Fabrication of microphase-separated polyurethane/cellulose nanocrystal nanocomposites with irregular mechanical and shape memory properties

Abstract

Low molecular weight poly(ethylene glycol) (PEG)-based polyurethane (PU)/cellulose nanocrystal (CNC) nanocomposites were prepared using in situ polymerization and pre-polymer approach. PEG was used as soft segment, and 1,4-butanediol (BDO) as chain extender and hexamethylene diisocyanate (HDI) were used as hard segment. Also, effect of CNC loading on different properties of the resulting nanocomposites such as microstructure, thermal properties, and microphase separation of soft and hard segments was investigated. Mechanical properties and shape memory behaviors were determined by tensile and shape memory tests, respectively. Due to low molecular weight of soft segment, the net effect of hydrogen bonding on different properties of nanocomposites is well investigated here. Results showed that introduction of CNCs into PU matrix influenced the hydrogen bonding between different moieties of structure, which resulted in different microphase separation states. Also, CNCs had no significant effect on thermophysical and thermal properties. However, tensile strength, elongation at break, and modulus as mechanical properties were affected significantly. Nanocomposites containing up to 0.5 wt.% of CNC had improved modulus, tensile strength, and elongation at break compared to neat PU, whereas higher amounts of CNC resulted in lower modulus, tensile strength, and elongation at break. Shape memory behaviors were evaluated using tensile test. Nanocomposites showed shape memory behavior up to 0.5 wt.% of CNCs, and at higher CNCs loading, no shape memory behavior was observed.