PCE is used as a solvent on a wide array of organic soils and contaminants. It is valued for its solvent capacity for clothing in the dry cleaning industry, for oil, grease and buffing compounds on metal parts and for baked-on carbon, dirt and oil on automotive parts and brakes. The following sections provide a brief overview of the alternatives for these three uses. For more detailed information, see TURI's "Five Chemicals Alternatives Assessment Study" on our web site.
Alternatives for Dry Cleaning
Since the 1960s, the dry cleaning industry has predominantly used PCE as its primary cleaning solvent. There are over 550 dry cleaning facilities in Massachusetts that report their activities as part of DEP's Environmental Results Program. These facilities use over 970 thousand pounds of PCE, resulting in the generation of 600,000 pounds of hazardous waste. With the emergence of viable alternatives, and with pressure from states, communities and building owners to move away from PCE, the amount of PCE used by drycleaners has been decreasing.
Dry cleaning performance is influenced by operating times, amount of clothes cleaned, quality of cleaning, compatibility with a wide range of clothing materials, pre-spotting requirements, and post cleaning handling (e.g., pressing). The overall performance of a dry cleaning process depends on soil chemistry, textile fabric type, transport medium (aqueous or non-aqueous), chemistry of additives such as detergents and surfactants, the use of spotting agents, and other process considerations. Additional properties to consider include evaporation rate and ease of purification through distillation. In addition, the solvent should not cause fabric to unnecessarily fade, shrink, weaken, or bleed color and should be compatible with detergents.
Several dry cleaning alternative chemicals and processes are currently available on the market. The most widely used alternatives are hydrocarbon-based systems from three manufacturers. Capitalizing on the success of these hydrocarbon systems, one manufacturer created a mixture of hydrocarbons (isoparaffins) with a hydrofluoroether and a perfluorocarbon to further enhance its performance (expanded cleaning capabilities) and improve safety (by raising the flash point). Another option uses volatile methyl siloxane as the cleaning solvent. Glycol ether-based alternatives are also used to a lesser extent.
Non-solvent based alternative dry cleaning systems currently on the market include carbon dioxide and wet cleaning. Carbon dioxide, as either a liquid or a supercritical fluid, can be used with specialized equipment to clean garments. Typically, liquid carbon dioxide is maintained under a pressure of 700 pounds per square inch and is combined with detergents specifically designed for this process. Companies are also using wet cleaning processes for more dry clean-only garments. These processes rely on water, detergent, conditioners and/or degreasers to clean the garment. Wet cleaning processes sometimes use specialized equipment designed to minimize temperature and agitation or to create a fine mist to deliver the water-based detergents to the materials to be cleaned.
Alternatives for Vapor Degreasing
Over the years, preferred vapor degreasing solvents have included chlorofluorocarbons (CFCs), trichloroethane (TCA), trichloroethylene (TCE) and PCE. CFCs and TCA were found to cause ozone depletion and were phased out under the Clean Air Act. Currently, the primary solvent used in vapor degreasing operations is TCE. PCE is used less often than TCE, but is still used in significant quantities.
For vapor degreasing, key physical properties include: low vapor pressure, low latent heat, low boiling point, low flash point, low surface tension and high solvency powers. Typically, an alternative solvent's performance must be equal to or greater than the current vapor degreasing solvent in order to be adopted. PCE is generally used in degreasing operations because of its high boiling point, which allows the solvent to remove soils and waxes that lower-boiling solvents may not. The stability of the chemical makes it particularly useful in airless degreasing systems where low emissions mean less virgin solvent and stabilizers need to be added.
There are many reasons why companies continue to use vapor degreasing rather than liquid phase (e.g., aqueous) cleaning such as:
- Aqueous-based cleaning processes are less efficient at producing clean and dry parts.
The high surface tension typical of aqueous cleaning formulations inhibits the ability of the cleaner to get into small, blind holes without implementing a significant process change. Solvents in the vapor form are more successful at cleaning these hard to
- The capital investment already put into existing equipment used for vapor degreasing can pose a barrier to change.
Switching to aqueous systems does, however, represent a feasible alternative to many solvent-based vapor degreasing operations, though it may involve additional process time and capital investment. Each company's cleaning needs are unique and a cleaning process should be specifically tailored for those needs. Information on the success of the TURI Lab's efforts in helping companies switch to aqueous-based vapor degreasing alternatives can be found at www.cleanersolutions.org.
For facilities that prefer to investigate vapor-phase solvent degreasing alternatives, there are many alternative solvents that have been researched and tested for performance in TURI's Lab and elsewhere. Effective drop in replacement solvent alternatives include n-propyl bromide (nPB), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), hydrofluoroethers (HFEs) and volatile methyl siloxanes (VMSs). These drop-in solvents have purchase costs that range from 3 to 43 times greater than that of PCE on a per gallon basis. Some savings may be achieved using the drop-in solvents through lower operating temperatures.
Because each of the solvent alternatives has some level of concern regarding health and/or environmental impacts, it is worth considering the following safer alternatives:
- Alternative cleaning processes such as aqueous or semi-aqueous,
- Working within the supply chain to eliminate hard-to-remove contaminants on the parts requiring cleaning, and
- Investigating process changes to prevent contamination and cleaning altogether.
Alternatives for Automotive Aerosols
PCE is found in a wide range of consumer aerosol products. For aerosol products PCE can be used as a solvent in a cleaner or spotting agent and a carrier in a glue, adhesive, lubricant or car detailing product. Some of the consumer aerosol products containing PCE listed on the Household Products Database, found at http://householdproducts.nlm.nih.gov, include; Liquid Wrench Super Lubricant with Teflon (65-80%), Gumout Professional Non Flammable Brake Parts Cleaner (50-90%), Hagerty Silversmiths Spray Polish (30.5%) and Champion Spot It Gone (45-50%).
A major concern for consumer and worker health and safety is the wide variety of automotive aerosol detailing products and cleaners that contain PCE in high concentrations. Engine cleaning aerosol products include those that are used externally and those used for more sensitive internal engine parts (e.g., carburetors and fuel injection systems). The major use in the automotive industry for PCE-based aerosols, however, is for brake cleaning. Alternatives for brake cleaning are available and include aqueous parts washers and aerosol products that do not contain PCE.
Performance considerations for effective aerosol brake cleaners include efficiency, drying, and residue. Aerosol brake cleaners allow quick repairs, only requiring spraying on of cleaner and wiping off of cleaner and soils. As part of the cleaning process, road dirt, grease and oils must be cleaned off and fibers from brake pads must be wetted and removed.
Many solvent mixtures can be aerosolized and used for brake and automotive parts cleaning or degreasing. Main components in some of the cleaners found on the market are heptane, C9-C12 hydrocarbons, toluene and xylene. Aqueous-based aerosolized products and aqueous parts cleaners have also proven to be effective.
The TURI Lab has conducted performance testing in the laboratory as well as field evaluations on alternative aerosol brake cleaners. Evaluation of formulations containing soy and acetone utilizing nitrogen as a propellant in a rechargeable and refillable spray delivery system are under way. Preliminary laboratory results indicate that these alternative brake cleaning aerosols have equivalent performance to PCE based products. Many of these alternative aerosol products are cost comparable to the PCE based products. For on these performance and field tests see the TURI Lab's website, www.cleanersolutions.org.
(For section references, see endnote #2)