The durability of bamboo based on its chemical and mechanical properties is a crucial consideration for the wood-based industry due to its vulnerability to insects and microorganisms. We investigated the dynamic changes of chemical and mechanical properties of
Bamboo has become the most important non-wood material for the wood-based industry due to its easy propagation, fast growth and high productivity [
In the vast rural areas of south of China, it is often not possible to transport bamboo culms to factories in time for processing and utilization after being logged. They are air-dried
Moso bamboo (
The control groups of 9 culms (3 culms in each of the 3 age groups) were used to analyze the chemical and mechanical properties, and the soluble sugar and starch contents. For analytical comparison, 27 culms (3 culms in each of the three age groups from three drying periods) were exposed for drying under natural climatic conditions (3, 6 and 12 months) and the rest 27 culms of three age groups were stored in pond water for the same time periods.
We oven-dried the internode strips at 60°C for 24 h and ground in a Wiley mill (FW100, China). Milled material passing a 40-mesh sieve but retaining on 60 mesh screen was used for chemical analyses, which were carried out in compliance with the Chinese National Standards for Testing and Materials. We carbonized the milled samples in a porcelain crucible on an electric stove and then in a muffle furnace at 575 ± 25°C for 2 h. Ash samples were then taken out, cooled to room temperature and weighted (Ash-GB/T 2677.3-93). And then, we added 5 mL of 6 mol/liter HCl which was evaporated in a steam bath. Based on three repetitions, distilled water was used to rinse the residue which was then filtered, and moved to the same muffle furnace and heated at 575 ± 25°C for 2 h and SiO2 weight was obtained (SiO2-GB/T7978). We packaged the milled samples using filter paper and loaded them in a Soxhlet extractor. Benzene alcohol solution (2:l) was applied for 6 h water-bath extraction and the extracts were weighed (Toluene–alcohol extractives-GB/T10741-89). The residue was unpackaged and moved into a conical flask for 2 h water-bath with 15 mL of sulfuric acid (72%). Then, we added distilled water to 560 mL, and after 4 h water-bath, we filtered the solution, rinsed the residue using distilled water, which was dried and weighed to determine acid-insoluble lignin content. Filtrate of the acid-insoluble lignin was metered by ultraviolet spectrophotometer (752 N Hengping) under the absorbance at 205 nm to be acid-soluble lignin (Lignin-GB/T 2677.8-94, GB/T 10337-2008). After 6 h water-bath for extraction, samples were loaded into a conical flask, and mixed with 65 mL distilled water, 0.5 mL acetic acid, and 0.75 g sodium chlorite. After 1 h water-bath at the constant temperature 75°C, and then mixed with 0.5 mL acetic acid and 0.75 g sodium chlorite. We obtained whitish materials after four repeated procedures. Filtering and rinsing with distilled water was practiced until filtrate from the solution presented no acidity. Lastly, we washed the residue 3 times using acetone, dried and holocellulose weight was obtained (Holocellulose-GB/T 2677.10-1995). Each test was triplicated.
We determined the soluble sugar and starch contents using the phenol-sulfuric acid method [
The samples for mechanical properties were derived from internodes 11 (middle portions of the culms), which were usually one of the longest internodes of the culms. These internodes were stored in a conditioning room maintained at 23°C and 65% relative humidity until moisture content (12%) was achieved. The procedures used for the determination of mechanical properties (compressing strength, tensile strength and bending strength) were conducted according to the Chinese National Standards for Testing Methods for Physical and Mechanical properties of bamboo (GB/T 15780-1995). Each test was triplicated.
The average chemical compositions of the
Storage condition | Position | Age class | Ash | SiO2 | Ethanol–benzene extracts | Lignin | Holocellulose | ||
---|---|---|---|---|---|---|---|---|---|
Acid-soluble | Acid-insoluble | Lignin | |||||||
Control | I | 1.83A | 0.28AB | 4.59A | 2.61A | 29.42A | 32.03A | 65.97A | |
II | 1.68A | 0.21B | 4.62A | 2.82A | 29.27A | 32.09A | 67.24A | ||
III | 0.98B | 0.36A | 5.11A | 2.81A | 28.62A | 30.48A | 66.59A | ||
Top | 1.36a | 0.23a | 4.58a | 2.76a | 28.27a | 31.01b | 67.69a | ||
Middle | 1.72a | 0.33a | 4.88a | 2.83a | 30.09a | 32.92a | 66.34a | ||
Bottom | 1.42a | 0.29a | 4.85a | 2.67a | 28.94a | 30.67b | 65.77a | ||
3M Water stored | I | 1.12A | 0.28A | 0.80B | 2.08A | 25.60A | 27.68A | 67.93A | |
II | 1.17A | 0.34A | 2.05A | 1.78B | 24.29A | 26.07A | 66.68A | ||
III | 0.59B | 0.34A | 1.89A | 2.15AB | 24.84A | 26.99A | 69.49A | ||
Top | 0.94a | 0.41a | 2.05a | 1.95a | 23.90a | 25.85a | 67.60a | ||
Middle | 1.25a | 0.27a | 1.85a | 2.00a | 26.10a | 28.10a | 69.95a | ||
Bottom | 0.68a | 0.27a | 1.73a | 2.07a | 24.72a | 26.79a | 66.55a | ||
3M Air dried | I | 2.77A | 0.46B | 1.37B | 1.88B | 19.42B | 21.30B | 65.97A | |
II | 1.70B | 0.28B | 2.05A | 2.43A | 22.70A | 25.13A | 67.21A | ||
III | 0.79C | 0.91A | 1.89AB | 2.15AB | 22.63A | 24.80A | 66.59A | ||
Top | 1.68a | 0.56a | 1.89a | 2.42a | 21.05a | 23.46a | 66.15a | ||
Middle | 2.00a | 0.46a | 1.69a | 2.07a | 21.24a | 23.31a | 66.12a | ||
Bottom | 1.58a | 0.60a | 1.73a | 1.99a | 22.45a | 24.40a | 67.51a | ||
6M Water stored | I | 0.74A | 0.22A | 4.52A | 2.10B | 23.83A | 25.93A | 62.86B | |
II | 0.76A | 0.23A | 4.86A | 2.96A | 21.89B | 24.85A | 66.02A | ||
III | 0.75A | 0.25A | 5.12A | 3.06A | 24.00A | 25.98A | 66.29A | ||
Top | 0.66a | 0.33a | 4.53a | 2.71a | 23.43a | 26.11a | 64.68a | ||
Middle | 0.81a | 0.20a | 5.18a | 2.60a | 22.92a | 25.52a | 64.76a | ||
Bottom | 0.79a | 0.16a | 4.78a | 2.84a | 23.37a | 25.13a | 65.74a | ||
6M Air dried | I | 2.71A | 0.27B | 1.38A | 2.26A | 28.59A | 30.85A | 65.91B | |
II | 2.11A | 0.22B | 0.90A | 1.81A | 30.25A | 32.06A | 72.83A | ||
III | 2.01A | 0.65A | 0.98A | 2.45A | 29.45A | 31.31A | 73.95A | ||
Top | 2.19a | 0.39a | 1.23a | 2.19a | 30.58a | 32.77a | 66.91b | ||
Middle | 2.13a | 0.41a | 1.10a | 2.26a | 28.36a | 30.63a | 71.23ab | ||
Bottom | 2.49a | 0.35a | 0.94a | 2.06a | 29.35a | 30.72a | 74.54a | ||
12M Water stored | I | 0.91A | 0.30A | 3.40A | 2.73A | 22.57A | 25.30A | 63.81A | |
II | 0.60A | 0.25B | 2.87A | 2.24A | 22.43A | 24.74A | 64.71A | ||
III | 0.61A | 0.42A | 3.81A | 2.54A | 22.99A | 25.53A | 67.27A | ||
Top | 0.71a | 0.37a | 3.35a | 2.32a | 21.46a | 25.75a | 65.31a | ||
Middle | 0.81a | 0.26a | 4.05a | 2.63a | 23.35a | 25.98a | 65.07a | ||
Bottom | 0.61a | 0.35a | 2.68a | 2.56a | 23.19a | 23.77a | 65.40a | ||
12M Air dried | I | 2.21A | 0.38B | 2.56A | 1.58B | 22.47B | 24.05B | 64.37A | |
II | 1.60B | 0.34B | 2.00A | 2.51A | 24.13AB | 26.64AB | 62.47B | ||
III | 1.18B | 0.57A | 1.79B | 2.11AB | 27.38A | 28.68A | 64.92A | ||
Top | 1.50a | 0.45a | 2.37a | 1.99a | 23.98a | 25.97a | 64.42a | ||
Middle | 1.64a | 0.37a | 2.22a | 1.85a | 23.26a | 25.12a | 63.88a | ||
Bottom | 1.85a | 0.48a | 1.76a | 2.35a | 26.73a | 28.28a | 63.47a |
Capital letters (A, B, C) in the same column denote the statistical difference of the chemical compositions among different culm ages at
Under the air-dry condition, the average ash content of
Under the air-dry condition, the SiO2 content of
Under the air-dry condition, the ethanol-benzene extract of the culms showed an obviously decreasing trend, and the lowest value occurred in 6-month culm (1.09%). While under the water storage condition, the ethanol-benzene extract declined in the 3rd month, but did not show significantly decreasing trend in the 6th and 12th month (
Under the air-dry condition, the lignin content of
The holocellulose content was stable and showed no obvious difference under both the air-dry and water storage condition as compared to that of the control. In addition, no specific trend was found with the increment of storage time (
Soluble sugar and starch are the principal forms of carbohydrate storage in vegetative tissues of plants [
Age class | Position | Control | 3M | 6M | 12M | |||
---|---|---|---|---|---|---|---|---|
AD | WS | AD | WS | AD | WS | |||
I | Top | 1.13a | 1.96a | 2.24a | 1.54a | 1.97a | 1.26a | 2.51a |
Middle | 1.73b | 2.21b | 2.31a | 1.53a | 2.05a | 2.79b | 2.49a | |
Bottom | 2.63c | 2.52b | 2.76a | 2.88b | 2.57b | 2.84b | 2.16a | |
Mean | 1.83A | 2.23A | 2.44B | 1.98A | 2.19B | 2.28A | 2.38A | |
II | Top | 2.23b | 1.96a | 1.71a | 2.43b | 1.46a | 2.32b | 2.62b |
Middle | 1.58a | 2.21ab | 1.76a | 1.54a | 2.07b | 2.34b | 2.30b | |
Bottom | 2.16a | 2.52b | 1.91a | 1.53a | 1.61a | 1.54a | 1.85a | |
Mean | 1.94B | 2.41A | 1.79A | 1.84A | 1.77A | 2.07A | 2.26A | |
III | Top | 2.68b | 2.23b | 1.59a | 2.41a | 2.05a | 2.96a | 1.73a |
Middle | 2.14a | 1.60a | 1.66a | 2.10a | 1.97a | 2.73a | 2.65b | |
Bottom | 2.29a | 2.23b | 1.96a | 2.77a | 1.78a | 2.66a | 2.85b | |
Mean | 2.33B | 1.95A | 1.74A | 2.43B | 1.93A | 2.78B | 2.41A | |
Means | Top | 2.13a | 2.26a | 1.83a | 2.37a | 1.83a | 2.58a | 2.48a |
Middle | 2.05a | 2.15a | 1.93a | 2.01a | 2.06a | 2.28a | 2.37a | |
Bottom | 2.01a | 2.07a | 2.22a | 1.86a | 2.05a | 2.36a | 2.20a |
Capitalized letters (A, B, C) in the same column denote the statistical difference among different culm ages at
Age class | Position | Control | 3M | 6M | 12M | |||
---|---|---|---|---|---|---|---|---|
AD | WS | AD | WS | AD | WS | |||
I | Top | 3.21a | 1.45a | 2.03a | 1.90a | 1.53a | 2.73a | 1.77a |
Middle | 2.19b | 1.49a | 1.95a | 1.87a | 1.21b | 3.21a | 1.72a | |
Bottom | 2.85b | 1.46a | 1.70a | 1.81a | 1.18b | 2.09a | 1.80a | |
Mean | 2.75AB | 1.47B | 1.89A | 1.86A | 1.31B | 2.68AB | 1.76A | |
II | Top | 4.09a | 3.18a | 1.76a | 1.66a | 1.41a | 2.05a | 1.47a |
Middle | 2.78b | 3.12a | 1.88a | 1.43a | 1.25a | 2.27a | 1.64a | |
Bottom | 2.95b | 2.65a | 1.74a | 1.67a | 1.32a | 1.99a | 1.43a | |
Mean | 3.27A | 2.99A | 1.79A | 1.59B | 1.33B | 2.11B | 1.52AB | |
III | Top | 2.75a | 2.98ab | 2.21a | 1.99a | 1.64a | 4.00a | 1.69a |
Middle | 2.60a | 3.85a | 1.76b | 2.23a | 1.43a | 3.15b | 1.34a | |
Bottom | 2.52a | 2.24b | 1.88ab | 1.97a | 1.44a | 3.16b | 1.38a | |
Mean | 2.63B | 3.05A | 1.95A | 2.06A | 1.51A | 3.44A | 1.47B | |
Means | Top | 3.35a | 2.54ab | 2.00a | 1.85a | 1.53a | 2.93a | 1.64a |
Middle | 2.52b | 2.52a | 1.86a | 1.84a | 1.30b | 2.88a | 1.57a | |
Bottom | 2.77b | 2.12b | 1.77a | 1.82a | 1.31b | 2.41a | 1.54a |
The biologically perishable properties of bamboos are assumed to be mainly caused by its high sugar and starch contents, which are excellent foods for fungi or insects [
Under the air-dry condition, the soluble sugar content of
In our study, both the starch and the soluble sugar content of the
The physical and mechanical properties of bamboo depend on many factors such as species, season, soil, height, age, presence of node section, environmental conditions [
Age class | Position | Control | 3M | 6M | 12M | |||
---|---|---|---|---|---|---|---|---|
AD | WS | AD | WS | AD | WS | |||
I | Compressive strength | 69.62a | 52.94b | 50.08b | 48.06b | 56.85b | 65.89a | 61.69b |
Bending strength | 124.08b | 109.17b | 123.55b | 71.23c | 135.25b | 84.96c | 191.06a | |
Tensile strength | 210.79a | 204.98a | 195.42a | 213.94a | 183.58a | 219.48a | 202.71a | |
II | Compressive strength | 74.26a | 43.99b | 58.01ab | 53.67ab | 53.00ab | 67.53a | 57.85ab |
Bending strength | 148.29a | 106.37b | 115.23b | 119.49b | 142.28a | 109.51b | 124.08ab | |
Tensile strength | 216.63b | 219.32b | 207.13b | 243.58a | 220.69b | 256.21a | 234.80a | |
III | Compressive strength | 73.62a | 58.74ab | 48.83b | 59.61ab | 50.76b | 69.23a | 60.57ab |
Bending strength | 140.14a | 79.82c | 105.42b | 107.82b | 133.17a | 119.96b | 114.74b | |
Tensile strength | 248.88a | 256.90a | 204.23b | 206.66b | 187.74c | 240.13a | 208.19b | |
Means | Compressive strength | 72.50 | 51.89 | 52.31 | 53.78 | 53.54 | 67.55 | 60.04 |
Bending strength | 137.50 | 98.45 | 114.73 | 99.51 | 136.90 | 104.81 | 143.29 | |
Tensile strength | 225.43 | 227.07 | 202.26 | 221.39 | 197.34 | 238.61 | 215.23 |
Low-case letters (a, b, c) in the same row denote the statistical difference of the mechanical properties under different conditions at
The compressive strength of the
In terms of furniture manufacturing, bending strength appears to be an important material property of wood [
Under the air-dry condition, the mean tensile strength of the
There are some explanations for strength reduction based on earlier research, such as decreasing equilibrium moisture content of wood and volumetric expansion, degradation of wood components (cellulose and especially the hemicelluloses), and evaporation of extractives [
The chemical and mechanical properties of