Polypropylene (PP) bead foams were
prepared by autoclave foaming using n-pentane and
CO2 as the blowing agents. PP foams blown with n-pentane had foaming temperatures of 92–96 °C,
expansion ratios of 10–50 times, and a signal T
m at 150.1 °C, while PP foams blown with CO2 had foaming temperatures of 151–153 °C, expansion ratios
of 8–20 times, and dual melting peaks at 164.0 and 140.9 °C.
Polyethylene (PE) addition was used to improve the foaming behavior
of PP and to induce the formation of dual and multiple T
m in PP/PE foams. A differential scanning calorimetry
procedure was carried out to simulate the steam-chest molding of bead
foams. Interbead bonding was found to be determined by the heat of
fusion of T
mc (crystal melting of the
newly formed crystals during fast cooling), ΔH
mc. Recrystallization of the PE component contributed
to the increase of ΔH
mc, which potentially
improved interbead bonding of the molded PP/PE bead foams.