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The circular economy promotes plastic recycling, waste minimization, and sustainable materials. Hence, the use of agricultural waste and recycled plastics is an eco-friendly and economic outlook for developing eco-designed products. Moreover, new alternatives to reinforce recycled polyolefins and add value to agroindustrial byproducts are emerging to develop processable materials with reliable performance for industrial applications. In this study, post-consumer recycled high-density polyethylene (rHDPE) and ground rice husk (RH) of 20% w/w were blended in a torque rheometer with or without the following coupling agents: (i) maleic anhydride grafted polymer (MAEO) 5% w/w, (ii) neoalkoxy titanate (NAT) 1.5% w/w, and (iii) ethylene–glycidyl methacrylate copolymer (EGMA) 5% w/w. In terms of processability, the addition of RH decreased the specific energy consumption in the torque experiments with or without additives compared to neat rHDPE. Furthermore, the time to reach thermal stability in the extrusion process was improved with EGMA and MAEO compatibilizers. Tensile and impact test results showed that using coupling agents enhanced the properties of the RH composites. On the other hand, thermal properties analyzed through differential scanning calorimetry and thermogravimetric analysis showed no significant variation for all composites. The morphology of the tensile fracture surfaces was observed via scanning electron microscopy. The results show that these recycled composites are feasible for manufacturing products when an appropriate compatibilizer is used.

Composites of bio-based aliphatic poly-functional epoxy resin reinforced with high concentration of bio-silica were prepared by a solvent free method. The unmodified bio-silica (BS) was obtained from rice husk. Two amine hardeners were used: one was based on polyethylene oxide (PEO) and the other on polypropylene oxide (PPO). The epoxy-amine systems were reinforced with 10, 20, 30 and 40% weight fraction to the unreinforced epoxy resin. The structure and morphology of the BS was analyzed by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), respectively. These techniques were also used to determine the silica dispersion degree in the polymer matrix. Thermal characterization was carried out using a Differential Scanning Calorimetry (DSC) and Thermogravimetric Analyses (TGA). The glass transition temperature, Tg, increased significantly for both polyetheramine cured systems incorporating 10 wt% and 20 wt% of the BS; nevertheless, the best performance was observed in PEO networks. The thermal stability at 5% of weight loss temperature increased consistently with reinforcement concentration up to ~ 21% and ~ 10% compared to neat PEO and PPO cured networks, respectively. Tensile strength and Young modulus for PEO systems showed similar results up to 30 wt% of BS, whereas for PPO networks they decreased relentlessly at 20 wt% of BS. PEO composites showed an overall increase in the Shore D hardness testing. Water swelling experiment illustrated greater hydrophilicity of PEO compared to filled and unfilled PPO systems. The water absorption remains unaltered up to 20 wt% of BS, revealing a good interaction between both networks and filler. It was clearly illustrated the difference in the effect of hydrophilicity (PEO) and the hydrophobicity (PPO) in the epoxy composite results. A better compatibility and good correlation between mechanical and thermal properties were observed in 10 wt% of BS in both polyetheramine cured networks. Keywords-Rice husk silica, bio-silica reinforced polymers, bio based thermosets, aliphatic bio-epoxy composites, polymer composites.

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