One Day Symposium on Greener Adhesives and Sealants, held at the Society of the Chemical Industry, 15, Belgrave Square, London, 5th December 2007
This meeting was very well attended. There were very few spare seats in the auditorium. As usual, some useful discussions took place. The topic is of increasing interest as the world continues to discuss greenhouse gases, carbon dioxide and methane and other emissions and the sustainability of our current lifestyles compared to world resources and the size of the total world population. Action is required or these problems will become more pressing in the future if we do not deal with them now.
The first talk, with the very appropriate title of ‘Bio-resources for Adhesives and Sealants’, was given by Professor James Clark of the Green Chemistry Centre of Excellence at the University of York.
He started by stating that the term “greenness” is difficult to define. He then pointed out that 90% of all the chemicals we use come from oil, which we know is running out, and which will run out in the foreseeable future and even sooner if we take no action to reduce consumption. In view of the ever increasing use of cars and air transport and the growth in China and India in particular, we are clearly not even attempting to reduce consumption in total. Great efforts are being made to produce more efficient cars and aircraft but an improvement of ten percent followed by a doubling of vehicle numbers will only produce a large increase in total consumption and carbon dioxide output. Clearly new and renewable sources of power and useful chemicals are required.
Bio-fuel refineries were mentioned and the concept that waste was the next big resource was discussed. Prof. Clark mentioned wheat, straw and other plant and food waste as sources of raw materials. He stated that oil will eventually run out and that the only source of carbon, which is available in sufficient volume and with a sufficiently short life cycle, is from plants including trees, grasses, algae and crops; the term often used to describe the non-food part is “biomass”. The problem then is that we cannot grow biomass and food on the same area of land and we need the land to provide food for a world population that is too large but which would also like all these chemicals to be available to provide a desirable lifestyle. The problem is clearly greater than chemistry alone and requires political action on a world wide basis. A further problem, which leads us into the next talk, is that we are becoming more aware of the toxicity of many of the chemicals we use and have come to rely upon. These will become progressively more strictly regulated and require authorisation for their use as approved materials.
The second presentation, entitled ‘REACH a driver for change’, was given by Dr. Jo Lloyd, Technical Director of Reachready.
REACH is the EU regulation for the Registration, Evaluation and Authorisation of CHemicals that came into force in 2007. Its aim is to protect human health and the environment from the potential risks arising from the use of chemicals. She said that REACH applies to all substances whether used alone or in preparations containing other materials. It covers all uses of substances and all parts of the life cycle of these substances i.e. production, use in the production of other materials, safety in use and safe waste disposal or re-cycling.
Manufacturers and Importers have to register substances. Suppliers must assess risks to customers. It is intended to benefit responsible manufacturers if people insist on buying safer materials. It will also benefit downstream users, exposed persons and eventually the environment. All substances to be used will have to be registered and accurate information for downstream users must be supplied to ensure safe usage.
Companies will be expected to share data with competitors to minimize the cost of collecting the data required. This could be a problem as it is likely to affect EU competitiveness with the rest of the world, unless they adopt the same system and standards.
The intent is to concentrate on the most dangerous substances first but it will be a long and costly job. Real difficulty will occur in cases like Chromic Acid Anodizing where vast amounts of testing have been done and in service experience shows the results to be good but the chemical is dangerous and needs careful handling. The most dangerous materials will be eliminated from use if it proves technically possible to find alternatives. This will lead to some hard negotiations.
The third paper was given by Gary Critchlow of Loughborough University and was entitled ‘Friendlier surface treatments of metals’; a very timely topic in view of the previous one.
He discussed a number of surface treatments designed to be more environmentally friendly. Gary began by discussing the use of a seaweed-based treatment for stainless steel.
A long list of cleaning methods was given designed to remove organic contaminants from the surface. Sea Power was mentioned as a natural detergent based on seaweed. It needs to be combined with sodium hydrogen orthophosphate to obtain good results. The use of ultrasonics significantly increased its effectiveness. The use of alkaline and acid based etches was shown, by AES, to modify the surface oxide by enrichment of the chromium in the surface oxide but the thickness of the oxide layer was reduced by both acid and alkaline etches.
For hot-dipped galvanized mild steel (HDG) a treatment known as TEA-CO2 laser (Transversally Excited Atmospheric-CO2 laser) ablation was tested. It gave better results than degreasing. In the same durability trials, a commercially-available phosphate–based wet chemical treatment was shown to provide bond durability significantly inferior to the TEA-CO2 laser. In contrast, a chromate–based process gave markedly superior durability.
Alternative anodizing methods were also discussed. In this trial two methods were studied. These were electrolytic phosphoric acid de-oxidising plus sulphuric acid anodizing (EPAD plus SAA) and alternating current-direct current anodizing (ACDC).
Both approaches have demonstrated that they produce ideal bonding surfaces and provide structurally sound joints when bonded using an epoxy primer/adhesive combination to levels equivalent to the existing CAA (Chromic Acid Anodising) as indicated in a range of tests. Contact Gary for further details.
The fourth topic, ‘Developments in reduced toxicity sealants’, was presented by Steve Shaw of Dstl.
He suggested an alternative title, 'Will “greener” sealants provide the required properties for our applications'. This is a common problem. The more-toxic materials often do a better job. Meeting technical requirements with more friendly materials can prove difficult but is the ideal solution if it can be achieved and a worthwhile target to set.
More recent sealants were discussed and also the fact that fuel additives have changed over the years. Fuel tanks are a harsh environment for sealants where good performance is essential. Tests have been carried out using the following fluids: fuel, water, water plus fuel system icing inhibitors (fsii) and 100% fsii. Some discussion took place on the effect of one component in a mixture on the absorption of another. This had not been studied.
Sealants can be damaged if the solubility parameter of a fluid or mixture is close to that of the sealant itself. If allowed to dry out at any time, say during maintenance lay-off, the solubility parameter will vary depending on how much of the components of the fuel, with the highest vapour pressure, have evaporated from the mixture. It was stated that more recent sealant formulations exhibit a greater degree of uptake in 60% fsii /water in comparison to chromate cured systems.
The fifth topic entitled, ‘Adhesive technology and the sustainability of the environment’ was given by David Packham from the Materials Research Centre at the University of Bath.
This was a challenging topic because David pointed out that the philosophy of continuous growth, upon which our commercial/industrial policy has been based since Adam Smith, must now consider the fact that this world has finite resources. This means that we cannot sustain either an ever-increasing population or an ever-increasing demand from the existing population. Neither can we continue to contribute ever larger amounts of carbon dioxide and methane to an already polluted atmosphere.
These are philosophical/political issues that scientists, engineers and politicians can no longer ignore. They must be dealt with in conjunction with politicians as we have reached a point where Engineers and Scientists can no longer be sure of solving these problems. We can try to deal with technical issues but we cannot increase the size of available resources.
A useful definition was presented that says, “Sustainable development is development that meets the needs of the present without affecting the needs of future generations to meet their needs”.
Clearly our present consumption of oil does NOT meet this very sensible principle. When it runs out it is going to be very difficult to power all our existing transport and heating systems using solar power, wind and wave power and other renewable resources. How much more land shall we need for agriculture if we cannot use tractors? We shall need to plough our fields with horses that will need fields of grass to provide their power. That same land cannot be used to grow bio-fuel or to feed humans.
Moving on to adhesives the use of new polymers derived from plant sources was discussed. It is possible to derive polyurethanes from plant sources and also epoxies. This is good news to many of us who use these products. The bad news is that they may be more expensive and require good quality agricultural land to produce them; polyhydroxyalkanoates are possible alternatives to polyesters.
David then discussed the use of energy to produce these materials and showed tables of data to show that an energy crisis is approaching fast. He then discussed pollution and concluded with the worrying thought that most adhesives are at present derived from non–renewable resources: mostly oil. He recommended a full life-cycle analysis to ensure not only efficiency in use but lower environmental impact. This could usefully be applied to all products.
Taxation and subsidy systems need to encourage the right decisions to be made in terms of environmental and sustainability factors. He concluded by saying that despite some changes that can be effected in this way, as long as the economic system seeks continuous (exponential) growth, adhesive technology will not be sustainable. I agree and think it applies to every other technology as well. A very thought provoking topic that deserves serious thought and action.
The sixth topic, ‘Industrial Adhesive Product Development and Sustainability’ was presented by William Hally from Henkel Product Development in Dublin.
This company covers a wide range of chemical activity of which the adhesive brands (including Loctite, Teroson, Hysol and Liofol) are some of the ones that concern us. Loctite now includes Hysol who make high quality aerospace adhesives. William used almost the same definition of sustainability as David Packham.
He added another useful thought, “Sales and Profit should be achieved in a socially responsible manner”. These issues are important because good companies wish to be in business for the long term. Sustainability is therefore as essential to their survival as to the rest of us who are their customers. Within a company, the task of product development groups is to maintain their product range, develop new products and accept responsibility for the chemistry of new products. This means that new regulations on dangerous chemicals may mean their removal and thus create a need to find acceptable alternatives that give the same or better performance. Henkel operate “watch lists” and try to get early warning of materials that may need to be replaced. They incorporate changes required by REACH. William mentioned that some company doctors are in contact with insurance companies and may adopt a stricter attitude than regulatory bodies. Occasionally a supplier may be concerned enough to stop supplying a particular product.
He said that at the moment, industrial customer drivers are product efficiency, functionality, quality and cost; this could expand in the future to include environmental/sustainability drivers but there are few concrete examples. However, end users are concerned for their own safety. He used the example of an Irish supermarket study of cleaning products where cost was of primary importance to consumers when compared to the environment as they would not choose to pay increased prices.
He then discussed the removal of lead from solders and phthalates from adhesives but these were removed by regulation not by customer choice. He concluded by saying that customer needs were unclear. I guess this is because we all want improvements but don’t want to pay for them as most budgets are tight. This could be an increasing problem that requires legislation to provide a “level playing field”. William concluded by saying that sustainability is a core value at Henkel, that core values translate to clear directions, and that Regulatory pressures and chemical re-classifications are drivers for change and the pace of this change is increasing.
The seventh and final topic for the day, was entitled ‘Dis-assembly of adhesive joints for re-cycling’ and was presented by Professor Allan Hutchinson of Oxford-Brookes University.
With much legislation on re-cycling one of the problems with adhesive bonding is that dismantling prior to re-cycling is difficult using the present materials. Cars and other vehicles in particular are expected to be almost completely re-cycled at the end of their service lives. This is likely to be extended to other products. The labour and energy costs of re-cycling also need to be considered and minimized by design. Making vehicles last longer could help. This could also mean making parts that need maintenance or replacement much more easily accessible and ensuring spares availability for longer periods.
Techniques for dis-assembly of bonded joints include mechanical destruction (difficult), solvent methods (atmospheric problems) and the use of thermal energy (reduces adhesive mechanical properties).
The choice of technique depends on the nature and number of adherends and whether the parts are to be re-used or re-cycled. Methods need to be easy to use, low cost, rapid, give clean separation, produce no hazardous by-products and cause minimal damage to the adherends. It is important that reverse bonding procedures do not affect the performance in service of the adhesives.
Thermal methods were discussed. These cause thermo-expandable microspheres (TEM), incorporated in either the primer or adhesive layer, to expand at particular trigger temperatures. The nature of a microsphere system, marketed by De-Bonding Ltd, was discussed together with the debonding mechanisms and associated process variables. Preliminary experimental results were presented for short-term bulk adhesive and bonded joint performance. Long-term durability tests have yet to be done.
This seems a useful method but will mean re-qualification of many existing adhesives if these microsphere systems are incorporated and this will be costly. However, it should make it possible to comply with legislation on re-cycling.
It was another interesting day that raised many philosophical issues that need to be addressed.
Of particular interest is the need to minimise the use of energy, toxic materials and the emission of undesirable gases into the atmosphere and to develop the use of materials from sustainable natural renewable sources. The management of the world in a sustainable way is clearly a very serious issue and the sooner we take action the better.