Deterioration of metal–organic framework crystal structure during fabrication of poly(l‐lactic acid) mixed‐matrix membranes

Abstract

Poly(L-lactic acid) (PLLA) and metal-organic framework (MOF) mixed-matrix membranes were prepared by melt extrusion of PLLA with 5% (w/w) of either activated or water-saturated Cu 3 (BTC) 2 (Cu 3 (C 9 H 3 O 6 ) 2 (H 2 O) 3 ·xH 2 O, HKUST-1). The morphology and the stability of injection-molded samples were evaluated using thermogravimetric analysis, differential scanning calorimetry, gel permeation chromatography, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The presence of activated and saturated MOF crystals increased the cold crystallization onset temperature as compared to neat PLLA. This can be attributed to the MOF crystals incorporated in the PLLA matrix, which decreased the mobility of PLLA and thus impeded the crystallization process. According to the XRD results, the activated MOF crystals were successfully incorporated into the PLLA matrix without altering the crystal structure of the MOF. Moreover, the findings from permeability and tensile tests as well as SEM imaging indicated good interfacial interactions between PLLA and activated MOF. However, during melt extrusion of PLLA with saturated MOF, water molecules from the saturated MOF altered the MOF crystal structure and contributed to the degradation of the PLLA polymer by reducing its molecular weight by around 21%.

Effect of MIL‐53 (Al) MOF particles on the chain mobility and crystallization of poly(L‐lactic acid)

“…At these higher MOF loadings, the cold crystallization peaks were absent in the second heating cycle due to reduced chain mobility which could be ascribed to strong polymer‐filler interactions. The decreased percentage crystallinity with increase in the MOF content can be correlated to the decreased mobility of the polymeric chains . Although, change in the percentage crystallinity appear to be relatively smaller primarily due to amorphous nature of the polymer.…”

“…Controlled oxygen gas permeability may help in extending the shelf‐life of respiring produce. For oxygen mass transfer, 20 wt % MIL‐53 (Al) was carefully chosen based on the previous research works and based on its quadrupole moment and polarizability . Table shows O 2 permeability coefficients of PLLA and PLLA‐20% MIL‐53 (Al) MOF.…”

“…A shift in the onset of cold crystallization temperature of the PLLA-1% MOF composition can be attributed to the good interactions between the polymeric chains and the MOF crystals and high surface area of MOF hindering the segmental mobility of the polymeric chains. 1,3,28 Such topological constraint can affect crystallization kinetics and viscoelastic properties of the materials. Gagliradi et al 28 studied the interfacial interaction of poly(dimethylsiloxane) with 20% and 40% silica nanoparticles and poly(vinyl acetate) with 40% silica nanoparticles.…”

“…Fillers, functional materials, additives, or modifiers have been widely used to improve the functionality of polymeric matrices, including strength, stiffness, hardness, durability, permeability, and controlled selective exchange of gases for various applications. [1][2][3] Interfacial interactions between the matrix and filler play an influential role in polymer-filler dynamics. Surface area, concentration, and particle size of the filler influence the polymeric chain structure, segmental mobility, and crystallinity.…”

“…On the other hand, poor interfacial interactions lead to interfacial voids or defects. 1,3,[5][6][7][8] Poly(lactic acid) (PLA) is a bio-based, biodegradable, and compostable polymer that has consolidated its market presence due to technocommercial advancement, growing production capacity, and economic viability. 9,10 PLA is a clear, rigid thermoplastic with mechanical strength comparable to poly(ethylene terephthalate) and polystyrene.…”