Prepare Polypropylene Foam Sheet By Beam Irradiation

In this paper, Beam irradiation was used to make linear Polypropylene crosslink in order to improve its foamibility. Factors such as the usuage of irradiation sensitizer, dose, composition and the atmosphere which affect crosslinking degree are discussed. Effects of extrusion parameters, the usuage of blow agent, foaming temperature, foaming time, crosslinking degree on foam density and cell diameter were studied. Effects of roller press, foaming temperature, the decomposition of blow agent on strength of foam were discussed. A foaming sheet with a density about 0.1g/cm~3 , cell diameter about 0.329～0.614mm , and cell density about 6.16×10~4～1.33×10~5 /cm~3 was prepared. Experiments indicate:Polyfunctional monomer (SR444) can enhance the efficency of crosslinking greatly. Only when the content of sensitizer matches the dose of irradiation we can get high gel fraction with low degradation, Gel content is a function of sensitizer dosage and irradiation dose. Only when the dosages of the two matched each other, can we get high gel fraction with low degradation. When irradiation around nitrogen atmosphere, can lower irradiation dose and get higher gel content.At low extrusion temperature (170℃), the decomposion of blow agent can be avoided. When the gel fraction was lower than 11 per cent, we can not get good foam material. Foaming temperature and foaming time are the most important factors which affect foam shape, foam density, and cell density.Roller press can improve the foam flexility notably. Foamed at220～235℃, foam can maintain higher mechanical strength. When the blowagent partly decomposed, the foam maintains the charactor of toughness asthe pure polypropylene does.