## 3 Results and Discussion  
### FTIR Analysis  
FTIR provides information about the chemical functional groups present in the sample and allows us to monitor any changes due to the treatment. Treatment with NaOH generally caused degradation of the rubber chain, which resulted in some modifications towards the rubber chemical structure and generated more polar groups. NaOH surface treatment caused oxidation and aging of the rubber resulting in more functional groups that contains oxygen as carbonyl, carboxyl, and hydroxyl. These functional groups improve rubber polarity hence improves rubber hydrophilicity that helps enhancing the rubber polymer adhesion [11; 17]. Figure 5 shows the main absorbance peaks for the all treated and untreated rubber crumbs. The FTIR spectra of the treated rubbers shows changes in peak intensity, in which the peaks become more prominent as the treatment concentration increases. It can be observed that the spectra for both the untreated and treated rubber display peaks at 3400 cm\({}^{-1}\), which reflect O-H stretching hydroxyl group vibrations. The O-H peak intensity of treated rubber is higher than the untreated rubber, which shows the presence of more O-H groups and intermolecular hydrogen bonding [28; 44]. The O-H peak intensity gets higher for the 7% and 10% NaOH as it represents, the increased number of O-H groups caused by the extensive oxidation due stronger alkaline on the rubber. Notable peaks were also observed at wavenumbers of 2853 cm\({}^{-1}\) and 2924 cm\({}^{-1}\) for all treated and untreated rubber crumbs resulting from the alkyl stretch of C-H bond vibration. For these peaks, it can be observed that it has higher intensity for 7% and 10% NaOH treated rubber when compared to 1% and 4% NaOH because more intensive alkaline treatment further oxidized the rubber and induces the formation of more functional groups on the rubber surface [45; 46; 47]. Figure 5: FTIR spectra for untreated rubber crumbs and treated rubber crumbs with different NaOH concentrations. Note that in the spectra of the untreated rubber a weak band at 1756 cm\({}^{-1}\) appeared; however, with the NaOH treatment the peaks were more pronounced. The intensity of this carbonyl C=O stretch become slightly higher for 7% and 10% NaOH, which represents an increase in the amount of carbonyl groups due to more extensive surface oxidation by stronger alkaline [28; 30]. The carbonyl groups which are more hydrophilic had improved the hydrophilicity of the rubber surface which enhanced the adhesion between rubber and the polyester. A noticeable peak between 660 cm\({}^{-1}\) and 880 cm\({}^{-1}\) in the spectra can be observed for the rubber treated with 7% and 10% NaOH if compared to 1% and 4% NaOH, which signified the presence of more C-H bond stretching connecting to carbon-carbon double bond. The spectra also show that there are obvious multiple bands in between 1450 cm\({}^{-1}\) and 1750 cm\({}^{-1}\), indicating the existence of more C=C bonds [11]. Apparent peaks can be observed for 7% and 10% NaOH treated crumbs at 1429 cm\({}^{-1}\) that represent the decrement of the double bond C=C due to partial degradation of some constituents because of the because stronger alkaline treatment. The degradation of these elements due to physical changes in the rubber surface such as the formation of more micro-cracks and rougher surfaces. At 1215 cm\({}^{-1}\) a quite noticeable peak can be observed for 10% NaOH treated rubber, which is caused by the vibration of S=O stretching indicating the appearance of more sulphonic groups. The appearance of more sulphonic groups may be due to the effect of breaking of some of the sulfur cross-links due to the high concentration NaOH treatment [11; 28; 45; 46; 48]. Apparently, NaOH treatment caused oxidation of the rubber, thus creating more polar groups, such as carbonyl and hydroxyl groups on the rubber surface, creating a large number of functional groups to attach to the polar group on the polyester.