The toughening mechanism in hybrid epoxy-silica-rubber nanocomposites (HESRNs)

Two different size nanosilica (NS) particles, nominally 20 nm and 80 nm in diameter, and carboxyl terminated butadiene acrylonitrile (CTBN) were blended into a lightly crosslinked, DGEBA/piperidine epoxy system to investigate the toughening mechanisms in hybrid epoxy-silica-rubber nanocomposites (HESRNs). Adding small amount of NS particles into CTBN toughened epoxies further improved the fracture toughness to a level that could not be achieved by increasing CTBN content alone. Interestingly, this toughening effect is diminished when NS particles clustered at high CTBN contents. In addition, the effect of NS particle size on toughening behavior was not considerable, except the case when NS clustering is observed. According to the SEM and TOM investigations, the plastic zone, which consists of shear banding and matrix dilation, is further enlarged in front of the crack tip in HESRNs. Irwin’s model is used to evaluate the process zone concept and the result indicates that zone shielding is credited for the toughening mechanism in these HESRNs.     

Toughening by nanostructure

Block copolymer modified epoxy resins have generated significant interest since it was demonstrated that the combination could lead to nanostructured thermosets through self-assembly. Over moderate to high polymer concentration the system behaves as expected for a block copolymer in a solvent selective for one block. Two types of copolymers have been studied: non-reactive and reactive modifiers. Morphologies such as copolymer vesicle and spherical/wormlike micelles can be formed under the appropriate conditions. The enhancement of the modified thermosets' mechanical properties depends on the morphology adopted by the polymers. Besides improving mechanical properties, the morphology was found to also have an effect on the glass transition in the studied systems. In this review we collect the available data on the block copolymers used to fabricate nanostructured epoxy resins and critically appraise the properties reported.     

Toughening mechanisms of ZTA ceramics at cryogenic temperature (77 K)

ZTA ceramics containing 20 wt% ZrO₂ were fabricated at different sintering temperatures (1450, 1500 and 1550 °C) by SPS and HP processes, respectively. The influence of sintering process on the mechanical properties of ZTA ceramics at 298 K and 77 K was investigated. It can be seen that the bending strength and fracture toughness of samples prepared by the two processes both improved at cryogenic temperature. The stress-induced martensitic transformation toughening mechanism was confirmed by the in-situ Raman technique. The tetragonal ZrO₂ would be even more easy to transform because of the residual stress generated when temperature decreased from 298 K to 77 K. Therefore, the transformation toughening effect would become stronger, result in the increase of mechanical properties.     

Preparation and thermal properties of epoxy-silica nanocomposites from nanoscale colloidal silica

Epoxy-silica nanocomposites were obtained from directly blending diglycidylether of bisphenol-A and nanoscale colloidal silica and then curing with 4,4-diaminodiphenylmethane. The epoxy-silica nanocompoites showed good transparency and miscibility observed with AFM, SEM, and TEM. The thermal stability of the epoxy resins was improved with the incorporation of the colloidal silica. However, a depression on the glass transition temperature of the resins was observed, owing to the plasticizing effect of the colloidal silica. Moreover, the nanoscale colloidal silica did not show effectively synergistic effect on char formation and flame retardance with phosphorus.     

环氧树脂增韧的研究进展

综述了环氧树脂(EP)增韧的几种方法以及增韧机理的研究进展,并指出了存在的问题和发展方向。     

酚醛树脂的增韧方法及增韧机理分析

综述了酚醛树脂的主要增韧方法,详细地分析和总结了各种增韧方法的增韧机理。结果表明:增韧方法可以归结为内增韧和外增韧两大类,不同的增韧方法对应不同的增韧机理。     

Toughening mechanisms of rubber modified thin film epoxy resins

An epoxy terminated polybutadiene (ETPB) was synthesized and utilized to enhance the toughening of an epoxy system, in both bulk and coating states. In the first step, the fracture energy of the modified samples was determined using a single edge notched type specimen in a three point bending (SEN3PB) geometry. The effective toughening mechanisms of bulk epoxy specimens were examined using scanning electron microscopy (SEM). The results showed that plastic void growth, cavitation and shear yielding mechanisms were the main toughening mechanisms of the bulk epoxy systems. In the next step, mechanical properties (i.e. impact resistance, flexibility, cupping resistance and hardness) and adhesion of the thin film specimens were evaluated in accordance to the amount of synthesized ETPB. The results showed that the mechanical properties of the ETPB modified epoxy resins considerably improved. In all cases, it was found that the improvement of the mechanical properties reached a maximum at 7.5 wt.% and then began to decrease with further increase in ETPB content. The effective toughening mechanisms in the modified thin films were also examined using SEM and compared to the bulk types. In contrast to the bulk types, the results showed that crack arresting and shear yielding were active mechanisms in thin films. The contribution of these mechanisms led to the improvement of adhesion and mechanical properties by energy dissipation.     

硬相粒子（PS）与弹性体（CPE）增韧聚氯乙烯研究

将最新的硬相增韧技术与传统的弹性体增韧方法相结合，对聚氯乙烯树脂进行改性，制备了综合性能优异的ＰＶＣ／ＣＰＥ／ＰＳ三元合金材料，其具有高韧性、高强度的特征，并能改善ＣＰＥ增韧ＰＶＣ时，耐热性，加工流动性变差的缺点。本文探讨了其改性效果的主要因素及增韧机理。     

Toughening of poly(butylene terephthalate) by AES terpolymer

AES, a terpolymer of acrylonitrile-EPDM(ethylene/propylene/diene elastomer)-styrene, was blended in poly(butylene terephthalate) (PBT). Uniaxial tensile tests were carried out at various strain rates on blends containing 0-50 wt% of AES in order to study the yielding behavior of PBT in these blends by the Eyring equation. It was found that stress concentration factor (γ) increases sharply when a small content of AES is incorporated in the PBT matrix, but further incorporation seems to have small effect and γ levels out, a behavior that can be explained by the blend morphology and AES mechanical characteristics. The effect of AES content on the notched Izod impact strength of PBT blends was also examined in depth. It was found that a supertough blend can be achieved with at least 30 wt% of AES in PBT in appropriate molding temperature. Macroscopic and microscopic observations indicate that dilatational process play an important role on the toughening mechanism in PBT/AES blends at notched Izod impact tests.     

Toughening of poly(butylene terephthalate) with epoxy-functionalized acrylonitrile-butadiene-styrene

Glycidyl methacrylate (GMA) functionalized acrylonitrile-butadiene-styrene (ABS) copolymers have been prepared via an emulsion polymerization process. These functionalized ABS copolymers (ABS-g-GMA) were blended with poly(butylene terephthalate) (PBT). DMA result showed PBT was partially miscible with ABS and ABS-g-GMA, and DSC test further identified the introduction of GMA improved miscibility between PBT and ABS. Scanning electron microscopy (SEM) displayed a very good dispersion of ABS-g-GMA particles in the PBT matrix compared with the PBT/ABS blend when the content of GMA in PBT/ABS-g-GMA blends was relatively low (<8 wt% in ABS-g-GMA). The improvement of the disperse phase morphology was due to interfacial reactions between PBT chains end and epoxy groups of GMA, resulting in the formation of PBT-co-ABS copolymer. However, a coarse, non-spherical phase morphology was obtained when the disperse phase contained a high GMA content (≥8 wt%) because of cross-linking reaction between the functional groups of PBT and GMA. Rheological measurements further identified the reactions between PBT and GMA. Mechanical tests showed the presence of only a small amount of GMA (1 wt%) within the disperse phase was sufficient to induce a pronounced improvement of the impact and tensile properties of PBT blends. SEM results showed shear yielding of PBT matrix and cavitation of rubber particles were the major toughening mechanisms.     

橡胶增韧聚合物机理

详细综述了橡胶增韧聚合物机理的研究进展,并对影响增韧效果的诸多结构因素进行了分析和讨论。     

氧化锆增韧陶瓷材料的结构性能和应用

介绍了ZrO2的结构、性能，ZrO2增韧陶瓷材料的生产工艺及应用，并论述了ZrO2，增韧补强的机理。     

Toughening mechanism of SAN resin

SAN resin poly(styrene-co-acrylonitrile) combine, the gloss and transparency of PS with added chemical resistance, high heat distortion temperature, dimensional stability and stiffness characteristics. However brittleness restricts its wider application. The morphology, impact behavior and toughening mechanism of four rubbers toughened SAN resin were investigated in this study.     

Polypropylene-polyhedral oligomeric silsesquioxanes (POSS) nanocomposites

In this paper, the influence of the functionalisation of polyhedral oligomeric silsesquioxanes (POSS) cages on the preparation and properties of polypropylene (PP) based nanocomposites is studied.POSS with different chain lengths (octamethyl-, octaisobutyl- and octaisooctyl-POSS) are taken in to account and melt mixed with PP. The resulting composites are characterised as regards thermal and morphological characteristics by means of DSC, TGA, SEM and X-ray diffraction.A good dispersion is obtained particularly at low loadings of POSS functionalised with longer organic chains.Important features are recognised as regards the crystallisation behaviour of PP by octamethyl- and octaisobutyl-POSS: The former acting as a nucleating agent and the second inducing PP polymorphism.     

聚苯乙烯增韧研究进展

综述了近年来用普通塑料、工程塑料、稀土、刚性粒子和弹性体等改性聚苯乙烯的进展情况。     

Toughening of dimethacrylate resins by addition of ultra high molecular weight polyethylene (UHMWPE) particles

The effects of the addition of UHMWPE particles, of nominal 〈80 μm〉 size, on the fracture toughness, flexural modulus and strength of composites made with dimethacrylate resins (60/40 wt/wt BisGMA-TEGMA) were investigated as a function of volume fraction of UHMWPE (0-60 vol%) and particle surface treatment. Interfacial shear strengths (τ) were measured via microbond shear strength tests using Spectra900™ (UHMWPE) fibers and BisGMA-TEGMA beads. τ increased by a factor of 4 compared with untreated UHMWPE, and surface treated particles improved the mechanical properties of the composite. Fracture toughness (K_IC) and flexural modulus (E) increased with increased volume fraction of UHMWPE, with maximum K_IC/E increases (at 60 vol%) of 238%/25% compared with the neat resin. SEM images showed debonding as well as yielding and fibrillation of the UHMWPE particles, suggesting that these were significant toughening mechanisms.     

PMMA增韧改性方法及机理

综述了聚甲基丙烯酸甲酯增韧改性的几种方法及机理,主要包括共聚增韧、共混增韧、形态控制增韧。     

新型PBT增韧剂对PBT增韧的研究

采用新型双官能化增韧剂SWR-6B对PBT及增强PBT进行增韧研究。结果表明，随着增韧剂SWR-6B用量的增加，PBT的冲击强度显著提高；当其质量分数为10％时，冲击强度为lO．OkJ／mz，是纯PBT的2倍；在增强PBT中的效果也优于其它增韧剂；且SWR-6B在改善冲击强度的同时，材料的拉伸性能，弯曲性能下降较少，是一种比较理想的PBT增韧剂。同时对比了SWR-6B和美国杜邦MN-PTW及法国阿托AX8900等对PBT及增强PBT性能的影响。     

改性核壳增韧母料的制备及应用

以马来酸酐接枝物为改性剂制得增韧母料,考察了这种母料对均聚聚丙烯的增韧效果以及增韧体系的微观结构,探讨了这种增韧体系的增韧机理。结果表明：这种增韧母料具有典型的核壳结构,与传统增韧母料相比,能够以更小的尺寸均匀分散在聚丙烯树脂中,既能获得较高的韧性,又保持了良好的刚性,使增韧母料的用量显著减少。     

树脂合金化增韧改性环氧树脂研究进展

综述了EP的树脂合金化增韧改性;介绍了近年来EP增韧方法及相应的增韧机理研究进展;着重讨论了橡胶类弹性体、热塑性树脂、热致液晶聚合物、互穿网络结构、纳米粒子和核壳聚合物等增韧改性EP新技术。