j. Cosmet. Sci., 53, 199-208 (July/August 2002) Development and characterization of rosin-based polymer and its application as a cream base V. T. DHANORKAR, R. S. GAWANDE, B. B. GOGTE, and A. K. DORLE, Department of Pharmaceutical Sciences, University Campus (V. T.D., R.S.G., A.K.D.), and Laxminarayan Institute of Technology (V. T.D., B.B.G.), Nagpur University, Nagpur 440 010 (MS), India. Accepted for publication January 31, 2002. Synopsis The literature contains many references to the wide range of uses of rosin-based polymers, but little has appeared in the area of rosin-based polymers used as cream bases. Various rosin polymers based on glycerol, sorbitol, and pentaerythritol were prepared and screened for efficacy as cream bases. Among these polymers, polymer 2 (glycerol-based) is reported in the present study as it produced creams with a better stability and release profile as compared to other creams. The creams were formulated employing polymer 2 (P2) and Tween 60 as surfactants. The stability of the prepared creams, as well as the diclofenac diethylammonium release pattern, was investigated using particle size analysis, conductivity, relative dielectric constant, spreadability, and irritation potential measurement, and was compared with that of creams containing Tween 60 (RT) prepared in the laboratory. The release of the drug, diclofenac diethylammonium, was measured after eight hours and compared with a standard cream (RT) and a marketed cream (RM). INTRODUCTION Rosin and its derivatives are widely used in paints (1), primers (2), cosmetics (3), microencapsulating materials (4), and pharmaceutical coating materials (5). Rosin and its derivatives are also used as binding agents in tablet formulation (6). Rosin is a solid resinous material obtained naturally from various varieties of pine tree (7,8). The prin- ciple commercial sources of rosin are Pinus soxburghi, Pinus/ongifo/ium, Pinus pa/ustrius, and Pinus toeda. Rosin is composed of approximately 90% rosin acids and 10% non- acidic materials. Rosin acids are monocarboxylic acids having the typical molecular formula (C2oH3oO 2. There are two types: the abletic acid type (9) and the primaric acid type (10). Rosin is reported to have emulsifying properties (11). The use of rosin-based esters was previously reported in cream bases (12). Based on these data and work carried out in our Address all correspondence to V. T. Dhanorkar. 199

200 JOURNAL OF COSMETIC SCIENCE laboratory, we were prepared to detect the utility of rosin-based polymers as a cream base. The rosin-based polymers were prepared by the esterification of rosin with glycerol and pentaerythritol at 220-240øC in the presence of sodium sulphide and sodium bisulphate as catalysts. The primary aim of the present work is to evaluate polymer 2 as a cream base. The cream-containing polymer 2 (R2) was also studied for its stability and the release profile of diclofenac diethylammonium. The prepared cream was compared with a standard cream containing Tween 60 (RT) and a marketed preparation (RM). EXPERIMENTAL MATERIALS The procured materials along with their sources are as follows: rosin N grade (Tayebai Ebrahimji Pettodwala, Mumbai), glycerol (Qualigen), sorbitol (Qualigen), Tween 60 (S.D. Fine), maleic anhydride (Qualigen), pthaleic anhydride (Qualigen), castor oil (P.J. Chemicals, Nagpur), glycerin (Qualigen), isopropyl myristate (Qualigen), cetyl alcohol (S.D. Fine), stearyl alcohol (S. D. Fine), propylene glycol (Qualigen), and diclofenac diethylammonium (Crossland Laboratories Ltd., Pune). Distilled water was used when collected fresh. The polymers based on rosin were prepared in the Laboratory of Phar- maceutical Sciences, Nagpur University, Nagpur. PREPARATION AND DETERMINATION OF THE PHYSICOCHEMICAL PROPERTIES OF ROSIN-BASED POLYMERS Preparation of rosin-basedpolymers. The reaction of polymer synthesis was conducted in a four-neck two-liter glass reactor. This reactor was fitted with a condenser, stirrer, and temperature control arrangement. The reaction temperature was maintained within +2øC with the help of an accurate thermometer. As a first step, rosin, part of the maleic anhydride, castor oil, and sodium sulphide and sodium bisulphate (catalysts) were added to the reactor and the temperature was slowly raised to 160øC. The reaction was maintained at this temperature for one hour. After this, the temperature was lowered to 120øC and glycerol and sorbitol were added slowly after about 15 minutes. The cooling was continued for three to four hours at 210-250øC. At the end of this period, the calculated solvent, part of the maleic anhydride, and pthaleic anhydride were slowly added after about 15 minutes. Further cooling was done at a lower temperature for three to four hours until the desired acid value was reached. Finally, xylene was stripped off totally by heating at a slightly higher temperature (150øC) using a vacuum. The sample was finally strained through a fine mesh and stored carefully. During the process, the acid value of the product was determined intermittently as reported previously (13). Determination ofphysicochemicalproperties of rosin-basedpo/ymer. The acid value is the num- ber that expresses in milligrams the amount of KOH necessary to neutralize the free acids present in one gram of the substance. The acid value of the polymers was deter- mined by using the test described in the Indian Pharmacopoeia (Pharmacopoeia of India, 1996). The maximum acid value for rosin-based polymer should not exceed more than 10. Two grams of rosin-based polymer was dissolved in 50 ml of a mixture of equal volumes of ethanol (95%) and ether previously neutralized with 0.1 M KOH to phenolphthalein