Effect of Hygrothermal Treatment on the Porous Structure and Nanomechanics of Moso Bamboo

Abstract

Hygrothermal treatment is an environmentally friendly and efficient modification method. In this study, Moso bamboo was modified with hygrothermal treatments, and the results of nitrogen adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM) and nano indentation (NI) were then examined. Interestingly, the samples that underwent hygrothermal treatment at 180 °C and 117% RH (relative humidity) had the highest crystallinity (36.92%), which was 11.07% statistically larger than that of the control samples. Simultaneously, the total pore volume and average pore diameter (2.72 nm) dramatically decreased by 38.2% and 43.7%, respectively. The NI elasticity and hardness of the samples also reached the highest values under this condition; both increased by nearly 21% as compared with the control samples. Therefore, 180 °C is a favorable hygrothermal treatment temperature for Moso bamboo modification due to the porosity changes and the improvement of the nanomechanics of the cell walls. Moso bamboo is a renewable and abundant material that is also biodegradable and environmentally friendly 1. In the past few decades, more attention has been paid to the development of bamboo products as sustainable, cost-effective, and ecologically responsible alternative structural materials 2. For example, bamboo weaving, bamboo scrimber, and laminated bamboo can be used in outdoor flooring, landscaping, and structural applications 3-5. However, Moso bamboo, which is characterized by large amounts of hydrophilic hydroxyl groups and limited crystallinity, is unsatisfactory for engineered materials, which require a high dimensional stability and good mechanical properties. Therefore, modifications will be better to improve the dimensional stability and mechanical strength of Moso bamboo 6-8. Hygrothermal treatment is thought to be one of the most efficient methods of modification with minimal environmental hazards 9. Studies of the three polymeric components (cellulose, hemicellulose, and lignin) after the heated or superheated steam treatment of woods have already been published 10-12. Processing by superheated steam leads to the pyrolysis of these polymeric components 13. According to previous studies, hemicellulose, as the most reactive biomass component, will be hydrolyzed into oligomeric and monomeric structures depending on the temperature 14-16. During superheated steam processing, carbonic acids, mainly acetic acid, might initially be formed due to the cleavage of the acetyl groups of particular hemicelluloses 17-19 , leading to autocatalytic reactions of the cell wall constituents and an increase of relative crystallinity 13,20. Lignin is the least reactive woody component, but high-temperature conditions will increase the reactivity of the lignin and the bonds within the lignin complex will be cleaved, causing autocondensation 19. Moreover, it has been suggested that the hydroxyl groups in the microfibrils first degrade in amorphous regions during the hygrothermal process. There is a clear correlation between the ch...

Physical and Mechanical Properties of Bamboo Oriented Strand Board Under Various Post-Thermal Treatment Duration

“…Post-thermal treatment is an environmentally friendly technique because it does not use chemicals. The hygrothermal treatment has been shown to improve the dimensional stability of OSB (Ye et al 2020). The studies related to the post-thermal treatment of OSB have been carried out.…”

Cell Wall Pore Structures of Bamboo as Relation to Species and Tissue Types

“…Previous studies have focus on the quantitative determination of pore structure (e.g., pore shape, surface area, pore size distribution, pore volume) in micropore (<2 nm), mesopore (2-50 nm), and macropore (>50 nm) in native or pretreated wood cell (Chang et al, 2009;Yin et al, 2015). Very recently, the in uence of different treatments on the pore structure of bamboo has gaining much attention (Ye et al, 2020;Liu et al, 2021;Su et al, 2021a, b), but the native pore structure, especally the microspores, has not been fully characterized. Various techniques, such as gas sorption isotherms, mercury intrusion porosimetry, solute exclusion, thermoporosimetry, microscopic observations are available for determining pore structure of cell walls of plant materials (Papadopoulos et al, 2003).…”

Evaluation of surface properties of betung bamboo (Dendrocalmus asper) strands under various heat treatment duration and temperature

“…Each species of bamboo can be characterized by the average diameter of the culm and the stem wall thickness [6]. The bamboo culm wall contains a chain of cellulose and hemicellulose inside a matrix of lignin [7]. Bamboo can also be classified based on vascular bundle.…”

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