Preparation And Properties Of PLA/TPU Blends Via Reactive Extrusion

Poly(lactic acid)(PLA) is a renewable polymer that has caught many attentions.Thermoplastic polyurethane(TPU) is a biocompatible material that has excellent performance.TPU has been used to successfully toughen PLA. In this paper, reactive melt blending method is used to further improve the performance of PLA/TPU(80/20) blends. By adding different types of chain extenders and changing their contents, the PLA/TPU blends are prepared. The phase morphology, dynamic rheological properties, thermal properties and mechanical properties are investigated. On this basis, PLA/TPU blends with different contents of Joncryl ADR-4370 chain extender are foamed by batch foaming,the cellular structures are studied.With the addition of 4,4-methylene diphenyl diisocyanate(MDI), The proportion of the hard segment for TPU is enlarged. The compatibility between the PLA and TPU phases changes little. It is confirmed by analyzing the dynamic rheological behaviors and gel contents of the PLA/TPU blends that, with increasing MDI content, the TPU chains are extended, then branched TPU chains appear, and finally crosslinked structure also appears in the TPU chains. From the thermogravimetric analysis, the thermal degradation temperature(Td) values of the blends increase by 4~5 °C with the addition of MDI. For the blend with 0.8wt% MDI, the impact strength and the elongation at break reach 100.6 k J/m2 and 392.4%,respectively. The former is about 1.9 and 32.5 times of that for the blend without MDI and the PLA, respectively. Upon addition of the MDI, the PLA/TPU blends not only are largely toughened but also exhibit some increase in the tensile strength.With the addition of Joncryl ADR-4370, the compatibility between the PLA and TPU phases are improved. It is confirmed by analyzing the dynamic rheological behaviors and gel contents of the PLA/TPU blends that, the molecular weight as well as the amount and length of branched chains of the PLA/TPU blends keep increasing with increasing Joncryl contents.However, with the addition of the Joncryl, the Td of PLA/TPU blends changes little and then decreases with a Joncryl content of 1.5 wt %. when 1 wt% Joncryl is added in, the impact strengths, elongation and tensile strength of the PLA/TPU reach 78.9 k J/m2, 368.2% and 37.8MPa, which is about 1.5, 2.1 and 1.2 times of that for the blend without Joncryl, respectively.PLA/TPU blends with different contents of Joncryl ADR-4370 are formed and it is found that, the increased melt viscosity which is cased by the addition of Joncryl decreases the mean cell size and increases the cell density of formed PLA/TPU samples. But an excess of Joncryl leads to the opposite effect. For PT′-0 samples, the contribution and morphology of the cellulars can be controlled by changing the foaming temperature. For PLA/TPU blends with0.5 wt% Joncryl samples, increased saturation pressure can increase the mean cell diameters and cell density. In the condition of 180 °C, 15 MPa and 180 °C, 18 MPa, a small amount of connected cellulars appear in all foaming samples.