Also known as Methylene Chloride or DCM, Dichloromethane (CH2Cl2) is a clear, colourless, volatile liquid with a sweet ether-like odour that is commonly used as a solvent in sprayable and hand applied adhesive systems. The use of DCM in products can sometimes be a hot topic with the clients we work with; so here we discuss the pros and cons of Dichloromethane.
Contact adhesives are made by dissolving natural or synthetic rubbers in a solvent. When the adhesive is applied to the substrates the solvent constituent evaporates leaving behind a tacky glue line which will grab to the substrate and to itself (contact adhesives are applied to both surfaces unless making a temporary bond).
A FAST DRYING SOLVENT
Dichloromethane's volatility and ability to dissolve in a wide range of organic compounds is what makes it very useful to the adhesive industry. In chemistry, a volatile substance is defined as a substance which can readily change from a solid or liquid form to a vapour form, i.e. having a high vapour pressure and a low boiling point. Dichloromethane will evaporate very quickly, meaning adhesives containing DCM will general be those with the fastest drying times. The flash off (evaporation) time for dichloromethane based adhesives is very fast, so when you have applied adhesive to both surfaces it is ready to bond almost immediately. A non-chlorinated product would require additional time to 'tack up' before it is ready to be bonded.
As a liquid, Dichloromethane does not have a flash point and will not make a flammable vapour-air mixture until it reaches temperatures well over 100°C. It also has a very high auto-ignition temperature of 556°C which means it can be stored safely at room temperature and is not easily ignitable like other volatile solvents. Replacing dichloromethane with other solvents in a product will increase the flammability of the adhesive and it's ability to form vapour-air mixtures that are flammable.
HEALTH & SAFETY CONCERNS
Even though Dichloromethane is the least toxic of the simple chlorohydrocarbons, it still has serious health risks. Being a highly volatile solvent makes it an acute inhalation hazard. It can also be absorbed through the skin. Symptoms of acute overexposure to dichloromethane via inhalation include difficulty concentrating, dizziness, fatigue, nausea, headaches, numbness, weakness, and irritation of the upper respiratory tract and eyes.
The International Agency for Research on Cancer (IARC) has concluded that there is enough evidence in experimental animals, but not in humans, that dichloromethane can cause cancer. Therefore, they have classified dichloromethane as being suspected of causing cancer in humans, products that previously carried the safety phrase 'Possible risk of irreversible effects' now carry the even scarier safety phrase 'Suspected of causing cancer'.
SAFE WORKING PRACTICES
It should be noted that working with any chemicals poses some kind of inherent risk, and health and safety considerations can be minimised by safe working practices. Including but not limited to...
To summarise, Non-chlorinated products are bit slower and more flammable, but do not contain dichloromethane, a probable carcinogen.