Thermal Stability

The thermal stability was measured by TGA; unmodified PET showed a one-step decomposition at an average temperature of 424 ◦C (Figure 2a), whereas pure hydrogel of PHEMA obtained as a by-product from UV modification showed a loss of volatile compounds at 120 ◦C (<5%) and thermal decompositions at 285, 374, and 434 ◦C average temperatures (Figure 2e). Pure PHEMA hydrogel obtained by gamma irradiation showed similar steps of weight loss at average temperatures of 118, 286, 402, and 436 ◦C (Figure 3c); however, the percentages of weight loss were different. These differences in thermal decomposition may be due to crosslinking induced by gamma radiation forming C-C bonds increased the thermal stability of the hydrogel [21]. PHEMA decomposition occurred via a complex depolymerization mechanism [44]; therefore fabrics grafted with PHEMA by the photochemical method showed three decomposition steps similar to its hydrogel at 278, 360, and 445 ◦C (Figure 2b), whereas PET modified by gamma irradiation also showed three decomposition steps at 249, 311, and 444 ◦C (Figure 3b).

**Figure 2.** Weight loss and 1st derivate curves of (**a**) unmodified PET, (**b**) UV PET95:5:0.5 (67% hydrogel), (**c**) UV PET100:0:0.5 (96% hydrogel), (**d**) UV poly(HEMA-co-PEGMA) hydrogel, and (**e**) UV PHEMA hydrogel.

**Figure 3.** TGA curves of (**a**) unmodified PET, (**b**) γ60 PET100:0:50 (257% hydrogel), (**c**) γ60 PHEMA hydrogel, (**d**) γ60 PET90:10:50 (400% hydrogel), and (**e**) γ60 poly (HEMA-co-PEGMA) hydrogel.

These results allowed us to confirm the grafting of PHEMA onto PET fabrics. On the other hand, when poly (HEMA-co-PEGMA) was grafted, small differences in thermal stability were observed; pure hydrogel from the photochemical method showed the same values of thermal decompositions at 287, 378, and 440 ◦C but with different percentages of weight loss (Figure 2d), whereas pure poly (HEMA-co-PEGMA) hydrogel, obtained by gamma irradiation (Figure 3e), showed decomposition steps at 286, 376, 398, and 432 ◦C. PET modified with poly (HEMA-co-PEGMA) by the photochemical method showed three steps of decomposition at 242, 389, and 446 ◦C and PET modified by gamma irradiation also showed three steps of decomposition at 247, 389, and 445 ◦C. Results confirmed that the hydrogel were attached to PET fabrics.
