Preparation Of Collaborative Core-shell Microencapsulated Intumescent Flame Retardants And Study On The Properties Of Crosslinking Flame Retardant Ethylene-vinyl Acetate

Intumescent flame retardants (IFRs) have been considered to be a promising method, which is because they are low toxicity, low smoke, halogen free, and also very efficient. However, IFRs may reduce the mechanical properties and other properties of the materials because the rather different polarities of IFRs and EVA make them thermodynamically immiscible. Furthermore, this IFR system is moisture sensitive and thus is easily attacked by water and exuded during the service life, resulting in a decrease in the flame-retardant properties of the polymer composites. To deal with the above problems, microencapsulation with proper shell material is a good choice, and the electron beam irradiation can be used to enhance the mechanical property and other related physical properties. The research work of this dissertation is composed of the following parts:1. Flame-retardant EVA by silica-gel microencapsulated ammonium polyphosphate (SiAPP) and char-forming agent (CFA) have been cross linked by electron beam irradiation. A joint effect on the flame retardancy is observed in the flame-retardant compositions consisting of the MCAPP and CFA. The optimum EVA/SiAPP/CFA (2:1) system has a LOI value of32.5and can pass the UL-94V-0rating. With the increase of irradiation dose, LOI values increase slightly. This may be attributed to the higher char formation during thermal degradation of the sample at higher irradiation dose. In addition to the enhancement of LOI value, the volume resistivity and mechanical and thermal properties of the irradiated EVA composites are also evidently improved at suitable irradiation dose. However, these properties decrease at higher irradiation dose because of the electron beamirradiation-induced oxidative degradation or chain scission. The water treatment results showed that the sample can still past UL-94test after treatment by water for7days at50℃, indicating an excellent water resistance. Furthermore, OMMT is used as synergist in EVA/SiAPP/CFA system. The XRD and TEM results demonstrated that the OMMT is well dispersed in the EVA matrix. The LOI and UL-94results showed that a synergistic effect on the flame retardancy of EVA nanocomposite existed between the IFR and OMMT. With the addition of1wt%OMMT and24wt%IFR, the LOI value of EVA/IFR/OMMT nanocomposite increased from30.5%to33.5%. The tensile strength of the irradiated EVA nanocomposite is evidently improved at160kGy dosage, increased from12.6MPa to18.5MPa. RT-FTIR andTG-IR show that OMMT can act as a barrier, which could decrease the thermal decomposition rate and limit gas diffusion.2. Silane precursor microencapsulated intumescent flame retardant (IFR) was prepared by sol-gel process and then modified with vinyltrimethoxysilane (A-171) with the goal of that the vinyl group functionalized silica microcapsule could be introduced into EVA matrix through crosslinking, which will enhance the compatibility and dispersion between EVA matrix and microencapsulated IFR. The FTIR results indicated silane precursor microencapsulated IFR were successfully prepared, and the WCA results indicated that silane precursor results in the transformation of hydrophilic to hydrophobic of IFR surface. As expect, the functionalized organic group double bond after crosslinking make the MCAPP and MCPER be incorporated into EVA three-dimensioned network, which can enhance the dispersion of MCFR and the compatibility between EVA matrix and MCFR This is reason why the EVA/MCAPP/MCPER composites demonstrate higher TS values than those of EVA/APP/PER composites in the range of0-300kGy. The silica-gel shell can be served as synergist and can isolated the flame retardant from EVA matrix, so the EVA/MCAPP/MCPER system have higher volume resistivity and thermal stability than those of EVA/APP/PER system.3. Polyurethane microencapsulated expandable graphite (PUEG) is prepared and used in EVA with silica-gel microencapsulated ammonium polyphosphate (SiAPP). The results of FTIR, XPS and SEM indicated PUEG is successfully prepared. The PUEG leads to an increase in the initial degradation temperature, thermal stability and the expanded volume. The EVA/SiAPP/PUEG composite has the higher safety in a fire hazard and can still pass aUL-94V-0rating after being treated with70℃hot water for168h. Because of good interfacial adhesion between fillers and the EVA matrix, the EVA/SiAPP/PUEG composite shows better mechanical and dynamic mechanical thermal properties than those of the EVA/APP/EG composite. Phenolic resin modified polyurethane microencapsulated ammonium polyphosphate (PPUAPP) is prepared through in-situ polymerization. Compared with the APP, the PPUAPP demonstrates lower water solubility and higher flame retardance. With35%loading, the EVA/APP composite LOI value is25%and obtain V-2rating. While the EVA/PPUAPP composite can get V-0rating and LOI value as high as31.5%. After treated by70℃water for24h, the EVA/APP composite get no rating. However, EVA/PPUAPP composite treated by70℃water for144h, can still pass UL-94test, indicating excellent water resistance. Moreover, the EVA/PPUAPP shows lower peak heat release rate and higher fire safety in cone calorimeter test.4. Biodegradable biomass microencapsulated APP is prepared through in-situ polymerization. The shell of cellulose acetate butyrate(CAB) microencapsulated APP (CABAPP) and EVA have the same acetyl group, which may have similar polarity. According to the theory of similarity and intermiscibility, the CAB shell material may increase the water resistance of IFRs and enhance the compatibility and dispersion betweem EVA matrix and CAB microencapsulated IFRs. The WCA results indicated that MCAPP has excellent water resistance and hydrophobicity. The results demonstrated that MCAPP enhanced interfacial adhesion, mechanical, electrical, and thermal stability of the EVA/CABAPP/polyamide-6(PA-6) system. The microencapsulation not only imparted EVA/CABAPP/PA-6with a higher LOI value and UL-94rating but also could significantly improve the fire safety. The cyclodextrin (CD) microencapsulated APP (CDAPP) is prepared and use it in EVA. The shell CD and the core APP of CDAPP can be served as carbonization agent and acid source. A series of different core/shell weight ratio of CDAPP was prepared. The water solubility and flame retardce results indicated the core/shell weight ratio of MCAPP is2/1demonstrated higher flame retardancy and lower water solubility. Furthermore, because of shell of CDAPP, the EVA/CDAPP demonstrate better water durability, fire safety and mechanical properties than those of EVA/APP/CD.