Studies On Flame Retardant Properties Of Poly(Lactic Acid) Foams

Polylactic acid (PLA) is one of the most promising plastics quickly becoming one of popularalternatives to traditional petroleum-based plastics, because it is bio-based environmental friendlypolymers and exhibits many properties that are better than many petroleum-based plastics.However, its application scope is still very limited at the moment because of its brittle nature, lowcrystallization ratio,and high resin price. It is a promising way to improve the mechanical propertiesof PLA and expand its applications by preparing PLA foams using supercritical CO2foamingtechnology. Similar to other polymer resin, PLA is flammable, it can only pass the UL-94HB leveland reach21%LOI value. A flame retardant treatment to PLA is necessary. The traditional IFRadditives exhibit poor flame retardant efficiency in PLA, at addition of2030wt%, PLA canreaches the UL-94V0rating, but the addition of a large amount of inert FR fillers tends to affectthe foaming behavior of polymers significantly.The purpose of this paper is try to synthesize thedesirable poly(lactic acid)(PLA) foams with high flame retardancy.This study is to prepare satisfactory PLA/FR foams with high foam expansion, well-definedcell structure,and excellent flame retardant properties.A halogen-free FR was selected, usinggraphene, starch and PTFE as charring agent. The main content is listed below:(1) The FR fillers were uniformly dispersed in PLA matrix.With the introduction of5wt%FR, the LOI value of PLA increased significantly up to26.5%and passed the UL-94V-0rating,PLA/FR foams with high foam expansion, well-defined cell structure, but it presented the flamingdripping. The addition of graphene improved the char formation and anti-dripping effects obvious,but the preparation of PLA foam with graphene loading might be very difficult.(2) Starch as a natural charring agent improved PLA/FR composites the char formation,anti-dripping effects obviously and the LOI value improved to30.6%. In the rightconditions,PLA/FR foams with high foam expansion, well-defined cell structure.(3) PTFE as a polymer charring agent was added to improve the fire resistance of PLA. Theshort fibrous structure formed of PTFE in the process to improve the melt strength of thecomposite system of the PLA, thereby increasing the char formation of PLA/FR composites, and the system of anti-dripping properties slightly improved, meanwhile, well-defined cell morphologycomposite were obtained, but the whole cell foam expansion ratio is not high.