The Preparation And Characterization Of Halogen Free And Biodegradable Flame Retardant Polylactic Acid

As a bio-based environmental friendly polymer, polylactic acid (PLA) has been used in many areas due to its biocompatibility, high transparency, ease of fabrication and good mechanical properties. However, its flammability cannot meet industrial requirements in many cases. An ideal flame retardant PLA composite should be biodegradable and environmental friendly.In this paper, several bio-based materials such as chitin, chitosan and casein have been introduced into PLA by melt-blending as flame retardants.Firstly, chitin has been used as a new charring agent. Chitin together with ammonium polyphosphate (APP) and melamine (MEL) has formed a new intumescent flame retardant formulation. This IFR system can promote the formation of a homogeneous and compact intumescent char. With the presence of 20% APP/chitin/MEL (2/1/1), the LOI value is increased to 26 and UL-94 is improved to V-0.Secondly, the chitosan and APP have been added into PLA. Chitosan and APP show obvious synergistic effect in terms of LOI and UL-94 test results. PLA containing 2% chitosan and 5% APP can pass UL-94 V-0 rating, and has a LOI value of 33.1. The char formed at the presence of the combination of chitosan and APP is denser and more than that formed at the presence of each component individually at the same amount.Finally, casein has been introduced to PLA as an effective flame retardant. It has been found that the LOI of the PLA sample is increased to 24.6 and can pass V-0 rating in UL-94 test after only adding 5% casein. It is suggested that non-flammable gas and phosphorous salts are produced by casein during combustion. The non-flammable gas protects the PLA matrix. And the phosphorous salts catalyze the char forming process.