A new route towards embedding fibrillated cellulose in a non-polar thermoset matrix without any use of organic solvent or chemical surface modification is presented. It is shown that microfibrillated lignocellulose made from cellulose with high residual lignin content is capable of stabilising an emulsion of unsaturated polyester resin in water due to its amphiphilic surface-chemical character. Upon polymerisation of the resin, thermoset microspheres embedded in a microfibrillated cellulose network are formed. The porous network structure persists after conventional drying in an oven, yielding a mechanically stable porous material. In an application experiment, the porous material was milled into a fine powder and added to the polyester matrix of a glass fibre-reinforced composite. This resulted in a significant improvement in fracture toughness of the composite, whereas a reduction of bending strength and stiffness was observed in parallel.
Keywords: composite reinforcement; microfibrillated cellulose; suspension polymerization; unsaturated polyester resin.