Environmental Resistance of POM: Long-term Aging in Chemical and UV Exposure
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Environmental Resistance of POM: Long-term Aging in Chemical and UV Exposure
Like all thermoplastics, POM’s long-term durability is influenced by environmental exposure. Its behavior under chemical attack and ultraviolet (UV) radiation becomes especially important in outdoor, automotive, and chemically aggressive environments. Understanding how POM ages and degrades under these conditions is key to ensuring material reliability and long-term performance.
Chemical Resistance and Degradation Mechanisms
POM exhibits generally good resistance to many chemicals, particularly hydrocarbons, alcohols, esters, and solvents. It is also resistant to fuel, lubricants, and many types of cleaning agents, making it a popular choice in automotive fuel systems and industrial fluid handling components like bushings and blades.
However, its vulnerability becomes apparent in the presence of strong acids, oxidizing agents (such as bleach or nitric acid), and alkaline solutions at elevated temperatures. Exposure to these can initiate a degradation process that leads to chain scission, molecular weight reduction, and surface embrittlement.
One of the most concerning failure modes is environmental stress cracking (ESC), which occurs when mechanical stress is combined with chemical exposure, particularly in tight tolerance assemblies where surface tension is high.
In long-term applications, it’s essential to assess not only direct material compatibility but also the possibility of chemical leaching from adjacent components or sealing compounds that may trigger degradation over time.
UV Exposure and Photooxidative Aging
In outdoor or UV-exposed environments, POM is susceptible to photooxidative degradation. UV radiation breaks down the polymer backbone, generating free radicals that further react with oxygen in the air. This process leads to discoloration, surface chalking, and significant reductions in impact strength and elongation at break.
Without protection, unmodified POM parts may begin to degrade within months of continuous UV exposure.
Surface degradation can propagate internally, especially in thinner-walled parts. This is particularly critical in outdoor structural applications, such as agricultural machinery components (gears), window hardware (roller wheels), or exposed automotive components.
To address this issue, POM compounds can be stabilized using UV absorbers, carbon black, or HALS (hindered amine light stabilizers), which absorb or neutralize the damaging effects of sunlight. These additives extend the material's service life but must be carefully selected to avoid compromising mechanical or processing characteristics.
Service Life and Preventive Measures
While POM offers strong short-term and medium-term performance in many environments, its long-term reliability is dependent on material selection, additive formulation, and design considerations. For chemically aggressive environments, copolymer grades tend to offer better resistance than homopolymers. For UV exposure, UV-stabilized or pigmented grades are strongly recommended.
Where long-term exposure is unavoidable, designers should also consider protective coatings, mechanical shielding, or component replacement intervals as part of preventive maintenance strategies.
Summary
POM performs reliably in many chemical environments, showing strong resistance to fuels, alcohols, and lubricants, which makes it ideal for automotive and industrial fluid-handling parts. However, exposure to strong acids, oxidizing agents, or high-temperature alkalis can trigger degradation mechanisms such as chain scission, embrittlement, and environmental stress cracking (ESC), particularly in high-stress or precision assemblies. To ensure long-term stability, designers must evaluate not only direct chemical compatibility but also potential leaching effects from adjacent materials or sealants.
In UV-exposed environments, POM is prone to photooxidative degradation, which can cause discoloration, surface erosion, and loss of impact strength. Without UV stabilizers, degradation may begin within months, especially in outdoor applications like agricultural machinery or automotive parts. Using UV-absorbing additives such as HALS or carbon black can significantly improve resistance but must be balanced with processing demands. For extended service life, UV-stabilized or copolymer grades, surface protection, and planned maintenance strategies are essential.
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