Preparation Of DOPO-modified Polyisoprene And Study On Its Flame Retardancy

Polyisoprene(PI)rubber is a very important material in polymers and the most commonly used rubber in the world.However,the PI rubber is composed of C and H elements,which determines its extremely flammable nature.The limiting oxygen index is only about 18%,and because many occasions and industries now require good flame retardancy of rubber products.Therefore,it will become very meaningful to improve the flame retardancy of PI.PI rubber foams are also widely used in daily life.Due to the foaming of the material,the specific surface area becomes larger,which increases the contact area with the air,and the material becomes more flammable.Therefore,the flame retardancy of the PI foams is necessarily required.Firstly,the unsaturated bond of PI was partially oxidized into epoxy bond using peroxyformic acid to prepare epoxidized PI(EPI),and then the P-H bond on DOPO reacted with the epoxy bond to graft DOPO onto the main chain of PI to prepare DOPO modified EPI(EPI-DOPO).By controlling the degree of epoxidation and DOPO,EPI with different epoxidation degrees and EPI-DOPO with different DOPO grafting degrees were prepared.Through infrared spectroscopy and nuclear magnetic resonance analysis,it is proved that peroxyformic acid can oxidize the unsaturated double bonds in PI to form epoxy bonds,and the P?H bond on DOPO successfully reacted with the epoxy bond and grafted onto the main chain of PI.The flame-retardant test shows that epoxidation cannot change the inherent flammability of PI,and grafting DOPO can endow natural rubber with excellent flame retardancy,which can pass the UL94 V-0rating.The flame-retardant mechanism of DOPO was investigated through TG-IR,and it was found that the flame-retardant of DOPO follows the gas phase mechanism.Secondly,the prepared EPI-DOPO was used as an additive flame retardant to blend with PI to prepare PI/EPI-DOPO composites,and the effect of different mass fractions of EPI-DOPO as an additive flame retardant was explored.The results show that using EPI-DOPO as an additive flame retardant can improve the flame retardancy of PI;when the added mass fraction is 40wt%,the PI/EPI30%-DOPO composite material can pass the UL94 V-0 level.Finally,the EPI-DOPO/nano-SiO₂ composites were prepared by incorporating Nano-silica and EPI-DOPO of different mass fractions into PI.Then EPI-DOPO/Nano-SiO₂ composite foams were prepared via a batch foaming process with CO₂ as the foaming agent.The experimental results show that the batch foaming method can successfully prepare EPI-DOPO/Nano-SiO₂ composite foams.The foam sample of pure EPI-DOPO has poor cell structure,high expansion ratio,and the horizontal combustion level only reaches HF-2;when Nano-silica is introduced as a heterogeneous nucleating agent,the cell structure is improved,the cell size is reduced,and the expansion ratio is reduced.The cell density is increased by up to 10⁵orders of magnitude,which greatly improves the foam level combustion level and passes HF-1.