Cellulose nanocrystals functionalized with amino-silane and epoxy-poly(ethylene glycol) for reinforcement and flexibilization of poly(lactic acid): material preparation and compatibility mechanism

Abstract

Cellulose nanocrystals (CNCs) have attracted considerable attention as nanofillers to enhance the crystallization of poly(lactic acid) (PLA) and to improve the mechanical properties of the composites. There are two challenges: the inferior thermostability of CNCs and the compatibility of CNCs and polymeric matrix. Poly(ethylene glycol) epoxide, a compatibilizer and carrier, was grafted on CNC surfaces using γ-aminopropyltriethoxysilane as an intermediate, in order to overcome those two challenges. Thermogravimetry analysis indicated that the initial decomposition temperature of the modified CNCs was increased by approximately 150 °C in comparison with the pure CNCs. Results from SEM and UV–Vis transmittance spectra revealed homogeneous dispersion of the modified CNCs in PLA matrix. Polarizing microscope and differential scanning calorimeter measurement showed the improvement of crystallization property. The stress–strain analysis showed that the strength and elongation at break of the composite were also improved with the addition of modified CNCs. The hydrophobicity of the modified CNCs was characterized with the contact angle measurement, which indicated that the contact angle was increased by 20°. The increase of the initial decomposition temperature of the modified CNCs suggested that the inferior thermostability has been improved, and the improvement of transmittance, crystallization and mechanical properties suggested that the compatibility of CNCs to PLA has been improved. The two challenges, the inferior thermostability and compatibility to PLA of CNCs has been improved with the functionalization with amino-silane and epoxy-poly(ethylene glycol).