Extrusion Cycles Research Articles

Mechanical recycling of acrylonitrile-butadiene-styrene copolymer and high impact polystyrene from waste electrical and electronic equipment to comply with the circular economy

IntroductionAcrylonitrile-butadiene-styrene copolymer (ABS) and high impact polystyrene (HIPS) are plastics typically found in waste electrical and electronic equipment (WEEE or e-waste). As such, recycling is a beneficial method for reintroducing polymeric materials from electrical and electronic equipment to the same production cycle. This study aimed to investigate mechanical recycling of ABS and HIPS from WEEE reprocessed six times, totaling 24 cycles.MethodsReprocessing was performed by extrusion and test specimens were obtained by injection. The technical aspects assessed before and after reprocessing were mechanical properties (tensile, flexural and impact strength), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR) and melt flow index (MFI), compared with those of reprocessed virgin polymeric materials. The environmental aspect was evaluated by monitoring energy consumption and solid waste generation during each reprocessing cycle.ResultsAverage energy consumption per extrusion and injection cycle was 0.7 and 2.0 kW/kg, respectively. There was a 30% increase in MFI from the first to sixth reprocessing cycle for virgin HIPS (5.5 g/10 min in 200°C and 5 kg), the largest among the polymers. The values for virgin ABS (6.0 g/10 min in 200°C and 5 kg) and ABS and HIPS from WEE increased by 11–15% from the first to sixth cycle. Impact strength was affected from the second reprocessing cycle onwards for ABS e-waste (14% decrease) and in the fifth cycle (16% decrease) for HIPS e-waste.DiscussionThe thermal, tensile and flexural properties of the virgin and post-consumer materials remained almost unchanged as the number of reprocessing cycles increased, indicating that these materials have the potential and properties for reintroduction into the same production cycle.

Effect of Repeated Extrusion Cycles on the Structure and Properties of Polypropylene/Polyolefin Elastomer/Organic Montmorillonite Nanocomposites Using a β-Nucleating Agent

In this study the compatibilizer, maleic anhydride/hydroxyethyl acrylate-grafted-polyolefin elastomer (POE-g-MAH/HEA), was utilized in the preparation of polypropylene/polyolefin elastomer/organic nano-montmorillonite (PP/POE/OMMT) nanocomposites with a β-nucleating agent (β-NA) via twin-screw extrusion. The impact of repeated extrusion cycles (up to three) on the properties and structure of the nanocomposites was investigated. The results indicated that the dispersion of the OMMT within the polymer matrix improved with increased extrusion cycles, thereby enhancing the interfacial interactions between the constituents. In addition, the OMMT platelets led to increased crystallinity of the nanocomposites, accompanied by polymer chain degradation. The second extrusion cycle resulted in the nanocomposite with the best melt strength and mechanical properties. Additionally, the three cycles of additional repeated extrusion significantly enhanced the thermal stabilities of the nanocomposites.

Mechanism of plasticity enhancement of AZ31B magnesium alloy sheet by accumulative alternating back extrusion

Accumulative alternating back extrusion was a potential fine-grain modification method. In this paper, it was an innovative attempt to develop high-performance magnesium alloy sheet by this process. Under the condition of 350 K, commercial AZ31 magnesium alloy was made into billet by accumulative alternating back extrusion, and then extruded into fine-grain magnesium alloy sheet. Through a systematic study of its microstructure and mechanical properties, the results showed that the initial state had an important influence on the evolution of the structure during extrusion. After accumulative alternating back extrusion to produce the billet, the grain size of the sheet obtained by extrusion was significantly refined, which was related to the accumulation of deformation and grain refinement during the alternating loading process. Grain refinement caused the proportion of dynamic recrystallization inside the sheet with 2 cycles of accumulative alternating back extrusion to drop to 27%. With the increase of extrusion cycles from 2 to 4, the high density of dislocations led to an increase in the proportion of dynamic recrystallization and finer grains. The texture changed from strong basal texture to weak bimodal texture. The results of uniaxial tensile test show that due to grain refinement and texture change, the yield strength was significantly reduced, and the plasticity was significantly improved. It was verified that accumulative alternating back extrusion was meaningful for subsequent processing, and it also provided scientific guidance for the development of fine-grained magnesium alloy sheet.

Material-Preserving Extrusion of Polyamide on a Twin-Screw Extruder.

In the context of plastics recycling, plastics are processed several times. With each new melting and extrusion the plastic is damaged, which can have a negative effect on product properties. To counteract material damage, special additives such as chain extenders can be used, which are intended to lead to post-polymerization during processing. A linear chain extension is important here, as branching and crosslinking can lead to uncontrolled changes in the plastic's properties. To investigate the suitability of specialized linear chain extenders for polyamides, a polyamide-6 was processed several times and the molar mass distribution was evaluated after each extrusion cycle. Three series of tests were carried out. First, the plastic was regranulated five times without additives and twice with different concentrations of chain extenders on a twin-screw extruder. The results of the study show that not only can molar mass degradation be prevented with the appropriate additive, it is even possible to achieve a material buildup during processing. In our experiments, the polydispersity of the molar mass distribution remained nearly identical despite multiple extrusions. Thus, reactive extrusion makes it possible for the corresponding plastics to be processed several times without the molar mass decreasing. If a sufficiently pure material flow can be ensured during recycling, the number of possible reprocessings of the plastic can be significantly increased without the need to add virgin material.

Mechanical recycling of PLA: Effect of weathering, extrusion cycles, and chain extender

AbstractThis work evaluated the reprocessing of PLA with a high melt flow index (MFI). PLA samples were prepared by extrusion using a chain extender (Joncryl ADR‐4368) and subjected to two additional extrusion cycles with or without exposure to accelerated weathering. The results showed drastic affectations of PLA properties by weathering. The MFI increased from 65 to 137 g/10 min by reprocessing, while reprocessed and weathered samples reached a MFI of 417 g/10 min after three extrusion cycles. The addition of Joncryl prevented PLA degradation (MFI of 170 g/10 min after three extrusion cycles, even when weathering was performed). Additionally, the tensile strengths of weathered samples were substantially decreased (67%) compared to only reprocessed samples (14%). In this sense, PLA mechanical recycling is a good alternative if it is not exposed to harsh weathering conditions, in which case a chain extender is needed to get reasonable properties. Otherwise, reprocessing accelerated the composting of PLA, and the chain extender addition did not limit it.

Effect of low-temperature quasihydroextrusion on the structure and physical properties of CuCrZr alloy

The work is devoted to the study of changes in the structural and physical properties of the precipitation-hardened CuCrZr alloy under the influence of low-temperature (77 K) quasihydroextrusion with various degrees of deformation at liquid nitrogen temperature with subsequent aging. Prior to quasihydroextrusion, commercial alloy samples were annealed and quenched from the premelting temperature to obtain a supersaturated solid solution of alloying elements in the copper matrix. After quasihydroextrusion, the microstructure, lattice constant, pole densities, tensile strength and yield strength, microhardness (in different cross-sections of the extrudate), and electrical conductivity of the CuCrZr alloy were studied depending on the degree of deformation by quasihydroextrusion. It is shown that the deformation degree determines the kinetics of decomposition of the supersaturated solid solution and its structure. As a result of extrusion, an anisotropic structure of the matrix and precipitates is formed, which also determines the anisotropy of material properties. Subsequent aging leads to a significant decrease in the anisotropy of properties. With an increase in the deformation degree during extrusion (before aging), a significant monotonous increase in physical and mechanical properties occurs. However, in the range of deformation degrees of 40–50%, an anomalous “jump” of all measured properties and structural parameters is observed. The study proposes a physical mechanism that explains the experimental results. The mechanism is based on the occurrence of two kinetically differently directed processes: dynamic aging and its inhibition due to an increase in the defectiveness of the material. The latter process manifests itself essentially at low temperatures. In general, low-temperature quasihydroextrusion makes it possible to obtain a complex of sufficiently high mechanical and electrical characteristics of the CuCrZr alloy at relatively low degrees of deformation for one extrusion cycle, which is facilitated by low deformation temperature.

Plasticized Mechanical Recycled PLA Films Reinforced with Microbial Cellulose Particles Obtained from Kombucha Fermented in Yerba Mate Waste.

In this study, yerba mate waste (YMW) was used to produce a kombucha beverage, and the obtained microbial cellulose produced as a byproduct (KMW) was used to reinforce a mechanically recycled poly(lactic acid) (r-PLA) matrix. Microbial cellulosic particles were also produced in pristine yerba mate for comparison (KMN). To simulate the revalorization of the industrial PLA products rejected during the production line, PLA was subjected to three extrusion cycles, and the resultant pellets (r3-PLA) were then plasticized with 15 wt.% of acetyl tributyl citrate ester (ATBC) to obtain optically transparent and flexible films by the solvent casting method. The plasticized r3-PLA-ATBC matrix was then loaded with KMW and KMN in 1 and 3 wt.%. The use of plasticizer allowed a good dispersion of microbial cellulose particles into the r3-PLA matrix, allowing us to obtain flexible and transparent films which showed good structural and mechanical performance. Additionally, the obtained films showed antioxidant properties, as was proven by release analyses conducted in direct contact with a fatty food simulant. The results suggest the potential interest of these recycled and biobased materials, which are obtained from the revalorization of food waste, for their industrial application in food packaging and agricultural films.

Electromagnetic properties of composite filaments with ferromagnetic fillers for 3D printing

The paper presents the results of a study of composite materials based on the polymer acrylonitrile styrene acrylate (ACA) and filler M-type hexaferrite (BaFe12O19). The results of X-ray diffractometry of hexaferrite powder are presented. The porosity of the obtained composite filament samples was studied. After 9 extrusion cycles, the porosity is reduced to less than 1%. In the EHF range, the transmission coefficient through a sample of a composite material was measured. A sharp decrease in the transmission coefficient is observed in the frequency range from 42 to 55 GHz, which is due to the natural ferromagnetic resonance in BaFe12O19 hexaferrite.

Toward the Decarbonization of Plastic: Monopolymer Blend of Virgin and Recycled Bio-Based, Biodegradable Polymer.

Decarbonization of plastics is based on two main pillars: bio-based polymers and recycling. Mechanical recycling of biodegradable polymers could improve the social, economic and environmental impact of the use of these materials. In this regard, the aim of this study was to investigate whether concentrations of the same recycled biopolymer could significantly affect the rheological and mechanical properties of biodegradable monopolymer blends. Monopolymer blends are blends made of the same polymers, virgin and recycled. A sample of commercially available biodegradable blend was reprocessed in a single-screw extruder until two extrusion cycles were completed. These samples were exposed to grinding and melt reprocessed with 75% and 90% of the same virgin polymer. The blends were characterized by tensile tests and rheological tests. The results obtained showed that while multiple extrusions affected the mechanical and rheological properties of the polymer, the concentration of the reprocessed material present in the blends only very slightly affected the properties of the virgin material. In addition, the experimentally observed trends were accurately predicted by the additive model adopted.

Recycled Poly(hydroxybutyrate-co-valerate) as Food Packaging: Effect of Multiple Melt Processing on Packaging Performance and Food Contact Suitability

This study examines the opportunity of using recycled poly(hydroxybutyrate-co-valerate) (PHBV) as food packaging. The recyclability was evaluated by assessing the effect of repeated polymer processing (up to four extrusion cycles) on the structural and barrier properties of the material, as well as its ability to produce neo-formed chemicals susceptible to migrate into food. It was shown that increasing the number of processing cycles results in a decrease of the polymer molecular weight, leading to a decrease of mechanical properties, balanced by a maintenance of the crystalline structure and of the thermal stability. The oxygen and water vapour transfer properties were also maintained after four cycles suggesting that r-PHBV-based packaging can retain its property and use panel. The specific migration of crotonic acid, one of the main products of the thermomechanical degradation of the PHBV was measured in three different food simulants. In all cases, it did not exceed the specific migration limit (SML) set at 0.05 mg/Kg food, revealing the food contact suitability of non-contaminated recycled PHBV under test conditions.

Simulating the recycling of milk bottles in the UK: Influence of blending virgin and repeatedly melt-extruded high-density polyethylene

The UK Dairy Roadmap has set a target of achieving 50 wt.-% high density polyethylene (HDPE) recyclate in their HDPE milk bottles. Such high recyclate content will lead to the accumulation of HDPE recyclates that have been subjected to different number of melt extrusion cycles in the supply chain. This work investigates the structure-property relationship of blending virgin HDPE (vHDPE) with these different grades of repeatedly melt-extruded HDPE (rHDPE). HDPE was subjected to 10, 20 and 50 melt-extrusion cycles and blended with vHDPE. No significant difference in terms of melt rheology, tensile properties and overall migration in acidic and aqueous environments of the blends of the different rHDPEs with vHDPE was observed when compared to vHDPE. This study demonstrates the feasibility of blending up to 50 wt.-% rHDPE of different grades with vHDPE as set out in the UK Dairy Roadmap.

Detecting multiscale periodicity from the secular effusive activity at Santiaguito lava dome complex (Guatemala)

Santiaguito, Guatemala, represents one of the best cases of active lava dome complex in the world, producing lava flow effusion, weak explosive activity, and cycles of lava dome extrusion over varying timescales. Since the inception in 1922, it has shown a remarkable constant eruptive activity, characterized by effusion of blocky domes and lava flows punctuated by moderate explosions of gas-and-ash and pyroclastic flows. In this study, we reconstruct the time evolution of discharge rates of Santiaguito across one entire century, from 1922 to 2021, combining, for the more recent activity, new satellite thermal data. By using discrete Fourier transform (DFT) and Morlet wavelet analyses, we identify three fundamental periodicities in subsets of the 1922–2021 time-series: (i) long term (ca. 10 years), (ii) intermediate term (ca. 3.5 years), and (iii) short term (from ca. 1 year to ca. 3 months), which are comparable with those observed at other lava dome eruptions at calc-alkaline volcanoes. Such inferred periodicities provide a powerful tool for the interpretation of the non-linear eruptive behaviour and represent a pivotal benchmark for numerical modelling aimed to reconstruct the dynamics of the magma feeding system based on a time-averaged discharge rate dataset.Graphical

STUDY OF A MODIFIED MELAMINE SPONGE AND ITS LIPOPHILIC AND HYDROPHOBIC PROPERTIES

In this study, silicone rubber and silicone oil were used to modify melamine sponge to obtain lipophilic and hydrophobic properties. The result showed that the modification had no effect on the intrinsic properties of sponges such as the structure and elasticity. After modification, the melamine sponge changed from hydrophilic to superhydrophobic, and the contact angle could reach 155.7°. In addition, this sponge also maintained its good oil-absorption performance and showed its excellent selective oil absorption in an oil-water mixture. Using xylene to simulate pollutants, the oil-absorption rate of the modified sponge could reach 44 g/g while the contact angle and oil-absorption rate of the sponge showed no significant changes after 20 cycles of oil-absorption experiments. The sponge showed a reliable and stable oil-absorption effect after repeated extrusion cycle experiments. The above experiments proved that the modification method and modified sponge have broad application prospects in oil-water separation.

Turning Molecular Springs into Nano-Shock Absorbers: The Effect of Macroscopic Morphology and Crystal Size on the Dynamic Hysteresis of Water Intrusion-Extrusion into-from Hydrophobic Nanopores.

Controlling the pressure at which liquids intrude (wet) and extrude (dry) a nanopore is of paramount importance for a broad range of applications, such as energy conversion, catalysis, chromatography, separation, ionic channels, and many more. To tune these characteristics, one typically acts on the chemical nature of the system or pore size. In this work, we propose an alternative route for controlling both intrusion and extrusion pressures via proper arrangement of the grains of the nanoporous material. To prove the concept, dynamic intrusion–extrusion cycles for powdered and monolithic ZIF-8 metal–organic framework were conducted by means of water porosimetry and in operando neutron scattering. We report a drastic increase in intrusion–extrusion dynamic hysteresis when going from a fine powder to a dense monolith configuration, transforming an intermediate performance of the ZIF-8 + water system (poor molecular spring) into a desirable shock-absorber with more than 1 order of magnitude enhancement of dissipated energy per cycle. The obtained results are supported by MD simulations and pave the way for an alternative methodology of tuning intrusion–extrusion pressure using a macroscopic arrangement of nanoporous material.

Tough Engineering Hydrogels Based on Swelling-Freeze-Thaw Method for Artificial Cartilage.

Articular cartilage, which exhibits toughness and ultralow friction even under high squeezing pressures, plays an important role in the daily movement of joints. However, joint soft tissue lesions or injuries caused by diseases, trauma, or human functional decline are inevitable. Poly(vinyl alcohol) (PVA) hydrogels, which have a water content and compressive strength similar to those of many tissues and organs, have the potential to replace tough connective tissues, including cartilage. However, currently, PVA hydrogels are not suitable for complex dynamic environments and lack rebound resilience, especially under long-term or multicycle mechanical loads. Inspired by biological tissues that exhibit increased mechanical strength after swelling, we report a tough engineered hydrogel (TEHy) fabricated by swelling and freeze-thaw methods with a high compressive strength (31 MPa), high toughness (1.17 MJ m-3), a low friction coefficient (0.01), and a low energy loss factor (0.22). Notably, the TEHy remained remarkably resilient after 100 000 cycles of contact extrusion and remains intact after being compressed by an automobile with a weight of approximately 1600 kg. The TEHy also exhibited excellent water swelling resistance (volume and weight changes less than 5%). Moreover, skeletal muscle cells were able to readily attach and proliferate on the surface of TEHy-6, suggesting its outstanding biocompatibility. Overall, this swelling and freeze-thaw strategy solves the antifatigue and stability problems of PVA hydrogels under large static loads (>10 000 N) and provides an avenue to fabricate engineering hydrogels with strong antifatigue and antiswelling properties and ultralow friction for potential use as biomaterials in tissue engineering.

Advanced and traditional processing of thermoplastic polyurethane waste

In this work different ways to valorise discarded ear tags made of TPU from livestock sector were studied. This singular residue does not require separation from other plastics like other industrial and urbane wastes, which could contribute to simplify its management. Firstly, mechanical processing was carried out by several cycles of consecutive extrusion and injection processes. The material obtained in each process was characterized using different physical, chemical and mechanical characterization techniques in order to study the degradation as a consequence of processing cycles. Thereafter, suitable filaments for 3D printing were obtained and the effect of infill pattern in the mechanical properties of the printed pieces was investigated. Besides, an electrospun mat constituted by TPU waste microfibers was successfully obtained by electrospinning, and its morphology together with superficial and mechanical properties were characterized. Results showed that these applications were suitable options to valorise TPU waste consisting of discarded ear tags.

Closed-loop thickness control and sensor placement in extrusion blow moulding

Extrusion blow moulding (EBM) is a polymer forming technique used to manufacture hollow plastic parts, such as fuel tanks. In this work, the feasibility of using closed-loop control in EBM is explored to compensate for machine drift and disturbances. A control system is proposed to regulate the extrusion process in EBM. The extrusion controller aims to increase process consistency by minimizing part thickness deviations. The thickness of the extrudate is measured during the extrusion cycle and any deviation from the desired thickness profile is compensated by changing the die gap in real time. The controller, which offers flexibility in thickness sensor placement, features a Smith predictor configuration embedding an H∞ controller. It compensates for the input-dependent polymer transport delay, the nonlinear steady-state swell, and nonminimum phase necking effects affecting the extrudate. This extrusion control technique may help reduce the production rate of off-specification parts and improve product quality.

Reprocessing of polymer blends from WEEE: A methodology for predicting embrittlement

For recycling purposes, the thermal degradation of post-consumed (pc) ABS/HIPS and PP/PE blends derived from waste electrical and electronic equipment (WEEE) was obtained by multiple extrusions. The evolution of molar mass (Mw), melt flow index (MFI), and ultimate elongation (εr) of reprocessed blends was evaluated as a function of extrusion cycles. The degradation mechanism of ABS/HIPS blends corresponds to a random chain scission as indicated by a diminution of εr correlated to an increase in MFI and decrease in Mw after 30 cycles of extrusion. The same type of degradation mechanism occurs on the PP/PE blend as shown by the drop in Mw and thus an increase in MFI by a factor of six but only after 11 cycles, thus suggesting the higher thermomechanical resistance of ABS/HIPS. The beginning of the critical molar mass for embrittlement (M'c) zone was reached around 130 and 200 kg/mol for ABS/HIPS and PP/PE, respectively, which can be related to the beginning of the critical MFI zone around 12 and 63 g/10 min (230 °C/2.06 kg), respectively. As a result, we propose an innovative embrittlement criterion using MFI measurements that allow a quick and easy analysis of post-consumed polymer blends.

Effects of Reprocessing on Acrylonitrile–Butadiene–Styrene and Additives

Acrylonitrile–butadiene–styrene (ABS) is one of the most extensively used engineering polymers. It is necessary to study the recycling of ABS because of environmental, economic and energy reasons. In this study, an ABS resin was processed using a torque rheometer at different temperatures and for different numbers of cycles. Pyrolysis gas chromatography mass spectrometry (Py-GC/MS) was used to study the effects of the processing parameters on additives. Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance spectroscopy, and gel permeation chromatography (GPC) were used to analyse the structural changes in the resin. GPC results showed that after processing at 290 °C using the torque rheometer, large size soluble polymeric components increased. The increase in the large size soluble polymeric components after processing at 290 °C was probably related to the crosslinking reactions in the grafted polybutadiene. Furthermore, chemical analysis of the ABS resin samples after multiple extrusion cycles in a twin-screw extruder indicated that reprocessing considerably affected the ABS resin.

The Tragedy of Alzheimer's Disease: Towards Better Management via Resveratrol-Loaded Oral Bilosomes.

Alzheimer’s disease (AD) is a neurodegenerative disease where oxidative stress plays a major role as a key pathologic factor. The study aims to develop resveratrol (RES)-loaded bilosomes for oral use, aiming to enhance RES bioavailability. RES-loaded bilosomes were prepared using the thin-film hydration technique. The effect of different formulation variables viz. the number of extrusion cycles, drug concentration and the effect of pH of the medium and cholesterol addition on the physicochemical properties of the prepared bilosomes was investigated. Results revealed the successful entrapment of RES into bilosomes. An optimized formula was selected, showing the lowest particle size (189 ± 2.14), acceptable PDI (0.116) and entrapment efficiency (76.2 ± 1.36). In vivo studies on a streptozotocin-induced animal model of AD showed the preeminence of bilosomes over traditional drug suspension to enhance mice memory via Y-maze and Morris water maze tests. Moreover, mice treated with the optimized formula exhibited decreased COX2, IL-6, amyloid-beta peptide and Tau protein levels compared to the drug suspension. Immuno-histochemical analysis revealed a significant decrease of glial fibrillary acidic protein values and microglial cell count in mice treated with bilosomes. Finally, it could be advocated that RES-loaded bilosomes could be a promising drug delivery system to control AD.