Preparation Of Foamed Polypropylene And Investigation On Its Foamability

In recent times, Polypropylene(PP) has been receiving considerable attention with better thermal stability, strength and environmental friendly character s than polystyrene, which has become a attractive candidate as foamed materials. At present the EPP beads of PP have implemented industries and manufacturing process in Europe, United States, Japan and other countries. Although in our country great progress has been made over the years, there are still a distance to realize industrialization. Owing to semi crystalline feature, PP has a very thin viscosity when the temperature is higher than the melting point so as to be difficult to wrap gas. What else, the foamed temperature range only in 4 ℃, the bubble holes present uneven distributions and the performance is unstable. Therefore, in order to modify foamed PP master batch, the primary task is to improve the melt strength, employing a variety of methods.In this paper, based on the ordinary PP powder as raw material, nanosilica, long basalt fiber, EVA and ABS as modifier, four kinds of modifier/PP master batch have been prepared through co-rotating twin-screw extruder to blend PP with modifier under the high temperature melt blending. The rheological behavior, melting and crystallization behaviors of master batch were were characterized. With regard to adding Si O2, in PP matrix, through SEM microscopic observation, when the content is small, Si O2 is uniformly dispersed in PP matrix, when the content is more than 6%, Si O2 is prone to reunite. The rheological analysis shows that 6%Si O2/PP has the highest melt viscosity, comparing with other Si O2/PP master batch, which is suitable for foaming master batch.In the preparation of BF/PP master batch, multiple shares of basalt fibres were joined through the extruder Ⅱ area set feed inlet. After granulation, a certain amount of master batch were investigated by calcina method, which was used to determine the content of BF in the master batch. Through SEM microscopic observation, BF has a good dispersion in PP matrix, and through the rheological analysis, the melt viscosity of 9%BF/PP was determined to be the highest, comparing with other master batch of BF/PP, which is more suitable for foaming master batch.With regard of the rheological characterization of EVA/PP, the results show that in the of EVA/PP master batch, the highest melt viscosity is the 25%EVA/PP, which is more suitable for foaming master batch. Through the rheological analysis of the of ABS/PP, the melt viscosity of 8%ABS/PP was determined to be higher than the rest of the ABS/PP master batch, which is more suitable for foaming master batch.After melt extruding five kinds of master batch, which include pure PP, 6%Si O2/PP, 9%BF/PP, 25%EVA/PP and 8%ABS/PP, the EPP beads have been produced by supercritical CO2 method. Through the structural characterization of EPP beads, the foaming temperature interval of five kinds of master batch ha s been determined, which was 176~180℃, 170~184℃, 176~186℃, 170~188℃, 178~186℃, respectively; In the foaming process, with the increase of foaming temperature, the corresponding foaming pressure has decreased, while the foaming ratio has increased with the rise of temperature. The maximum foaming ratio of pure PP, 9%BF/PP and 8%ABS/PP was 22~25 times, while 6%Si O2/PP, 25%EVA/PP was 40~42 times; With the rise of foaming temperature and foaming ratio, the size of cells increased as well as the density of cells was getting bigger. After analys is, the dominant factors of the difference of foaming behavior between five kinds of foaming master batch were identified, that is the melt viscosity. The melt viscosity should not be moderate, otherwise the EPP beads of high foaming ratio would not be obtained.