Effect Of Process Parameters On Foaming And Crystallization Behavior In The Isotactic Polypropylene Batch Foaming

Polypropylene foams have some excellent properties, which can be widely used in daily necessities,aircraft,automotive,etc. The cell size and density have a significant impact on the performance of the products during the polypropylene foaming process, so we can control the cell size and density to improve the performance of the products by regulating the process parameters. In addition, polypropylene is a typical semi-crystalline polymer, the crystallization behavior during polypropylene foaming process affects cell size and density and changes the performance of the products. Therefore, it has an important theoretical and practical significance on the research of the crystallization behavior,foaming behavior and effect of foaming on the crystallization behavior of polypropylene.This paper mainly studied the isotactic polypropylene crystallization behavior, foaming characteristics and their relationship under different process parameters, determing the desired temperature range in which the cells can be produced. The crystallization behavior and foaming properties of isotactic polypropylene were analyzed by differential scanning calorimetry(DSC), scanning electron microscopy(SEM), wide angle X-ray diffraction(WAXD) and universal type Rubber & Plastic density, abrasion index, foaming rate tester, the main contents and conclusions are presented here:1. Effect of process parameters on the crystallization behavior of isotactic polypropyleneWithin the certain pressure and temperature range, as the CO2 pressure and temperature increased, the melting point of the samples does not change substantially, the initial melting temperature gradually increases, the crystallinity of isotactic polypropylene also has an improvement, but not significantly.2. Effect of process parameters on the foaming behavior of isotactic polypropyleneIn the batch foaming process the infiltration pressure and temperature play a crucial role on the foaming behavior of isotactic polypropylene. The study found that some nuclear pores can form in the isotactic polypropylene when the temperature is below 193℃, but apparent collapse,mergers and rupture phenomena occur in the cells of the sample with the temperature higher than 196 ℃, therefore the desired temperature interval in which it can generate the ideal cells is 193℃-196℃. With increasing infiltration pressure, the apparent density of the foamed isotactic polypropylene samples gradually decreases, reducing the cell size, increasing the cell density, improving gradually expansion ratio. With increasing the temperature in the certain temperature range, the apparent density decreases and then increases, decreasing cell density, increasing cell diameter, expansion ratio reduces after increasing.3. Effect of foaming on the crystallization behavior of isotactic polypropyleneThe isotactic polypropylene foaming process has an important influence on the crystallization behavior during the foaming process. CO2 induced a large amount of imperfect crystal in the isotactic polypropylene. With increasing the infiltration pressure, the melting point and crystallinity of isotactic polypropylene gradually increases, but not significantly; with increasing temperature, melting point reduces after increasing, crystallinity gradually reducing. When compare to the unfoamed samples, melting point of foamed i PP samples increases and the degree of crystallinity decreases at the same temperature and infiltration pressure.