Study And Application Of Halogen-Free Flame Retardant Polylactic Acid Composites With High Water Resistance

In the field of construction,the flame retardant composite materials are often affected by environmental humidity,rain and domestic water during their use,resulting in water absorption,deformation,cracks and even internal structure damage of the composite material plates,which affects the aesthetics of the building and cause safety hazards.Therefore,flame retardancy and water resistance are important indicators for measuring the performance of composite materials.As a kind of polymer material which can replace petroleum-based polymers,polylactic acid has numerous advantages,such as excellent physical and mechanical properties,solvent resistance,biodegradability,biocompatibility,halogen-free and convenient for secondary processing and molding,so it is widely used in the fields of automobile,biomedicine,packaging,electronics,agriculture and other fields.Howerver,similar to many petroleum-based polymer materials,polylactic acid has a low limit oxygen index(?20%),is flammable in the air with severe melt dripping,and poor flame retardant,which to a large extent limits the wide application of polylactic acid materials and their derivatives in the field of high flame retardant requirements.Flame retardant compound modification of polylactic acid is one of the effective methods to take advantage of polylactic acid materials and extend the application of polylactic acid materials to flame retardant building materials.This paper starts with the modification of halogen-free flame retardants and performs flame retardant toughening treatment on polylactic acid materials in order to develop composite materials with excellent comprehensive properties,especially waterproof performance.The main research work is as follows:1?The surface modification treatment of metal hydroxide flame retardant compound materials Mg(OH)₂and Al(OH)₃was first performed to enhance the interfacial compatibility between inorganic particles and polylactic acid matrix resin.Four different types of surface modifier molecules(silane coupling agent KH 570,titanate coupling agent CS-201,aluminate coupling agent and sodium stearate)were selected to performed wet modification treatment and dosage optimization on the Mg(OH)_2/Al(OH)₃mixed flame retardant,and the modified flame retardant is characterized by activation index,X-ray diffraction,and thermogravimetric analysis.The results showed that the interface modifier molecules only act on the surface of the flame retardant particles,and the modified flame retardant particles changed from"hydrophilic"to"hydrophobic",as well as also effectively improved the flame retardant effect and waterproof performance of the polylactic acid composites.In addition,through the fire resistance limit test of the mixture of Mg(OH)₂/Al(OH)₃with different proportions and particle sizes,the optimal proportion of metal hydroxides was determined as Mg(OH)₂:Al(OH)₃is 6:4,Mg(OH)₂particle size is 2.89?m,and Al(OH)₃particle size is 4.98?m.2?The halogen-free flame-retardant polylactic acid composite material was prepared by compression molding with doped with appropriate amount of fillers and metal hydroxides.By optimizing the composition,proportion and process of the composite materials,the physical and mechanical properties,fire-retardant properties and internal structure of polylactic acid composites were characterized and analyzed by density,water resistance,flexural strength,temperature difference resistance,fire resistance,vertical combustion(UL 94),thermogravimetric analysis and scanning electron microscope.When the proportion of Mg(OH)₂/Al(OH)₃mixed flame retardant reaches 55 wt%,the polylactic acid composites with excellent physical,mechanical and flame retardant properties were obtained,and the flame retardant property passed the V-0 level of UL 94test.3?By incorporating basalt fiber,glass fiber and polypropylene fiber,the bending strength of halogen-free flame retardant polylactic acid composite material is increased.When adding 6mm polypropylene fiber with a content of 1.0 wt%,the bending strength of the polylactic acid composite can be significantly improved,and the impact on other properties of the composite can be ignored.We have carried out a systematic and in-depth study on the surface modification principle,synergistic flame retardant effect and toughening mechanism of composite materials.We have develop a flame-retardant polylactic acid composite material with excellent comprehensive properties,and provide basic data and theoretical guidance for the construction filed application of halogen-free flame-retardant polylactic acid.