Abstract
Herein, a one-pot strategy was used to prepare hydrophobic cellulose nanocrystals (CNCs) surface-modified with tannic acid and octadecylamine. By this strategy, CNCs derived from wood (W-CNC) and tunicates (T-CNC) were modified in situ and incorporated into a polylactic acid (PLA) matrix using two methods, without first drying the CNCs. Films of PLA-CNC nanocomposites were prepared both by solution casting and by wet compounding in a thermo-kinetic mixer, followed by melt extrusion. Various properties of these PLA nanocomposites were evaluated herein, along with an assessment of how these properties vary with the type of CNC reinforcement. Cast films with a hybrid mixture of wood and tunicate CNCs displayed improved mechanical properties compared to either wood or tunicate CNCs, but extruded films did not show this hybrid effect. The water vapor permeability of the extruded nanocomposite films with 1% CNCs was reduced by as much as 60% compared to the PLA films. The composite films also showed enhanced biodegradation compared to neat PLA films. These results demonstrate that wet compounded PLA composites produced with wood or tunicate CNCs modified using a one-pot, water-based route have improved barrier and biodegradation properties, indicating a potential for packaging applications without having to dry the CNCs.
Highlights
In the pursuit of alternatives to non-renewable petroleum-sourced materials, growing interest has been directed toward renewable resources and their sustainable derivatives that possess similar performance characteristics
Successful modification of the T-cellulose nanocrystals (CNCs) and W-CNCs was determined by three complementary techniques described here and in Supplementary S2
The presence of both asymmetric (2860 cm−1) and symmetric (2940 cm−1) CH2 stretches from the C18 alkyl chain combined with both primary (1560 cm−1) and secondary (1490 cm−1) N–H bending signals present in the FTIR data indicates that this increased hydrophobicity of the modified CNCs was due to the presence of ODA on the surface of the tannic acid (TA)-CNCs [19,34,35]
Summary
In the pursuit of alternatives to non-renewable petroleum-sourced materials, growing interest has been directed toward renewable resources and their sustainable derivatives that possess similar performance characteristics. As the polymer is exposed to humidity, water molecules permeate the polymer, causing it to undergo hydrolysis reactions, which degrade its structure [5] To address these issues, researchers are attempting to modify PLA with nanofillers that can reduce vapor transmission through the composite material, which may slow hydrolysis-based degradation [6,7]. Hydrophobic CNCs have been demonstrated to enhance the mechanical, thermal, and vapor barrier properties of PLA, properties which have historically represented pitfalls when PLA is considered as a replacement for conventional plastics [15,17] These hydrophobic CNC surface modifications often come with formidable economic and environmental shortcomings, limiting their industrial potential [18]. The materials prepared in this work are novel in several ways, demonstrating the feasibility of a green, low-cost, one-pot, hydrophobic CNC surface modification, and providing insight into the unique properties afforded by the resulting PLA–CNC composites
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