Purpose
Ultraviolet (UV) irradiated cross-linking technology has the advantages of high efficiency and low power consumption. In order to employ the UV cross-linking technology in manufacturing EPDM rubber cable insulation layer, LLDPE is mlet-blended into EPDM to improve its mechanical property and UV cross-linking efficiency. LLDPE/EPDM composites with different contents of LLDPE are prepared. The crystallization characteristics and electrical properties of UV crosslinked LLDPE/EPDM materials are investigated.
Experimental
The thermal elongation of LLDPE/EPDM composites with different irradiation time was tested to determine the optimal irradiation time. The crystal morphology, crystallinity and crystal structure of the composites were characterized and analyzed by SEM, DSC and XRD. At last, the effects of different plastic/rubber ratio on the mechanical and electrical properties of LLDPE/EPDM composites were investigated.
Results
The thermal elongation results show that the composites can achieve enough cross-linking degree under UV irradiation for 12s. SEM results show that with the increase of EPDM content, the crystals of LLDPE becomes looser. When the contents of EPDM and LLDPE are evidently different (20:80 or 80:20), their compatibility is poor and phase separation widely occurs in the composites. When the difference between the contents of EPDM and LLDPE is small, their compatibility becomes better and the interface becomes indistinct. The DSC curves show that there are two temperature peaks during melting and crystallization in the LLDPE/EPDM composites. Moreover, with the increase of LLDPE content, the crystallization melting temperature and the crystallinity of LLDPE/EPDM composites increase. XRD patterns indicate that the crystalline form in the composites are not changed. Therefore, the two crystallization peaks correspond to different aggregation forms rather than different crystal forms. Tensile test shows that the strength of LLDPE/EPDM composites increases with the increase of LLDPE content. The AC breakdown test and dielectric spectra show that the dielectric properties deteriorate when the contents of LLDPE and EPDM are largely different and become relatively better when blended with similar mass contents. 
Conclusions
LLDPE/EPDM composites can achieve enough cross-linking degree with a high efficiency through UV irradiation. EPDM can change the microstructure of LLDPE/EPDM composite, making the crystals looser but do not change the crystal forms in LLDPE. The addition of LLDPE can greatly improve the mechanical properties of EPDM. When the weight content of LLDPE is 40% and 60%, LLDPE has good compatibility with EPDM and the electrical properties of LLDPE/EPDM composites are comparable to the neat LLDPE.
 

EPDM,LLDPE,UV irradiated cross-linking