## 3 Results
### Washability (Wet Scrub Resistance)  
Washability, or wet scrub resistance, is the ability of the paint film to resist scrubbing or wet abrasives without losing many paint components from the surface of the substrate. Washability was measured by counting the number of scrubbing and wet abrasive cycles until the entire paint film was finished or by measuring the weight loss of the coating after 1000 cycles [40; 41]. The high or low number of wet scrub or abrasive cycles indicates the ability of the paint film to protect the substrate from dirt or abrasion by water. The ability of the paint film to protect the substrate from scrubbing or wet abrasives is influenced by the performance of binders and additives as a cover layer [40; 41; 42]. Based on the evaluations carried out in this study, the type and concentration of binders play an important role in film formation, such as adhesion, various optical and mechanical properties, and resistance to exposure to solvents or chemicals [14; 43]. Figure 2 shows the paint washability of various binders, including commercial polyvinyl acetate (PVAc) based binders and modified and unmodified natural rubber latex (NRL). Commercial binder-based paints such as PVAc (sample PVAc-4) had the best washability (wet scrub resistance) at nine cycles for a binder concentration of 4%. In the paint based on the concentrated NRL of the binder (sample CNRL-4), the best washability values were obtained for only five cycles at the same binder concentration. CNRL-4 exhibits poor wet scrubbing and abrasion resistance. This is because NRL is a colloid that is not completely soluble in water, although it is inherently hydrophilic, which increases the sensitivity of NRL to water [8; 44]. The high water sensitivity in the CNRL-4 sample is related to the mechanical properties of NRL, which have poor porosity because its adsorption properties are influenced by the amorphous molecular structure [45]. NRL has an unsaturated bond where the unsaturated bond determines the polarity, which is very important in determining the adhesion properties of a natural rubber material and its derivatives [17; 32; 33]. The combination of the concentrated NRL properties results in a binder with suboptimal performance. The film is formed flexibly, soft with adhesion, and has low scrub and wet abrasion resistance [32; 46]. Figure 1: The FT–IR Spectra of NRL, NRL\(-\)g\(-\)MMA and NRL\(-\)g\(-\)St. The problem of using NRL as a binder can be overcome by grafting with polar materials, epoxidation, depolymerization to reduce the molecular weight of NRL, adding fillers, and combining NRL with synthetic polymers [8,32]. In this study, styrene (St) and methyl methacrylate (MMA) monomers were grafted in NRL. The purpose of grafting these monomers was to improve the adhesive properties of NRL through the formation of polarity sites. In addition, grafting certain monomers can also increase water resistance [8,32,34]. It can be seen in Figure 2 that NRL grafted styrene monomer (NRL\(-\)g\(-\)St) has increased the paint's resistance to wet rubbing and abrasion. The performance of NRL grafted with styrene reached the optimal point at the ratio of 20% styrene monomer (NRL\(-\)g\(-\)20%St) with a washability value of 11 cycles at the same binder concentration (Sample NgSt20-4). Grafting of more than 20% styrene monomer reduces the performance of NRL as a binder. The grafting of more than 20% styrene monomer reduces grafting efficiency and allows not all monomers to be grafted onto the NRL polymer chain. This is because the increase in the number of monomers grafted also increases the energy to form NRL and styrene polymerization. Many possibilities will occur if the concentration of styrene increases. In addition to requiring more energy to form polymerization, increasing the concentration of styrene monomers increases the chances of forming styrene homopolymerization. In addition, the excess number of monomers in styrene limits the NRL active site to bind paint components and link them to the substrate [47,48].