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UV-Stabilized Natural and Colored Halogen-Free Flame-Retardants
Abstract
There is growing interest in halogen-free flame-retardant (HFFR) compounds that are colored (non-black) and used in applications where ultraviolet (UV) light stabilization is required. The desire to color code cables necessitates the use of UV stabilizer systems other than the carbon black traditionally used. Based on an understanding of the mechanisms for degradation of HFFR compounds in sunlight, a robust system for stabilizing natural HFFR compounds to sunlight has been developed. We present tensile and elongation data for several natural and colored HFFR compounds exposed to accelerated UV light to demonstrate the effectiveness of this robust UV stabilization system. A natural HFFR compound with excellent UV stability, flame-retardant properties and physical properties is presented. This natural, UV stabilized HFFR compound significantly exceeds the UV stability requirement in UL 1581 and the UV stabilizer does not exude to the surface when the HFFR compound is used as a cable jacket.
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Jacketing compounds for industrial cable applications require robust mechanical properties, oil resistance, and flame resistance. These performance attributes can be achieved by incorporating metal hydroxides and coupling agents into a polymer compound. In this paper, we examine effects of metal hydroxides and coupling agents on mechanical properties and flame resistance. In particular, we investigate how the tensile properties, limiting oxygen index, and various parameters measured from the cone calorimetry (peak heat release rate, time to ignition, and time to peak heat release rate) are affected by various magnesium hydroxides, aluminum trihydroxide, and coupling agents. Finally, a compound with excellent performance attributes for industrial cable applications is presented.
The preferential surface photooxidation of many unstabilized commercial polypropylene films in air was found to originate from the presence of surface chromophores, such as -OOH and >C=O, rather than from diffusion control of the degradation, or morphological effects. This was established by the use of attenuated total reflection and transmission ir spectroscopy to determine the photooxidation product distribution within various uv-irradiated film samples. The oxidation of commercial film samples was compared with either uv or γ initiation, and was also studied under controlled O2 diffusion conditions. After uv irradiation, specially prepared film samples showed either little surface oxidation (films pressed under a N2 atmosphere) or enhanced surface reaction (films exposed to O3 or an O2 corona discharge prior to irradiation). The observed surface photooxidation of commercial films is believed to result from a limited thermal oxidation of the film surfaces during manufacture. The stability of various commercial films is compared and discussed in terms of the extrusion technique used in their manufacture and fluorescent emission spectrum of each sample. The relevance of the results both to the photostabilization and to the accelerated decomposition of polypropylene films is considered.
The yields of volatile products (CH3COOH, CO2, CO, CH4, H2) have been measured for the radiolysis (gamma rays from 60Co) and the photolysis (u.v. rays of 2537 Å) of polyvinylacetate (PVA) at room temperature. The experimental data have been compared with the yields of main chain scission and cross-linking. It can be concluded that, in the radiolysis, radicals produced by side group scission are involved in the main chain reactions. Further, examination of the u.v. and visible absorption spectra indicates that gamma irradiation of PVA at room temperature results in the formation of polyenes. In the photolysis of PVA, the quantum yields for volatile products are much lower than those for cross-linking and chain scission. This suggests that those main chain reactions proceed through excited states. A new band appears at 295 nm in the absorption spectrum of u.v.-irradiated PVA, but its significance has not been elucidated.
Study was made of the compatibilization of polyethylene/aluminum hydroxide (PE/ATH) and polyethylene/magnesium hydroxide (PE/MH) composites with composition 60/40 wt%. Compatibilizers were hydroxyl or carboxylic acid functionalized copolymers prepared in our laboratory with metallocene catalysts and commercial butyl acrylate, maleic anhydride, epoxy, and acrylic acid functionalized polyethylenes. Comparison was made with stearic acid treatment of the composites. The effect of polymeric compatibilizers on the properties of the composites was studied by tensile and impact tests, dynamic mechanical analysis, differential scanning calorimetry, morphology studies, and flammability tests. Adhesion of the PE/ATH and PE/MH composites was significantly improved, as seen in morphology studies in the changed fracture mechanism. The improved adhesion was particularly reflected in the mechanical properties: an improvement in both stiffness and toughness was achieved with use of the functionalized copolymers prepared with metallocene catalysts. According to cone calorimetry, flame retardancy properties of the composites did not deteriorate upon addition of compatibilizers.
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