Investigation on the properties of poly(l-lactide)/thermoplastic poly(ester urethane)/halloysite nanotube composites prepared based on prediction of halloysite nanotube location by measuring free surface energies

In this study, the poly(l-lactide)/thermoplastic poly(ester urethane) (PLA/TPU) blend was employed as the matrix for preparation of nanocomposites with several halloysite nanotube (HNT) concentrations. This design was hypothesized based on a morphological conversion according to the assessment of thermodynamic equilibrium calculated by the contact angle measurements. HNTs as nanoparticles were applied to create PLA/TPU nanocomposites with more polymer interfaces for greater interactions, more compatibility, and a higher toughness. The addition of adequate HNTs, which have a thermodynamic inclination of settling in the low viscosity PLA phase, penetrates in the PLA phase and saturates the surface of this phase, as a result, the sea-islands transforms to quasi-cocontinuous morphology. If the added HNT is more, the nanoparticles not only disperse in the PLA phase and the interface but also penetrate into the TPU and agglomerate in some areas. The predicted morphology and microstructure were observed by the SEM and elemental analyses. The chemical structure changes and thermal properties of composites were investigated by the FTIR, DSC and TGA, respectively. The thermal stability of nanocomposites was investigated and shown that this property was improved by the presence of HNT in the nanocomposites. Also, the mechanical properties of the prepared composites, including elongation at break, tensile strength, elastic modulus, toughness, impact strength and hardness were reinforced. The melt flow properties of the designed composites were also investigated by the dynamic rheological analysis. Due to the reinforced thermal stability, fortified mechanical properties, high toughness and high melt elasticity, the designed composites are capable of being used in several applications such as packaging, thermal sealing, thermoforming, and melt spinning of plastics.