This novel study explores a comprehensive approach, combining fiber and matrix structure–property relationships. By integrating alkali treatment, fiber mapping, and intrinsic fiber properties, this work offers a unique perspective on the mechanical, physical, and thermal properties of biodegradable composites of reinforced polypropylene (PP) and plasticized poly (lactic acid) (PLA), with 25 wt% Kenaf (KBF), Bagasse, Hemp fibers and softwood fibers serving as a control. To enhance fiber–matrix interaction, fibers underwent alkaline treatment using 5% sodium hydroxide (NaOH) for one hour. The mechanical properties, including tensile strength, Young’s modulus, and impact strength, were evaluated alongside physical and thermal properties such as fiber mapping, brightness, heat deflection temperature (HDT), melting temperature, melt flow ratio (MFR), and melt flow index (MFI). Scanning electron microscopy (SEM) was used to assess the biocomposites’ morphology. The results showed that fiber reinforcement improved the tensile and impact strength of PP composites, particularly for treated Bagasse (6.6% and 22%) and Hemp (7% and 44.7%), while Kenaf exhibited minimal change, indicating its inherently high strength. A slight increase in tensile strength and Young’s modulus was observed in all PLA-based composites. The addition of 25% fiber enhanced the thermal properties of both treated and untreated fiber-reinforced composites. Among PP composites, those reinforced with treated fibers exhibited the highest HDT, with Kenaf achieving the best performance (124 °C), followed by Bagasse (93 °C). The HDT values for untreated fibers were 119 °C for KBF, 100 °C for softwood, 86 °C for Bagasse, and 79 °C for Hemp. PLA composites showed a slight increase in HDT with fiber reinforcement. Differential Scanning Calorimetry (DSC) revealed a slight decrease in melting temperature for PP composites and a slight increase for PLA composites. Fiber mapping analysis indicated that Kenaf had the highest aspect ratio, contributing to superior mechanical performance, while Hemp had the lowest aspect ratio and exhibited weaker mechanical properties. Overall, Kenaf and Bagasse fibers demonstrated superior mechanical and thermal properties, comparable to those of softwood fibers, whereas Hemp exhibited moderate performance. The variations in composites behavior were attributed to differences in fiber mapping, alkaline treatment, and the intrinsic properties of both the polymer matrices and the reinforcing fibers. These findings highlight the potential of treated natural fibers, particularly Kenaf and Bagasse, in enhancing the mechanical and thermal properties of biodegradable composites, reinforcing their suitability for sustainable material applications.

The aim of this research work was to investigate the influence of parameters such as particle size, mass/solvent ratio, temperature and spray drying on the tannin extraction process in order to develop cost-effective methods with better environmental and structural performance. The pods of Acacia nilotica ssp. tomentosa (ANT) were fractionated into three fractions, coarse fraction (C) (>2 mm), medium fraction (M) (1–2 mm), and fine fraction (F) < 1 mµ), and extracted with different water-to-pod ratios (2:1, 4:1 and 6:1) at different temperatures (30, 50 and 70 °C). The best results were scaled up using the three fractions of ANT, its bark and the bark of Acacia seyal var. seyal (ASS). Part of their extract was spray dried. The tannin content and total polyphenolic materials were evaluated using standard methods. Their adhesives were tested for their tensile strength. Tannins of ASS were characterized by ¹³C NMR and MALDI-TOF. The results revealed that the fine fraction (F) gave the highest percentage of tannins in both small and scaled-up experiments. The results of the tensile strength conformed to the European standard. The ¹³C NMR spectra of ANT and ASS showed that the bark contained condensed tannins mainly consisting of procyanidins/prodelphinidin of 70%/30% and 60%/40%, respectively. MALDI–TOF spectra confirmed the results obtained by ¹³C NMR and detailed the presence of flavonoid monomers and oligomers, some of which were linked to short carbohydrate monomers or dimers.

This study aims to develop high-performance biocomposites for structural applications using kenaf, bagasse, hemp, and softwood fibers bonded with phenol-formaldehyde (PF) and phenol-urea-formaldehyde (PUF) adhesives, commonly used in particleboard manufacturing. A simple, low-cost fiber treatment was applied by adjusting the fiber pH to 11 and 13 using a 33% NaOH solution, following standard protocols to enhance fiber–adhesive interaction. The effects of alkaline treatment on the chemical structure of bagasse, kenaf, and hemp fibers were investigated using Fourier Transform Infrared Spectroscopy (FTIR) and correlated with composite mechanical performance. PF and PUF were applied at 13% (w/w), while polymeric diphenylmethane diisocyanate (pMDI) at 5% (w/w) served as a control for untreated fibers. The fabricated panels were evaluated for mechanical properties; modulus of elasticity (MOE), modulus of rupture (MOR), and internal bond strength (IB), and physical properties such as thickness swelling (TS) and water absorption (WA) after 24 h of immersion. FTIR analysis revealed that treatment at pH 11 increased the intensity of O–H, C–O–C, and C–O bands and led to the disappearance of the C=O band (~1700 cm⁻¹) in all fibers. Bagasse treated at pH 11 showed the most significant spectral changes and the highest IB values with both PF and PUF adhesives, followed by kenaf at pH 13, exceeding EN 312:6 (2010) standards for heavy-duty load-bearing panels in dry conditions. The highest MOE and MOR values were achieved with kenaf at pH 11, meeting EN 312:4 (2010) requirements, followed by bagasse, while softwood and hemp performed less favorably. In terms of thickness swelling, bagasse consistently outperformed all other fibers across pH levels and adhesives, followed by Kenaf and Hemp, surpassing even pMDI-based composites. These results suggest that high-pH treatment enhances the reactivity of PF and PUF adhesives by increasing the nucleophilic character of phenolic rings during polymerization. The performance differences among fibers are also attributed to variations in the aspect ratio and intrinsic structural properties influencing fiber–adhesive interactions under alkaline conditions. Overall, kenaf and bagasse fibers emerge as promising, sustainable alternatives to industrial softwood particles for structural particleboard production. PF and PUF adhesives offer cost-effective and less toxic options compared to pMDI, supporting their use in eco-friendly panel manufacturing. FTIR spectroscopy proved to be a powerful method for identifying structural changes caused by alkaline treatment and provided valuable insights into the resulting mechanical and physical performance of the biocomposites.