Abstract
In this study, the effects of free quenching on mechanical physical and thermal behaviours of high density Polyethylene (PEHD) have been investigated. Three different thermal treatments were used: A first free quenching from the melt state to air, a second free quenching from 130°C to different temperatures and finally an annealing .The results have shown that an improvement of the impact strength and elongation at break can be obtained after a first quenching to air. However, a second quenching at 0°C gives better results and a correlation between the mechanical and thermal properties is observed. The improvement of these properties is obtained to the detriment of other properties like elasticity modulus, density, vicat softening temperature (VST) and heat distortion temperature (HDT). The improvement of impact strength and elongation at break after the second quenching is probably linked to the existence of a relaxation mode located around this temperature. Keywords : free quenching; polyethylene, mechanical, physical, thermal. DOI : 10.7176/CPER/59-03
Highlights
High density polyethylene PEHD is one of the most important commodity polymers which is widely used in various applications
One can notice that the Izod impact strength values decrease with the increase of the second quenching temperature
Unotched Izod impact strength of PEHD as a function of second quenching temperature Generally the impact resistance of semi-crystalline polymers depends on the crystalline phase that develops during heat treatment
Summary
High density polyethylene PEHD is one of the most important commodity polymers which is widely used in various applications. The generation of residual stresses (RS) is known to improve Izod impact strength of amorphous polymers like polycarbonate [3].The study of the effect of residual stresses (RS) induced by free quenching on the mechanical behaviour of semi-cristalline polymers is one way to understand the relationship between the microstructure and the macroscopic properties of macromolecules such as polyethylene. The RS are totally attributed to volumetric fluctuations, associated with the relaxation kinetics at the glass transition temperature (Tg). This leads to an incomplete viscoelastic relaxation during solidification. In order to avoid a contribution of flow induced orientation, free quenching experiments have been used by several investigators on semicrystalline and amorphous polymers [8-10]
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