Herein, high density polyethylene (HDPE) matrix was applied as the polymer matrix for its excellent overall performance and low price. In the study, antioxidants (0.5 phr) and ultraviolet absorber (1 phr) were added into the polymer matrix (100 phr) to investigate their influence on UV resistance, respectively. The macroscopic properties and microstructure changes of the samples were both investigated through the characterizations of Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), mechanical properties and thermogravimetric analysis (TGA). This work also conceived the three methods of capturing free radicals generated by photoaging, decomposing peroxides generated by photoaging, and absorbing ultraviolet light to achieve anti-aging effects. The results showed that the UV absorber improves the UV resistance of the material better than the antioxidant. After irradiation for 600 h under the aging condition of 0.51 w/m2@λ = 340 nm, the samples added with UV absorber also still maintain their mechanical properties at a high level. For comparison, the samples added with antioxidants presents poor mechanical properties only after irradiation for 200 h. Besides, the crystallinity of HDPE and HDPE added with antioxidant significantly increased after irradiation, but the crystallinity of HDPE introduced with UV absorber presents slight changes before and after irradiation. Meanwhile, all the irradiated samples also maintained the original excellent thermal stability. According to the obtained results, the aging mechanism was also analyzed.

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UV resistance of versatile plastics has been received attention for a long time, especially of high‐density polyethylene (HDPE). It was studied systematically that hindered amine light stabilizer (HALS) with different molecular structures had an effect on the UV resistance of HDPE. The molecular weights of the two HALS were 423.7 and 2100–3000 g/mol, respectively. It was found that the low‐molecular‐weight HALS outperforms the polymeric one of HDPE matrix in UV resistances due to the different molecular structures. HDPE‐containing HALS with different molecular structures followed different degradation mechanisms during artificial accelerated aging. In addition, HDPE matrix composites with low‐molecular‐weight HALS show better mechanical properties than the polymeric one because of the decrease of delay of molecular chain fracture during irradiation. Therefore, HDPE matrix composites with low‐molecular‐weight HALS have better UV degradation resistance. However, polymeric HALS has the advantage of hard to move out of the sample surface.