A structural chemistry look at composites recycling

Navarro, Carlos A.; Giffin, Cassondra R.; Zhang, Boyang; Yu, Zehan; Nutt, Steven; Williams, Travis J.

doi:10.1039/d0mh01085e

Cited by 61 publications

(62 citation statements)

References 43 publications

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“…It might be attributed to the strong mechanochemical action in the S3M process, which destroyed the ether bond and other chemical bonds of the WEP, forming numerous functional groups such as methylene, amino, and hydroxyl groups. The increase in carbonyl content was attributed to the oxidation of part of the methylene and hydroxyl groups in the WEP under strong mechanochemical action and heat (generated during equipment operation) to form carbonyl groups . EDX test showed that the oxygen content of the WEP powder increased significantly after the S3M treatment (Table S1).…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, weak bonds in the WEP would be destroyed first, such as C 6 H 5 O-CH 2 and C–N bonds, the bond strengths of which were 268 and 305 kJ/mol, respectively. , Some stronger bonds like C–C bond with a bond strength of 332 kJ/mol would be broken with further milling, destroying the crosslinking structure of the WEP. After these bonds were broken, a large number of free radicals would be generated, and those free radicals could react with water and oxygen in the air or other radicals to produce some new alkanes, alcohols, and other substances . As a result, the number of groups such as hydroxyl, amino, methyl, and methylene increased significantly.…”

Section: Resultsmentioning

confidence: 99%

“…However, the chemical recovery process is complicated and high cost. , Even though numerous lab-scale experiments have been carried out, only a few studies have reached industrial or semi-industrial scale . Mechanical recycling mainly uses impact, shearing, compressing, and other mechanical forces to pulverize the waste epoxy, and pulverized epoxy resins typically are reused as fillers. − Mechanical recycling is an industrial way that is simple in process, and no harmful substances are produced without changing their molecular structure in the recycling process . However, traditional mechanical recycling is only a simple crushing of waste epoxy, and is difficult to destroy the crosslinking structure of the epoxy effectively, which leads to poor interfacial strength on the surface of the epoxy powder and poor mechanical strength of final composites. , The recycled material can only be used as inorganic filler with low value.…”

Section: Introductionmentioning

confidence: 99%

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

Kang

Yang

Bai

et al. 2021

ACS Sustainable Chem. Eng.

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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.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Kang

Yang

Bai

et al. 2021

ACS Sustainable Chem. Eng.

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“…The crucial drawback of composites is that they are challenging to recycle, especially carbon fiber-reinforced composites due to their hardness and chemical stability [ 6 ]. However, the significant commercial value of carbon fiber-reinforced composites recycling lies in recovering long high modulus fibers with a high intrinsic value for their reuse in high-grade applications.…”

Section: Introductionmentioning

confidence: 99%

Recycling of Carbon Fiber-Reinforced Composites—Difficulties and Future Perspectives

Borjan

Knez

2021

Materials

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Carbon fiber-reinforced composites present an exciting combination of properties and offer clear advantages that make them a perfect replacement for a spread of materials. Consequently, in recent years, their production has dramatically increased as well as the quantity of waste materials. As future legislations are likely to prevent the use of landfills and incineration to dispose of composite waste, alternative solutions such as recycling are considered as one of the urgent problems to be settled. This study presents the leading technologies for recycling carbon fiber-reinforced composites, focusing on chemical recycling using sub- and supercritical fluids. These new reaction media have been demonstrated to be more manageable and efficient in recovering clean fibers with good mechanical properties. The conventional technologies of carbon fibers recycling have also been reviewed and described with both advantages and drawbacks.

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“…However, it is difficult to replace the existing thermosetting plastics due to poor properties and high cost. Chemical recovery is regarded as a more promising method because it can produce useful chemicals and potentially achieve upcycling [6,17–19] . However, the highly crosslinked three‐dimensional network makes it quite difficult for the epoxy thermosets to undergo degradation [20–27] .…”

Section: Introductionmentioning

confidence: 99%

Multicycling of Epoxy Thermoset Through a Two‐Step Strategy of Alcoholysis and Hydrolysis using a Self‐Separating Catalysis System

Wang

Feng

et al. 2021

ChemSusChem

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Plastic has now become a contradiction between civilization and pollution that human society has to resolve. The recycling of thermosetting plastics in waste plastics is a huge challenge since they are difficult to remold like thermoplastic plastics due to their high crosslinking density. Here, a new strategy was developed to achieve multicycling of anhydride‐cured epoxy thermosets. The process consisted of mild and high‐efficiency alcoholysis catalyzed by potassium phosphate/low‐boiling alcohol system, and subsequent fast hydrolysis to obtain degradation products rich of carboxyl groups. The degradation products were reused as curing agent to prepare new anhydride‐cured epoxy thermosets without sacrifice of high strength and stability. Moreover, the new epoxy thermosets could still be repeatedly recycled using the same protocol. The insolubility of potassium phosphate in ethanol at room temperature made the separation and reuse of the catalyst more convenient. The use of low‐boiling alcohol not only allowed high‐efficiency degradation but also enabled easy separation from the degradation products. The excellent degradation performance was attributed to the improved swelling of the thermoset and the increased solubility of potassium phosphate induced by small amounts of water in the alcohol. This research provides a recycling method that can reintegrate thermoset waste plastics into remodeling ones under the background of circular economy.

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A structural chemistry look at composites recycling

Abstract: Composite materials, especially carbon fiber-reinforced polymers (CFRPs), are an emerging class of structural materials now commonly used in aircraft, marine, and other applications, with emerging large-scale use in the automotive...

Cited by 61 publications

References 43 publications

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

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

Recycling of Carbon Fiber-Reinforced Composites—Difficulties and Future Perspectives

Multicycling of Epoxy Thermoset Through a Two‐Step Strategy of Alcoholysis and Hydrolysis using a Self‐Separating Catalysis System

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