EXTENDED CHAIN CRYSTALS. VI. ANNEALING OF POLYETHYLENE UNDER ELEVATED PRESSURE.
RENSSELAER POLYTECHNIC INST TROY N Y DEPT OF CHEMISTRY
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Polyethylene crystals of different degree of perfection were annealed at 5.1 kb pressure for 20 hours at varying temperatures and analyzed by electron microscopy, thermal analysis, and density determination. No annealing took place until the temperature of annealing was close to the melting point of the starting material. Up to 235C increasing solid state annealing was observed. Mixed crystals of up to 0.989 gcu cm density and 1,500 A thickness in the chain direction could be produced. At slightly higher temperature recrystallization to extended chain crystals rather than annealing occurred. Annealing at atmospheric pressure seems to be similar in nature, but takes much longer times for comparable perfection. From a comparison of annealing and crystallization it is concluded that polymer crystallization goes through a stage of internally imperfect order during which most of the observed chain extension occurs. Estimates of this outer imperfect layer of a growing crystal place its depth at 30,000 A. Author
- Physical Chemistry