Preparation And Characterization Of Chlorinated Polypropylene In Aqueous Suspension

Chlorinated isotatic polypropylene (CIPP) is a modified product of. polypropylene (IPP) and has better adhesion and fire resistance. This paper was devoted to the chlorination of IPP by aqueous suspension process, which was simple and produced little pollution. The chlorination laws were investigated and the chlorination mechanism and kinetics model were proposed. The results will provide the basement for industrial preparation of CIPP.Chlorination of IPP in aqueous suspension required well dispersion of IPP in water. Study of aqueous dispersion in 500mL flask showed that reducing temperature and solid/liquid ratio, rising agitation speed and particle size benefited aqueous dispersion of IPP. When temperature and solid/liquid ratio were fixed, the system had upper and lower critical agitation speeds. Dispersants had no function on aqueous dispersion of IPP when the agitation speed was less than lower critical agitation speed. IPP could be well dispersed in water with no surfactants by agitation when the agitation speed was greater than upper critical agitation speed. So, agitation speed should be greater than lower critical agitation speed in chlorination process. The dispersion effect of sodium dodecyl benzyl sulfate (SDBS) was better than that of sodium dodecyl sulfate (SDS) and polyvinyl pyrrolidone (PVPP).The thermal-initiated chlorination process of IPP could be divided into two steps: surface reaction-control stage (about within 1hr) and ash layer diffusion-control stage (about after 1hr). A surface reaction-control model and a ash layer diffusion-control model were proposed and conversion equations were obtained:chlorination process was controlled by ash layer diffusion. The chlorine content decreased from particle surface to center.The chlorination rate and uniformity could be improved by decreasing the actic index, molecular weight and particle size of IPP, and surface grafting of MAH onto IPP. Adding of inertia swelling agent, and alternate crushing and chlorination, could accelerate particle surface renewal and increase the chlorine content, uniformity and solubility of products. Metal ion inhibited the chlorination. Adding of dispersant, raising the feeding rate of chlorine and agitation speed could promote diffusion ofchlorine in gas and liquid phase and remove the effect of outer diffusion. Higher temperature benefited producing of chloride radicals, rising of reaction activity and chlorine diffusion. Too high temperature could facilitate the degradation of IPP and reduce product property. The activation energy E was 30.69 kJ/mol and thefrequency factor A was 3.015 s-1 in the surface reaction stage under thermalinitiation. Both UV-photo and thermal initiation could promote chlorination. Continuous lighting was better than intermittent lighting. E=28. 10kJ/mol and A =51.02 s-1 in the surface reaction stage under both UV-photo and thermal initiation.The structure, melting point, crystallization degree, solubility and degradation of CIPP were studied. The results showed that p-, s- and t- hydrogen were substituted in turn as the chlorination proceeded, a crystal wasn't destroyed, but the crystallization degree decreased and melting point reduced gradually. Crystal was destroyed completely and CIPP could be dissolved in methylbenzene (20wt%) when the content of chlorine of CIPP achieved 63%. The thermal stability of CIPP decreased, and it was easy to degradate, as chlorine content increased.