Water-assisted mixing and compression moulding of ethylene-acrylic acid copolymer reinforced with nano-cellulose

Licentiate thesis, 2018

The concerns regarding aspects of global warming, depleting oil resources, accumulation of plastics in landfills has served as motivation to move towards utilizing sustainable and renewable resources to fulfil our needs. In the present work, the reinforcing capabilities of cellulose nanofibrils (CNF) and modified/unmodified cellulose nanocrystals (CNC) based composites prepared through water-assisted mixing, drying and compression moulding was explored. At the water-assisted mixing, compositions consisting of an aqueous dispersion of a poly(ethylene-co- acrylic acid) copolymer, nanocellulose suspension and excess water of about 96 %, were used to prepare the composites. The final composites had a dry loading content of 10 to 70 vol.% CNF or 0.1 – 10 wt.% CNC.

The CNF based composites showed an increase in strength and stiffness with increasing cellulose nanofibril content. At the highest loading content of 70 vol.% the composites exhibited an improved strength and stiffness by a factor of 3.5 and 21, respectively while still maintaining an elongation of 5 %. The composites with 20 vol.% cellulose content confirmed a well dispersed reinforcement in the matrix through computed tomography. The composites had a stiffening threshold around 30 vol.% CNF content which coincided with the CNF concentration at which the effective stiffness of the composite was maximum. Furthermore, the strength and strain at break of CNF composites were higher than pulp based composites but the same could not be said for the stiffness. The CNC based composites on the other hand showed a strong influence of the CNC on yield behaviour and ductility of the composites, especially at higher CNC contents (10 wt.%). Dynamic mechanical analysis revealed indications of strong interactions between the grafted components and the matrix or between the grafted components themselves which was confirmed by the mechanical test data. However, the improved thermal stability of the modified CNC (almost 100 °C improvement) was not observed when they were introduced into the composites owing to alkalinity of the matrix that resulted in degrafting.