Influence of cellulose nanomaterial dimensions on the crystalline structure and properties of thermoplastic starch composites

Thermoplastic starch (TPS) is increasingly recognized as a promising candidate for the manufacture of sustainable and biodegradable materials. In this study, we investigate how the dimensions of cellulose nanomaterials (CNMs) influence crystalline structures during the gelatinization and retrogradation of TPS. CNMs with systematically varied dimensions were prepared via acid hydrolysis of cellulose nanofibrils. X-ray diffraction and differential scanning calorimetry analyses confirmed that decreasing CNM dimensions promoted the disruption of aggregated amylopectin (AP) clusters, leading to the release and crystallization of long amylose (AM) chains into Vh-type structures. In contrast, larger CNMs preserved the AP clusters, favoring the formation of B-type double helices. This dimension-dependent transition of crystalline structures significantly influenced the mechanical properties of TPS composites. Toughness improved by up to 34 % compared to neat TPS, particularly with intermediate CNMs (average length ∼ 233 nm), promoting a favorable balance between strength and elongation. Furthermore, CNM incorporation uniformly reduced water adsorption by approximately 20 %, while oxygen permeability decreased from 1.61 to 0.52 cm³·mm·m⁻²·day⁻¹·atm⁻¹ with decreasing CNM dimensions. These findings demonstrate that CNM dimensions enable tailored crystalline structure development and property optimization in TPS composites for diverse applications.