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Photodegradation of Polymer Materials Used for Film Coatings of Controlled‐Release Fertilizers

The photodegradation of three types of polymer materials were studied: polyolefin, polyurethane (PU) and a copolymer of styrene, and butyl acrylate and methyl methacrylate (P(St-co-BA-co-MMA) latex). These polymers have been mostly used as film coating materials for producing controlled-release fertilizers. Among the three types of polymers, the P(St-co-BA-co-MMA) latex film degraded at the highest rate and the film surface became porous under ultraviolet irradiation. The polyolefin and PU films slightly degraded under the same conditions. The mass loss of the polymer latex film reached 26.7 g m-2 and the film thickness reduced by 27 μm after 432 h of irradiation under ultraviolet light. The tensile strength of the latex film decreased by 77% after 360 h of irradiation. Under ultraviolet irradiation, the weak cross-link chain in the film was broken and the connections between the microspheres were destroyed. A photo-oxidative aging reaction occurred in the -CH- groups of the microspheres, which weakened the tenacity of the latex film. This resulted in the easy release of microspheres from the film, which led to the loss of film mass, decrease in film thickness, and reduction in film tensile strength. The special mechanism by which P(St-co-BA-co-MMA) latex is significantly photodegraded makes this polymer a promising coating material for controlled-release fertilizers.