DSC Analysis

PET is a semi-crystalline polymer with a *Tg* at 80 ◦C and a *Tm* at 253 ◦C (Figure 4a); fabrics modified with PHEMA or poly(HEMA-co-PEGMA) by photochemical (UV) method and gamma irradiation showed small variations, which are highlighted in Tables 3 and 4, respectively. Pure hydrogels are amorphous polymers; the one obtained by UV treatment with 5% of PEGMA showed a *Tg* at 83 ◦C (Figure 4c), whereas the one obtained by gamma irradiation with 10% of PEGMA showed a *Tg* at 96 ◦C (Figure 5c). The modified fabrics showed different *Tg* values; in Tables 3 and 4, we can observe that the higher the PEGMA percentage, the lower the *Tg* and by UV treatment, the higher the EGDMA (crosslinker) content, the higher the *Tg* value.

**Figure 4.** Differential scanning calorimetry (DSC) curves of (**a**) PET, (**b**) UV PET95:5:0.25 96% hydrogel, and (**c**) UV PHEMA hydrogel.

**Table 3.** Results by DSC for PET fabrics modified with hydrogel, obtained by the photochemical method.


**Table 4.** Results by DSC for PET fabrics modified obtained by the direct gamma irradiation method.


**Figure 5.** DSC curves of (**a**) PET, (**b**) γ60 PET90:10:30 400% hydrogel, and (**c**) γ60 poly(HEMA-co-PEGMA) hydrogel.

On the other hand, the higher the gamma radiation dose at a given HEMA:PEGMA ratio, the higher the grafting percentage and the higher the *Tg* value; this as a result of a higher crosslinking effect. In the case of the melting temperature, it was observed that the *Tm* was maintained between 253 and 255 ◦C, which indicated that the crystalline regions were not affected by the grafting methods; therefore, the grafting was mainly performed in the amorphous regions of PET, independently of the method used.
