Document Type : Research Paper

Authors

• Masood Kafi ¹
• Rahmat Madandoust ²
• Heydar Dashti Nasserabadi ¹
• Javad Torkaman ³

¹ Department of Civil Engineering, Cha.C., Islamic Azad University, Chalus, Iran

² Department of Civil Engineering, University of Guilan, Rasht, Iran

³ Department of Wood and Paper Industry, University of Guilan, Rasht, Iran

Abstract

Background and Objectives: Cellulosic fibers particularly plant-based fibers have gained increasing importance as sustainable alternatives to synthetic materials in composite, automotive, and construction industries due to their renewability, low production cost, light weight, and favorable mechanical properties. Bamboo, characterized by its rapid growth, orderly fibrous structure, high strength, and biodegradability, represents a prominent resource for bio‑composites. The bamboo cell wall is primarily composed of cellulose, hemicellulose, and lignin, with cellulose microfibrils embedded in a flexible hemicellulosic matrix within the primary wall. However, the intrinsic hydrophilicity and weak interfacial bonding of bamboo fibers pose major challenges in composite applications, necessitating chemical and thermal modification. This study aims to evaluate the effectiveness of boric acid (H₃BO₃), sodium hydroxide (NaOH), and boiling-water treatments on the physical and structural properties of bamboo. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were employed to characterize the modifications.
Materials and Methods: Bamboo samples (Phyllostachys vivax) were air-dried and cut into 3 × 3 cm specimens. The samples were divided into four groups: untreated control, boiling-water treatment (6 h immersion), boric acid treatment (1 h immersion in 6% solution), and sodium hydroxide treatment (10 h immersion in 1% solution). Prior to treatment, samples were oven-dried at (103 ± 2°C), and mass, volume, and density were recorded. Surface and thickness swelling were quantified using stereo-microscope images analyzed in Image J. Water absorption was measured at 24, 48, and 72 hours, and subsequently at weekly intervals up to four weeks. Molecular structural changes were assessed using FTIR, and microstructural variations were examined through SEM imaging.
Results: Physical assessments revealed that control samples exhibited moderate reductions in mass (8.38%) and volume (3.91%) after oven-drying. Samples treated with boiling water and NaOH showed increased density due to substantial mass and volume loss associated with extractive degradation. In contrast, boric acid treatment resulted in lower mass loss and a notable 6.80% increase in volume, leading to reduced density. After 28 days of immersion, all chemical and thermal treatments increased water absorption. Boric acid treatment exhibited the highest water uptake due to the hygroscopic nature of boron, whereas NaOH treatment showed increased porosity resulting from lignin and hemicellulose removal. Regarding swelling, boiling-water and NaOH treatments increased swelling, while boric acid treatment effectively reduced it through the formation of cross-linking bonds. FTIR analysis indicated that NaOH treatment degraded hemicellulose and lignin. In the boric acid spectrum, a reduction in hydroxyl peak intensity and the emergence of new B–O cross-linking bands were observed. SEM images confirmed a compact structure in the control sample, slight porosity in the boiling-water treatment, boron deposition in the boric acid treatment, and pronounced porosity in the NaOH treatment. These observations clearly demonstrated the role of boric acid in producing high water absorption but low swelling, and the role of NaOH in generating high swelling yet improved fiber–matrix adhesion.
Conclusion: This study demonstrates that chemical and thermal treatments effectively alter the bamboo cell-wall structure. Boric acid treatment, despite increasing water absorption, significantly reduces swelling and provides desirable dimensional stability for structural applications of bamboo—particularly as reinforcement in concrete. Conversely, NaOH treatment increases swelling and porosity but enhances fiber–matrix adhesion in composites. These findings, supported by spectral and microscopic analyses, address the challenges associated with the hydrophilicity of plant fibers and highlight the strong potential of bamboo in bio‑composite applications. Future research should focus on optimizing combined treatments and evaluating the industrial performance of treated bamboo products.

Keywords

• Keywords: Bamboo
• Water Absorption
• Swelling
• Spectroscopy
• Electron Microscopy

Main Subjects

• Wood Modification and Wood Preservation