Towards Sustainable PP Composites: The Roles of Pineapple Crown Fibers ( PCFs ) and Functional Additives on the PP Rheological and Viscoelastic Behaviors

ABSTRACT This research presents a comprehensive rheological and viscoelastic study of polypropylene (PP) composites reinforced with pineapple crown fibers (PCF) and compatibilised using carboxylic acids (hexanoic acid, C6; hexanedioic acid, CC6), and polypropylene grafted with maleic anhydride (PPgMA). Combined experimental framework encompassing dynamic mechanical analysis (DMA), small‐amplitude oscillatory shear (SAOS), Generalized Maxwell modeling, continuous relaxation/retardation spectra were applied to investigate changes in PP/PCF interface in both melt and solid states. The incorporation of PCF increased the storage modulus (E′) of PP by approximately 65% at 30°C, from 910 to 1501 MPa, indicating restricted chain mobility. Among the compatibilised systems, CC6 exhibited the highest stiffness, reaching 1982 MPa at 30°C (further 32% increase relative to the non‐compatibilised composite), while reducing the adhesion parameter A from 0.138 to 0.081. Addition of PCF results in formation of a percolated filler‐network, increasing the zero‐shear viscosity from 1.42 × 10 3 to 2.01 × 10 4 Pa·s, and suppressing terminal relaxation behavior. The addition of compatibilisers reduced the zero‐shear viscosity to 8.57 × 10 3 –1.01 × 10 4 Pa·s, indicating disruption of fiber‐fiber interactions and enhanced fiber dispersion. Coupling agent produces different viscoelastic signatures. C6 exhibits limited interfacial efficiency and partial plasticisation; CC6 promotes localized bridging interactions, enhancing stiffness while retaining residual network contribution; PPgMA restores matrix entanglement dynamics and yields the most homogeneous stress‐transfer behavior. The study corroborates the use of relaxation and retardation spectra as tools to detect the governing mechanism in reinforced composites: fiber networking governing stress relaxation and/or interfacial adhesion controlling delayed deformation. These findings contribute to the proposal of combined framework linking rheological observables to interfacial physics and support use of carboxylic acids as a viable alternative to petrochemical compatibilisers.