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Introduction Wide diffusion of electronic products and shortening of product life cycles have generated huge amount of E-wastes in the society every year. On handling the increasing volume of E- wastes, PCB recycling is recognized as one of the most difficult tasks because of their complex construction and the consequent complicated mixture of materials [1]. PCBs are installed in almost all kinds of electrical equipment and electronic products. A recent study by EPA shows that in 2007 from obsolete computers, cell phones and TVs such three sources, approximately 500 million pounds of PCB wastes were generated in the United States; only about 18% (by weight) were recycled, while most were disposed of, primarily in landfills [2]. The Wisconsin households have about 20 million pounds of PCBs from computers, cell phones and TVs every year to be recycled (please note that this number does not include millions of pounds of PCBs from Wisconsin businesses and institutions around the state) [3]. Effective from January 2010, Wisconsin Electronics Recycling Law requires manufacturers to take-back and recycle such obsolete electronics as computers, TVs and printers from Wisconsin households and K-12 public schools; the law also bans the landfill and incineration of most electronic wastes in Wisconsin starting from September 1, 2010 [4]. As a result, PCB recycling has emerged as an urgent issue for electronics manufacturers and recycling industry, in both Wisconsin state and the United States. PCBs primarily consist of three basic parts: a non-conducting substrate or laminate, conductive circuits printed on or inside the substrate, and the mounted components. The most widely used substrate is the FR4 (FR=Flame Retarded), which is made up of fiberglass reinforced epoxy resin with a brominated flame retardant in the epoxy matrix. Another widely used laminate is the FR2 laminate that is made up of paper reinforced phenolic resin with flame- retardants added. PCB substrates are composed of layers of copper foils and fiberglass polymers, with different layers bonded by epoxy resins. PCBs have high recycling value because it contains a number of precious metals (Au, Ag, Pd and Pt), and base metals (Cu, Fe, Ni, and Sn). However PCB also contains such toxic metals as lead, mercury, antimony, cadmium, chromium, beryllium, etc. which needs proper handling and special treatment. In current practice, PCBs are shredded and ground into powders for material separation and recycling, which makes it difficult to separate metal chips from polymer powders, and more importantly, causes fine particle emissions of toxic elements into the environment [5]. Alternative methods capable of recycling PCBs in more efficient and environmentally friendly way are greatly needed by both the electronic industry and society. Supercritical fluid (SCF) has been studied in our preliminary tests with demonstrated potential to address such challenges in current PCB recycling. SCF has superior solvent power and is widely used as solvent for extraction in industrial processes [6]. Application of SCF treatment of PCB wastes can resolve the bonding materials (resins) from the woven glass fibers and metallic components in the PCB substrate and hence can easily separate the recoverable materials. Our preliminary studies have evidenced that with a small quantity of environmentally benign co-solvents H2O, the resin (bond material) can be decomposed in SCF CO2, thus the substrate layers of PCBs are automatically separated, as shown in figure 1. The pilot study demonstrated that the copper foils and other reinforced materials remain in their original forms, which make subsequent recovery process much easier. 4PDF Image | Recycling Printed Circuit Board Wastes Through Supercritical Fluid Delaminating
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