Preparation And Research Of Novel Heat-shrinkable Maerials

Heat shrinkable material was a smart material, whose shape can be changed orrestored by heating. It has now become a new type of material, widely used in the businessof cable protection, pipeline transportation, commodity package and so on. Thedevelopment of technology makes more demands on the heat shrinkable material itself,and at present, there is an increased demand for highly flame retardant heat shrinkablematerial.In this paper, low density polyethylene (LDPE) and ethylene-vinyl acetate copolymer(EVA) were selected as polymer matrix material, adopting chemical crosslinking methodsfor the preparation of heat shrinkable materials. Heat shrinkable material with excellentmechanical properties was successfully prepared by this method and was able to return toits original state quickly under the environment of120℃glycerin.Based on PE/EVA heat shrinkable material, flame retardant effect of heat shrinkablematerial can be achieved by the addition of flame retardant. In this paper, two inorganicflame retardants aluminum hydroxide (ATH) and red phosphorus were selected to realizethe flame retardant effect. When ATH was used only, the flame retardancy can be achievedto UL94V-0with the addition of140ATH; however, when highly filled, the mechanicalproperties of heat shrinkable material degraded significantly, especially in poor elongationat break, which cannot satisfied the use requirments. The dispersible uniformity of ATH inPE/EVA system could be improved by using stearic acid to process ATH, thus improvingthe mechanical properties of the prepared heat shrinkable material while degrading theflame retardancy.With the compound addition of ATH and red phosphorus, the flame retardancy ofPE/EVA system can be achieved to UL94V-0as the amount of ATH was greatly reduced.In order to improve the shortcomings of red phosphorus like easy to moisture absorption,hard to keep, poor compatibility with the polymer and so on, both methods of organic andinorganic coating were adopted respectively to process the surface of red phosphorus. Theproperty of red phosphorus processed by using NaOH and aluminum sulfate as the rawmaterial to process was stable in the air, the problem of moisture absorption improved. Bytitration method and scanning electron microscope (SEM) for characterization, it was indicated that Aluminum hydroxide formed a dense layer in the surface of the redphosphorus. The experimental results showed that among the PE/EVA heat shrinkablematerials, those with high content of EVA possessed better property. PE/EVA heatshrinkable material with a formula of PE：EVA：ATH：RP=20：80：40：10has betterproperty, tensile strength is11.54MPa, elongation at break is573%, heat shrinkable rate is66.15%, heat shrinkable reducing rate is98.76%, and it can be through the flame retardanttest of UL94V-0.Microencapsulated red phosphorus encapsulated by melamine-formaldehyde resin canbe prepared through the method of in-situ polymerization, and different Microencapsulatedred phosphorus can be prepared by changing the ratio of formaldehyde and melamine. Byscanning electron microscope (SEM) and Fourier Transform Infrared Spectroscopy forcharacterization, it indicated that the melamine-formaldehyde resin encapsulated the redphosphorus powder well. The dispersibility of the encapsulated red phosphorus in PE/EVAheat shrinkable material is good, among which the ratio of formaldehyde and melamine is10:1, the mechanical properties of PE/EAV heat shrinkable material prepared byencapsulated red phosphorus is the best. As the content of red phosphorus in theorganically microencapsulated red phosphorus was not very high, hence lots of flameretardants needed to add to make the flame retardancy of heat shrinkable material achieveto V-0. The experiments indicated that the mechanical properties of heat shrinkablematerial prepared by using the microencapsulated red phosphorus and improved ATH asthe flame retardants degraded less as the increase of the total amount of flame retardants.When the total amount o flame retardants was80, the flame retardancy of heat shrinkablematerial can be achieved to V-0when ATH: microencapsulated red phosphorus=64:16.The best ratio of the formula is PE: EV: ATH: MRP-3=20:80:64:16. This kind of heatshrinkable material has good mechanical properties, tensile strength is10.48MPa,elongation at break is456%, heat shrinkable rate is64.70%, heat shrinkable reducing rateis98.72%, and it can be through the flame retardant test of UL94V-0.