| Polyethylene resin, when applied in the wire and cable materials, often has to reach the excellent flame retardance and high resistance to thermal aging. On the one hand, the effects of the kinds and molecular weight of various antioxidants on the thermal aging progress of cross-linking polyethylene (XLPE) were studied and the results revealed that the molecular weight and structure of antioxidants were of great importance to lengthen the lifetime of XLPE. On the other hand, the influence of the coating composition and structure on its thermal stability, combustion performance and fire resistance was investigated. The flame retardant systems were optimized for the protection of XLPE with high resistance to thermal aging. This dissertation consists of the following parts:(1) Based on the intumescent flame retardant mechanism, the ratios of tri(acryloyloxyethyl) phosphate (TAEP) to melamine-based acrylate resin (MAAR) were adjusted to prepare a series of flame-retarded coatings containing phosphorus and nitrogen by UV-cured technology. The characterization of the flammability and the char morphologies of these coatings displayed that the highly intumescent char with compact outer layer and lots of thin-walled large pore structure in the inner layer for the PN-2which containing2/1mass ratio of TAEP to MAAR. The investigation for the thermal degradation process of the coatings showed that the decomposition of the blowing agents could be catalyzed by the acid source. Moreover, the amount of many evolved gas products, even extremely toxic carbon oxide, decreased obviously. The intumescent char layer, however, still presented large weight loss at high temperature due to the oxidative-degradation. So a series of the coatings containing phosphorus-nitrogen-silicon or phosphorus-nitrogen-boron were prepared. It can be found from the results of their flammability that the coatings with suitable amount of silicon or boron elements can produce the char layer with higher mechanical strength, but also exhibited little negative effect on the formation of dramatically intumescent char layer. Furthermore, the study of their thermal degradation gave the clear results that the addition of silicon-or boron-bearing monomers could endow the char layer with high tolerance of the oxidative-degradation at high temperature. Besides, to our surprise, the release of carbon oxide for these coatings could effectively be suppressed. (2) It is relied that the improving efficiency of antioxidants on the stabilization of XLPE can be attained by retarding the physical loss and chemical exhaustion of antioxidants. To begin with, the influence of several hindered phenolic antioxidants with different molecular weight on the aging progress of XLPE was studied and it was found that the higher the molecular weight of antioxidant, the slower the aging development of XLPE. Then the primary antioxidant1010was combined with various second antioxidants to stabilize XLPE and the results showed that sulfur-bearing second antioxidants presented a better synergistic effect with antioxidant1010than phosphorus-containing ones. Finally, a novel sulfur-containing hindered phenolic antioxidant with a high molecular weight was prepared and its effect on protecting XLPE was compared with that of two antioxidants with similar structure. It was shown that the chemical circumstance of sulfur atom is the key point to determine the stability of antioxidants and the effect on the protection of XLPE. In other words, the antioxidants, in which sulfur atom is not bonded directly onto or have two direct chemical linkages with the hindered phenolic group, displayed better resistance to the electron-beam irradiation and better protection of XLPE from thermal aging.(3) On the basement of the above study, the optimized flame retardant systems (TAEP/MAAR/SiMA) were used to protect XLPE. The flammability analysis by cone calorimeter showed that the extremely intumescent flame retardant coatings could effectively reduce the HRR and PHRR and postpone the mass loss and heat transfer, but had difficulties in avoid the combustion of XLPE due to the crack of the cured coating or the rigid char layer led by the large deformation of XLPE exposed to heat flux.(4) In order to show the good points of XLPE wire and cable materials prepared in this dissertation, several significant properties of XLPE flame-retarded by the coating and ATH, respectively, were compared. It was shown that ATH worsened the mechanical properties, volume resistivity and tolerance of thermal aging of XLPE, which was ascribed to the poor compatibility of ATH with XLPE. In addition, it is noteworthy that XLPE flame-retarded by the coating presented the slower heat release rate and more moderate mass loss than XLPE flame-retarded by ATH, despite the lower THR for the latter. |
PDF Full Text Request