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Alternatives

There are a number of alternatives to nPB for degreasing, cleaning, and adhesive applications.

Degreasing

Alternatives to nPB for use in degreasing and precision cleaning operations include aqueous cleaning processes and other halogenated and non-halogenated organic solvents. For vapor degreasing, some key physical properties that dictate which alternative is appropriate include: low latent heat, low boiling point, high flash point, low surface tension and high solvency powers. Safer alternatives to solvent-based degreasing include aqueous and semi-aqueous processes, including the use of soaking or ultrasonic equipment.
The TURI Lab can help identify appropriate process- and application-specific alternatives. In addition, some facilities may be able to redesign their processes to eliminate the need for degreasing steps.

Other alternatives for metal degreasing include hydrocarbon solvents, such as terpenes, alcohols, acetone, ketones and acetates. However, exposure to these solvents can result in health effects ranging from acute (e.g,. eyes and respiratory irritation, dizziness, nausea, confusion) to chronic (e.g., liver and kidney problems). In addition, many such solvents are highly flammable. TCE is an effective metal degreaser, but is an unsuitable substitute for nPB because of well-documented health effects including carcinogenicity and neurotoxicity. Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) also pose significant hazards, such as ozone depletion (HCFCs) and global warming (HFCs). Other drop-in substitutes, such as hydrofluoroethers and volatile methyl siloxanes, are effective, but have been less studied in terms of their health and environmental impacts.

Dry Cleaning

The least toxic alternatives to nPB for both environmental and public health in dry cleaning applications are carbon dioxide (CO2) and professional wet cleaning systems. CO2 systems clean garments by using CO2 as either a liquid or as a supercritical fluid in specialized equipment. However, the equipment for CO2-based systems is increasingly difficult to obtain. In addition, CO2-based systems require highly pressurized gas, which creates its own work health and safety hazards. Professional wet cleaning is an aqueous process that uses computer-controlled washers and dryers, specifically formulated detergents and specialized tensioning equipment to clean and finish garments. While detergents may cause skin and eye irritation, TURI research and analysis has determined that professional wet cleaning is a safer and cost-effective alternative to solvent-based dry cleaning. TURI has worked with garment cleaning facilities in Massachusetts helping them to convert from perc to professional wet cleaning. Results show good cleaning quality, fewer health hazards, and natural resource savings.

Hydrocarbon-based solvents are another popular replacement solvent for dry cleaning operations. These solvents require process changes and present fire hazards. In addition, comprehensive toxicity testing has not been conducted. Toxicity studies to date suggest that current hydrocarbon-based solvents are safer than nPB. The volatile methyl siloxane solvent D5 (decamethylcyclopentasiloxane), is also a substitute solvent in dry cleaning, but is a combustible liquid, and so poses some flammability concerns. In addition, there is concern about persistence and bioaccumulation in the environment, and possible carcinogenicity from a study showing an increased incidence of uterine tumors in rats.

Adhesives

Alternatives to nPB used as the solvent carrier in adhesive products include both non-solvent and solvent substitutes. Hot melt adhesives appear to be the least toxic alternative that are suitable for some, but not all applications. Other non-solvent-based alternatives are available including aqueous-based carriers using latex or latex-synthetic blends. However, there are worker sensitization concerns associated with latex and some aqueous-based carriers may contain ammonia which can irritate the eyes, respiratory tract and skin. Additional process changes may be required if aqueous-based alternatives are used.

Some solvent adhesive formulations use acetone, and while they are generally low in toxicity they have a very low flashpoint so systems must be in place to minimize the chance of fire or explosion. Other solvent-based formulations may contain mineral spirits, petroleum solvents, petroleum distillates and naphthas that present additional human health and/or environmental concerns.

Solvent-based formulations using methylene chloride or TCE are undesirable alternatives to nPB-based products given their significant human health and environmental health impacts.

Endnotes

Onasch, J. A feasibility and cost comparison of perchloroethylene dry cleaning to professional wet cleaning: case study of Silver Hanger Cleaners, Bellingham, Massachusetts. Journal of Cleaner Production. 2011;477-482.