We investigate the microstructure, thermal stability, melt‐rheological behavior, and mechanical properties of sustainable composites based on a modified poly(lactic acid) (PLA) matrix and cellulose nanofibril (CNF) fillers. For this purpose, glycidyl methacrylate (GMA)‐grafted PLA (PLA‐g‐GMA) was fabricated via reactive melt‐mixing of neat PLA with GMA and it was melt‐compounded with different CNF filler loadings (0.5–10.0 wt%). The NMR and FT‐IR spectroscopic analyses of PLA‐g‐GMA/CNF composites confirmed that GMA was successfully grafted on the PLA backbone and that there are intermolecular chemical reactions and specific interactions between the GMA group of the PLA‐g‐GMA matrix and the hydroxyl group of the CNF filler in the composites. As the result, the glass transition and cold‐crystallization temperatures of the PLA‐g‐GMA matrix in the composites were measured to increase with the increase of CNF loading. In addition, the thermal decomposition temperature of the PLA‐g‐GMA matrix as well as the residue at 500°C of the composites increased with the CNF loading, resulting from the barrier and flame retardation roles of CNFs to the PLA‐g‐GMA matrix. The elastic storage moduli, impact strength, and complex viscosity were found to be higher for the composites with higher CNF loadings, which is due to the good interfacial adhesion between the PLA‐g‐GMA matrix and the CNF filler in the composites at glassy, rubbery, and melt states.

We conducted a study to analyze the impact of short aramid fibers (AFs) on the melt-rheological behavior, thermal transition, thermal stability, and mechanical durability of thermotropic liquid crystal polyesters (TLCPs). By using different AF loading contents ranging from 3–15 wt%, we produced TLCP matrix composites through masterbatch-based melt-compounding and injection-molding. The SEM images and FT-IR spectra demonstrate that the AFs are dispersed in the TLCP matrix with a microfibrillar structure through good interfacial adhesion caused by specific intermolecular interactions between the TLCP and AFs. As a result, the complex viscosity, shear storage/loss moduli, and thermal transition (melt-crystallization, glass transition, and melting) temperatures of the composites increase with increasing AF filler content. However, the melt-crystallization and melting enthalpies increase only at low AF loading contents of 3–5 wt%. At high AF contents of 7–15wt%, the enthalpies decrease owing to the partial aggregation of AF fillers. The thermogravimetric analysis proves that the thermal stability of TLCP/AF composites improves when the AF filler is introduced. The dynamic mechanical analysis using the stepped isothermal method shows that the addition of 5 wt% AF to the TLCP leads to an approximately 150% improvement in elastic moduli and long-term mechanical durability at elevated temperatures.