Experimental and Gaussian Process Regression Validation of the Effects of Nano Clay (Montmorillonite) on Properties of Thermo Plastic Starch Hydroxyapatite

Abstract

This study considers the development of composite from biodegradable bioplastic obtained from starch of wasted cassava peels using hybrid fillers which are hydroxyapatite from egg shell waste and Montmorillonite (MMT) nanoclay as reinforcing filler through solution casting. The experimental analysis was validated using the Gaussian Process Regression (GPR). The hybrid composite film was prepared by weighing thirty grams (30 g) of the starch inside a beaker, into which 8 ml of glycerol, 2 ml of olive oil, and 8 ml of vinegar were added. The control solution was prepared without hydroxyapatite and nanoclay and made up to 150 ml with distilled water. The solution was mixed thoroughly then the mixture was heated on a hot plate at 70˚C. The mixture was stirred continuously till it starts to gel, after which the mixture was spread on an aluminum tray and left for 2 to 3 days to dry. This procedure was repeated for the composite formulations by incorporating a fixed amount of 4.5 g of hydroxyapatite (corresponding to 15 wt.% relative to the dry starch weight) alongside varied amounts of montmorillonite nanoclay at 1 wt.% (0.3 g), 3 wt.% (0.9 g), and 5 wt.% (1.5 g) respectively, relative to the total dry weight of the starch matrix. The solution was thoroughly mixed, heated at 70 ˚C and stirred continuously till it started to gel, and thereafter dried for 3 days. The developed composite was evaluated via morphological, structural, thermal and mechanical analysis. From the scanning electron microscopy (SEM) test, the morphology of the composite surface showed homogeneity with no visible agglomerates, while the x-ray diffraction (XRD) results indicate that with increasing the volume fraction of the nanoclay in the polymer matrix, the crystallinity peaks of the biopolymer become wider to become amorphous. The 3% nanoclay offers the best balance between strength and flexibility before aggregation issues reduce performance in the 5% nanoclay However, the thermogravimetric analysis (TGA) shows that the thermoplastic starch with 5% nanoclay has the highest thermal stability at 790°C. The GPR model demonstrated strong predictive capability for the nanocomposite properties with R² values between 0.91-0.95, RMSE values ranging from 1.18-16.50 and MAE values between 0.75-13.30. Thus, this outcome indicates low prediction error and high agreement between predicted and experimental values. This study is significant as it enhances the application of bioplastics, encourages waste-to-wealth conversion, reduces waste generation, and promotes environmental sustainability.