Crystallinity as a selection criterion for engineering properties of high-density polyethylene. [25 commercial high-density PEs]

Journal Article · Sat Jun 01 04:00:00 EDT 1985 · Polym. Eng. Sci.; (United States)

DOI:https://doi.org/10.1002/pen.760250909· OSTI ID:5189000

Hoffman, D M; McKinley, B M

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), Journal Name: Polym. Eng. Sci.; (United States) Vol. 25:9; ISSN PYESA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360402* -- Polymers & Plastics-- Structure & Phase Studies-- (-1987)
360403 -- Materials-- Polymers & Plastics-- Mechanical Properties-- (-1987)
360404 -- Materials-- Polymers & Plastics-- Physical Properties-- (-1987)
CREEP
CRYSTALLIZATION
DATA
DENSITY
ENGINEERING
EXPANSION
EXPERIMENTAL DATA
HIGH TEMPERATURE
INFORMATION
MECHANICAL PROPERTIES
MELTING POINTS
MOLECULAR WEIGHT
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
POLYETHYLENES
POLYMERS
POLYOLEFINS
THERMAL EXPANSION
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE
VISCOSITY