| Poly(ethylene terephthalate)(PET) has been widely used in food packaging, agricultural production, fiber textile and life sciences and many other fields due to its good dimensional stability, chemical stability, and insulation. However, PET has rigid molecular chain structure and strong crystallizability, which results in a bad compatibility with other polymers and a high surface energy unsuitable for adsorption, adhesion, printing, plating, etc. Therefore, modification of PET has long been a hot research topic and attracted extensive attentions.This dissertation aimed at preparing PET film modified with functional polymers and PET resins with high toughness. Taking advantage of the principle of radiation chemistry, porous PET/polymer composite film was first fabricated. Furthermore, crosslinked polymer microspheres with special morphologies were synthesized to be used as the compatibilizer in PET/elastomer blends to improve the toughness of the blends. The research works in this dissertation involve the following four parts:1. The preparation of porous PET/Polyacrylic acid/polyacrylonitrile (PET/PAA/PAN) composite film by radiation grafting technique. Generally, AN monomers cannot be grafted on PET film by γ-ray radiation because the radiation chemical yield of radicals of AN (GAN(R·)) is5.6,much larger than that of PET (GPET(R·)=0.02). In our work, AA monomers were first grafted on PET film induced by γ-ray radiation. The grafting degree of AA increases with the absorbed dose and the ambient temperature. As a result, the hydrophilicity of PET/PAA composite film also increases with the grafting degree of AA. The static water contact angle of PET film decreases from76°(for original PET film) to66°(for PET/PAA composite film) with the increase of the grafting degree of AA, and then levels off. AN monomers could be grafted easily on the PET/PAA composite film under γ-ray radiation. The morphology of the film surface changed with the absorbed dose. Combined with the results of XPS, AFM and SEM, it was found that a porous PET/PAA/PAN composite film could be prepared, and the size of pores on the film surface could be tuned by the absorbed dose. The porous PET/PAA/PAN composite film can keep the wettability of pristine PET film. Unlike usual porous film, this film not only has excellent properties of PET substrate (such as high mechanical strength and chemistry stability), but also has excellent weathering resistance of PAN which is grafted on the surface layer.2. The preparation of micro-and submicro-sized PET microspheres. Compared with PET film, the micro-and submicro-sized PET microspheres have much larger specific surface area and readily disperse into the monomer solutions or polymer matrix so that they can be surface-modified effectively. However, there are few reports on the preparation of micro-and submicro-sized PET microspheres. In this work, we first studied the solubility of PET powder in a few solvent system to select a proper PET solution (in PhOH/C2H2Cl4,1/2w/w) as the oil phase to form an emulsion with the help of SDS. Then drop the emulsion into the precipitator (ethanol) under a proper condition. Finally, PET microspheres with a size of200nm～2μm were obtained. This preparation method of PET microspheres is promising in the surface or bulk modification of PET, and expands the potential applications fields of PET3. The surface modification on PET microspheres induced by y-ray radiation. The above prepared micro-sized PET microspheres were dispersed in the grafting solution of St or AN, respectively. After being irradiated by y-ray, the surface of PET microspheres was attached with PS or PAN microspheres with a size of200～300nm, forming raspberry-like PET/PS or PET/PAN composite microspheres. When a mixed grafting monomer composed of St and MMA were used, or carboxyl-modified PET microspheres were dispersed in grafting solution of AN monomers, the grafted PS or PAN microspheres would have smaller size and distribute more homogeneously around the PET microspheres. The prepared raspberry-like PET/PS or PET/PAN microspheres could be spun into a film. The static water contact angles of these spin coatings are nearly the same with that of the pure PET film.4. The study on the compatibilization of PET/elastomer blends by crosslinked polymer microspheres with special morphologies. Polymeric composite microspheres sometimes are prepared to be used as polymer compatibilizer. In our work, we prepared crosslinked PS microspheres with three kinds of morphologies. First, cage-like PS and PMMA microspheres were synthesized emulsion polymerization induced by10MeV electron beam under a dose rate of400kGy/min at room temperature. The relationship between the polymerization rate and the concentration of monomer and emulsifier was found as Rp∞[M]1.16[E]0.45. The conversion of styrene under high dose rate is so low that porous PS microspheres are obtained. The molecular weight and particle size of the porous PS microspheres are also dependent on the radiation stability of the monomers and the corresponding polymers. Crosslinked multi-hollow PS microspheres were obtained after the prepared porous PS microspheres were swollen by St and DVB, and then irradiated by y-ray. Second, crosslinked carboxylated PS microspheres were synthesized by radiation dispersion polymerization of St and a little amount of AA and DVB. Finally, asymmetric crosslinked PS/SiO2Janus microspheres were synthesized by radiation seed emulsion polymerization. The above mentioned three crosslinked polymeric microspheres were respectively melt-blended with PET and toughener ST-2000. The results of notched Izod impact strength of PET and its blends show that the impact strength of PET/ST-2000blend in the presence of the carboxylated PS microspheres or asymmetric PS/SiO2Janus microspheres is33%higher than that of PET/ST-2000, and twice as large as that of pure PET, which indicates these two crosslinked polymer microspheres can improve the compatibility of PET and ST-2000. However, crosslinked multi-hollow PS microspheres have no contributions to the impact toughness of PET/ST-2000blend. |
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