Research On The Layered Separation Of Waste Printed Circuit Board By Dimethyl Sulfoxide At Low Temperature And Atmospheric Pressure

As the United Nations Environment Program (UNEP), the total amount of wasteprinted circuit boards (WPCBs) heaps up to million tons yearly, with a5-10%annualincrease predicted. Because WPCBs are hazardous but resource-rich, recycling hasbeen the promising alternative treatment in the replacement of incineration andlandfill. In this study, layered separation of FR-4typed WPCBs by dimethyl sulfoxide(DMSO) was carried out at low temperature and atmospheric pressure. It offers anovel method for recycling valuable materials singly and preventing environmentalpollution. Moreover, analysis about swelling process, solvation ability and molecularinteraction was put out to interpret this innovative technology.WPCBs are heterogeneous mixture with cured brominated epoxy resins, metals,and glass fibers, etc. Their multilayer construction is laminated by press and heat andadhered by cured brominated epoxy resins, which leads to the bottleneck to recyclethe individual components from WPCBs directly. When using DMSO to delaminateWPCBs, the optimal parameters are as follows: soaking temperature of130oC,WPCBs/DMSO mass ratio of1:5, size of WPCBs with1×1cm. No decompositionof DMSO or brominated epoxy resins was detected during the process by ionchromatography and GC-MS analysis. Meanwhile, recycling of DMSO can beachieved by filtered and rotary evaporated. Through flotation and coarse crushing, theseparated delaminated mixture was reused as industrial raw materials or adsorbents.Based on the analysis of swelling curve, it can be confirmed that the delamination ofWPCBs is caused by the swelling from interlayer resins, which is in line with Schottsecondary swelling kinetics model. Besides, the soaking temperature and solventpolarity are the key parameters to delaminate WPCBs.On the other hand, equilibrium swelling method was applied to calculate thethree-dimensional solubility parameters of WPCBs and synthetic brominated epoxyresins, which was validated by group estimation method and multicomponent liquidmixtures. This method has made it possible to predict the swelling of WPCBs andselect the suitable solvent or mixed solvents for recycling of various typed WPCBs. In combination of the swelling curve, the curve of dissolved bisphenol A resin,the red shift of-OH by FTIR, and the reduction of the glass transition temperature (Tg)and the activation energies, the swelling process of cured resins can be divided intotwo parts:1) with the temperature rising to Tg, the movement of cross-linking chainsare enhanced, leading to the expansion of free space. Then, physical cross-linking isstrengthened between DMSO and cross-linking chains of cured resins throughhydrogen bonds, which destructs the original network structure, and thus makesinterlayer adhesion weakened.2) Smaller cross-linking segments and gel fraction areinfiltrated into DMSO in form of entire chains, contributing to the hydrogen bondsand solvation ability. Then, the structural stability of the resin network and theinterlayer adhesive strength are weakened further, leading to the delamination ofWPCBs.