Contact Angle and Surface Free Energy of PVC and Eudragit RS 100 in Binary Mixture Study

Abstract

Polyvinyl chloride (PVC) and ammonio methacrylate copolymer (Eudragit RS 100) were used as models in binary mixture tablets of direct compression study. Eudragit RS 100 is a copolymer synthesized from acrylic and methacrylic acid esters with a low content of quaternary ammonium groups. Combination of PVC and Eudragit RS 100 of different polarities and knowing the surface free energy values allow the possibility of predicting the tensile strength of the tablets. Specimens of 500 mg in the form of thin plates (25 mm x 12.5 mm), were made by compressing each powder at 20 000 MPa compression pressure using a special punch and die set. A Howden Universal Testing Machine was used to compress the powder. Contact angle measurements of the samples were carried out using a Wilhelmy balance, ran by a Cahn Dynamic Contact Angle Machine while different test liquids media such as water, glycerol, formamide and PEG 200 were used in the study. The surface free energy values of the solid materials were calculated using Wu’s equation. The results showed large differences between the advancing and receding contact angle values for both materials when tested with glycerol: PVC ( 0_a ) and PVC (0_r) were 93.2 and 65.24 while Eudragit RS 100 (0_a) and Eudragit RS 100 (0_r) were 94.56 and 68.18 respectively. The surface free energy values for PVC using PEG 200-glycerol liquid pair were g_s: 38.01, g_s^d: 33.42, g_s^p: 4.59 and for Eudragit RS 100 using formamide-glycerol liquid pair were g_s: 75.03, g_s^d: 51.66, g_s^p: 23.37, respectively. The results showed harder solid material like Eudragit RS 100 had higher surface free energy compared to elastic material like PVC.