Functional properties and stability of PLLA-metal organic framework based mixed matrix membranes.

摘要

Poly(lactic acid) (PLA) is a commercially available bio-based, biodegradable and compostable polymer with many new applications in the packaging industry. However, PLA has certain limitations such as poor barrier, low impact resistance, poor tear resistance and low toughness, which hinder its functionality as a packaging material. The purpose of this study was to explore and understand new avenues to improve the mechanical properties and functionality of the PLA for various industrial applications including packaging. PLA-metal organic framework (MOFs) mixed matrix membranes (MMMs) were fabricated with these objectives in mind. MOFs are a new class of crystalline coordinate polymers with applications in gas storage, catalysis and gas separation, and they can be used to produce PLA composites to improve its mechanical properties and functionality.;Copper benzene tricarboxylate Cu3(BTC)2 MOF was successfully synthesized by microwave synthesis and characterized using X ray diffraction (XRD), scanning electron microscopy (SEM) and surface area studies. During the fabrication of MMMs, it is important to maintain the integrity of MOF crystals to achieve the desired properties and functionality. Activated Cu3(BTC)2 MOF crystals were incorporated into PLA by melt extrusion process using twin screw micro-compounder without any damage to the Cu3(BTC)2 MOF crystal structure, which helped in preserving the functional properties of MOF in the polymer matrix. The effect of residual water in the MOF structures was evaluated. It was found that residual water could be detrimental to the morphology of the crystals during extrusion processing and can compromise the final properties of MMM.;The presence of MOF particles in the polymer improves the toughness of the PLA matrix. We observed that under the uniaxial tensile stress the triaxial stress generated at the interface of PLA MOF crystals led to cavitation induced by debonding. Cavitation mechanism generated local plastic deformation followed by strain softening leading to the improved toughness. Parallel plate rheological studies were performed to understand the interaction of MOF particle with the PLA and the effect of these particles on the processing of MMM. Rheological and differential scanning calorimetric studies provided evidence of strong PLLA-MOF interactions.;CO2 permeability of PLLA-20% wt. Cu3(BTC) 2 MOF mixed matrix membranes increased by around 38% as compared to neat PLLA. The perm-selectivity (&agr;CO2/O2) of PLLA-20% MOF increased from 7.6 to 10.3, respectively. The permeability coefficient for trans-2-hexenal increased by 60% with the addition of 20% MOF. Permeability coefficients of various gases and organic molecules are strongly influenced by the kind of interactions between the microporous materials, matrix and permeants. This study will help in the advancement of our understanding of mixed matrix membranes prepared from bio-based polymeric matrix for various industrial and commercial applications including food and pharmaceutical packaging.