Evaluating alternatives

What makes a good drycleaning process?

Dow's drycleaning industry development leader
and perchloroethylene product steward offers her views

By Janet Hickman
Drycleaners need a means of evaluating information about new cleaning processes, many of which are proposed as alternatives to perchloroethylene drycleaning.

Here are a few tips to help you when you study this information.

Over the years, as cleaning technology has developed and the political climate has changed, the key objective of the fabric care industry has remained constant: to clean and finish garments and household textiles to a condition as close to "like new" as possible.

In meeting this objective, any method is acceptable as long as:

• It provides an acceptable quality product.
• It is economical.
• And it can be used in a safe and environmentally sound manner.

People with a long memory of drycleaning may remember when professional cleaning was done in centralized locations using benzene, carbon tetrachloride, or petroleum solvents, as well as water, and the neighborhood cleaning shop was a drop off point often with tailoring the main on-site occupation. Turn-around time was generally a week or more.

After the Second World War, consumers demanded faster turnaround. To meet this, the industry decentralized.

The introduction of perc helped: here was a solvent which was non-flammable and safe to handle, and which used equipment economical enough to be installed in the neighborhood drycleaning shop. Same-day service became a reality.

Since that time, perc drycleaning has been able to carry drycleaners through a variety of changes in fashion -- even including the polyester leisure suit.

The 1990s have brought a new health and environmental challenge. New methods of tracing extremely small quantities of chemicals in the environment -- in urban air, groundwater, soil and the atmosphere of both the workplace and the home -- have led to stringent laws governing waste emissions and waste disposal. And they have led to consumer advocacy groups who call for no trace chemicals in the environment.

The industry, fortunately, is responding successfully to these challenges. No matter which cleaning process is used, specific cleaning, equipment, safety and environmental considerations must govern any textile care process:

Cleaning considerations

• Good solvency properties for a significant portion of common soils.
• Compatible with other textile treating products.
• Does not damage textiles.

Equipment considerations

• Process equipment must be economically feasible.
• Must be able to concentrate, recover, reclaim and recycle the solvent.

Safety considerations

• Flammability.
• Toxicity.
• Carcinogenicity.

Environmental considerations

• VOC (i.e. contributor to smog).
• ODP (i.e. depleter of stratospheric ozone).
• Global warming potential.
• Acid rain.
• Bioaccumulation.
• Groundwater considerations.

Choosing the appropriate cleaning process for your application requires that you give careful consideration to all the factors set out above. The process of choice, then, should be the one which addresses all these considerations in the most overall economic manner.

Advantages of perc
Perchloroethylene has been the principal drycleaning solvent for a number of years because:

• Its high solvency (KB value of 90) dissolves most of the oils, grease and fats the drycleaner is faced with. Detergents and spotting chemicals have been developed for the other stains and soils.
• Perc's low viscosity (0.84 centipoise) and low surface tension (32 dynes/cm) allow it to penetrate fibers rapidly to dissolve soils.
• Because perc is hydrophobic, it doesn't swell the fibers.
• The high density of perc (13.5 lbs./gal.) not only facilitates mechanical action in the washing cycle, it also helps the separation of solvent from water in the recovery process.
• Its high evaporation rate (1.5 compared to n-butyl alcohol, the standard) provides for reasonable drying times at moderate temperatures.
• Most importantly, it was perc's virtual non-flammability that led to its wide use when decentralized drycleaning plants became standard in the industry after World War II.

Addressing the hazards
Comparing perc, then, to our list of considerations, we find that it fills the needs of drycleaners in almost all respects.

The key concerns are, as with any chemical, understanding the hazards. In this case understanding the toxicity issues and whether it is or is not a human carcinogen.

To address these hazards, a perc-based process has to control emissions so that employees and the public get as little exposure as possible, thus minimizing the potential risk.

As far as toxicity is concerned, there is virtually no risk to employees or customers of a drycleaning plant when the solvent is handled properly.

Most current regulations are based primarily on toxicology studies, including cancer studies, which were done on laboratory animals. However, different species of animals, including humans, metabolize chemicals differently. Thus, one cannot assume that a cancer effect in one animal species will predict cancer in another species without understanding the metabolic processes in the species.

Perc producers, trade associations, industry experts and many independent scientists agree that when you consider all the available scientific evidence, there is no cancer risk to humans when perc is used properly. In fact, the science advisory board of the U.S. Environmental Protection Agency (EPA) has concluded that "there is no compelling evidence of human cancer risk" for perc.

The practice of including an assessment of the metabolic differences of species is now acknowledged by regulators, and it is just now being included in the process regulators follow for risk assessments.

Producers of perchloroethylene, committed to the continued safe use of this solvent, support the industry in two ways. They are funding additional long term health studies which will ultimately help answer these complicated questions. They are also working with regulatory agencies to make sure that the most advanced scientific methods are used to evaluate perc.

Issues with other processes
For other drycleaning processes, the considerations may call out issues which are quite different from those involved with perc. For example, they might include:

• In the case of a water-based system, the development of very controlled drying equipment to minimize shrinkage, and waste water recycle equipment to manage the demand for fresh process water.
• For petroleum-based solvents, the development of higher flash-point products combined with appropriate explosion-proof equipment, as well as appropriate solvent recycling and maintenance procedures.
• For liquid carbon dioxide technology, the development of appropriate safety features for high pressure operation, and new detergents.
• When evaluating any alternative cleaning process, it is important to study it in light of all the considerations, making sure that all aspects of the process have been accounted for.
• When we take advantage of the positive attributes of perchloroethylene while rigorously addressing ways to minimize potential exposure, drycleaning with perc turns out to be the one procedure which most closely meets the industry's objectives. But we need to continue sound scientific studies which will clarify the solvent's toxicity properties, as well as design further improvements which will minimize potential risks.

Janet Hickman is Dow's drycleaning industry development leader and perchloroethylene product steward. This article was originally published in the summer 1997 issue of Dow's Spot News.

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Date created: December 2, 1997