EXTENDED CHAIN POLYMER CRYSTALS
Abstract
Linear polyethylene was crystallized from the melt under pressure up to 5300atm and at temperatures up to 236 C. A specially designed pressure stat was used, which could maintain constant elevated hydrostatic pressure up to 6500atm for long periods of time. Crystallization conditions of constant supercooling and constant cooling rates were employed. Electron micrographs of fracture surfaces obtained from these pressure-crystallized samples show that the formation of extended chain lamellae is the dominant mode of crystallization when high crystallization pressure (greater than 3500atm) and temperature (greater than 170 C) are employed. Extended chain lamellae as thick as 3 microns were observed. The chains were found to be oriented perpendicular to the surfaces of lamellae. DTA of the samples showed that the polymer molecules crystallize primarily in the form of folded chain lamellae at crystallization pressures up to 2000atm, their melting points becoming higher with increasing pressure. At pressures ranging from 2000atm to 3500atm, folded chain lamellae gradually give way to extended chain lamellae. The high temperature peak, which first appears in this pressure range, reaches a plateau of 140 C at 4000atm.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1965
- Accession Number
- AD0463881
Entities
People
- Tamio Arakawa
Organizations
- Rensselaer Polytechnic Institute