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There are on-going investigations on the utilization of pineapple leaf fibre (PALF) as a cheap, safe, and eco-friendly natural fibre. The present work aimed to improve PALF preparation using ultrasonication, investigate the adsorption kinetic and thermodynamic aspects of PALF dyed with berberine dye, and to assess their associated molecular interactions. It was found that concomitant PALF exposure to NaOH solution (5% w/v) plus ultrasonication for 20 min successfully removed non-cellulosic substances from the fibre surface in a very much shorter time compared with the traditional non-ultrasound assisted method (24 h). An adsorption isotherm study of dyeing, the treated fibre with the natural yellow dye berberine revealed a strong adsorption dependence on the pH of the berberine solution with optimal uptake occurring at pH 9–10. A deeper assessment of the mode of dye binding was undertaken by DFT − based calculations on a model cellulose unit and berberine. It revealed that the interaction between berberine and cellulose (PALF) at pH 9.00 was likely to be substantially stronger than at lower pH. From the adsorption kinetic results, a higher affinity and more dye uptake were observed before equilibrium was reached. The adsorption isotherm data could be represented by the Langmuir isotherm (R2 > 0.99). The enthalpy change (ΔH°) and entropy change (ΔS°) values of dyeing were found to be −17.0 kJ mol−1 and −19.4 J mol−1 K−1 respectively, which pointed to the dye adsorption being an exothermic process. The negative standard affinity (Δµo) values at the different temperatures of 30, 60, and 80 °C were −11.2, −10.6, and −10.2 kJ mol−1, respectively. It affirmed the dye adsorption process as a spontaneous one. Higher temperatures resulted in a lower affinity and reduced dye uptake compatible with the process being exothermic. Berberine is a potentially useful natural dye for PALF without the need for additives. [ABSTRACT FROM AUTHOR]