| Polytetrafluoroethylene (PTFE) has attracted a great attention due to its desirable properties, such as good thermal stability, chemical inertness, low coefficients of friction and low surface energy. However, PTFE has poor compatibility with other polymer materials, and it is difficult to disperse PTFE in other polymer matrix. Thus, it is important to explore the surface modification method of PTFE which can improve the compatibility of PTFE with other polymers without destroying the structure and property of PTFE. Aiming to prepare PTFE composite particles with good dispersion ability and used as plastics modifiers, seeded emulsion polymerizations using commercial PTFE latex particles as seed, acrylate monomer and styrene/acrylonitrile as coating monomers, were carried out in this thesis. Influences of polymerization technology, seed concentration, emulsifier concentration on the polymerization stability, mean size and size distribution, morphology of PTFE composite particle were investigated. The dispersion behavior of PTFE composite particles in poly(vinyl chloride) (PVC) or ABS, and influence of PTFE composite particles on fusion properties of PVC and anti-dripping properties of ABS were also studied.Firstly, seeded emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA) as monomer in the presence of PTFE seeds was conducted to synthesize PTFE-ACR core-shell composite particles. The influence of monomer addition policy, seed and emulsifier concentrations on polymerization stability, particle size distribution and morphology of composite particles were studied, and the optimum reaction conditions were obtained. It was found that the stability of semi-batch emulsion polymerization was better than that of batch emulsion polymerization. PTFE-ACR composite particles with size of 296nm, core thickness of 55nm, were prepared by semi-batch emulsion polymerization at 15% PTFE concetration and with the addition of pure monomers (1/8 monomers was added initially). When the concentration of OP-10 was in range of 0.5-1.0%, the mean size of PTFE-ACR composite was increased with the increase of OP-10 concentration. The particle size and core-shell structure of the resulting PTFE-ACR composite particles were confirmed by transmission electron microscopy (TEM). St-AN seeded emulsion copolymerization in the presence of commercial PTFE latex particles as the seeds were carried out, and influence of monomers adding policy, the composition and usage of OP-10/sodium dodecylsulfate (SDS) composite emulsifier on the polymerization stability, average size and size distribution, and morphology of composite latex particles were investigated. It was found the polymerization stability of semi-continuous emulsion copolymerization added with pre-emulsified monomers was better than that of batch emulsion copolymerization and semi-continuous emulsion copolymerization added with pure monomers. The mean size of PTFE-SAN composite latex particles was greater than that of PTFE seeds when the total usage of OP-10 and SDS was lower than 4wt% (based on monomers) and OP-10/SDS mass ratio in range of 1/2 to 2. When the total usage of OP-10 and SDS was greater than 4wt%, the mean size of PTFE-SAN latex was lower than that of PTFE seeds due to the secondary particle formation of SAN. PTFE-SAN composite particles exhibited spherical shape with PTFE coated by SAN, while PTFE seeds exhibited rod or egg-like shape.It is proved by TEM and SEM that PTFE-ACR composite particles have good dispersion in PVC. PTFE-ACR composite particles could be used as PVC processing aids to shorten the fusion time of PVC. When the usage of PTFE-ACR composite particles was 0.5%, the fusion time of PVC was reduced from 1.25min to 0.47min, and the equilibrium torque was slightly decreased.PTFE-SAN composite particles were used as the flame retardant modifier of ABS. It is shown that PTFE-SAN composite particles wew dispersed well in ABS after melt-blending. The fusion of ABS was accerated as PTFE-SAN composite particles added, while the melt flow index (MFI) of ABS was significantly decreased after blending with PTFE composite particles. The addition of PTFE composite particles was efficiently decreased the combustion rate of ABS, and the modifer ABS exhibited the anti-dripping properties. |
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