Chemical modification of cellulose nanocrystals and their application in thermoplastic starch (TPS) and poly(3‐hydroxybutyrate) (P3HB) nanocomposites

Abstract

The effect of sulfated (original), carboxylated (oxidized), and Jeffamines M2005‐grafted cellulose nanocrystals (CNCs) on the barrier and mechanical properties of thermoplastic starch (TPS) and poly(3‐hydroxybutyrate) (P(3HB)) matrices was investigated. CNCs were first oxidized via a catalytic reaction using NaClO as an oxidant and then grafted with an amine‐terminated ethylene oxide (EO)/propylene oxide (PO) copolymer (Jeffamine) by an amine‐acid coupling reaction. A degree of oxidation (DO) of 0.108 (mol/mol of anhydroglucose) was attempted for the carboxylated CNCs, whereas a degree of substitution (DS) of 0.04 (mol/mol of anhydroglucose) was determined for the M2005‐grafted CNCs. These values indicated satisfactory reactive process, with yields of 68% and 47.3% for the carboxylation and peptide coupling reactions, respectively. Fourier‐transform infrared spectroscopy (FTIR) analysis showed bands at 1643 cm−1 and 1550 cm−1 in the spectrum of M2005‐grafted CNCs, which qualitatively indicated the amide bond formation. In addition, the morphology and the zeta potential of modified CNCs ensured their homogeneity, stability, and surface degree of charge. In spite of a decrease in the solubility in water of the modified crystals, the procedure of chemical modification used avoided any variation in their crystalline structure and thermal stability. Then, the incorporation of sulfated, oxidized, or M2005‐grafted CNCs in matrices of TPS and P(3HB) allowed to produce reinforced nanocomposite films, with excellent barrier properties. Therefore, the chemical compatibility between CNCs and the polymer matrices is essential to produce attractive nanocomposites with improved mechanical properties for industrial applications.