Processing and property improvement in isotactic polypropylene
by heterogeneous nucleation (English version)
Polimery 2000, No 11-12, 786
SummaryCrystallization temperature (Tm) was measured for poly-(ethylene-b-propylene) copolymer in relation to 0–0.5 wt.% of a single-component nucleating agent (NA) (natrium benzoate, talc, or sorbitol derivatives) (Fig. 1) and the content of the pseudohexagonal β-phase in PP-i (tacticity 95.6%, 97.1%; MWD 3.9, 6.3, resp.) was studied in relation to 0–0.2 wt. % of pimelic acid—calcium stearate used as a two-component NA (Fig. 3). Starting with ~ 0.2 wt % NA, the Tm leveled out. Thus, upwards of 0.15–0.25 wt. %, NA failed to raise Tm. However, even low amounts of NA gave rise to homogeneous morphology, regardless of the processing conditions (cf. Figs. 4–6). β-phase orientation was studied in relation to position along flow path at mold temperatures of 45°C and 90°C (Fig. 7). Heterogeneous-nucleated PP-i revealed somehow „frozen” flow-elongated and flow-sheared macromolecular chains, i.e., a higher level of macromolecular orientation. Nucleators, β-phase formation, heterogeneous nucleation and like problems are reviewed (44 refs.).