Effective Parameters on the Heat Shrinkability of Cross-Linked Low-Density Polyethylene/Poly(ethylene vinyl acetate) blends
Hossein Ali Khonakdar, Jalil Morshedian, Mahmood Mehrabzadeh, Hassan Eslami
Member of Academic Staff in IPPI
Iran
Keywords: Shrinkability , Termo-Propertie, Crosslinked
Heat shrinkable materials are widely used in various industries. Semi-crystalline polymers such as low-density polyethylene (LDPE), like other polyolefines, are common heat shrinkable polymers widely used in industries.
An enormous amount of work has already been carried out on the heat shrinkability of the above-mentioned semicrystalline polymers, but there is little systematic information concerning the shrinkability and effective parameters on the shrinkability of the blends.
The use of poly(ethylene vinyl acetate) (EVA) blends is of high interest, particularly in cable industry, due to good resistance of stress cracking and easy of cross-linking.
In this work, heat shrinkable property is achieved by first compounding LDPE/EVA blends with various amount of peroxide in a twin extruder at about 130°C.The resulting granules were molded to shape and chemically cross-linked by compression molding. A process of heating-stretching-cooling was then performed on the samples while on a tensile machine.
Thermal analysis of the cross-linked LDPE/EVA blends was investigated by Differential Scanning Calorimetry. Shrinkability and effective parameters on it were also investigated using Thermal Mechanical Analysis. A reduction in the melting point and heat of fusion (DHf), was observed with increasing dicumyl peroxide (DCP) concentration.
Studies on the heat shrinkablity of the samples show that samples stretched above the melting point have a higher shrink temperature than those stretched around the crystal transition temperature. Aslo, by increasing the peroxide content, the shrink temperature is decreased. These may be attributed to the formation of new spherullites as well as the amount and the size of crystals.
Furthermore, in samples elongated at 120°C (above the melting point), rate of stretch has no effect on the shrink temperature.
The results show that the extent of strain has no effect on the temperature of shrink, but rather on the ultimate shrinkage value.