Environ. Sci. Technol. 2008, 42, 624–628
Phenolic Molding Compound Filled with Nonmetals of Waste PCBs
Nonmetals reclaimed from waste phenolic cellulose paper printed circuit boards (PCBs) are used to replace wood flour in the production of phenolic molding compound (PMC). The results indicate that filling of nonmetals in PMC improves the charpy notched impact strength and heat deflection temperature (HDT) and reduces flexural strength and rasching fluidity. Rasching fluidity decreases dramatically with the increase of the content of nonmetals. To ensure sufficient properties of PMC, the optimal added content of nonmetals is 20 wt %, which results in a flexural strength of 70 MPa, a charpy notched impact strength of 2.4 KJ/m2, a HDT of 168 °C, a dielectric strength of 3.9 MV/m, and a rasching fluidity of 103 mm, all of which meet the national standard data. When the added content of nonmetals is 20%, the charpy notched impact strength, HDT, and rasching fluidity of PMC decrease, and the flexural and dielectric strengths decrease at first and then increase with decreasing particle sizes. All the results indicate that making PMC with nonmetals of waste PCBs can resolve environmental pollution, reuse nonmetals in different fields, and provide a new method for resource utilization of nonmetals from waste PCBs.
PCBs, but it may cause secondary pollution and resourcewasting. S. Yokoyama and M. Iji have carried out many studies on the recycling of glassfiber-resin powder taken from PCBs (6, 7). In their studies, nonmetals reclaimed from waste PCBs could be used as fillers for other products, such as construction materials, decorating agent, adhesives, and insulating materials. Mou Peng also presented new methods in which the nonmetal waste is used to make formative models, compound boards, or related products (8). Phenolic molding compound (PMC) is produced with phenolic resin, acting as a bonding agent , various fillers, solidifiers, and colorants under high temperature and a certain pressure. Because of their relative cheapness, ease of fabrication, high mechanical strength, heat resistance, and high dielectric strength, PMC is widely used and in demand for radios, kitchen utensils, and electronic switches. Increasing production of PMC in recent years has greatly increased the need of wood flour, which is used as an organic filler in the molding compounds. With the timber resource depletion and the increasing price of wood flour, it is an urgent assignment for producers of PMC to protect timber resources and reduce the cost of raw materials by finding alternative materials for wood flour. A. Y. Kharade studied the effect of partial replacement of wood flour filler by lignin on the properties of molding powders (9). Samir Hattali also studied the behavior of replacement of wood flours by alpha grass soda lignin (10). To our knowledge, there is little published information about reusing nonmetals reclaimed from PCBs as a filler of PMC. In this study, nonmetals reclaimed from paper-based circuit board scrap were used to replace wood flour for producing modified PMC. Effects of the contents and particle sizes of nonmetals on the properties of PMC were investigated. Therefore, from the use of renewable resources and environmental protection viewpoints, a study to analyze the possibility of substituting wood flour by nonmetals and develop a modified type of PMC with lower cost and better properties than traditional PMC can be very useful and practical.
Introduction
Experimental Section
Printed circuit boards (PCBs) contain nearly 28% metals, including Cu, Al, Sn, etc. The purity of precious metals in PCBs is more than 10 times higher than that of rich-content minerals (1, 2). Recycling of PCBs is an important subject not only from the treatment of waste but also from the recovery of valuable materials because the amount of waste PCBs is dramatically increasing. Mechanical-physical processes are attracting more attention than hydrometallurgy and pyrometallurgy (3, 4). The mechanical-physical approach involves a crushing process that aims to strip metal from the base plates of waste PCBs, and then different methods are used to separate metals from nonmetals (5). Metals such as Cu, Al, and Sn, are sent to recovery operations. However, the significant quantities of nonmetals in PCBs (up to 70%) present an especially difficult challenge for recycling. The nonmetal portions of PCBs mainly consist of thermoset resins and reinforcing materials. Thermoset resins cannot be remelted or reformed because of their network structure. Incineration is not the best method for treating nonmetals because of inorganic fillers such as glass fiber, which significantly reduces the fuel efficiency. Disposal in landfill is the main method for treating nonmetal parts of
Crushing and Separating of PCBs. In this study, the technology for recycling PCBs was a two-step crushing and corona electrostatic-separating process. The waste PCBs were a kind of single-sided phenolic cellulose paper PCB. The PCBs were first pulverized in a process consisting of a coarsecrushing step and a fine-pulverizing step, using a shearing machine and a hammer grinder. Then, an electrostatic separator was used to separate the metals from the nonmetals (11). After they were separated, the nonmetals were screened by a vibrating screen. A stack of five sieves with hole widths
JIE GUO, JIA LI, QUNLI RAO, AND ZHENMING XU* School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People’s Republic of China
Received June 1, 2007. Revised manuscript received August 30, 2007. Accepted October 16, 2007.
* Corresponding author phone: +86 21 54747495; fax: +86 21 54747495; e-mail:
[email protected]. 624
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 2, 2008
TABLE 1. Formulations of PMC ingredients
content (wt %) of content (wt %) of reference PMC modified PMC
phenolic resin wood flour nonmetals talc powder hexamethylenetetramine calcium carbonate magnesium oxide nigrosine stearic acid 10.1021/es0712930 CCC: $40.75
43 34 11.6 7 0.6 0.6 1.6 1.6
40-47 5-25 10-40 3-15 7 0.6 0.6 1.6 1.6
2008 American Chemical Society
Published on Web 12/12/2007
FIGURE 1. Schematic illustration of crushing and electrostatic separating of PCBs.
FIGURE 2. Particle-size distribution of nonmetals. ranging from 0.3 to 0.07 mm were selected. Specimens were agitated for 20 min; then the mass of nonmetals collected on each sieve was weighed to calculate the particle size distribution. The materials used to study the effect of the particle size of the nonmetals on the properties of PMC were ground into three size ranges : 0.3-0.15, 0.15-0.07, and
