Preparation of cellulose nanocrystals coated with polymer crystals and their application in composite films

Abstract

AbstractIncreasing the dispersibility of cellulose nanocrystals (CNCs) as a reinforcing material is highly desirable to obtain composites with enhanced mechanical properties. To this aim, nanocomposite fibers (NCF(CNC/polymer)) were fabricated by coating CNCs with polymer crystals. Poly(vinyl alcohol) (PVA) and poly(vinyl alcohol‐co‐ethylene) (EVOH) were crystallized from a dilute solution in the presence of CNCs, which acted as nucleating agents for polymer crystal growth on the CNC surface. NCF consisting of CNCs coated with PVA crystals (NCF(CNC/PVA)) and CNCs coated with EVOH crystals (NCF(CNC/EVOH)) were successfully obtained. Both NCF(CNC/polymer) showed good dispersibility in water, even after drying, and were used to prepare composite films with improved mechanical properties. The reinforcement effect of NCF(CNC/PVA) was greater than that of pure CNCs and NCF(CNC/EVOH). The PVA composite films exhibited optical transmittance above 99% compared with additive‐free PVA films. No agglomerates appeared even under the optical microscopic observation of the PVA composite film, and NCF(CNC/PVA) dispersibility was extremely good. NCF(CNC/PVA)‐added PVA composite films exhibited increased glass transition temperature compared with additive‐free PVA films, and the crystallinity of the PVA film increased. The highly dispersed CNCs in the PVA matrix and the increase in the glass transition temperature and crystallinity caused an increase in the mechanical modulus of the PVA composite film at low NCF(CNC/PVA) content. Furthermore, the effect of the morphologies of cellulose nanofibers and CNCs on the mechanical properties of the composite films prepared using the respective NCFs was investigated.