A Review of Wet Compounding of Cellulose Nanocomposites

Interfacial Compatibility of Core-Shell Cellulose Nanocrystals for Improving Dynamic Covalent Adaptable Networks' Fracture Resistance in Nanohybrid Vitrimer Composites

The development of polymeric nanocomposites with dynamic covalent adaptable networks and biobased nanomaterials has been a promising approach toward sustainable advanced materials, enabling reprogramming and recycling capabilities. Herein, a core-shell nanohybrid of functionalized cellulose nanocrystals (CNCs) is explored to provide crucial interfacial compatibility for improving the covalent adaptable networks of epoxy-thiol vitrimers in fracture resistance. The poly(ε-caprolactone) (PCL) shells grafted from CNC surfaces can be cross-linked with the covalent adaptable networks via a hot-pressing transesterification process. According to the additive concentration and annealing temperature, the stress relaxation behavior of nanohybrid vitrimer composites can be effectively regulated by the core-shell PCL-grafted CNC (CNC-PCL) nanohybrids from a dispersed to cross-linked interaction. The addition of 15 wt % of the core-shell CNC-PCLs exhibits the reinforced improvement of nanohybrid vitrimer composites in the average Young's modulus of 2.5×, fracture stress of 5.4×, and fracture strain of 2.0×. The research findings might have profound implications for developing synergistic interfacial compatibility between dynamic vitrimer networks and functional nanoparticles for advanced polymeric nanocomposites.

Polylactic Acid Cellulose Nanocomposite Films Comprised of Wood and Tunicate CNCs Modified with Tannic Acid and Octadecylamine

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.

Influence of Lactic Acid Surface Modification of Cellulose Nanofibrils on the Properties of Cellulose Nanofibril Films and Cellulose Nanofibril-Poly(lactic acid) Composites

In this study, cellulose nanofibrils (CNFs) were modified by catalyzed lactic acid esterification in an aqueous medium with SnCl2 as a catalyst. Films were made from unmodified and lactic acid-modified CNF without a polymer matrix to evaluate the effectiveness of the modification. Ungrafted and lactic acid-grafted CNF was also compounded with poly(lactic acid) (PLA) to produce composites. Mechanical, water absorption, and barrier properties were evaluated for ungrafted CNF, lactic acid-grafted CNF films, and PLA/CNF composites to ascertain the effect of lactic acid modification on the properties of the films and nanocomposites. FTIR spectra of the modified CNF revealed the presence of carbonyl peaks at 1720 cm-1, suggesting that the esterification reaction was successful. Modification of CNF with LA improved the tensile modulus of the produced films but the tensile strength and elongation decreased. Additionally, films made from modified CNF had lower water absorption, as well as water vapor and oxygen permeability, relative to their counterparts with unmodified CNFs. The mechanical properties of PLA/CNF composites made from lactic acid-grafted CNFs did not significantly change with respect to the ungrafted CNF. However, the addition of lactic acid-grafted CNF to PLA improved the water vapor permeability relative to composites containing ungrafted CNF. Therefore, the esterification of CNFs in an aqueous medium may provide an environmentally benign way of modifying the surface chemistry of CNFs to improve the barrier properties of CNF films and PLA/CNF composites.