Cellulose nanofibril-reinforced composites using aqueous dispersed ethylene-acrylic acid copolymer

Natural cellulosic fibres such as wood pulps are well known reinforcing agents in composites and the high strength and large aspect ratio of nano-scale cellulose fibrils make them suitable as reinforcement in composite materials (Berglund and Peijs 2010 ; Oksman et al. 2016 ). Recent developments in cellulose pulp processing have made nano-sized cellulose fibrils commercially available (Saito et al. 2007 ). Since cellulose is one of the most abundant organic polymer in the world, it has the potential to be an inexpensive reinforcing filler material in thermoplastics. A major drawback of using cellulose nanofibrils (CNF) as reinforcement in thermoplastics is however the difference in hydrophilic nature between cellulose and the usually hydrophobic matrix phase polymer. Moreover, it can be argued that dewatering and drying of cellulose nanomaterials promotes irreversible bonding between nanofibrils, as discussed in Fernandes Diniz et al. ( 2004 ). This incompatibility can affect the mixing of the cellulose in the matrix and can lead to aggregation of cellulose fibre/fibrils resulting in a non-uniform thermoplastic composite (Ariño and Boldizar 2012 ). Insufficient compatibility can also result in poor fibre–matrix adhesion, leading to poor stress transfer and inferior mechanical properties. In addition, the low thermal degradation temperature of cellulose limits the range of processing temperatures and the selection of applicable polymer matrices. Common matrices used in melt extrusion of CNF are polyesters such as poly(lactic acid) (PLA) (Jonoobi et al. 2010 ), due to its renewable origin and biodegradability. Other common matrices used are polyethylene and polypropylene (Boldizar et al. 1987 ), which have relatively low melting temperatures and are common bulk polymers.