Natural rubber (NR) composites filled with silica are typically used for tire tread applications owing to their low energy consumption and low rolling resistance. Tire tread properties vary broadly depending on the compound formulation and curing conditions. Silica loading is recognized as a critical factor influencing the mechanical properties of the composites. In this work, we aim to investigate the effect of silica loading (10–50 phr) on the mechanical properties of NR composites. Silica was prepared from rice husk waste via chemical treatment and subsequent calcination at 600 °C. Prior to the compound mixing process, silica was modified by a silane coupling agent to improve compatibility with the NR matrix. The NR compounds reinforced with silane-modified silica from rice husk were prepared using a two-roll mill machine. The scorch and cure times increased as the silica loading increased. The mechanical properties of the NR composites, including tensile strength, elongation at break, modulus, hardness, and abrasion loss, were examined as a function of silica loading. Tensile strength increased and reached the maximum value at 20 phr but decreased at high loading owing to the agglomeration of silica in the NR matrix. With increasing silica loading, hardness and modulus increased, whereas elongation at break and abrasion resistance decreased slightly. These results indicate that NR composites filled with silica are stiffer and harder at a higher silica loading due to the strong interaction between silica and the NR matrix, inhibiting the segmental mobility of rubber chains. We anticipate that the compound formulation presented in this work could potentially be adapted to tire tread applications.

Supercapacitors are promising energy storage devices owing to their high power density and excellent cycling stability. The conversion of biomass waste into activated carbon with hierarchical pore structures has emerged as a sustainable strategy for developing high-performance supercapacitor electrodes. Herein, activated carbons were synthesized from macadamia nut shell (MNS) waste via a two-step process comprising carbonization at 600 °C and subsequent chemical activation with potassium hydroxide (KOH) at 800 °C, using weight ratios of carbonized MNS to KOH of 1:1, 1:2, and 1:3. The resulting activated carbons exhibited an amorphous structure with a predominant microporosity. KOH activation substantially increased the specific surface area from 325 to 1362 m² g^–1 through gas evolution, etching, and potassium intercalation, thereby promoting the predominant micropore formation along with partial mesopore development. Increasing the KOH ratio induced greater structural disorder, widened micropores, increased the mesopore fraction, enriched C–O functionalities, and suppressed CO and O–CO groups. Electrochemical measurements in a 6 M KOH electrolyte using a three-electrode system revealed that the sample activated at a 1:3 ratio delivered a maximum specific capacitance of 170 F g^–1 at 1 A g^–1 and exhibited predominantly electric double-layer capacitor (EDLC) behavior with a minor pseudocapacitive contribution, as confirmed by power-law, Trasatti, and Dunn analyses. This performance is attributed to its large specific surface area, partially developed mesoporosity, and enhanced surface wettability. A symmetric coin-cell supercapacitor assembled using this material delivered an energy density of 5.4 W h kg^–1 and a power density of 2500 W kg^–1, while maintaining excellent cycling stability over 10,000 charge–discharge cycles at 3 A g^–1. These results reveal the potential valorization of MNS-derived activated carbons as sustainable and efficient electrode materials for high-performance supercapacitors.

Activated carbon fibers (ACFs) were successfully synthesized from kapok via a two-step process: (i) pre-carbonization and (ii) chemical activation. The pre-carbonization temperature was varied at 300℃, 400℃, and 500℃. The mixing ratio of the pre-carbonized product and potassium hydroxide (KOH) was 3:1, while the activation temperature was 800℃. The effect of pre-carbonization temperature on the morphology, surface area and porosity, chemical functional group, and phase structure of ACFs was investigated and discussed. The characterization results showed that ACFs exhibited an amorphous carbon structure with a hollow fiber shape resembling the kapok. The specific surface area decreased from 487 m2×g-1 to 326 m2×g-1 as the pre-carbonization increased. The pore structure of ACFs possessed a major contribution of micropores, and mesopores became more dominant at a high pre-carbonization temperature. The potential use of ACFs as electrode materials in supercapacitors was electrochemically tested by cyclic voltammetry and galvanostatic charge-discharge measurements. The ACFs obtained from pre-carbonization at 500℃ had the highest specific capacitance of 31.9 F×g-1 at a current density of 1 A×g-1. The results in this work will be a helpful guideline for the further design and development of ACFs from kapok for supercapacitor applications.

Thermal treatment of CNPs synthesized via SPP in an inert environment could result in the development of micropores and the decrease of surface oxygen functionality, which affect their charge storage properties when used as supercapacitor electrodes.