Investigation of saponins as biosurfactants for emulsion gel polymerization of styrene under reduced temperature
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Date
2024
Journal Title
Journal ISSN
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Faculty of Science, University of Kelaniya Sri Lanka
Abstract
Emulsion gel polymerization is a technique that enables polymerization to occur at reduced temperatures. This technique has gained attention for its environmentally friendly nature, lower energy requirements, enhanced polymerization efficiency, and potential for industrial scalability. This study majorly aimed to explore emulsion gel polymerization utilizing biobased surfactants as alternatives to conventional synthetic surfactants such as cetyltrimethylammonium bromide (CTAB). Additionally, it sought to determine the optimal concentration of the biobased surfactants and examine the properties of the resulting polymer. The polymerization process consists of four primary components: the monomer: styrene, the initiator: azobisisobutyronitrile (AIBN), the gelling agent: fumed silica (FS), and the crude soapnut extract (SE) serving as the surfactant. Saponin-type biosurfactants were extracted from the ground pericarp powder of the soapnut fruit (Sapindus sp.) through maceration extraction at room temperature. This extraction utilized a solid-liquid ratio of 1:10 (grams to milliliters) with distilled water. The crude soapnut extract (SE) was subsequently obtained through a filtration process. Styrene was polymerized using the emulsion gel technique via a free radical polymerization mechanism for 24 hours at room temperature in glass vials. Following polymerization, the samples were dried and ventilated to achieve constant weights. To characterize the resultant polystyrene (PS), the polymer was extracted from the composites by dissolving in toluene and subsequent precipitation in distilled water. The percentage polymerization weight conversions were calculated to determine the optimal SE concentration. This process involved two steps: initially, crude SE solution was used to assess the viability of saponins in emulsion gels; subsequently, freeze-dried SE (FD-SE) powder was employed to optimize the surfactant concentration. In both steps, monomer-to-polymer conversion exceeded 80% within one day. For the SE solution, the optimal concentration was 1.5 ml, achieving an 85.4% conversion. For the FD-SE powder, the optimal amount was 0.4 g per 0.5 ml of water, resulting in an 83.0% conversion. Scanning electron microscope (SEM) analysis revealed that the surface morphology of the emulsion gel polymerized composites exhibited a near-circular shape with void spaces. The differential scanning calorimetric analysis revealed that the glass transition temperature (Tg) of the synthesized PS is 96 oC which is slightly lower than the Tg obtained using CTAB. The gel permeation chromatographic analysis revealed that the reduction of Tg is due to the low molar mass of the polymer synthesized from saponin surfactant which can be attributed to the non-ionic nature of the surfactant compared to the cationic CTAB. However, this investigation demonstrated the feasibility of synthesizing polystyrene at ambient temperature using saponin-based surfactants. Additionally, the potential of other natural surfactants derived from various biological sources for emulsion gel polymerization merits further exploration.
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Keywords
Biosurfactants, Emulsion gel polymerization, Low-temperature polymerization, Polystyrene, Saponins.
Citation
Jalathge J. S.; Maddumaarachchi M. A. M. (2024), Investigation of saponins as biosurfactants for emulsion gel polymerization of styrene under reduced temperature, Proceedings of the International Conference on Applied and Pure Sciences (ICAPS 2024-Kelaniya) Volume 4, Faculty of Science, University of Kelaniya Sri Lanka. Page 102