Effect of carboxylated cellulose nanocrystal acetylation on PLA nanocomposite crystallization behavior

• cCNCs and acetylated cCNCs were dispersed in PLA using ethyl lactate (EtLa). • Green solvent (EtLa) improved PLA chain mobility and crystallization efficiency. • Avrami analysis revealed a shift to 3D spherulitic growth in PLA with cCNCs. • 1.5 wt.% cCNCs significantly increased PLA crystallization rate at 100°C. • Acetylated cCNCs enhanced PLA crystallization at temperatures of 110 and 120°C. Polylactic acid (PLA) has garnered increasing attention as a biodegradable polymer derived from renewable resources; however, its relatively slow crystallization rate restricts its broader use in wider applications. We address this challenge by producing PLA nanocomposites with carboxylated cellulose nanocrystals (cCNCs) and acetylated cCNCs (AcCNCs) in ethyl lactate (EtLa), a bio-based, non-toxic solvent. The crystallization behavior and thermomechanical properties of the nanocomposites were measured using X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and polarized light microscopy (PLM). For PLA-cCNC nanocomposites, Avrami analysis confirmed a transition from two- to three-dimensional spherulitic growth. The addition of cCNCs or AcCNCs with a low degree of substitution (i.e., DS = 0.06) in PLA led to increased crystallization rates. This demonstrated that the cCNCs and AcCNCs enhanced heterogeneous nucleation and the use of EtLa enhanced PLA chain mobility. XRD measurements revealed an increase in average crystallite size when cCNCs and AcCNCs were added to the PLA, signifying improved crystal development. Although both cCNCs and AcCNCs promoted PLA crystallization, the nucleating efficiency of AcCNCs was hampered by reduced compatibility with the EtLa solvent, likely leading to some AcCNC aggregation. The results show how leveraging a greener solvent (EtLa) and utilizing cCNCs can effectively address PLA crystallization limitations, thereby expanding opportunities to enhance high-performance, sustainable materials in packaging, additive manufacturing, and biomedical engineering.