Reactive Extrusion of Polylactic Acid/Cellulose Nanocrystal Films for Food Packaging Applications: Influence of Filler Type on Thermomechanical, Rheological, and Barrier Properties

Abstract

In this study, we successfully demonstrate single-step industrially scalable reactive extrusion of polylactic acid (PLA)/ cellulose nanocrystal (CNC)-based cast films which leads to reduced necking, improved processability, melt strength, and rheological behavior. PLA chains grafted onto CNCs, formed cross-linked gel-like structures of high molecular weight (M w ≈ 150−245 kDa), with varying grafting efficiency (14%−67%) or gel-fraction yield (16%− 69%), depending on the type of compatibilizers used. The reactively processed films show reduction in both oxygen properties (20%− 65%) and water vapor barrier properties (27%−50%), along with improved thermomechanical properties. These films finds potential applications for the storage of oil-and dairy-based products, which show shelf lives of ∼5 months and ∼2 weeks, respectively, and are within the standard migration limits, as per the set legislations. Therefore, the present study provides a novel, easily processable extrusion-based approach for manufacturing sustainable PLA/ CNC-based green and eco-friendly films with improved recyclability, biodegradability, and nontoxicity for potential applications as food packages on a commercial scale.

Surface texture and barrier performance of poly(lactic acid)–cellulose nanocrystal extruded‐cast films

“…The formation of CNC agglomerates was expected because hydrophilic cellulose nanoparticles are difficult to disperse in nonpolar (hydrophobic) polymers because of their strong hydrogen‐bonding forces . The presence of CNC agglomerates in the films implied that the mechanical shearing actions applied to the CNCs in the high‐intensity mixer at a speed of 22,000 rpm for approximately 2 min was not sufficient to break the CNCs into individual nanofibrils.…”

“…The evaporation of the solvent may increase the energy consumption in the film manufacturing process and arouse environmental concerns because some solvents may be toxic to workers and the environment . Melt processing (a continuous process) is an alternative for the manufacture of PLA–CNC composite films without the use of solvent . However, this method has not been studied extensively.…”

Biocomposites of poly(lactic acid) and lactic acid oligomer‐grafted bacterial cellulose: It's preparation and characterization

“…To achieve material properties comparable to other benchmark packaging plastics, various strategies are devised such as stereo‐complexation, blending, addition of nano‐ and micro‐fillers, and so on . Reinforcement of PLA matrix by addition of fillers such as cellulose nanocrystals, chitosan, gum, hydroxyapatite, silk, and so on can be used to form bionanocomposites with the desired properties for packaging . Superiority of filler reinforced polymer bionanocomposites is dictated by dispersion and interfacial adhesion.…”

Crystallization kinetics, morphology, and hydrolytic degradation of novel bio‐based poly(lactic acid)/crystalline silk nano‐discs nanobiocomposites

“…Most routine examples include clay, talc, carbon black, etc . Apart from these, few renewable materials have also been integrated like cellulose nanocrystals, chitosan, sucrose palmitate, etc . The crystallization of polymer affects the material properties and also process control which is indispensable part of polymer processing .…”