A new way of synthesis for bimodal polymer suspensions with polymeric stabilisers
A crucial applications parameter for high setting speeds of wood glues is a high solids content of the dispersion. The limitation of the solids content is given by the maximum possible packing of the monomodal dispersion. For random closed packing this value is 0.63. In this case the viscosity of the dispersion becomes very high. This problem of a high viscosity at high solids content can be overcome by a multimodal or bimodal particle size distribution of the dispersion. In this article a new procedure for synthesizing bimodal vinyl acetate dispersions is presented by using tailor-made polymeric stabiliser systems. In a series of experiments it is shown that it is possible to produce dispersions with a bimodal particle size distribution and a high solids content in a short one-step semi-continuous emulsion polymerisation process by employing these tailor-made polymeric stabilisers. The use of a poly(vinyl alcohol) (PVA) blend consisting of high- and low-molecular-weight PVA leads to an emulsion polymerisation process where the bimodality can be easily controlled by varying the PVA ratio. A hydrophobic modification of the high-molecular-weight PVA containing additional alkyl chains leads to a good control of only small particles. A qualitative model is suggested for this emulsion polymerisation process. The “new” polymer dispersions show a high setting speed on wood that correlates to the particle size distribution and is comparable to that of high solids content dispersions made by other processes. A major advantage of the one-step process that is its easy control.
KeywordsPolymer suspensions Dispersion Polymeric stabiliser Emulsion polymerisation Poly vinyl alcohol Poly vinyl acetate Latex Bimodal Bidisperse Particle size distribution Setting speed
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