Crystallinity as a selection criterion for engineering properties of high-density polyethylene. [25 commercial high-density PEs]
The differential scanning calorimeter (DSC) was used to discriminate among 25 commercial high density polyethylenes (HDPE) on the basis of their degree of crystallinity and melting temperature. The area under the melting endotherm correlated directly and inversely with creep and thermal expansion measurements. Since high crystallinity was related to the design required properties of density, creep, and thermal expansion, DSC studies readily identified eight of the more promising polymers from the group of 25. The overall crystallization kinetics of polyethylenes with 75% crystallinity were analyzed by the Avrami and Fischer-Turnbull equations. Results indicate small disk-like spherulites (Avrami n = 2) following nucleation-controlled growth kinetics. These conclusions are in reasonable agreement with polarizing microscope observations. An equilibrium melting temperature between 141 and 142/sup 0/C was estimated from Hoffman-Weeks plots. Processing thick parts from highly crystalline polyethylene is difficult because of the 14% volume change on crystallization. Higher degrees of crystallinity are associated with moderate molecular weight, so the viscosity range of these polyethylenes is not especially suited for processing by extrusion. These caveates necessitate tradeoffs between optimal design properties and processing requirements for HDPE parts. 26 references, 11 figures, 2 tables.
- Research Organization:
- Lawrence Livermore National Lab., CA
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 5189000
- Journal Information:
- Polym. Eng. Sci.; (United States), Vol. 25:9
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
POLYETHYLENES
CRYSTALLIZATION
MELTING POINTS
CREEP
DENSITY
ENGINEERING
EXPERIMENTAL DATA
HIGH TEMPERATURE
MOLECULAR WEIGHT
THERMAL EXPANSION
VISCOSITY
DATA
EXPANSION
INFORMATION
MECHANICAL PROPERTIES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
POLYMERS
POLYOLEFINS
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE
360402* - Polymers & Plastics- Structure & Phase Studies- (-1987)
360404 - Materials- Polymers & Plastics- Physical Properties- (-1987)
360403 - Materials- Polymers & Plastics- Mechanical Properties- (-1987)