Rheological properties of cellulose nanocrystal suspension

Abstract

Cellulose nanocrystal (CNC) is a unique nanomaterial that have received considerable attention due to its good individual mechanical properties and was proven as a good reinforcing filler to various polymer matrix. Thermoplastic polyurethane (TPU), have been widely used for lots of application like automobile, aerospace and medical industries. However, because of its chemical structure, TPU have significant deficiencies like low tensile strength as working with high force application. Thus, CNC has been used to overcome this limitation. This research was conducted to investigate the rheological properties of CNC in TPU and water matrix. CNC were obtained from microcrystalline cellulose (MCC) via sulphuric (CNC-S) and phosphoric (CNC-P) acid hydrolysis. CNCs (1 wt%, 2 wt% and 5 wt%) were dispersed in TPU and water matrix. CNC produced and its suspension were undergoing Field Emission Scanning Electron Microscopy (FESEM) and rheological test to identify the morphology and rheological behaviour respectively. CNC-S obtained has diameter of 17 ± 4 nm and length of 225 ± 100 nm, while CNC-P has diameter of 20 ± 5 nm and length of 231 ± 127 nm. The aspect ratio for CNC-P and CNC-S are 11 and 13 respectively. The rheology properties like viscosity of CNC-S were compared to CNC-P in both matrices. The viscosity of the TPU/CNC-S and TPU/CNC-P solutions recorded highest value at 5 wt% of CNC loading similar result was recorded as well in water matrix. In TPU, at shear rate of 0.1 s−1, the viscosity of TPU/CNC-S is 192.1 Pa.S and TPU/CNC-P solution is 173.4 Pa.S. Meanwhile, in aqueous suspension, at shear rate of 0.1 s−1, the viscosity of CNC-P recorded higher value than CNC-S suspension at 772,800 Pa.S and 1045 Pa.S respectively. This has proven that type of acid in CNC production and suspension matrix influence the rheological properties of CNC suspension.