Structural modification and encapsulation process of palygorskite for development of flame retardant additives: study of their thermal and mechanical properties in PLA/EVA blends

In this work, we described the structural modification of palygorskite (Pal) and its use in the preparation of flame retardant (FR) additives. Theses FR additives were prepared by an encapsulation process involving in situ polymerization reaction between melamine and diisocyanate. The structural modification of Pal and the encapsulation process were characterized by FTIR and SEM techniques. These FR additives were incorporated into polymer blends of poly(lactic acid) (PLA) and ethylene vinyl acetate (EVA) by melt mixing. The compounds obtained from mixing FR additives and PLA/EVA were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), cone calorimetry, limiting oxygen index (LOI), and plastics flammability standard (UL 94, HB). The incorporation of FR additives showed a significant change in the thermal properties of the PLA/EVA composites. We observed a marked reduction in the peak heat release rate during cone calorimetry tests and significant increase of LOI value. A reduction in the horizontal burn (HB) rate was also observed in the UL-94 test. The results obtained confirmed the notable increase in thermal stability and FR characteristics of the PLA/EVA composite, which was attributed to the formation of a homogeneous protective carbon layer on the surface of the composite samples. This composite showed excellent FR characteristics with good mechanical properties, which is a good option to obtain flame retardant composites with better performance. These results demonstrated that this methodology is a promising way to meet the growing demand for high-performance materials with flame retardant characteristics, using composites with sustainable and ecological materials.