Preparation and characterisation of UV irradiation cross-linked LDPE/EVA blends M. A. Shamekhi 1 , S. H. Jafari* 2 , H. A. Khonakdar 3 and M. Ehsani 3 Ultraviolet induced cross-linking of low density polyethylene/ethylene vinyl acetate melt mixed blends were explored in presence of trimethylolpropane trimethacrylate (TMPTMA) and benzophenone (BP) as cross-linking agent and photoinitiator respectively. On the basis of gel content, it was found that 1 wt-%TMPTMA, 1 wt-%BP and irradiation time of 100 s represent the optimum parameters for photocross-linking of this system. Infrared spectroscopy was also used to follow the cross-linking reactions. Differential scanning calorimetry analysis showed that the heat of fusion reduces upon cross-linking development in the system, implying that crystallisability of the samples is suppressed with increasing cross-link bonds. Thermal stability of samples as a function of irradiation time goes through a maximum and then diminishes. Mechanical examinations in tensile mode proved that elongation at break of neat and blended specimens drops significantly with increasing degree of cross-linking, while variations of Young’s modulus of the blends show a composition dependent behaviour in which crystallisability of the samples is a major determinant. Keywords: UV irradiation, Cross-linking, Polyethylene, Ethylene vinyl acetate copolymer, Blends Introduction A well established strategy employed to modify the performance of polymers is inducing a series of cross- link bonds within the polymer structure usually reached via two versatile tools, chemicals and radiation. The latter is a cleaner methodology and both normally apply for the bulk material. The reaction which occurs during the latter process is basically the same as in chemical cross-linking except that the radicals are generated by the incidence of rays with the polymer surface. 1,2 Radiation cross-linking has found practical utilisation especially in cross-linking of polyolefins for electrical insulation and other specialty applications. Ultraviolet (UV) and ionising radiations play a substantial role in integrated circuit technology. 3 A number of patents indicate the interest for using UV light for inducing surface cross-linking since it inhibits plasticiser and additives from exuding from material surface. It has also been reported that a wide variety of polymers, including thermoplastics, thermosets, rubbers and composites, were successfully modified with UV treatment to improve adhesive performance. 4 For instance, photo- initiated cross-linking of polyethylene (PE) has been studied extensively for many years and has led to recent industrial application for manufacturing of cross-linked PE. 5–19 Blending is commonly used to obtain enhanced certain properties of the polymers. 20 In this regard, blending low density polyethylene (LDPE) with ethylene vinyl acetate (EVA) copolymer has been reported to impart improved properties such as flexibility, tough- ness, higher shrinkage at low temperature and a lower thermal conductivity when compared to neat LDPE. A number of inherent features of EVA such as structural similarity with LDPE, high polarity (due to polar nature of the acetoxy side group), low temperature flexibility and good impact strength (toughness) have turned EVA to a candidate of choice for blending with LDPE. 21–29 To further modify the performance of this system, i.e. LDPE/EVA (wherein most often EVA forms the minor phase), numerous attempts have been made on its cross- linking by means of chemical agents and high energy radiation (electron beam and gamma ray) cross-linking and sensibly enhanced mechanical and thermal perfor- mances have been observed. 30–43 This treated system is currently used in heat shrinkable materials for wire and cable insulation and foam materials. 4,37 Although, UV photocross-linking has drawn much interest in the field of polymer modification, to the best of our knowledge, no attempt has yet been made on UV photocross-linking of LDPE/EVA blends while it is satisfactorily efficient for some homopolymers such as poly(vinyl chloride) and PE. 4,12,44,45 In the current study, the authors aim to focus on the UV irradiation treatment of LDPE/EVA blends in terms of gel content through optimising the process conditions and then investigate the subsequent effects on the mechanical and thermal properties in particular in 1 Department of Polymer Engineering, Islamic Azad University, Sarvestan Branch, Fars, Iran 2 Department of Polymer Engineering, Islamic Azad University, Omidiyeh Branch, PO Box 164, Omidiyeh 6373193714, Khuzestan State, Iran 3 Iran Polymer and Petrochemical Institute, PO Box 14965-115, Tehran, Iran *Corresponding author, email shjafari@hotmail.com ß Institute of Materials, Minerals and Mining 2010 Published by Maney on behalf of the Institute Received 2 September 2009; accepted 11 June 2010 DOI 10.1179/174328910X12777566997739 Plastics, Rubber and Composites 2010 VOL 39 NO 10 431