One of the most important resources for determining which plastic should be used in a chemical environment is a chemical resistance chart for plastics. These charts show how compatible different plastics are with a variety of chemicals and other fluids that fall on all points of the pH scale, from milk to mineral oil to fruit juice. However, the chart only gives you a snapshot of how a plastic might perform — there are several other environmental factors that need to be understood and considered before you can make a truly informed decision.
Factors Accounted for in Chemical Compatibility Charts
There are three factors, or interactions, that just about all chemical compatibility charts for plastics can tell users about: chemical attack, environmental stress cracking and physical absorption. Knowing what these factors mean in the relationship between plastics and chemicals can go a long way toward informing your choice of plastics for different applications.
When a plastic and a chemical are not compatible, the chemical essentially attacks the plastic in a reaction that causes the polymer structure to break down. This occurs at a molecular level and causes the chains that bind the structure together to weaken, become more susceptible to impact and even fail. Part failure can be disastrous for any facility, so be sure to only choose plastics that are up for the job and monitor parts as instructed to ensure they get replaced or repaired when needed.
Environmental Stress Cracking
Chemical attacks are sometimes considered ESC (environmental stress cracking) when related to vulnerabilities in the plastic's structure. ESC occurs in conjunction with internal and external stresses on a plastic. Internal stresses are placed on a plastic part during fabrication and processing, while external stresses occur from the mechanical load on the part. So, when a chemical weakens the plastic's structure, the forces already at work on a plastic cause thin, spiderweb-like cracking that could seriously affect a part's performance.
This process is a bit different from a chemical attack since it doesn't affect the molecular structure of the polymers. However, it does seriously affect the physical structure of the plastic part. When chemicals are absorbed into the plastic, it can make the part go soft or brittle, fluctuate in weight and even change in dimension.
Factors Accounted for in Chemical Compatibility Charts
While chemical attack, environmental stress cracking and physical absorption are all serious and important factors covered by a chemical compatibility chart, plastics can be affected by a variety of other factors as well.
Temperature plays a massive role in determining how a plastic will interact with a chemical. You should always specify temperature requirements when choosing a plastic because it could influence the type of plastic or additional applications needed to craft a successful system. For example, polyolefins like HDPE and polypropylene function best at low to moderate operating temperatures. However, when temperatures get too high, they tend to go soft and even begin to lose their form. If a holding cabinet, tank or piece of food processing equipment will be placed in an area with extremely high temperatures, HDPE and polypropylene would not be ideal choices.
It's also important to know how long a part will be exposed to chemicals before choosing your plastic material — even chemical resistant plastics can begin to break down after long exposure. As such, it's important to maintain plastic parts by wiping away any spills and splatters that may occur. If fluids and chemicals will be sitting inside of a plastic tank or another part for extended periods of time, you should always "over-engineer," or choose a plastic that can more than handle your specifications.
A chemical in its pure form is very different from one that's been watered down. As such, it's crucial that you choose a plastic that can stand up to a chemical at whatever concentration specification you require. In some chemical compatibility charts, multiple entries will be shown detailing how well a polymer resists chemicals at different concentrations. If this is not the case, it would be best to consult with your parts supplier about what a specific plastic can handle.
Chemical Resistance Chart for Plastics from A&C Plastics
Many of the plastics offered at A&C Plastics are able to resist chemicals all across the pH spectrum. However, as we've explained, certain plastics are better at resisting certain chemicals than others. In the chemical resistance guide for plastics below, you'll see whether a plastic sustains no chemical attack or absorption, moderate attack or severe attack by the various materials listed. Moderate attack means that the plastic can handle exposure but will have a limited lifetime, while severe means the plastic will decompose quickly.
|Acetic acid, concentrated|
|Freon, Frigen (liquid)|
|Hydrogen sulphide (saturated)|
|Phenol (aqueous solution)|
|Phosphoric acid (concentrated)|
|Soap solution (aqueous solution)|
|Urea (aqueous solution)|
Continue Learning About the Chemical Resistance of Plastics
As you may have guessed from our name, A&C Plastics is ready to help you learn about everything plastic. On top of our chemical resistance guide for plastics, we have a treasure trove of other resources on all the chemically resistant plastics we offer and the qualities that make them great for an amazing variety of tasks and applications. If you want to learn more about any of our products, or about who we are as a company, contact A&C Plastics today.CONTACT US TODAY