Flame retardancy of biocomposites based on thermoplastic starch

Abstract

The flame retardancy of fully biodegradable, natural fiber reinforced thermoplastic starch (TPS) composites was studied in this work. Thermoplastic starch of significantly reduced flammability could be prepared by using a phosphorus containing polyol for plasticizing starch. The thermal degradation of the obtained flame retarded TPS was compared to conventional glycerol-plasticized TPS using not only TGA and DSC but also LP-FTIR (Laser pyrolysis FT-IR coupled method) measurements, which allowed the identification of all the gaseous degradation products. The flame retardant TPS matrix was reinforced with chopped flax fibers and woven linen-hemp fabrics. Due to the embedding of biofibers significant increase in tensile and impact properties of TPS could be achieved, however, the flammability characteristics of the biocomposites, measured by LOI, UL-94 and cone calorimetric tests, become inferior to those of the unreinforced TPS matrix, thus the flame retardant treatment of the reinforcing natural fibers was indispensable. The thermal behaviour and flame retardancy of biofibers, investigated by TGA and cone calorimetry, showed substantial improvement as a consequence of their phosphorous surface treatment. The prepared fully biodegradable biocomposites, comprising of TPS matrix plasticized with P-polyol and P-treated biofibers, exhibit increased mechanical performance accompanied with excellent flame retardancy: pass V-0 rating in UL-94 test, reach LOI of 32 vol. %, and show with 45 % reduced pkHRR during combustion than the unreinforced TPS reference.