Environmental Protection

Environmental issues have gained increasing im­portance over recent decades. The following is an example of a positive contribution to the environ­ment: The car manufacturing industry uses up to 88 lb (40 kg) of adhesive sealants in each vehicle. The main objective of this is to save energy in the form of fuel by means of so-called “lightweight design”, whereby less weight has to be moved over the lifetime of the car and so resources are saved (e.g. 3-liter car). On the other hand, the adhesives in this same example could burden the environment if there are residues left over from the application and any cleaning. At the end of the lifecycle of the car, the adhesive that was used must not adversely affect the recycling process and must be disposed of in accordance with regulations. In order to determine the effects on the environment, an environmental assessment is carried out. The expected concentration in the environment is calculated using a model. Simultaneously, the concentration at which no harm is expected to environmental organisms is deter­mined. The calculation models and determination methods are laid down in international standards. An adverse effect on or harm to the environment can be excluded with certainty if the Predicted Environmental Concentration is less than the predicted concentration for which no harm to environmental organisms occurs (Predicted No-Effect Concentration), taking into account safety factors.

  • Air: The emission of organic solvents is detrimental to air quality. As such, considerable efforts have been made by the adhesives industry over many years to switch to low-solvent adhesives and where possible solvent-free adhesives. There has been considerable success, and this has also been beneficial for health protection. Bonding today is responsible for less than 3% of all the solvent emissions in Europe. The few large-scale applications in industry operate with solvent-recovery plants.
  • Water: With dispersion adhesives there is a particular risk of contaminating surface waters. Organic polymers and prepolymers, although not easy to biodegrade, can be removed in biological treatment plants with the excess sludge. The use of these adhesives in handicraft work, in the home and for DIY work normally results in only relatively small amounts of adhesive ending up in large amounts of wastewater (communal treatment works). As polymers usually have low toxicity for water organisms and due to the very low concentrations of adhesives in the waste­water, an adverse effect on the treatment plant and adjacent surface waters (outfall) is not expected in this case. In industry, residual adhesive and rinse water must be disposed of in accordance with waste legislation.
  • Soil: When used by private individuals, liquid adhesive residues are usually collected in the hazardous waste collection boxes, but are also often disposed of with the rest of the household waste. The amounts involved here are however small. For industrial and commercial users, disposal must be carried out in accordance with the so-called waste code numbers (to be found on the safety sheets), which determine how the waste is disposed. Adhesive residues are normally disposed of as landfill or incinerated. Regarding the latter, specific contamination of the air by the incineration plants is not expected. The energy used in the manufacture of the adhesives can be partially recovered here.

Assessing The Environmental Impact of Adhesives

  • Production of Adhesives and Adhesives in Industrial Use: In industry, residues of cured adhesives and also non-crosslinked and liquid adhesives occur as waste. The former, as solid materials, are either directly passed on as waste for disposal, or are preferably passed on for recycling. In the least favorable environmental scenario they are disposed of as landfill. They are however usually recycled, either via composting or for energy recovery via incineration. Depending on how they have been treated, liquid adhesives are discharged with the wastewater and are either directly passed to a treatment plant or, if necessary, passed to a treatment plant after under­going a specific pretreatment. There they are bio­degraded or removed.
  • Adhesive in the Home: Adhesives used in the home have to be considered in different groups. Solid adhesive waste from the home such as hardened paper or wood glue is usually disposed of with the rest of the household waste. Water is usually used to remove water-soluble, hardened adhesives in the home, for example for removing wallpaper paste. This adhesive-con­taining water is disposed of with the household wastewater via the water treatment plant. The adhesive components, e.g. cellulose derivatives, which are dissolved to varying extents, can easily be eliminated under real environmental conditions, meaning that only very small amounts enter the outfall (river). When composting is used for recycling, cellulose decomposes slowly but thoroughly - as known for plant materials.

    Adhesives used in the home (e.g. roofing adhes­ives) or around the home (e.g. for the car) are exposed to processes that can wash out the adhesive, such as rain. This means that a small amount of adhesive ends up in drain water and then directly enters surface waters.

    Considering all the adhesives that are in use, the expected environmental concentration is determined. The most unfavorable scenario is assumed in order to ensure that all conceivable pos­sibilities have been taken into account.

Outlook

Adhesives as a whole do not represent a major environmental problem. Nevertheless, cured and non-recyclable residues as well as excess adhes­ive from applications are waste materials. These materials not only have to be disposed of, but also represent an unnecessary use of materials and resources. The principle of recyclable design, made possible by having detachable bonded joints, will be important in the future. Besides technologies for separating bonded materials, a further challenge of bonding technology will be resource-friendly opti­mization of production and application processes. It will be necessary to incorporate non-removable adhesive into future recycling processes. This will mean that the adhesive to be used for manufacturing a component will have to be customized to the recycling process at the end of the component’s lifetime.