Dissolution of Brominated Epoxy Resins by Dimethyl Sulfoxide To

Article pubs.acs.org/est

Dissolution of Brominated Epoxy Resins by Dimethyl Sulfoxide To Separate Waste Printed Circuit Boards Ping Zhu,*,†,‡ Yan Chen,†,‡ Liangyou Wang,†,‡ Guangren Qian,†,‡ Wei Jie Zhang,†,‡ Ming Zhou,§ and Jin Zhou∥ †

Zhejiang Provincial Key Laboratory of Solid Waste Treatment and Recycling, College of Environmental Science and Engineering, Zhejiang Gongshang University, Hangzhou, 310018, China ‡ College of Environmental and Chemical Engineering, Shanghai University, 99 Shangda Road, Shanghai 200444, China § Semiconductor Manufacturing International (Shanghai) Corporation, 18 Zhangjiang Road, Shanghai 201203, China ∥ Institute of Microelectronics, Peking University, No. 5 Yiheyuan Road, Haidian District, Beijing 100871, China S Supporting Information *

ABSTRACT: Improved methods are required for the recycling of waste printed circuit boards (WPCBs). In this study, WPCBs (1−1.5 cm2) were separated into their components using dimethyl sulfoxide (DMSO) at 60 °C for 45 min and a metallographic microscope was used to verify their delamination. An increased incubation time of 210 min yielded a complete separation of WPCBs into their components, and copper foils and glass fibers were obtained. The separation time decreased with increasing temperature. When the WPCB size was increased to 2−3 cm2, the temperature required for complete separation increased to 90 °C. When the temperature was increased to 135 °C, liquid photo solder resists could be removed from the copper foil surfaces. The DMSO was regenerated by rotary decompression evaporation, and residues were obtained. Fourier transform infrared spectroscopy (FT-IR), thermal analysis, nuclear magnetic resonance, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to verify that these residues were brominated epoxy resins. From FT-IR analysis after the dissolution of brominated epoxy resins in DMSO it was deduced that hydrogen bonding may play an important role in the dissolution mechanism. This novel technology offers a method for separating valuable materials and preventing environmental pollution from WPCBs.

■

solution.9 Kim and Zhu leached copper by electro-oxidation of the metal powders separated from WPCBs.5,10 Havlik leached metals from residues that were obtained from vacuum pyrolysis using hydrochloric acid.6 Oishi leached Cu directly from mixtures of crushed WPCBs using an alkaline reagent ((NH4)2SO4 + NH4Cl) and then treated the leachate in an extraction−electrodeposition process to obtain pure copper.11 Recently, Ma and Guan attempted to dissolve brominated epoxy resins in WPCBs using nitric acid; however, the leaching rate was too low.12,13 From the above-mentioned processes, it can be seen that aqueous solvents, such as strong acids and alkalis, are usually used to treat WPCBs in hydrometallurgical processes. These processes often generate large amounts of waste acid, alkaline liquid, and sludge thereby causing secondary pollution. Furthermore, the treatment process is often complex as hydrometallurgy combined with pyrolysis (or

INTRODUCTION The production of printed circuit boards (PCBs) is the foundation of the electronic industry as PCBs are an essential component in virtually every electrical and electronic device. New technological innovations continue to accelerate the replacement of electronic devices, leading to a significant increase in waste PCBs (WPCBs).1,2 WPCBs are a mixture of approximately 30% metal and 70% nonmetal. The metals include Cu, Pb, Sn, and other assorted precious metals while the nonmetal polymer materials consist of thermoplastic and thermosetting resins, such as brominated epoxy resins, which are used as flame retardants. Because WPCBs are manufactured by a laminating process which is done by placing the stack of materials in a press and applying pressure and heat for a period of time, it is very difficult to separate the individual components from WPCBs.3−8 Hydrometallurgy is typically employed to extract precious metals, such as Au, Ag, and Pt, and base metals, such as copper, from WPCBs. Zhu1 leached Au and Cu from WPCBs using a highly selective acid reagent (H2O2 + H2SO4). Kinoshita leached Au and Ag from WPCBs using an acid thiourea © 2013 American Chemical Society

Received: Revised: Accepted: Published: 2654

September 11, 2012 January 28, 2013 February 11, 2013 February 11, 2013 dx.doi.org/10.1021/es303264c | Environ. Sci. Technol. 2013, 47, 2654−2660

Environmental Science & Technology

Article

Table 1. Main Composition of WPCBs As Determined by X-ray Fluorescence Al

Sn

Pb

Ca

Fe

Na

Sr

content (wt %) element

element

14.000 Br

Cu

4.647 Si

1.857 S

0.004 Cr

3.314 Cl

0.081 P

1.318 K

0.378 Ba

content (wt %)

16.246

24.061

17.624

0.051

3.317

0.056

0.108

12.938

heated from 25 to 220 °C at a rate of 2 °C/min in a nitrogen atmosphere. The TMA curve is shown in Figure S1 (Supporting Information (SI)) and the glass transition temperature of the WPCBs is 130.12 °C. Methods. The experiment to separate the pretreated 1−1.5 and 2−3 cm2 WPCBs consisted of a 0.5-L, four-necked flask equipped with nitrogen gas inlet. Figure S2 (SI) shows a schematic diagram of the reactor. In the presence of nitrogen gas, the 1−1.5 cm2 sized WPCBs were treated in DMSO at 60 °C for 45, 90, and 210 min, and then at 90 and 135 °C for 60 and 10 min, respectively. The 2−3 cm2 sized WPCBs were treated in DMSO at 60, 90, and 135 °C for 480, 90, and 20 min, respectively. The solid to liquid ratio (S/L) was controlled at 1:2 (w/v). Solid−liquid separation was conducted after the reaction. The treated WPCBs were washed using deionized water, air-dried, and weighed using an electronic balance (FA214). Their images were taken using a metallographic microscope (EPLPHOT 300) and digital camera. The relative mass changes of the 1−1.5 cm2 sized WPCBs dissolved in DMSO at 60 °C with increase in time were calculated as follows:

physical mechanics methods) is usually required to treat WPCBs. Continued research into the recycling of WPCBs is therefore required. In this study, a nonaqueous rather than aqueous solvent was used to separate WPCBs. Dimethyl sulfoxide (DMSO, (CH3)2SO) is an excellent nonaqueous solvent that acts as both a soft (sulfoxide sulfur) and hard base (sulfoxide oxygen). DMSO is polar, aprotic, and odorless with low toxicity, high boiling point (189 °C), and slightly high viscosity (2.2 mPa·s, 20 °C). DMSO dissolves numerous organic and inorganic chemicals effectively but does not corrode metal. The excellent safety characteristics of DMSO have led to its use in a wide range of applications, notably as a cleaning agent for electronic components, as a reaction solvent for pharmaceuticals, in agricultural chemicals, and as a solvent for cellulose dissolution.14−16 More importantly, DMSO is highly stable below 150 °C.17−19 Maintaining DMSO at 150 °C for 24 h results in an expected loss of between 0.1 and 1.0%. It has been reported that only 3.7% volatile material is produced when DMSO is held for 72 h at its boiling point (189 °C). In addition, DMSO is remarkably stable in the presence of most neutral or basic salts and bases, but acid will promote its decomposition. To the best of our knowledge, no previous study has investigated the separation of WPCBs using DMSO. In this paper, the effects of WPCB size, temperature, and time on the use of DMSO in separating WPCBs were investigated and the product dissolved in the DMSO was analyzed by Fourier transform infrared spectroscopy (FT-IR), thermal analysis, nuclear magnetic resonance, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The aim of this research was to develop a novel technique for separating valuable materials from WPCBs and to prevent environmental pollution from WPCBs.

ΔW = W2 − W1

ΔW is the relative mass of WPCBs. W2 and W1 are the WPCB masses at the next and previous time point, respectively. The concentration of brominated epoxy resins in WPCBs dissolved in DMSO was determined using a UV absorption spectrometer (UV5300PC, Shanghai Metash Instruments Co., Ltd., China). A 1-mL sample was diluted to 50 mL in a volumetric flask with 25% ethanol solution, and a 1-cm cell was used to determine the concentration of bisphenol A (a component of bromine epoxy resin) at a wavelength of 282 nm (the absorption maximum of bisphenol A). Then, the concentration of brominated epoxy resins in the WPCBs was calculated according to the proportional relationship of the brominated epoxy resin and bisphenol A. The used DMSO was vaporized under decompression using a rotary process to obtain regenerated DMSO, and residues were precipitated from the used DMSO. Regenerated DMSO was used to treat the 2−3 cm2 sized WPCBs continuously at 135 °C, 20 min, and a solid to liquid ratio of 1:2 (w/v). This process was repeated 20 times. The unused and used DMSO, brominated epoxy resins in WPCBs, and residues were analyzed using FT-IR (IFS 55, Bruker Company, Fällanden, Zurich, Switzerland) with a KBr pellet method. Solid samples of brominated epoxy resins in WPCBs were obtained as follows. First, the LPSRs and copper were removed from the WPCBs. Then, the brominated epoxy resins in the glass fibers were scraped off. A mass of brominated epoxy resin powder (1 mg) was ground with 100 mg of KBr and pressed into a transparent sheet. Finally, the sheet was analyzed by FT-IR. The sample preparation for the brominated epoxy resins that had dissolved in the DMSO was as follows: brominated epoxy resin powders were ground with DMSO at 90 °C for 90 min and the S/L ratio was controlled at 10:1, 8:1, and 5:1. Then, 1 mg of mixed sample was ground with 100 mg

■

MATERIALS AND METHODS Materials. WPCBs were collected from a solid waste disposal center in Shanghai, China. WPCBs were the motherboards of personal computers, and electronic components (ECs) in the WPCBs were removed manually. The WPCBs were multilayered structures composed of woven glass fiber, brominated epoxy resin (as flame retardant), and metals. The main components of the WPCBs as assessed by X-ray fluorescence (XRF-1800, Shimadzu Limited, Kyoto, Japan) are shown in Table 1. WPCBs without ECs (known as bare boards) were cut into fragments of approximately 1−1.5 and 2−3 cm2 using scissors prior to conducting the experiment. All reagents were AR grade products from Shanghai Sinopharm Chemical Reagent Co., Ltd. (China). The glass transition temperature of the brominated epoxy resin in WPCBs was determined by a thermomechanical analyzer (TMA, Q400EM,TA Instruments, America). First, the liquid photo solder resists (LPSRs) in the WPCBs were scraped off, and then the WPCBs were dried in an oven (CS101-1D, Chongqing Sida Instrument Co., Ltd., China) at 100 °C for 2 h. Finally, 2−10 mg of the samples was placed into a crucible and 2655

dx.doi.org/10.1021/es303264c | Environ. Sci. Technol. 2013, 47, 2654−2660


Article

Figure 1. Metallographic photographs of (a) untreated WPCBs, (b) WPCBs treated in DMSO for 45 min at 60 °C, and (c) WPCBs treated in DMSO for 90 min at 60 °C (1−1.5 cm2).

Figure 2. (a) FT-IR and (b) 1H NMR spectra of unused DMSO and DMSO used 20 times.

foils at 135 °C. The rising temperature accelerated the diffusion of DMSO into the WPCB board from its edges, which reduced the separation time (Figure S4). However, separation of the 2−3 cm2 sized WPCBs was incomplete when the WPCBs were placed in DMSO at 60 °C for 480 min. When the DMSO was heated to 90 °C and maintained at this temperature for 90 min, the 2−3 cm2 sized WPCBs were separated completely (Figure S5). When the temperature was maintained at 135 °C for 20 min, separation of the WPCBs was complete (Figure S6). Figure S6a shows that the copper foils were separated from the WPCBs but the solders were still bound to the copper foils. The results indicate that DMSO does not react with metals, LPSRs, and glass fibers. Consequently, it is presumed that the delamination and separation of the WPCBs occurred by the dissolution of the brominated epoxy resins within the WPCBs by DMSO. It can be seen from Figure S1 that the glass transition temperature of the brominated epoxy resin in WPCBs is 130.12 °C, which indicates the initiation of movement of the brominated epoxy resin chains. When the heating temperature of the WPCBs was lower than the glass transition temperature of the brominated epoxy resin, the brominated epoxy resin chains were frozen. The brominated epoxy resin in WPCBs is dissolved by removing small segments thereof, and its dissolution rate is slow. In addition, because the increase in WPCB size causes an increase in the mass transfer resistance, it is difficult for the DMSO to penetrate the WPCBs and dissolve the brominated epoxy resins. Therefore, the separation of 1−1.5 cm2 WPCBs was complete at 60 °C for 210 min, but that of the 2−3 cm2 WPCBs was incomplete at 60 °C for 480 min when the heating temperature of the WPCBs was close to or higher than the glass transition temperature of the brominated epoxy resin. The rate of brominated epoxy resin dissolution into DMSO becomes fast because its chains became active and the mass transfer of the DMSO penetrating the WPCBs was enhanced. Thus, 1−1.5 cm2 WPCBs ]were separated very quickly and separation of the

of KBr and pressed into a transparent sheet. Finally, the sheet was analyzed by FT-IR. The thermal behavior was examined by thermogravimetry−derivative thermogravimetry−differential thermal analysis (TG-DTG-DTA; STA 449C, NetzschGerätebau GmbH, Germany). The samples (5.000 mg) were placed in a Pt−Rh crucible and heated from 25 to 800 °C at a rate of 8 °C/min. Scanning electron microscope energydispersive X-ray spectroscopy (SEM-EDS, JSM-6700F, Jeol Ltd., Japan) analyses were conducted at an accelerating voltage of 20 kV. Deuterated DMSO and chloroform were used in nuclear magnetic resonance studies (NMR; Bruker AV 400 AVANCE 500 MHz spectrometer, Bruker Company, Fällanden, Switzerland). The samples were prepared by submerging the brominated epoxy resins of the WPCBs in the deuterated DMSO with a S/L sample ratio of 1:8 and 1:5. NMR samples were heated at 90 °C for 90 min, and spectra were recorded with 16−32 scans for the 1H NMR measurements at room temperature.

■

RESULTS AND DISCUSSION WPCB Delamination and Separation. Figure 1 shows metallographic photographs of untreated and treated WPCBs of 1−1.5 cm2. By comparing Figure 1a with b, it can be seen that the WPCBs delaminated when submerged in DMSO at 60 °C for 45 min. When the time was increased to 90 min, delamination of the WPCBs became noticeable (Figure 1c). When the heating time increased from 90 to 210 min, the WPCB separation went to completion (Figure S3). Copper foils and glass fibers were obtained but the LPSRs in the WPCBs still adhered to the copper foil surfaces (Figure S3a).Then, 1−1.5 cm2 WPCBs were submerged in DMSO at 90 and 135 °C, respectively. The delamination rate of the WPCBs was visibly faster with a delamination time of only 30 min at 90 °C (Figure S4a-1) and 5 min at 135 °C (Figure S4b1), respectively. WPCB separation went to completion after 60 and 10 min at 90 and 135 °C, respectively (Figure S4a-2,a-3 and S4b-2,b-3,b-4). The LPSRs were removed from the copper 2656



Article

2−3 cm2 WPCBs was also achieved at 90 and 135 °C, respectively. DMSO Regeneration and Solid Residue Analysis. Rotary decompression evaporation was used to treat the used DMSO. Evaporated gases were cooled using a condenser to obtain regenerated DMSO. It can be observed clearly that the unused and regenerated DMSO were colorless, and the used DMSO was yellow (Figure S7). It is likely that DMSO dissolves the brominated epoxy resins in WPCBs, causing their color change. Figure S7d shows the residues remaining after evaporation. FT-IR and 1H NMR spectra of unused DMSO and DMSO used 20 times are shown in Figure 2. Both spectra are the same, which indicates that the chemical properties of the DMSO did not change. Figure 3a and b show the FT-IR spectra of the brominated epoxy resins in WPCBs and the residues. Hydroxyl, phenyl, and

°C, which is the pyrolysis temperature range of the brominated epoxy resins in WPCBs.21,22 Figure 5 shows the 1H NMR spectra of the DMSO and the DMSO that dissolved the brominated epoxy resins in the

Figure 3. FT-IR spectra of (a) brominated epoxy resins in WPCBs and (b) solid residues.

Figure 5. 1H NMR spectra of DMSO and DMSO + base materials of WPCBs: (a) DMSO, (b) WPCBs:DMSO (1:8), (c) WPCBs:DMSO (1:5).

WPCBs at S/L ratios of 1:8 and 1:5, respectively. The NMR signal of DMSO was at 2.5 ppm (Figure 5a). After the brominated epoxy resins in the WPCBs were dissolved in DMSO, the 1H NMR spectrum changed to that shown in Figure 5b and the NMR signal of the brominated epoxy resins was found to be weak. With increasing concentration of brominated epoxy resins, the NMR signals became strong (Figure 5c), and the 1H proton spectra of the brominated epoxy resins were assigned. It can be observed that the α and β protons in the brominated epoxy resins were responsible for

ether groups (the molecular structure of the brominated epoxy resin) are present. Therefore, it is assumed that the residues may be brominated epoxy resins in WPCBs which were dissolved in DMSO.20 Thermal analysis was used to confirm the residue composition. Figure 4a and b show the TG-DTA-DTG curves of the brominated epoxy resins in the WPCBs and residues. The significant residue mass losses were similar to those of the brominated epoxy resins in the WPCBs, occurring at 300−380

Figure 4. TG-DTA curves of (a) brominated epoxy resins in the WPCBs and (b) solid residues. 2657



Article

Figure 6. Properties of DMSO used to dissolve the brominated epoxy resin from WPCBs. (a) Change with time in brominated epoxy resin concentration from dissolving WPCBs at 60 °C; (b) different concentrations of DMSO used 20 times in dissolving brominated epoxy resin from WPCBs at 135 °C.

the signal at 4.0−4.3 ppm, which corresponds to literature results.20,23,24 The 1H NMR spectra indicate that the brominated epoxy resins in the WPCBs can be dissolved in DMSO. Finally, SEM and EDS analyses were used to observe the surface morphology of the residues and to examine their composition (Figure S8). The surface morphology of the residues was slightly different from the brominated epoxy resins in the WPCBs (Figure S8a and b). However, the residues contained elements characteristic of brominated epoxy resins, such as carbon, oxygen, and bromine, and these elemental contents were the same as those in the WPCBs (Figure S8a-1 and b-1). Based on FT-IR, TG-DTA-DTG, 1HNMR, and EDS analyses, it was concluded that the residues were the brominated epoxy resin in the WPCBs. Figure 6a shows the change in brominated epoxy resin concentrations from dissolving WPCBs at 60 °C with increase in time. The increase was slow from 10 to 60 min and rapid thereafter. This time-dependent trend was also seen in the morphological analysis shown in Figure 1b and c. To verify the DMSO reusability, different concentrations of DMSO used 20 times for dissolving brominated epoxy resin at 135 °C were evaluated (Figure 6b). The capacity of DMSO to dissolve the brominated epoxy resin did not change. From the perspective of protecting the environment and decreasing costs, it is noteworthy that DMSO can be regenerated. After the WPCBs had been separated completely, a mass balance was conducted with results shown in Table 2. The DMSO loss was approximately 2%, and all material components of the WPCBs could be recovered. The content of copper in WPCBs is approximately 14% and the glass fiber mass is the highest of all recovered materials. Mechanism of Swelling and Dissolution of Bromine Epoxy Resin. Swelling Behavior of WPCBs. Figure 7 shows

Figure 7. Relative change in WPCB mass with time.

the relative change in WPCB mass over time. The relative mass reached a maximum value after treatment with DMSO at 60 °C for 0.5 h and then decreased with time. This phenomenon can be explained by the fact that DMSO penetrates the WPCBs to soften the brominated epoxy resin and absorbs on WPCBs after the 0.5 h reaction. This causes the WPCBs to swell and their mass to increase. With increasing time, the amount of DMSO absorbed on the WPCBs decreased gradually until the swelling of WPCBs reached saturation and the amount of brominated epoxy resin dissolved in the DMSO solution increased gradually, causing the relative WPCB mass to decrease. This is consistent with the work of Timothy et al.24 As observed in Figure 2, which illustrates the separation of the WPCBs, the swelling of the WPCBs caused an increase in its thickness (Figure 1b and c). Infrared Spectrum of DMSO Dissolving Brominated Epoxy Resins in WPCBs. The brominated epoxy resins in the WPCBs blended with DMSO were ground at 90 °C for 90 min. Information regarding structural changes was collected by FTIR analyses. The FT-IR analyses were based on the identification of absorption bands associated with the vibrations of functional groups of the brominated epoxy resins in the WPCBs. The broad band in the WPCBs spectrum at 3600− 3100 cm−1, with a maximum at 3427.07 cm−1, was assigned to stretching vibrations of the OH groups.20,25 Figure 8a, b, c, and d shows the FT-IR transmittance spectra for the WPCB, WPCBs: DMSO (10:1), WPCB:DMSO (8:1), and WPCB:DMSO (5:1)samples, respectively, as a function of wavelength in the range of 4000−500 cm−1. A minor shifting of the peaks at 3600−3100 cm−1 was observed in the transmission band of the WPCBs/DMSO blends, which indicates that a

Table 2. Mass Balance of WPCBs Treated by DMSO item raw material mass before experiment mass of various WPCB components after experiment

DMSO mass after experiment

mass balance (g) DMSO WPCBs copper glass fiber epoxy resin solder resist

50 25 3.5 17.0 4.0 0.5 49 2658



Article

The difficulty in separating WPCBs with DMSO increases as the size of the WPCBs increases and the temperature of the submerged WPCBs decreases. When the temperature was increased to and maintained at 135 °C for 20 min, the 2−3 cm2 sized WPCBs were separated completely and the LPSRs were removed from the copper foil surface. Rotary decompression evaporation was used to treat used DMSO and resulted in regenerated DMSO and solid residues. The analyses indicated that the solid residues were brominated epoxy resins. A mass balance indicated that DMSO and the WPCB compositions were almost completely recovered. The interaction mechanism of DMSO in WPCB separation is presumed to be that DMSO swells WPCBs and a hydrogen bond interaction between DMSO and brominated epoxy resins occurs. This ability to separate WPCBs is in accordance with the principle of sustainability by decreasing the processing costs of recycling WPCBs.

Figure 8. Infrared spectra of brominated epoxy resin of WPCBs and brominated epoxy resin of WPCBs + DMSO: (a) WPCBs, (b) WPCBs:DMSO (10:1), (c) WPCBs:DMSO (8:1), (d) WPCBs:DMSO (5:1).

■

relatively low amount of interaction was present between the brominated epoxy resins and DMSO. The hydroxyl stretching vibrations band shifted to a lower wavelength with increasing amount of DMSO, and red-shifted 30.69 cm−1 relative to hydrogen bonding interactions between the −OH belonging to the bromine epoxy resins and the O−S belonging to DMSO. Thus, it is presumed that the process of separating WPCBs may be hydrogen bond interactions. DMSO penetrates the WPCBs to dissolve the brominated epoxy resins by the hydrogen bond, which, in turn, makes the WPCBs swell and achieve separation. Because DMSO is an excellent hydrogen bond acceptor, it may result in the formation of three possible hydrogen bonds between the brominated epoxy resin and DMSO. Figure 9a

ASSOCIATED CONTENT

S Supporting Information *

Figure S1, TMA curve of the brominated epoxy resin in WPCBs; Figure S2, Schematic diagram of reactor for treating WPCBs with DMSO; Figure S3, Digital photographs of 1−1.5 cm2 sized WPCBs treated in DMSO at 60 °C; Figure S4, Digital and metallographic photographs of 1−1.5 cm2 sized WPCBs treated in DMSO; Figure S5, Digital photographs of 2−3 cm2 sized WPCBs treated in DMSO at 90 °C; Figure S6, Digital photographs of WPCBs treated in DMSO at 135 °C; Figure S7, Photographs of (a) unused DMSO, (b) used DMSO, (c) regenerated DMSO, and (d) solid residues; Figure S8, Micrographs and EDS of WPCBs (a, a-1) and solid residues (b, b-1). This information is available free of charge via the Internet at http://pubs.acs.org/.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

Figure 9. Potential role of hydrogen bonding between brominated epoxy resin and DMSO.

■

ACKNOWLEDGMENTS We are grateful for support of key personnel in the Shanghai Municipality (S30109), the Opening Project of Zhejiang Provincial Key Laboratory of Solid Waste Treatment and Recycling (SWTR-2012-05), and Shanghai Science and Technology Commission (10dz1205302).

shows the hydrogen bond of H···O···Br. The sulfur pulls electrons toward the oxygen in the DMSO, which accepts the hydrogen from the hydroxyl groups in the brominated epoxy resin. Meanwhile, the bromine in the brominated epoxy resin pulls electrons toward itself. Figure 9b shows the hydrogen bonds of O···S···O···H. The oxygen in the brominated epoxy resin can pull electrons toward the sulfur of the DMSO, which are transferred into the oxygen of DMSO for accepting the hydrogen from the hydroxyl in the brominated epoxy resin. Figure 9c shows that the hydrogen in the methyl group of the DMSO may form hydrogen bonds with bromine and oxygen in brominated epoxy resins. The exact mechanism of DMSO dissolving brominated epoxy resins in WPCBs will be researched in the future. In addition, the strong polarity of DMSO is favorable for dissolving polar brominated epoxy resins, and does not dissolve aliphatic hydrocarbons except for acetylene. LPSRs (acrylate oligomer) are a type of aliphatic hydrocarbon polymer, which is not dissolved by DMSO.25−29 In general, the bare boards of WPCBs, a typical electronic waste, can be separated completely using DMSO, which achieves the aim of the separation of metals and nonmetals.

■

REFERENCES

(1) Zhu, P.; Gu, G. B. Recovery of gold and copper from waste printed circuits. Chin. J. Rare Met. 2002, 26, 214−216. (2) Guo, J. Y.; Guo, J.; Xu, Z. M. Recycling of non-metallic fractions from waste printed circuit boards: A review. J. Hazard. Mater. 2009, 168, 567−590. (3) Nusruth Mohabuth, P.; Hall, N. M. Investigating the use of vertical vibration to recover metal from electrical and electronic waste. Miner. Eng. 2007, 20, 926−932. (4) Gu, W. X.; Huang, C.; Yang, Y. C.; Zhu, P.; Li, C. H. Recovery of Aurum from waste printed circuit boards. Environ. Sci. Technol. (Wuhan, China) 2008, 31, 98−100. (5) Zhu, P.; Fan, Z. Y.; Lin, J.; Liu, Q.; Qian, G. R.; Zhou, M. Enhancement of leaching copper by electro-oxidation from metal powders of waste printed circuit board. J. Hazard. Mater. 2009, 166, 746−750.

2659



Article

(6) Havlik, T.; Orac, D.; Petranikova, M.; Miskufova, A.; Kukurugya, F.; Takacova, Z. Leaching of copper and tin from used printed circuit boards after thermal treatment. J. Hazard. Mater. 2010, 183, 866−873. (7) Kim, E. Y.; Kim, M. S.; Lee, J. C.; Jeong, J. K.; Pandey, B. D. Leaching kinetics of copper from waste printed circuit boards by electro-generated chlorine in HCl solution. Hydrometallurgy 2011, 107, 124−132. (8) Yang, H. Y.; Liu, J. Y.; Yang, J. K. Leaching copper from shredded particles of waste printed circuit boards. J. Hazard. Mater. 2011, 187, 393−400. (9) Kinoshita, T.; Akita, S.; Kobayashi, N. Metal recovery from nonmounted printed wiring boards via hydrometallurgical processing. Hydrometallurgy 2003, 69 (1−3), 73−79. (10) Kim, E. Y.; Kim, M. S.; Lee, J. C.; Yoo, K. K.; Jeong, J. K. Leaching behavior of copper using electro-generated chlorine in hydrochloric acid solution. Hydrometallurgy 2010, 100, 95−102. (11) Oishi, T.; Koyama, K.; Alam, S.; Tanaka, M.; Lee, J. C. Recovery of high purity copper cathode from printed circuit boards using ammoniacal sulfate or chloride solutions. Hydrometallurgy 2007, 89, 82−88. (12) Ma, L. Z.; Li, T. Recovery of epoxy resin in waste printed circuit boards by solvent method. J. Kunming Univ. Sci. Technol., Sci. Technol. 2010, 35 (4), 85−88. (13) Guan, C. J. Study on recycling of non-metal material of different types of waste printed circuit boards. J. Shanghai Second Polytechnic Univ. 2011, 28 (3), 223−229. (14) Chen, X. R.; Zhang, H. Y.; Tian, X. Y. DMSO application development prospects. Chem. Ind. Eng. Prog. 2000, 1, 53−56. (15) Dean, J. A. Lange’s Chemistry Handbook (Chinese Version 13th); 1991; p 918. (16) Åsaöstlund, D. L.; Nordstierna, L.; Holmberg, K.; Nydén, M. Dissolution and Gelation of Cellulose in TBAF/DMSO Solutions: The Roles of Fluoride Ions and Water. Biomacromolecules 2009, 10, 2401−2407. (17) Technical Bulletin Reaction Solvent Dimethyl Sulfoxide; Gaylord Chemical Corporation, 2011; pp 6−16. (18) Zhang, Z. G.; Qian, X. M. Experimental study on thermal stability of DMSO. Chin. Saf. Sci. J. 2006, 16 (9), 100−104. (19) Chen, X. R.; Zhang, H. Y.; Tian, X. Y. Property and application of dimethyl sulfoxide. Liaoning Chem. Ind. 2000, 29 (1), 31−35. (20) Lam, T. T.; Vickery, T.; Tuma, L. Thermal hazards and safe scale-up of reactions containing dimethyl sulfoxide. J. Therm. Anal. Calorim. 2006, 85 (1), 25−30. (21) Hou, X. Y. Epoxy resin of instrumental analysis techniques. Inf. Copper Clad Laminate 2007, 3, 27−35. (22) Guo, Q. J.; Yue, X. H.; Wang, M. H.; Liu, Y. Z. Pyrolysis of scrap printed circuit board plastic particles in a fluidized bed. Powder Technol. 2010, 198, 422−428. (23) Cui, Q.; Li, A.; Gao, N. B. Thermogravimetric analysis and kinetic study on large particles of printed circuit board wastes. Waste Manage. 2009, 29, 2353−2360. (24) Ž igon, M.; Osterdkar, U.; Šebenik, A. NMR investigation of non-brominated and brominated epoxy ester prepolymers. J. Mol. Struct. 1992, 267, 123−128. (25) Baker, T. J.; Schroeder, L. R.; Johnson, D. C. Formation of methylol cellulose and its dissolution in polar aprotic solvents. Presented at the ACS/CSJ Chemical Conference, Honolulu, HI, April, 1979. (26) Li, H.; Shen, X. Y.; Gong, G. L.; Wang, D. Compatibility studies with blends based on hydroxypropylcellulose and polyacrylonitrile. Carbohydr. Polym. 2008, 73, 191−200. (27) Augdahl, E.; Klaeboe,, P. Spectroscopic studies of charge transfer complexes. VIII. Sulphoxides and iodine cyanide. Acta Chem. Scand. 1964, 18, 18−26. (28) Chetri, P.; Dass, N. N.; Sarma, N. S. Development of a catalyst for solution of poly(vinylalcohol) in non-aqueous medium. Chin. J. Polym. Sci. 2008, 26, 399−404.

(29) Yaun, T. Q.; He, J.; Xu, F.; Sun, R. C. A new vision in the research of biomass resources: Complete-lignocellulose-dissolution system. Prog. Chem. 2010, 22, 471−481.

2660


Dissolution of Brominated Epoxy Resins by Dimethyl Sulfoxide To

Recommend Documents