Viscoelastic properties of polyethylene at elevated temperatures on the basis of two-process model for stress relaxation
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Stress relaxation at room and elevated temperatures of high density (HDPE) and linear low-density polyethylene (LLDPE) has been investigated. Viscoelastic parameters (elasticity moduli and viscosity coefficients) of amorphous and crystal fraction at temperatures 18, 40, 60, 80 and 100 degreesC are determined by using two-process model for stress relaxation of polyethylene. The results show that amorphous viscosities of both polyethylene types clearly satisfy the Arrhenius dependence on temperature. Therefore, in the amorphous fraction of examined polyethylenes at elevated temperatures, there is a process with temperature independent activation energy. The estimated activation energies DeltaH approximate to 62.5 kJ/mol for LLDPE and DeltaH approximate to 59 kJ/mol for HDPE of that process are compared with activation energies determined from the time temperature superposition of experimental relaxation curves and with literature data.
Keywords:amorphous fraction / crystal fraction / stress relaxation / viscoelastic
Source:Materials Science Forum, 2000, 352, 195-200
- Trends in Advanced Materials and Processes, 3rd Yugoslov-Materials-Research-Society Conference, Sep 20-24, 1999, Herceg Novi, Yugoslavia