Polyurethane foam mechanical reinforcement by low-aspect ratio micro-crystalline cellulose and glass fibres

The effect of fibre length and fibre aspect ratio on the reinforcement of soybean-based polyurethane foams was investigated. Micro-crystalline cellulose fibres and 260-µm long glass fibres embedded inside polyurethane foams were studied separately. Using X-ray tomography, it was determined that short micro-crystalline cellulose fibres were found solely embedded within the cell struts of the polyurethane foam. The cell struts were reinforced by the micro-crystalline cellulose fibres based on composite theory. An attempt was made to predict the reinforcement by using existing micro-mechanical models including the rule of mixtures and shear-lag theory. The overall foam compressive modulus increased based on the reinforcement of the cell struts and correlated with the foam mechanics model developed by Gibson and Ashby. The intermediate length 260-µm long glass fibres were found to span cells in polyurethane foam and were not embedded within the cell struts. These glass fibres did not contact each other. The reinforcement performance of the intermediate length glass fibres was found to be worse than the short micro-crystalline cellulose fibres. Therefore, these intermediate length fibres that span cells should be avoided for use in reinforcement of soybean-based polyurethane foams.