Brominated Epoxy Resin Research Articles

High-efficiency co-liquefaction of brominated epoxy resin and low rank coal in supercritical water: Waste recycling and products upgrading

With the acceleration of upgrading electronic information products, a large amount of electronic waste was generated. Brominated epoxy resins (BERs) are the main nonmetallic components of e-waste. The recycling of BERs has attracted people's attention due to their potential environmental risks. Low rank coal is difficult to efficiently utilize due to its high moisture content, oxygen content and low calorific value. This study developed an efficient co-liquefaction strategy for BERs and low rank coal by supercritical water (SCW) process. Under optimized conditions (temperature of 425 °C, reaction time of 60 min, solid-to-liquid ratio of 1:10 g/mL, and BERs-coal mass ratio of 1:4 g/g), the total conversion efficiency of co-liquefaction reached 56.76 %. When the temperature was 325–425 °C, there was a positive synergistic effect between BERs and low rank coal co-liquefaction, and the highest synergy efficiency of 11.13 % was reached at 400 °C. The introduction of BERs could significantly reduce the oxygenated compounds and the heteroatomic compounds in the liquefied oil products, improving the quality of oil products. The co-liquefaction promoted the production of phenolic chemicals and inhibited the cross-linking reaction of the decomposition products from low rank coal, and realized the synchronous conversion of BERs and low rank coal. The C-Br bond in the residue was significantly weakened after co-liquefaction. The oil products did not contain brominated organic compounds, also demonstrating the potential of the co-liquefaction process for debromination of BERs.

Treatment of brominated epoxy resin waste in subcritical dimethylformamide wastewater: Upcycling of brominated epoxy resin and dimethylformamide degradation

The debromination and upcycling of brominated epoxy resin (BER) waste is important for the e-waste treatment, while the degradation and removal of N, N-dimethylformamide (DMF) is the critical step for the DMF wastewater treatment. In this study, a co-treatment strategy was proposed for the BER waste and DMF wastewater by the subcritical water process. The co-treatment was carried out using subcritical DMF wastewater (SDW) as the reaction medium. The results showed a significantly synergistic effect between the BER conversion and DMF degradation in the SDW process. The optimal reaction conditions were as follows: reaction temperature of 300 °C, solid-to-liquid ratio of 1:15 g/mL, DMF wastewater of 30000 mg/L and reaction time of 60 min. Under the optimal reaction conditions, the debromination ratio of the BER was 98.57 %, the degradation ratio of the DMF reached 99.59 %, and phenolic substances with a purity of 86.61 % were recovered. The formation of HBr from the debromination of the BER was the most significant factor affecting the pH of the system, which had a noticeable impact on the degradation of the DMF. The main degradation products of the DMF were dimethylamine (DMA), methylamine (MA), NH3, NH4+, and CO2. The products degraded from the DMF could significantly promote the debromination and conversion of the BER. Life cycle assessment (LCA) analysis showed that the SDW process had low CO2 emissions. It is believed that the SDW process proposed in this study is an efficient technology for the synergistic treatment of the BER waste and DMF wastewater.

Selective upcycling of brominated epoxy resin by subcritical water ammonia process with waste copper-based catalyst: Production of high purity methyl pyrimidine/phenols and copper recovery

Tetrabromobisphenol A epoxy resin (TBBPAER) is the main non-metallic component of electronic waste. The scale of electronic waste production and the accompanying TBBPAER waste disposal problems represent a great opportunity for chemical upcycling. But the chemical upcycling of TBBPAER faces great challenges due to its high bromine content and thermally stability. In this study, a subcritical water ammonia (SWA) process combined with waste copper-based catalyst (WCC) selectively converted TBBPAER in high yields (63.46 % at 300°C for 15 min and 73.66 % for 60 min) to low molecular-weight liquid products including high value-added methyl pyrimidine and phenols. The electron transfer among multivalent copper species contained in the WCC promoted the production of free radicals OH, O2−, NH2, and :NH, which resulted in the efficient conversion of TBBPAER and a 99.29 % of debromination ratio. The molecular chain of TBBPAER was snipped by OH and NH2 to produce tetrabromobisphenol A groups (TAG) and ternary carbon groups (TCG). The further degradation of TAG resulted in the producing of phenol chemicals with a purity of 91.8 % (GC peak area%). The further cyclization of TCG induced by :NH produced methyl pyrimidine with a purity of 91.9 % (GC peak area%). The formation of copper ammonia complex led to the leaching/recovery of 86.6 % of copper from the WCC. The SWA-WCC approach demonstrated how TBBPAER waste could be a viable feedstock for the producing of high value-added methyl pyrimidine and phenol chemicals. This study provided a novel sustainable strategy for synchronous treatment/upcycling of the two different wastes of TBBPAER and WCC. The leaching toxicity test of Cu and Zn for the solid residue after the co-treatment showed that their leaching concentrations were much lower than the hazardous waste standard.

Copper leaching from ultrasonically treated milled waste printed circuit boards: investigation of parameters optimization and kinetics.

Waste printed circuit boards (WPCBs) encompass abundant metals (gold, silver, and copper), along with other harmful materials including brominated epoxy resins, plastics, and heavy metals (lead, mercury, and cadmium). Direct burning and landfilling of WPCBs may cause severe health issues and impair the environment. Therefore, sustainable treatment of WPCBs is necessary to recover valuable metals and remove hazardous materials before disposal. The present work investigates the separation of copper-rich metallic fractions from the WPCBs by the combination of hammer milling and ultrasonic irradiation. Initially, discarded mobile phone PCBs are pre-processed and shortened into 1 × 1 cm2. Downscaled WPCBs are fed into the hammer mill to obtain the fine ground powder. The Powdered WPCBs are further processed through ultrasonic treatment to acquire metal-rich fraction. XRD, SEM-EDS, and ICP/AAS analysis revealed that the current technique can efficiently separate the metal-rich fraction without using toxic solvents. Results show the enhancement of copper fraction from 42.73 to 87 wt. % after ultrasonic treatment of WPCBs ground powder. Further, nitric acid leaching has been implemented to metal-rich fractions, and the parameters have been optimized for copper leaching with the assistance of response surface methodology (RSM) of the design of experiments (DOE). Quantitative dissolution (98.96%) of copper occurred using 3.5M nitric acid within 3h at 30°C with 50 GPL pulp density and 500rpm agitation speed. Finally, the kinetics of the leaching process were studied to conform the kinetics model. Moreover, the activation energy for diffusion (19.075kJ/mole) and reaction kinetics model (13.29kJ/mole) has also been calculated. The low energy consumption due to room temperature pre-treatment and effective leaching ensures the industrial feasibility of the proposed process.

Preliminary strategy and product analysis of microwave pyrolysis of waste printed circuit board

AbstractIn this study, microwave pyrolysis of waste printed circuit boards (WPCBs) was carried out in an inert atmosphere, and the effects of pyrolysis temperature and nitrogen flow rate on the yield and composition of pyrolysis products were investigated. With the increase of pyrolysis temperature, the yield of liquid product increases gradually, and the yield of solid product decreases gradually. At 600°C, the yield of each phase tends to be stable. When the temperature continues to rise, the content of H2 and CO decreases, and the content of C6 ~ C9 in the liquid product decreases. Microwave heating promotes the pyrolysis of brominated epoxy resin, which helps to improve the recovery rate of valuable substances and reduce the environmental impact of waste treatment. This study demonstrates that the microwave pyrolysis of WPCBs in nitrogen atmosphere has great potential in the green recovery process.

A novel subcritical water synergistic co-treatment of brominated epoxy resin and copper-based spent catalysts: debromination, phenol production, and copper recovery

In this study, a high-efficiency co-treatment strategy for brominated epoxy resin (BER) and copper-based spent catalyst (CBSC) was developed by using subcritical water (SubCW) process. Multivalent species of copper released from CBSC could accelerate the electron transfer of the SubCW system and efficiently catalyze radical reactions to promote the debromination and decomposition of BER, and had an effect on the capture and binding of bromine species. Meanwhile, the formation of HBr by the BER debromination resulted in a decrease in the system pH and markedly enhanced the leaching/recovery of Cu from CBSC. The optimal conditions of the SubCW co-treatment process were as follows: reaction temperature of 350 °C, solid-to-liquid ratio of 1:30 g/mL, BER-to-CBSC mass ratio of 10:1 g/g, and reaction time of 60 min. Under the optimal conditions, 97.12 % of the Br could be removed from BER by the SubCW co-treatment process and a high-purity phenol (64.09 %) could be obtained in the oil phase product, and 86.44 % of Cu in the CBSC could be leached and recovered. The introduction of CBSC significantly changed the decomposition path of BER. Compared to the SubCW process without CBSC, bromine-free oils products could be obtained by the co-treatment process of BER and CBSC at low-temperature. This study provided a novel understanding of resource conversion mechanism of BER and CBSC in subcritical water medium via the synergistic effect between the two different waste streams to improve treatment efficiency and synchronously recover high-value products.

Mechanical and Thermal Analysis of Duroplastic Matrix Composites over a Range of Temperatures.

It is commonly acknowledged that polymer composites in service are often subjected to not only intricate mechanical loads but also harsh environmental conditions. The mechanical and thermal properties of five particular composites are explored here. The composites are composed of laminates of glass cloth type "E" sheet infilled with a duroplastic matrix. This is a thermoset polymer-epoxy resin with different molecular weights. The composites were fabricated by IZOERG company, which is based in Poland. The final articles were 1.5 mm thick by 60 cm long and 30 cm wide, with the glass layers arranged parallel to the thickness. Young's modulus and tensile strength were measured at room temperature. Using the thermal analysis of dynamic mechanical properties (DMTA), the values of the storage modulus and the loss modulus were determined, and the damping factor was used to determine the glass transition temperature (Tg). It was revealed that the nature of changes in the storage modulus, loss modulus, and damping factor of composite materials depends on the type of epoxy resin used. Thermal expansion is a crucial parameter when choosing a material for application in cryogenic conditions. Thanks to the TMA method, thermal expansion coefficients for composite materials were determined. The results show that the highest value of the coefficient of thermal expansion leads the laminate EP_4_2 based on brominated epoxy resin cured with novolac P. Duroplastic composites were characterized at cryogenic temperatures, and the results are interesting for developing cryogenic applications, including electric motors, generators, magnets, and other devices.

New insights into brominated epoxy resin type WPCBs pyrolysis mechanisms: Integrated experimental and DFT simulation studies

Pyrolysis is a recycling technology for waste circuit boards (WPCBs) with a wide range of applications. In this research, the brominated epoxy resin (BER) type WPCBs were taken as the research object, and the optimal pyrolysis process parameters were determined. Combined with experiments and density functional theory (DFT) calculations, the pyrolysis gaseous generation pattern and product distribution of BER type WPCBs were analyzed, and the generation mechanism of phenol, bromide and other pyrolysis products was investigated in depth. The results of the study showed that the pyrolysis rate of WPCBs exceeded 95 % under optimal reaction conditions. In the initial phase of the pyrolysis of WPCBs, the BER's CO bonds and a portion of Ph-Br bonds will be broken, leading to the production of intermediates such propylene oxide, bisphenol A, isopropyl alcohol, tetrabromobisphenol A and HBr. Among them, propylene oxide can generate ethylene oxide through free radical reaction. In the second stage, intermediates such as bisphenol A undergo homolytic cleavage and radical addition to form phenols, bromides, alcohols, ketones and other pyrolysis products.

Negative-carbon recycling of copper from waste as secondary resources using deep eutectic solvents

Copper plays a crucial role in the low-carbon transformation of global communities with prevalent use of electric vehicles. This study proposed an environmentally friendly approach that utilizes a deep eutectic solvent (DES), choline chloride-ethylene glycol (ChCl-EG), as green solvent for the selective extraction of copper from scrap materials. With hydrogen peroxide as an oxidizing agent, the copper species from the printed circuit boards (PCBs) scraps were efficiently leached by the DES through oxidation-complexation reactions (conditions: 25 min, 20 °C, and 5 wt% H2O2). Molecular dynamics and density functional theory were performed to simulate the intricate cascade of interactions between copper species and hydrogen bond donors/acceptors of DES, providing insights into the mechanistic processes involved. Copper was selectively recovered from the DES leachate containing impurities (e.g., Pb2+, Sn2+, and Al3+) through electrodeposition via a diffusion-controlled reaction under a constant potential mode. A comprehensive life cycle assessment of the process demonstrated that the utilisation of DES in the extraction of copper from waste PCBs could result in significant reduction in carbon dioxide emissions (−93.6 kg CO2 eq of 1000 kg waste PCBs), thus mitigating the carbon footprint of global copper use through the proposed solvometallurgical recycling process of secondary resources.

Quantum chemical study on the catalytic debromination mechanism of brominated epoxy resins

The study employed Density Functional Theory (DFT) to investigate the catalytic debromination mechanism of brominated epoxy resins (BERs) by iron (Fe) and copper (Cu) catalysts. By introducing electric field (EF), intramolecular electron transfer and polarization effects on BERs debromination were explored and experimentally validated. Results indicated that the bond dissociation energy (BDE) of the C-Br bond was 312.27 kJ/mol without catalysis, while with Fe, Cu, and EF, it was 114.47 kJ/mol, 94.85 kJ/mol, and 292.59 kJ/mol, respectively, enhancing reactivity. EF parallel to the C-Br bond and oriented toward the C atom, altered electrostatic potential and dipole moment around C-Br bond, leading to 68.60% and 50.19% increment in electronic contribution difference and molecule polarity, respectively, thereby reducing the C-Br BDE. Fe and Cu facilitated electron transfers with BERs, inducing reactions between their negative electrostatic potentials and Br's positive potential, changing electron sharing, resulting in 19.87% and 12.11% increase in polarity, respectively, and further BDE reduction. Structural modifications by the EF and catalysts also intensified van der Waals forces with bromine atoms and decreased spatial hindrance, collectively making C-Br bond breakage easier. Experiments revealed the EF enhanced BERs' debromination efficiency but hindered Fe/Cu's catalysis at lower temperatures.

Co-pyrolytic interactions and products of brominated epoxy resin and polyethylene terephthalate: TG-FTIR analysis and machine learning prediction

Pyrolysis is an effective approach for organic waste utilization, and the co-pyrolysis of multiple materials holds potential for both environmental and economic benefits. Brominated epoxy resin (BER) and polyethylene terephthalate (PET) are widely used organic materials in modern society, and the productions of their corresponding wastes are increasing annually. However, limited research has been conducted on the co-pyrolysis of BER and PET. In this study, mixtures of BER and PET were prepared in various proportions, and thermogravimetry (TG) and thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) analyses were employed to investigate the reaction characteristics, volatile product compositions, and evolution during co-pyrolysis. Synergistic effects were observed at lower temperatures in the major reaction stage for mixtures with PET content below 40%, while inhibitory effects were noted at higher temperatures. For mixtures with PET content over 40%, the antagonistic effect was more prominent. The main volatile products during co-pyrolysis were identified as CO2, benzoic acid, and alcohols, and their evolutions exhibited complex changes due to interactions. In addition, machine learning algorithms successfully predicted real-time volatile emissions, with the random forest model proving accurate. This study enhanced understanding of organics interactions during thermal treatment and would contribute to the reduction of environmental pollution.

Effects of Additives on the Mechanical and Fire Resistance Properties of Pultruded Composites.

Under high temperatures, fiber-reinforced polymers are destroyed, releasing heat, smoke, and harmful volatile substances. Therefore, composite structural elements must have sufficient fire resistance to meet the requirements established by building codes and regulations. Fire resistance of composite materials can be improved by using mineral fillers as flame-retardant additives in resin compositions. This article analyzes the effect of fire-retardant additives on mechanical properties and fire behavior of pultruded composite profiles. Five resin mixtures based on vinyl ester epoxy and on brominated vinyl ester epoxy modified with alumina trihydrate and triphenyl phosphate were prepared for pultrusion of strip profiles of 150 mm × 3.5 mm. A series of tests have been conducted to determine mechanical properties (tensile, flexural, compression, and interlaminar shear) and fire behavior (ignitability, flammability, combustibility, toxicity, smoke generation, and flame spread) of composites. It was found that additives impair mechanical properties of materials, as they the take place of reinforcing fibers and reduce the volume fraction of reinforcing fibers. Profiles based on non-brominated vinyl ester epoxy have higher tensile, compressive, and flexural properties than those based on brominated vinyl ester epoxy by 7%, 30%, and 36%, respectively. Profiles based on non-brominated epoxy resin emit less smoke compared to those based on brominated epoxy resin. Brominated epoxy-based profiles have a flue gas temperature which is seven times lower compared to those based on the non-brominated epoxy. Mineral fillers retard the spread of flame over the composite material surface by as much as 4 times and reduce smoke generation by 30%.

Mechanical analysis of multilayer composite materials with duroplastic matrix after exposure to low temperatures

Cryogenic engineering is gaining more and more interest in various industry sectors, which leads to an intensive search for effective solutions. The article presents the findings of mechanical testing conducted on glass-epoxy laminates at room temperature and after long-term contact with liquid nitrogen.To compare the impact properties and flexural strength, the samples were tested under cryogenic and room conditions, and then the fracture locations were identified using the Leica DVM6 microscope. The study brings value to the emerging field of cryogenic engineering by providing valuable information on the mechanical properties of glass-epoxy composites under cryogenic conditions.It has been found out that immersing the glass-epoxy composites into the Dewar had minimal influence on impact and flexural strength properties. The most noticeable changes were observed in the case of the EP_4_2 composite. The material consists of a solution of brominated epoxy resin in an organic solvent. It is used to produce laminates in electrical engineering and printed circuits in electronics, where it should exhibit excellent impact properties.One of the prospective research directions is a thorough analysis of the mechanical properties of the developed composite materials during cryogenic cycles.The study aims to determine the effect of different compositions of glass fabric-reinforced resin with a weight of 205 g/m2 on the mechanical properties of the developed composite materials at both room temperature and after long-term exposure to liquid nitrogen. Those investigations serve as surveillance for developing of new material solutions directed towards cryogenic applications and are essential for subsequent stages of research.

Products and bromine migration characteristics of non-metallic components of waste printed circuit boards pyrolysis in a fluidized bed pyrolyzer

This study investigated non-metallic components (NMCs) of waste printed circuit boards (WPCBs) pyrolysis in a fluidized bed pyrolyzer (FBP). The pyrolysis temperature was set at 350–750 °C. K2CO3, ZnO, CaO and Fe2O3 were added at the temperature of 650 °C to stabilize Br. The characterization of pyrolysis char, pyrolysis oil and pyrolysis gas were analyzed. Migration and transformation of Br in NMCs pyrolysis was investigate. Brominated epoxy resin cracking and Br fixation mechanism were proposed. Pyrolysis oil yield reached the highest at 650 °C. Phenols were the main components of pyrolysis oil, it increased with temperature and reached the highest at 650 °C. The proportion of esters and ketones were 2–4% and 2–3%, respectively. The secondary cracking during pyrolysis correlated the secondary release of CO2, CO, CH4 and H2. Br mainly distributed in pyrolysis oil in the form of HBr and reached the maximum at 550 °C. Organic bromides was mainly bromophenols in pyrolysis oil. Br distributed in pyrolysis char was mainly inorganic bromines in the form of brominated salts. Bromines in pyrolysis gas were mainly CH3Br, C2H5Br, C3H7Br, C3H5Br. K2CO3, CaO effectively promoted Br fixation through neutralization reaction, direct elimination and dissociation adsorption. ZnO, Fe2O3 promoted bromides cracking.

Mechanistic insights into catalysis of in-situ iron on pyrolysis of waste printed circuit boards: Comparative study of kinetics, products, and reaction mechanism

Pyrolysis is a potential recovery method for waste printed circuit boards (WPCBs), but the organic brominated products are toxic and hazardous. Iron has been used as a catalyst for debromination from pyrolysis oil, but the effects of in-situ iron on WPCBs pyrolysis is still not well understood. Herein, the pyrolysis mechanism for laminates of PCBs in the absence and presence of iron was studied via analyzing pyrolysis characteristics, kinetics, and products. According to the thermogravimetry experiments, pyrolysis of all samples could be divided into four stages, and iron accelerated the pyrolysis reaction by decreasing the activation energy as calculated using the Starink method. Volatiles released during the heating process were continuously determined by TG-FTIR-MS, and products generated at different pyrolysis temperatures were collected and characterized. The obtained results exhibited that iron promoted the generation of gaseous products and facilitated the conversion of organic bromides to inorganic bromides. Therefore, retaining iron was beneficial to energy saving and environmental protection for WPCBs pyrolysis. In addition, the decomposition mechanisms of brominated epoxy resin with and without iron were proposed. This work would contribute to the improvement and application of WPCBs pyrolysis technology.

Microwave-assisted organic swelling promotes fast and efficient delamination of waste printed circuit boards

A large amount of waste printed circuit boards (WPCBs) that contain valuable metals, namely gold and copper, are produced annually. WPCBs are constituted by a multi-layer structure reinforced by a brominated epoxy resin (BER), which is very difficult to separate into the metallic and non-metallic components. The main aim of this work was to evaluate the ability of microwave for assisting in the delamination of WPCBs by organic swelling of the BER. Additionally, its performance was compared with other strategies (thermostatic and ultrasonic baths) previously described in the literature. Firstly, a library of solvents [dimethyl formamide (DMF), dimethyl acetamide (DMAc), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), cyclohexanone (CH), γ-butyrolactone (GBL), tetrahydrofurfuryl alcohol (TFA) and dimethyl malonate (DM)] was selected based on the calculation of Hansen solubility parameters plus others exclusion parameters and their performance to detach all components of WPCBs (25 mm2) was tested by microwave (200 °C for 10 min), thermostatic (153 °C for 10 min) and ultrasonic (60 °C for 25 h) baths. Microwave showed to be the most efficient approach and the delamination order for WPCBs was: NMP > DMSO >DMF > DMAc. Subsequent optimization of key parameters (dimensions of WPCBs and reaction time) were obtained: dimensions of 225 mm2 using NMP (solid/liquid ratio of 300 g/L) at 200 °C with 2 cycles of 10 min. In conclusion, microwave-assisted swelling revealed to be more efficient and faster process to delaminate WPCBs into metallic and non-metallic components, which are important advantages when envisaging a future industrial waste management implementation.

Dissolution and separation of non-metallic powder from printed circuit boards by using chloride solvent

Non-metallic components (NMC) in waste printed circuit boards (WPCBs) are made of the thermosetting epoxy resin and glass fiber, which has been a research concern in the waste recycling area. The recycling of thermosetting epoxy resin is a serious challenge due to their permanent cross-linked structure. An efficient approach to chemical recycling of epoxy resin for resource reutilization was developed in this research. ZnCl2/CH3COOH aqueous solution was selected as catalysts system to decompose epoxy resin under a mild reaction condition. The influence of reaction parameters such as reaction temperature, time, liquid-solid ratio and ZnCl2 amount on the decomposition efficiency of epoxy resin and reaction mechanism were investigated. The physical and chemical properties of NMC, reaction solvent and decomposed products were analyzed using scanning electron microscope(SEM), Fourier transform infrared spectroscopy (FT-IR) and Gas chromatography–mass spectrometry (GC–MS). Results showed that up to 81.85% of epoxy resin could be dissolved by using a temperature of 190 °C during 8 h with a mixture of acetic acid (15 wt%): ZnCl2 (5 g) 20 mL/g. Incompletely coordinated zinc ions enables the cleavage of CN, CBr and CO bonds in the thermosetting brominated epoxy resin, which was mainly converted to phenol, 2-Bromophenol and 2, 4-Dibromophenol with high resource value. And the functional groups of ethyl acetate and acetic acid maintained chemical structure before and after reaction. This research provided a practical approach to the dissolution and reutilization of NMC in WPCBs.

Dissolution of brominated epoxy resin for environment friendly recovery of copper as cupric oxide nanoparticles from waste printed circuit boards using ammonium chloride roasting

This work focuses on development of an environment benign approach for separation of brominated epoxy resin (BER) and recovery of copper (Cu) as copper oxide (CuO) from end-of-life waste printed circuit boards (PCBs). The typical Cu concentration in PCBs varies in the range of 60 kg/t – 270 kg/t of Cu, which is much higher than its respective mineral ores. In the present work, dimethylformamide (DMF) was used for dissolution of BER followed by roasting with ammonium chloride (NH4Cl) for recovery of Cu. Separation of BER provides better metallic surface exposer and mitigates the possibility of formation of toxic polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) during the roasting process. More than 97% of BER was separated from the PCBs using DMF as solvent at 140 °C. The investigation revealed that at reaction conditions, dry HCl vapour formed due to decomposition of NH4Cl, reacts with Cu in presence of air to form CuCl2. The solid residue obtained after roasting was subsequently treated with water for extraction of CuCl2. More than 93% Cu was extracted when the delaminate PCBs (DPCBs) was roasted at optimum conditions of temperature: 275 °C, NH4Cl dose: 300%, and time: 180 min. From the leached solution, Cu was precipitated using ammonia solution as precipitating agent, which subsequently calcined at 500 °C to obtain 98% pure CuO nanoparticles (NPs).

Phosphorus and bromine modified epoxy resin with enhanced cryogenic mechanical properties and liquid oxygen compatibility simultaneously

Herein, epoxy resins for composite liquid oxygen (LOX) fuel tanks are modified with phosphorous flame retardant (DOPO) and brominated epoxy resin (EX48). With the incorporation of DOPO and EX48, the processing properties requirements for the hot-melt prepreg are contented with the significantly enhanced viscosity of the modified epoxy resin. At the same time, the tensile performance, flexural performance and fracture toughness of epoxy resin at room temperature and 90 K are improved with the introduction of DOPO and EX48. In addition, the epoxy resin of EP/P7.7/Br40 offers a highest limited oxygen index of 33.5% and a lowest LOX impact sensitivity of 5% with the eliminated LOX incompatible reactions including explosion and combustion. Consideration of the excellent cryogenic mechanical properties and LOX compatibility, combined with ideal viscosity for hot-melt prepreg preparation, the epoxy resin modified with DOPO and EX48 simultaneously is attractive as the polymer matrix for composite LOX fuel tanks.

New insights into the debromination mechanism of non-metallic fractions of waste printed circuit boards via alkaline-enhanced subcritical water route

The debromination of brominated epoxy resins (BERs) from waste printed circuit boards (WPCBs) is of great challenge due to its high structural stability. An enhanced subcritical water (SCW) process with alkaline additive is proposed for efficient debromination of BERs, and the mechanism of alkaline additive on bromine removal has been investigated. More than 95.11% of bromine is removed under the optimal conditions. Both enhanced fiberglass destruction and BERs degradation contribute to the efficient debromination process. Structure of Ca−Al, Si−O, and Al−O bonds in fiberglass is destroyed by alkaline corrosion, releasing BERs into the solution and facilitating the debromination process. Meanwhile, phenol, 2-bromophenol and catechol are the main products of BERs degradation. Nucleophilic substitution reaction by the bimolecular process dominantly contribute to the debromination. The energy barrier of the bimolecular process is only 15.9 kcal/mol, which is much lower than that of the direct dissociation energy of C−Br bond (168.3 kcal/mol). Ion association of KOH is weaker than that of NaOH in the alkaline-enhanced SCW process due to the difference of cation radius, proved by ab initio molecular dynamics simulation. An efficient approach for WPCBs debromination under mild conditions has been proposed.