Surface modification and improvement of adhesive bondline shear strength in strands derived from date palm leaflets using selective chemical treatments

Document Type : Research Paper

Authors

1 Department of Paper Science and Engineering, Faculty of Wood & Paper Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.

2 Department of Wood and Paper Science, Faculty of Natural Resources, University College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

10.22059/jfwp.2026.407901.1384

Abstract

Introduction: The shortage of wood resources and growing environmental concerns have led to increasing attention toward agricultural residues as alternative raw materials for engineered wood products. Date palm leaflets offer potential for use in products such as oriented strand board (OSB) and laminated strand lumber (OSL). However, the cuticular layer, rich in waxes and extractives, hinders effective bonding with industrial resins. The objective of this study was to modify the surface structure of date palm leaflets through chemical treatments to enhance adhesion and improve the mechanical performance of bio-based composites.
Method: In this work, palm leaflets were subjected to individual and combined chemical treatments including sodium hydroxide (NaOH), sulfuric acid (H₂SO₄), and n-hexane. Surface and structural properties were characterized using water drop contact angle measurements, Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and a stereomicroscope. To assess the effectiveness of treatments on adhesive bonding, lap shear strength tests were conducted using two types of resins, phenol formaldehyde (PF) and polymeric diphenylmethane diisocyanate (pMDI), according to ASTM D7998.
Results: The results indicated significant modifications in the surface properties of treated samples. Contact angle measurements revealed reduced values after treatment, confirming improved wettability. FTIR spectra showed the weakening or removal of carbonyl and carboxyl functional groups due to different chemical treatments, demonstrating successful fat and wax elimination. FESEM and stereoscopic observations demonstrated changes in texture and porosity, as well as the removal of surface coatings. The shear strength test of the glue line also indicated that the combined n-hexane–hydroxide (HN) treatment produced the greatest improvement in bonding performance. When isocyanate resin was used, the shear strength in the HN treatment increased to 1.9 MPa, indicating a strong interaction between the treated surface and the resin, while the control sample recorded only about 0.28 MPa.
Conclusion: The findings of the present study showed that date palm leaflets contain a significant amount of waxes that disrupt adhesion. Modifying the surface of date palm leaflets using chemical treatments can significantly improve resin adhesion to the leaf surface and enhance mechanical strength. In addition to adhesion strength, the physical condition of the leaflets and environmental considerations are important for achieving sustainable production. Overall, this research paves the way for sustainable utilization of agricultural residues in the development of biobased composites.

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References

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Forest and Wood Products
Volume 79, Issue 1
June 2026
Pages 1-18

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