Preparation, Structure And Properties Of Poly(Vinyl Chloride)/Hydrotalcite Nanocomposites

Aiming at getting poly(vinyl chloride)/hydrotalcite(PVC/LDH) naonocomposites with predominant properties, two innovative routes were proposed in this thesis. One was carrying out vinyl chloride in-situ suspension polymerization in the presence of LDH surface modified with zinc stearate. The other was conducting vinyl chloride suspension polymerization in the presence of dodecyl sulfonate-pillared LDH. The polymerization behavior, structure and properties of composite resins and composite materials were studied.At first, the rules of VC suspension polymerization in the presence of LDH nanoparticles surface modified with zinc stearate, were investigated. Compared to pure VC suspension polymerization system, the pressure of reaction system started to decrease early, and the conversion decreased at the same pressure drop. This was caused by the absorption of VC monomer to LDH. Adding of LDH had no significant effect on the polymerization rate, particle size and particle size distribution of composite resin and molecular weight and its distribution of PVC.The morphology and properties of PVC/LDH composite were investigated It showed that LDH particles dispersed homogeneously in PVC in nanoscale, and partially intercalated by PVC. The thermal stability of PVC/LDH composites resin increased as LDH fraction increased. The storage moduli (E') of PVC/LDH nanocomposite samples were all higher than that of pristine PVC, especially below glass transition region. While, the loss moduli (E") of PVC/LDH namocomposite samples were higher than that of pristine, mainly in the glass transition region. Tanδ and glass transition temperature changed no more for PVC/LDH nanocomposites. Incorporating of LDH nanoparticles had significantly influences on the mechanical properties of PVC, Young's modulus, tensile strength and Charpy impact strength of PVC/LDH nanocomposite increased as LDH weight fraction increased when LDH weight fraction was less than 5wt%.Taking advantage of the exchange ability of the interlayer anion of LDH, the dodecyl sulfonate-pillared LDH with formation of Mg0.67Al0.33(OH)2(DS)0.32·2.1H2O have beensuccessfully assembled by ion exchang of Mg0.67Al0.33(OH)2(CO3)0.16· 1.07H2O. The optimal conditions of intercalating were obtained as follows: pH=4, T=70℃, nSDS/nLDH =2, reactio time is 2h, drying temperature is 50℃.The crystal structure and chemical structure of LDH-SDS were analyzed. The results showed that the original interlayer carbonate ions of LDH could be completely replaced by dodecyl sulfonate under controlled conditions. FTIR result showed that there were static power and hydrogen bond between the host and guest. A supermolecular structure model of pillared LDH was proposed based on the above results.Following this, PVC/LDH-SDS composites were prepared by in-situ suspension polymerization and direct melt processing. The morphology and properties of PVC/LDH-SDS composites were investigated. From TEM micrographs, it showed that the size of most LDH particles were greater than 100 nm in composites prepared by the second method. While, LDH particles were mostly exfoliated, dispersed homogeneously and in orientation in PVC matrix with nanoscale, in composite prepared by the first method. Corresponding, composite prepared by the first method had greater modulus, tensile and impact strength than that of composites prepared by the second method. It also found the thermal stability of PVC/LDH-SDS composite resins increased as LDH-SDS content increased. The equilibrium processing torques decreased with the increasing content of LDH-SDS at first and increased when LDH-SDS content was relatively higher.