Formulations of chemically crosslinked and radiation-crosslinked low-density polyethylene (LDPE) containing an intumescent flame retardant such as ammonium polyphosphate were prepared. The influence of blending LDPE with a poly(ethylene vinyl acetate) copolymer (EVA) and the effects of various coadditives, including polyethylene grafted with maleic anhydride (PEgMA), vinyl silane with boric acid, and talc, on the mechanical and thermal properties were investigated. Chemical crosslinking by dicumyl peroxide and crosslinking by ionizing radiation from an electron-beam accelerator were both used and compared. Improved mechanical properties were observed by the partial replacement of LDPE with EVA. Similar mechanical or thermal properties were observed with coadditives such as PEgMA and vinyl silane with boric acid. The addition of a small amount of talc improved the tensile strength of the formulations. All crosslinked formulations showed good thermal stability on the basis of the retention of mechanical properties after thermal aging for 168 h at 1358C and a hot-set test.
Formulations of chemically crosslinked and radiation-crosslinked low-density polyethylene (LDPE) containing an intumescent flame retardant such as ammonium polyphosphate were prepared. The influence of blending LDPE with poly(ethylene vinyl acetate) (EVA) as well as the effects of a coadditive such as talc on flammability was investigated. Chemical crosslinking by dicumyl peroxide and crosslinking by ionizing radiation from an electron-beam accelerator were both used and compared. An increase in the limiting oxygen index (LOI) was found by the partial replacement of LDPE with EVA. The effect of talc on the flammability depended on the amount of talc in the formulations. The addition of a small amount of talc increased LOI and reduced smoke during cone calorimeter measurements. A higher amount of talc led to a decrease in the LOI values. Formulations crosslinked by ionizing radiation yielded lower LOI values than chemically crosslinked formulations. This could be attributed to the use of trimethylolpropane triacrylate as a crosslinking coagent in formulations crosslinked by ionizing radiation.
Formulations of chemically cross-linked poly(ethylene vinyl acetate) (EVA) and low density polyethylene (LDPE) blends containing intumescent flame retardant such as ammonium polyphosphate (APP) were prepared. Influence of polyethylene grafted with maleic anhydride (PEgMA), boric acid or combinations of them as well as various EVA/LDPE ratios on flammability, mechanical, thermal and electrical properties was investigated. Flame retardancy was found to be improved after addition of boric acid to APP formulations. On the other hand, mechanical properties decreased for formulations containing boric acid. Combination of boric acid with PEgMA gives formulations with good mechanical and thermal properties as well as good flame retardancy. Good thermal properties based on retention of mechanical properties after thermal aging were observed for all formulations due to introduction of cross-linking. All formulations show also good electrical properties.KEY WORDS: Mechanical Properties / Flame Retardance / Ammonium Polyphosphate / Talc / Crosslinking / Polyolefins due to their good mechanical properties, good resistance to chemicals and easy processing is used in many applications. However, they have some disadvantages such as low melting temperature, low thermal stability, high flammability as well as poor compatibility with additives. Compatibility of additives with polyolefins can be improved by addition of some compatibilizers or coupling agents.1 Thermal properties of polyolefins can be improved by small addition of stabilizers. A small quantity of processing stabilizers is usually added to prevent oxidative degradation of polyolefins caused by combined action of shear, heat and oxygen during their melt processing. Phenolic antioxidants are widely used as processing stabilizers for polyolefins.2,3 They act as scavengers of oxygen-centered alkoxy and peroxy radicals, but they are not able to provide long term heat stability. 4 The flame retardancy of polyolefins on the other hand can be improved using flame retardants. There are several types of flame retardants which are used to improve flame retardancy of polyolefins. Recently, there is a trend to avoid use of halogenated flame retardants due to environmental and safety concerns. Thus, as main non-halogenated flame retardants, mainly metal hydroxides 1,5-8 or intumescent flame retardant (IFR) systems 9-16 are used. Very good efficiency in flame retardancy of polyolefins can be achieved using IFR systems. However a higher loading of IFR additive is needed than that of some halogen-containing flame retardants. This results in lowered mechanical properties of the flame-retardant materials. Thus, the flame retardant efficiency of IFR should be further improved. To improve the performance of IFR in polyolefins, synergistic agents such as boroxo siloxanes (products of reaction of poly siloxanes with boric acid), 9,10 clays and nanoclays 13,14 or some metal-containing compouds 15,16 which can enhance the flame-retardant action of IFR can be used.In recent work, 17 current a...
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