Strengthening efficacy of spherical starch nanoparticles and surrounding interphase in polymer nanocomposites

Although extensive experimental data exist, modeling studies on the tensile strength of starch-filled nanocomposites remain incomplete, hindering the optimization of formulations. In this study, the Nicolais-Narkis model is modified and expanded by introducing the interfacial parameter a, enabling the estimation of tensile strength in starch-based nanocomposites. The enhanced model incorporates critical factors such as interphase thickness, interphase strength, and starch particle size. Experimental data from various starch-filled samples are utilized to validate the proposed model. Furthermore, parametric analyses are conducted to evaluate the influence of all relevant parameters on the interfacial parameter a and the overall strength of the nanocomposites. The results indicate that a starch radius (R) of 20 nm with an interphase depth (t) of 50 nm yields interface parameter (a) of 10, resulting in a 300 % improvement in nanocomposite strength. In contrast, R = 90 nm and t = 15 nm result in a < 0, offering no reinforcement. These findings underscore that smaller nanoparticles and a denser interphase significantly enhance nanocomposite strength. Conversely, larger nanoparticles and a thinner interphase fail to improve the mechanical properties. Additionally, the highest values of a and nanocomposite strength are achieved with the weakest polymer matrix and the most robust interphase. In contrast, a strong polymer matrix and a weak interphase lead to a < 0, resulting in no reinforcement.