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High pressure non‐isothermal processing, of linear polyethylenes
Author(s) -
Kulkarni K. M.,
Broutman L. J.,
Kalpakjian S.,
Emery D. B.
Publication year - 1976
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760160104
Subject(s) - materials science , composite material , modulus , isothermal process , ultimate tensile strength , linear low density polyethylene , spherulite (polymer physics) , molding (decorative) , polyethylene , compression molding , rigidity (electromagnetism) , young's modulus , compression (physics) , high density polyethylene , polymer , thermodynamics , mold , physics
Articles with increased rigidity can be obtained by compression molding at high pressures as shown by experiments with five types of linear polyethylene. The materials, with weight average molecular weight ranging up to 1,000,000 were molded at pressures as high as 80,000 psi. The material temperature was 149–204°C, and the tooling was at 38°C. The duration of load was typically 3 mins, and the thickness of the molded disks was 12.7 mm. The results show that at high molding pressure the tensile modulus of the material is nearly twice that of materials molded conventionally at low pressures. This increase in modulus occurs for all the materials studied and even for a duration of load of only one min. The causes for this large increase in modulus were investigated with the help of density and melting point measurements and optical and electron microscopy. It was observed that the spherulites showed a distinctive and systematic change with the forming pressure. A hypothesis is proposed to explain the high modulus phenomenon on the basis of the kinetics of spherulite formation.