The Synthesis Of POSS And Its Application In PET Composites

Due to its low cost and high performance, poly(ethylene terephthalate)(PET) has been widely used in many technical applications such as fiber, bottles, films, and engineering plastics in automobiles and electronics. However, flammability of polyester is one of the main drawbacks associated with the use of PET. In order to expand the application, successful strategies to reduce the flammability of polyester are extremely necessary. It is known that the cyclotriphosphazenes derivatives as a novel type of halogen-free flame retardant show the dramatically high efficiency in flame retardancy, which make them attractive as candidates for halogen-free fire resistant additives. In our previous work, Para-allyl ether phenol derivative of cyclophosphazene(PACP) was prepared successfully and used as a filler to modify the flame retardant properties of PET by melt blending. The results indicated that the presence of organophosphorus would lead to a high brittle nature of the polymer. So the aim of this research is to select the appropriate additives to improve the mechanical properties with keeping the flame retardancy of the material at the same time. In recent years polyhedral oligomeric silsesquioxanes(POSS) additives have been incorporated into a number of polymers as copolymers, grafts, or as melt blends. The advantages gained from using POSS come from its hybrid organic-inorganic nature whose inorganic core potentially provides molecular reinforcement, and the incorporation of POSS molecules into polymers also lead to a successful improvement of the flammability, thermal or mechanical properties.In this study, two types of POSS having different side groups were blended with PET and PACP to prepare the POSS/PACP/PET composites. The mechanical, thermal and flame retardant properties of the composites were discussed. In summary, this dissertation is composed of the following parts:(1) OPh-POSS and OVi-POSS were firstly synthesized through the hydrolysis andcondensation reaction by using Ph Si Cl3 and C2H3Si(OCH3)3 as the raw material and characterized by FTIR and NMR respectively. The thermal property and the mechanism of thermal degradation of POSS were investigated by TGA. It was found that OPh-POSS showed similar TGA curves both in N2 and air at the lower temperature. There was no weight loss before 400 o C, and the one degradation temperature(T-5%) occurred at 440 o C. The sample showed a high thermal stability, producing 40.9% and 30.7% stable residue at 850 o C, respectively. However, the different thermal behaviors of OVi-POSS in different atmosphere were shown in TGA curves. In N2 the one degradation temperature(T-5%) of POSS was 225 o C, and the residue equal to 1.9% of the initial weight was left at 850 o C. In air the POSS showed a better thermal-oxidative stability due to organic fraction peroxidation overlapping with vinyl polymerization. The one degradation temperature(T-5%) was 328 o C, leading to a final 70.0% thermally stable residue at 850 o C.(2) A series of composites were prepared based on PET, OPh-POSS and PACP by direct melt blending. The mechanical, thermal and flame retardant properties of composites were studied. The results revealed that OPh-POSS particles dispersed in PET at the size of approximately 500 nm with aggregation, which had little effect on the mechanical property of composites. Incorporation of OPh-POSS into PET significantly enhanced the crystallization rate and crystallization temperature with the Tc of composites increase by 20 o C than that of pure PET. The decrease of storage modulus in the glass transition state and the decrease of Tg suggested that PACP has plasticization effect on PET. However, combination OPh-POSS with PACP made a significant increase in modulus and Tg for all of the blend samples. The HRR curves of the composites showed two peaks, and the PHRR and THR were decrease to 318.0W/g and 14.7k J/g by MCC. The synergistic effect of PACP and OPh-POSS enhances the thermal stability and fire-resistance of the char layer which builds up on the surface of the burning polymer.(3) A series of melt-blend samples were prepared based on PET, OVi-POSS and PACP by pre-dispersion mixing in order to improve the dispersion of POSS particles. The mechanical, thermal and flame retardant properties of composites were studied. The results revealed that a high degree of dispersion of OVi-POSS was obtained in PET at the size of 100~200nm. The introduction of 1.0%OVi-POSS distinctly increased the mechanical property of composites, reaching from 38.12 MPa for pure PET to 64.37 Mpa for 1.0%OVi-POSS/PET. Incorporation of OVi-POSS into PET also significantly enhanced the crystallization rate and crystallization temperature with theTc of composites increase by 35 o C than that of pure PET. MCC curves shows that the combustion process of the composites presented an obvious shoulder peak and the value of PHRR decreased obviously. The competitive effects of OVi-POSS on the enhancement of stability of the char layer result in a balance for synergistic flame retardant effect of OVi-POSS and PACP.