EXTRACTION OF CALCIUM CARBONATE FROM WASTE EGGSHELLS AS FILLERS IN COMPOSITES

Abstract

Large amounts of eggs are consumed in different forms around the world, which results in a massive amount of eggshells. These eggshells can end up in landfills, rivers or coastal waters which can impact public health, contamination of water resources and pollute the environment. Furthermore, in recent years, special focus is given to industrial sectors that are sources of pollution to the environment. Mineral limestone, which is made of calcium carbonate (CaCO3) is used as filler materials for polymer composites to reduce the cost and improve certain properties. On the other hand, eggshells contain high amounts of CaCO3 with some organic membranes but are generally considered as a waste. In this study, to utilize waste eggshell as an alternative to limestone, thermal and chemical treatments are investigated to produce purified eggshell powder. Polymer composites were made using bio-epoxy resin with different amounts of eggshell, purified eggshell and limestone fillers (5, 10 and 20 wt. %). Trace analysis of fillers, microscopic morphology, thermal and mechanical properties of fabricated composites are evaluated. The filler powders were sieved using 20 and 32 μm size standard sieves. The particle size analysis using ImageJ software showed average particle diameters of 11.2 and 23.8 μm for 20 and 32 μm sieved powders, respectively possibly due to the presence of some lower particle sizes as a result of grinding. Eggshell powder had a higher weight loss when heated to 850 °C for 2 h than pure limestone powder due to the removal of organic membranes. Eggshell powder had a lower density than purified eggshell and limestone particles due to the presence of low density membrane. Composites with eggshell fillers absorbed higher water than composites with purified eggshell and limestone filler due to the presence of organic membrane in eggshell. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed 87.5 ± 0.5 wt. % of CaCO3 content in pure eggshell, which increased to 95.0 ± 0.5 wt. % in purified eggshell due to the absence of organic membrane as a result of thermal and chemical treatments. Scanning electron microscopic (SEM) analysis of fractured surfaces showed a flat and mirror-like surface for bio-epoxy, which became rougher when loaded with eggshell fillers. Tensile, flexural and Charpy impact strengths decreased as the filler content was increased for all fillers. However, tensile and flexural modulus improved significantly and showed maximum values at 20 wt. % for all three fillers. Thermogravimetric analysis (TGA) analysis showed higher weight losses between 300-550 °C for eggshell powder than purified eggshell and limestone due to the decomposition of the organic membranes. Economic analysis for an egg breaking plant in Lethbridge, Alberta showed that approximately 705,000 kg of CaCO3 could be produced annually by recycling waste eggshell. This research not only presents a way to reduce waste eggshell, but also shows a method to purify them for use as bio-epoxy composite filler materials. Bio-epoxy composites with eggshell fillers could be used in applications with higher tensile and flexural modulus with reduced cost such as plastic chairs, tables, skateboards, glass frames, boats, bicycles and toys.