Mechanical Properties and Solid State Structure of Photodegraded Polyoxymethylene and Effect of UV-Stabilizers Modification

Abstract

Ultraviolet (UV) light exposure can lead to photodegradation of polyoxymethylene (POM), resulting in a change of its physical and chemical properties. Benzophenone UV absorber (UV-9), benzotriazole light stabilizer (UV-327), and hindered amine light stabilizer (LD-622) were used as UV stabilizers to improve the photostabilization of POM. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) were employed to characterize POM before and after aging. The change of its solid state structure during the aging process was investigated. The surface molecular weight and the mechanical properties of modified POM after UV aging were also determined. The results showed that the degradation of amorphous molecules mainly occurred at the surface while crystalline reorganization occurred in the interior part of the sample as a result of the UV irradiation, both of which led to an increase of the crystallinity. After UV irradiation for 1000 h, the elongation at break and notched Charpy impact strength were only 16.6% and 27.4% of the initial sample, respectively. However, 1% to 3% of the additives could reduce the chain scission and restrain the recrystallization of POM after UV irradiation. Furthermore, mechanical properties were maintained to a certain degree by adding the UV stabilizers.

Keywords:

• mechanical properties
• photodegradation
• polyoxymethylene
• solid state
• UV stabilizer

Acknowledgements

We would like to thank the generous financial support by the following grant: National Natural Sciences Foundation of China, Grant NO. 50873069.