Study On Flame Retardancy And Thermal Conductivity Of Polyvinyl Alcohol Composites

Polyvinyl alcohol（PVA）is one of the few degradable polymer materials,with various preparation methods.Because hydrogen bonds can be formed between or within its molecules,PVA has the advantages of strong hydrophilicity,good biocompatibility and biodegradability,and PVA materials are widely used in the manufacture of packaging films,chemical coatings,adhesives and paper.However,PVA,like other polymer materials,is a flammable material,which seriously affects its further development.Therefore,it is of great significance to develop an efficient and environmentally friendly flame retardant PVA.In this work,three different modified boron nitride（BN）flame retardants were designed and synthesized,and they were combined with guanidine phosphate（GP）,ammonium polyphosphate（APP）and aluminum hypophosphate（AHP）into PVA,and the effects of different ratios of flame retardants on the flame retardancy and thermal conductivity of polyvinyl alcohol composites were studied in detail.（1）A flame retardant thermal conductive filler Si O₂@BN was synthesized by hydrolysis of ethyl orthosilicate,and its structure and morphology were characterized.Si O₂@BN and guanidine phosphate（GP）were added to PVA by solution blending to form PVA composite.The results showed a 28.3%limiting oxygen index（LOI）of the PVA composite with 2 wt.%Si O₂@BN and 8 wt.%GP.Its the peak heat release rate（p HRR）and total heat release rate（THR）were both decreased by 65.2%and 44.4%,respectively,compared with those of pure PVA.In addition,its the thermal conductivity was increased by 82.4%compared with that of pure PVA.The flame retardant mechanism might be due to the physical barrier effect of Si O₂@BN and the non-flammable gas generated by the decomposition of GP when heated to dilute the oxygen concentration,and the generated phosphoric acid,that promoted the dehydration and carbonization of PVA.（2）The flame retardant thermal conductive filler ZIF-67@BN was prepared by modifying ZIF-67 on the surface of BN by the in-situ synthesis method,and its structure and morphology were characterized.ZIF-67@BN and ammonium polyphosphate（APP）were added to PVA by solution blending to form PVA composite.The results showed that the LOI value of this PVA composite with 1 wt.%ZIF-67@BN and 7 wt.%APP reached28.1%.Its p HRR and THR were reduced,and its ignition time（TTI）was increased to 70s.In addition,its thermal conductivity of pure PVA was increased from 0.1904 W.m^-1·K^-1of pure PVA to 0.3264 W.m^-1·K^-1.The main reasons for these might be the physical barrier effect of ZIF-67@BN and catalytic carbonization;meanwhile,the non-flammable gas generated by the decomposition of APP when heated diluted the oxygen concentration,and the phosphoric acid and metaphosphate generated promoteed the dehydration and carbonization of PVA.（3）A third new flame retardant thermal conductive filler was prepared by using tannic acid（TA）surface modified BN,referred to as TA@BN.Its structure and morphology were characterized.TA@BN and aluminum hypophosphate（AHP）were added to PVA by solution blending to form PVA composite.A resultant 28.2%LOI value of the PVA composite was achieved with 2 wt.%TA@BN and 8 wt.%AHP.Its p HRR and THR were both decreased.In addition,its thermal conductivity was increased from0.1904 W.m^-1·K^-1as of pure PVA to level of 0.3256 W.m^-1·K^-1.That was attributed to the physical barrier effect of TA@BN and the formation of graphitized carbon catalyzed by AHP,which led to an improvement in the flame retardant property of the PVA material.Figure[55]Table[14]References[102]...