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What changes occur in the coating properties of polyester powder coatings after resin degradation
source：www.cnjindu.com | Release time：2026年09月19日1、 Changes in appearance and performance
Loss of gloss (decreased light retention rate): Chain breakage and micro roughness on the surface of the resin, reduced specular reflection, and gradual decrease in gloss; Slow in the early stage, degradation to a certain extent leads to a rapid decline in gloss.
Color change, yellowing/fading: photo oxidation generates chromogenic carbonyl groups, and the light colored coating shows obvious yellowing; After losing the resin coating, the pigment fades and the color difference Δ E increases.
Powdering (the most typical feature): The surface resin degrades and cracks, losing its wrapping around the pigment and filler, and white powder appears upon wiping, which is a characteristic phenomenon of outdoor aging of polyester.
Surface morphology defects: Microscopic appearance of micropores and pores; In severe cases, microcracks, cracks, and peeling may occur; The humid and hot environment is accompanied by swelling, and later local peeling occurs.
2、 Mechanical properties
Reduced toughness and brittleness: cross-linking network is disrupted, molecular chains become shorter, and fracture elongation is significantly reduced; The impact strength decreases, making it more susceptible to cracking due to impact.
Hardness change: There may be a slight increase in the early stage, but the hardness decreases after deep degradation.
Deterioration of wear resistance: The surface resin powder becomes more prone to abrasion due to friction.
Glass transition temperature Tg changes: cross-linking is disrupted, Tg decreases, and it is more prone to softening and sticking at high temperatures.
3、 Adhesion and substrate interface
Resin degradation, changes in coating internal stress, and gradual decrease in adhesion;
Moisture and salt ions are more likely to penetrate the coating/metal interface, resulting in foaming, coating bulging, and detachment from the substrate;
Once the interface is invaded by water or corrosive media, subsurface corrosion will occur.
4、 Chemical resistance and barrier (anti-corrosion) performance
Water absorption rate increases: The resin network generates micropores, making it easier for water to penetrate, further accelerating hydrolysis and forming a vicious cycle.
Chemical resistance decreases: acid resistance, alkali resistance, salt spray resistance, and solvent resistance deteriorate; Rust spots are more likely to occur in salt spray tests.
Barrier failure: The complete coating is the barrier layer; After resin degradation, the dense structure is destroyed, making it easier for corrosive media to penetrate the coating and reach the metal substrate.
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