Chemical Resistance Applications
Resin floors have been used for many decades to provide chemically resistant protective coatings, generally for concrete bases but also for metal or other structures. The need for such chemical resistance is not restricted to the more obvious heavy chemical industries but can apply in a wide variety of situations. The range of aggressive materials may range from cleaning or sterilizing preparations, to oils and fuels, to food products or derivatives, to natural or synthetic fats and oils, to highly aggressive acids, alkalis and solvents. The function of the flooring may be to protect the concrete against direct surface erosion or to prevent attack on the reinforcement with consequent loss of structural integrity. Increasingly, chemically resistant floors have an environmental purpose of preventing surface liquids from contaminating the ground beneath the structure.
In either case it is essential, first of all, that the flooring is effectively impermeable, to prevent aggressive agents reaching the concrete below. And then, that the flooring is itself unaffected by repeated or continuous contact with the aggressive agent.
No one product will be resistant to all the possible contaminants encountered. Different resin types will be resistant to different classes of chemical and consequently the flooring has to be selected that is appropriate for the specific working conditions. This will require precise definition of what aggressive agents may be present but also how they are dealt with in general housekeeping. For example it is unlikely, simply for reasons of health and safety, that the most aggressive chemicals would be left in contact with the floor for any length of time before they are cleaned off.
There are a number of factors that will affect the resistance of a resin based flooring system to attack by chemical agents:
- The resin / polymer basis of the flooring
- The degree of cure of the floor system prior to chemical attack
- The thickness of the flooring
- The type and reactivity of the chemical agent
- The physical properties and concentration of the chemical agent
- Acidity / alkalinity / solvency / compatibility
What is a Chemical Attack?
In the broadest terms the attack of a resin floor surface must be considered to be the breaking down of the polymer structure such that it is unable to fulfill its function. This may become evident as erosion of the surface, softening or embrittlement leading to early wear, blistering or delamination. Secondary effects may occur such as the development of a superficial stain, the progressive yellowing of the base resin or the discoloration of a pigment. In some cases visual changes may not be serious if the long term durability of the floor is not affected but will be undesirable if aesthetics are important.
Method of Attack
There are a variety of methods of attack of a floor system, including:
Solvent attack: This is primarily a physical process where the solvent is absorbed into the body of the resin binder, giving rise to swelling of the surface and disruption of the bond structure. This disruption leads to a softening of the resin binder, increased wear and loss of film integrity. Each cycle increases the ease with which the solvent is absorbed resulting in surface wrinkling, progressive breakdown of the reason and delamination.
In the early stages of the attack this may appear to be a reversible process, with the coating “drying out”; however the damage is progressive and irreversible. The effect is limited to the area of spillage. The rate of breakdown will be a function of the type of resin polymer, its density of cross linking, the length of time that the spillage remains on the surface, and the nature of the attacking solvent. (Small molecule materials tend to cause far more damage than larger molecules).
Chemical attack by acid or alkali: Here the attack is primarily chemical in nature and is a result of the breakdown of the resin polymer by chemical reaction, leading to a weakening of the surface. This generally results in increased mechanical damage, loss of surface finish, increased wear and premature failure. This is generally a visible process in terms of the occurrence being localised to the area of the spillage, and is a “ top down“ process with increasing severity as a result of repeated spillage.
Resistance of the Binder to Chemical Attack
Certain resin polymers are more resistant to attack by chemicals than others due to lower reactivity or difficulty of the attacking agent to approach the polymer. There are a number of resin chemical types that can be used for this application, which then cover a wide range of flooring classes. The selection of type is dependent on the nature of the application and the performance requirements of the floor.
In general terms, the higher the resin content and the cross linked density of the system, the better the chemical resistance will be. The incorporation of specifically chemically resistant materials in a system can improve resistance to specific chemicals. It is important that any resin surface that is exposed to chemical attack is correctly mixed, applied and cured under the specified conditions for the period necessary to achieve full chemical cure. The premature exposure of a floor to certain materials may result in the permanent damaging of the floor and long term performance.
Level of Exposure and House Keeping
It is important to assess the level of exposure of a floor to spillages of chemicals. It should be borne in mind that the very nature of these materials places a duty on employers to ensure that proper house keeping and cleaning are undertaken in the event of a spillage. The presence of solvents can increase the risk of fire: the presence of spillages of acids or alkalis can give rise to burn hazards for staff etc. and can result in damage to plant and machinery.
Where chemical spills can occur it is vital the proper provision is made for the immediate removal of spillage in a safe and effective manner. This should be undertaken by trained operatives using the most appropriate methods for the materials concerned, followed by the cleaning of the surface, and the proper disposal of the waste generated. It is often not understood that the spillage of a 1 % aqueous solution on a surface can result in the exposure to far higher (30-50 %) concentrations as a result of the material drying out on the surface. The damage that these high concentration effects can cause far exceeds that which would be expected from repeated exposure to the 1 % solution. This in practice means that a surface should be thoroughly cleaned after a spillage and well rinsed to remove any residues, rather than that the surface spillage should just be mopped up.
Similarly the exposure of a surface to a single material at a given concentration may have very different effects if that material is mixed with other materials, this is particularly noticeable where materials are present that encourage the wetting out of the chemical on the surface (surfactants detergents etc.)
Chemical Resistance Testing
Historically there have been a wide variety of methods used for the testing of protective coatings, similarly there have been a number of ways of interpreting and describing this information. In general terms the methods fall into two groups, standardised methods and company specific methods. When considering the data that these methods generate, care must be taken to ensure that the method is relevant to the application that is being proposed. It should also be remembered that the tests are indicative, that they are undertaken with a specific laboratory grade material on a small test piece of the flooring product made under perfect laboratory conditions.
Methods used have ranged from swab tests where a swab soaked in the test liquid is placed on the surface of a resin flooring sample for a limited period and the effect on the surface assessed visually. At the other end of the scale many manufacturers used variants of an ASTM method in which cast cylinders of the resin flooring (generally 25 mm high x 25 mm diameter) are totally immersed in the test liquid for lengthy periods of time, often several years and the cylinders assessed visually before crushing them to give a quantitative assessment of the chemical resistance. However this latter method is much more severe than likely service conditions except in the case where resin coatings are used as tank linings.