Simple treatment strengthens pineapple leaf fibers for sustainable composites
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Pineapple leaf fiber has long been valued in parts of Southeast Asia for traditional uses, including basketry in Malaysia and Thailand and textile applications in the Philippines. Its high cellulose content and ready availability as an agricultural residue have also made it attractive as a reinforcement for polymer composites.
Alkali treatment has long been used to improve natural-fiber composites, but whether it actually strengthens the fibers themselves has remained unclear.
A new study by Thanistha Akarapoowadol, Kheng Lim Goh and Taweechai Amornsakchai, published in ACS Omega, builds on this longer history of use by examining how a simple and widely used alkali treatment can more consistently improve the fiber's structural and mechanical properties for epoxy composite reinforcement.
Alkali treatment, usually carried out using sodium hydroxide, is already one of the most common methods for improving natural fiber composites. It is typically understood as a way to clean the fiber surface by removing noncellulosic materials such as lignin and hemicellulose, thereby improving bonding between the fiber and polymer matrix.
However, this explanation is incomplete. Many previous studies have attributed better composite performance mainly to improved fiber–matrix adhesion, even though composite testing alone cannot easily separate interfacial effects from changes occurring within the fiber itself.
Moreover, improvements in the intrinsic mechanical properties of natural fibers after alkali treatment are not universal. While some fiber species show enhanced performance, others exhibit little improvement or even reduced stiffness following treatment. These differences suggest that the response to alkali treatment depends strongly on the internal structure of each fiber.
The new study shows that alkali treatment can strengthen the fiber itself, rather than merely improving its bonding with the surrounding polymer. Using X-ray diffraction, the researchers found that the cellulose I crystalline phase was retained, while the crystalline order of the fiber increased. This structural refinement was linked to the removal of amorphous components such as hemicellulose and lignin.
To measure the fiber's intrinsic mechanical properties, the team used the Impregnated Fiber Bundle Test, which reduces the influence of fiber–matrix interfacial adhesion. The results showed that alkali treatment increased the fiber modulus from 18 to 29 GPa and the fiber strength from 390 to 530 MPa. These findings provide direct evidence that alkali treatment strengthens the fiber itself, rather than improving composite performance solely through better fiber–matrix bonding.
These fiber-level improvements translated into stronger composites. When 20 wt% treated pineapple leaf fiber was incorporated into epoxy, the resulting unidirectional composites showed increases of 200% in flexural modulus, 180% in flexural strength and 400% in notched impact resistance compared with neat epoxy.
The findings help clarify why alkali treatment can work effectively for pineapple leaf fiber composites. Rather than improving performance only through better adhesion, the treatment can also reinforce the fiber's internal structure. This provides a clearer basis for designing stronger, more reliable biobased composites from agricultural residues.
Because pineapple leaves are an abundant agricultural byproduct in many tropical countries, including Thailand, improving their reinforcing performance could increase the value of agricultural waste, reduce reliance on synthetic reinforcements and support the development of sustainable materials within the circular bioeconomy. More broadly, the work illustrates how agricultural residues can be converted into value-added materials for advanced engineering applications.
Publication details
Thanistha Akarapoowadol et al, Effect of Alkali Treatment on the Mechanical and Structural Properties of Pineapple Leaf Fiber for Epoxy Composite Reinforcement, ACS Omega (2026). DOI: 10.1021/acsomega.5c07292
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Citation: Simple treatment strengthens pineapple leaf fibers for sustainable composites (2026, July 8) retrieved 13 July 2026 from https://phys.org/news/2026-07-simple-treatment-pineapple-leaf-fibers.html
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