Preparation And Characterization Of Poly(Vinyl Chloride)/Nanometer Hydrotalcite Composite Resins

Hydrotalcite (HT) can be used for poly(vinyl chloride) (PVC) modification to improve the thermal stability, flame retardance and other properties of PVC. However, nanometer HT (nano-HT) particles are easy to aggregate and difficult to be dispersed uniformly in PVC matrix due to the great polarity difference between HT particles and PVC. Aiming to improve the dispersion of nano-HT particles in the PVC matrix, and thus to achieve the effective modification function of nano-HT to PVC, the surface modification and pre-dispersion of nano-HT, VC suspension polymerization in the presence of surface modified nano-HT were carried out in this thesis. The structure and properties of the resulting PVC/nano-HT composites were characterized.Firstly, the pre-dispersion of nano-HT was carried out by using ultrasonic method, the particle size and stability of aqueous dispersion of nano-HT was studied. It was found that the size and size distribution index decreased as the ultrasonic time and the concentration of dispersing agent increased. The aquous dispersion of nano-HT particles with size of about 100nm was obtained and added in vinyl chloride (VC) suspension polymerization system. It was showed that the thermal stability of PVC/nano-HT composite resins was obviously improved. The thermal stability time of composite resins measured by congo red method increased about 53 minutes, and the decomposition temperature of composite resins at 5% weight loss increased about 23°C, compared with pure PVC resin.Secondly, HT was surface modified by alkyl phosphonate. The effect of treatment conditions, such as temperature, time, modifier usage, on the absorption amount or efficiency were studied. X-ray and FT-IR were performed to characterize the HT before and after treatment. It was showed that only the surface of HT was modified by alkyl phosphonate, and the layer structure and layer spacing of HT were not changed. Theactivation index was used to characterize the treating efficiency and the optimium surface modification was obtained. VC suspension polymerization in the presence of HT surface modified with alkyl phosphonate was carried out. It was found that compared to pure VC suspension polymerization system, the pressure of reaction system started to decrease earlier, and the conversion decreased at the same pressure drop. It was also found that the thermal stability of PVC/nano-HT composite resins was better than pure PVC resin.Furthermore, the PVC/nano-HT composites were obtained after melt-processing of the two kinds of composite resins mentioned above. The morphology, flame retardance and mechanical properties of PVC/nano-HT composites were studied. From TEM micrographs, it was showed that the most of HT particles dispersed uniformly in the polymer matrix with nanoscale. It was also found that the impact strength of PVC/nano-HT composites increased as HT content increased and the impact strength of PVC/nano-HT composites prepared by in-situ polymerization was much better than that of the composites prepared by direct melt processing.At last, the composite aqueous dispersion of nano-HT and nano-CaCO₃ was prepared by ultrasonic method, and PVC/HT-CaCO₃ composite resins were prepared via in-situ suspension polymerization in the presence of compound aqueous dispersion of HT and CaCO₃. The thermal stability, flame retardance and mechanical properties of composite resins were studied. It was found that the thermal stability time of composite resins measured by congo red method increased about 34 minutes, and the decomposition temperature of composite resins at 5% weight loss increased about 20°C when compare to pure PVC resins. When 5% HT- CaCO3(1:1) was incorporated in the composite, the maximum smoke density of PVC/HT-CaCO₃ composites resins reduced 47.5%, and the Charpy impact strength composite increased about 100%, compared with pure PVC.In conclusion, PVC/nano-HT composites with uniformly dispersed nanoparticles, excellent thermal stability and low smoke density were prepared by the above three methods. The results were useful for the industrial development of PVC/nano-HTcomposite resins.