Surface Grafting of Cellulose Nanocrystals Affects Interfacial Interaction and Crystallization of Polycaprolactone

ABSTRACT Polycaprolactone (PCL) has a lower mechanical modulus than other biodegradable polymers, which restricts its applications. In this work, 2,2,6,6‐tetramethyl‐1‐piperidinyl (TEMPO)‐oxidized cellulose nanocrystals (TONC) were modified by long‐chain PCL diols to prepare grafted nanocellulose (TONC‐g) and blended with PCL via a micro‐compounder. DSC, XRD, and POM were used to characterize the thermal and crystalline properties of PCL/cellulose nanocrystals (CNC), PCL/TONC, and PCL/TONC‐g biocomposites, while an interfacial rheometer was utilized to examine the interfacial tension of three cellulose nanocrystal aqueous dispersions with PCL chloroform solution. Polarized light micrographs demonstrated that both modified and unmodified CNC could induce rapid crystallization of the polyester matrix, and isothermal crystallization kinetic analysis revealed that CNC could significantly decrease the half‐crystallization time of PCL, with PCL/TONC‐g exhibiting the shortest half‐crystallization time. Interfacial analysis confirmed that grafting PCL‐diol onto TONC‐g improved their compatibility with the PCL matrix. Pendant drop tensiometry measured an interfacial tension of only 12.4 mN m −1 for TONC‐g against 100 mg mL −1 PCL, which is substantially lower than that of unmodified CNC or TONC. This improved affinity, further supported by Gibbs adsorption analysis, is attributed to the grafted PCL‐diol chains, which act as an efficient compatibilizer at the interface.