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Getting stuck in. The case for ‘green’ glue
October 12, 2014
Shoes are generally built to last… no pun intended. They have to be tough and durable because they are a product which the consumer literally walks all over. Manufacturers are therefore keen to ensure that their product is both high in quality and robust enough to provide the longevity that consumers demand.
In today’s environmentally conscious market, more and more focus is placed on implementing processes that benefit both the environment and the workforce. One of the most hazardous aspects of shoe manufacture is the use of glue. However, much like licking your elbow or sneezing with your eyes open, it is impossible to manufacture shoes without using glue.
Most glues are solvent-based but there was a shift during the 1990s towards using less hazardous, water-based adhesives in footwear manufacturing. Despite some success stories (Kinney’s shoes in Pennsylvania managed to implement the use of water-based adhesives to great success in 1994), the general fear of soles tearing apart from their uppers meant that there was still a prevalent bias towards using solvent-based adhesives.
In 2005, one research (1) showed that workers in the footwear industry were at a higher risk of certain cancers with the most prominent being nasal cancer and leukaemia. This was generally due to their regular exposure to solvents in degreasers, cleaners, primers, and – in particular – solvent-based adhesives (SBA).
The highlighting of these potential health hazards led to renewed interest into the development of adhesives with no organic solvents – water-based adhesives (WBA). Follow up research, using control groups with both WBA and SBA showed that WBA were a better option for safeguarding the health of footwear workers. The big question was: ‘will the glue bear up to the stress and strains placed on the shoes?’
Bayer MaterialScience (2) have spearheaded the introduction into the footwear industry of ‘green bonding’ technology; their WBA is harmless to people and the environment. Its use effectively removes the risk of health damage from solvent poisoning and it has proved incredibly effective in its intended use.
It is important though to ensure that the surfaces intended to be glued are rough in order to achieve a ‘key’ for maximum adhesion. With the bonding surfaces ‘roughed’ the WBA is found to be at least as effective as SBA.
Hydrosoluble glue is milky white with an emulsion-like texture, but once dried it becomes transparent, unlike SBA which generally experiences a yellowing when dried. WBA can be applied to each of the bonding processes inherent in shoe production, for example, heel sets, molding EVA / Phylon midsole, attaching uppers, etc.
The first advantage of WBA is, of course, the obvious benefit of ensuring the well-being of your most important asset – your workforce. Use of WBA will greatly reduce the risk to your worker’s health and therefore maximise attendance and productivity. Another benefit to consider is the reduction of storage costs. WBA are less volatile than their solvent based counterparts and do not require special storage conditions as the risk of fire is greatly reduced.
As environmental issues continue to dominate the news, and as more pressure is brought to bear for companies to be more environmentally responsible, WBA certainly look to be the way forward for the footwear industry.
(1) Comparison of genetic damage in Brazilian footwear-workers exposed to solvent-based or water-based adhesive.
Heuser VD1, de Andrade VM, da Silva J, Erdtmann B. http://www.ncbi.nlm.nih.gov/pubmed/15866469