<p>This study examines the flexural, dynamic mechanical, and rheological behavior of polylactic acid (PLA) composites reinforced with date palm fibers (DPF) subjected to alkaline (NaOH) and enzymatic treatments. The effect of fiber content and surface modifications was systematically evaluated. Flexural testing revealed that fiber incorporation increased PLA stiffness by up to 36% at 20 vol.% but reduced its strength. However, fiber treatments significantly improved composite performance relative to untreated systems rather than virgin PLA. NaOH-pectinase treatment yielded the highest modulus by 59%, while NaOH-xylanase/pectinase treatment enhanced strength, reaching values within 8% of neat PLA. Dynamical mechanical analysis confirmed these trends, showing a higher storage modulus and a lower damping factor for the treated composites, indicative of improved fiber-matrix interfacial adhesion. Interfacial interactions were further assessed using the degree of entanglement, adhesion factor, effectiveness coefficient, reinforcing efficiency factor, and Cole–Cole analysis. Rheological results showed that virgin PLA exhibits nearly Newtonian behavior, whereas composites display increased viscosity, enhanced elasticity, and more pronounced shear-thinning, especially at high volume fractions. Unlike conventional alkali-treated natural fiber composites, this work demonstrates that enzymatic treatment, particularly with pectinase, enables selective interface optimization, leading to a better balance between strength and stiffness, along with improved viscoelastic performance.</p> Graphical Abstract <p></p>