## 2 Experimental Design and Methodology
### Characterization Processes  
In accordance with the methodology delineated in Section 2.2, the resultant biocomposites were subjected to a battery of physical and chemical tests to assess pivotal performance parameters, including mechanical strength, thermal stability, and chemical compatibility. These tests are fundamental to the evaluation of the mechanical durability, thermal stability, and other pertinent properties of the biocomposites, which are essential for determining their suitability for a range of applications. Figure 1: Borosilicate glass reactor schematic. In this study, the ratios of HSO, CPP, and MDI were identified through a comprehensive literature review, which underscores their substantial contributions to the mechanical and thermal properties of polyurethane biocomposites [29; 30; 31]. RSM was employed for the purposes of experimental design. RSM is the preferred method for multi-factor experimental analyses, as it allows for the determination of the effects of independent variables and the optimization of processes. As previously indicated in the Introduction, this methodology is of great significance in the development of biocomposite materials. Moreover, a more precise methodology within the RSM framework, namely the Central Composite Design (CCD), was employed to systematically evaluate the effects of HSO, CPP, and MDI on material properties. A second-order polynomial model was fitted to the data, including linear, quadratic, and interaction terms. The model's robustness was assessed using ANOVA, R\({}^{2}\), and lack-of-fit tests. Validation was performed by comparing predicted values with experimental results, confirming the model's reliability and applicability [32]. The essential details of the pivotal parameters utilized in the experimental process are presented in Table 1.  
The volumetric densities of the specimens were calculated based on mass and volume measurements. For this purpose, the specimens were prepared in molds with dimensions of 20 \(\times\) 10 \(\times\) 100 mm\({}^{3}\). Weight measurements were conducted using an analytical balance with a precision of 0.0001 g. The dimensions of the specimens were measured with a precise digital caliper and used for volume calculations. Tensile tests were performed to determine the mechanical properties of the biocomposite specimens. The specimens were prepared according to the ASTM D638-22 standard and had a gauge length of 30 mm and a cross-sectional area of 5 \(\times\) 5 mm\({}^{2}\)[33]. The tests were conducted at room temperature with a loading rate of 1 mm/min using a UTEST Universal Tensile Testing Machine with a 1 kN capacity. \begin{table}
\begin{tabular}{c c c c} \hline
**Experiments** & **CPP (g)** & **HSO (g)** & **MDI (g)** \\ \hline  
\end{tabular}
\end{table} 
Table 1: Experimental study plan for biocomposite production. The hardness properties of the specimens were determined using the Shore A hardness test. Measurements were conducted in accordance with the ASTM D2240-15 standard [34]. In the hardness tests, disk-shaped specimens with a diameter of 50 mm and a thickness of at least 10 mm were used. For each specimen, measurements were taken at five different points on the surface, and the average of these measurements was calculated to determine the final hardness value. To determine the thermal properties of the biocomposite specimens, thermal conductivity tests were conducted. The tests were performed according to the ASTM D5334-14 standard using the Thermtest TLS-100 (Veddige, Sweden) device [35]. The specimens were prepared in cylindrical shapes with a diameter of 50 mm and a height of 100 mm, and a hole with a diameter of 2.5 mm and a depth of 50 mm was drilled in the center of each specimen. During the course of the measurements, the device probe was inserted into the aforementioned hole, and the thermal conductivity values were recorded directly by the device in question. Three measurements were taken for each specimen, and the resulting values were averaged.