Preparation and Performance Study of Bamboo-Wood Mixed Hollow Particleboard

Hollow particleboard possesses characteristics such as sound insulation, thermal insulation, impact resistance, dimensional stability, low susceptibility to deformation, and a smooth surface. It is an ideal filling material for wooden door cores and can also be used for partition walls and dividers in large office spaces. Compared to regular particleboard, hollow particleboard requires only half the amount of raw materials to produce the same volume, meeting the requirements for door cores, partition walls, and other applications. It offers advantages such as resource conservation and high added value. In the context of sustainable development, hollow particleboard is gradually becoming a promising green and environmentally friendly product in China’s engineered board industry. By utilizing residual materials from bamboo product processing and mixing them with wood shavings, hollow particleboard retains the characteristics of hollow particleboard while also conserving resources by making use of bamboo processing remnants.

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This article provides an overview of the development history of hollow particleboard and the situation of bamboo resources in China. It explores the production process and performance of bamboo-wood mixed hollow particleboard by mixing residual materials from bamboo product processing with wood shavings. Additionally, it attempts to use the material to manufacture wooden door panels and analyze its social and economic benefits, providing insights for the industry.

Development History of Hollow Particleboard

Hollow particleboard originated in the late 1940s in Europe when Otto Kreibaum from West Germany invented the vertical extruder, known as the Okal system. As the main production equipment in hollow particleboard production lines, the introduction of the vertical extruder marked the emergence of the vertical extrusion process for hollow particleboard. Currently, Sonae Arauco, a company based in Germany, is the world’s largest manufacturer of hollow particleboard. Since 1951, the company has been producing particleboard using the extrusion method and now operates 37 modern presses with 31 varieties of extruded particleboard, with an annual output of 600,000 cubic meters.

In the mid-1990s, the Chinese wooden door industry experienced rapid development, and the extrusion method of particleboard gained popularity due to its advantages of continuous production and smooth surface, making a resurgence in the entire industry. By improving extrusion equipment and incorporating internal mold tubes, the produced hollow particleboard demonstrated excellent sound insulation, heat preservation, and thermal insulation properties, making it an ideal material for high-end door cores. Before 2006, there were only a few hollow particleboard manufacturers in China, with a limited total annual production that could not meet the demand of the wooden door industry. In recent years, the production of hollow particleboard in China has experienced considerable development and expansion. By the end of 2020, there were approximately 200 hollow particleboard production lines in China, with an annual production capacity of around 1.5 million cubic meters.

Preparation of Bamboo-Wood Mixed Hollow Particleboard

Raw Materials

Wood Shavings: Procured from Yuanchuang Wood Products Factory in Jiangshan City, these wood shavings are derived from branch materials of Masson pine. They have a moisture content of 47% and are in the form of small flakes (refer to Figure 1). The shavings have lengths ranging from 5 to 25 mm, widths from 2 to 6 mm, and thicknesses from 1 to 4 mm.

Figure 1

Residual Materials from Bamboo Product Processing: Procured from Guangdu Bamboo Products Factory in Jiangshan City, these residual materials are derived from the processing of moso bamboo products. They have a moisture content of approximately 40%. It is important to use the residual materials within 1 to 2 days of bamboo product processing, as prolonged storage can lead to the development of a sour odor. The residual materials are crushed to produce bamboo shavings. After crushing, the bamboo shavings primarily have a flake-like, needle-like, or powdery form (refer to Figure 2).

Figure 2

Adhesive: Urea-formaldehyde resin, model KX-351, with a pH value of 7.8 and a viscosity of 22.38 s (measured using a #4 cup at 23°C). It has a solid content of 51.32%.

Additives: Paraffin wax is added as a waterproofing agent and to enhance the smoothness of the surface of the bamboo-wood mixed hollow particleboard.

Solid Wood Hollow Particleboard: Three randomly selected hollow particleboard samples of the same batch, with dimensions of 2,090 mm*1,180 mm*28 mm, commonly used in wooden door manufacturing by Jiangshan Europen Door Company, are taken as control samples for performance comparison in this experiment.

Production Process of Bamboo-Wood Mixed Hollow Particleboard

Since there is currently no well-established process for producing bamboo-wood mixed hollow particleboard, the author has developed a production process based on previous experimental experience (see Figure 3). The production process for the bamboo-wood mixed hollow particleboard in this experiment is similar to that of solid wood hollow particleboard, with the difference lying in the preparation of bamboo shavings from residual materials of bamboo product processing.

Figure 3

Currently, there are three main processes for manufacturing hollow particleboard: vertical extrusion, horizontal extrusion, and flat pressing. For this experiment, the vertical extrusion method was selected. Following the process flow depicted in Figure 3, 220 bamboo-wood mixed hollow particleboard panels with dimensions of 2,090 mm*1,180 mm*28 mm were produced through the extrusion process.

Raw Materials: Pine wood shavings with a moisture content of around 47%; residual materials from bamboo product processing, crushed into bamboo shavings with a moisture content of around 40%.

Mixing and Drying of Shavings: The bamboo shavings and wood shavings are mixed in a 3:1 ratio (by wet weight) and dried using a drying machine. The moisture content of the dried bamboo-wood mixed shavings is approximately 10% to 11%.

Sorting: The dried bamboo-wood mixed shavings are sorted into fine powdery material, qualified needle-like shavings, and oversized shavings. The fine powdery material is collected for use as fuel, while the oversized shavings are recycled and further crushed. The resulting sorted bamboo-wood mixed shavings can be seen in Figure 4.

Figure 4

Gluing: The bamboo-wood mixed shavings are glued using a mixing machine, and the glued shavings are then transferred to the vertical extrusion machine.

Extrusion: The extrusion process involves the reciprocating movement of the extrusion head to compress the glued shavings. As the extrusion head moves upward, the glued shavings enter the extrusion machine through the gap between the left and right pressure plates and the extrusion head. The glued shavings inside the extrusion machine are compressed by the combined force of the pressure plates and the extrusion head as it moves downward. The heat generated by the pressure plates and the extrusion pins helps cure the adhesive, resulting in the formation of a continuous solid panel that is extruded from the machine. The extrusion process is carried out at a unit pressure of 1.01 MPa, with a heating temperature of 175 to 185°C and a heating time of 4 minutes.

Performance Testing Methods

Three randomly selected samples of the bamboo-wood mixed hollow particleboard are taken for performance testing. According to the specifications of LY/T 1856—2009 “Hollow Particleboard by Extrusion Method,” the following properties are tested for both the bamboo-wood mixed hollow particleboard and the solid wood hollow particleboard samples: moisture content, thickness swelling after water absorption, density, static bending strength, and internal bond strength. Additionally, according to the provisions of GB/T 17657—2013 “Test Methods of Physicochemical Properties of Particleboard and Fiberboard” (perforation extraction method), the formaldehyde emission of the two types of hollow particleboard samples is tested. The average values of the performance test results from the three samples are used as the physical and chemical performance test results for the bamboo-wood mixed hollow particleboard produced in this experiment.

Performance Test Results

Appearance:

The samples of the bamboo-wood mixed hollow particleboard produced in the experiment are shown in Figures 5 and 6. Figure 7 presents a visual comparison between the surface of the solid wood hollow particleboard and the bamboo-wood mixed hollow particleboard. From Figure 7, it can be observed that the bamboo shavings have smaller dimensions compared to the wood shavings, and their shape is predominantly needle-like. The solid wood hollow particleboard exhibits a brownish color, while the bamboo-wood mixed hollow particleboard has a yellowish color. This difference in color is attributed to the fact that the solid wood hollow particleboard is made entirely of pine wood, whereas the bamboo-wood mixed hollow particleboard consists of a combination of bamboo shavings and wood shavings. Bamboo shavings have a light yellow color, resulting in the overall yellowish hue of the board surface.

Figure 5: Sample of bamboo-wood mixed hollow shavings board

Figure6:  Surface of the sample of bamboo-wood mixed hollow shavings board

Figure 7: Surface comparison between the two types of hollow shavings boards

Physical and Chemical Performance

The results of the physical and chemical performance tests for the two types of hollow particleboard are presented in Table 1. According to Table 1, the bamboo-wood mixed hollow particleboard, produced using bamboo processing residues, meets all the required performance indicators specified in LY/T 1856—2009. Furthermore, its performance is comparable to that of the solid wood hollow particleboard. The density of the bamboo-wood mixed hollow particleboard is slightly higher at 0.34 g/cm3 compared to the density of the solid wood hollow particleboard at 0.33 g/cm3. The bending strength and internal bond strength of the bamboo-wood mixed hollow particleboard are 2.5 MPa and 0.30 MPa, respectively, slightly lower than the values for the solid wood hollow particleboard at 2.6 MPa and 0.43 MPa, respectively. The water absorption thickness expansion of the bamboo-wood mixed hollow particleboard is 3.0%, slightly higher than the 2.5% of the solid wood hollow particleboard. The formaldehyde emission level of the bamboo-wood mixed hollow particleboard (measured by perforation extraction method) is 5.7 mg/100 g, slightly lower than the 5.9 mg/100 g of the solid wood hollow particleboard. These results indicate that utilizing bamboo processing residues to produce bamboo-wood mixed hollow particleboard is feasible.

Table 1: Physical and chemical performance test results of the two types of hollow shavings boards.

Bamboo-Wood Hollow Particleboard in Wooden Doors

Preparation of Bamboo-Wood Hollow Particleboard Door Panels

The bamboo-wood mixed hollow particleboard, produced in the experiment, is used for the production of door panels in wooden doors (as shown in Figures 8 and 9). The quality of the door panels is tested according to LY/T 1923—2020 “Interior Wooden Doors,” and the quality of the doors produced meets the requirements specified in LY/T 1923—2020. The performance of the bamboo-wood mixed hollow particleboard used in the door panels is comparable to that of the commonly used solid wood hollow particleboard in the current wooden door manufacturing industry. Therefore, the bamboo-wood mixed hollow particleboard produced in the experiment can be used for the production of door panels in wooden doors.

Figure 8: Bamboo-wood mixed hollow shavings board used as the core board for a wooden door leaf

Figure 9: Sample of a wooden door leaf with bamboo-wood mixed hollow shavings board

Analysis of Social Benefits

China is a country rich in bamboo resources, and bamboo has strong regenerative capabilities, with bamboo forest areas increasing at a rate of 2% annually. In contrast, the supply and demand for timber are imbalanced, and there is a significant gap in timber supply. The traditional bamboo industry generates a large amount of processing residues. By utilizing bamboo processing residues to manufacture bamboo-wood mixed hollow particleboard, not only can the high added value utilization of bamboo resources be realized, but it also helps to substitute some timber resources, thereby alleviating the imbalance between timber supply and demand in China. This approach contributes to the sustainable utilization of resources and promotes environmental sustainability.

Economic Benefit AnalysisTaking the production specification of 2,090 mm*1,180 mm*28 mm for the bamboo-wood hollow particleboard as an example, the production cost of 1 m³of bamboo-wood hollow particleboard is estimated. The results are shown in Table 2.

Table 2: Estimated Production Cost of 1 m³ of Bamboo-Wood Mixed Hollow Particleboard

According to Table 2, the estimated cost of producing 1 m³ of bamboo-wood mixed hollow particleboard is approximately 909.49 yuan. However, during the trial production process, it was found that there is a significant loss and low utilization rate of bamboo processing residues. The purchased bamboo processing residues had a higher content of bamboo powder, but after drying and wind selection, the amount of bamboo shavings entering the bamboo-wood mixed particleboard was significantly reduced. Therefore, in this experiment, the amount of wet bamboo shavings used had to be three times that of wet wood shavings to achieve a dry weight ratio of approximately 1:1 between bamboo and wood shavings. Currently, the prices of full wood hollow particleboards of the same specifications vary, ranging from approximately 800 to 1,200 yuan per 1 m³. The cost of bamboo-wood mixed hollow particleboard is 909.49 yuan, which is in the middle range. Moreover, there is a possibility to reduce the production cost of bamboo-wood hollow particleboard through optimization of process parameters and other methods. Therefore, based on the results of this experiment, the production of bamboo-wood mixed hollow particleboard is economically feasible.

Conclusion and Recommendations

The utilization of bamboo processing residues and wood shavings in a 1:1 dry weight ratio to produce bamboo-wood mixed hollow particleboard is feasible. The resulting bamboo-wood mixed hollow particleboard meets the requirements of LY/T 1856-2009 in terms of moisture content, density, static bending strength, internal bond strength, and formaldehyde emission (perforation extraction method) of 5.7 mg/100 g. Its performance is comparable to that of commonly used full wood hollow particleboard in the manufacturing of wooden doors.

Based on the analysis of the social and economic benefits of bamboo-wood mixed hollow particleboard, it is evident that utilizing bamboo processing residues to produce bamboo-wood mixed hollow particleboard contributes to resource conservation, environmental protection, and mitigation of the wood supply-demand imbalance in China, aligning with the principles of sustainable development. Moreover, it demonstrates economic viability. However, compared to full wood hollow particleboard, the production of bamboo-wood mixed hollow particleboard still faces challenges such as significant loss of bamboo shavings, low utilization rate, slightly higher adhesive usage, and production costs. Therefore, it is recommended to develop suitable adhesives for bamboo-wood mixed hollow particleboard and conduct research on the influence of bamboo shavings morphology and bamboo-wood shavings ratio on the performance of bamboo-wood mixed hollow particleboard. Exploring optimized production processes for bamboo-wood mixed hollow particleboard will be beneficial.

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