# Characterizing the Tensile Behaviour of Woven and Composite Fabrics under UV Exposure
## 4 Results and Discussions
### Microstructure Analysis  
Visual inspection of the surface morphology of the engineered fabrics was essential. Prior to the SEM, the colour of composite fabric subjected to outdoor weathering was observed (by the naked eye) to be brown colour (originally yellow). However, the woven fabric was observed to exhibit no change in colour (originally black). The change in colour observed in the composite fabric was mainly contributed by the accumulation of dust on the polymer surfaces. This statement warrants further studies through SEM micrographs. Aside from the aforementioned, there was no discernible difference visible to the human eye. Figures 6 and 7 depict SEM micrographs of engineered fabrics at various exposure levels. Figure 6 indicates the SEM micrograph of an unexposed woven fabric with an even and smooth surface morphology. All fibres were positioned in a closely packed and well-aligned interlaced structure. The virgin sample showed no signs of degradation. After the first month of outdoor weathering tests, significant white spots with a rough surface texture were observed on the polymer surface under a magnification of \(\times\)3000. Such white spots were also observed in the remaining months of the weathering test (not shown here). Additionally, SEM micrographs captured at \(\times\)30 magnification indicated a minimum extent of degradation through the loosening of fibres at the edges after the first month, as shown in Figure 6. For the remaining months of weathering tests, SEM micrographs captured at \(\times\)30 magnification indicated a certain extent of degradation through significant changes in the polymer structure, specifically its fibre alignment. Where the fibres tended to spread apart from each other and become loose, this effect was more significant under prolonged UV exposure. In general, the fibres in UV-degraded woven fabrics showed a loose structural alignment after prolonged UV exposure. Figure 7a-f depicts the surface microstructure behaviour of composite samples. Similar to woven samples, the unexposed composite sample shown in Figure 7a indicates a smooth and even surface appearance with no degradation. The significant white spots were also present in the composite fabrics (see Figure 7b) after the first month, and subsequently decreased in the remaining months (see Figure 7c-f), which was associated with the formation of greater microcracks width. No degradation was observed at the end of the first month of UV exposure. Unlike woven fabric, the degradation mechanism was shown by the presence of microcracks (in the transverse fibre direction) that were observed after the second month of weathering testing. These microcracks continued to develop with a significant increase in width. At the end of the second month of exposure, microcracks with a maximum width of 165 nm were observed, and progressively increased to 478 nm after the final month. Figure 5: (**a**) Tensile retained strength percentage of woven and composite geotextiles in both machine (MD) and cross-machine directions (CD); (**b**) retained strain percentage of woven and composite geotextiles in both machine (MD) and cross-machine directions (CD). Geotextiles placed in the outdoor environment were subjected to ambient air conditions that consisted of particulate matter (i.e., PM10 and PM2.5) responsible for air quality regulatory purposes. Both PM10 and PM2.5 (i.e., particulate matter with diameters of 10 microns and 2.5 microns or less, respectively) were considered to be a part of the indicators in assessing the air quality index (AQI) of this research study. Other indicators comprising the AQI include gaseous pollutants such as ozone, sulfur dioxide, and nitrogen dioxide. Both engineered fabrics indicated a significant number of white spots on the polymer surface after outdoor weathering, which is attributed to the deposition of atmospheric particulate matter. This supports the preliminary visual observation.