Mechanochemical degradation of brominated flame retardants in waste printed circuit boards by Ball Milling

ACS Sustainable Chem. Eng.

Bai

et al. 2021

Epoxy resin is one of the most popular thermosetting resins and has been widely used in many fields for its excellent performance. However, the stable crosslinking structure of waste epoxy (WEP) caused poor interfacial compatibility, which makes it very difficult to be recycled. This paper reported a novel method for recycling the waste epoxy through partial de-crosslinking and recrosslinking processes via solid-state shear milling (S3M). The waste epoxy was effectively pulverized into an ultrafine powder about 17 μm and the crosslinking density decreased from 3.43 × 10 −3 to 2.69 × 10 −3 mol/mL. The C−N, C−C, and C−O−C bonds in the WEP were broken by the mechanochemical action and many hydroxyl and amino groups were formed on the surface of the WEP powder, which could react with the epoxy and curing agent to form the new crosslinking network. The interface strength between the WEP powder and epoxy (EP) resin matrix was improved greatly and there were no voids that could be observed by scanning electron microscopy (SEM) after the re-crosslinking process. The maximum tensile strength, flexural strength, and non-notched impact strength of WEP/EP composites reached up to 42.2 MPa, 73.2 MPa, and 8.8 kJ/ m 2 , which means 62, 41, and 109% enhancement, respectively. This low-cost, high-efficiency, and environmentally friendly method shows great potential for value-added recycling of thermosetting resins.

Section: Resultsmentioning

confidence: 99%

Novel Application of Mechanochemistry in Waste Epoxy Recycling via Solid-State Shear Milling

Kang

ACS Sustainable Chem. Eng.

Bai

et al. 2021

“…After milling for 60 min, the number of particles >45 μm decreased. After milling for 120 min, particles >45 μm disappeared completely, showing that the degradation of TCPP continued over time (Wang et al, 2020). The smaller the particle size and the larger the specific surface area of ZVI, the stronger the reaction activity.…”

Section: Degradation Of Tcpp Under Different Conditions In the Ps+fe ...mentioning

confidence: 98%

Degradation of tris(1-chloro-2-propanyl) phosphate by the synergistic effect of persulfate and zero-valent iron during a mechanochemical process

Qiao

Qian

et al. 2022

Environ Sci Pollut Res

This study revealed a dual pathway for the degradation of tris (1-chloro-2-propanyl) phosphate (TCPP) by zero-valent iron (ZVI) and persulfate as co-milling agents in a mechanochemical (MC) process. Persulfate was activated with ZVI to degrade TCPP in a planetary ball mill. After milling for 2 h, 96.5% of the TCPP was degraded with the release of 63.16, 50.39 and 42.01% of the Cl − , SO4 2− and PO4 3− , respectively. In the first degradation pathway, persulfate was activated with ZVI to produce hydroxyl (•OH) radicals and ZVI is oxidized to Fe(Ⅱ) and Fe(Ⅲ). A substitution reaction occurred as a result of the attack of •OH on the P-O-C bonds, leading to the successive breakage of the three P-O-C bonds in TCPP to produce PO4 3− . In the second pathway, a C-Cl bond in part of the TCPP molecule was oxidized by SO4• − to carbonyl and carboxyl groups. The P-O-C bonds continued to react with •OH to produce PO4 3− . Finally, the intermediate organochloride products were further reductively dechlorinated by ZVI.However, the synergistic effect of the oxidation (•OH and SO4• − ) and the reduction reaction (ZVI) did not completely degrade TCPP to CO2, resulting in a low mineralization rate (35.87%). Moreover, the intermediate products still showed the toxicities in LD50 and developmental toxicant. In addition, the method was applied for the degradation of TCPP in soil, and high degradations (>83.83%) were achieved in different types of soils.

“…After milling for 60 min, the number of particles >45 μm decreased. After milling for 120 min, particles >45 μm disappeared completely, showing that the degradation of TCPP 256 continued over time (Wang et al, 2020). The smaller the particle size and the larger the specific surface area of ZVI, the stronger the reaction activity.…”

Section: Degradation Of Tcpp Under Different Conditions In the Ps+fe 0 +Mc Treatment Processmentioning

confidence: 98%

Degradation of Tris(1-chloro-2-propanyl) Phosphate by the Synergistic Effect of Persulfate and Zero-valent Iron During a Mechanochemical Process

Qiao

Qian

et al. 2021

Preprint

This study revealed a dual pathway for the degradation of tris (1-chloro-2-propanyl) phosphate (TCPP) by zero-valent iron (ZVI) and persulfate as co-milling agents in a mechanochemical (MC) process. Persulfate was activated with ZVI to degrade TCPP in a planetary ball mill. After milling for 2 h, 96.5% of the TCPP was degraded with the release of 63.16, 50.39 and 42.01% of the Cl−, SO42− and PO43−, respectively. In the first degradation pathway, persulfate was activated with ZVI to produce hydroxyl (·OH) radicals and ZVI is oxidized to Fe(Ⅱ) and Fe(Ⅲ). A substitution reaction occurred as a result of the attack of ·OH on the P–O–C bonds, leading to the successive breakage of the three P–O–C bonds in TCPP to produce PO43−. In the second pathway, a C–Cl bond in part of the TCPP molecule was oxidized by SO4·− to carbonyl and carboxyl groups. The P–O–C bonds continued to react with ·OH to produce PO43−. Finally, the intermediate organochloride products were further reductively dechlorinated by ZVI. However, the synergistic effect of the oxidation (·OH and SO4·−) and the reduction reaction (ZVI) did not completely degrade TCPP to CO2, resulting in a low mineralization rate (35.87%). Moreover, the intermediate products still showed the toxicities in LD50 and developmental toxicant. In addition, the method was applied for the degradation of TCPP in soil, and high degradations (>83.83%) were achieved in different types of soils.Speciality: Phosphorus flame retardants; Advanced oxidation process; Ball milling