Studies On Stability And Viscosity Of Polymer/Polyether Polyols Suspension

Polymer polyols (POP) are a type of modified polyether polyols synthesized by grafting copolymerization of styrene (St), Acrylonitrile (AN) and/or other unsaturated monomers in liquid polyether, which are widely used to produce high load bearing flexible polyurethane (PU) foam and semi-flexible PU foam. Since using methods of 'Graft From'and'Graft through', POP have the polyether polyols as continuous phase while polystyrene-co-acrylonitrile (SAN) dispersed uniformly. Thus POP not only represent the original toughness of polyether polyols for PU foam, but also the rigidity of vinyl copolymer. POP with good stability, high solid content and low viscosity are preferred in both POP's preparation and polyurethane's production, which is vital to industrial production.This paper adopts graft copolymerization experiments to synthesize a serious of POP products to discuss the factors that affect POP's stability and particle size & PSD, and then the viscosity model of suspension system. The vinyl monomers using in this paper are styrene and acrylonitrile, while tert-amylperoxy-2-ethylhexanoate and dimethyl 2,2'-azobis (2-methylpropionate) as initiators.Firstly, the effects of experiment factors on system stability, particles size and PSD are studied, including macromer type and concentration, St/AN ratio, monomer /polyether ratio, chain transfer agent (CTA) concentration, temperature, initiator type and concentration, time and feeding methods. The experimental results demonstrate that macromer plays a decisive role in the stability of POP. Macromers with multi-branched-chain and high molecular weight are more conducive to the stability of the POP suspension. For the same macromer, particle size decreases and viscosity first decreases and then increased accompany with concentration increasing. The increase of the proportion of St can improve product color, particle stability, resulting larger particle size and low viscosity, but also the decrease of reaction rate and monomer conversion. The increased Monomer/polyether ratio and CTA concentration both can increase the PSD of POP. Besides, the increased monomer ratio results high solid content and CTA results low molecular weight. Temperature has great effect on reaction rate and particle stability. Initiator has few influences on particle size. For semi-batch process, a fast feeding rate significantly increases the particle size distribution, and the addition methods of macromer and chain transfer agent play a decisive role on the system stability.Secondly, we discussed several viscosity models to fit our POP suspension system. Based on the most suitable model of Quemada, an empirical equation is established to describe the viscosity of POP considering the effects of solid content, PSD and temperature. This expression can be given asFinally, the influence of shear rate on viscosity of suspension system is taken into consideration. POP suspension system is not sensitive to shear rate when solid content is less than 30%, but obviously behaves a shear-thinning—shear-thickening shear-thinning phenomenon while solid content is more than 30%, especially in suspension system of multimodal distribution.