Deformation Mechanisms and properties optimization of PVC with core-shell impact modifier

我国是世界上聚氯乙烯产量最大的国家。由于在氯乙烯分子中氯的含量大于50%，而氯又是制碱工业的必然副产物，因此聚氯乙烯工业成为氯碱平衡中的主要杠杆。随着近年来世界石油资源的日益短缺和价格的上涨及国内聚氯乙烯产能过剩，开发聚氯乙烯的新用途，发展聚氯乙烯树脂的改性具有深远的意义。本工作的目的是以开发PVC核壳结构改性剂MBS和注塑级PVC/ABS合金为背景，对核壳粒子改性的聚氯乙烯的屈服机理和改性剂性能优化进行了研究。 对于增韧剂的研究，人们总是希望用最少的增韧剂用量来达到最好的增韧效果，即提高增韧剂的增韧效率，而且MBS改性的PVC在应用时还需要保持较高的透光率和具有一定的抗应力发白的能力。为此我们成功开发了具有高增韧效率、高透明及抗应力发白的MBS增韧剂，并研究了MBS结构特性对PVC/MBS共混物力学性能及屈服机理的影响。结果表明：粒径范围在80nm~280nm的橡胶粒子均能有效地对PVC进行增韧。大粒径的MBS通过空洞化释放三维静张应力引发基体的屈服来吸收能量，而小粒径的MBS不能产生空洞，但同样能引起基体的屈服起到增韧的作用。为了兼顾PVC/MBS共混物的韧性和透明性，我们在制备MBS时将一部分苯乙烯单体与丁二烯共聚结合来提高丁苯胶乳的折光指数与PVC基体相匹配，而另一部分苯乙烯单体以接枝的方式结合，这样可以保持MBS的弹性，并且制备的PVC/MBS共混物具有高韧性和高透明；同时我们发现MBS的内包容物及多层结构都会削弱PVC/MBS共混物的透光率。研究表明橡胶粒子的空洞化是引发共混物应力发白的主要原因。为此通过制备小粒径及具有一定交联程度的MBS来抑制空洞的产生，制备了兼有抗应力发白和韧性的MBS。成功开发了多个牌号的MBS产品，并在吉化集团公司建成了年产5000吨的生产车间，实现了MBS的工业化生产。 由于PVC的熔体流动性较差，通过与熔体流动性好的ABS树脂共混，成功开发了注塑级PVC/ABS合金。ABS树脂是SAN树脂和PB-g-SAN的共混物，在PVC中加入ABS使增韧对象由PVC基体转化为PVC/SAN共混基体，并研究了基体性质的改变对增韧效果的影响。结果表明随着PVC/ABS共混体系基体中PVC含量的增加共混物的冲击强度显著增加，形变机理发生了由银纹向剪切屈服的转变。China is the country with the largest yield of Poly (vinyl chloride) (PVC) resin. Since half of the molecular weight of vinyl chloride comes from the chlorine element, which is the product of alkaline industry, the Poly (vinyl chloride) industry has become more important for the balance of alkaline industry. With the shortage of the oil resource, the rise of price and the overplus of PVC, the development of modified PVC industry has become more important. This work was based on the industry of MBS core-shell modifier and PVC/ABS alloy and focused on the deformation mechanisms and properties optimization of core-shell rubber modified PVC. As to impact modifier, it is hoped that the modified blends can obtain the maximum toughness with the least dosage of impact modifier, which is called to improve the modifier toughening efficiency. When the modified PVC is used in practice, the transparency and anti-stress whitening properties are needed in some condition. The MBS modifier with high toughening efficiency, transparency and anti-stress whitening properties has been developed successfully in our study. MBS core-shell modifiers with different structures synthesized by seed emulsion polymerization were used as impact modifiers of PVC. Results showed that MBS with different rubber particle sizes ranged from 80nm~280nm could toughen PVC effectively. MBS with large particle size could cavitate and relieve the triaxial tension and thereby promote shear yielding of the PVC matrix, while MBS with small particle size could promote shear yielding of the PVC without cavitation of rubber particles. In order to obtain PVC/MBS blends with good transparency and toughness, a portion of St monomer in MBS was copolymerized with butadiene to match the refractive index of SBR to PVC. It was also found that the inclusion and the multi-layer structure of MBS could impair the transparency of blends. The study also showed that the cavitation of rubber particles was the main cause of stress whitening. So the MBS with anti-stress whitening property and high toughening efficiency was obtained by controlling the particle size and cross-linking degree of MBS to restrain the cavitation of rubber particles. A series of products of MBS have been developed successfully, and a plant with annual yield of 5000 ton of MBS has been built up in Jilin City by Jilin Chemical of China National Petroleum Corporation (CNPC). Injection-molded grade PVC/ABS alloy has been prepared successfully by blending ABS resin with PVC to overcome the poor melting fluidity of PVC. ABS resin is blends of SAN resin with PB-g-SAN. When ABS resin was introduced into the PVC, the matrix of the blends varied from PVC to PVC and SAN blends. The effect of the matrix composition on the toughening efficiency has been investigated. It was found that the impact strength of PVC/ABS blends increased with the PVC content in the matrix and the deformation mechanism transited from crazing to shearing yielding