Cellular Structure And Properties Of PP/POE Foams Prepared By Several Methods

Polypropylene?PP?foams are widely used in automobile and packing fields due to their advantages of low cost,good heat resistance and recyclability.Foams employed in different applications should have different cellular structures.So,it is significant to prepare PP foams with various cellular structures to satisfy the needs of applications.In this dissertation,the supercritical carbon dioxide?Sc-CO₂?foaming for PP/ethylene-octene?POE?blends and PP/POE multilayered sheets was performed via one-step or two-step depressurization.The foams with several cellular structures were obtained.The influences of foaming parameters on cellular structure and performance of the foams were analyzed.The PP/POE blends were foamed with batch foaming via one-step depressurization,and the PP/POE foams?only POE phase foaming?with an average cell diameter?D?less than 10?m were obtained under lower foaming temperature.With the rises of POE content and foaming temperature,D increased and the cell density?N?decreased.With the rise of saturation pressure,N increased.The elongation at break of the PP/POE foams?with closed-cell structure?gradually increased as increasing the POE content from 20 wt%to 40 wt%.Instead,when further increasing the POE content to 50 wt%,the elongation at break of the PP/POE foams?with open-cell structure?decreased.When the POE content was 30 wt%,the elongation at break and impact strength of PP/POE foams increased with the rise of saturation pressure.The PP/POE blends were foamed with batch foaming via one-step and two-step depressurization,and the PP/POE foams?both PP and POE phase foaming?were obtained under higher foaming temperature.The foams with unimodal cellular structure were prepared by one-step depressurization,and the uniformity of cell size was improved with saturation pressure increasing from 12 MPa to 18MPa.The foams with bimodal cellular structure were prepared by two-step depressurization at saturation pressure of 12 MPa.At saturation pressure of 18 MPa,the foams with trimodal cellular structure were obtained under the first pressure drop range from 2 MPa to 5 MPa;the bimodal structure were obtained at the first pressure drop of 6 MPa.When the foam densities of PP/30POE foams were similar,compressive strength of the foam with trimodal cellular structure was 11.4 times of that with unimodal cellular structure;thermal conductivity of the former sample was half of that of the latter sample.The PP/POE multilayered sheets were foamed with batch foaming via one-step depressurization,and the PP film/POE foam multilayered foams were obtained under lower foaming temperature.At lower pressure?10 MPa?and slower depressurization rate?10 MPa/s?,the D of POE foam layer was significantly decreased with increasing the number of layers.When the number of layers increased from 16 to 64,the mechanical and thermal insulation properties of the multilayered foams were improved.The impact strength in normal direction was approximately 3 times of that in transverse direction.Foams with completely closed cell obtained at 60?had better mechanical properties than that with partial open cell obtained at70?.Foams with smaller cellular structure obtained at 15 MPa had higher mechanical and thermal insulation properties than that with larger cellular structure obtained at 10 MPa.