Study On Mechanism Of Fragmentation Of Waste Printed Circuit Board By High Voltage Pulse

Resource utilization of waste printed circuit board （WPCB） is an effective way forrecycling of resources, protecting environment and obtaining considerable economicbenefits. However, the crush is the main reason for restricting resource utilization ofWPCB. On the basis of the selective crushing characteristic of high voltage pulse（HVP）, the fragmental experiments were performed. The metals in WPCB wasseparated from nonmetals effectively and metal enrichment was also realized.Furthermore, the energy consumptions of various theories of comminutionmechanisms of crushing were studied, according to the distribution of size fractions,characteristic of degree of liberation and surface features of crushed products obtainedunder different experiment conditions. The crushed products were characterized by XRay Fluorescence Spectrometry （XRF） and analyzed with SEM/EDS and GC/MS. Inorder to investigate the products and detailed pyrolysis mechanisms for WPCB duringHVP crushing process, we used ReaxFF reactive force field to perform a series ofmolecular dynamics simulations （MDSs） on model compound of. According to theMDSs results, we studied the effects of pyrolysis on the fragmentation of WPCB andliberation of metals from nonmetals.The results show that the yield is prominent for+2mm size fraction but not for-2mm, which is different from the results of mechanical crushing process. On the otherhand, The WPCB can be crushed and the metals in WPCB can be concentratedsimultaneously. The pureness of copper in-2mm size fraction increased with thevoltage and the number of pulses of HVP. Although the yield of-2+0.5mm sizefraction was32.39wt%, in total88.67wt%of copper in WPCB was concentrated inthis fraction with voltage of170kV and600pulse.The average particle size decreased with the increase in energy consumption perweight of WPCB. And the average monomer dissociation degree is decided by thepulse energy of voltage.The voltage influences mainly the monomer dissociationdegree of+2,-2+1.5mm size fraction.The degree of liberation of-1.5mm size fractionfrom crushed products is100%under different experiment conditions. The resultindicate that the-1.5mm size fraction is almost produced after the separation betweencopper foil and epoxy-glass cloth laminate.Broken WPCB by high voltage pulse, energy consumption of fragmentation isproportional to the increment of the square root of the quantity of crushed product particles. The Number equation was established: E=KN（D-1.5-d-1.5）. The result ofnon-line fitting demonstrate that the empirical formula, Number equation, applies toresearch energy consumption of process that crushed WPCB by high voltage pulse. Onthe other hand, the result show that The Chemical Reaction of organics in WPCB hasoccurred under the action of thermal energy, which could also be the main mechanismto crush WPCB.The surface features of solid products were studied with SEM. The results exhibitthat under the high temperature condition caused by HVP, modeling and thermaldecomposition reaction of epoxy has occurred. The compounds, which were producedin thermal decomposition, dissolved in water were analyzed with GC/MS. The resultsshow that few soluble organic matters were generated during HVP crushing process.ReaxFF molecular dynamics simulations （MDSs） results show that both thetemperature and the heating rate strongly affect the decomposition of epoxy resins andcured epoxy resins. both increased in final temperature and heating rate shorten theinitiation time. The results show that the decomposition of epoxy resins modelcompound is initiated by ether linkage cleavage reaction with the lowest activationenergy. We found CH₂O formation to be the first reaction to occur. Other mainsmall-molecule products observed in our simulations include H₂O, CO and H₂. ReaxFFMDSs results show that the cleavages of nitrogen-and oxygen-bridge bonds areinitiation reaction of the decomposition of cured epoxy resins model compound. Theresults show that the cleavages of nitrogen-and oxygen-bridge bonds are initiationreaction. We found that at lower temperatures the primary product is H₂O, whereas athigh temperatures H₂is dominant one and the larger carbon cluster containinggraphene-related structure prefers to formation. Furthermore, other small molecularproducts found include CH₄, HCN, NH₃and CO₂.ReaxFF MDSs provide that the increase of local pressure in discharge channelscaused by the pyrolysis gas during HVP crushing process is also the main factor forliberation between metals and nonmetals. The agreement of these results with availableexperimental observations demonstrates that ReaxFF can provide useful insights intothe complicated bulk thermal decomposition of organic materials under extremeconditions at the atomistic level.