论临界粒子间距判据是适用的;而随着温度的升高,发现临界粒子间距依赖于碳酸钙粒子的尺寸,表明高温条件下,Wu氏增韧理论临界粒子间距判据不再适用。     

ASYMPTOTIC ANALYSIS OF PLANE-STRAIN MODE I STEADY-STATE CRACK GROWTH IN TRANSFORMATION TOUGHENINGCERAMICS(Ⅱ)

I.IntroductionThemechanismoffracturetoughnessenhancementinceramicshasbeenwidelystudiedsincetheearlyl98Os.ThepioneeringconstitutivemodeldevelopedbyBudianskyetal.ll1includestheeffectofplasticdiIation,butneglectsthetransformation-inducedshearstrain.Andtheirc…     

Effect of reactive compatibilization on the properties of poly(butylene terephthalate)/acrylonitrile–ethylene–propylene–diene–styrene blends

Blends of poly(butylene terephthalate) (PBT) with 30 wt % acrylonitrile–ethylene–propylene–diene–styrene (AES) were prepared with methyl methacrylate (MMA)/glycidyl methacrylate (GMA)/ethyl acrylate (EA) terpolymers (MGEs) as compatibilizing agents. These acrylic terpolymers were miscible with the styrene–acrylonitrile (SAN) phase of AES, whereas the epoxide groups of GMA could react with the PBT end groups; this could lead to the formation of grafted copolymers (PBT‐g‐MGE) at the PBT/AES interface during the melt processing of the blends if at least a fraction of this interface was formed between the PBT and SAN phases. This study found evidence of the aforementioned interfacial structure through the effectiveness of the MGE terpolymers in promoting the compatibilization, as evaluated by dynamical mechanical analysis, through the increase in the viscosity of the blends, and through the reduction of the AES particle size dispersed in the PBT matrix. These effects became more intense with an increase in the overall concentration of GMA in the blends and with a reduction of the molecular weight of MGE. Another effect promoted by the compatibilization was a remarkable reduction of the brittle–ductile transition temperatures of the blends, which was correlated with the reduction of the AES particle size. However, this correlation between the brittle–ductile transition temperatures and particle size did not hold for the blend with the lowest AES particle size, which showed a high ductile–brittle transition temperature. These mechanical behaviors were examined on the basis of the current theory of the toughening of thermoplastics, which takes into account the importance of the rubber interparticle distance and the cavitation process of these particles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1244–1259, 2005     

ASYMPTOTIC ANALYSIS OF PLANE-STRAIN MODE I STEADY-STATE CRACK GROWTH IN TRANSFORMATION TOUGHENING CERAMICS(Ⅱ)

Based on a constitutive law which includes the shear components of transformation plasticity, the asymptotic solutions to near-tip fields of plane-strain mode I steadity propagating cracks in transformed ceramics are obtained for the case of linear isotropic hardening. The stress singularity, the distributions of stresses and velocities at the crack tip are determined for various material parameters. The factors influencing the near-tip fields are discussed in detail.Project supported by the National Natural Science Foundation of China     

On the effect of nano-particle clustering on toughening of nano-composite ceramics

In this paper, two and three-dimensional clustering models are developed to characterize the effect of nano-particle clustering on toughening of nanocomposite ceramics. It is found that crack pinning toughens the nano-composite ceramics because a higher stress intensity factor is needed for crack to propagate around or to pull-out the nano-particle. The nano-particle along the grain boundary steers the crack into the matrix grain due to the strong cohesion between the nanoparticle and the matrix. Since the fracture resistance of the grain boundary is lower than that of the grain lattice, the higher the probability of transgranular fracture induced by nano-particles, the tougher is the nano-composite. However, both crack pinning and transgranular fracture are affected by nano-particle clustering. Nanoparticle clustering, which increases with increasing volume fraction of nano-particles, leads to reduction of both the strength and toughness of the nano-composite ceramics. The larger the size of the clustered particle, and the more defects it contains, the easier it is for the crack to pass through the clustered particle, which means that the nano-particle clustering can reduce toughening induced by crack pinning and transgranular fracture. The theoretical prediction, based on the combination of the three mechanisms of nano-particles, is in agreement with the experimental data. The project supported by the National Natural Science Foundation of China (19891180) and the Research Grants Council of the HKSAR, China(HKU7081/00E)     

Crystallization behavior and toughening mechanism of poly(ethylene oxide) in polyoxymethylene/poly(ethylene oxide) crystalline/crystalline blends

In this study, the unique crystallization behavior of poly(ethylene oxide) (PEO) in polyoxymethylene (POM)/PEO crystalline/crystalline blends was examined in detail. This study was the first to report the typical fractionated crystallization of PEO in POM/PEO blends when PEO is fewer than 30 wt.%. The delayed crystallization temperature of PEO was confirmed at about 5°C to 14°C by using differential scanning calorimetry and perturbation–correlation moving‐window 2D correlation IR spectroscopy. Wide‐angle X‐ray diffraction indicates that no new crystal structures or co‐crystals were generated in POM/PEO. The statistical calculations of scanning electron microscopy photos show that the average diameter of PEO particles is 0.227 µm to 1.235 µm and that the number of small particles is as many as 10⁹ magnitudes per cm³. Theory analysis establishes that the delayed crystallization of PEO is a heterogeneous nucleation process and not a homogeneous nucleation process. A significant toughening effect of PEO to POM was also observed. The impact strength of POM/PEO acquires a maximum of 10.5 kJ/m² when PEO content is 5%. The impact strength of the blend increases by 78.0% compared with pure POM. To improve the toughening effect, the best particle size is established between 0.352 and 0.718 µm, with a PEO particle spacing of 0.351 µm to 0.323 µm. The number of corresponding particles was 0.887 × 10⁹ per cm3 to 3.240 × 10⁹ per cm³. A PEO toughening model for POM was proposed to provide a new and effective way to solve the problem of POM toughening. Copyright © 2014 John Wiley & Sons, Ltd.     

增韧环氧树脂的微结构和力学性能的正电子湮没

用正电子湮没方法（PALS）和动态力学分析（DMA）方法研究了增韧剂和温度对环氧树脂的自由体积和力学性能的影响．根据正电子素（o-Ps）湮没寿命τ3随温度的变化，玻璃化转变温度Tg和次级转变温度Tβ被确定．实验结果表明，在稀释环氧树脂基体中加入增韧剂会使样品中产生较强界面相互作用，并且明显地改变了材料的结构转变温度Tg和Tβ，使得增韧样品比稀释样品具有更高的玻璃化转变温度Tg．一个很有意义的发现是，低温下力学性能的改变明显地大于室温下力学性能的改变．文中从原子尺度自由体积特性和界面相互作用的角度探讨了温度对样品力学性能影响的机理．     

钇对陶瓷刀具材料Al2O3/TiCN的强韧化效应

在已 研制的含烯土Ａｌ２Ｏ３／ＴｉＣＮ陶瓷刀具材料的基础上，采用ＳＥＭ，ＴＥＭ和能谱分析等方法探讨了Ｙ的强韧化效应。稀土增强Ａｌ２Ｏ３／ＴｉＣＮ陶瓷刀具材料力学性能改善的原因在于，Ｙ的添加能在一定程度上积聚杂质，Ｗ，Ｆｅ和Ｃｒ等，从而起到清洁界面、提高界面结合强度的作用。