Isotactic polypropylene (iPP) was doped with pimelic acid/calcium stearate to promote the formation of the hexagonal (b) crystals during melt crystallisation. The conversion of growth pattern from the b- to the a-phase due to lowering of the crystallisation temperature was studied by a two-step crystallisation process in a DSC. The polymer melt was first allowed to crystallise isothermally at 130°C to produce almost pure b-phase and then the crystallising polymer was cooled to different temperatures between 115 and 25°C for a second-step crystallisation. It was found that the amount of a-phase was negligible after the second-step crystallisation process at 85°C or above. When the secondstep crystallisation process was below 85°C, however, the amount of a-PP increased abruptly with a corresponding drop in the b-phase. This indicated that a major conversion of the b-growth to a-growth occurred near 85°C. Recrystallisation of the b-phase during heating was dependent upon the heating rate as well as the crystallisation condition of the samples.
Посилання на статтю:
Conversion of growth and recrystallisation of b-phase in doped iPP / J.X. Li, W.L. Cheung // Polymer. – 1999. – N 40. – P. 2085–2088.