Pineapple leaf fibers strengthened by alkali treatment for sustainable composites

Pineapple leaf fibers can be significantly enhanced through a simple alkali treatment, according to a study published on July 8, 2026, by researchers at Newcastle University in Singapore. This treatment improves the fibers' structural and mechanical properties, making them suitable for sustainable natural-fiber epoxy composites.

Improving Fiber Strength Through Alkali Treatment

Pineapple leaf fiber has been traditionally used in Southeast Asia for various applications, including basketry and textiles. With its high cellulose content and availability as an agricultural byproduct, it presents an attractive option for reinforcing polymer composites. The study led by Thanistha Akarapoowadol and colleagues focuses on how alkali treatment can enhance the intrinsic mechanical properties of these fibers.

Typically, alkali treatment involves the use of sodium hydroxide, which cleans the fiber surface by removing noncellulosic materials such as lignin and hemicellulose. Previous research has often linked improved composite performance to better fiber-matrix adhesion. However, this study reveals that alkali treatment can also strengthen the fibers themselves.

Key Findings on Fiber and Composite Performance

Using X-ray diffraction, the researchers confirmed that the cellulose I crystalline phase remains intact while the crystalline order of the fiber increases post-treatment. The removal of amorphous components contributes to this structural refinement. To assess the fibers' intrinsic mechanical properties, the team employed the Impregnated Fiber Bundle Test, which minimizes the influence of fiber-matrix interfacial adhesion.

• Fiber modulus increased from 18 GPa to 29 GPa.
• Fiber strength improved from 390 MPa to 530 MPa.

These results provide clear evidence that alkali treatment enhances the fiber's intrinsic properties, translating into stronger composites. When 20 wt% treated pineapple leaf fiber was incorporated into epoxy, the resulting composites demonstrated remarkable increases:

• 200% increase in flexural modulus
• 180% increase in flexural strength
• 400% increase in notched impact resistance

Implications for Sustainable Materials

The study's findings underscore the potential for utilizing pineapple leaves, which are often considered agricultural waste, as a valuable resource in developing sustainable materials. By enhancing the performance of these fibers, the research supports a transition towards more eco-friendly biobased composites.

This work illustrates the broader implications of converting agricultural residues into high-performance materials, contributing to the goals of a circular bioeconomy. As countries like Thailand look to reduce reliance on synthetic reinforcements, this research paves the way for innovative applications in engineering and manufacturing.