A plastic component exposed to the wrong fluid does not always show it right away. When it finally fails, the chemistry of how is written into the polymer itself.
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Chemical attack changes the polymer itself — not just its shape. A solvent that swells and softens a part, an acid or base that hydrolyzes ester or amide linkages in the backbone, or oxygen that drives chain scission at elevated temperature all leave a chemical fingerprint that a stress-only failure never produces: a measurable drop in molecular weight, a shifted infrared spectrum, a changed crystallinity. That fingerprint is what separates true chemical attack from environmental stress cracking, where the polymer’s chemistry is largely unchanged and the damage is a physical crazing response to a specific stress-and-agent combination. Confusing the two leads investigations toward the wrong root cause — and the wrong party.
Each attack pathway leaves a distinct chemical signature — distinguishing them is what determines whether the cause was material selection, contamination, or misuse.
Absorption of an incompatible solvent swelling the polymer, reducing modulus and strength — reversible at first, permanent if low-molecular-weight species are extracted.
Water cleaving ester, amide, or urethane linkages in the backbone, accelerated by elevated temperature or pH — common in polyesters, nylons, and polyurethanes.
Oxygen, often catalyzed by heat or metal ions, attacking the polymer backbone and reducing molecular weight until the material embrittles.
Strong acids or bases directly degrading susceptible functional groups, often visible as surface etching, pitting, or discoloration.
A compatible-looking fluid leaching plasticizer or stabilizer out of the compound, leaving it progressively brittle without touching the base polymer itself.
Trace metal-ion or residual-catalyst contamination accelerating oxidative or hydrolytic breakdown far beyond what the base resin would show alone.
Chemical attack is confirmed by measuring what changed in the polymer itself, not by how the part looks.
A confirmed attack mechanism has direct consequences for several parties at once:
A sample of the actual fluid the part contacted, plus its safety data sheet and concentration, is often as decisive as the part itself. Do not clean, rinse, or discard either.
Chemical attack changes the polymer’s chemistry — measurable chain scission, a new carbonyl or hydroxyl peak on FTIR, a drop in molecular weight by GPC, or visible swelling and softening. Environmental stress cracking, by contrast, requires a sustained tensile stress and produces almost no measurable chemical change; the mechanism is physical, not chemical, and the polymer’s molecular weight is essentially unchanged before and after. The two are easy to confuse from a photograph and straightforward to separate in the lab, and the distinction usually decides whether liability falls on the material, the fluid, or the design that put the part under stress.
Often, yes, within a range. FTIR identifies the chemical signature left behind — the specific carbonyl, ester-cleavage, or crosslinking pattern a given class of chemical produces — and that signature can be compared against known attack profiles for solvents, acids, oxidizers, and other agent classes. It rarely names a single product, but it commonly narrows the candidate list enough to be cross-checked against what was actually stored, used, or spilled at the site.
By comparing the damage pattern against what the specified material is documented to tolerate. Established chemical-compatibility data and immersion testing under ASTM D543 or equivalent protocols show what a given resin should withstand from a given chemical class. If the damage is consistent with normal, expected exposure and the material still failed, that points to a material-selection error. If the damage pattern implies a chemical or concentration inconsistent with the specified service environment, that points toward contamination, misuse, or an undocumented process change.
Not necessarily, and that is what makes it dangerous. Softening, swelling, discoloration, or crazing are common but not universal — some attack mechanisms progress through internal chain scission with little surface change until the part is loaded and fails well below its expected strength. This is why mechanical testing and molecular-weight analysis matter even on parts that look intact: a part can be chemically compromised and cosmetically normal at the same time.
The part itself without cleaning or rinsing, and — critically — a sample of the actual chemical, fluid, or vapor the part contacted, along with its safety data sheet and concentration if known. The fluid sample is frequently as decisive as the part, because it lets a lab run a controlled comparison exposure rather than relying on reported concentrations or product literature alone.
Technical briefings from our work in this area.
Identifying the chemical on a failed part and proving it caused the failure are two separate tasks. What FTIR, thermal analysis, molecular weight and controlled exposure each establish.
readChemical resistance data is generated at one concentration, one temperature and no applied stress. Most compatibility disputes live in the distance between that test and the part in service.
readChemical attack is not one process. Solvation, extraction, hydrolysis and oxidation are chemically distinct, leave different signatures, and each implies a different exposure history.
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