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Products Made from Nonmetallic Materials Reclaimed from Waste Printed Circuit Boards
TSINGHUA SCIENCE AND TECHNOLOGY ISSN 1007-0214 07/18 pp276-283 Volume 12, Number 3, June 2007
Products Made from Nonmetallic Materials Reclaimed from Waste Printed Circuit Boards* MOU Peng (牟 鹏), XIANG Dong (向 东), DUAN Guanghong (段广洪)** Department of Precision Instruments and Mechanology, Tsinghua University, Beijing 100084, China Abstract: Printed circuit boards (PCBs) are in all electronic equipment, so with the sharp increase of electronic waste, the recovery of PCB components has become a critical research field. This paper presents a study of the reclaimation and reuse of nonmetallic materials recovered from waste PCBs. Mechanical processes, such as crushing, milling, and separation, were used to process waste PCBs. Nonmetallic materials in the PCBs were separated using density-based separation with separation rates in excess of 95%. The recovered nonmetals were used to make models, construction materials, composite boards, sewer grates, and amusement park boats. The PCB nonmetal products have better mechanical characteristics and durability than traditional materials and fillers. The flexural strength of the PCB nonmetallic material composite boards is 30% greater than that of standard products. Products derived from PCB waste processing have been brought into industrial production. The study shows that PCB nonmetals can be reused in profitable and environmentally friendly ways. Key words: printed circuit boards (PCBs); electronic waste; reclaimation; reusing
Introduction According to statistical data released by the National Bureau of Statistics of China, about 20 million electronic household appliances (including televisions, washing machines, refrigerators, air conditioners, and personal computers) and 70 million cell phones have come to their end-of-life every year since 2001. As a key component in electronic equipment, large amounts of waste printed circuit boards (PCBs) are generated by all this consumption of electronic appliances. PCBs form about 3% by weight of the total amount of electronic scrap[1]. The process of reusing recovered metals from PCBs is already quite mature. However, the Received: 2006-06-26; revised: 2006-09-21
﹡ Supported by the National High-Tech Research and Development (863) Program of China (No. 2004AA420120)
﹡﹡ To whom correspondence should be addressed. E-mail: [email protected]; Tel: 86-10-62773404
recovered nonmetallic materials are not so widely reused. PCBs contain 70% to 80% nonmetals with the main nonmetallic ingredients being epoxy resins, glass fibers, and bromized flame retardant. Traditionally, most of these materials have been directly landfilled or incinerated[2]. However, disposal in landfills and incineration may cause environmental problems. Studies on resin reuse have emerged in recent years to meet more strict environmental protection legislations. The research falls into two groups. (1) Physical reuse Yokoyama and Iji[3-6] used recycled resin powder as filler for epoxy resin products, such as paints, adhesives, decorating agents, and building materials, and found that the resin powder improved the mechanical and thermal expansion properties of the products when compared to the usual fillers, such as talc, calcium carbonate, and milled glass fiber. Their physical recycling applications are interesting but the amount of PCB nonmetals used in these products is very limited,
MOU Peng (牟 鹏) et al：Products Made from Nonmetallic Materials Reclaimed from …
usually less then 10%, so these applications will not promote large scale recycling. (2) Chemical recycling Economy and Andreopoulos[7] developed a method to directly recycle and reuse thermosetting resins as a crosslinkable copolyester. Dang et al.[8] found that amine cured epoxy resins were not resistant to acid solutions and completely decomposed in high concentration acids at high temperatures. However, the recycled resins showed higher mechanical strength than virgin resin. They used a similar process to recycle glass fiber reinforced epoxy resins (GFRP)[9]. Chen et al.[10] created reworkable thermosets with cleavable linkages and studied their chemical and thermo-mechanical breakdown mechanisms. Although chemical recycling is a promising route for converting plastic wastes to their original constitutes, much more research and development on chemical recycling is needed to reduce the high cost and improve the quality. This paper describes the reuse of recovered PCB nonmetals after physical recovery in more practical and profitable ways for a variety of products.
1
Physical Properties of the Recovered Nonmetallic Powder
The nonmetallic powder physically separated from the waste PCB mainly consists of resins and glass fibers which do not need to be separated in what would be a relatively expensive process since their combined characteristics are very useful[11]. Therefore, the nonmetals can be reused “as is” with no waste or pollution. The particle size distribution and the bulk density are the most important properties when considering physical reuse. The size distribution is shown in Fig. 1.
Fig. 1 Particle size distribution of PCB nonmetallic powder
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The data indicates that most of the PCB nonmetallic powder is concentrated in sizes from 38.5 µm to 200 µm, with all of the size ranges within this range having similar amounts of nonmetals. Thus, the powder applications can be based on the granularity. The bulk density of the recovered nonmetal powder was about 2.0 g/cm3.
2
Reuse of Recovered Nonmetallic Materials from Waste PCBs
The recovered nonmetallic materials can be used in several ways based on the physical characteristics of the nonmetallic powder. 2.1
Construction material filler
Many previous applications have used the recovered nonmetallic materials as filler or agent for construction materials, from concrete to various framing materials. Researchers have sought improved construction materials with better mechanical strength, less environmental impact, and less cost. However, little actual data is available describing the reuse of recovered resins in construction materials with many of these studies only in the feasibility stage, so the actual usefulness is uncertain. For construction materials, the flexural and compressive strengths are the two most important properties. Compared with the main materials in concrete, cement, sand, and water, the recovered nonmetallic PCB powder is lighter than cement and sand, has finer granularity which makes the microstructure more reliable, and contains coarse glass fibers which improve mechanical strength. All of these properties can improve the mechanical strength. The optimum proportion of nonmetallic powder in the construction material should be carefully determined to maximize both the flexural and the compressive strengths. Six different percentages of recovered nonmetallic powder were used to make construction materials that were tested according to the China National Testing Method for Cement Mortar (GB177-85). The detailed compositions of the bricks made from the sand and PCB nonmetallic powder are listed in Table 1. Some bricks made from the recovered PCB nonmetallic powder are shown in Fig. 2.
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Table 1
Composition of brick material
Sample
Portland cement (g)
Sand (g)
PCB nonmetals (g)
Water (mL)
R1 R2 R3 R4 R5 R6
540 505 474 446 422 400
1351 1199 1066 949 844 750
0 63 118 167 211 250
238 222 208 196 186 176
Fig. 2 Bricks made using recovered nonmetallic PCB material
The flexural and compressive strengths of the modified and standard bricks are listed in Table 2. Table 2 Flexural and compressive strengths Sample R1 R2 R3 R4 R5 R6
Flexural strength (MPa) 8.30 8.18 8.76 8.65 8.03 7.42
Compressive strength (MPa) 0.43 0.43 0.44 0.46 0.35 0.31
The strength data was measured seven days after the bricks were made as stipulated in the China National Standard on Concrete. From the data in Table 2, sample R3 has the best flexural strength while sample R4 has the best compressive strength. Therefore, sample R3 or sample R4 or some composition of these two would give the best result. The reuse of recovered nonmetals as filler to make construction materials is feasible but not very attractive since the improvements in the flexural and compressive strengths are quite limited with less than 10% when compared with the standard concrete (R1) and the replaced materials in the original concrete, the sand and cement, are cheap and abundant, so this substitution will not give a good economic return. Therefore,
current research on the use of recycled PCB material as construction materials seeks simply to find some use for the recycled material even it is a relatively small amount. 2.2
Modeling material
There are many kinds of models used for exhibitions or for decorations. Most models are made from gesso, plastic, or other materials. Resin powder has many similar or better physical properties than gesso, including lighter weight, waterproof, easy to mold, and higher mechanical strength (due to the glass fibers). Therefore, the recovered nonmetals can be used as a substitute for statues, ornaments, and other models. Three different moulding processes have been used to make models from recovered PCB nonmetals. (1) Models made from PCB nonmetals and an adhesive Three key factors, the type of adhesive, the blending ration between the nonmetallic powder and the adhesive, and the pressure during the modeling process, affect the molding process. The recycled PCB nonmetallic material is a powder so it cannot hold a shape, so an adhesive must be used to form the material. Resin-type adhesives were used for their potential affinity with the recovered nonmetallic powder to improve the final properties. Two other adhesives were used for comparison. The final results showed that all the models were solid but had poor mechanical strength. The first reason for the poor strength is the manner by which the adhesive combines with the resin powder. With the various adhesives used for comparison, the forces between the powder and the adhesive were physical rather than chemical, so the strength was limited. In addition, the moldings were made by hand, so the molding pressure was relatively low and not uniform. The models had a large number of small air holes inside the models due to the manual processing which reduce the model’s strength. The mechanical strength of the models can be improved by increasing the pressure in the mold to reduce the air holes inside the model. Another measure is to adjust the blending ratio between the resin powder and the adhesive. Using less adhesive will reduce the cost when the mechanical strength is not compromised. (2) Models made from PCB nonmetals and decorative cement Here, the PCB nonmetallic material was not used as
MOU Peng (牟 鹏) et al：Products Made from Nonmetallic Materials Reclaimed from …
a filler but as the main material with the models designed as ornaments. A special decorative cement served as the adhesive. The material was cast as a cube and as a computer mouse as shown in Fig. 3 to validate its molding ability according to the China National Standard on Construction Material.
Fig. 3 Models made from PCB nonmetallic powder and a decorative cement
The results showed that the models held together well and had good mechanical strength, but were heavier than standard models and had poor surface quality. The model surfaces were quite coarse and needed further processing. In general, the resin adhered well to the cement and with some improvements, especially the surface treatment, the molding process could be efficient and useful. (3) Models made from nonmetallic powder, decorative cement, and fillers Some filler was added to the powder and the decorative cement to improve the model’s characteristics. Wood chips and silver sand were used as the preferred fillers because they are very cheap and abundant, but the results were not an improvement over the previous results. The wood chips reduced both the weight and the mechanical strength since they do not adhere to the nonmetals. The sand increased the strength but had no effect on the weight or the surface quality. When compared with the use of the PCB nonmetallic powder as filler for construction materials, the use in models, though not perfect, has better prospects since the recovered material is not just a filler, but the main materials, so the reuse has more value. 2.3
Composite boards made from PCB nonmetallic materials
Composite boards are used extensively in many fields including automobiles, furniture, amusement equipment, and decorative materials. The most attractive aspect of making composite boards from PCB
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nonmetallic materials is the potential economic benefit. In general, products made from composite boards are high value products with large profit margins. A wide variety of products can be made from composite boards for various applications. PCB nonmetallic materials were used to make composite boards into various products for the Beijing SBL Amusement Equipment Co., Ltd. Talc and silica powder are currently the two main materials used for making the composite boards used by the company. Recovered nonmetallic powder was then substituted for these products to make the composite boards. (1) Production of the composite boards The PCB nonmetallic powder recovered from the PCBs has coarser granularity than the talc and silica powders. Figure 1 shows that more than half of the nonmetallic powder particles are between 90 µm and 500 µm in size. The silica and talc powders are finer with granularities around 50 µm. Theoretically, the composite board should have better mechanical strength with the coarser grains. In addition, the PCBs contain glass fibers with many remaining after the crushing process. Though these glass fibers are smaller after the crushing, they are still larger than the rest of the nonmetallic powder so they serve as a frame in the composite boards which further strengthen the material. Finally, the most important and useful characteristic of the recovered nonmetallic material is their compatibility with the epoxy resin adhesive used by the company to bind the filler and the fibers, so the recovered PCB nonmetallic material has better affinity with the adhesive than silica and talc, which suggests better moulding properties and mechanical strength. The composite boards have multiple layers of fibers and fillers combined by the adhesive. The talc, silica, or recovered nonmetal material is filled between these layers at some pressure. About 90% of procedures were done manually in a complicated and experiencebased process. The original board making procedure was improved on two ways. First, a pressing machine was introduced to provide even and stable high pressures to the mould. This machine was a critical improvement which remarkably reduced the air holes in the board which will greatly improve the mechanical strength. Secondly, the working and holding temperatures were both increased and held longer which enhanced the curing procedure
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and provided more stable board properties. The main components in the composite boards are listed in Table 3. Potassium peroxide was also used as a curing agent. During the board production process, the stirring rate ranged from 450 r/min to 750 r/min with a curing time of 2 hours. Composite boards made from talc, silica, and the PCB nonmetallic material are shown in Fig. 4. Table 3 Main components in composite boards Ingredients Glass fiber cloth Epoxy resin Fillers PCB nonmetals
Fig. 5 Comparison of tensile strength
Ratio (wt.%) 30-45 35-40 5 15-30
Fig. 6 Comparison of tensile modulus of elasticity Fig. 4 Composite boards made from talc, silica, and the PCB nonmetallic material
During the production process, the boards made from the recovered PCB nonmetallic materials were found to be more easily shaped and flattened than the talc and silica boards. The blending time was also shortened greatly and the mixture was more uniform and reliable than the silica and talc mixture. These improvements may be attributed to the good affinity between the recovered material and the resin-based adhesive. (2) Mechanical strength The mechanical strength is the most important characteristic of the composite boards. Four different proportions were used to find the best ratio of nonmetallic material in the composite boards. 25% (wt.) of talc and silica were used in the composite boards as a result of years of experience at the company. The seven mechanical indexes measured in the tests were the tensile strength, tensile modulus of elasticity, flexural strength, flexural modulus, impact toughness, interlaminar shear strength, and punching shear strength. The results are shown in Figs. 5-11. Four proportions (15%, 20%, 25%, and 30% (wt.)) of recovered nonmetallic materials are expressed as P1, P2, P3, and P4. Figures 5-8 show that the composite board containing 15% (wt.) PCB nonmetallic powder has the best
Fig. 7 Comparison of flexural strength
Fig. 8 Comparison of flexural modulus
combination of properties for the four primary properties of the tensile strength, the tensile modulus of elasticity, the flexural strength, and the flexural modulus. Only the interlaminar shear strength is somewhat low. The talc board also has excellent properties, so it is the main material used by the company to make composite boards and related products.
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the recovery not only recycles waste PCBs, but also earns a profit. 2.4
Fig. 9 Comparison of impact toughness
Fig. 10 Comparison of interlaminar shear strength
Fig. 11 Comparison of punching shear strength
The composite board made with 30% (wt.) nonmetallic powder has the worst properties since there must be too many PCB materials for the adhesive to link. The comparison of the seven key mechanical properties indicates that the recovered material can be used as a substitute for silica and talc to make composite boards and other products. The outstanding characteristic of the nonmetallic material board is its flexural strength, which was enhanced by more than 50% for the 15% blending ratio when compared with talc. Therefore, this is good for products that mainly bear bending stresses. The use of PCB nonmetallic materials to make composite boards is a promising application since composite boards are used extensively in many manufacturing fields. The economic return should be considerable. So,
Specific products made from PCB nonmetallic materials
Analysis of the mechanical properties indicates that the recovered PCB nonmetallic material can best be used to make products which endure greater bending stresses because of its excellent flexural strength. The technology has now been used in two typical products. (1) Sewer grates In China, about 90% of the sewer grates are made of cast iron[12], which are valuable and often stolen by thieves. Beijing lost about 24 000 grates (3.4% of the total) in 2004, which were worth about RMB 28 million. In the first half of 2005, 8000 grates were stolen. The loss of sewer grates is a serious social problem, which has not only caused great property loss, but also creates potential threat to passersby and cars. In addition, the demand for new sewer grates for new construction is also enormous. China is rapidly developing with municipal construction, needing about 4 million grates per year. Therefore, to prevent such thefts, more and more sewer grates are being made of composite materials in China. Steel-fiber concrete and glass fiber reinforced plastic (FRP) are the two commonly used materials. The main characteristics of grates made from these materials are listed in Table 4. Table 4 Characteristics of grates made from steelfiber concrete and FRP[12] Material Steel-fiber concrete FRP
Merits Lower cost and worthless to thieves Designable surface and better strength
Deficiencies Brittle, poor strength, and heavier Higher cost and poor impact strength
The process used to make composite boards from the PCB nonmetallic material was also used to make the sewer grates shown in Fig. 12. The main advantages of these grates are lower cost and better mechanical strength, especially the flexural strength. Another important point is that the PCB nonmetallic material is a recycled material, so the process makes use of materials that would otherwise be sent to landfills.
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Fig. 12 Grate made from recovered PCB nonmetallic material
The grates meet the strength requirements of the China National Building Standard Specification (CJ/T 130-2001) for use in sidewalks and main roads, so the grates can be widely used. This will considerably reduce the theft of grates. (2) Surfboat in amusement park The Beijing SBL Amusement Equipment Co., Ltd mainly makes products for amusement equipment, such as roller coasters, bumper cars, racing cars, and various boats and trains. The boats are one of SBL’s main products. The boat decks are subjected to large bending pressures. The composite board can be effectively used in the deck and body of boats. The boat making process is shown in Fig. 13.
materials, to make models, in composite boards, and in practical products, such as sewer grates and small boats. The first two schemes are not very attractive due to their low economic return and practical application potential. Though these applications are better than landfills and incineration, many improvements are still needed to further promote these use. The last two schemes, using recovered PCB nonmetallic material to make composite boards and related products are much more attractive applications. First, they have great market demand which will pave the way for the use of a large amount of recovered PCB nonmetallic material. Secondly, they have potential to bring considerable profit when applied to practical products. Both the sewer grates and the boats are high value added products which will be effective solutions for recovering nonmetallic materials of waste PCBs. References [1]
Bernardes A, Bohlinger I, Rodriguez D, Milbrandt H, Wuth W. Recycling of printed circuit boards by melting with oxidising/reducing top blowing process. In: TMS Annual Meeting. Orlando, USA, 1997.
[2]
Li Jianzhi, Puneet Shrivastava, Gao Zong, Zhang Hongchao. Printed circuit board recycling: A state-of-the-art survey. IEEE Transaction on Electronics Packaging Manufacturing, 2004, 27(1): 33-42.
[3]
Yokoyama S, Iji M. Recycling of thermosetting plastic waste from electronic component production process. In: Proceeding of 1995 IEEE International Symposium on Electronics and the Environment. USA, 1995: 132-137.
[4]
Yokoyama S, Iji M. Recycling of printed wiring boards with mounted electronic parts. In: Proceeding of 1997 IEEE International Symposium on Electronics and the Environment. USA, 1997: 109-114.
[5] Fig. 13 PCB nonmetallic material deck
The first batch of boats with the PCB nonmetallic material deck has already passed performance tests and is being used in the Shijingshan Amusement Park of Beijing.
Iji M. Recycling of epoxy resin compounds for moulding electronic components. Journal of Materials Science, 1998, 33: 45-53.
[6]
Yokoyama S, Iji M. Recycling system for printed wiring boards with mounted parts. In: Proceeding of 1999 Environmentally Conscious Design and Inverse Manufacturing. Tokyo, Japan, 1999: 814-817.
3
Conclusions
This paper describes several methods for reusing recovered nonmetals from waste PCBs. The PCB nonmetallic material can be reused in construction
[7]
Economy J, Andreopoulos A G. A new concept for recycling of thermosetting resinⅠ: The case of crosslinkable copolyesters. Polymer for Advanced Techonologies, 1996, 7: 561-570.
[8]
Dang Weirong, Kubouchi Masatoshi, Yamamoto Shurou,
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[9]
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Sembokuya Hideki, Tsuda Ken. An approach to chemical
[11] Mou Peng, Wa Layiding, Xiang Dong, Gao Jiangang,
recycling of epoxy resin cured with amine using nitric acid.
Duan Guanghong. A physical process for recycling and
Polymer, 2002, 43: 2953-2958.
reusing waste printed circuit boards. In: Proceedings of the
Dang Weirong, Kubouchi Masatoshi, Sembokuya Hideki,
2004 IEEE International Symposium on Electronics and
Tsuda Ken. Chemical recycling of glass fiber reinforced epoxy resin cured with amine using nitric acid. Polymer, 2005, 46: 1905-1912. [10] Chen Jir Shyr, Christopher K B, Mark D P. Characteriza-
the Environment. Scottsdale, USA, 2004: 237-242. [12] Yi Changping, Liu Jun, Zeng Jingcheng, Zeng Jianxiang. Present status and developing trend of compound well lids. FRP and Compound Material, 2004, 4: 43-45. (in Chinese)
tion of thermally reworkable thermosets: Materials for environmentally friendly processing and reuse. Polymer, 2002, 43: 131-139.
Norway’s Prime Minister Visiting Tsinghua University Prime Minister Jens Stoltenberg of Norway visited Tsinghua on March 27. Tsinghua President Gu Binglin welcomed Mr. Stoltenberg. The two exchanged ideas on climate change, energy saving, and environmental protection. Mr. Stoltenberg delivered a speech entitled “International Cooperation on Climate Change” in the Main Building. Tsinghua Vice President Chen Jining hosted the speech. “You have a unique opportunity and mission,” said Mr. Stoltenberg to the seated students, encouraging them to save the global environment for future generations by “making technology leaps of unprecedented scale and scope” in the future. “Nothing is more of a privilege than seeking knowledge with a free mind and keeping pace with the advances of the times,” said the Prime Minister. Mr. Stoltenberg said that he believes Norway and China can both gain from cooperating with each other. “A Chinese-Norwegian partnership would be a win-win-situation.” He also emphasized the importance of using advanced technology to solve climate change problems.
(From http://news.tsinghua.edu.cn，2007-03-27)
Products Made from Nonmetallic Materials Reclaimed from Waste Printed Circuit Boards* MOU Peng (牟 鹏), XIANG Dong (向 东), DUAN Guanghong (段广洪)** Department of Precision Instruments and Mechanology, Tsinghua University, Beijing 100084, China Abstract: Printed circuit boards (PCBs) are in all electronic equipment, so with the sharp increase of electronic waste, the recovery of PCB components has become a critical research field. This paper presents a study of the reclaimation and reuse of nonmetallic materials recovered from waste PCBs. Mechanical processes, such as crushing, milling, and separation, were used to process waste PCBs. Nonmetallic materials in the PCBs were separated using density-based separation with separation rates in excess of 95%. The recovered nonmetals were used to make models, construction materials, composite boards, sewer grates, and amusement park boats. The PCB nonmetal products have better mechanical characteristics and durability than traditional materials and fillers. The flexural strength of the PCB nonmetallic material composite boards is 30% greater than that of standard products. Products derived from PCB waste processing have been brought into industrial production. The study shows that PCB nonmetals can be reused in profitable and environmentally friendly ways. Key words: printed circuit boards (PCBs); electronic waste; reclaimation; reusing
Introduction According to statistical data released by the National Bureau of Statistics of China, about 20 million electronic household appliances (including televisions, washing machines, refrigerators, air conditioners, and personal computers) and 70 million cell phones have come to their end-of-life every year since 2001. As a key component in electronic equipment, large amounts of waste printed circuit boards (PCBs) are generated by all this consumption of electronic appliances. PCBs form about 3% by weight of the total amount of electronic scrap[1]. The process of reusing recovered metals from PCBs is already quite mature. However, the Received: 2006-06-26; revised: 2006-09-21
﹡ Supported by the National High-Tech Research and Development (863) Program of China (No. 2004AA420120)
﹡﹡ To whom correspondence should be addressed. E-mail: [email protected]; Tel: 86-10-62773404
recovered nonmetallic materials are not so widely reused. PCBs contain 70% to 80% nonmetals with the main nonmetallic ingredients being epoxy resins, glass fibers, and bromized flame retardant. Traditionally, most of these materials have been directly landfilled or incinerated[2]. However, disposal in landfills and incineration may cause environmental problems. Studies on resin reuse have emerged in recent years to meet more strict environmental protection legislations. The research falls into two groups. (1) Physical reuse Yokoyama and Iji[3-6] used recycled resin powder as filler for epoxy resin products, such as paints, adhesives, decorating agents, and building materials, and found that the resin powder improved the mechanical and thermal expansion properties of the products when compared to the usual fillers, such as talc, calcium carbonate, and milled glass fiber. Their physical recycling applications are interesting but the amount of PCB nonmetals used in these products is very limited,
MOU Peng (牟 鹏) et al：Products Made from Nonmetallic Materials Reclaimed from …
usually less then 10%, so these applications will not promote large scale recycling. (2) Chemical recycling Economy and Andreopoulos[7] developed a method to directly recycle and reuse thermosetting resins as a crosslinkable copolyester. Dang et al.[8] found that amine cured epoxy resins were not resistant to acid solutions and completely decomposed in high concentration acids at high temperatures. However, the recycled resins showed higher mechanical strength than virgin resin. They used a similar process to recycle glass fiber reinforced epoxy resins (GFRP)[9]. Chen et al.[10] created reworkable thermosets with cleavable linkages and studied their chemical and thermo-mechanical breakdown mechanisms. Although chemical recycling is a promising route for converting plastic wastes to their original constitutes, much more research and development on chemical recycling is needed to reduce the high cost and improve the quality. This paper describes the reuse of recovered PCB nonmetals after physical recovery in more practical and profitable ways for a variety of products.
1
Physical Properties of the Recovered Nonmetallic Powder
The nonmetallic powder physically separated from the waste PCB mainly consists of resins and glass fibers which do not need to be separated in what would be a relatively expensive process since their combined characteristics are very useful[11]. Therefore, the nonmetals can be reused “as is” with no waste or pollution. The particle size distribution and the bulk density are the most important properties when considering physical reuse. The size distribution is shown in Fig. 1.
Fig. 1 Particle size distribution of PCB nonmetallic powder
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The data indicates that most of the PCB nonmetallic powder is concentrated in sizes from 38.5 µm to 200 µm, with all of the size ranges within this range having similar amounts of nonmetals. Thus, the powder applications can be based on the granularity. The bulk density of the recovered nonmetal powder was about 2.0 g/cm3.
2
Reuse of Recovered Nonmetallic Materials from Waste PCBs
The recovered nonmetallic materials can be used in several ways based on the physical characteristics of the nonmetallic powder. 2.1
Construction material filler
Many previous applications have used the recovered nonmetallic materials as filler or agent for construction materials, from concrete to various framing materials. Researchers have sought improved construction materials with better mechanical strength, less environmental impact, and less cost. However, little actual data is available describing the reuse of recovered resins in construction materials with many of these studies only in the feasibility stage, so the actual usefulness is uncertain. For construction materials, the flexural and compressive strengths are the two most important properties. Compared with the main materials in concrete, cement, sand, and water, the recovered nonmetallic PCB powder is lighter than cement and sand, has finer granularity which makes the microstructure more reliable, and contains coarse glass fibers which improve mechanical strength. All of these properties can improve the mechanical strength. The optimum proportion of nonmetallic powder in the construction material should be carefully determined to maximize both the flexural and the compressive strengths. Six different percentages of recovered nonmetallic powder were used to make construction materials that were tested according to the China National Testing Method for Cement Mortar (GB177-85). The detailed compositions of the bricks made from the sand and PCB nonmetallic powder are listed in Table 1. Some bricks made from the recovered PCB nonmetallic powder are shown in Fig. 2.
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Table 1
Composition of brick material
Sample
Portland cement (g)
Sand (g)
PCB nonmetals (g)
Water (mL)
R1 R2 R3 R4 R5 R6
540 505 474 446 422 400
1351 1199 1066 949 844 750
0 63 118 167 211 250
238 222 208 196 186 176
Fig. 2 Bricks made using recovered nonmetallic PCB material
The flexural and compressive strengths of the modified and standard bricks are listed in Table 2. Table 2 Flexural and compressive strengths Sample R1 R2 R3 R4 R5 R6
Flexural strength (MPa) 8.30 8.18 8.76 8.65 8.03 7.42
Compressive strength (MPa) 0.43 0.43 0.44 0.46 0.35 0.31
The strength data was measured seven days after the bricks were made as stipulated in the China National Standard on Concrete. From the data in Table 2, sample R3 has the best flexural strength while sample R4 has the best compressive strength. Therefore, sample R3 or sample R4 or some composition of these two would give the best result. The reuse of recovered nonmetals as filler to make construction materials is feasible but not very attractive since the improvements in the flexural and compressive strengths are quite limited with less than 10% when compared with the standard concrete (R1) and the replaced materials in the original concrete, the sand and cement, are cheap and abundant, so this substitution will not give a good economic return. Therefore,
current research on the use of recycled PCB material as construction materials seeks simply to find some use for the recycled material even it is a relatively small amount. 2.2
Modeling material
There are many kinds of models used for exhibitions or for decorations. Most models are made from gesso, plastic, or other materials. Resin powder has many similar or better physical properties than gesso, including lighter weight, waterproof, easy to mold, and higher mechanical strength (due to the glass fibers). Therefore, the recovered nonmetals can be used as a substitute for statues, ornaments, and other models. Three different moulding processes have been used to make models from recovered PCB nonmetals. (1) Models made from PCB nonmetals and an adhesive Three key factors, the type of adhesive, the blending ration between the nonmetallic powder and the adhesive, and the pressure during the modeling process, affect the molding process. The recycled PCB nonmetallic material is a powder so it cannot hold a shape, so an adhesive must be used to form the material. Resin-type adhesives were used for their potential affinity with the recovered nonmetallic powder to improve the final properties. Two other adhesives were used for comparison. The final results showed that all the models were solid but had poor mechanical strength. The first reason for the poor strength is the manner by which the adhesive combines with the resin powder. With the various adhesives used for comparison, the forces between the powder and the adhesive were physical rather than chemical, so the strength was limited. In addition, the moldings were made by hand, so the molding pressure was relatively low and not uniform. The models had a large number of small air holes inside the models due to the manual processing which reduce the model’s strength. The mechanical strength of the models can be improved by increasing the pressure in the mold to reduce the air holes inside the model. Another measure is to adjust the blending ratio between the resin powder and the adhesive. Using less adhesive will reduce the cost when the mechanical strength is not compromised. (2) Models made from PCB nonmetals and decorative cement Here, the PCB nonmetallic material was not used as
MOU Peng (牟 鹏) et al：Products Made from Nonmetallic Materials Reclaimed from …
a filler but as the main material with the models designed as ornaments. A special decorative cement served as the adhesive. The material was cast as a cube and as a computer mouse as shown in Fig. 3 to validate its molding ability according to the China National Standard on Construction Material.
Fig. 3 Models made from PCB nonmetallic powder and a decorative cement
The results showed that the models held together well and had good mechanical strength, but were heavier than standard models and had poor surface quality. The model surfaces were quite coarse and needed further processing. In general, the resin adhered well to the cement and with some improvements, especially the surface treatment, the molding process could be efficient and useful. (3) Models made from nonmetallic powder, decorative cement, and fillers Some filler was added to the powder and the decorative cement to improve the model’s characteristics. Wood chips and silver sand were used as the preferred fillers because they are very cheap and abundant, but the results were not an improvement over the previous results. The wood chips reduced both the weight and the mechanical strength since they do not adhere to the nonmetals. The sand increased the strength but had no effect on the weight or the surface quality. When compared with the use of the PCB nonmetallic powder as filler for construction materials, the use in models, though not perfect, has better prospects since the recovered material is not just a filler, but the main materials, so the reuse has more value. 2.3
Composite boards made from PCB nonmetallic materials
Composite boards are used extensively in many fields including automobiles, furniture, amusement equipment, and decorative materials. The most attractive aspect of making composite boards from PCB
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nonmetallic materials is the potential economic benefit. In general, products made from composite boards are high value products with large profit margins. A wide variety of products can be made from composite boards for various applications. PCB nonmetallic materials were used to make composite boards into various products for the Beijing SBL Amusement Equipment Co., Ltd. Talc and silica powder are currently the two main materials used for making the composite boards used by the company. Recovered nonmetallic powder was then substituted for these products to make the composite boards. (1) Production of the composite boards The PCB nonmetallic powder recovered from the PCBs has coarser granularity than the talc and silica powders. Figure 1 shows that more than half of the nonmetallic powder particles are between 90 µm and 500 µm in size. The silica and talc powders are finer with granularities around 50 µm. Theoretically, the composite board should have better mechanical strength with the coarser grains. In addition, the PCBs contain glass fibers with many remaining after the crushing process. Though these glass fibers are smaller after the crushing, they are still larger than the rest of the nonmetallic powder so they serve as a frame in the composite boards which further strengthen the material. Finally, the most important and useful characteristic of the recovered nonmetallic material is their compatibility with the epoxy resin adhesive used by the company to bind the filler and the fibers, so the recovered PCB nonmetallic material has better affinity with the adhesive than silica and talc, which suggests better moulding properties and mechanical strength. The composite boards have multiple layers of fibers and fillers combined by the adhesive. The talc, silica, or recovered nonmetal material is filled between these layers at some pressure. About 90% of procedures were done manually in a complicated and experiencebased process. The original board making procedure was improved on two ways. First, a pressing machine was introduced to provide even and stable high pressures to the mould. This machine was a critical improvement which remarkably reduced the air holes in the board which will greatly improve the mechanical strength. Secondly, the working and holding temperatures were both increased and held longer which enhanced the curing procedure
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and provided more stable board properties. The main components in the composite boards are listed in Table 3. Potassium peroxide was also used as a curing agent. During the board production process, the stirring rate ranged from 450 r/min to 750 r/min with a curing time of 2 hours. Composite boards made from talc, silica, and the PCB nonmetallic material are shown in Fig. 4. Table 3 Main components in composite boards Ingredients Glass fiber cloth Epoxy resin Fillers PCB nonmetals
Fig. 5 Comparison of tensile strength
Ratio (wt.%) 30-45 35-40 5 15-30
Fig. 6 Comparison of tensile modulus of elasticity Fig. 4 Composite boards made from talc, silica, and the PCB nonmetallic material
During the production process, the boards made from the recovered PCB nonmetallic materials were found to be more easily shaped and flattened than the talc and silica boards. The blending time was also shortened greatly and the mixture was more uniform and reliable than the silica and talc mixture. These improvements may be attributed to the good affinity between the recovered material and the resin-based adhesive. (2) Mechanical strength The mechanical strength is the most important characteristic of the composite boards. Four different proportions were used to find the best ratio of nonmetallic material in the composite boards. 25% (wt.) of talc and silica were used in the composite boards as a result of years of experience at the company. The seven mechanical indexes measured in the tests were the tensile strength, tensile modulus of elasticity, flexural strength, flexural modulus, impact toughness, interlaminar shear strength, and punching shear strength. The results are shown in Figs. 5-11. Four proportions (15%, 20%, 25%, and 30% (wt.)) of recovered nonmetallic materials are expressed as P1, P2, P3, and P4. Figures 5-8 show that the composite board containing 15% (wt.) PCB nonmetallic powder has the best
Fig. 7 Comparison of flexural strength
Fig. 8 Comparison of flexural modulus
combination of properties for the four primary properties of the tensile strength, the tensile modulus of elasticity, the flexural strength, and the flexural modulus. Only the interlaminar shear strength is somewhat low. The talc board also has excellent properties, so it is the main material used by the company to make composite boards and related products.
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the recovery not only recycles waste PCBs, but also earns a profit. 2.4
Fig. 9 Comparison of impact toughness
Fig. 10 Comparison of interlaminar shear strength
Fig. 11 Comparison of punching shear strength
The composite board made with 30% (wt.) nonmetallic powder has the worst properties since there must be too many PCB materials for the adhesive to link. The comparison of the seven key mechanical properties indicates that the recovered material can be used as a substitute for silica and talc to make composite boards and other products. The outstanding characteristic of the nonmetallic material board is its flexural strength, which was enhanced by more than 50% for the 15% blending ratio when compared with talc. Therefore, this is good for products that mainly bear bending stresses. The use of PCB nonmetallic materials to make composite boards is a promising application since composite boards are used extensively in many manufacturing fields. The economic return should be considerable. So,
Specific products made from PCB nonmetallic materials
Analysis of the mechanical properties indicates that the recovered PCB nonmetallic material can best be used to make products which endure greater bending stresses because of its excellent flexural strength. The technology has now been used in two typical products. (1) Sewer grates In China, about 90% of the sewer grates are made of cast iron[12], which are valuable and often stolen by thieves. Beijing lost about 24 000 grates (3.4% of the total) in 2004, which were worth about RMB 28 million. In the first half of 2005, 8000 grates were stolen. The loss of sewer grates is a serious social problem, which has not only caused great property loss, but also creates potential threat to passersby and cars. In addition, the demand for new sewer grates for new construction is also enormous. China is rapidly developing with municipal construction, needing about 4 million grates per year. Therefore, to prevent such thefts, more and more sewer grates are being made of composite materials in China. Steel-fiber concrete and glass fiber reinforced plastic (FRP) are the two commonly used materials. The main characteristics of grates made from these materials are listed in Table 4. Table 4 Characteristics of grates made from steelfiber concrete and FRP[12] Material Steel-fiber concrete FRP
Merits Lower cost and worthless to thieves Designable surface and better strength
Deficiencies Brittle, poor strength, and heavier Higher cost and poor impact strength
The process used to make composite boards from the PCB nonmetallic material was also used to make the sewer grates shown in Fig. 12. The main advantages of these grates are lower cost and better mechanical strength, especially the flexural strength. Another important point is that the PCB nonmetallic material is a recycled material, so the process makes use of materials that would otherwise be sent to landfills.
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Fig. 12 Grate made from recovered PCB nonmetallic material
The grates meet the strength requirements of the China National Building Standard Specification (CJ/T 130-2001) for use in sidewalks and main roads, so the grates can be widely used. This will considerably reduce the theft of grates. (2) Surfboat in amusement park The Beijing SBL Amusement Equipment Co., Ltd mainly makes products for amusement equipment, such as roller coasters, bumper cars, racing cars, and various boats and trains. The boats are one of SBL’s main products. The boat decks are subjected to large bending pressures. The composite board can be effectively used in the deck and body of boats. The boat making process is shown in Fig. 13.
materials, to make models, in composite boards, and in practical products, such as sewer grates and small boats. The first two schemes are not very attractive due to their low economic return and practical application potential. Though these applications are better than landfills and incineration, many improvements are still needed to further promote these use. The last two schemes, using recovered PCB nonmetallic material to make composite boards and related products are much more attractive applications. First, they have great market demand which will pave the way for the use of a large amount of recovered PCB nonmetallic material. Secondly, they have potential to bring considerable profit when applied to practical products. Both the sewer grates and the boats are high value added products which will be effective solutions for recovering nonmetallic materials of waste PCBs. References [1]
Bernardes A, Bohlinger I, Rodriguez D, Milbrandt H, Wuth W. Recycling of printed circuit boards by melting with oxidising/reducing top blowing process. In: TMS Annual Meeting. Orlando, USA, 1997.
[2]
Li Jianzhi, Puneet Shrivastava, Gao Zong, Zhang Hongchao. Printed circuit board recycling: A state-of-the-art survey. IEEE Transaction on Electronics Packaging Manufacturing, 2004, 27(1): 33-42.
[3]
Yokoyama S, Iji M. Recycling of thermosetting plastic waste from electronic component production process. In: Proceeding of 1995 IEEE International Symposium on Electronics and the Environment. USA, 1995: 132-137.
[4]
Yokoyama S, Iji M. Recycling of printed wiring boards with mounted electronic parts. In: Proceeding of 1997 IEEE International Symposium on Electronics and the Environment. USA, 1997: 109-114.
[5] Fig. 13 PCB nonmetallic material deck
The first batch of boats with the PCB nonmetallic material deck has already passed performance tests and is being used in the Shijingshan Amusement Park of Beijing.
Iji M. Recycling of epoxy resin compounds for moulding electronic components. Journal of Materials Science, 1998, 33: 45-53.
[6]
Yokoyama S, Iji M. Recycling system for printed wiring boards with mounted parts. In: Proceeding of 1999 Environmentally Conscious Design and Inverse Manufacturing. Tokyo, Japan, 1999: 814-817.
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Conclusions
This paper describes several methods for reusing recovered nonmetals from waste PCBs. The PCB nonmetallic material can be reused in construction
[7]
Economy J, Andreopoulos A G. A new concept for recycling of thermosetting resinⅠ: The case of crosslinkable copolyesters. Polymer for Advanced Techonologies, 1996, 7: 561-570.
[8]
Dang Weirong, Kubouchi Masatoshi, Yamamoto Shurou,
MOU Peng (牟 鹏) et al：Products Made from Nonmetallic Materials Reclaimed from …
[9]
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Sembokuya Hideki, Tsuda Ken. An approach to chemical
[11] Mou Peng, Wa Layiding, Xiang Dong, Gao Jiangang,
recycling of epoxy resin cured with amine using nitric acid.
Duan Guanghong. A physical process for recycling and
Polymer, 2002, 43: 2953-2958.
reusing waste printed circuit boards. In: Proceedings of the
Dang Weirong, Kubouchi Masatoshi, Sembokuya Hideki,
2004 IEEE International Symposium on Electronics and
Tsuda Ken. Chemical recycling of glass fiber reinforced epoxy resin cured with amine using nitric acid. Polymer, 2005, 46: 1905-1912. [10] Chen Jir Shyr, Christopher K B, Mark D P. Characteriza-
the Environment. Scottsdale, USA, 2004: 237-242. [12] Yi Changping, Liu Jun, Zeng Jingcheng, Zeng Jianxiang. Present status and developing trend of compound well lids. FRP and Compound Material, 2004, 4: 43-45. (in Chinese)
tion of thermally reworkable thermosets: Materials for environmentally friendly processing and reuse. Polymer, 2002, 43: 131-139.
Norway’s Prime Minister Visiting Tsinghua University Prime Minister Jens Stoltenberg of Norway visited Tsinghua on March 27. Tsinghua President Gu Binglin welcomed Mr. Stoltenberg. The two exchanged ideas on climate change, energy saving, and environmental protection. Mr. Stoltenberg delivered a speech entitled “International Cooperation on Climate Change” in the Main Building. Tsinghua Vice President Chen Jining hosted the speech. “You have a unique opportunity and mission,” said Mr. Stoltenberg to the seated students, encouraging them to save the global environment for future generations by “making technology leaps of unprecedented scale and scope” in the future. “Nothing is more of a privilege than seeking knowledge with a free mind and keeping pace with the advances of the times,” said the Prime Minister. Mr. Stoltenberg said that he believes Norway and China can both gain from cooperating with each other. “A Chinese-Norwegian partnership would be a win-win-situation.” He also emphasized the importance of using advanced technology to solve climate change problems.
(From http://news.tsinghua.edu.cn，2007-03-27)