PSI - Issue 82

Lenka Markovičová et al. / Procedia Structural Integrity 82 (2026) 274 – 280 L. Markovičová et al./ Structural Integrity Procedia 00 (2026) 000–000

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polyamideimides (PAI) are widely used in structural, automotive, and electrical applications because of their excellent mechanical properties, thermal resistance, and chemical stability. However, when exposed to outdoor environments, these polymers are subjected to various degradation factors such as ultraviolet (UV) radiation, humidity, temperature fluctuations, and oxygen, which can significantly influence their long-term performance and durability, Kondo et al. (2022), Greene (2021) and Patil (2017). Ultraviolet radiation is particularly detrimental, as it initiates photooxidative reactions that result in chain scission, crosslinking, and oxidation of polymer macromolecules, Kondo et al. (2022) and Rajendran (2025). These reactions lead to a decrease in molecular weight, surface embrittlement, color fading, and crack formation. The intensity and rate of degradation depend on several factors, including the wavelength and intensity of the radiation, exposure time, the presence of stabilizers, and the polymer’s chemical structure, Shi (2016). In semi-crystalline polymers such as polyamides, degradation typically begins in the amorphous phase, leading to a progressive deterioration of mechanical integrity, Fayolle (2008). The incorporation of inorganic fillers or fibers is one of the most effective ways to enhance the resistance of polymers to environmental aging. Short glass fibers (SGF) are commonly used as reinforcement in polyamide matrices to improve stiffness, strength, and dimensional stability, Lou (2021). However, the presence of fibers can also affect the degradation behavior of composites by modifying the diffusion of oxygen and light through the material, as well as by influencing the stress distribution within the matrix during photochemical aging, Liao (2024). Several studies have reported that a higher fiber content can act as a UV shield, reducing the depth of photooxidation and delaying the onset of mechanical degradation, Liao (2024) and Brebu (2020). Nevertheless, the interfacial adhesion between the fibers and the polymer matrix remains a critical factor influencing the composite’s durability under UV exposure. The present study focuses on the characterization of degradation mechanisms in polyamide (PA) and polyamideimide (PAI) composites reinforced with short glass fibers under controlled UV irradiation. The objective is to evaluate the influence of fiber content on the mechanical, microstructural, and rheological properties of the materials, and to identify the relationship between UV-induced chemical changes and the observed macroscopic behavior. Understanding these correlations is essential for optimizing composite formulations and ensuring reliable performance of polymer components used in outdoor and automotive applications. 2. Experimental materials and methods The composite consists of a matrix—a mixture of polyamide and polyamide-imide—and a filler—glass fibers. The manufacturing designation of the glass fiber is GF: 672, with a fiber length of 4 mm and a diameter of 10 µm. Three types of composites were supplied, each containing a different filler content: 10%, 20%, and 30%. In addition, samples exposed to UV radiation were also available. These samples were subjected to artificial aging in a Cofomegra Solarbox 1500e UV chamber for 500 hours, where the light source was a xenon lamp. The hardness test was carried out according to the standard STN ISO 868 (64 0129) Plastics and ebonite — Determination of hardness by durometer (Shore hardness) using a THS-210 durometer, type D (Fig. 1).

Fig. 1. Durometer THS-210 type D.