Solid State Shear Milling Research Articles

Poly(vinyl alcohol)-Assisted Exfoliation and Grafting Modification of Boron Nitride Nanosheets with a High Aspect Ratio via a Continuous Production Method for Energy Storage and Thermal Management.

Hexagonal boron nitride nanosheets (BNNS) integrating many extraordinary properties are usually combined with polymers to fabricate multifunctional dielectric materials for energy storage and thermal management. Unfortunately, the existing technologies for producing BNNS generally have the disadvantages of inefficiency and low product quality, which significantly hinder the wide application of high-value nanocomposites. Herein, a novel poly(vinyl alcohol) (PVA)-assisted pan-milling method based on the innovative solid-state shear milling (S3 M) technology is reported for the production of high-quality BNNS. The uniform three-dimensional (3D) shear force field generated by pan milling not only ensured the high aspect ratio of BNNS (the average lateral size of ∼954 nm and the average thickness of ∼3.7 nm) but also induced the mechanochemical reaction between PVA and BNNS to achieve in situ grafting modification on the BNNS surface. The simultaneous high-quality exfoliation and surface modification of BNNS positively contributed to the mechanical, dielectric, and thermal conduction properties of BNNS/PVA nanocomposites. At the BNNS content of 10 wt %, the BNNS/PVA composite film exhibited excellent robustness (Young's modulus of 5305 MPa and the tensile strength of 83 MPa), with a satisfactory breakdown strength (Eb of 134.7 MV/m) and dielectric constant (∼5 at 1000 Hz). In addition, the substantial improvement of thermal conductivity (from 0.88 to 5.59 W·m-1·K-1) guaranteed the stability of the dielectric properties of the nanocomposites at high temperatures. This pan-milling method characterized by green and efficiency is highly scalable to other two-dimensional (2D) layered materials, providing a practical strategy for the industrial fabrication of nanocomposites in elevated-temperature energy storage.

Fabrication of high performance polypropylene based blends from ethylene vinyl acetate-based sole waste via solid-state shear Co-milling

Ethylene vinyl acetate copolymer (EVA) foam products with cross-linked structure are now widely used in the fields of functional footwear. However, due to their cross-linked structure and complex composition, they are quite difficult to be recovered in large scale after disposal, causing serious environmental pollution. Based on our self-designed solid-state shear milling (S3M) equipment, a novel co-milling technology was established to recycle ethylene vinyl acetate-based sole waste (ESW) and reuse it to strengthen and toughen polypropylene (PP). The effects of co-milling on PP/ESW powders as well as blends were studied, and the results showed that the existence of PP promoted the solid pulverization of ESW, so formed the powders with smaller size and wider distribution. Ascribing to the partial de-crosslinking of ESW during co-milling process, the contact area and the molecular entanglements at their interfaces increased, effectively improving the compatibility between PP and ESW. In this way, the simultaneous enhancement and toughening of ESW on PP were achieved. After co-milling, ESW phase in blends significantly decreased and no visible phase interface was observed. With 20 co-milling cycles, the tensile strength and impact toughness of PP/20 wt% ESW blend respectively increased from 21.9 MPa to 3.79 kJ/m2 to 25.4 MPa and 5.83 kJ/m2, both higher than most other similar PP based materials. This work provides a new strategy for high-quality and efficient recycling of ESW in large scale, and fabrication of high-performance PP based materials.

Green Recycling of Carbon/Carbon Composites by Solid-State Shear Milling Technology as a Polyamide Multi-Functional Modifier.

Carbon/carbon (C/C) composite materials are widely used in aerospace, the military and nuclear energy. The outstanding mechanical qualities of C/C composites mean that they are difficult to crush and recycle using traditional technology. The current recycling methods primarily involve stacking and landfill disposal. Therefore, achieving efficient and environmentally friendly recycling of carbon/carbon (C/C) composites is an urgent and challenging issue. In this work, we reported a simple high-value recycling approach for carbon-carbon frictional composite material (CFCM). The solid-state shear milling (S3M) technology is employed to achieve ultrafine milling of carbon matrices in carbon/carbon (C/C) composite materials while preserving carbon fibers. By this means, carbon fibers and the carbon matrix were mainly split, and the prepared composite powder had combined functionalities of conductivity, thermal conductivity, reinforcement, and wear resistance. The experimental results showed that the tensile strength of the material increased from 64.35 MPa to 72.79 MPa after being compounded with PA6, and the thermal conductivity increased from 0.211 W/mK to 0.611 W/mK. The friction coefficient was reduced from 0.51 to 0.36, a reduction of 25.4%, and the heat deflection temperature was increased from 47.2 °C to 108.2 °C. The S3M technique proposed in this work is an efficient, high-value, and scalable recycling strategy for CFCM, which can be used to produce value-added products and has great application prospects.

Preparation and Performance of PBAT/PLA/CaCO3 Composites via Solid-State Shear Milling Technology

Replacing traditional disposable, non-biodegradable plastic packaging with biodegradable plastic packaging is one of the key approaches to address the issue of “white pollution”. PBAT/PLA/inorganic filler composites are widely utilized as a biodegradable material, commonly employed in the field of packaging films. However, the poor dispersion of inorganic fillers in the polymer matrix and the limited compatibility between PBAT and PLA have led to inferior mechanical properties and elevated costs. In this work, we propose a simple and effective strategy to improve the dispersion of nano-CaCO3 in a PBAT/PLA matrix through solid-state shear- milling (S3M) technology, combined with mechanochemical modification and in situ compatibilization to enhance the compatibility between PBAT and PLA. The impact of varying milling conditions on the structure and performance of the PBAT/PLA/CaCO3 composites was investigated. During the milling process, PBAT and PLA undergo partial molecular chain fragmentation, generating more active functional groups. In the presence of the chain extender ADR during melt blending, more branched PBAT-g-PLA is formed, thereby enhancing matrix compatibility. The results indicate that the choice of milling materials significantly affects the structure and properties of the composite. The film obtained by milling only PBAT and CaCO3 exhibited the best performance, with its longitudinal tensile strength and fracture elongation reaching 22 MPa and 437%, respectively. This film holds great potential for application in the field of green packaging.

Finite Element Analysis of the Structure and Working Principle of Solid-State Shear Milling (S3M) Equipment.

Solid-state shear milling (S3M) equipment is an evolution from traditional stone mills, enabling the processing of polymer materials and fillers through crushing, mixing, and mechanochemical reactions at ambient temperature. Due to the complex structure of the mill-pan, empirical data alone are insufficient to give a comprehensive understanding of the physicochemical interactions during the milling process. To provide an in-depth insight of the working effect and mechanism of S3M equipment, finite element method (FEM) analysis is employed to simulate the milling dynamics, which substantiates the correlation between numerical outcomes and experimental observations. A model simplification strategy is proposed to optimize calculation time without compromising accuracy. The findings in this work demonstrate the S-S bond breakage mechanism behind stress-induced devulcanization and suggest the structural optimizations for enhancing the devulcanization and pulverization efficiency of S3M equipment, thereby providing a theoretical foundation for its application in material processing.

Preparation of high performance thermal conductive composites from aluminum plastic packaging waste via Solid-state Drawing

Aluminum-plastic multilayer films have been widely used as the top-grade packaging material due to their exceptional barrier properties. However, the recycling of aluminum plastic packaging waste (APPW) poses a great challenge. To address this issue, we proposed a facile method for recycling APPW using solid-state drawing technology to produce high performance thermal conductivity composites for the first time. The ultrafine APPW with good processability was obtained by solid-state shear milling (S3M), with a low electrical conductivity of less than 10−12 S/cm. The subsequent solid-state drawing of both the aluminum sheet and polymer chain resulted in the formation of an oriented crystalline structure, with the Al sheet acting as an effective nucleating agent. This resulted in a significant increase in tensile strength for HDPE/APPW (30 %) composites, from 21.4 MPa to 116.1 MPa at the drawing ratio of 5. In addition, the in-plane thermal conductivity of HDPE/APPW (50 %) composites reached an impressive 2.5 W/mK, with the tensile strength of 78.8 MPa. Our findings demonstrate the potential of utilizing APPW for the production of value-added composites without requiring separation, with possible applications in heat management for emerging electrical systems and electronic devices.

Preparation of Polyoxymethylene/Exfoliated Molybdenum Disulfide Nanocomposite through Solid-State Shear Milling.

In this paper, the solid-state shear milling (S3M) strategy featuring a very strong three-dimensional shear stress field was adopted to prepare the high-performance polyoxymethylene (POM)/molybdenum disulfide (MoS2) functional nanocomposite. The transmission electron microscope and Raman measurement results confirmed that the bulk MoS2 particle was successfully exfoliated into few-layer MoS2 nanoplatelets by the above simple S3M physical method. The polarized optical microscope (PLM) observation indicated the pan-milled nanoscale MoS2 particles presented a better dispersion performance in the POM matrix. The results of the tribological test indicated that the incorporation of MoS2 could substantially improve the wear resistance performance of POM. Moreover, the pan-milled exfoliated MoS2 nanosheets could further substantially decrease the friction coefficient of POM. Scanning electron microscope observations on the worn scar revealed the tribological mechanism of the POM/MoS2 nanocomposite prepared by solid-state shear milling. The tensile test results showed that the pan-milled POM/MoS2 nanocomposite has much higher elongation at break than the conventionally melt-compounded material. The solid-state shear milling strategy shows a promising prospect in the preparation of functional nanocomposite with excellent comprehensive performance at a large scale.

Fabrication of biodegradable Poly(butylene adipate-co-butylene terephthalate) bead foams through solid utilization of chitin and controllable incorporation of porous structure

The pollution caused by waste plastics is becoming increasingly serious, and utilizing the biodegradable materials, that can be completely degraded in nature, is considered to be one of the most promising ways to solve this problem. Poly(butylene adipate-co-butylene terephthalate) (PBAT), as the commonly used biodegradable polymer material, is subjected to the problem of high cost, poor mechanical performance, and low melt strength at high temperatures. Herein, a novel strategy combining solid utilization of biomass material chitin and incorporation of porous structure was developed to fabricate the PBAT bead foams, relying on the solid-state shear milling (S3M) and supercritical carbon dioxide (scCO2) foaming technologies. Chitin scraps were super finely pulverized and uniformly combined with PBAT, and the PBAT-based bead foams with controllable cell structure, improved mechanical performance, and low cost after foaming the composite. When the content of chitin was 20%, the tensile strength and Young’s modulus of PBAT/chitin bead foam were 0.72 MPa and 2.14 MPa, respectively, much higher than that of neat PBAT bead foam, expressing the great significance to broadening the application field of degradable plastics.

Mechanochemically-induced C–S bond transalkylation exchange in the waste nitrile rubber (NBR)/Poly (vinyl chloride) (PVC) insulation materials

Vulcanized acrylonitrile-butadiene rubber (NBR)/poly (vinyl chloride) (PVC) blends are mainly served as insulation rubber-plastic materials. During manufacturing and use, amounts of waste NBR/PVC materials are produced. However, traditional methods of reusing waste are inappropriate. Herein, we innovatively proposed the utilization of mechanochemistry to induce the conversion of irreversible C–S cross-linked bonds in waste NBR/PVC insulation materials into dynamically reversible vitrimer-like network structures. The vitrimer-like structure endowed mobility to the global molecular chains in NBR/PVC materials. And thus, it was essential for the reclaimed products to eliminate the difference between the residual network within waste NBR/PVC materials and the devulcanized phase, improving the mechanical properties. More interestingly, waste NBR/PVC powder dynamically modified by trimethylsulfoniumiodide (TMSI) restored the ability to mix with other materials via thermal processing. The HNBR + CuSO4 compounds were then blended with the modified NBR/PVC powder to prepare mechanically excellent composites with optimum stress of 14.6 MPa and strain of 481.0%. The continuity of the matrix was critical to the mechanical properties of the recycled products, and solid-state shear milling (S3M) played a crucial role in this process, as characterized by various experiments.

The structure and properties of mechanochemically modified acrylonitrile butadiene rubber (NBR)/poly (vinyl chloride) (PVC) scraps and fresh NBR composites

Vulcanized acrylonitrile-butadiene rubber (NBR)/poly (vinyl chloride) (PVC) blends are mainly served as insulation rubber-plastic materials. However, methods to reuse the waste NBR/PVC composites lack research. Here, we found that the mechanochemically modified waste NBR/PVC composites powders (WNPP) could be an alternative to fresh NBR. According to the results, the optimal replacement amount of WNPP for NBR was 20%, and the highest feasible proportion was 40%. WNPP treated by solid-state shear milling technology (S3M) would have a high degree of desulfurization, and the cross-linked chains within WNPP would be transformed into free chains. While co-vulcanizing, the sulfur agents and heat would induce the free chains of WNPP to react with the polymer chains of the NBR substrate, thereby generating dangling chains to form a robust interfacial layer. It was beneficial for the improvement of the mechanical properties of reclaimed products. And the strain of the excellent recycled sample (20C) reached 707%. Moreover, the modified WNPP in the co-vulcanized rubber represented heterogeneity because of the internal residual crosslinked network and the not-melting PVC plastic phase. Although the heterogeneity of WNPP damaged the continuity of the NBR matrix, it also brought a better hysteresis loss capability to the composite. In conclusion, this work expanded the mechanochemical application scope in recycling NBR/PVC wastes.

Mechanochemical reclaiming and thermoplastic re-processing of waste Acrylonitrile-butadiene rubber (NBR)/poly (Vinyl Chloride) (PVC) insulation materials

Cross-linked acrylonitrile-butadiene rubber (NBR)/poly(vinyl chloride) (PVC) blends are extensively served as commercial insulation foams. However, methods to reclaim the wasted NBR/PVC composites are usually inappropriate, causing severe pollution. Herein, we reported that the waste NBR/PVC composites powders (WNPP) with high thermal stability and degree of reclaiming were prepared by solid-state shear milling technology (S3M). Furthermore, the reclaimed products via thermoplastic re-processing had excellent mechanical properties, and the optimal stress and strain were increased by 208.2 % and 269.4 %, respectively, compared with the products made from virgin scraps. Through the investigation of each sample's molecular chains and thermal properties, it was found that when the cross-linked polar rubber-plastic composites are reclaimed, the molecular chains of the rubber phase would be close to each other. The interaction among polar groups would be enhanced, which is the main contributing factor limiting the movability of the polymer chains. And the interaction between the polar rubber and plastic phases would also increase, which is beneficial for the compatibility of the two phases. Moreover, there is a phase separation between the de-crosslinked continuous phase and the residual cross-linked network region for the re-processing products.

Highly Efficient Pyrolysis of Waste High-Temperature Vulcanized Silicone Rubber Assisted by Mechanochemical Milling

High-temperature vulcanized silicone rubber (HTV SIR) possesses great chemical resistance and high thermal stability, but these excellent performances also impede its recycling. In this respect, the waste HTV SIR from retired composite insulators with/without the KOH catalyst was ground by solid-state shear milling (S3M). The morphology and structure of silicone rubber powder were analyzed, and the pyrolysis behaviors of the obtained silicone rubber powders were revealed by thermogravimetry (TG) and pyrolysis gas-phase/mass spectrometry (Py-GC/MS). The results show that the mechanochemical milling via S3M could significantly reduce the particle size of silicone rubber and destroy the cross-linking structure of the waste HTV SIR, thus leading to an obvious improvement in the sol fraction. The maximum weight loss rate temperature of waste HTV SIR with the KOH catalyst assisted by mechanochemical milling was 150 °C lower than those without milling. Moreover, a greatly reduced catalytic pyrolysis duration along with more concentrated pyrolysis products at 400 °C was achieved after grinding three times. At last, the pyrolysis mechanism of the waste HTV SIR assisted by mechanochemical milling is proposed. These obtained results provide a great potential for large-scale recycling of waste silicone rubber with stable structure and complex components.

Green recycling of aramid fiber waste as the friction modifier of POM by solid state shear milling technology

AbstractAramid fiber is widely used in aerospace, machinery, construction, and other fields for its high strength, high elastic modulus, lightweight, and superior comprehensive performance. However, because aramid fiber is difficult to be melted and reprocessed, efficient and environmentally friendly recycling of aramid fiber waste (AFW) is an urgent and challenging issue. In this work, we reported a facile way to recycle AFW for the preparation of friction‐resistant polyoxymethylene (POM)/AFW composites. The ultrafine AFW powder with 64.69 μm in size was fabricated by solid state shear milling (S3M) technology, which broke the amide bond due to the strong compression and shearing during milling. With the increase of milling cycles, the roughness and active groups on the surface of AFW were increased, which was contributed to improving the compatibility between AFW and POM matrix. The morphology observation indicated a good dispersion of AFW in POM. The mechanical property test results showed that the flexural strength increased from 52.69 MPa to 80.12 MPa with 20 wt.% AFW. As a friction modifier, the addition of AFW could improve the tribological properties of POM/AFW composites, and the coefficient of friction (COF) and wear rate of composites with 20 wt.% AFW could decrease by 53.02% and 69.52%, respectively. The S3M technology presented in this work is an efficient and industrialized strategy for AFW recycling to prepare value‐added products, which has great potential in the engineering application field.

Fabrication of high-performance piezoelectric composite from commingled waste plastic films via a novel physicomechanical technology

The highly efficient and environmentally friendly reuse of waste plastics is always a big challenge worldwide, especially for commingled waste plastics. In this study, based on a novel pan-milling equipment, a simple, efficient and green physicomechanical technology, i.e. solid-state shear milling (S3M) technology, was established to realize the high-quality reuse of the commingled waste plastic films (CWPF) composed of polypropylene (PP), nylon 6 (PA6), polyethylene terephthalate (PET) and polyethylene (PE), as well as their good complexation with BaTiO3. Under the strong 3D-shear force of this milling equipment, the proper phase size of CWPF and the good compatibility between the components in CWPF were achieved, endowing the milled CWPF powders with significantly improved reprocessability. After milling for 30 cycles, ascribing to the formation of the fibrous phases, the tensile strength of the reprocessed CWPF sheet reached 18.7 MPa, increasing by 285% compared with the one without milling. Through co-milling, BaTiO3 piezoelectric particles were successfully incorporated into CWPF, and high-performance CWPF/BaTiO3 composite sheets were obtained. With 15 vol% BaTiO3, the composite sheet has the flexural strength of 17 MPa and compressive strength of 90 MPa, and could directly produce 95 V and 1.56 μA piezoelectric outputs to power 20 LED bulbs, or to charge a 1 μF commercial capacitor to 6.03 V within 100 s, surpassing most of BaTiO3 containing piezoelectric energy harvesters reported thus far, thus having great potential applications in the piezoelectric field, e.g. piezoelectric road.

Tailoring Three-Dimensional copper framework in polyamide 6 for High-Performance thermal management applications

Polymer plays an essential role in efficient thermal management of high-performance electronic devices, but the cooling efficiency of polymer composites is limited by some technical difficulties, such as the lack of thermal transport pathways and high cost of nano filler. Herein, we introduced solid-state shear milling (S3M) technology to prepare copper flakes (Cu-f) and constructed an enhanced Cu flakes network through hot-pressing of Cu and polyamide 6 (PA6) particles with different melt temperature. The low melt temperature PA6 coating on Cu flake surface acted as a glue to tightly connect Cu flakes and high melt temperature PA6 particles, thus generating an enhanced filler network. This brings the PA6/Cu-f network composites with a record high thermal conductivity at 6.3 Wm−1Κ−1, which is 3 times higher than that of traditional PA6/Cu-s composites (1.8 Wm−1Κ−1) at 80 wt% Cu loading. Basing on Foygel’s model from effective medium approximation theory, the PA6/Cu-f network composites had a lower thermal contact resistance (Rc) of 9.8 × 103 KW−1 and interfacial thermal resistance (ITR) of 6.3 × 10−8 W−1m2K. In LED lamps cooling performance test, PA6/Cu-f network composite showed 15 °C lower than traditional PA6/Cu-s composite in operating temperature. We believed that with the excellent thermal management ability and low cost, the PA6/Cu-f network composites open up opportunities for efficient thermal management in high power density devices.

Using Asphalt as an Additive for Waste Cross-Linked Polyethylene Recycled Materials to Improve Thermoplastic Processing.

With good insulation, cross-linked polyethylene (XLPE) cables are widely used as an important basic material for power transportation. Due to being insoluble and infused, the cross-linked network structure caused a challenge in the recycling of waste XLPE, which is usually treated by incineration and landfilling. In this research, XLPE was part-de-cross-linked via solid-state shear milling (S3M) technology, but the resulting powder was difficult to process. In order to improve the re-processability of XLPE, asphalt with a similar structure was added during the thermoplastic processing. To deeply understand the influence of asphalt on the matrix, the compatibility, dispersion, and rheological properties of the composites were characterized. Due to the good compatibility between de-cross-linked XLPE and asphalt, the viscosity of the composites decreased significantly. Some sea-island structures also formed in composites, which increased the toughness of the composites, so the elongation at break reached as high as 322%. The use of asphalt to achieve the processing performance of part-de-cross-linked XLPE powder was highly effective. Furthermore, the prepared composites showed potential application in the field of waterproofing, which could recycle waste XLPE cables on a large scale.

Effect of solid-state shear milled natural rubber particle size on the processing and dynamic vulcanization of recycled waste into thermoplastic vulcanizates

Natural rubber (NR) and crosslinked polyethylene (XLPE) waste streams were devulcanized by solid state shear milling (S3M), producing a fine powder that may be more easily reprocessed. Understanding devulcanization and the nature of decrosslinked thermoset materials is of utmost importance for turning these waste steams into functional products. It was found that the devulcanized powders contained significant concentrations of radicals, which may be active in the subsequent revulcanization process. The produced devulcanized powders were converted into recyclable thermoplastic vulcanizates (TPVs) by twin screw extrusion. Reprocessing of these powders into value-added products is an important step in recycling and the use of extrusion allows for high throughput and industrial viability. Herein, we demonstrate that the optimal conditions for reprocessing are dependent upon the particle size of the devulcanized powder. Furthermore, dynamic vulcanization is affected by the nature of these recyclate powders. The successfully prepared TPVs showed similar properties to virgin materials, with a high elongation to failure. Therefore, the conversion of waste rubber into the rubber phase of a TPV shows significant promise in moving towards sustainable products, providing the revulcanization step can be well controlled.

Combining Solid-State Shear Milling and FFF 3D-Printing Strategy to Fabricate High-Performance Biomimetic Wearable Fish-Scale PVDF-Based Piezoelectric Energy Harvesters.

High-performance flexible piezoelectric polymer-ceramic composites are in high demand for increasing wearable energy-harvesting applications. In this work, a strategy combining solid-state shear milling (S3M) and fused filament fabrication (FFF) 3D-printing technology is proposed for the fabrication of high-performance biomimetic wearable piezoelectric poly(vinylidene fluoride) (PVDF)/tetraphenylphosphonium chloride (TPPC)/barium titanate (BaTiO3) nanocomposite energy harvesters with a biomimetic fish-scale-like metamaterial. The S3M technology could greatly improve the dispersion of BaTiO3 sub-micrometer particles and the interfacial compatibility, resulting in better processability and piezoelectric performance of the nanocomposites. Typically, the FFF 3D printed energy harvester incorporating 30 wt % BaTiO3 showed the highest piezoelectric outputs with an open-circuit voltage of 11.5 V and a short-circuit current of 220 nA. It could hence drive nine green LEDs to work normally. In addition, a 3D-printed biomimetic wearable energy harvester inspired by an environmentally adaptive fish-scale-like metamaterial was further fabricated. The fish-scale-like energy harvester could harvest energy through different deformation motions and successfully recharge a 4.7 μF capacitor by being mounted on a bicycle tire and the tire's rolling. This work not only provides a 3D printing strategy for designing diversified and complex geometric structures but also paves the way for further applications in flexible, wearable, self-powered electromechanical energy harvesters.

High-Value Recycling of Isotactic Polypropylene-Based Plastic Waste as a Crystallization Promoter for High-Performance Polypropylene Random Copolymers

Highly efficient recycling of nonrenewable resources is increasingly important at the global concern of resource crisis and environmental issue. Here, a new strategy for value-added application of isotactic polypropylene (iPP)-based plastic waste as a crystallization promoter was proposed, and cigarette packaging film (CPF) waste as a typical single-component iPP was used as a representative example to demonstrate the successful application. First, the CPF wastes were pulverized into ultrafine powders under three-dimensional shearing force generated by solid-state shear milling equipment. Then, the CPF powders as a crystallization promoter were incorporated into a polypropylene random copolymer (PPR) in the presence of a β-nucleator by utilizing high-chain stereoregularity and strong crystallization nature to cultivate rich β-crystals. Finally, the outstanding combination of strength and toughness of the as-prepared PPR sample was exemplified by the increases of 66 and 25.8% in elongation at break and impact strength over a pure PPR sample at the guarantee of mechanical strength. This simple blending approach also can be extended easily to the recycling of the other polypropylene-based waste plastics and thus is an important step toward solving global plastic pollution.

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

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 re-crosslinking 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/m2, 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.