Fabrication and Characterization of Bio-epoxy Eggshell Composites

Abstract

Low cost fillers such as mineral limestone (LS) are added to polymers in an effort to improve their properties. Waste eggshells (ES), a by-product of the egg breaking plant industry, contain high content of calcium carbonate (CaCO3) but are generally discarded to landfills at a cost to the company. The use of waste ES as an alternative to mineral LS filler added to bio-epoxy resin was investigated in this study.

Untreated and stearic acid (SA) treated ES and LS fillers (5, 10 and 20 wt. %) were used in fabricating bio-epoxy composite materials via a solution mixing method. Chemical analysis of the filler materials, microstructural examination, physical and mechanical properties of the fabricated composites were evaluated.

The particle density of ES was found to be smaller than that of LS particles. The average particle size was 21.2 ± 2.0 µm, 11.5 ± 1.0 µm, 25.1 ± 2.2 µm and 12.8 ± 2.2 µm for ES, SA treated ES, LS and SA treated LS, respectively. SEM images showed untreated ES and LS particles varied in shape possibly due to grinding during processing. Both untreated and SA treated fillers had rhombohedral-like morphology. Pores were observed in ES due to its characteristic structure compared to the LS particles, which had no visible pores. Fractured surfaces of the composites showed flat and cleavage features for unfilled bio-epoxy composites compared to filled composites which showed jagged surfaces. The density of the composites increased with increase in filler loading for all filler types. Similarly, the void content and water absorption increased with increase in filler loading with 20 wt. % ES composites having the highest values. XRD analysis indicated the presence of calcite, while ICP-MS showed 88 wt. % ± 0.7 CaCO3 in ES, slightly less than the mineral LS as a result of the residual organic membranes still attached. The tensile strength, flexural strength and Charpy impact toughness of the composites reduced with increase in filler loading. However, the flexural modulus improved with increasing filler loading and was maximum at a filler content of 20 wt. % for all filler types. The Charpy impact energy of unfilled bio-epoxy at – 40 °C dropped appreciably to about 58 % of its room temperature value. Economic analysis showed that ~ 18,117,000 kg of CaCO3 can be recovered from waste ES annually in Canada for various applications and can serve as potential replacement of about 1.00 % of mined mineral LS. This research presents promising results for the use of ES as an alternative to LS in bio-epoxy composites for selected applications such as laminating surfboards and skateboards.