Structure-property relations of 55 nm particle-toughened epoxy

55-nm rubber particles significantly toughened two epoxy systems without loss of Young’s modulus, tensile strength and glass transition temperature. Transmission Electron Microscopy (TEM) showed that the nanoparticles are uniformly dispersed in matrix and have blurred interface with epoxy. 5 wt% rubber nanoparticles increased the critical strain energy release rate (G_1c) of Jeffamine D230 (J230)-cured epoxy from 175 J/m² to 1710 J/m², while the 10 wt% increased G_1c of diaminodiphenyl sulfone (DDS)-cured epoxy from 73 J/m² to 696 J/m². This is explained by comparing the surface-surface interparticle distance and total particle surface of nanocomposites with those of composites. The higher the matrix stiffness, the more nanoparticles needed for toughening. Although the 10 wt% J230-cured nanocomposite showed a 50% larger size of stress-whitened zone than the 5 wt% J230-cured nanocomposite, the 5 wt% nanocomposite showed a higher toughness. These nanoparticles were found to pose barriers to the vibration of crosslinked matrix molecules, leading to higher glass transition temperatures. While the matrix shear banding caused by nanoparticle expansion and growth is the major toughening mechanism for the J230-cured nanocomposites, the matrix plastic void growth and deformation are most probably the major mechanisms for the DDS-cured system. Under tensile loading, the nanoparticles in the DDS-cured epoxy created fibrils of 100-200 nm in diameter and 3-5 μm in length. TEM analysis in front of a subcritically propagated crack tip showed a number of voids of 30-500 nm in diameter in the vicinity of the crack, implying that rubber nanoparticles expanded, grew and deformed under loading. Unlike conventional epoxy/rubber composites in which all of the rubber particles in the crack front cavitated under loading, only a portion of the nanoparticles in this study expanded to create voids. Huang and Kinloch’s model developed from composites was found not fit well into these nanocomposites.     

高灼热丝环保型阻燃增强PBT的研制

通过阻燃剂的多元复配研究开发了高灼热丝环保型阻燃增强聚对苯二甲酸丁二醇酯(PBT)。采用以下阻燃剂体系进行复配实验:十溴二苯乙烷、溴化聚苯乙烯、多元复合型阻燃剂、三氧化二锑。最终确定:多元复合型阻燃剂加上三氧化二锑这个阻燃体系可以使PBT获得最高的灼热丝值,可以通过800℃灼热丝试验。     

废旧聚丙烯编织袋回收料改性应用研究

废旧聚丙烯(PP)编织袋回收料分别与回收聚乙烯(PE)、回收橡胶粉、木粉共混,制备了增韧PP材料、热塑性弹性体和木塑复合材料,采用力学性能测试、SEM和DSC分析等手段对其性能和结构进行了表征。结果表明:随着回收聚乙烯(PE)含量的增加,回收PP/PE共混物的拉伸强度和冲击强度迅速提高;回收PP/橡胶粉共混物中加入聚丙烯接枝马来酸酐(PP-g-MAH)能起到增容的效果,随PP-g-MAH含量的增加,共混物的拉伸强度上升,永久变形减小;在回收PP/木粉复合材料中加入PP-g-MAH后,复合材料的冲击强度明显提高。     

新型环氧灌封胶的研究

通过环氧树脂、增韧剂、固化剂及固化促进剂的筛选 ,完成了一种在 130℃下、剪切强度大于 10MPa、不开裂、韧性好的环氧树脂灌封胶的研制工作 ,同时介绍了该灌封胶的主要性能指标     

ABS/PBT/弹性体三元共混合金的研究

研究了弹性体NBR和SBS对ABS／PBT共混合金体系的力学性能和熔体质量流动速率的影响，并对共混合金的相容性进行了研究。结果表明：加入弹性体NBR后，共混合金在保持较好刚性的同时，断裂伸长率和韧性得到了较大的改善。当NBR用量为20份时，共混合金的断裂伸长率提高了313％，冲击强度提高了54％；SBS对ABS／PBT共混合金的增韧效果不明显，加入弹性体后，ABS／PBT共混合金体系的粘度增大，MFR降低，但仍明显好于纯ABS。     

Toughening of polypropylene with calcium carbonate particles

Polypropylene-CaCO₃ composites were prepared on a twin screw extruder with a particle content of 0-32 vol%. The influence of particle size (0.07-1.9 μm) and surface treatment of the particles (with and without stearic acid) on the toughening properties were studied. The matrix molecular weight of the polypropylene was also varied (MFI 0.3-24 dg/min). The experiments included tensile tests, notched Izod impact tests, differential scanning calorimetry (DSC), scanning electron microscopy and rheology experiments. The modulus of the composites increased, while the yield stress was lowered with filler content. This lowering of yield stress was connected to the debonding of the particles from the polypropylene matrix. From DSC experiments it was shown that the particle content had no influence on the melting temperature or crystallinity of the PP phase, also particle size showed no effect on the thermal properties. The impact resistance showed large improvement with particle content. The brittle-to-ductile transition was lowered from 90 to 40 °C with the addition of CaCO₃ particles. Notched Izod fracture energy was increased from 2 up to 40-50 kJ/m². The stearic acid coating on the particle surface showed a large positive effect on the impact strength. This was mainly due to the improved dispersion of the CaCO₃ particles. Aggregates of particles clearly had a detrimental effect on the impact behaviour of the composites. The smaller particle sizes (<0.7 μm) showed coarse morphologies and this lowered the toughening efficiency. The molecular weight of the polypropylene matrix had a profound effect on the toughening properties. A higher molecular mass shifted the brittle-to-ductile transition towards lower temperatures. At the higher filler loads (>20 vol%), however, still problems seem to occur with dispersion, lowering the toughening efficiency. Of all particle types used in this study the stearic acid treated particles of 0.7 μm were found to give the best combination of properties. From the study of the micro-toughening mechanism it was shown that at low strain the particles remain attached to the matrix polymer. At higher strain the particles debond and this leads to a change in stress state at the particle size level. This prevents crazing of the matrix polymer and allows extensive plastic deformation, resulting in large quantities of fracture energy.     

Fracture micromechanisms of bioabsorbable PLLA/PCL polymer blends

Poly(l-lactide) (PLLA) has actively been used as a biomaterial for resorbable bone fixation devices for use in orthopedic and oral surgeries. Recently, in order to improve the fracture properties of brittle PLLA, polymer blends of PLLA and a ductile bioabsorbable polymer, poly(ε-caprolactone) (PCL), have been developed. The aim of the present study is to elucidate details of the fracture behavior and toughening mechanisms of PLLA/PCL blends. PLLA/PCL blends with different PCL contents were developed, and the critical energy release rate at crack initiation, G_in, was then measured to assess the effect of PCL content. It was shown that G_in is dramatically improved by blending PCL with PLLA, and the maximum 51% of increase of G_in is acheived with 5 wt% of PCL. Polarizing optical microscopy (POM) and scanning electron microscopy (SEM) of crack growth behavior were also performed to characterize the fracture mechanism. PLLA/PCL showed multiple craze formation in the crack-tip region, and elongated fibrils and voids construct the crazes. SEM of fracture surface also indicated that stretched fibril structures are formed on the surface as a result of elongation of PCL spherulites under high tensile stress condition in the crack-tip region. Thus, these damage formations are considered to be the primary energy dissipation mechanisms that resulted in the improvement of fracture energy.     

变频器在玻璃钢化设备中的应用

本文主要讲述了玻璃钢化的主要原理及变频调速技术在玻璃钢化设备中的应用。     

MORPHOLOGICAL STUDIES RELATING TO THE FRACTURE STRESS AND FRACTURE TOUGHNESS OF SILICON NITRIDE

Abstract— Microstructure and mechanical properties of HP (Hot Pressed), HP/GP (Gas Pressed), and HP/HIP (Hot Isostatic Pressed)—Si₃N₄ are studied using scanning electron microscopy, bending tests and the indentation fracture method. The grain diameter distribution is analyzed to clarify the relationship between microstructure and mechanical properties; and also the bending strength and fracture toughness. It is shown that bending strength increases with decreasing grain diameter. The results also show that a Hall—Petch type of relationship is obtained between grain diameter and fracture strength. The fracture toughness shows a linear relationship with , where σ_F= bending strength, β= a proportionality factor and d _a= average grain diameter, and is closely related to the aspect ratio of Si₃N₄ grains. It is concluded, from the morphological analysis, that a microstructure composed of Si₃N₄ grains, with both a small grain diameter and a large aspect ratio, is effective in improving both the fracture strength and fracture toughness.     

高抗冲聚苯乙烯的阻燃及增韧研究

采用十溴二苯醚(DBDPO)和三氧化二锑(Sb_2O_3)为阻燃复合体系对高抗冲聚苯乙烯(HIPS)进行阻燃改性,研究了阻燃复合体系对HIPS共混材料阻燃性能和力学性能的影响.结果发现:当DBDPO与Sb_2O_3的质量比为3:1时,HIPS共混材料的氧指数达到28%,阻燃效果较好,同时力学性能损失较小;加入无机阻燃剂可以抑制HIPS共混材料燃烧,明显降低发烟量;并比较了增韧剂种类和用量对HIPS共混材料阻燃性能和力学性能的影响.