Cellulose Nanocrystals versus Microcrystalline Cellulose as Reinforcement of Lignopolyurethane Matrix

Cellulose nanocrystals (CNC) exhibit remarkable properties such as being lightweight, renewability, nanoscale dimension, raw material availability, and a unique morphology. They have been widely used in film-forming composites, but the literature is scarce concerning bulky-composites (i.e., non-filmogenic). Microcrystalline cellulose (MCC) is widely available and has emerged as an important material for the reinforcement of composites. This investigation focuses on the preparation of non-filmogenic composites prepared from a polyurethane-type matrix, based on modified lignosulfonate and castor oil, reinforced with CNC or MCC, aiming to compare their reinforcing capacity. CNC was obtained through the acid hydrolysis of MCC. Sodium lignosulfonate was chemically modified using glutaraldehyde to increase its reactivity towards isocyanate groups in the synthesis of lignopolyurethane. The results show that adding CNC or MCC led to materials with improved impact strength, flexural properties, and storage modulus compared to pristine lignopolyurethane. With the exception of the flexural modulus, which was higher for the CNC-reinforced composite compared to the MCC-reinforced composite, all other properties were similar. The set of results indicates that CNC and MCC are promising for the reinforcement of polyurethane-type matrices. Bulky materials with good properties and prepared from high renewable raw material contents were obtained, meeting current expectations concerning sustainable development.