Effects of ammonium polyphosphate and casein on the properties of poly (lactic acid)

In this paper, ammonium polyphosphate (APP) and casein (CSN) were added to poly (lactic acid) (PLA) to improve flame retardancy and maintain biodegradability. The flame retardancy, mechanical, and thermal properties of PLA/APP/CSN composites were evaluated, and the optimum ratio of APP and CSN was determined. The results showed that with the addition of 9 wt% flame retardant (APP:CSN=5:4), the limiting oxygen index (LOI) of the PLA/APP/CSN composite reached 28.3%, and passed the UL-94 V-0 rating at 3 mm, char residue increased at 800°C and smoke emission was also significantly reduced compared to addition of APP without the addition of CSN. Besides that, the cone calorimeter result showed that the peak heat release rate and total heat release of the PLA/APP/CSN-5 composite were 18.2% and 13.3%, respectively, lower than those of pure PLA. The addition of flame retardants inevitably led to a reduction in tensile and flex strength values, but the impact strength was improved.