Development of Reaction Injection Moulded Polyurethane Foam Including Assessment of Densification and Reinforcement for use as a Structural Core in Rotationally Moulded Products

摘要

To improve the performance of specific rotomoulded products being developed at a local company, reinforcement of the hollow core of the products with reaction injection moulded polyurethane (RIM PU) foam was investigated. Improvement of the foam mechanical properties was also investigated, with density variation and the addition of short glass fibre reinforcement. Testing showed the foam's mechanical properties were not directly relative to density. When foam density was doubled from 300 to 600kg/m3, the tensile strength increased by a factor of 2.7 and the modulus by a factor of 2.5. For ME1020 (fibre type) 6mm chopped fibre reinforced foam, these increases were larger, at factors of 3.0 and 2.6 for strength and modulus, respectively. For 300kg/m3 foam, fibre made negligible difference to the tensile strength, but the ME1020 reinforced foam was found to have 29% higher modulus than the neat foam at the same density (for 5wt% fibre composites). The 101C (fibre type) reinforced foam performed poorly, even showing a decrease in strength when compared to the neat foam at 600kg/m3 (for 5wt% fibre composites). The bending creep properties of reinforced foam was found to be higher than that of the neat foam in most cases, with ME1020 fibre composite foam performing better than 101C fibre reinforced composites in all cases. 5wt% ME1020 fibre reinforced foam was found to have impact strengths over twice that of neat foams at the same density. Impact strength improvements were also seen for 101C fibre reinforced foam, but to a lesser extent for both foam densities tested.Morphological analysis of foam tensile fracture surfaces was undertaken and many interesting observations were made. Features such as cell elongation and fibre alignment with the foam flow direction were consistent with foam literature, but some unique features were observed. These include a localised 'string' cell packing trend, and also microscopic areas of localised plastic deformation in cell walls, which were visible as wrinkled surfaces on the foam cell walls. Modification of the (rotomoulded) skin to foam interface was investigated, as this parameter will likely affect the service performance of the whole product. Experimentation with various methods to increase the skin/foam interfacial shear strength was undertaken, and large improvements were attained with methods trialled and developed. These included adding particles to the rotomoulding charge, which became embedded in the inner skin of the moulded part, and protrude from the inner surface. These particles 'key' into the foam which fills the product's hollow core. Other interfacial shear strength improvement concepts for equipment to be developed were also proposed. One concept proposed is an innovative modification to plasma treatment equipment currently available, which could be used to treat the inner surface of hollow products, to improve the bonding between the inner rotomoulded surface and the foam. Another concept is proposed which may oxidise the inner rotomoulded part surface, but, only at the very end of the rotomoulding cycle, so that the bulk polymer is not degraded. The purpose of this deliberate oxidation is to achieve results similar to those attained by plasma or flame treatment currently used by industry for improving the wettability of PE products.