Formulation And Properties Of UV Crosslinked Low Voltage EPDM Cable Insulation Material

In order to employ the high-efficiency,low-power-consumption ultraviolet light technology for the cross-linking of the ethylene propylene diene monomer（EPDM）rubber cable insulation layer and achieve the goal of energy conservation,pollution reduction and efficient production,it is necessary to develop EPDM insulation compound with low content of solid fillers.In this thesis,the selected EPDM was used as matrix resin,and prepared crosslinked EPDM composites by using Benzophenone as photoinitiator,triallyl isocyanurate（TAIC）as co crosslinking agent,and reinforcing EPDM with linear low-density polyethylene or a small amount of nano-SiO₂.The effects of irradiation time,additive type and content on the properties of UV crosslinked EPDM materials were systematically studied.Firstly,the thermal elongation test and stress strain test were carried out for three kinds of UV crosslinked EPDM materials with different irradiation time.It was found that with the increase of irradiation time,the crosslinking degree of EPDM increased,but the mechanical properties decreased rapidly,and the materials were degraded during the crosslinking process.Combined with the crosslinking characteristics and processability,the optimal irradiation time was finally determined as 12s,and EPDM 1703P was selected as the matrix resin.For UV crosslinked nano-SiO₂/EPDM composites,with the increase of SiO₂content,the mechanical properties and AC breakdown strength of SiO₂/EPDM composites first increase and then decrease,the permittivity remains basically unchanged and the loss factor increases;Compared with unreinforced EPDM,the hardness of SiO₂/EPDM material is basically unchanged,and the crosslinking degree of the sample decreases.The properties of 2SiO₂/EPDM material can meet the standard requirements.Considering performance and cost optimization,the addition amount of nano SiO₂is finally determined as 2 phr.For UV crosslinked LLDPE/EPDM blends,the crosslinking efficiency and mechanical properties of LLDPE/EPDM were significantly higher than those of unreinforced EPDM,but the flexibility of rubber materials decreased and the hardness increased.SEM,AC breakdown strength and dielectric spectrum results show that EPDM could refine LLDPE crystalline particles and inhibit LLDPE crystallization.With the increase of LLDPE addition,the isolated LLDPE crystals gradually change into continuous crystals,the overall AC breakdown field strength shows an increasing trend,and the overall dielectric constant and loss factor shows a decreasing trend.The results of DSC and XRD illustrate that there are two aggregation states of the same crystal form in LLDPE/EPDM material,and the blending of EPDM and LLDPE will not produce new crystal form.From the perspective of practical application,when the content of LLDPE is 10 wt%,its properties can meet the application requirements.The screening results of antioxidant formula showed that 0.5 phr antioxidant 1010 could not only improve the heat aging resistance properties of EPDM material,but also significantly inhibit the synchronous degradation of EPDM in the process of UV crosslinking,and barely affect crosslinking reaction efficiency.It is suitable to be used as the antioxidant formula of UV crosslinked low-voltage EPDM insulation materials.In contrast,UV stabilizers inhibit the efficiency of UV crosslinking reaction,and attenuate the inhibitory effect of antioxidants on the photodegradation of EPDM.According to the results of stress strain test,thermal aging,AC breakdown strength and AC dielectric property test,the advantages of SiO₂/EPDM material are low hardness and small amount of ingredients,but it has a certain impact on the cross-linking degree of the material;LLDPE/EPDM material compoundhas the advantages of good strength,high crosslinking efficiency,but hardness is escessive.The properties of the two UV crosslinked low-voltage EPDM cable insulation materials obtained in this thesis meet the standard requirements and can be promising materials apply in different occasions.Compared with the thermal crosslinking production mode,the UV crosslinking technology remarkably improves the production efficiency.