Effect of additives on the interfacial strength of poly(l-lactic acid) and poly(3-hydroxy butyric acid)-flax fibre composites

The interfacial shear strength (IFSS), evaluated by single fibre pull-out tests was quantified for various biopolymer-flax fibre composites that were modified with additives. The additives included a plasticiser (glycerol triacetate) (GTA) absorbed onto/into the fibres, 4,4'-thiodiphenol (TDP) that is capable of forming hydrogen bonds between the matrix and cellulose from the fibres, and a hyperbranched polyester (HBP) to impart improved fracture toughness. Fibres were washed with acetone to remove the surface impurities and dried under vacuum before absorption of plasticiser and adsorption of thiodiphenol. It was found that the different additives significantly influenced the IFSS for the biopolymer-flax fibre systems while extraction with acetone had a no effect on the IFSS compared with the untreated fibres. The use of TDP imparted the most significant increase in IFSS whilst the HBP had an opposing effect. The use of ESEM corroborated with the findings of the single fibre pull-out tests.