Abstract
Graphene oxide(GO)/polylactic acid (PLA) nanocomposite, prepared using a solvent-free melt mixing processing, is investigated as a potential oxygen barrier packaging film in this work. In order to disperse GO homogeneously in PLA matrix, hydrophobic silane coupling agent, i.e., γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560), is used to modify the graphene oxide sheets. The modified GO is able to be well bonded to the PLA due to the formation of covalent bonds between the epoxy groups of KH560 and the carboxyl and hydroxyl terminal groups of PLA. Furthermore, the thermal stability of GO is enhanced due to the long alkyl side chain of KH560, which could also increase the crystallinity of PLA. As a result, the crystallinity of PLA is significantly improved because of the linear KH560 chains, which can act as nucleating agents to improve the crystallization. The KH560-GO helps to reduce the O2 permeability of KH560-GO/PLA composite films via a dual-action mechanism: (1) providing physical barrier due to their native barrier properties, and (2) by resulting in higher degree of crystallinity. The as-prepared KH560-GO0.75/PLA is able to exhibit ca. 33% and ca. 13% decrease in the PO2 than the neat PLA and GO0.75/PLA film, respectively. Finally, the mechanical properties and impact fractured surfaces indicate that the increase in the tensile strength and elongation at break value of KH560-GO/PLA are due to the strong interfacial adhesion and the strong bonding between the epoxy group of KH560-GO and hydroxyl and carboxyl acid terminal groups of PLA matrix.
Highlights
Food packaging is highly essential in extending the shelf life of food, and to maintain or even enhance the food quality and consistency
It can be observed that after modifying graphene oxide (GO) with the silane coupling agents, D band appears to be more prominent for KH560-GO as compared to its unmodified cm−1 which are attributed to the D and G bands, respectively
As a result of the sp3 defects within the sp2 carbon framework in GO, this leads to an 3 defects within the sp2 carbon framework in GO, this leads to an counterpart
Summary
Food packaging is highly essential in extending the shelf life of food, and to maintain or even enhance the food quality and consistency. One of the strategies to impart high barrier property to the polymer film is through the incorporation of impermeable fillers (nanoplatelets) into the polymer matrix [10,11,12,13]. As a popular filler material, graphene oxide (GO) is highly attractive for its exceptional gas barrier properties due to its closely packed planar structure, substantial aspect ratio, and significantly high specific surface area. Three main synthesis strategies are most commonly adopted in the fabrication of GO/polymer nanocomposite; solution mixing, melt mixing, and in situ polymerization. A GO/PLA nanocomposite system fabricated from melt mixing processing is investigated for its gas barrier properties. The processing effects of melt mixing and previously reported solution mixing on the dispersion and gas barrier performance of GO/PLA are compared in this work. The long alkyl side chain of KH560 could increase the thermal stability of GO, and simultaneously increase the crystallinity of PLA
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