Plastic failure analysis: can chemical analysis show why a molded part cracked, yellowed or turned brittle?
Short answer
We can investigate chemical evidence consistent with cracking, yellowing or brittleness in a molded plastic part. The findings can narrow possible explanations, but chemistry alone does not establish the complete failure mechanism or assign responsibility. The useful comparison is an affected part and an unfailed part from the same batch or specification, with their histories recorded.
What are you really asking when a plastic part fails?
Did contact chemistry contribute to cracking or surface change?
Environmental stress cracking can involve stress acting with contact chemicals such as cleaners, lubricants or migrated plasticizers, without requiring a different base resin. We would look for foreign compounds near the crack and compare them with remote regions and the declared contact materials. Plasticizer or other small-molecule loss can contribute to hardening and brittleness, while surface enrichment can produce tackiness or bloom.
Do yellowing and brittleness point to ageing or the wrong material?
Oxidation and thermal ageing can leave oxidation products alongside changes in antioxidants and light stabilizers. Yellowing can involve antioxidant transformation products or pigment and filler changes, so color alone cannot identify its cause. A wrong or mixed resin may conflict with the declared polymer and filler pattern, while possible recycled-content clues do not prove a recycled fraction or its source.
Could contamination or processing residue explain the affected region?
Foreign inclusions and retained mold-release ingredients can introduce chemistry different from the surrounding plastic, but detection alone does not establish that they caused failure. Our polymer-additive guide addresses the ingredient package itself; this page asks how chemical differences relate to the failure question.
How would we approach a plastic part cracking analysis?
1. We would record the symptom, failure timeline, processing, storage and contact history, then define the affected and unfailed specimens so the comparison tests a specific explanation.
2. We would sample near the crack, farther away, and from surface and bulk separately, preserving location identities to distinguish local contamination from whole-part composition.
3. We would use FTIR to compare the principal polymer family and suitable oxidation-related features, producing a relative chemical comparison rather than an absolute ageing score.
4. We would use GC-MS, or GC-MS/MS where needed, for suitable volatile and semi-volatile compounds, plasticizers and solvent residues, identifying supported differences between regions and controls.
5. We would use LC-MS/MS and high-resolution LC-MS for accessible antioxidants, light stabilizers and their transformation products, checking retained ingredients alongside possible consumption patterns.
6. We would select XRF and XRD for relevant elemental and crystalline-phase clues, with ICP-MS or ICP-OES for suitable filler, pigment, catalyst-residue or foreign-element questions.
7. We would compare the findings item by item, stating which explanations the evidence supports, which it argues against within the tested scope, and which remain open.
Why can these techniques reveal chemical differences around a failure?
FTIR reads molecular-bond absorption patterns, so corresponding regions can reveal a different polymer family or relative oxidation-related changes when the signals are interpretable. GC-MS and GC-MS/MS separate suitable gas-phase compounds and examine mass-spectral evidence, helping distinguish accessible plasticizers and contact residues from the polymer background. LC-MS/MS and high-resolution LC-MS investigate suitable dissolved nonvolatile additives, with fragments and accurate mass helping assess candidate stabilizers and transformation products.
XRF provides elemental clues and XRD can distinguish suitable crystalline phases, while ICP-MS and ICP-OES investigate relevant elements after appropriate preparation. These observations answer different chemical questions; none measures the stress that acted on the part or uniquely establishes when a contaminant arrived. Matching sample regions and histories is therefore essential before treating a changed signal as evidence of the failure mechanism.
What will the failure-analysis report say, and what will it leave open?
The English PDF would give a conclusion card, component table, supported proportion estimates, data appendix and unresolved items, distinguishing observations from interpretations. Oxidation is compared relatively; missing controls, unequal histories and inaccessible ingredients can leave competing explanations unresolved. This study does not provide mechanical-property, fracture-morphology, impact or tensile testing, or lifetime predictions; we do not assign liability or issue conclusions for claims or litigation.
Which failed plastic parts should you declare before shipping?
New unused parts failing at inspection, assembly, storage or laboratory testing need declaration and SDS review, alongside an unfailed control. Parts removed from service are used goods and are not received from overseas. This includes field failures and end-user returns. If the part comes from an electronic or battery-containing device, propose the separated plastic part rather than the complete device. Solvent-based contact liquids are not received as supplied; declare them and propose an alternative specimen for review. Use our inquiry page and shipping guide; ship after agreement, payment and an acceptance number.
Which related guides should you read?
Our residue guide focuses on identifying surface material and candidate sources; Our good-and-bad batch guide explains paired composition comparisons across matched material states; Our molded-shell guide addresses base-polymer identification and comparison with specified candidate grades; Our flexible-PVC guide focuses on identifying plasticizer and stabilizer families within that material.
FAQ
Does finding a cleaner near a crack prove environmental stress cracking?
A cleaner-related compound near a crack is a contact clue; chemical evidence alone does not establish the stress state or prove environmental stress cracking.
Does a smaller antioxidant signal prove that the supplier added too little?
A smaller antioxidant signal can reflect consumption, migration, extraction or measurement response, so it does not by itself establish the original dosage.
What can you conclude without an unfailed control?
Without an unfailed control, we can describe supported chemistry in the affected part, but many differences and competing failure explanations cannot be resolved.