“Tying the Knot”: Enhanced Recycling through Ultrafast Entangling across Ultrahigh Molecular Weight Polyethylene Interfaces

Christakopoulos, Fotis; Troisi, EM Enrico; Friederichs, Nic; Vermant, Jan; Tervoort, Theo A.

doi:10.1021/acs.macromol.1c01427

Cited by 19 publications

(14 citation statements)

References 59 publications

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“…This could be improved by the addition of a coloring agent to color the powder so that the wavelength of the laser can be absorbed by it. Lastly, for the case of UHMWPE processed through SLS, good adhesion between the powder particles could be achieved by using disentangled UHWMPE powder that has been shown to rapidly re-entangle upon melting, through a mechanism that deviates from slow reptation kinetics [ 128 ].…”

Section: Discussionmentioning

confidence: 99%

Additive Manufacturing of Polyolefins

2022

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Polyolefins are semi-crystalline thermoplastic polymers known for their good mechanical properties, low production cost, and chemical resistance. They are amongst the most commonly used plastics, and many polyolefin grades are regarded as engineering polymers. The two main additive manufacturing techniques that can be used to fabricate 3D-printed parts are fused filament fabrication and selective laser sintering. Polyolefins, like polypropylene and polyethylene, can, in principle, be processed with both these techniques. However, the semi-crystalline nature of polyolefins adds complexity to the use of additive manufacturing methods compared to amorphous polymers. First, the crystallization process results in severe shrinkage upon cooling, while the processing temperature and cooling rate affect the mechanical properties and mesoscopic structure of the fabricated parts. In addition, for ultra-high-molecular weight polyolefins, limited chain diffusion is a major obstacle to achieving proper adhesion between adjunct layers. Finally, polyolefins are typically apolar polymers, which reduces the adhesion of the 3D-printed part to the substrate. Notwithstanding these difficulties, it is clear that the successful processing of polyolefins via additive manufacturing techniques would enable the fabrication of high-end engineering products with enormous design flexibility. In addition, additive manufacturing could be utilized for the increased recycling of plastics. This manuscript reviews the work that has been conducted in developing experimental protocols for the additive manufacturing of polyolefins, presenting a comparison between the different approaches with a focus on the use of polyethylene and polypropylene grades. This review is concluded with an outlook for future research to overcome the current challenges that impede the addition of polyolefins to the standard palette of materials processed through additive manufacturing.

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Section: Discussionmentioning

confidence: 99%

Additive Manufacturing of Polyolefins

2022

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“…18 For a molecular chain explanation, it was discovered via neutron scattering tests that the mean square radius of gyration increases abnormally during melting, de Gennes calls them "chain explosion" or "melting explosion". 16,19 The melting explosion should be a special type of melting of very highly regularized UHMWPE crystals. Current research has focused on the utilization of this phenomenon to promote instantaneous adhesion between UHMWPE surfaces and interparticle welding efficiency.…”

Section: Introductionmentioning

confidence: 99%

“…Current research has focused on the utilization of this phenomenon to promote instantaneous adhesion between UHMWPE surfaces and interparticle welding efficiency. Recent research on autoadhesion during sintering has shown that nascent commercial UHMWPE is also capable of melting explosion and is critical for the success of sintering. ,, It is usually accepted that the diffusion distance of chains during healing is related to only temperature and time. However, the melting explosion shows that the chain diffusion is also closely related to melting behavior.…”

Section: Introductionmentioning

confidence: 99%

Research on Chain Diffusion and Entanglement via Controlling the Sintering Process of Nascent UHMWPE

Wang,

Chen

2024

Macromolecules

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The diffusion and entanglement of molecular chains have a significant impact on ultrahigh-molecular-weight polyethylene (UHMWPE) processing and product qualities. During sintering, the relationship between the melting behavior and chain diffusion in nascent UHMWPE remains unclear. In this work, nascent UHMWPE with different degrees of entanglement was used for sintering under different temperature conditions. Tensile drawing experiments performed above the melting point were used to study the degree of chain diffusion. The results reveal that the chain diffusion degree is proportional to the heating rate (S) at the same sintering temperature when S is above 1 °C/min. The chain diffusion is more sensitive to the sintering temperature at higher heating rates. The melting process suggests that rapid heating is necessary for melting explosion, which leads to a rapid chain diffusion. When heated slowly, crystals are melted more gently, and the chains may melt successively from the surface to the center, resulting in a lesser degree of chain diffusion or entanglement. Finally, the high melting point of nascent crystals and the variation of the melting point with heating rate may be related to the increasing entropy during melting.

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“…Consequently, to these properties changes, the applications of the mechanically recycled polymers have to be adapted [10][11][12]. Whereas the majority of recycled high and low-density polyethylenes (HDPE and LDPE) are however produced that way, Ultra High Molecular Weight Polyethylenes (UHMWPE), mostly used for high-performance applications due to their superior mechanical properties, are more difficult or impossible to process due to their high viscosity [13]. The other principal way of recycling polymers is by chemical recycling, which consists of a chemical transformation leading to new raw materials.…”

Section: Introductionmentioning

confidence: 99%

Data-Driven Modelling of Polyethylene Recycling under High-Temperature Extrusion

et al. 2022

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Two main problems are studied in this article. The first one is the use of the extrusion process for controlled thermo-mechanical degradation of polyethylene for recycling applications. The second is the data-based modelling of such reactive extrusion processes. Polyethylenes (high density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHMWPE)) were extruded in a corotating twin-screw extruder under high temperatures (350 °C < T < 420 °C) for various process conditions (flow rate and screw rotation speed). These process conditions involved a decrease in the molecular weight due to degradation reactions. A numerical method based on the Carreau-Yasuda model was developed to predict the rheological behaviour (variation of the viscosity versus shear rate) from the in-line measurement of the die pressure. The results were successfully compared to the viscosity measured from offline measurement assuming the Cox‑Merz law. Weight average molecular weights were estimated from the resulting zero-shear rate viscosity. Furthermore, the linear viscoelastic behaviours (Frequency dependence of the complex shear modulus) were also used to predict the molecular weight distributions of final products by an inverse rheological method. Size exclusion chromatography (SEC) was performed on five samples, and the resulting molecular weight distributions were compared to the values obtained with the two aforementioned techniques. The values of weight average molecular weights were similar for the three techniques. The complete molecular weight distributions obtained by inverse rheology were similar to the SEC ones for extruded HDPE samples, but some inaccuracies were observed for extruded UHMWPE samples. The Ludovic® (SC-Consultants, Saint-Etienne, France) corotating twin-screw extrusion simulation software was used as a classical process simulation. However, as the rheo-kinetic laws of this process were unknown, the software could not predict all the flow characteristics successfully. Finally, machine learning techniques, able to operate in the low-data limit, were tested to build predicting models of the process outputs and material characteristics. Support Vector Machine Regression (SVR) and sparsed Proper Generalized Decomposition (sPGD) techniques were chosen to predict the process outputs successfully. These methods were also applied to material characteristics data, and both were found to be effective in predicting molecular weights. More precisely, the sPGD gave better results than the SVR for the zero-shear viscosity prediction. Stochastic methods were also tested on some of the data and showed promising results.

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“Tying the Knot”: Enhanced Recycling through Ultrafast Entangling across Ultrahigh Molecular Weight Polyethylene Interfaces

Cited by 19 publications

References 59 publications

Additive Manufacturing of Polyolefins

Additive Manufacturing of Polyolefins

Research on Chain Diffusion and Entanglement via Controlling the Sintering Process of Nascent UHMWPE

Data-Driven Modelling of Polyethylene Recycling under High-Temperature Extrusion

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