Waterborne polyurethane dispersions (PUDs) are widely used in formulations ranging from coatings to adhesives to inks due to the excellent adhesion and film-forming properties they provide in low-VOC systems. Traditionally, cosolvents such as N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP) are used during the synthesis of PUDs. However, these solvents have been well documented in posing health, safety, and regulatory concerns. Eastman manufactures TamiSolve™ NxG, an ideal replacement cosolvent for NMP and NEP for PUD synthesis that reduces health risks, enhances physical properties, and facilitates cost savings.
What Is TamiSolve™ NxG?
TamiSolve™ NxG is a polar aprotic solvent with similar Hansen Solubility Parameters to NMP, providing good solubility for several types of polymers and making it an ideal replacement for NMP as a PUD coalescent solvent. Compared to NMP, TamiSolve™ is not classified as a cytotoxic, mutagenic, and reproductive (CMR) toxin and is not labeled as being hazardous to the environment. For a complete comparison of toxicity and environmental hazard classification between TamiSolve™ and NMP, refer to
this article.
Performance Advantages in Waterborne PUD Formulations
Beyond regulatory considerations, cosolvent selection plays a critical role in maximizing PUD synthesis efficiency, enabling broad formulation latitude, and optimizing final film performance. TamiSolve™ NxG demonstrates meaningful advantages over conventional pyrrolidone solvents in both dispersion and coalescence behavior.
Reduced Dispersing Agent Requirements
As polyurethane polymers are inherently hydrophobic, hydrophilic monomers such as dimethylolpropionic acid (DMPA) are commonly incorporated into polyurethane backbones to enable dispersion into water. When NMP or NEP is used, higher DMPA levels are often required to compensate for the polyurethane polymer’s limited solvency, which can negatively impact water resistance and mechanical properties.
TamiSolve™ NxG provides exceptionally high solvency for polyurethane prepolymers while remaining readily dispersible in water, enabling smooth dispersion at reduced hydrophilic monomer content. Studies have shown that prepolymers using TamiSolve™ NxG dispersed cleanly without flocculation and produced smaller average particle sizes (0.045 µm) compared to NMP-based systems (0.081 µm). Dispersions using TamiSolve™ NxG also demonstrated superior heat-aging stability, remaining clean after seven days at elevated temperature. This improved dispersion efficiency inherently allows formulators to reduce DMPA usage, helping better maintain physical properties.
Enhanced Coalescence and Lower Solvent Demand
Film coalescence is critical to achieving continuous, defect-free PUD films with optimal mechanical performance. Traditional formulations often require high levels of cosolvents, which act as coalescents, to achieve acceptable room-temperature coalescence, increasing VOC content.
Due to its high solubility for polyurethanes, TamiSolve™ NxG delivers significantly improved coalescence efficiency. Experimental results showed that only 1.75 parts of additional NxG were required to achieve room-temperature coalescence, compared to 6.0 parts for NMP and 7.0 parts for NEP. This reduced total solvent content to 23.05% of PUD solids, compared to more than 37% for NMP-based systems. Though TamiSolve™ NxG is not classified as a VOC-exempt solvent, this reduction in solvent content helps reduce the total VOC content of PUDs, which provides better compatibility with low-VOC systems.
Additionally, despite having lower cosolvent volume, dispersions using TamiSolve™ NxG demonstrated rapid dry-to-touch times and strong hardness development, ultimately matching or exceeding NMP-based systems, particularly under oven-dry conditions.
