When approaching a new polyurethane cleaning application, it is important to first determine the class of polyurethane materials to be cleaned. A wide variety of polyurethane materials are used in industrial and commercial applications, and the multiple chemistries employed give the various polyurethanes unique physical properties and solubilities.
The second consideration in developing a polyurethane cleaning system is possible reactivity. It is critical that the cleaning materials employed (solvents and additives) do not have the potential to react with the polyurethane prepolymers and/or curing agents. In general, peroxides, along with primary and secondary amines and other reactive substances, should not be used.
The third consideration is selection of the optimum solvent system for the defined cleaning task. Selection of the best solvent is based on the following criteria: efficient cleaning of polyurethane residue materials; low toxicity; good environmental profile (non-HAP solvent, non-ozone depleting, non-SARA reportable); sustainable sourcing and price stability; and cost-effectiveness over the useful life of the solvent.
A fourth consideration in selecting the cleaning solvent and additives is whether the spent cleaning solutions will be recycled or disposed of offsite. Spent solutions are most commonly recycled via vacuum distillation. It is therefore necessary to select materials that have appropriate, moderate boiling points. Also, any high-boiling additives that are not distillable would have to be replenished in the clean, recycled solvents.
The fifth consideration towards an efficient polyurethane cleaning process is to perform laboratory-scale cleaning trials on these materials, while replicating the stage of cure at the cleaning site, i.e., prepolymer, partially cured polymer or fully cured polymer. Once the optimum solvent or solvent blend has been determined, the cleaning process can begin.
Parts Cleaning
Small parts, such as spray guns, nozzles, fittings, hoses, etc. are best cleaned by submersion in a bath of the cleaning solvent. Parts are soaked in the bath for the length of time required to dissolve and loosen the resin. Some form of mechanical action, such as solvent circulation through a pump, stirring or ultrasonic vibration can speed the cleaning process. Parts cleaning is usually done at ambient temperature. Moderate warming of the solvent often aids removal of the resin. Once the resin is partially dissolved and loosened, scraping and/or brushing can be effective.
Process Equipment Cleaning
Large process equipment, such as reactors, tanks, mixers, etc. are best cleaned by circulating the cleaning solvent around a closed loop. The solvent is pumped from a holding tank and sprayed at high pressure onto the surfaces to be cleaned. A spray ball or series of nozzles are typically used to spray all surfaces. The solvent then drains from the vessel back to the holding tank. The cleaning solvent is heated to the maximum temperature allowable, considering safe handling procedures, thermal stability of the solvent and system materials of construction. Process pump lines, filters, meters, etc. are cleaned by circulating the cleaning solvent through them, in a closed loop configuration. Maximum allowable solvent temperatures are used, as described above.
A well designed engineering approach to a polyurethane cleaning requirement will result in an effective, safe, environmentally responsible, costeffective and sustainable cleaning process.
Jerry Vasek is vice president of Sales for Vertec Biosolvents, Inc. (Downers Grove, IL). He can be reached at (630) 960-0600, or visit the Web site at www.vertecbiosolvents.com.
According to Custom Fabricating and Supplies, a cleanroom is ideal for converting, die cutting, laminating, slitting, packaging and assembly of medical-grade products.
