Rheological properties of cellulose nanocrystals isolated via mechanical methods in thermoplastic polyurethane matrix

Abstract

Thermoplastic polyurethanes (TPU) are known for their versatility because they have both thermoplastic and elastomeric properties. Improvement of TPU properties can be accomplished by reinforcement with nanoscale fillers. Cellulose nanocrystals (CNC) are the most attractive nano-filler for reinforcement purposes in polymer matrices because of their high crystallinity and biodegradable materials. Mechanical methods to isolate CNC has sparked interest among researchers due to environmental demands (less solvent consumption). Lately, several researchers also have revealed some remarkable improvement of TPU through the addition of CNC. Thus, this study was aimed to produce CNC via mechanical methods for and to study the rheological properties of CNCs in the TPU matrix to gain insight interactions between CNCs and TPU. Isolation of CNCs via two methods: ultra-sonication (CNC-U) and nano-grinding (CNC-N) methods have been carried out. Then, the CNCs (0.5–2 wt%) were added into the TPU network employing the solution mixing method. The CNC was characterized via FESEM and the rheological behaviour was investigated on TPU/CNC solution. The main outcomes are that CNC-N has shown a higher aspect ratio (10–15), higher yield (>40%), and lower time and energy consumption than CNC-U. Rheological properties of TPU/CNC solution offer its structure-properties relationship via the increase in the concentration of CNCs. At 2 wt% concentration, TPU/CNC-N shows higher viscosity (19.5 Pa.s) than TPU/CNC-U (15.9 Pa.s). Thus, it was proven that the nanocomposite tends to act as a solid than liquid due to higher elastic behaviour. Furthermore, we can suggest the utilization of mechanical methods to produce a high yield of CNCs in notify the environmental issues.