Traditional Extrusion Research Articles

Polymer microsphere inks for semi-solid extrusion 3D printing at ambient conditions

Extrusion-based 3D printing methods have great potential for manufacturing of personalized polymer-based drug-releasing systems. However, traditional melt-based extrusion techniques are often unsuitable for processing thermally labile molecules. Consequently, methods that utilize the extrusion of semi-solid inks under mild conditions are frequently employed. The rheological properties of the semi-solid inks have a substantial impact on the 3D printability, making it necessary to evaluate and tailor these properties. Here, we report a novel semi-solid extrusion 3D printing method based on utilization of a Carbopol gel matrix containing various concentrations of polymeric microspheres. We also demonstrate the use of a solvent vapor-based post-processing method for enhancing the mechanical strength of the printed objects. As our approach enables room-temperature processing of polymers typically used in the pharmaceutical industry, it may also facilitate the broader application of 3D printing and microsphere technologies in preparation of personalized medicine.

Coordinated deformation characteristics and its effect on microstructure evolution of LA103Z Mg-Li alloy in reciprocating rotary extrusion

The uneven metal flow and inhomogeneous microstructure on the cross-section of the extruded bar are mainly induced by the uncoordinated deformation during the traditional extrusion process, which seriously restricts its production and application. These defects are more prominent for the dual-phase Mg-Li alloy due to the phase transformation and the difference in flow between soft and hard phases. In order to solve the uncoordinated deformation in traditional extrusion, the reciprocating rotary extrusion (R-RE) process based on harmonic oscillation of die is proposed. The experiment and numerical simulations of the reciprocating rotary extrusion process were carried out at rotating frequency of 2.5 and 5 Hz, extrusion velocity of 1 mm/s, forming temperature of 290℃, die extrusion ratio of 12 and die rotating angle of ±6°. The coordinated deformation mechanism from macroscopical flow and microstructure in reciprocating rotary extrusion was investigated deeply. Meanwhile, a novel theoretical method was proposed to describe coordinate deformation characteristics quantitatively. The results indicated that the reciprocating rotary extrusion significantly reduces the forming load and accumulates more strain. The more uniform metal flow contributes to coordinated deformation. The extrusion deformation factors are proposed to reveal the coordinated deformation mechanism. In addition, the deformation body characteristic zone is novelly divided into six zones by combination of flow pattern and microstructure evolution.

An innovative approach for overcoming challenges in the stacked extrusion forming of Mg/Al composite plates

This study successfully produced Mg/Al composite plates with Cu transition layer, thus overcoming the limitations of traditional stacked extrusion methods in achieving satisfactory bonding of Mg/Al laminates. The relationship between the microstructure and mechanical properties of composite plates under three extrusion temperatures was revealed, and the deformation process and failure modes of composite plates were investigated. Microstructure observations revealed that the Cu layer exhibited a discontinuous distribution characteristic, and its thicker area effectively impeded the diffusion of Mg and Al elements, thus inhibiting the formation of Mg-Al intermetallic compounds (IMCs). The extrusion temperature did not significantly affect the distribution of the precipitates and texture in the Mg/Al layers. The grain size of the Mg layer showed a growing tendency with rising extrusion temperature, while that of the Al layer remained relatively constant. Mechanical results indicated that the strength of the composite plates decreased as the extrusion temperature increased, which was attributed to the weakening of fine grain strengthening in the Mg layer and dislocation strengthening in the Al layer. Additionally, higher extrusion temperature markedly reduced the elongation of the composite plate, potentially due to accelerated element diffusion at the interface and the discontinuous distribution of the Cu layer, resulting in significant enrichment of IMCs. The Mg-Cu IMCs accumulated and formed in the thicker Cu layer areas, along with Mg-Al IMCs formed in the weaker Cu layer areas, served as crack sources, resulting in cracking of the composite plate during the tensile and eventual failure.

Material compatibility and processing challenges in droplet deposition modelling additive manufacturing: A study on pharmaceutical excipients Polyvinylpyrrolidone/vinyl acetate (PVP/VA) and Polycaprolactone (PCL)

Additive manufacturing (AM) enables the production of complex, lightweight, and customized components with superior quality. Selecting the right materials considering their thermal properties, printability, and layer adhesion is crucial in melting-based AM techniques. This study investigates Droplet Deposition Modelling (DDM), an innovative material extrusion process that utilizes thermoplastic granules. DDM is distinguished by its shorter manufacturing times and a wider range of materials, setting it apart from traditional material extrusion methods such as fused filament fabrication. We investigated the printability and part quality in DDM using two common pharmaceutical excipients: Polyvinylpyrrolidone/vinyl acetate 6:4 (PVP/VA), which is highly brittle, and Polycaprolactone (PCL), known for its low solubility and role in controlled drug release. Different ratios of PVP/VA and PCL were compounded via hot melt extrusion (HME) and used in DDM to study the impact of ingredient content on printability and part quality, employing geometrical models to assess material compatibility and printability. The study revealed that increasing PVP/VA content leads to higher viscosity, reduced flowability, and uneven deposition, with formulations of 80 % and 100 % PVP/VA showing poor processability. In contrast, formulations with 60 % and 40 % PVP/VA exhibited smooth processing and compatibility with DDM. We identified processing temperature and Drop Aspect Ratio (DAR) as key factors influencing material printability and part quality. Elevated processing temperatures and reduced DAR were found to increase interface temperatures, reduce diffusion, and potentially cause the 'elephant feet' issue. Additionally, smaller droplet sizes and material characteristics, such as higher interfacial tension in PCL, could lead to coalescence. Our findings highlight the complexities in optimizing DDM processing parameters and material blends, underscoring the need for careful formulation design to achieve high-quality 3D printed products.

Effects of broken β-Mg17Al12 and non-uniform Mg2Pb particles introduced by EX-ECAP on microstructure and mechanical properties of Mg–Pb-9.2Al-0.8B alloys

Mg–Pb-9.2Al-0.8B alloy faces a significant strength-toughness balance problem in applications. To address this challenge, severe plastic deformation was applied to the alloy by combining traditional extrusion with multi-pass equal channel angular pressing (EX-ECAP). The research delves into the microstructural evolution (including broken β-Mg17Al12 and non-uniform Mg2Pb particles) and its effects on the strengthening mechanisms. The synergistic effects of grain boundary strengthening due to grain refinement, Orowan strengthening, geometrically necessary dislocation strengthening, and coefficient of thermal expansion strengthening collectively enhance the tensile strength and ductility, balancing the strength and toughness. The results showed an impressive ultimate tensile strength of 386.1 MPa, which is 2.33 times that of the as-cast alloy. The altered fracture morphology clearly indicated a transformation from brittle to brittle-ductile fracture mode. During the deformation process, the activation of dislocations, atomic-scale ripples, minor lattice distortions, and kink bands enhance the macroscopic flexibility. The introduction of EX-ECAP presents new opportunities for manufacturing high-performance Mg–Pb-9.2Al-0.8B alloy through integrated deformation techniques.

Hybrid coaxial 3D printing with nested-screw mechanism: Optimizing material integration and structural performance for coaxial designs

The emergence of multi-material extrusion systems has opened up new possibilities for 3D printing, spurring research on the combination of diverse materials and structures to enhance part quality and performance. In this work, a nested-screw coaxial co-extrusion 3D printing mechanism was designed for hybrid coaxial structures to address the viscosity matching limitation that is present in traditional coaxial extrusion. The high-viscosity shell material, with 3 wt% added carbon fiber, can be extruded and printed at room temperature. This suggests that the nested-screw can be used to adjust the high viscosity difference between the core and shell materials for co-extrusion. A model for coaxial extrusion was developed to establish appropriate printing parameters for the hybrid integration of materials and structures in coaxial designs. The resulting model for determining the printing parameters of the C-S structure improves dimensional stability and print repeatability. The coaxial printing was also employed to validate the bionic coaxial structure of antlers. The influence of the core-shell material and structure combinations on strength and toughness was thoroughly examined, enabling the optimization of structures with superior strength-toughness combinations. The comparative truss structure tests demonstrated that the core-shell structure enhanced damage absorption by 30.1 % compared to a single-structure design. This confirms the adjustability of mechanical properties in printed systems through a combination of hybrid materials and structure.

Polymeric field synergy principle: Revealing the intrinsic mechanism of screw channel optimization to enhance thermal management and process efficiency

The process efficiency and energy efficiency of extrusion equipment emerge as pivotal challenges constraining the development of the polymer extrusion industry. This article presents a new principle of polymeric field synergy to guide the solution to the low mixing efficiency and energy utilization efficiency of traditional extrusion equipment. Finite element analysis was conducted on four novel unconventional screw configurations and compared with the traditional single-thread screw. Results revealed that more complicated melt flow patterns generated in the modified novel screw configurations enhanced the stretching deformation or helical flow. The stretching or helical flows to varying degrees during the melt extrusion process thereby improved the mixing and heat transport efficiency. Among them, helical flow induced by the Maddock element exhibited the most significant impact on stretching flow and ductile deformation in the flow field. Simultaneously, the helical flow caused radial motion of the internal material, significantly promoting the synergy between the velocity field, velocity gradient field, and temperature gradient field. This enhanced radial heat and mass transport efficiency within the screw channel, subsequently improving the overall operational efficiency of the equipment. The results of the finite element analysis have substantiated the scientific validity of the polymeric field synergy principle.

UV-assisted robotic arm freeforming of SiOC ceramics from a preceramic polymer

Material extrusion is a very common and facile additive manufacturing technique for ceramic materials, allowing for rapid design and fabrication of 3D structures without expensive tools. However, fabricating sophisticated structures with large spanning parts and overhanging features using this technology is still a challenge. Here, UV-assisted additive manufacturing is enabled by performing material extrusion with the assistance of UV light using mixture of a preceramic polymer and a photopolymer. The rheological properties of the ink were investigated under UV light radiation to optimize the printing parameters to achieve excellent printability. Complex ceramic structures were fabricated with this method, such as spiral and truss structures, which would be very difficult to obtain using traditional material extrusion without sacrificial supports. These structures have potential application in lightweight ceramic components, such as sandwich structures.

High-ductility Mg-9Li-1Zn-2Gd-1.2Mn alloy prepared via traditional hot extrusion

The dual-phase Mg-9Li-1Zn-2Gd-1.2Mn alloys were prepared by traditional hot extrusion at 200 °C, 250 °C, and 300 °C, respectively. The microstructure of as-extruded Mg-9Li-1Zn-2Gd-1.2Mn alloy is remarkably refined, and the mechanical properties are significantly improved compared with the as-cast alloy. The Mg-9Li-1Zn-2Gd-1.2Mn alloy extruded at 200 °C exhibits the best comprehensive mechanical properties among the alloys with the yield strength (YS), ultimate tensile strength (UTS), and elongation to failure (εef) are 141 MPa, 166 MPa, and 57%, respectively. The dispersed second phases and Zn segregation along the grain boundary inhibit the growth of recrystallized grains and reduce the grain size, contributing to high ductility. Then, the unstable stacking fault energy of {0001}<11 2‾ 0> slip system (γusf(basal)) and surface energy of {0001} plane (γs(basal)) in Mg and Mg-Li-Gd-Zn supercells are characterized by first-principles calculation. The results indicated that the value of γusf(basal) decreased from 259 mJ/m2 to 249 mJ/m2, while the value of γs(basal) increased from 537 mJ/m2 to 597 mJ/m2. The lower γusf(basal) promotes the initiation of basal slip and higher γs(basal) leads to a lower cracking tendency, revealing the ductility improvement by adding Li, Zn, and Gd elements. This work provides an effective strategy to prepare high-ductility Mg-Li alloys.

3-D printed meat alternatives based on pea and single cell proteins and hydrocolloids: Effect of paste formulation on process-induced fibre alignment and structural and textural properties

Extrusion-based 3D food printing can be used as an alternative structuring technique to traditional extrusion processing for creating meat-like structures. This study focused on 3-D food printing to generate structures analogous to meat by using various combinations of texturized pea protein fibrils, microbial Single Cell Protein (SCP) and hydrocolloids locust bean gum and/or sodium alginate. Simple moulding was utilized as benchmarking to better understand the 3D printing-induced structural effects. To gain understanding of the interactions between proteins of different origin (plant and SCP) and with hydrocolloids, structural, textural and rheological properties were analysed. Oscillatory stress sweeps of all printing pastes revealed elastic-dominant rheological behaviour (G′ 4000–6000 Pa) with a defined yield stress (25–60 Pa) explaining their printability and shape stability. X-ray microtomography of ion-crosslinked analogues showed a printing-induced preferential alignment of fibrils in the direction of nozzle movement, while moulding led to a random orientation. Textural characterization via bi-directional cutting tests demonstrated higher cutting force in transversal (FT) over longitudinal (FL) direction in 3D-printed samples and equal forces in moulded samples. The anisotropy index (AI = FT/FL) of printed samples ranged between 1.4 and 2.5, indicating anisotropic texture, and 0.8–1 for moulded samples indicating isotropic texture. This study demonstrated the applicability of paste-extrusion in generating anisotropic structures analogous to meat by process-induced fibril alignment. The results support further development of 3D food printing technology in design of sustainable meat alternatives resembling whole-muscle meat.

Achieving high strength-ductility synergy in a dilute Mg-Gd-Zn-Zr alloy with heterogeneous structure via hot extrusion

The common problem of low tensile yield strength (TYS) prevails in high ductility dilute-alloying Mg-RE alloys prepared by traditional hot extrusion. The design strategy of heterostructures in the microstructure of Mg alloys can effectively improve the strength-ductility synergy in mechanical properties, which is expected to break the trade-off dilemma between strength and ductility. In this work, we successfully prepared a series of high ductility as-extruded Mg-Gd-Zn-Zr alloys with all elongations (ELs) greater than 26.0% at room temperature. By controlling the extrusion process and thus introducing heterogeneous fiberous structure, we finally obtained a superior Mg-1.5Gd-0.5Zn-0.5Zr (wt.%) alloy with strength-ductility synergy, which exhibits a TYS of 246 MPa, ultimate tensile strength (UTS) of 274 MPa and an EL of 29.0%. The microstructure examination for the alloy with the heterostructure reveals that the structure consists of alternating filamentous deformed-grain and fine-grain layers. The overall fine grains in the microstructure, a large amount of nanoprecipitates and the relatively high density of residual dislocations contribute to the high TYS of the alloy. The alloy maintaining high ductility is attributed to the activation of multiple slip systems, especially the active and mobile <c+a> dislocations, the inhibition of the P-type dislocation to B-type dislocation transition, {10 1¯ 2} tensile twinning generated early during tensile testing, and full intergranular slip transfers caused by high geometric compatibility. The present work can further promote the development of dilute-alloying Mg-RE alloys with high strength-ductility synergy.

The Principle of Steam Explosion Technology and Its Application in Food Processing By-Products.

Steam explosion technology is an emerging pretreatment method that has shown great promise for food processing due to its ability to efficiently destroy the natural barrier structure of materials. This narrative review summarizes the principle of steam explosion technology, its similarities and differences with traditional screw extrusion technology, and the factors that affect the technology. In addition, we reviewed the applications in food processing by-products in recent years. The results of the current study indicate that moderate steam explosion treatment can improve the quality and extraction rate of the target products. Finally, we provided an outlook on the development of steam explosion technology with a reference for a wider application of this technology in the food processing field.

Deformation Characteristics of Asymmetric Gradient Extrusion in Preparing Ultra-Fine-Grained Bulk Materials

In this paper, a novel method for the preparation of ultra-fine-grained bulk materials called asymmetric gradient extrusion (AGE) is proposed. In AGE, the cross-section of the extrusion channel is a rectangle, and two inclined planes are staggered along the extrusion direction. To realize repetitive extrusion, the thickness of the workpiece is limited to be equal to the width of the channel outlet. In order to study the mechanism of ultra-fine grain formation in AGE, the deformation characteristics of AGE were investigated. First, the slip line field method was used to theoretically analyze the deformation characteristics and grain splitting in AGE. Then, the plastic deformation behavior of bulk samples in AGE and traditional extrusion was investigated and compared with the finite element method. In addition, the deformation characteristic and microstructure variation of pure copper bulk samples in AGE were experimentally investigated. The results showed that the deformation characteristics of workpieces were highly related to the two inclined planes within the die channel. Two independent deformation zones can be formed with increasing distance between the two inclined planes. The shear effects in each deformation zone lead to grain splitting during extrusion. Compared with traditional extrusion, the advantage of AGE is its amazing ability to form high and uniform strain during extrusion, which leads to the formation of small and uniform grains in the workpiece. After six passes of AGE, an average grain size of 0.6 μm can be achieved. The enhancement and accumulation of dislocations within grains was the dominating mechanism of grain fragmentation. AGE shows impressive potential in the preparation of ultra-fine-grained bulk materials.

COMBINED EXTRUSION OF GLASSES WITH A CONICAL BOTTOM. EXPERIMENTAL VERIFICATION OF THEORETICAL FORMULAS IN COMBINED EXTRUSION

Cold combined extrusion of cups with a conical bottom part made of a hardening material is considered. The methods for performing specific calculations of the deforming force for various geometric parameters of free and constrained extrusion are demonstrated in detail. Comparison with the experimental data obtained during the extrusion of aluminum alloy AD1 shows the high accuracy of the derived calculation formulas. It is confirmed that for most of the working stroke, the force of the combined extrusion will be significantly less than the force of the traditional extrusion.

Improved Loading Capacity and Viability of Probiotics Encapsulated in Alginate Hydrogel Beads by In Situ Cultivation Method.

The objective of this research was to encapsulate probiotics by alginate hydrogel beads based on an in situ cultivation method and investigate the influences on the cell loading capacity, surface and internal structure of hydrogel beads and in vitro gastrointestinal digestion property of cells. Hydrogel beads were prepared by extrusion and cultured in MRS broth to allow probiotics to grow inside. Up to 10.34 ± 0.02 Log CFU/g of viable cell concentration was obtained after 24 h of in situ cultivation, which broke through the bottleneck of low viable cell counts in the traditional extrusion method. Morphology and rheological analyses showed that the structure of the eventually formed probiotic hydrogel beads can be loosed by the existence of hydrogen bond interaction with water molecules and the internal growth of probiotic microcolonies, while it can be tightened by the acids metabolized by the probiotic bacteria during cultivation. In vitro gastrointestinal digestion analysis showed that great improvement with only 1.09 Log CFU/g of loss in viable cells was found after the entire 6 h of digestion. In conclusion, the current study demonstrated that probiotic microcapsules fabricated by in situ cultivation method have the advantages of both high loading capacity of encapsulated viable cells and good protection during gastrointestinal digestion.

COMBINED EXTRUSION OF GLASSES WITH A CONICAL BOTTOM. EXPERIMENTAL VERIFICATION OF THEORETICAL FORMULAS FOR RESTRICTED TRADITIONAL EXTRUSION WITH STRENGTHENING

Cold constrained traditional extrusion of cups with a conical bottom made of a hardening material is considered. Methods for performing specific calculations of the deforming force for various geometric parameters of extrusion with a temperature effect are demonstrated in detail. Comparison with the experimental data obtained by extruding brass L63 and steel 12Kh18N9T shows the high accuracy of the derived calculation formulas.

COMBINED EXTRUSION OF GLASSES WITH A CONICAL BOTTOM. EXPERIMENTAL VERIFICATION OF THEORETICAL FORMULAS WITH FREE TRADITIONAL EXTRUSION WITH HARDENING

Cold free traditional extrusion of cups with a conical bottom made of a hardening material is considered. The methods for performing specific calculations of the deforming force for various geometric parameters of free extrusion are demonstrated in detail. Comparison with experimental data obtained by extrusion of aluminum alloy AD1 and brass L63 shows the high accuracy of the derived calculation formulas.

Improving the Yield of Feruloyl Oligosaccharides from Rice Bran through Enzymatic Extrusion and Its Mechanism

Rice bran, rich in feruloyl arabinoxylan, is a good source of feruloyl oligosaccharides (FOs). To prepare FOs, bran was often hydrolyzed by amylase and protease to remove starch and protein and then hydrolyzed by xylanase, which was time-consuming and had a low yield. To solve the above problems, enzymatic extrusion was used to treat rice bran, and the effects of traditional hydrolysis, a combination of traditional extrusion and hydrolysis (extrusion-hydrolysis) and enzymatic extrusion on the yield of FOs were investigated and compared in this study. It was found that traditional extrusion and enzymatic extrusion significantly increased the yield of FOs. Particularly, the yield of FOs resulting from enzymatic extrusion was increased to 5.78%, while the yield from traditional hydrolysis was 4.23%. Microscopy analysis showed that extrusion damaged the cell wall of bran, which might increase the accessibility of xylanase to arabinoxylan and the yield of FOs. Spectroscopy analysis suggested that FOs obtained by different pretreatments had similar structures. It was obvious that enzymatic extrusion saved the time for removal of starch and protein and increased the yield of FOs. In addition, the highest yield of FOs was found at the moisture content of 30% and the screw speed of 50 rpm. This study provided an efficient method for the preparation of FOs that is suitable for industrial production.

COMBINED EXTRUSION OF GLASSES WITH A CONICAL BOTTOM. EXPERIMENTAL VERIFICATION OF THEORETICAL FORMULAS IN TRADITIONAL EXTRUSION WITHOUT HARDENING

The necessity of experimental verification of the accuracy of the theoretical calculation of the force of traditional extrusion of glasses with a conical bottom is substantiated. The extrusion of a non-hardening material simulating hot deformation is considered. The methods for performing specific calculations of the deforming force for various extrusion geometric parameters, both for free and constrained extrusion, are demonstrated in detail. Comparison with the obtained experimental data shows the high accuracy of the derived calculation formulas.

Tailoring good combinations among strength, ductility and damping capacity in a novel Mg-1.5Gd–1Zn damping alloy via hot extrusion

Magnesium alloys with excellent comprehensive properties need to be developed due to the urgent demand in vibration and noise reduction or elimination fields. Herein, a novel high damping Mg-1.5Gd–1Zn alloy that exhibits strength and ductility similar to or even better than those of previously reported low-alloyed high-performance Mg-Gd-Zn alloys is developed by traditional hot extrusion. The specific results show that the good performance combinations of the as-extruded alloys are 314/211/145 MPa for the tensile yield strength (TYS), 21.0%/31.0%/33.0% for the elongation (EL) and 0.017/0.02/0.023 (at strain amplitude ε = 10−3) for the damping value Q−1 at room temperature. In addition, the damping curves for the tested as-extruded alloys exhibit three or two internal friction (IF) peaks during the elevated temperature damping test. Therefore, the resulting microstructures are systematically characterized in the as-extruded alloys. Meanwhile, the damping capacity and its mechanism are thoroughly analyzed and discussed. The alloy combines strength, ductility and damping capacity well, demonstrating its practicability in the reduction or elimination of noise and vibrations.