Small scale mixing phenomena during reaction injection moulding

Small scale mixing and polymerization between reaction injection moulding (RIM) reactants which form polyurethanes or polyureas, were observed with microscopy. This provided resolution of phenomena which occur in the range of scales from about 0.1 μm to 100 μm, and times from second to minutes. Mixing of RIM reactants at such small scales may affect the rate and specificity of polymerization by establishing a short diffusional path length. When two drops of RIM reactant phases were contacted, it was observed that one phase often dispersed into the other, depending on the particular chemical system. Dispersion was also observed in material made using a small RIM machine. The scale of dispersion varied from ∼0.1 |Gmm in polyurea systems to ∼3 |Gmm in polyurethane systems. It is believed that interfacial chemistry and forces generated during mixing determine the scale of dispersion. The smaller the dispersion, the faster the rate of polymerization if diffusion is a limiting event. Thus, a change in dispersion size, caused by interfacial chemistry, is a mechanism which influences the rate of polymerization, and may affect ultimate product behaviour by altering a characteristic scale of segregation.