Abstract
In this study, an innovative composite was fabricated in which the matrix is partially derived from natural sources and the filler from undervalued eggshell waste material. The effect of coating eggshells and mineral limestone with 2 wt.% stearic acid on the mechanical properties of a bio-epoxy matrix was investigated. Eggshells and limestone (untreated and stearic acid-treated) fillers were added to the bio-epoxy matrix in quantities of 5, 10, and 20 wt.% loadings using a solution mixing technique. The CaCO3 content in eggshells was confirmed to be 88 wt.%, and the crystalline phase was found to be calcite. The stearic acid coating did not show any decrease in crystallinity of the fillers. Scanning electron microscopy (SEM) displayed changes in the fractured surfaces, which infers the fillers altered the bio-epoxy polymer. The mechanical property results showed enhancements in the composite tensile modulus and flexural modulus compared to the pure bio-epoxy, as expected. In contrast, despite the improvement in the tensile and flexural strengths of the stearic acid-treated fillers, the composite strength values were not higher than those of the unfilled bio-epoxy matrix. The energy absorbed by all composites in Charpy impact tests fell below that of the pure bio-epoxy and decreased with an increase in filler content for both untreated and stearic acid-treated fillers tested at 23 and −40 °C. Statistical analysis of the results was conducted using Statistical Analysis Software (SAS) with ranking based on Tukey’s method. The study identified that the addition of 5, 10, and 20 wt.% in a bio-epoxy matrix may be acceptable provided the end product requires lower tensile and flexural load requirements than those of the pure bio-epoxy. However, filler loadings below 5 wt.% would be a better choice.
Highlights
In recent years, there has been an uptake in the use of polymer composites for various applications due to their light weight, high specific stiffness, and moderate strength properties
The study suggested heating eggshells to 450 ◦ C would allow the organic membranes to be removed without changing the composition of CaCO3 ; there is an apparent color change to gray with carbon remnants [22]
It is well known that calcination of CaCO3 above 800 ◦ C causes conversion into calcium oxide (CaO)
Summary
There has been an uptake in the use of polymer composites for various applications due to their light weight, high specific stiffness, and moderate strength properties. During and after World War II (1940s) there was an increase in the production and development of synthetic polymers and plastics produced from petroleum resources [1]. Synthetic epoxy is frequently utilized in diverse applications due to its simple processing methods, good elevated temperature properties, and exceptional strength. Epoxy polymers have a higher purchase cost than other thermoset polymers; in the aerospace industry, more than two-thirds of polymers utilized are based on epoxy [2]. Bio-based epoxy resins could serve as substitutes to petroleum-based epoxy resins
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