The mechanical, structural, and morphological properties of polystyrene under fatigue combined with accelerated aging were investigated by mechanical fatigue, gel permeation chromatography (GPC), gel percentage, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM).
The mechanical fatigue behavior was evaluated under load control (Instron universal testing machine 8874) following the ASTM-D3479 [13] standard. The experimental conditions used included a load rate of LR = 0.5, frequency of 5 Hz at 25°C, and 50% relative humidity. For each group, five samples of type 1 ASTM-D638 [14] were tested.
The microhardness test was carried out using a Shimadzu Microdurometer with a pyramidal penetrator containing a square diamond base with an angle of 136° in each of the specimens to assess the surface hardness, according to the ASTM E384-11 standard testing method [15]. A load of 0.05 kgf was used for 30 s.
GPC was used to determine the weight-average molecular weight (Mw) and polydispersity (Mw/Mn) of the samples, before and after UV irradiation on the investigated times. These GPC tests were performed on a Shimadzu chromatography system (RID 20A) at 25°C using PA-grade chloroform as both the solvent and mobile phase, at a flow rate of 1 mL/min. Mass standards of monodisperse polystyrene were used to calibrate the GPC system.
The percentage of gel produced by the radiation action, before and after exposure to UV-B, was determined by extracting the non-crosslinked fraction in a Soxhlet extractor following the ASTM D-2765 standard testing method [16]. Decahydronaphthalene P.A. was used as a solvent for 6 h under reflux (189–192 °C) at a rate of 40 drops per min. The insoluble fraction was dried at 110 °C for 12 h until the mass remained constant. The degree of crosslinking was estimated using Equation 3,