The Inuence of Saturated Steam on Moso Bamboo Quasi-static Micromechanical Properties: NanoScale Evaluation

: 14 In this paper, in order to analyze the quasi-static properties of Moso bamboo, a 15 new, environmentally friendly and eco-friendly method was used for bamboo thermal 16 modification under the effect of saturated steam. Under saturated steam heat treatment, 17 the chemical composition in bamboo decreased, and the bamboo cell wall shrunk 18 slightly. The increased crystallinity index of cellulose and decreased intensity of peaks 19 belong to hemicellulose were confirmed by XRD and Fourier transform infrared (FTIR) 20 spectroscopy. In addition, the highest modulus of elastic and hardness of treated 21 bamboo were 22.5GPa and 1.1GPa at 180℃/10 min. These conclusions confirmed the 22 micro-mechanical properties of the bamboo cell wall were enhanced by saturated steam 23 heat treatment. The 𝐄 𝐫 ′ of differently treated bamboo increased with increasing 24 temperature and time, while the 𝐄 𝐫 ′′ and tan δ negatively as a function of increasing 25 frequency. Furthermore, this thermal modification can be regarded as a useful, 26 environmental-friendly and eco-friendly treatment to outdoor use of bamboo-based materials.


Introduction
Bamboo belongs to the Gramineae family and has been widely used in many fields  36 However, bamboo is easily affected by fungi, moisture, and injurious insect due to its 37 abundance in polysaccharides and starch, which limits the outdoor utilization of 38 bamboo-based products. Meanwhile, when bamboo-based engineered bamboo 39 materials are applied for long-term usage, it is easy to produce problems like short 40 product life, low dimensional stability, and low resistance to biodegradation. So, it is 41 of great importance to improving the physical and mechanical properties of bamboo to 42 solve the above problems. 43 Thermal modification has been widely applied in making bamboo-based products, 44 which can effectively improve the physical and mechanical properties of bamboo 45 products. The aim of thermal modification is to change the polysaccharide and starch 46 content and microstructure of bamboo tissue, to improve the macro-mechanical 47 The different treated bamboo specimens were ground into powder and sieved 94 through an 80 mesh screen. The samples were then placed in an oven for 12 hours until 95 the moisture content was 0%. Then, the XRD method (Ultima-IV combination X-ray 96 diffractometer, Japan) was utilized to analyze the crystallinity of bamboo cellulose at 97 different treatment temperatures and times. Data were collected in the 2-theta scanning 98 range from 10° to 80°. Based on Segal's formula, the XRD analysis results constituted 99 the average of three replicate experiments, and relative crystallinity can be calculated 100 as below: where CrI represents the relative content of crystallinity, and I002 and Iam denote the

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The powders used in XRD analysis were also used to FTIR analysis on a FTIR 106 spectrometer (500-4000 cm -1 range, 32 accumulations, 2 cm -1 resolution; Bruker  The treated and untreated bamboo were possessed into the average size of 10*10*T 112 mm (length*width*thickness) and the density was tested by oven-drying method. Ten Where m0 represents the initial oven-dried specimen mass, m1 represents the 116 oven-dried specimen mass after saturated steam heat treatment 117

Chemical compositions analysis
In this step, the treated bamboo samples were ground and screened into powder using 40 and 80 screens. The main chemical composition (cellulose, hemicellulose, and 120 lignin content) of samples was determined and calculated according to NREL'S LAPs.

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All data were represented as averages of three replicate experiments, closest to 0.1%. indentations (see Figure 1). Loading was performed within 5s, the holding time was 5s, 129 and unloading terminated within 5s. A peak load (400μN) were applied to all indents.

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All data were averages of 30 valid data. hardness can be calculated as formula follows: where Pmax is the peak load, and A denotes the projected contact area of the indents at 135 peak load.
where Er, S(dP/dh), and β represent the combined elastic modulus of both the 137 specimen and indenter, the initial unloading stiffness, and the correction factor to indent 138 geometry (β = 1.034), respectively.

XRD analysis 220
Cellulose, the main composition of bamboo, is the main reason for the strength of     Nanoidentation. As is illustrated in Figure 8. the average creep ratio of the untreated 289 sample was 27.2%, which was higher than that of the treated bamboo cell wall. In the   to frequency, in other the main chain movements decreased with increasing frequency.

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In conclusion, the loss modulus decreased significantly. Enhanced frequency 314 contributed negatively to the loss tangent, this is due to the shorter molecular chain