Deformation mechanisms in rubber toughened semicrystalline polyethylene terephthalate

The deformation mechanisms of rubber toughened polyethylene terephthalate (PET) are studied with fractography of impact fractured samples and tensile dilatometry. The dispersed phase consists of a mixture of an ethylene-co-propylene rubber (EPR) and a compatibilising agent (E-GMA8: copolymer of ethylene and 8 wt% of glycidyl methacrylate). It is found that the ductile fracture behaviour, above the brittle-ductile transition temperature (T_bd), consists of a high degree of rubber cavitation and extensive matrix shear yielding, both in the fracture plane and the stress whitened zone surrounding the crack. A steep increase in the volume strain upon tensile loading confirms the presence of the rubber voiding mechanism in the PET/(EPR/E-GMA8) blend system. It is seen that the stress whitened zone below the impact fracture surface consists of different zones, depending on the test temperature. Below T_bd, a layer of a highly deformed structure is followed by a cavitation layer containing only a limited number of cavitaties. Increasing the temperature, causes the deformation layer to be replaced by a zone lacking structure. It is believed that part of the fracture energy has been dissipated in the form of heat inducing a relaxation in the structure. Dynamical mechanical analysis under superimposed axial stresses reveals that the dispersed rubber particles internally cavitate in the presence of volume strain. At increased volume strains, the biaxial stress state in the cavitated particle is disturbed, resulting in the rupture of the rubber chains closest to the void by a tearing mechanism; revealing that the rubber particle is damaged upon cavitation.     

熔融共混法制备聚合物／纳米无机粒子复合材料

简介了在熔融共混法制备聚合物/纳米无机粒子复合材料的研究中所取得的几点成果，包括：(1)无机纳米粒子的“表面有限钝化”；(2)增强外力作用促进纳米粒子分散；(3)纳米粒子的“沙袋结构”对聚合物的增韧。此外，研究还发现，PP弹性体／CaCO3体系与二元体系相同，仍然符合逾渗脆韧转变机制；当纳米CaCO3在聚烯烃中分散良好时，在一定范围内，填充量越大，复合材料熔体的表观粘度越低，流动性越好；挤出时在高剪切速率下有较宽的第二光滑区。     

高流动性PP／POE／纳米CaCO3复合材料的研制

利用双螺杆挤出机，通过熔融共混工艺制备了聚丙烯(PP)／聚烯烃热塑性弹性体(POE)／纳米CaCO3复合材料。利用扫描电子显微镜(SEM)观察了不同体系的形态，结果显示：纳米CaCO3和POE在PP／POE／nano-CaCO3中互相促进分布及均化。冲击试验结果表明：PP／POE／nano-CaCO3体系的缺口冲击强度较PP／POE、PP／nano-CaCO3和纯PP分别提高了65％，107％和178％。熔体流动速率测试显示：纳米CaCO3在PP／POE／nano-CaCO3中具有提高体系流动性的作用。     

苯乙烯-二元乙丙橡胶嵌段共聚物增韧聚丙烯

考察了苯乙烯-二元乙丙橡胶嵌段共聚物（SEP）和三元乙丙橡胶（EPDM）对聚丙烯（PP）的增韧作用。结果表明，SEP比EPDM具有更好的增韧效果。SEP以核-壳形态分布于PP基质中，有效地诱导PP基质产生银纹和剪切屈服，消耗大量的冲击能，SEP用量为10份时，PP/SEP共混材料的缺口冲击强度较纯PP的提高7-8倍，超过了20份EPDM增韧PP的效果，是一种新型的PP抗冲增韧改性剂。     

导电膜玻璃在化学钢化过程中的性能变化

比较了在线SnO_2:F和离线溅射ITO两种导电膜玻璃经过化学钢化过程之后在性能上的变化,并对变化机理进行了分析。     

Boron nitride nanoplatelets induced synergetic strengthening and toughening effects on splats and their boundaries of plasma sprayed hydroxyapatite coatings

Boron nitride nanoplatelets (BNNPs) with excellent mechanical properties were introduced into HA coatings fabricated through plasma spray in this research. SEM observation and Raman results revealed the added BNNPs retained their original structure even after harsh process and distributed homogeneously in the as-sprayed coatings. As compared with the monolithic HA coating, a 2.0?wt%BNNP/HA coating exhibited significant improvement (~ 40.3%) in fracture toughness and moderate enhancement (~ 20.0%) in indentation yield strength. Synergetic strengthening and toughening mechanisms which are operative through splat boundaries and individual splats were proposed. At splat boundaries, these embedded BNNPs induced stronger adhesion between the adjacent splats to resist splat sliding, which is evident from the fact that the calculated inter-splat friction force of an as-sprayed BNNP/HA coating was increased by ~7.3% at 2.0% BNNP weight fraction. Within splats, toughening mechanisms such as BNNP pullout, crack bridging by both anchored BNNPs and nanosized HA grains, crack deflection and crack propagation arrested by the embedded BNNPs were observed to improve toughness. Moreover, thermal mismatch between HA matrix and BNNPs during cooling process after plasma spray would induce the pre-existing dislocations formed around these BNNP nanofillers, which was assumed to hold out the effect of Orowan-type strengthening within splats.     

Effect of polystyrenes with different architectures on the β‐nucleating efficiency and toughening of isotactic polypropylene

The effect of polystyrenes (PSs) with different architectures (three‐arm star‐shaped polystyrene (sPS), comb‐like branched polystyrene (cPS) and linear polystyrene) on their β‐nucleating efficiency for isotactic polypropylene (iPP) during crystallization and final impact and the tensile properties of iPP/PS blends were investigated by dynamic rheological measurements, SEM, DSC, polarized optical microscopy, wide angle X‐ray diffraction and mechanical property measurements. The results show that the architecture of PS has marked influence on its dispersibility in iPP and β‐nucleating efficiency. For iPP/cPS blend, plenty of short side chains reduce the probability of cPS chain entanglements, facilitating the interdiffusion between iPP and cPS chains. A favorable interfacial interaction results in good dispersibility, high β nucleating efficiency and an excellent toughening effect of cPS on iPP. However, the relatively high chain entanglement degree of sPS may not be in favor of chain diffusion between iPP and sPS and therefore relatively poor dispersibility and toughening effect are obtained. The elongation at break and impact strength of iPP were dramatically improved, especially with the addition of 1 wt% cPS. The toughening mechanism of PS on iPP is the dissipated energy caused by cavitation and the β‐nucleating effect of PS. © 2018 Society of Chemical Industry     

Mechanical properties and microstructure of Al2O3-SiCw ceramic tool material toughened by Si3N4 particles

Al₂O₃-SiC_w toughened ceramic tools play vital role in high-speed machining of nickel-based superalloys due to their superior mechanical properties. Herein, owing to synergistic toughening mechanism, α-Si₃N₄ particles are employed as reinforcement phase into Al₂O₃-SiC_w ceramic composite to optimize mechanical properties of Al₂O₃-SiC_w ceramic tools. Moreover, the influence of Si₃N₄ content and sintering parameters on microstructure and mechanical properties of Al₂O₃-20 vol%SiC_w ceramic tool material is systematically investigated. Results reveal that appropriate amount of Si₃N₄ particles is required to effectively increase the density of Al₂O₃-SiC_w ceramic composites. The presence of Si₃N₄ particles leads to formation of novel β-sialon phase during hot-press sintering, which effectively enhances fracture toughness and flexural strength of Al₂O₃-SiC_w ceramic composites. It is observed that grain size of newly formed β-sialon phase is extremely sensitive to hot-pressing sintering conditions. The degree of chemical transformation of α-Si₃N₄ into Si_6-zAl_zO_zN_8-z (β-sialon) and z-value of Si_6-zAl_zO_zN_8-z are significantly influenced by sintering temperature. Overall, Al₂O₃-20 vol%SiC_w-15 vol%Si₃N₄ ceramic tool material, with 1.5 vol%Y₂O₃-0.5 vol%La₂O₃-0.5 vol%CeO₂ (YLC) sintering additive, rendered optimal mechanical properties after sintering at 1600 °C under 32 MPa for 30 min. Improved mechanical performance can be ascribed to synergistic toughening and strengthening influence of whiskers and particles.     

柚皮环氧树脂/埃洛石复合材料的制备及性能

以柚皮素为原料合成了新型柚皮环氧树脂,以埃洛石纳米管为改性剂、马来酸酐为固化剂采用浇注工艺制备了柚皮环氧树脂/埃洛石复合材料,考察了埃洛石纳米管用量对柚皮环氧树脂/埃洛石复合材料力学性能、动态力学性能、热稳定性的影响。结果表明:纯柚皮环氧树脂的冲击强度及玻璃化转变温度较双酚A型环氧树脂分别提高了3.05 kJ/m²,96℃;埃洛石纳米管能够显著提高柚皮环氧树脂/埃洛石复合材料的冲击强度,当埃洛石纳米管用量为0.8%(w)时,柚皮环氧树脂/埃洛石复合材料的冲击强度为5.50 kJ/m²,较纯柚皮环氧树脂提高了52.8%。     

摩托车用高抗冲耐化学PC/PBT合金材料制备与性能

针对摩托车塑料件材料需具有一定的韧性和刚性及较高耐化学性的要求,开发了摩托车用高抗冲耐化学聚碳酸酯(PC)/聚对苯二甲酸丁二酯(PBT)合金材料.探究了PC种类、含量,增韧剂种类、含量对PC/PBT合金材料物理力学性能的影响.结果表明,当选用硅氧烷PC AG2030,PBT 1100A作基材,且PC/PBT质量比为1:...