Preparation Of Layered Double Hydroxide And The Flame Retardancy Of Its Polyvinyl Alcohol Composite Film

According to statistics,the fire disaster in China in recent years has contributed to an average of more than 2,000 casualties and economic losses of nearly 3 billion RMB.In order to reduce the loss caused by fire,the government has introduced quite a few policies.One of the important aspects is the requirement of flame-retardant treatment of flammable products,as well as the strict fire rating and flame-retardant test specifications.In many types of combustibles,plastic foam is particularly important.The majority of them are lightweight,shock-absorbing,have good water-resistance and heat insulation,and are easy to process and inexpensive.Therefore,they are widely used in the packaging,waterproof,heat preservation,heat insulation,shock absorption and other industrial fields.Nevertheless,the halogen flame retardants used widely in the market have been proven to have serious environmental contamination and health hazards.Thence,there is an urgent need to develop new environmentally friendly flame retardants to fill this gap.This paper intends to improve the flame retardancy of plastic foam by designing a halogen-free flame-retardant film suitable for common plastic foam.On the one hand,it hopes to obtain a halogen-free flame-retardant system that meets current standards,and on the other hand,the influence of the morphology of the agent on combustion performance is expected to contribute to the richness of the flame retardant mechanism.Specifically,firstlyalayereddoublehydroxideflameretardant[Mg₄Al₂?OH?₁₂]CO₃·3H₂O?LDH?was synthesized using four different preparation methods,and their crystallization conditions and microscopic morphology were compared.SEM photographs depict that LDH samples prepared by microemulsion method and coprecipitation method are severely agglomerated.A hexagonal lamellar LDH having a width of about 2.1?m and a thickness of about 200 nm was prepared by a hydrothermal method.A solvothermal method was used to prepare honeycombed LDH clusters,on which the LDH wafers were about 200 nm in width and about 20 nm in thickness.It was also found that under the conditions of hydrothermal and solvothermal preparations,LDH crystals showed different preferred orientations in the course of different aging stage.Furthermore,composite films of LDH and polyvinyl alcohol?PVA?of these two morphologies were prepared by spin coating.Afterward,the burning properties of these films and the polystyrene foam covered by them were studied.Their morphologies were observed before and after burning.It was found that LDH/PVA film obtained good flame retardancy when LDH was synthesized by adding10??t?%solvothermal method.Compared with pure PVA film,the peak heat release rate is reduced by 86.8%,the total heat release is reduced by 69.6%,the peak temperature is increased to 469°C,and self-extinguishing is achieved in the horizontal burn test.By comparing two different morphologies of LDH,it was found that LDH had a role in promoting the decomposition of PVA,which gives rise to the heat release peak of PVA to move in the direction of low temperature,and honeycomb LDH could significantly increase the decomposition temperature of polyvinyl alcohol.This study illustrates that the LDH-containing flame retardant films have great potential for application.