Cross-linking of LDPE/wax Blends in the Presence of Dicumyl peroxide

- Apr 03, 2019-

Blending of existing common polymers is often used for the preparation of new materials. Over the years, numerous systems have been developed and commercialized.
 
A large part of polymeric blends is based on polyolefins, which are the widest used polymers in industry.Low-density polyethylenes (LDPEs) are often used in industry. They have high impact strength, low brittleness temperature, flexibility, film transparency and outstanding electro-insulation properties. Major markets are in food packaging products, industrial sheeting and trash bags.
 
Synthetic waxes (Fischer–Tropsch synthesis) are white, translucent, tasteless and odourless solids consisting of a mixture of solid hydrocarbons of high molecular weight. They are not soluble in many solvents due to their high crystallinity, but they dissolve in boiling xylene, as is the case with LDPE. They are used, inter alia, for the
preparation of candles, paper coating, protective sealant for food products and beverages, biodegradable mulch, stoppers for acid bottles, electrical insulation and others. They have low melt viscosity and a relatively high straight hydrocarbon chain character.

Cross-linking is a broadly used method for the modification of polymer properties. This process involves the formation of three-dimensional structures, gels,causing substantial changes in material properties.Different procedures may be used for the initiation of polyolefin cross-linking. One of them is based on macroradical formation via thermal decomposition of organic peroxides.A detailed description of the various initiation procedures has been given in a comprehensive review by Lazar et al.
In this paper we shall discuss some thermal properties such as melting temperature, crystallization temperature, as well as specific melting and crystallization enthalpies of cross-linked LDPE/wax blends and their dependence on the concentration of cross-linking agent (dicumyl peroxide) and wax content. As far as potential applications of LDPE/wax blends are concerned, lower viscosity of the melt (at temperatures lower than the efficient cross-linking temperature) and imperviousness to water can be expected.
 
If the wax content increases, the gel content after cross-linking decreases, since wax needs a much higher concentration of peroxide for crosslinking and therefore only the PE phase is cross-linked. Cross-linking with 2% of DCP is much more efficient, but still only the PE phase is cross-linked.
DSC curves for both 0.5% DCP and 2% DCP show only one endothermic peak for the blends consisting of 5 and 10% wax, despite the fact that pure wax has three peaks. A probable explanation is that LDPE and wax are miscible in the crystalline phase12 in this concentration region. The main endothermic peak is at about 100 °C and the presence of wax does not influence its position. From 20% wax we observe a second, broad peak at about 80 °C. This peak probably forms part of the wax melting endotherm. This means that LDPE and wax are only partially miscible in this concentration region.