Wednesday, 10 August 2016

Kiln Forming Myths 29 - Super Glue

The use of super glue in the kiln causes cyanide gas
This is not true.  But because it is such a persistent belief, a lot of detail is given below.  In short the precautions are: 

  • use the minimum amount, 
  • use an organic gas face mask, 
  • do not wear natural fibres or gloves, 
  • let the glue cure before placing it in the kiln, 
  • have the solvents at hand while using the glue.

Super glue is frequently used as a temporary fixative in assembly of kiln forming projects. There is some concern about safety, as it is known that super glue is made from cyanoacrylate, which it is feared will break down in the kiln into cyanide gas.

Greg Rawls, a certified industrial hygienist says

"I looked at the MSDSs for several forms of super glue. The main component is Ethyl 2-cyanoacrylate, which has a TLV of 0.2 ppm which is relatively toxic. [However,] the thermal decomposition products are carbon monoxide and carbon dioxide. I did not see a reference to cyanide gas. However, as I recall cyanide gas dissociates into elemental carbon and nitrogen at about 800 F. Since you use it in such small quantities, I would not worry about it. In my opinion the worst thing that could happen is you glue your fingers to the glass."

Safety issues

To treat the safety issues seriously and determine if you feel Greg Rawls' view is justified, you need to look at the issues of toxicity, reactions, adhesion of tissue, ventilation, first aid and decomposition products in the whole context.

The fumes from cyanoacrylate are a vaporized form of the cyanoacrylate monomer that irritate sensitive membranes in the eyes, nose, and throat. They are immediately polymerized by the moisture in the membranes and become inert. These risks can be minimized by using cyanoacrylate in well ventilated areas. About 5% of the population can become sensitized to cyanoacrylate fumes after repeated exposure, resulting in flu-like symptoms. It may also act as a skin irritant and may cause an allergic skin reaction. On rare occasions, inhalation may trigger asthma. There is no single measurement of toxicity for all cyanoacrylate adhesives as there is a wide variety of adhesives that contain various cyanoacrylate formulations.

The United States National Toxicology Program and the United Kingdom Health and Safety Executive have concluded that the use of ethyl cyanoacrylate is safe and that additional study is unnecessary. 2-octyl cyanoacrylate degrades much more slowly due to its longer organic backbone that slows the degradation of the adhesive enough to remain below the threshold of tissue toxicity, so the use of 2-octyl cyanoacrylate for sutures is preferred.

Reaction with cotton

Applying cyanoacrylate to some materials made of cotton or wool results in a powerful, rapid exothermic reaction. The heat released may cause serious burns, ignite the cotton product, or release irritating white smoke. Users should not to wear cotton or wool clothing, especially cotton gloves, when applying or handling cyanoacrylates.

Adhesion of the Skin

Various solvents and de-bonders can be used. These include:
·         Acetone, commonly found in nail polish remover, is a widely available solvent capable of softening cured cyanoacrylate
·         Nitromethane
·         Dimethyl sulfoxide
·         Methylene chloride
Commercial de-bonders are also available.

Warnings include:
·         It is a mild irritant to the skin.
·         It is an eye irritant.
·         It bonds skin in seconds.
·         Any skin or eye contact should be copiously flushed with water and medical attention be sought immediately.
·         Do not attempt to separate eye tissues – the bond will separate naturally within a few days.

·         Use goggles.
·         Do not wear cotton or wool clothing while using super glue
·         Ventilate the area well. Since cyanoacrylate vapours are heavier than air, place exhaust intake below work area. Activated charcoal filters using an acidic charcoal have been found effective in removing vapours from effluent air so the bench top air filters are suitable for use while using super glue.
·         Avoid use of excess adhesive. Excess adhesive outside of bond area will increase level of vapours.
·         Assemble parts as quickly as possible. Long open times will increase level of vapours.

Evaporation Effects
·         The effects of heating cyanoacrylate are not completely known. The flash point is known to be greater than 85ÂșC. As a precaution do not remain in the area of the kiln after that temperature has been reached.
·         The decomposition products are carbon monoxide and carbon dioxide. There is no reference in the literature to cyanide gas. It is highly unlikely that heat will cause the release of cyanide gas at any time during the heating. To be certain, you should make sure the evaporation of the glue is complete before firing the kiln.

See this tip for the use of super glue in kiln forming.