Studies On Preparation And Properties Of OVPOSS Cross-linked Low Density Polyethylene

Low density polyethylene (LDPE), as one of most common thermoplastic polymers, has been widely used as packing and cable materials due to its excellent physical and electrical properties. However, LDPE has a major drawback in applications, the relatively low limitation of service temperature. To solve this problem, LDPE is usually crosslinked before use.We report a new strategy for crosslinking of low density polyethylene (LDPE) by using a small amount of functional nanostructured hybrid agent, octavinyl polyhedral oligomeric silsesquioxane (OVPOSS), as the crosslinker, which dramatically decreases the amount of dicumyl peroxide (DCP) and thus avoids the chain scission, scorch, and production of small pores in conventional peroxide crosslinking strategy.By melt blending under an extruder, OVPOSS aggregates with the size of tens of nanometers are homogeneously distributed in the matrix of LDPE, as confirmed by SEM. FTIR, DSC, and rheometer are used to study the crosslinking process and product properties. We found that vinyl groups of OVPOSS are firstly activated by the initiator of DCP and then react with LDPE to form an integrated network. The crosslinking process is fast and highly efficient because each OVPOSS molecule has eight reactive vinyl groups. The reactions complete within 10 min at 175℃, which speed up as the increase in the content of DCP or OVPOSS.Based on the influences of the concentration of OVPOSS and the structure information of XLPE, the special dynamic rheological behavior was discussed in detail. The main conclusions are as following:In the presence of 0.2 phr DCP,0.2 wt% OVPOSS can form the critical gel network while 0.8 phr DCP is needed if there is no OVPOSS. In the presence of 0.2 phr DCP,0.5 wt% OVPOSS can effectively crosslink the composite sample with comparable properties to that with 2 phr DCP yet without OVPOSS. Thus obtained crosslinked LDPE should be suitable for high voltage cable materials.According to the melting, crystallization, and mechanical properties of XLPE, we found that the crosslinking reaction could strengthen the amorphous region as well as keep the strength of the crystal region. Only when it is over crosslinked would affect the mechanical properties of XLPE. Furthermore, the XLPE with excellent insulativities should be appropriate to used as the insulation materials.We believe that the approach by using functional agents is powerful to crosslink or functionalize other polymers for special properties and applications.