Document Type : Research Paper
Authors
1 University of Guilan
2 Department of Civil Engineering, Cha.C., Islamic Azad University, Chalus, Iran
3 Department of Wood and Paper Industry, University of Guilan, Rasht, Iran
Abstract
Abstract
Background and Objective: Cellulosic fibers, especially plant fibers, have gained importance as sustainable alternatives to synthetic materials in the composite, automotive, and construction industries due to their characteristics such as renewable, low production cost, light weight, and suitable mechanical properties. Bamboo, with its fast growth, regular fiber structure, high strength, and biodegradability, is an outstanding source for biocomposites. The bamboo cell wall consists of cellulose, hemicellulose, and lignin, with cellulose forming the hard core and hemicellulose forming the primary flexible wall. However, the inherent hydrophilicity and poor adhesion of bamboo fibers pose significant challenges in composite applications that require chemical and thermal modifications. The main objective of this study is to evaluate the effectiveness of modification treatment methods including boric acid (H3BO3), sodium hydroxide (NaOH), and boiling water on the physical and structural properties of bamboo. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to accurately evaluate the results.
Materials and Methods: Three-year-old bamboo (Phyllostachys vivax) samples were obtained from Lahijan city, Gilan province, and after drying in the open air, 3×3 cm pieces were separated from the area near the stem collar. The samples were categorized into four groups: control (SP-RA), boiling water treatment (SP-WA), boric acid (SP-BO), and soda (SP-SO). Before treatment, the samples were dried in an oven at 103 ± 2 °C and the mass, volume, and specific gravity were measured. The treatment conditions were as follows: 6 hours of immersion in boiling water (thermal), 1 hour of immersion in a 6% boric acid solution at 60 °C, and 10 hours of immersion in a 1% soda solution at 70 °C. The surface swelling percentage and thickness were calculated using stereo microscope images and Image-J software. The percentage of water absorption was measured at 24, 48, 72 hours and then weekly intervals. The changes in molecular structure were compared with FTIR (range 500-3500 cm-1) and microstructure of the samples with SEM images (magnification 20 µm) after gold coating.
Results: Physical studies showed that the control samples experienced a moderate decrease in mass (8.38%) and volume (3.91%) after drying in the oven. The samples treated with boiling water and sodium hydroxide showed an increase in density due to a significant decrease in volume and mass due to the decomposition of extractives. In contrast, boric acid treatment was associated with a smaller mass loss and a 6.80% increase in volume, which led to a decrease in density.
The results of water absorption after 28 days of immersion showed that all thermal and chemical treatments increased the percentage of water absorption. Boric acid treatment showed the highest water absorption due to the hygroscopic properties of boron, and soda treatment showed an increase in porosity due to the removal of lignin and hemicellulose. Regarding swelling, boiling water and soda treatments increased it, but boric acid treatment effectively reduced the percentage of swelling due to the formation of crosslinks.
FTIR results showed that sodium hydroxide treatment confirmed the removal of hemicellulose and the reduction of lignin. In the boric acid spectrum, a decrease in the intensity of the hydroxyl group peak and the appearance of new peaks related to B-O crosslinks were observed. SEM images confirmed the compact structure in the control sample, and a slight increase in porosity in boiling water, boron precipitation in boric acid treatment, and high porosity in sodium hydroxide treatment, respectively. These observations clearly demonstrated the effect of boric acid on high water absorption and low swelling, and the effect of sodium hydroxide on high swelling and better adhesion.
Conclusion: This study proved that chemical and thermal treatments effectively modify the structure of bamboo cell walls. Boric acid treatment significantly reduced swelling (despite increasing water absorption), providing favorable dimensional stability for strength applications such as concrete. In contrast, sodium hydroxide improved the adhesion of fibers to the composite matrix by increasing swelling and porosity. These results were comprehensively confirmed by spectral and microscopic analyses. These findings address the challenges of hydrophilicity of plant fibers and highlight the high potential of bamboo in biocomposites. Future research should focus on the optimal combination of treatments and industrial evaluation of the products.
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