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Thermal properties of strained thermoplastic polymers
Author(s) -
Möginger Bernhard,
Fritz Ulrich
Publication year - 1991
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.4990260211
Subject(s) - materials science , thermal expansion , composite material , amorphous solid , polymer , ultimate tensile strength , thermomechanical analysis , thermoplastic , enthalpy of fusion , thermal , thermodynamics , melting point , crystallography , chemistry , physics
Injection moulded tensile bars of several amorphous and semi‐crystalline thermoplastic polymers have been deformed uniaxially to a macroscopic strain of 40% so that they showed necked and unnecked regions. From both the necked and unnecked regions of the tensile bars the specific heat and the thermal expansion coefficient were measured. The specific heat of the necked regions decreases about 20% with respect to unstrained samples for semi‐crystalline polymers at temperatures between 40°C and 60°C and for amorphous polymers at temperatures between 50°C and 70°C. The thermal expansion coefficient becomes negative at these temperatures. A smaller negative expansion coefficient is observed even in the unnecked region although nearly no change in specific heat can be observed. There is also an increase in the heat of fusion of the semi‐crystalline specimens of the necked region. Strain rate dependent effects on specific heat and thermal expansion were not observed within the accuracy of thermal analysis.