What is the chemical compatibility of polymers?
Chemical resistance is a property that is defined by a material’s reaction to short or prolonged exposure to chemical products. A strong reaction leads to more damage, while a weaker one causes less deterioration, allowing the material to retain its original characteristics, such as its mechanical properties.
A material that remains stable when in contact with a chemical product will therefore be described as chemically resistant to that product. However, it's important to note that a plastic’s degree of resistance is often limited by factors such as temperature and exposure time. In the field of polymers, chemical resistance is a prized property because plastics are often used to manufacture basins, tanks and parts intended for corrosive environments involving direct contact with various chemicals. In order to choose the right plastic for a specific application, it's essential to evaluate the environment in which it will have to perform. For example, the following factors should be considered:
- type of chemicals,
- concentration of chemical agents,
- temperature of chemicals
- and additional mechanical constraints.
These elements play a major role in a polymer's ability to retain its mechanical properties and perform at optimum capacity over long periods of time. However, even chemically inert plastics, i.e., those with a broad spectrum of resistance in terms of pH degrees and chemical types, won't be able to withstand all chemical agents. It's therefore essential to evaluate the agent(s) in question to choose the right polymer and ensure its chemical compatibility.
Main categories of chemical products that normally come in contact with polymers
- Acids (e.g., hydrochloric acid, sulphuric acid, nitric acid) pH < 7
- Bases (e.g., ammonia, bleach, and several types of detergents) pH > 7
- Solvents and alcohols (e.g., methanol, ethanol or gasoline)
Standard plastics that are resistant to chemicals
PVC (polyvinyl chloride)
Mainly used in the construction sector and often grey, polyvinyl chloride is a plastic frequently used in the manufacturing of pipes and basins as well as various plumbing and ventilation parts and accessories. It has the advantage of being easy to work with, glue and weld.
Like PTFE, polypropylene is a chemically inert, food grade approved plastic. It can therefore be used for applications that come into direct contact with food. This polymer also has excellent mechanical properties, including outstanding flexural strength. In addition, it's highly resistant to standard chemicals. However, it's better to opt for a specialized plastic such as PTFE or PVDF for applications that come into contact with extremely corrosive products. Inexpensive compared to its counterparts, polypropylene is an excellent option for manufacturing large tanks.
HDPE (high-density polyethylene)
High-density polyethylene is a plastic often recognized for being rigid, stable and easy to weld. This versatile material is frequently used in the food and medical industries because of its advantageous chemical compatibility. It's one of the main materials used in the design of rotomolded tanks destined to contain chemicals or corrosive agents, among other liquids. It also has an excellent resistance to acid solutions.
High-performance chemical-resistant plastics
Part of the fluoropolymer family, polyvinylidene fluoride, commonly known as PVDF, is a high-performance plastic used in specialized applications, particularly in the chemical, food and medical industries. It's frequently used in the design of parts and liners that require high chemical resistance. Moreover, its mechanical properties are superior to those of PTFE. In addition to its chemical resistance, it's also resistant to acids and other high-temperature liquids. It's used to line regular and galvanization tanks where highly concentrated chemical agents are present.
More commonly known as Teflon, polytetrafluoroethylene is a polymer that is part of the fluoropolymer family and often used for the most demanding applications. Being chemically inert, this polymer is known for its excellent chemical resistance in addition to being food grade approved. It tolerates sterilization cycles at high temperatures as well as aggressive cleaning. Thanks to its combined chemical and thermal resistance, it's used in a wide range of medical, pharmaceutical and food applications. Although much denser than most plastics, it remains relatively light and impact resistant.
FRP (fibre reinforced plastic)
Often reinforced with glass fibres, FRP is a composite material very different from the above-mentioned plastics. Indeed, it isn't used to manufacture tanks or mechanical parts, but rather to design structures that are resistant to corrosion. In terms of strength, FRP structures can be compared to those made of steel. Perfectly adapted to humid and corrosive environments, FRP structures can also be cleaned with aggressive products without losing their properties. To learn more about FRP grating structures, see our articles:
- FRP for a Water Treatment Plant
- Durable and Non-Skid Work Structures for the Food Sector
- 4 Questions to Help You choose the Right Structural Materials
Applications of chemical-resistant plastics
- Tanks and storage tanks for chemical products
- galvanization tanks
- Pipes and tubes
- Laboratory equipment
- Medical equipment
- Mechanical parts
- Pulleys and pistons
- Parts of food machinery subject to frequent cleaning cycles
- Channels and other structural elements.