Polylactide/Halloysite Nanocomposite Foams: Particle Dispersion and Mechanical Strength

Abstract

Polylactide (PLA) foams have been used in biomedical applications such as scaffolding and tissue engineering due to its biocompatibility. However, its brittleness and low melt strength limit it wide range of applications. In this study, halloysite nanotube (HNT) was used in order to improve the properties of the PLA foams. PLA/HNT composites were compounded on twin screw extruder within constant concentration of HNT (0.5 wt%). In extruder processing, compounding was realized in two different ways. In the first one, PLA/HNT was melt-mixed by the addition of 1 wt% azodicarbonamide (AC) in order to enhance the dispersion of the nanoparticles in the matrix. In the second one, azodicarbonamide was not added into the extruder during compounding of PLA/HNT. After melt-mixing process, neat PLA and PLA/HNT pellets were subject to chemical foaming on a conventional injection molding machine and tensile test samples were obtained. Mechanical test and morphological investigations were made in order to observe the tensile properties and foam cell generation of PLA composites. It has been seen that HNT addition in 0.5 wt% increased the tensile strength and elongation of PLA/HNT about 50% and 70%, respectively. Morphological results showed that HNT could improve the cell formation of PLA foams by decreasing the cell pore size and cell density. The usage of AC in melt-mixing stage of the polymer composite induced a slight increment in the tensile properties of the material due to the dispersant and plasticizer effect of azodicarbonamide.