Balancing flexibility and strength of hydroxypropylated starch/cellulose nanofibrils biocomposites

Abstract

This study investigates the thermal-mechanical properties of hydroxypropylated starch (HPS) as a plasticizer for conventional thermoplastic starch (TPS) films, reinforced with cellulose nanofibrils (CNF). A previous study showed that hydroxypropylation of starch led to in-situ poly(propylene oxide) (PPO) formation, inducing gelatinization and yielding TPS with significant plasticizing effect. To address this, blending native cassava starch with HPS and incorporating CNF, as well as hydroxypropylated CNF (mCNF), was explored as a sustainable reinforcement strategy. Films were prepared by casting, and their properties were evaluated using tensile strength tests, Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TG). Results indicate that the incorporation of unmodified CNF significantly increased the tensile strength of HPS/TPS films, demonstrating its effective reinforcing capability. Conversely, adding mCNF led to a reduction in tensile strength, suggesting that the chemical modification of CNF may hinder its reinforcing efficiency due to altered interactions with the starch matrix. FTIR confirmed molecular interactions, while DSC and TG provided insights into thermal transitions and stability. This research emphasizes the potential of combining HPS, native starch, and CNF to create sustainable, high-performance starch-based biocomposites with reduced synthetic plasticizer content, offering a promising approach for diverse applications.