## 4 Future Perspectives  
The sustainability of ES composites is an issue with considerable relevance to various industries (Figure 9). Sustainability could be viewed from different perspectives such as cost, environmentally benign materials, feedstock abundance, and renewability of the raw materials. Table 10 provides an overview of various applications that utilize ESP in various fields of application, which contribute to sustainability. The utilization of ES waste for various applications apart from its use as adsorbent materials for pollutant removal are [PERSON] et al. [150]. This includes cement formulation production, dressings for burns, cosmetics, substrates for cell culture, templates for forming ordered tube networks [151], catalyst supports for immobilization of enzymes and ES-reinforced polymer composites. \begin{table}
\begin{tabular}{c c} \hline \hline
**Application** & **Reference** \\ \hline Thermosetting composite blends & [152; 153] \\ \hline Catalyst for biodiesel production & [154] \\ \hline Organic fertilizer & [155] \\ \hline Milk tablet supplement & [156] \\ \hline Adsorbent for carbon dioxide & [74] \\ \hline Pharmaceutical formulations for controlled-release & [157] \\ \hline Pigment coatings & [158] \\ \hline Lithium-sulphur batteries & [159] \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Utilization of ESP in different fields of application. Figure 9: Application of eggshell in various industries. Copied with permission [74]. ES composites are employed in pharmaceutical applications, such as for bone mineralization and growth in animals and in humans and for calcium deficiency therapies. As well, ES powder was used in maxillofacial surgery as a bone substitute, where ES powder is reported to reduce pain and increase bone density [25]. ES composite blends also find utility as fillers, where it was reported that blends of thermoplastic/eggshell composites enhanced various properties, such as lower density, higher crystallinity, good mechanical properties (tensile strength and Young's modulus), and high thermal resistance. A higher Young's modulus was observed in polypropylene blended with 40% ES filler as compared to that with similar quantity of abiogenic (mineral-based) CaCO\({}_{3}\)[179]. Similarly, improved properties such as higher crystallinity and lower density were obtained in PP blends with ES, in comparison with a mineral calcium carbonate mineral [25]. The corresponding PP composites can be applied in lightweight and low load-bearing applications [25]. Investigation on the properties of composite foams with cornstarch and ES revealed that with 0 to 6% ES filler, certain properties decreased, such as expansion ratio, foam unit density, and foam cell size, while others, like spring index, reveal an increase [180]. The utility of ES was not limited to thermoplastic composites alone, but also extends to thermoset composites, which were incorporated with epoxy resin to improve its mechanical toughness [181]. The morphology of the polymer, poly (styrene-ethylene-styrene) blended with ES showed good dispersion and minimum large voids [182]. Incorporation of ES as filler in natural rubber [152] revealed that the elastomer polymer composite had the highest tensile strength, swelling resistance, tear strength, and hardness compared to other