Studies On Autoclave Foaming Of Polypropylene And Polypropylene Blends

Expanded polypropylene(EPP) becomes one of the fastest growing foam products in theautomotive, transport packaging industries, because of its capacity to withstand repeated impactand compression, and an alternative to expanded polystyrene(EPS). It has been found that PPexhibits poor foamability because of its high crystallinity and low melt strength. The thesis isaimed at achieving the well-defined PP foams through studying the foaming behavior of PP andPP/PE blends.In this study, PP bead foams were prepared by autoclave foaming technology using n-pentaneand CO2as the physical blowing agent. Due to the higher solubility of n-pentane in PP andstronger plasticizing effect, PP bead foams can be prepared with n-pentane at lower foamingtemperature of91-96°C and higher expansion ratio of8-50times; than that prepared with CO2hadfoaming temperature of150-153°C and expansion ratio of8-20times. However, PP foamsprepared with CO2had double melting peaks in which the higher melting peak was from therecrystallization of the less perfect crystals during the CO2saturation process at high temperatures.Three kinds of PE, i.e., LDPE, LLDPE, HDPE, were blended with PP and the foamingbehavior of PP/PE blends were carried out with two kinds of foaming agent. It is found that PEaddition improved the foaming behavior of PP especially at low foaming temperature. A DSCtesting procedure including fast heating, isothermal treatment, and fast cooling was carried out tosimulate steam-chest molding of PP and PP/PE foams, in order to investigate the dual or multiplemelting peaks effect on the foam molding process. For the PP foams blown with CO2or PP/PEfoams, the Tmlowcontribute to the softening and fuse of bead foams’ surface, and Tmhighcouldstabilize cell structure and the crystals. The dual or multiple melting peaks were critical to generatestrong inter-bead bonding during the steam chest molding process.In this thesis, the foaming behavior of PP/rePP blends was carried out, and the steam-chestmolding of EPP and EPP/rePP bead foams was also studied. It is found that rePP addition with acertain amount improved the foaming behavior of PP and broadened the foaming temperaturewindow. Results on the mechanical properties of the molded product showed the molded PP/rePPproduct has smaller compressive strain under lower compressive stress, which may befavorable for the manufacturing of cushion, soft packing and so on.