Chemical-Resistant Resins for Process Equipment: Matching Materials to Aggressive Media

In process equipment, chemical compatibility is the first test a resin must pass. Tensile strength, heat resistance and cost are all factors, but ensuring process components can handle the harshest conditions is vital to success.

Aggressive media include acids and bases, solvents and hydrocarbons, oxidizers and industrial fluids, and the parts that handle them often run hot and under constant load. The right engineered resin exists for nearly every aggressive medium. The challenge is matching it to your exact chemistry, concentration, temperature and stress.How can chemicals attack plastics?

Plastics don’t corrode like metals. They degrade in several ways and that’s why choosing the right resin properties is so important. 

• Swelling. Solvents that are chemically similar to a polymer absorb into it, softening the material and changing its dimensions. Think about seals and threads. These are often the first to fail.
• Chemical attack. Strong oxidizers like nitric acid, chlorine and peroxides, as well as some strong bases, break down polymer chains and cause brittleness.
• Hydrolysis. Hot water and steam break down nylons, polyesters and polycarbonate over time.
• Environmental stress cracking (ESC). A chemical that barely affects an unstressed sample can crack a part under load or residual molding stress. 
• Permeation. Small molecules like HCl and chlorine can pass through an intact plastic wall and damage the metal behind it.

How do temperature and concentration affect resin selection? 

A resin that works at room temperature might not hold up in a hot process loop. As a rule of thumb, every 10°C rise can double the rate of attack. 

Concentration matters because dilute sulfuric acid is harmless to most engineering resins, but concentrated sulfuric acid attacks some of the best-performing ones. You’ll need a clear picture of what your equipment will handle, including upset conditions and cleaning cycles.

What are the leading chemical-resistant resins?

Polypropylene (PP)

• Cost-effective for water-based chemical service
• Can handle most acids, bases and salt solutions
• Low density 
• Its limits are temperature (around 80–100°C), oxidizing acids and aromatic or chlorinated solvents

PVDF

• Moldable fluoropolymer 
• Resistant to strong acids, chlorine, hypochlorite and hydrocarbons up to about 140°C
• Not suited for hot caustic, amines, ketones like acetone and solvents like NMP and DMF

PTFE

PTFE is nearly inert to all chemicals and serves to about 260°C. It can’t be injection molded because it doesn’t melt into a fluid state like normal plastics.

PFA and FEP

For a molded part with fluoropolymer-level resistance, PFA (to about 260°C) and FEP (to about 200°C) deliver nearly identical performance.

Polysulfone (PSU) and PPSU

Polysulfones handle hot water, steam, acids and bases well, which makes them common in sterilization and hot-water equipment. Ketones, esters and aromatic solvents can cause stress cracking. PPSU offers noticeably better solvent resistance than standard PSU.

PPS

PPS has no known solvent below about 200°C. It resists acids, bases, fuels and most organic chemicals while holding tight dimensions. Strong oxidizers are its main weakness.

PEEK

PEEK combines broad chemical resistance, service up to about 250°C and exceptional strength. When chemistry, heat and load are all at their peak, this is a great choice. Watch for concentrated sulfuric and nitric acid, as they will attack it. 

Chemical Compatibility Guide

Below are general ratings that apply at room temperature to unfilled resin. Grade, fillers and molding stress all affect real performance.

• Dilute acids: All resins above perform well.
• Concentrated sulfuric acid: PVDF and PTFE/PFA are top choices. PPS is good. Avoid PSU and PEEK.
• Concentrated nitric acid: PTFE/PFA are top choices. PVDF is good. Avoid PP, PSU and PEEK.
• Strong bases (50% NaOH): Nearly all resins perform well. PVDF declines as temperature rises.
• Chlorine and hypochlorite: PVDF and PTFE/PFA are the safest choices. PPS is limited.
• Aromatic solvents (toluene, xylene): PVDF, PTFE/PFA, PPS and PEEK are top choices. Avoid PP and PSU.
• Chlorinated solvents: PTFE/PFA and PEEK are top choices. Avoid PP, PSU and PPSU.
• Ketones (acetone, MEK): PTFE/PFA, PPS and PEEK are top choices. Avoid PVDF and PSU.
• Hot water and steam: PSU, PPSU, PPS, PEEK and PTFE/PFA are top choices. PP is limited.

What happens as the temperature rises?

Ratings can drop quickly as process temperature climbs. In 50% caustic, PVDF goes from good at room temperature to not recommended at 100°C. In concentrated HCl, PP and PSU both fail by 100°C, while PVDF holds up. PFA stays excellent across all of these conditions, and PEEK stays excellent in hot solvents.

How do I evaluate mixed chemicals for my equipment?

Your equipment often sees more than one chemical. Treat any blend as its own chemical until testing proves otherwise.

• Rate the mix by its worst component. One problem ingredient can affect the entire blend.
• Watch for surfactants and solvent carriers. These can speed up stress cracking and acid penetration.
• Include cleaning chemicals in your review. A weekly caustic wash often causes more damage than the process fluid itself.

Real-World Failure Modes

The below failures are common when engineers choose resins for strength or price instead of chemistry.

• Stress cracking. Polysulfone or polycarbonate parts crack at threads and inserts after exposure to solvents or disinfectants. The fix is PPSU, PPS or PVDF, combined with lower assembly stress.
• Swelling. PP in aromatic solvents swells, so seals leak and threads seize. A fluoropolymer, PPS or PEEK solves it.
• Caustic embrittlement. PVDF discolors and becomes brittle during hot clean-in-place cycles. A caustic-tolerant PVDF grade, PP or PFA is a better fit.
• Oxidation. PP crazes and cracks in hot hypochlorite or chlorine. PVDF or PFA handles oxidizing service.
• Hydrolysis. Nylon and polycarbonate lose strength in hot water. PSU, PPSU or PPS is the answer.
• Permeation. Acid vapor passes through a thin plastic wall and corrodes the metal behind it. Thicker walls or a lower-permeability resin prevent it.

In most of these cases the resin wasn’t a bad material. It was the wrong match for the combination of chemistry, temperature and stress.

Testing Protocols Engineers Should Require

Published compatibility data comes from unstressed test bars soaked in single chemicals. Before releasing a resin for production, require testing that reflects real conditions.

• ASTM D543 measures weight, dimensional and property changes after immersion. Practice B adds strain for parts under load.
• ISO 22088 evaluates environmental stress cracking. It’s especially important for polysulfones and other amorphous resins.
• ASTM D638 and ASTM D256 quantify tensile and impact strength retention after exposure.

Test in the actual process fluid at its full concentration range. Test at maximum service temperature plus a safety margin. Apply strain that represents assembly loads and molding stress. Test molded parts, not just bars, since knit lines and gate locations exist only in real geometry. Run tests long enough. Seven days catches quick failures, but critical parts deserve 30 to 90 days. Set pass/fail criteria up front. Common starting points are weight change within ±1–3%, at least 80% strength retention and no visible cracking.

Design and Molding 

The right resin can still fail if the part is designed or molded poorly.

• Reduce molded-in stress with uniform walls, generous radii and balanced filling.
• Place gates and knit lines away from threads, sealing surfaces and high-load zones.
• Use gas assist injection molding to reduce stress and sink in thick sections of large components.
• Build tooling for the resin. Fluoropolymers like PVDF require corrosion-resistant mold steel, and PPS and PEEK need hot, tightly controlled molds. Expert tool building protects performance over the life of the mold.
• Size the press to the part. Large housings and manifolds often require high tonnage injection molding, even at low volumes.

Choosing a chemical-resistant resin is an engineering decision that determines whether your process equipment runs for years without leaks, cracks or unplanned downtime or fails after a few months. 

At EnTech Plastics, we help engineers make that call with confidence. We provide engineered resin selection, expert engineering services, precision tooling and custom injection molding for large, demanding parts.

Facing an aggressive chemical environment or a part that keeps failing in the field? Request a free consultation and let’s solve it together.