The paper presents the results of the analysis of physical phenomena associated with the degradation processes of the surface layer of polymeric materials. During the interaction disturbance of ultraviolet radiation, atoms are knocked out of the polymer chains, thus breaking the macromolecules, which leads to the disturbance in the structural stability of the materials. The standardised test samples obtained using the injection moulding method were subjected to the degradation process in natural and accelerated conditions in the UV Test device. The degradation process in laboratory conditions was carried out during 750 hours with the use of lamps with a wavelength of 313 nanometers and an irradiation level of 0.76 W/m ², which corresponds to a period of 2 years in natural conditions. Using of thermogravimetric TGA and differential scanning calorimetry DSC analysis, the influence of energy applied from lamps and the energy reaching the earth’s surface on the change of melting enthalpy ∆ H_m, quantitative index of the crystalline phase and the temperature of phase changes were determined.