Effect of Carbon Black on Adhesion, Wettability, Roughness, Impact, and Hardness of Styrene Acrylic Polymer for Surface Treatment

Styrene acrylic polymer (SAP) coatings protect materials from damage. Their performance can be enhanced by adding microscopic materials such as carbon black (CB), which improves their surface energy and hardness. This research aimed to evaluate the effect of carbon black at concentrations of 5, 10, 15, and 20% using the casting method. SAP films with varying weight percentages of carbon black were prepared. The mixture was magnetically stirred at 25°C for 1 hour, then stirred in an ultrasonic bath for 30 minutes, poured into a 20 cm diameter mold, and dried at room temperature for 24 hours. The adhesion strength peaked at a 5% CB concentration, reaching approximately 590. However, higher concentrations caused a significant decrease in adhesion strength at 15% and 20% concentrations. Contact angles exhibited variable behavior, ranging from 86.93° at 5% to 35.53° at 20%, with a sharp decrease at 10% (54.52°). The surface roughness of pure SAP was 4.92 μm. Upon the addition of CB, the roughness peaked at 5% (9.69 μm), then decreased significantly with higher concentrations, stabilizing between 5.29 and 5.91 μm. Under increasing stress, films reinforced with 15–20% CB withstood the maximum device load (1880 g) without rupture, demonstrating high toughness. Hardness testing showed that CB affected the mechanical properties of the SAP. Hardness was highest at 5% CB (73.5°), with gradual increases and decreases thereafter, reaching 72.6° at 20%. The addition of CB to SAP improves mechanical properties and toughness up to a certain point (especially at 5%), after which further additives lead to decreased performance in adhesion and surface properties.