Expert Engineering Services

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.

When a component needs to operate in a high temperature environment, resin selection becomes a complex conversation. Getting it wrong can lead to component softening, mechanical failure and even equipment contamination. At EnTech Plastics, we carefully analyze the environments in which components must perform and we pay attention to all the details. What industrial machines run at a high temperature requiring specific resins? Ovens, dryers, motor assemblies, lighting fixtures and heat-adjacent industrial equipment all make the list. In this blog, we will take a look at how PEI, PPS, PEEK and other high-heat materials behave once tooling, molding conditions and long-term aging enter the picture. What should I know about maximum service temperature? Maximum service temperature is the highest limit of heat a material can handle safely for a long period of time. While resin datasheets showcase this number, that continuous use temperature describes a resin sitting in isolation under controlled conditions. It is not taking into account a molded, geometrically complex part carrying mechanical load, chemical exposure and thermal cycling all at once. Sustained mechanical stress or exposure to cleaning chemicals can contribute to a material fatiguing faster than with just steady-state heat. When engineers design around the full operating conditions the maximum service temperature is much more accurate and reliable. What is heat deflection temperature (HDT)? HDT measures the temperature at which a material begins to deform under a specified load. It is typically tested at 0.45 MPa or 1.82 MPa. This number gives a much clearer picture of real-world performance than continuous use temperature alone. It includes stiffness retention under load, not just chemical stability. This number matters most for components like motor housings, structural brackets near heat sources or any part that has to hold a tight tolerance or maintain a seal while hot. A resin can be thermally stable, meaning it doesn’t degrade or off-gas, while still going soft enough under load to warp, sag or lose critical fit. For parts that need to maintain dimensional integrity while under clamping force, spring load or its own weight at elevated temperature, HDT at the higher load value (1.82 MPa) is ideal. What is thermal expansion and why does it cause machine failures? When a part fails, coefficient of linear thermal expansion (CLTE), is often the root cause. Every plastic expands and contracts more than metal as temperature changes and when a molded component is mated to metal fasteners, inserts, or housings, mismatched expansion rates create stress at every thermal cycle. The result is loosened fasteners, cracked bosses around metal inserts, warped mounting flanges or seals that leak once the assembly cools back down from operating temperature. Designing for thermal expansion means thinking not just about the resin’s absolute temperature ceiling, but about how it will move relative to everything it’s fastened, bonded or press-fit against across the full expected temperature range. How does long-term thermal aging affect a machine? A resin’s initial mechanical properties are not indicative of what it will look like after years of sustained heat exposure. Long-term thermal aging describes how tensile strength, impact resistance and dielectric properties degrade over extended exposure at a given temperature. Some materials maintain their mechanical properties after thousands of hours at elevated temperature, while others degrade steadily, becoming brittle or lose impact strength well before they reach any dramatic failure point. If you need a machine to run for more than 10 years, think about industrial ovens, dryer components, motor assemblies, etc., thermal aging data is a vital piece to material selection. What are the differences in PEI, PPS, PEEK and other high-heat resins? Polyetherimide (PEI) PEI is a great choice for lighting components, electrical connectors and structural brackets near heat sources. Its natural transparency (in unfilled grades) is a differentiator for lighting and sight-glass applications. High heat deflection temperature Inherent flame resistance Dimensional stability Amorphous resin Because it’s amorphous rather than semi-crystalline, PEI doesn’t experience the same shrinkage variability tied to cooling rate that crystalline resins do. Polyphenylene Sulfide (PPS) PPS is ideal for motor components, pump housings and other parts exposed to oils, fuels or aggressive cleaning chemicals alongside sustained heat. PPS (glass-filled grades) is common in automotive and industrial motor applications where heat, chemical exposure and dimensional stability all matter at once. Semi-crystalline resin Solid chemical resistance Inherent flame retardance Strong dimensional stability Because PPS is semi-crystalline, its final mechanical and thermal performance is more sensitive to processing conditions than PEI’s. PEEK (Polyether Ether Ketone) PEEK is ideal for industrial machinery applications. Outstanding continuous use temperature Exceptional mechanical strength retention at elevated temperatures Excellent chemical and wear resistance Strong long-term thermal aging performance. PEEK earns its premium price tag in applications where failure isn’t an option. The right question isn’t whether PEEK can handle your application, it’s whether your application actually needs it. High-Heat Contenders Depending on the application, materials like polyamide-imide (PAI), liquid crystal polymer (LCP), and high-heat polyamides (such as PA6T or PA9T) are also on the list. LCP offers extremely low CLTE and excellent dimensional stability in thin-wall parts, making it a candidate for connectors and precision components near heat sources where PPS or PEI might not hold tolerance as tightly. Why does the molding process change the thermal performance? The same resin, molded two different ways, can deliver meaningfully different thermal performance in the finished part. This is especially true for semi-crystalline materials like PPS, where mold temperature and cooling rate directly influence the degree of crystallinity achieved. Higher crystallinity generally improves heat deflection temperature, chemical resistance, and dimensional stability. This requires molding at a higher mold temperature and longer cooling rates that a molder chasing fast cycle times might not be inclined to use. Achieving the crystallinity a demanding thermal application actually requires means controlling mold surface temperature, packing pressure and cooling time deliberately. Making the Resin Choice Specifying a high-temperature resin is a set of interconnected tradeoffs between continuous use temperature, HDT under realistic load, thermal expansion relative to mating components, long-term aging behavior, and how the molding process itself will influence the properties you actually get in a finished part. At EnTech, we work with engineers before a tool is ever cut. Whether you’re designing a component for a dryer interior, a motor assembly, a lighting fixture, or any other heat-adjacent industrial application, getting the resin selection and molding process right the first time saves you the far more expensive lesson of a field failure discovered after the part is already in service. Working through a high-temperature application? Talk to our engineering team about resin selection, tooling considerations and process controls for your next demanding project.