The effect of MDI on the structure and mechanical properties of poly(lactic acid) and poly(butylene adipate-co-butylene terephthalate) blends

Abstract

In this work, poly(lactic acid) and poly(butylene adipate-co-terephthalate) (PLA/PBAT 50/50) were melt-blended in the presence of 4,4′-methylene diphenyl diisocyanate (MDI) which acted as a reactive chain extender. The mechanical properties, phase morphology, thermal behavior and crystalline structure of the blends were investigated. Fourier transform infrared measurements revealed that some remarkable chemical interaction had taken place between the two polymers and MDI. Upon increasing the content of MDI, the blends showed increased tensile strength and elongation at break. With the addition of 0–2 wt% MDI, the impact strength of PLA/PBAT-MDI blends increased from 7.0 kJ m⁻² to 70.0 kJ m⁻². A large shift towards each other in terms of the glass transition temperature was observed by DMA and DSC analysis. SEM micrographs showed not only a reduction in the PBAT phase size but also a significant increase in interfacial adhesion between the PLA and PBAT phases with increasing of MDI. Furthermore, the toughening mechanism of the oriented samples was confirmed by wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) images; it was possible for the smaller crystallites of blends to form during the course of chain extension.