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The oil extraction of Calophyllum seeds using a conventional single screw press leads to an inferior yield and is perceived to be less efficient as well as difficult to operate. An innovative and flexible single screw press was, therefore, designed and investigated in this study to solve these problems. Moreover, the effects of the seeds’ moisture content, pressing temperature and seeds’ feed rate on the oil yield and quality were identified to determine the optimal oil extraction performance from the Calophyllum seeds. The study found that the seeds’ moisture content, pressing temperature and seeds’ feed rate generally affected the oil yield. The yield indeed improved as the pressing temperature and the seeds’ feed rate increased respectively from 45 to 75°C and 1.5 to 5 kg·h^–1. The oil yield also ameliorated as the seeds’ moisture content rose from 1.7 to 12.8%, but it was optimal when the seeds’ moisture content was 5.5%. The best oil yield of 80.6% was, thus, obtained with the seeds’ moisture content of 5.5%, a pressing temperature of 75°C and the seeds’ feed rate of 5 kg per h. Although the quality of the crude oil was poor with a high viscosity (³ 94 mm²·s^–1) and high acid value (³ 48 mg KOH/g), its density, saponification and iodine values were acceptable. After the oil refining process by degumming and neutralisation, its quality improved and met the Indonesian Biofuel Standards, except for its viscosity.

The development of conducting polymer-based supercapacitors offers remarkable advantages, such as good ionic and electronic conductivity, ease of synthesis, low processing cost, and mechanical flexibility. 3,4-ethylenedioxythiophene (PEDOT) is a conducting polymer with robust chemical and environmental stability during storage and operation in an aqueous environment. Yet, improving its electrochemical capacitance and cycle life remains a challenge for high-performance supercapacitors exceeding the current state-of-the-art. The fabrication of PEDOT composites with carbon nanomaterials and metal oxides is the commonly used approach to enhance capacitance and stability. This work discusses a comparative study to fabricate highly stable PEDOT derivative electrodes with remarkable specific capacitance via a straightforward electrochemical polymerization technique. The hydroxymethyl PEDOT (PEDOTOH) doped with perchlorate in a dichloromethane (DCM) solvent (197 F g−1) exhibits superior performance compared to the polymer formed in an aqueous solution (124 F g−1). Furthermore, the electropolymerized PEDOTOH on flexible Au/Kapton substrates was assembled into a free-standing symmetrical supercapacitor in an agarose additive-free gel. The use of agarose gel electrolytes can offer easy handling, no leakage, moderate ionic conductivity, and flexibility for miniaturization and integration. The supercapacitor reached a specific capacitance of 36.96 F g−1 at a current density of 13.7 A g−1, an energy density of 14.96 Wh kg−1, and a power density of 22.2 kW kg−1 among the highest values reported for PEDOT-based supercapacitors. The self-standing supercapacitor achieves an industry-par capacitance retention of ∼98% after 10000 charge/discharge cycles at 10 A g−1. This study provides insights into the effect of solvents and electropolymerization modes on the polymer structure and its electrochemical properties toward high-performance supercapacitor devices.

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