Tungsten disulphide nanotubes (WS2NTs) continue to attract interest as functional fillers for biopolymers. However, the combined technical challenges of effective dispersion of WS2NTs in polymer matrices and the promotion of strong interfacial interactions still need to be addressed. This work describes extensive characterisation of WS2NTs and WS2NTs nanocomposites in two model biopolymers, poly(lactic acid) (PLA) and chitosan.

WS2NTs were found to be thermally stable in air up to 400 °C and have aspect ratios up to 1000. When composites of PLA and WS2NTs, the shear stresses during extrusion resulted in breakage of NTs and a decrease in AR by >95%. Consequently, mechanical properties of nanocomposites, prepared by melt mix extrusion, were unchanged but also due to the poor interfacial interaction between NTs and PLA. Addition of WS2NTs induced heterogeneous nucleation of PLA and resulted in an increase in the rate of crystallisation and crystalline content by 15%.

To promote interfacial interaction between WS2NTs and PLA matrix, functionalization of WS2NTs using 3-aminopropyltriethoxysilane (APTES) was found to bind to the surface of NTs through the formation of siloxane networks. To avoid reduction of aspect ratio, composites of the APTES modified WS2NTs and PLA were prepared by solvent casting. The elongation at break and tensile toughness of the composite films produced using APTES functionalised WS2 were 600% that of the unfilled PLA.

The mechanical properties of chitosan were also enhanced on inclusion of WS2NTs, while glycerol helped promote the formation of a polyelectrolyte complex between the negatively charged NT surface and the positively charged amine groups of chitosan. The resultant films were much stronger (+40%) and tougher (+74%) that glycerol plasticised chitosan without sacrificing stiffness and ductility. The addition of WS2 NTs to glycerol plasticised chitosan improved the gas barrier properties of the chitosan, with a 50% and 80% reduction in O2 and CO2 permeability respectively. Additionally, these composites displayed antimicrobial efficacy against both Gram-positive and Gram-negative bacteria.