# Characterizing the Tensile Behaviour of Woven and Composite Fabrics under UV Exposure
## 4 Results and Discussions
### Tensile Properties Degradation  
The UV degradation suffered by engineered fabrics was further evidenced through FTIR spectrum dissolution. Figure 8 shows the FTIR spectra of the engineered fabrics under various UV exposure levels. The IR spectra are presented in the plot of absorbance against wavenumbers. The spectra of virgin samples were initially compared to reference spectra stored in the OMNIC software library databases to verify their polymer type. The spectral databases included a wide variety of reference spectral collections with detailed information which aimed to provide a more accurate comparison. Results indicated that the FTIR spectra of both samples closely resembled the characteristics of polypropylene atactic with a similarity of 87.84% (woven) and 86.81% (composite), in accordance with the [PERSON] polymer FTIR spectral library. The spectra similarity was characterized based on the reference absorption bands of polypropylene shown in Table 3[26; 29; 30; 31; 32]. With reference to Figure 8, the FTIR spectra were sensitive towards the climatic elements that generally altered throughout the time of day or month under the outdoor environment. Accordingly, during the sunshine hours, the FTIR spectrum closely approached the upper limit of 1, which indicated a maximum absorption of solar radiation. Conversely, during the raining hours and night-time, the spectra intensity approached the lower limit of 0, which indicated a minimal absorbance of solar radiation. However, this behaviour of spectrum intensity was not clear evidence for the UV degradation of polypropylene under long-term exposure. Polypropylene subjected to UV radiation undergoes a series of chain scissions in its macromolecules through the multi-stage complex reactions. Scheme 1 illustrates the simplified photo-oxidation process of polypropylene. The preliminary stage of photo-oxidation involves the formation of hydroperoxides (2), after which it undergoes hemolysis by the UV radiation under the conditions of oxygen availability to produce alkoxyl and hydroxyl radicals (3). Subsequently, reaction of alkoxyl radicals occurs through \(\beta\)-scission to produce ketones and primary radicals (4). These intermediate photoproducts, including free radicals, undergo further chain scissions which bring about deterioration towards the mechanical properties, such as tensile, shear, puncture resistance, etc. The final stage of degradation involves the photoproducts known as acetic acids in the form of solid and gas (i.e., volatile) phases. The formation of intermediate and final photoproducts from Scheme 1 can be tracked in the FTIR spectra (see Figure 8) through the corresponding absorption bands formed. In this research, the hydroxyl (O-H) and carbonyl (C=O) functional groups were used to monitor the extent of polypropylene degradation in conjunction with its chemical structural alteration, as shown in Scheme 1. Figure 7: SEM micrograph of composite fabrics at (**a**) Month 1, (**b**) Month 2, (**c**) Month 3, (**d**) Month 4, (**e**) Month 5, and (**f**) Month 6 of exposure. Figure 8a shows that the hydroxyl group (3800-3000 cm\({}^{-1}\)) formed a broad peak after the first month of outdoor exposure. The absorption peak in this region became notable under prolonged UV exposure. The development of a peak, indicating the presence of a hydroxyl group, served as evidence of the formation of hydroperoxides as the photoproduct in the early stage of photo-oxidation degradation (stage 2 in Scheme 1). Later, a significant peak was also observed due to the presence of a carbonyl group (1850-1650 cm\({}^{-1}\)) after the third month. This absorption band, specifically located at a wavenumber of 1713 cm\({}^{-1}\), was identified in Scheme 1 as acetic acid [33,34]. This photoproduct appeared to be increasing under prolonged UV exposure, which was observed through its remarkable peak formed after the final month.