Surface Tension Modification of NMP-based Paint Strippers

The increasing awareness of evposure to traditional paint strippers has prompted a search for altemativeproducts. Onegroup of such alternatives are formulations based on N-Methylpyrolidone (NMPkqn comparing NMP-based paint removers with more volatile products, the primary tradeoffs are stripping speed versus solvent inhalation, and product cost v e m wage cost. NMP-based paint removers work at a slower rate, but have dramQtically lower vapor pressures thus reducing the chances of solvent inhalation. In &ion, by lowering the sulface t e d n of these NMP fomrulas, the time required for their use may be decreased by as much as 40% Regarding cost, NMP blends may be more expensive to purchase, but approximately 40% less product k required to achieve similar stripping results. INTRODUCTION The solvents traditionally used in paint strippers include methylene chloride, methanol, acetone, and methyl ethyl ketone. In evaluating stripping speed, these products have some common properties that play a key role in their ability to quickly remove paint. All of these solvents consist of small, noncomplex molecules. This allows fast and efficient soIvent penetration of the cured paint or coating. They all have high vapor pressures resulting in fast evaporation rates. The quick evaporation of solvent aids in lifting paint from the substrate. They also have low surface tensions. This allows them to quickly "wet out" all surfaces, fill any surface pores, and begin immediate penetration of the paint film. In combination, these properties result in paint stripping formulas that can quickly and effectively remove most common paints and coatings. NMP, in comparison, has relatively different properties of molecular size, vapor pressure, and surface tension that result in slower stripping times. NMP is a larger molecule. As such, NMP simply requires more time to penetrate a given coating. NMP has a lower vapor pressure. After penetration of the coating, highly volatile solvents will lift paint as they flash back through the paint film. The low volatility of NMP slows this lifting process. NMP has a higher surface tension. The surface tension of NMP is nearly double that of other paint stripper solvents. If any of these key properties could be modified, perhaps the stripping speed of NMP could be improved as well. Molecular size is fixed, and although vapor pressures and surface