Why pH Adjustment Alone Is Not Enough in EVA–PU Blending

In many waterborne formulations, pH adjustment is the  tool used to address EVA–PU incompatibility. While pH control is important, relying on it alone often leads to short-lived success and delayed failures.

Raising EVA latex pH from acidic to near-neutral conditions can reduce immediate instability when blending with anionic PU. However, excessive alkalization frequently weakens EVA particle stabilization, particularly in systems relying on nonionic surfactants or PVA. This can result in flocculation after 24–72 hours, even if the freshly blended system appears stable.

Strong bases such as sodium hydroxide introduce localized high-pH zones that disrupt particle surfaces and accelerate destabilization. Gentler neutralizers, including ammonia or amino alcohols, provide better buffering and reduce the risk of ionic shock. Even then, pH should be adjusted gradually and monitored carefully.

Another overlooked factor is ionic strength accumulation. Neutralizers, dispersants, surfactants, and functional additives all contribute ions to the system. Over time, cumulative ionic strength compresses electrostatic repulsion forces, especially in anionic PU dispersions,  delayed instability.

For industrially robust systems, pH should be treated as one control parameter among many. Blending order, additive selection, and compatibility buffers often play a more decisive role in long-term performance than pH alone.

Formulations that only remain stable under perfectly controlled pH conditions are unlikely to survive real production environments. Robust EVA–PU systems are designed to tolerate normal process variations without failure.

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