Thermal stability and sedimentation mechanisms of water-based polymer suspensions: a case study on friction modifiers

Particle suspension stability is essential for the performance of functional fluids, but sedimentation failure is often induced by thermal fluctuations. In this study, the thermal stability and degradation mechanisms of a water-based suspension comprising water, sodium carboxymethyl cellulose (NaCMC), inorganic particles, and acrylic polymer emulsion are investigated under alternating temperature cycles (80 °C and −20 °C). Results found that suspension stability is significantly reduced by thermal conditions. The rheological and physical properties, including viscosity, particle content, and density, are altered during this process. The ageing is identified in three stages: i) unaged—no significant changes; microstructure uniformly dispersed; ii) mild ageing—viscosity changed markedly while particle content and density stayed stable, “Flocculent” structures appeared; iii) severe ageing: viscosity changed at a maximum rate, with pronounced variations in particle content and density. The “flocculent” structure developed into “snowflake crystals”. It is revealed by mechanism analysis that the long-chain NaCMC network is degraded by thermal cycles. Consequently, the protective polymer network is destroyed, leading to irreversible particle aggregation and sedimentation. These findings provide insights into the thermal degradation of water-based polymer suspensions. A theoretical basis is offered for improving the stability of such a functional suspension.