Compared with PS and PE, polypropylene (PP) foaming materials, which are the main members of the semi-crystalline thermoplastics family, have been slow to develop, and domestic commercial production has not been achieved so far, but PP foam has many unique advantages:
(1) The flexural modulus of PP is about 1.52 GPa, which is much higher than the 207 MPa of PE, so the static load capacity of PP foam is better than PE;
(2) The glass transition temperature of PP is lower than room temperature, so the impact performance of PP foam is better than that of PS foam;
(3) PS foam is softened and deformed when used above 105 °C; PE foam is rarely used above 100 °C, while PP foam has high heat distortion temperature (165 °C), excellent high temperature resistance, and can be used at high temperatures. Used in the environment;
(4) PP has very good chemical resistance and can compete with PE;
(5) Due to the presence of pendant methyl groups, PP is prone to β degradation, and PP foam is easy to recycle, and its environmental friendliness is superior to other foaming materials.
Based on the above advantages, PP foaming materials are very competitive in many industrial applications, especially in the automotive industry and food packaging industry, and can replace existing PS and PE foams with broad prospects.
However, the extrusion foaming of PP is very difficult. The main reason is that the foamability of PP is poor, and the processing window for extrusion foaming is very narrow. Experts have estimated that the temperature suitable for foaming through PP is only 4 °C. When the temperature rises to its melting temperature, the melt elasticity of PP drops sharply. The lower melt strength cannot guarantee the tensile stress on the cell wall during bubble growth, resulting in collapse and cracking of the bubble, so that PP The foam has a high opening ratio and cannot meet the requirements for use. Therefore, to prepare a PP foaming material, it is first necessary to improve its expandability from the viewpoint of raw materials.
The production technology of polypropylene foam sheet developed by Beijing Technology and Business University adopts domestic general-purpose polypropylene and high-melt-strength polypropylene produced abroad. Through optimized design, polypropylene foam sheet is produced on domestic equipment, and the cell density can reach 106 pieces/cm3, the density is as low as 0.6 g/cm3. Products can be widely used in the automotive industry and food packaging industry.
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