Study On The Silane Grafted And Self-crosslinking Polyethylene At Room Temperature

With a low specific weight and easy processing characteristics, polyethylene also has the advantage of high insulation resistance, excellent dielectric properties. Since polyethylene has a weak van der Waals forces between molecules, non-polar chain, so it has a poor compatibility with inorganic matters and polar polymers, poor heat change properties, and its mechanical strength is not high, which limits its applications. Grafting and crosslinking may be the feasible ways to adjust these disadvantages.The application of silane crosslinking can improve the performance of polyethylene, such as impact strength, heat resistance and segregation resistance. The polyethylene grafted or crosslinked by silane has disadvantages such as low speed and lack of homogeneity in crosslinking through traditional manners using hot water. In this thesis, self-crosslinked PE at room temperature was prepared through a two-step method by means of stearic acid and zinc oxide to release water. Followings are the main accomplishments:(1) Silane is one of the key factors in self-crosslinking. The absorbance ratio of LDPE-g-silane with silane A-151, silane HIT-176, silane A-171 and silane ZQ-172 is 0.424,0.906,0.777 and 0.730, respectively. And the gelation of crosslinked LDPE grafted by silane, which used silane A-151 and silane HIT-176, could surpass 65% after being crosslinked in hot water for 40 hours (at 90 degrees centigrade).(2) Silane could be grafted onto PE through TBPMA. The absorbance ratio of self-crosslinked LDPE increased with the content of TBPMA. The gel of self-crosslinked LDPE could surpass 71%. The best content of TBPMA is 0.15pbw; when the content of stearic acid and zinc oxide was 3.5pbw and 1.Opbw, respectively, the self-crosslinked LDPE could have the most amount of gel about 46.7%; Catalyst has litter influence on the performance of self-crosslinked LDPE when the content is 1.5pbw～3.0pbw; The gel of self-crosslinked LDPE which used silane A-151 and silane HIT-176 were 45%, 71%, respectively. The best content of silane HIT-176 is 2.5pbw.(3) Both grafted and crosslinked LDPE were studied using FTIR and differential scanning calorimeter (DSC). As a result, the reactions of silane grafting and self-crosslinking have excellent impacts on the change in crystallization behavior,the values of Avrami index(n) of LDPE was 2.52, while increased to 3.8～6.0 when the LDPE was grafted or cross-linked. The values of Avrami index increased to the maximum and then decreased with increasing loading of initiator, while decreased with increasing loading of catalyst. Compared with neat LDPE, the velocity constant of the crystallization of silane grafted LDPE became higher, while that of crosslinked LDPE became smaller.