Abstract
A large amount of plant waste from the sides of highways is trimmed and burned, which causes environmental pollution. In addition, headlight glare that occurs when two cars pass each other is dangerous. Traditional anti-glare boards are mostly made of metal, plastic, and other materials that easily age and are expensive to recycle. To recycle the plant waste and prevent glare-related accidents, in the present study, a painted wooden anti-glare board (WAB) was developed and its performance was investigated. In the WAB, there are 7 layers of eucalyptus veneers interlaced, and the mechanical strength of the board prepared with a gradient hot-pressing process after impregnation with phenolic resin was good (79.8 MPa). The wind load resistance of the WAB reached 864 N, which meets GB/T 24718 (2009) and is close to that of glass fiber-reinforced plastic anti-glare boards (914 N). After 10 cycles of weather resistance tests comprising submersion, freezing, and hot-drying, the average static bending strength of the WAB was 29.6 N/mm2. The limited oxygen index of the WAB was 26.1%. Therefore, the WAB showed good properties. The implemented research strategy broadens the application range of the wood composite material and endows it with high added value.
Download PDF
Full Article
Resin-impregnated Wooden Anti-glare Board and Its Outstanding Exterior Performance
Wanjia Yang,a,b,# Jian Liu,a,b,# Wei Zhang,a,b,* Derong Zhang,a,b Jianzhang Li,a,b Shifeng Zhang,a,b and Yanming Han c
A large amount of plant waste from the sides of highways is trimmed and burned, which causes environmental pollution. In addition, headlight glare that occurs when two cars pass each other is dangerous. Traditional anti-glare boards are mostly made of metal, plastic, and other materials that easily age and are expensive to recycle. To recycle the plant waste and prevent glare-related accidents, in the present study, a painted wooden anti-glare board (WAB) was developed and its performance was investigated. In the WAB, there are 7 layers of eucalyptus veneers interlaced, and the mechanical strength of the board prepared with a gradient hot-pressing process after impregnation with phenolic resin was good (79.8 MPa). The wind load resistance of the WAB reached 864 N, which meets GB/T 24718 (2009) and is close to that of glass fiber-reinforced plastic anti-glare boards (914 N). After 10 cycles of weather resistance tests comprising submersion, freezing, and hot-drying, the average static bending strength of the WAB was 29.6 N/mm2. The limited oxygen index of the WAB was 26.1%. Therefore, the WAB showed good properties. The implemented research strategy broadens the application range of the wood composite material and endows it with high added value.
Keywords: Highway; Plant waste; Glare, Wooden anti-glare board; Phenolic resin
Contact information: a: Key Laboratory of Wood-Based Materials Science and Utilization, Beijing Forestry University, No. 35 Tsinghua East Road, Haidian District, Beijing 100083, China; b: Beijing Key Laboratory of Wood Science and Engineering, Beijing Forestry University, No. 35 Tsinghua East Road, Haidian District, Beijing 100083, China; c: Research Institute of Forestry New Technology, Chinese Academy of Forestry, Xiangshan Road, Beijing 100091, China; #The first two authors contributed to this work equally
* Corresponding author: zhangwei@bjfu.edu.cn
INTRODUCTION
On both sides of highways around the world, a wide range of tall, fast-growing timber species, such as eucalyptus, poplar, and pine, have been extensively planted in large quantities in consideration of aesthetics, wind protection, and water and soil conservation. With the rapid development of highway construction, the amount of green waste, including trunks, branches, and leaves, on the sides of highways is rapidly increasing. Moreover, because priority is given to tree species with fast-growing wood, an enormous amount of trimmed branches is disposed via incineration or landfilling, which causes poor biomass resource utilization, and even fire and smoke that can easily cause secondary disasters. Therefore, the traditional plant waste treatment methods, such as incineration and landfilling, cannot meet the requirements of sustainable development, and the environmentally friendly and high-value-added utilization of plant waste is becoming an inevitable trend (Bai et al. 2010).
Low biomass resource utilization is not the only problem on the highway. There also is a problem of traffic accidents caused by glare phenomena. Glare is one of the main causes of traffic accidents on two-way highways. At night, the brightness of oncoming headlights changes substantially in an instant, thereby instantly decreasing the visual function of drivers and producing an uncomfortable light sense, which affects normal driving and can ultimately lead to traffic accidents (Zhang 2008) Traffic accidents caused by glare account for 12% to 15% of total traffic accidents (Tu et al. 2004), and anti-glare devices, such as fixed barriers (Bagui and Ghosh 2012) or plastic anti-glare devices (Tollazzi and Rencelj 2012), are therefore usually installed in the middle of two-way lanes. As an economic benefit, these devices also reduce the deceleration demand of vehicles, thereby reducing their running cost (Tian et al. 2014; Cherubini et al. 2019).
As an anti-glare device, anti-glare boards are a row of boards attached to the highway’s central isolation belt, each of which is about one meter high. They are installed on a metal fixed base and splint, such that every two boards are 1 to 1.5 meters apart. At low speeds, the driver can see through the gap between the anti-glare boards, enabling them to view what is going on in the opposite lane on the other side of the central isolation belt. But for the reason that straight lanes on the highway do not allow cars to travel in opposite directions in the same lane, a central barrier has been created that cannot be crossed. Therefore, it is not necessary to look at the opposite lane when the vehicle is driving at high speed, and the anti-glare boards in the driver’s line of sight forms a visual opaque wall due to the high speed and direction of viewing. So, the anti-glare boards can avoid the phenomenon that the driver’s visual function being suddenly reduced due to the sudden change of the opposite headlights.
The necessity of anti-glare devices for highway traffic safety has been recognized. Fernandes (2005) revealed the causes of glare and its threat to traffic safety. It was shown that anti-glare boards are an important means by which to solve the problem of glare on highways (Tian et al. 2014). The existing anti-glare devices utilized on highways can be divided into three categories, namely green fences, anti-glare nets, and anti-glare boards. Green fence anti-glare strategies refer to the planting of plants in the central area of the highway; plants have a good anti-glare effect and improve the landscape view, but the necessary investment is high. Moreover, because they are easily affected by the climate, they require long-term maintenance (Han et al. 2018). An anti-glare net is a reticular metal isolation layer covered with anti-rust paint and good ventilation; however, its anti-glare effect is poor and it can easily be affected by snow cover (Yi et al. 2016). Anti-glare boards are the main anti-glare measures implemented on highways due to their good shading, relatively small investment, low maintenance costs, aesthetics, and robustness to snow cover, among other factors. The existing anti-glare boards used on highways can be divided into three types, namely steel, plastic, and glass fiber-reinforced plastic (FRP) boards. Steel anti-glare boards are difficult to maintain, easily expanded by heat, and can easily fall off their base. In the event of a traffic accident, there is a great possibility of secondary injury resulting from the rupture of a steel anti-glare board, which increases the safety hazard of vehicles and personnel (Yi et al. 2016). Plastic anti-glare boards are primarily made of high-density polyethylene (HDPE), polyvinyl chloride (PVC), or acrylonitrile butadiene styrene (ABS) material, and can be made to look aesthetically pleasing. However, their temperature and weather resistance are poor, and these boards easily age and change color. In cold areas often subjected to low-temperature conditions, the material gets brittle and fragile; in contrast, in hot areas, the material softens. The FRP anti-glare boards are primarily made of glass fiber and epoxy resin. Due to its light weight, high strength, and corrosion, aging, and high-temperature resistance, FRP has become the most important material for anti-glare boards (Liang 2012; Li 2014). The FRP anti-glare plate is molded, it is a material that has an anisotropic characteristic, and the internal and external material is the same. However, FRP anti-glare boards greatly increase highway maintenance and operation costs, as they are expensive and difficult to recycle after aging.
A novel wooden anti-glare board (WAB) was developed in this study. In this new type of wood composite material, eucalyptus veneers are used as the wood substrate, which is made with trimmed eucalyptus branches, and the trimmed eucalyptus branches are sliced into eucalyptus veneers by a peeling machine. This substrate is efficiently filled with high-performance phenolic resin and is then solidified and formed under a certain temperature and pressure via the penetration of the small molecules of the resin into the wood pores. The weight ratio of the pre-impregnated wood veneer to the post-impregnated wood veneer is 1:1.3~1.4, which means that approximately 30% of the phenolic resin is soaked into the wood veneer. Phenolic resin is a highly crosslinked adhesive with excellent properties, such as a high bonding strength, acid and alkali corrosion resistance, ideal hardness, thermal stability, and water resistance, and is widely used in the preparation of plywood, particle board, oriented strand board (OSB), and other man-made boards (Aziz et al. 2019). According to previous studies, the static bending modulus of phenolic plywood is around 74.08 MPa when the hot-pressing pressure is 2.5 MPa (Wu 2012).
However, in contrast to ordinary decorative or building formwork phenolic plywood, anti-glare boards are used in outdoor environments. Highways and other outdoor environments are characterized by harsh conditions, including high and low temperatures, as well as occasional high humidity, high salinity, high light radiation, and high wind speeds. Under these conditions, ordinary wood-based panels are prone to corrosion, breaking, and aging, so anti-glare boards must have good weather resistance and mechanical properties. The impregnation of wood with phenolic resin can effectively prevent the biological degradation of the wood caused by rot fungus, improve the mechanical properties of the wood, and greatly improve the weather resistance, dimensional stability, strength, and other properties of the wood (Furuno et al. 2004; Hermawan et al. 2013).
The wood fiber of the proposed phenolic resin-impregnated WAB has good toughness, which can ensure that the WAB will not break easily when it is impacted by a high-strength external force. Additionally, the crosslinked network structure formed by the phenolic resin after curing has extremely strong rigidity, which can reduce the swinging range of the WAB under a strong wind load, improve the WAB’s anti-fatigue strength, and meet the strict practical requirements, such as functionality in high-temperature, high-salinity, and high-humidity environments (Shams et al. 2004). Therefore, the mechanical strength, weather resistance, aging resistance, and other performance indexes of wood composites modified with phenolic resin can meet the GB/T 24718 (2009) requirements and the actual use requirements of anti-glare boards (Yi et al. 2016).
The proposed phenolic resin-impregnated WAB also has the advantages of an excellent performance, low cost of raw materials, and the use of renewable raw materials and waste, and it has prospects in terms of economic value. Due to its higher mechanical strength, toughness, and stronger aging resistance, the proposed phenolic resin-impregnated WAB has a longer service life and can reduce highway maintenance costs. The service life of a plastic anti-glare board is generally two years, while that of an FRP anti-glare board is three to five years (Yi et al. 2016); in contrast, the design service life of the proposed WAB is more than five years. In addition, through the comparison of factory cost price, the cost price of eucalyptus anti-glare board is the lowest, while the cost price of glass fiber-reinforced plastic (FRP) board is 3 times that of wood composite material. Therefore, wood anti-glare board have a certain advantage in the cost price (Guan et al. 2016). The research and development of green, renewable, and low-cost anti-glare boards have important practical significance for the realization of the low-carbon, safe, and sustainable development of expressways.
EXPERIMENTAL
Materials
The materials used in this study included phenol, formaldehyde (37%), and sodium hydroxide (40%) (Beijing Lan-yi Chemical Product Limited Liability Company, Beijing, China). The size of the veneer used in the laboratory experiment was 0.4 m × 0.4 m, while the size of the veneer used in the factory experiment was 1.2 m × 0.8 m. Other materials included 1-mm-thick poplar veneer (PV), 1.2-mm-thick eucalyptus veneer (EV), and 0.5-mm-thick birch veneer (BV) with veneer moisture contents of 8% to 10% (Shandong Qian-sen Wood Group Co., Ltd., Shandong, China).
Preparation of phenolic resin
(1) Phenol was added to a reactor, after which water and the first batch of sodium hydroxide solution (40%) were added under stirring.
(2) The first batch of formaldehyde (37%) was slowly added, and the temperature was increased to 80 °C for 20 to 30 min. Heating was then stopped, and the temperature of the reaction solution was increased to above 90 °C via an exothermic reaction. The temperature was then maintained at 90 to 95 °C for 30 to 50 min.
(3) The temperature was reduced to 80 °C, and the second batches of formaldehyde (37%) and the sodium hydroxide solution (40%) were slowly added to the reactor. The temperature was then increased to 90 °C and maintained at 90 to 95 °C for 15 to 30 min.
(4) The viscosity was measured with a Grignard tube. When the viscosity of the glue reached 200 to 250 mPas (40 °C), the temperature was immediately lowered to 40 °C, and the material was discharged.
Preparation of WAB
WAB prepared in the laboratory
High-performance phenolic resin was used to efficiently impregnate the wood substrate. After the small molecules of the phenolic resin penetrated the wood pores, the resin was solidified and formed under a certain temperature and pressure.
The veneer treatment was as follows. The wood veneer was soaked in phenolic resin for 2 h, after which it was removed and the residual liquid was drained from the surface. The veneer was then dried in an air-blast drying oven at 60 °C for 1 h, after which it was removed and dried at room temperature.
The veneer arrangement was as follows. Seven pieces of veneer were placed in accordance with an alternating arrangement or a unidirectional arrangement. Copper mesh and iron gauze were added to the veneer with an alternating arrangement. Hot-pressing was conducted as follows. A gradient hot-pressing process was adopted, and the hot-pressing temperature was maintained at 120 to 150 °C. The hot-pressing time of the first stage was 500 to 600 s, and the hot-pressing pressure was 1.2 MPa.
Fig. 1. Preparation process of the WAB
Fig. 2. Dimensions and installation situation of the WAB
The hot-pressing time of the second stage was 60 to 120 s, and the hot-pressing pressure was 1.0 MPa. The hot-pressing time of the third stage was 10 to 60 s, and the hot-pressing pressure was 0.5 MPa. The pressure was then relieved.
The preparation process of the WAB is depicted in Fig. 1, and dimensions and installation situation of the WAB is shown in Fig. 2.
WAB prepared in a factory
Gradient hot-pressing technology was adopted to prepare a wooden anti-glare board in a factory. The hot-pressing temperature was maintained at 120 to 150 °C. The hot-pressing time of the first stage was 800 to 1000 s, and the hot-pressing pressure was 1.5 MPa. The hot-pressing time of the second stage was 500 to 600 s, and the hot-pressing pressure was 1.2 MPa. The hot-pressing time of the third stage was 150 to 300 s, and the hot-pressing pressure was 1.0 MPa. The board was then naturally cooled to room temperature, and the pressure was slowly released over 3 to 4 h. The WAB was then cut into sizes of 0.9 m × 0.27 m. The structure was made to look like bamboo, and the surface was decorated with bright-green weather-resistant anticorrosive paint.
As a material used outdoors, the WAB must be susceptible to the actual outdoor climate. Therefore, outdoor conditions throughout the year need to be simulated before being used on highways. Therefore, the strength of the WAB needs to be tested by simulating supersaturated weather conditions in the laboratory. Figure 3 presents the installation effect of the WAB on a highway under different weather conditions in four seasons. Different weather conditions in four seasons are mainly shown as wind in spring, hot sun in summer, heavy rain in autumn, and freezing snow in winter and the corrosion caused by the snowmelt agent (salt, for example) from a snowplow.
Fig. 3. Simulation of the road installation of the factory-prepared WABs: (a) wind in spring; (b) heat in summer; (c) rain in autumn; (d) snow in winter
Performance measurement of the WAB
The static bending strength, elastic modulus, and bending resistance of the WAB were measured according to the GB/T 17657 (2013). The wind load test method was measured by the National Traffic Safety Facilities Quality Supervision and Testing Center (Transportation Engineering Supervision and Testing Center). The reference standard was GB/T 24718. (2009).
Determination of the Weatherability of Eucalyptus Wood
The general scheme for weathering resistance and impact resistance testing is shown in Fig. 4.