PC vs PP chemical resistance is the question that decides whether a housing, valve or lab container survives its service environment. Polycarbonate is an amorphous engineering resin with outstanding clarity and heat resistance but a narrow chemical comfort zone. Polypropylene is a semi-crystalline commodity resin that shrugs off aqueous chemicals yet swells in hydrocarbons. Choosing between them is less about which plastic is stronger and more about which fluids the part will actually touch.
PC vs PP chemical resistance: what each resin tolerates
| Reagent | Polycarbonate | Polypropylene |
|---|---|---|
| Dilute mineral acids (10%) | Resistant | Satisfactory |
| Sodium hydroxide, up to 60% | Not resistant at 1% | Satisfactory at room temperature |
| Alcohols (ethanol, methanol) | Ethanol resistant; methanol attacks | Satisfactory at 21-49 °C |
| Acetone and ketones | Swells or dissolves | Surface attack at elevated temperature |
| Aromatic and chlorinated solvents | Swells or dissolves | Not recommended |
| Heptane, white mineral oil | Resistant | Not recommended |
| Hot water | Hydrolyses over time | Satisfactory |
Why polycarbonate fails: stress cracking and hydrolysis
Polycarbonate stress cracking is the failure mode buyers underestimate. PC can pass a coupon immersion test and still crack under applied strain — a snap-fit, press-fit boss or bolted bracket concentrates stress, and the same reagent that looked acceptable on the datasheet produces crazing within months. Ammonia-based cleaners, alkaline detergents and some alcohol-based flux removers all trigger it. Hot water above roughly 60-65 °C hydrolyses the carbonate linkage, which is why PC labware is rated near 65 °C and cannot be autoclaved. When a part must see alkalis, ketones, esters or aromatics, PC is the wrong resin unless stress is fully relieved and the grade is tested under load.
Why polypropylene holds up: non-polar and semi-crystalline
Polypropylene solvent resistance comes from structure. A non-polar, semi-crystalline matrix absorbs little water and resists aqueous acids, alkalis and alcohols; even 60% sodium hydroxide is satisfactory at room temperature. The trade-offs sit elsewhere: PP loses to oxidizing acids, and aromatic or chlorinated hydrocarbons attack it — the same solvent families that fail PC also fail PP. What looks like stress cracking in bleach is oxidative degradation, not environmental stress cracking, so stabilization and wall thickness matter more than stress relief. PP's ceiling is temperature, not chemistry: 90-100 °C continuous service versus 115-125 °C for PC, with heat deflection near 55-75 °C versus 124-137 °C.
Where chemistry meets the part: temperature, stress and duration
Datasheet ratings assume about 21 °C, unstressed coupons and short exposure. Real parts fail at corners: a rating that reads "resistant" at 20 °C can degrade at 60 °C, concentration doubles aggressiveness, and continuous immersion is harsher than splash. Test standards also differ by family: PP grades are commonly screened with ASTM D543 reagent exposure at 21 and 49 °C, while PC behavior is characterized under applied outer-fiber strain across days of exposure, so cross-resin chart comparisons stay directional rather than specification-grade. PC pp chemical compatibility decisions should therefore be made against the worst-case combination — highest temperature, highest concentration, longest contact and any molded-in stress — with immersion or strain-based data requested for the actual grade rather than the generic family chart.
How to choose between PC and PP
- Choose PC when the part needs clarity, impact strength or heat, and the fluid list excludes alkalis, ketones, esters and aromatics
- Choose PP when the part sees aqueous chemicals, detergents or disinfectants at moderate temperature
- Consider neither when fuels, solvents or oxidizing acids dominate; look at PA, POM or fluoropolymers instead
- When both property sets seem necessary, split the assembly: PC for the window, PP for the wetted body
Resin selection runs wider than two polymers: browse our plastic materials hub, or compare related pairs in our PC vs PMMA guide and PP vs PE comparison. Suppliers of both grades are listed in the company directory.
