Impacts of cellulose nanofibers on the morphological behavior and dynamic mechanical thermal properties of extruded polylactic acid/cellulose nanofibril nanocomposite foam

Abstract

Polylactic acid (PLA) foams were introduced as a good substitute for oil-based foams. Much research has been done on the autoclave of PLA foam, but discontinuous processes are not attractive for industries. In order to reduce the distance between the PLA foaming process and industrialization, it is necessary to introduce continuous processes. In this work, two solutions to improve the foaming of PLA are presented: using the extrusion process and adding cellulose nanofibers. So, in this study, a twin screw extruder was used by blowing agent, CO 2 , and in order to better dissolve the gas, a static mixer was used before the die. The molecular weight of the original PLA after extrusion has reduced in the range from 20%-28% due to the hydrolysis of the ester bond in the PLA. With the cellulose nanofiber loading, nucleation and cell density have enhanced. Scanning electronic microscope (SEM) microscopic images for the nanocomposites containing 1.5 wt% of cellulose nanofiber showed the highest cellular expansion and for the nanocomposites containing 2.0 wt% of cellulose nanofiber showed the most uniform cell distribution and it confirmed the density results and the calculated expansion ratio. Finally, by examining the dynamic-mechanical thermal analysis, it can be stated that the composition of cellulose nanofibers improves the mechanical and dynamic properties of cellulose nanofiber-reinforced PLA.

Progress in the Preparation, Properties, and Applications of PLA and Its Composite Microporous Materials by Supercritical CO2: A Review from 2020 to 2022

“…Sadeghi et al [ 73 ] added hydrophilic cellulose nanofibers (CNF) to PLA and prepared microporous foams by twin-screw extrusion foaming and found that the addition of CNF promoted cell nucleation and increased cell density. The molecular weight of pure PLA was reduced by about 25% after extrusion, probably due to the hydrolysis of ester groups that occurred during the melting process.…”

“…Sadeghi et al [ 73 ] reported preparing PLA/CNF composite foam materials by adding an appropriate amount of cellulose nanofibers (CNF) to PLA. The continuous extrusion foaming method was used to avoid the shortcomings of the discontinuous production of intermittent foaming and to meet the requirements of industrialization.…”

“… Principle of extrusion foaming process (reproduced with permission from Reference [ 73 ], Copyright 2021 Elsevier). …”

Surface modification of cellulose nanofibers by oxidative polymerization of tannic acid/ethanediamine and their polyvinylalcohol composites

“…The major drawbacks of CNF are its poor thermal stability, flammability, and lack of functionality, which make it difficult to improve the thermal properties and impart functionalities in CNF composites 7,8 . Surface modification of CNF or combination with other inorganic nanomaterials for construction of composites can potentially make up these problems, but these approaches are usually complex, and could compromise the biocompatibility or biodegradable of CNF 9–12 . Therefore, it is still a challenging task to fabricate multifunctional CNF composites with good properties while maintain the intrinsic advantages of CNF.…”

“…7,8 Surface modification of CNF or combination with other inorganic nanomaterials for construction of composites can potentially make up these problems, but these approaches are usually complex, and could compromise the biocompatibility or biodegradable of CNF. [9][10][11][12] Therefore, it is still a challenging task to fabricate multifunctional CNF composites with good properties while maintain the intrinsic advantages of CNF.…”