Studying Thermal Shrinkage Properties in Prepared Heat Shrinkable Cross-Linked Low-Density Polyethylene
Jalil Morshedian, Hossein Ali Khonakdar, Mahmood Mehrabzadeh, Hassan Eslami
Member of Academic Staff in IPPI( Iran Polymer and Petrochemical Institute)
Iran
Keywords: Morphology, Structure & Properties
Heat shrinkable polymers find wide applications in the packaging industry, the electrotechnical industry, the cable industry and in the preparation of heat-shrinkable tubes and connections. Semi-crystalline polymers such as low-density polyethylene (LDPE), like other polyolefines, are common heat shrinkable polymers widely used in industries. Various studies have already been devoted regarding the heat - shrinkability of the above - mentioned semi- crystalline polymers. But there is little systematic information available concerning the processing parameters affecting shrinkability.
In this work heat shrinkable property is gained by first compounding mixtures of
low-density polyethylene with varying amount of peroxide, and then extruding or molding the compound in to the required shape or form and then crosslinking it by chemical means, followed by heating and stretching and then cooled to "freeze-in" the oriented molecules (elastic memory). The thermal analysis of crosslinked low-density polyethylene was investigated by Differential Scanning Calorimetry (DSC). The behavior of shrinkability and effective parameters were also investigated using Thermal Mechanical Analysis (TMA).
Results showed the melting point and degree of crystallinity were reduced by increasing the peroxide concentration and the gel content as a measure of the degree of crosslinking was increased.
The stretching temperature of the crosslinked polymer considerably effected the shrink temperature so that the higher the stretching temperature, the higher the shrink temperature.
Moreover, the higher the crosslinking degree, the lower was the shrink temperature. These effects could be reasonably explained by the Hoffman theory and the fact that the stretching process induced more and new spherullites and was more effective when carried out before the melting, at temperatures around the crystal transition temperature