Study On Comprehensive Properties Of Nano-silica Improved PLA/TPU(90/10) Blend

Polylactice acid(PLA) is a green biodegradable material; however, its inherent brittleness severely limits its applications. In this paper, low content(10 wt%) of thermoplastic polyurethane(TPU) as an toughening aaaamodifier and appropriate contents of hydrophobic silica nanoparticles(Si O2) as interfacial modifiers were used to improve the toughness of PLA. PLA/TPU/Si O2 nanocomposites were prepared by melt mixing. Microstructure, mechanical, thermal and rheology properties of the prepared samples were investigated. Then, represent samples were foamed. The effect of Si O2 on the cellular structure of PLA/TPU blend foamed sample was analyzed.Both thermodynamic prediction and transmission electron microscopy micrographs demonstrate that most Si O2 nanoparticles distribute at interfaces between the PLA and TPU phases. This improves interfacial adhesion between the PLA and TPU phases, which is attributed to good bonding strength between the PLA and Si O2 via hydrophobic interaction and formation of hydrogen bonds between the TPU and Si O2. The PLA/TPU(90/10) blend nanocomposite with 2 wt% Si O2 exhibits an obviously high impact strength(about 5.0 and 12.6 times that of the corresponding blend and PLA, respectively) and higher tensile strength than the blend and even the PLA. Scanning electron micrographs on impact-fractured surface of the blend nanocomposite demonstrate that crazing mechanism is the main reason for its obviously improved impact toughness. Si O2 improves the thermal stability and cold crystallization temperature of the blend, but shows almost no influence on its crystal structure.Dynamic viscoelasticity shows that storage modulus and complex viscosity of PLA/TPU blend at low frequency were enhanced by addition of Si O2. The more the Si O2 is, the higher the elastic of the nanocomposite at low frequency appears. This is attributed to the Si O2 inter-particle and particle-polymer interactions, slowing down the chains mobility and elongating the relaxation time. Dynamic thermomechanical properties indicate that Si O2 improve the elastic modulus of PLA/TPU blend.Adding Si O2 into the PLA/TPU blend contributes to the reduction of cell average diameter and the increase of cell density. When the foaming pressure increases from 16 MPa to 18 and 20 MPa, the cellular structures of foamed samples show almost no change. The improved structure observed in the nanocomposite foams is attributed to the nucleating effects of Si O2 and improved rheological properties of the PLA/TPU blend by Si O2.