Draw Ratio Research Articles

DETERMINATION OF TECHNOLOGICAL CHARACTERISTICS OF PRESSABILITY

This article deals with the results of technological tests of pressability (Erichsen's - IE index and capping - limit drawing ratio (LDR)). It also presents on which material parameter (ductility, strain hardening exponent, coefficient of normal anisotropy...) should be given more emphasis when choosing a steel sheet, if stretching stress (uniaxial tension, biaxial tension) dominates during the production of stampings, or if dominates the “pull-pressure” technique (pulling out from under the flange).

Impact of molecular architecture and draw ratio on enhancement of targeted mechanical properties of machine direction oriented polyethylene films produced after blown film extrusion

Conventional multi-material multi-layer flexible packaging offers excellent properties. However, it has recycling challenges, necessitating a shift to mono-material multi-layer flexible packaging for example all-polyethylene (PE) packaging which can be tailored through various synthesis and processing methods for different layers. In this work, we study how the key molecular properties (number-average molecular weight ( Mn), weight-average molecular weight ( M w), molecular weight distribution (MWD), comonomer content (short chain branching)) and machine direction orientation (MDO) process draw ratio (MDX) influence the final morphology and mechanical properties of MDO-PE films which are intended as the outer layer of mono-material all-polyethylene multi-layer flexible packaging. Five PE grades and various blends were extruded and blown into films. Selected blown films were machine direction oriented to obtain the final MDO-PE films. Furthermore, one selected PE blown film was processed at different MDO process draw ratios while keeping other process parameters constant. From the molecular properties point of view, the higher molecular weight fractions provide a higher possibility for uniform stretching whereas lower molecular weight fractions provide a higher natural draw ratio and therefore higher modulus and stiffness enhancement. Further, the results show that increasing MDO process draw ratio leads to more fibrillation and increased crystallinity. Consequently, the tensile modulus and stiffness at the higher draw ratios increase as well and are comparable to conventionally used polymers in outer layers of multilayer flexible packaging. Thus, this work demonstrates that MDO-PE films with enhanced modulus can provide sufficient stiffness for the design of outer layer of mono-material multi-layer all-PE packaging which presents higher potential for mechanical recyclability.

Evaluating the Hydrothermal Stability of Superbase-Based Ionic Liquids in Cellulose Fiber Spinning.

This study highlights the substantially improved hydrothermal stability of 7-methyl-1,5,7-triazabicyclo[4.4.0] dec-5-enium [mTBDH]+ in [mTBDH][MeOCH2COO] compared to [mTBDH][OAc], as well as the strong cellulose dissolution capability of [mTBDH][MeOCH2COO] and excellent spinnability with a maximum draw ratio of 14. These findings demonstrate the high potential of using [mTBDH][MeOCH2COO] as the solvent to advance Ioncell fiber spinning technology by reducing the hydrolysis rate of [mTBDH]+, thereby minimizing loss during solvent recycling processes.

Dual-mode draw resonance instability regulated by concentration fluctuation in the polymer solutions casting

Based on the two-fluid model, we successfully simulated the film casting process of the polymer solution system and observed the unique response wave of the film thickness and the concentration via applying perturbation. We identify that this instability pattern is essentially the product under the coupling effect of viscoelastic stress and osmotic pressure from fluctuations on different scales, which causes it to exhibit biperiodic characteristics. We call this new instability mode known as dual-mode draw resonance instability. Among them, the concentration oscillation predominates, thereby limiting the critical draw ratio Drc of the system. Through sorting out the molecular image of the polymer concentration response to perturbation, the relevant parameters are extracted, and the law of their influence on the Drc further verifies our conclusion and provides guidance for actual production.

Poly(l-lactic acid) Janus Shape Memory Membranes with Uniform Vertically Penetrative Channels and Slit Pores for Enhanced Fog Collection: Synergistic Effect of Transport through Membranes and Sequential Sliding Behaviors of Water Droplets.

In this work, poly(l-lactic acid) (PLLA) Janus shape memory membranes with uniform vertically penetrative channels (SMEUVs) with slit pores have been fabricated with the help of template-assisting spray-coating and uniaxial tension at high temperature. During fog collection, superhydrophobic and hydrophilic surfaces act as the front (fog-facing) side and back side, respectively, in which the structural characteristics play essential roles. On one hand, the vertically penetrative channels in SMEUVs and the special pore geometry contribute to lower resistance, accelerating the transport of captured water through membranes (from the superhydrophobic side to the hydrophilic side). On the other hand, the movement of water droplets along the back side has been guided by the oriented structures of slit pores, promoting the detachment of droplets from the hydrophilic surface. Their synergistic effect removes captured water in a timely manner and provides fresh sites for the subsequent nucleation of water, enhancing fog collection performance. As a result, the optimal specimen (Janus SMEUVs with a draw ratio of 2.5, placed in the parallel direction) exhibits a much higher water collection rate (∼6×) relative to references (superhydrophobic and hydrophilic membranes). Our results are significant for sustainable development in view of both fog collection in arid regions and the biodegradability of PLLA.

Exploring interfacial tension role in the laminar morphology development in reactive compatibilized PP/EVOH

AbstractLaminar-like structures in PP/EVOH (80/20 wt%) blends were developed by in situ reactive compatibilization using a co-rotating intermeshing twin-screw extrusion without the imposition of post-die-forming elongation flows, i.e., draw ratio (DR) = 0. For that, a maleic anhydride-grafted homopolymer polypropylene (PP-g-MA) was added at 1, 1.5, and 3 wt% using a simple mixing protocol. The correlation between the laminar morphology observed via SEM with interfacial parameters was conducted by nonlinear regression of PP/EVOH viscoelastic response (Gʹ and Gʹʹ) applying the Monomodal Palierne Model to estimate interfacial tension. Uncompatibilized PP/EVOH formed a droplet-matrix morphology with high interfacial tension, indicating incompatibility. As PP-g-MA is added, a laminar-like structure is developed. The remaining droplets become smaller at higher content, with lower interfacial tension between the phases. This scenario hampers the stratification of the dispersed phase. At 3 wt% of PP-g-MA, the morphology returns to being a droplet-matrix, although with high adhesion between the phases. Graphical abstract

Drawing of fibres composed of shear-thinning or shear-thickening fluid with internal holes

We explore the drawing of a shear-thinning or shear-thickening thread with an axisymmetric hole that evolves due to axial drawing, inertia and surface tension effects. The stress is assumed to be proportional to the shear rate raised to the $n$ th power. The presence of non-Newtonian rheology and surface tension forces acting on the hole introduces radial pressure gradients that make the derivation of long-wavelength equations significantly more challenging than either a Newtonian thread with a hole or shear-thinning and shear-thickening threads without a hole. In the case of weak surface tension, we determine the steady-state profiles. Our results show that for negligible inertia the hole size at the exit becomes smaller as $n$ is decreased (i.e. strong shear-thinning effects) above a critical draw ratio, but surprisingly the opposite is true below this critical draw ratio. We determine an accurate estimate of the critical draw ratio and also discuss how inertia affects this process. We further show that the dynamics of hole closure is dominated by a different limit, and we determine the asymptotic forms of the hole closure process for shear-thinning and shear-thickening fluids with inertia. A linear instability analysis is conducted to predict the onset of draw resonance. We show that increased shear thinning, surface tension and inlet hole size all act to destabilise the flow. We also show that increasing shear-thinning effects reduce the critical Reynolds number required for unconditional stability. Our study provides valuable insights into the drawing process and its dependence on the physical effects.

Prediction of micro/meso scale forming limit for metal foils using a simple criterion

Accurately forecasting the forming limit of metal foils is essential in their micro-forming due to the appearance of necking failure easily. In order to accurately and easily forecast the forming limit of metal foils influenced by size effect, an idea for failure modeling of metal foils using the mechanism that different fracture modes of metal foils are related to shear bands is presented in this work. Based on the idea, a simple ductile failure criterion that considers the maximum shear stress and grain size effect but excludes the stress triaxiality is proposed, motivated by the demand to decrease the complexity of parameter calculation tests in micro-forming failure prediction. The proposed criterion and another criterion called as the μ-DF2022 model are applied to capture the forming limit curves of various thick copper and 304 stainless steel foils with different grain sizes to verify its advantage and performance, and the corresponding mechanisms of their prediction capabilities are also elucidated. Furthermore, the proposed and μ-DF2022 models are applied to forecast the limit drawing ratio of a 304 stainless steel foil to further show its performance and advantage in real micro-forming. The applications show that the proposed failure criterion effectively forecasts the forming limit of metal foils between equi-biaxial tension and uniaxial tension influenced by size effect. Moreover, the prediction accuracies using the proposed model and the μ-DF2022 model are comparable, whereas the proposed model does not require complex micro equi-biaxial tension tests, which are typically unavailable to many engineers and researchers, to calibrate its material parameters. Therefore, it is recommended to utilize the proposed criterion to capture the forming limit of metal foils in micro-forming. This work advances the forming limit modeling method of metal foils and provides insight into the application of uncoupled ductile failure criteria in the micro-forming of metal foils, which contributes to the development of their optimal micro-forming processes.

Effect of draw ratio and triggering temperature on properties of hydrothermal responsive shape memory microcomposite filaments

Effect of draw ratio and triggering temperature on properties of hydrothermal responsive shape memory microcomposite filaments

Poly(ethylene 2,5-furandicarboxylate) pole figures to determine the microstructural scheme upon uniaxial stretching: Link between orientation and crystallisation

The emergent biobased polymer poly (ethylene 2,5-furandicarboxylate), PEF, has been studied through an innovative approach based on pole figures and orientation factor calculation. PEF uniaxial stretching was performed with different mechanical conditions (different equivalent strain rates), up to several levels of strain and while considering different post-stretching cooling conditions (interrupted, unloaded and ruptured samples). Samples were stretched and interrupted before and after the Natural Draw Ratio (NDR), the deformation for which the material starts strain-hardening. When PEF strain-hardens, it reveals both an increase of the crystalline orientation and crystallinity ratio with the deformation imposed. Unloading the material at temperature tends to decrease partially crystalline orientation, especially regarding the aliphatic part of the chains. Moreover, stretching PEF up to high strains, superior to the NDR, leads to crystal fragmentation. After all, all experimental results were compared to a texture model. It appears that a texture can be developed upon stretching that is close to a fibre texture, as the furan cycles tend to be parallel to the specimen plane.

Effect of the crystal orientation on the enzymatic degradation rate of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) fibers

In this study, the relationship between the crystal orientation and enzymatic degradation rate of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) was investigated. The enzymatic degradation rates of melt-spun PHBH fibers were quantified via PHB depolymerase from Ralstonia pickettii T1, and the degradation rate decreased with increasing drawing ratio. The solid structure was investigated via differential scanning calorimetry and small-angle X-ray scattering, and kinetic analysis was performed, indicating that the degradation rate was affected not only by crystallinity and lamellar thickness but also by highly ordered structure. The highly ordered structure was examined via wide-angle X-ray diffraction. The enzymatic degradation rate from the fiber cross-sections was then quantified for the first time, and it increased with drawing ratio and was larger than that from the fiber sides. This result showed that the degradation rate varied depending on the crystal orientation. Furthermore, an enzymatic degradation test of PHBH ring-banded spherulites was conducted, and it was found that the degradation rate of flat-on lamellar crystals was greater than that of edge-on lamellar crystals. This is the first study to quantitatively evaluate the relationship between the crystal orientation and the enzymatic degradation rate.

The feasibility and rationale for utilizing high molecular weight PBT in the preparation of high-strength fiber

Polyethylene terephthalate (PET) industrial yarn is prone to damage during weaving due to its insufficient flexibility. Therefore, it is worth exploring whether polybutylene terephthalate (PBT) with improved flexibility can be utilized for the production of high strength and low modulus industrial yarn. In this study, a low velocity spinning multi-stage multi-ratio drawing technology route was employed for spinning, but PBT fibers only achieved a break strength of 5.1cN/dtex, which was lower than that of PET fibers (7.2cN/dtex). By comparing the multi-level structure evolution of PET and PBT during spinning, it was found that the core problem limiting the strength improvement of PBT fibers is due to the early formation of folded chain lamellar structure in PBT as-spun fibers during cooling, which hinders conformational transition during hot drawing and limits the drawing ratio. This has important implications for the development of PBT industrial yarn technology by adjusting the crystallization characteristics of PBT as-spun fibers.

Preparation and properties of phosphorus-containing thermotropic liquid crystal copolyester fibers with excellent flame retardance and mechanical property

In order to acquire polymeric fibers have both excellent flame retardance and mechanical properties, high molecular weight phosphorus-containing liquid crystal copolyesters derived from 6-hydroxy-2-naphthenic acid (HNA), terephthalic acid (TA) and 10-(2,5-dihydroxypheny)-10-hydro-9-oxa-10-phospha phenanthrene-10-oxide (DOPO-HQ) were synthesized via “one-pot” melt polymerization, and then the fibers were obtained by melt spinning method. The structure and property of the copolyesters were studied elaborately by experimental characterization technique and molecular simulation method. Shear shinning behavior was observed from rheology measurement, indicating that the copolyesters had excellent melt fluidity and spinnability. The rigidity of molecular chain was efficiently improved by the phosphorus-containing monomer DOPO-HQ and naphthalene HNA units which could be reflected by the molecular simulation results as well as high Tg values. The flame retardant mechanism of the phosphorus-containing flame retardant copolyester was systematically studied via limiting oxygen index (LOI), vertical burning (UL-94) test, cone calorimetry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the copolyesters exhibit synergistic flame retardant mechanism of gas phase and condensed phase. Meanwhile, mechanical property of the as-spun fibers could be significantly improved by increasing the spinneret draw ratio (SDR) attributed to high molecular chain orientation. The maximum tensile strength of the as-spun fiber was 0.77 GPa observed for P-HNA60P20 at a relatively low SDR of 29. It was shown the unique combination of good thermal stability, spinnability as well as mechanical and flame retardant properties of the copolyesters would make them could be used as high-performance flame retardant materials.

Effect of Viscosity and Air Gap within the Spinneret on the Morphology and Mechanical Properties of Hollow-Fiber Polymer Membranes for Separation Performance.

Hollow-fiber membranes for nanofiltration were prepared from the blending of Poly (ethylene glycol) (PEG) with Poly (vinyl chloride) (PVC) with different PEG molecular weights (400 and 4000 g/mol) and PVC via a dry/wet spinning process. In the spinning process, the effects of air gap, wind-up speed, dope extrusion rate, and bore extrusion rate were examined. In addition, the different lengths of the center tube, which acted as the inner-side fiber diameter during the preparation of hollow-fiber membranes, were studied. This research was investigated in order to observe the morphological, dielectric, and dynamic mechanical thermal properties to identify a suitable preparation of a hollow-fiber membrane for feasible applications. The morphology of the PVC-580 blended PEG-400 5 weight percent hollow-fiber membrane was seen to have a dense skin on both the inner and outer fiber surface, along with a suitable dope viscosity. Moreover, it offered finger-like substructures that could provide a high applicable feed-stream permeability and selectivity. Finger-like substructures were present on the near inner fiber surface at the controlled center-tube length of 0.3 cm, more so than at the center tube of 1 cm. This was because the solvent and non-solvent in the lumen tube exchanged more quickly than they did in the coagulant bath. The effect of the wind-up speed during the spinning process was significantly influenced by an affordable hollow fiber that can be indicated by the drawing ratio (λ). It was found that the drawing ratio of 3.3 showed a thickness thinner than 2.6 and 2.0, respectively. In summary, a controlled wind-up speed, an acceptable dope viscosity, and-most importantly-an agglomerated time resulted in membrane preparation.

Effect of CNT Oxidation on the Processing and Properties of Superacid-Spun CNT Fibers.

Spinning fibers from carbon nanotube (CNT)/superacid dispersions has emerged as a promising strategy for industrial-scale production of high-performance CNT fibers (CNTFs). The oxygen content and types of functional groups on CNT surfaces significantly influence dispersion, assembly processes, and fiber properties. In this study, Tuball-SWCNTs were purified and oxidized at varying levels. The dispersion behavior of CNTs with different oxidation levels in chlorosulfonic acid was systematically observed, and the mechanical properties of fibers spun from these dispersions were compared. By adjusting the dispersion concentration, highly oriented CNTFs were produced with a specific strength of 1.03 N/tex, a tensile strength of 1.59 GPa, and an electrical conductivity of 3.58 MS/m. Further investigations indicated that oxygen-containing functional groups decrease the coagulation rate, increasing the maximum draw ratio during spinning and improving CNT alignment in the fibers. Molecular dynamics simulations demonstrated that these functional groups (-OH, -COOH) enhance load transfer between CNTs through hydrogen bonding. This specific strength is the highest achieved using Tuball-SWCNTs for superacid-spun fibers, surpassing previous works due to the oxidation-controlled coagulation rate, enhanced fiber orientation, and improved load transfer via hydrogen bonding. This study provides insights for designing and optimizing high-performance CNTFs.

Excellent thermal conductive epoxy composites via adding UHMWPE fiber obtained by hot drawing method

AbstractThe continuous updating and iteration of electronic devices brings about a significant accumulation of heat. It is urgent to enhance the thermal properties of polymer‐based composites to alleviate the heat dissipation problem in the microelectronics industry. In this paper, the hot drawing process was introduced to increase the crystallinity of ultra‐high molecular weight polyethylene (UHMWPE) fiber and improve its thermal conductivity. The ultra‐high molecular weight polyethylene fiber/epoxy resin (UHMWPE fiber/Epoxy) composites with high thermal conductivity were prepared by compositing UHMWPE fiber with epoxy resin under vacuum conditions. Due to the good crystallinity of the UHMWPE fiber (86%), an efficient thermal conduction path is provided for phonons in the axial direction along the fibers. The results show that the thermal conductivity of the composites reaches a maximum of 3.51 W/mK (in‐plane), which is 17.47 times higher than that of the epoxy resin (0.19 W/mK). The thermography pictures indicate that the composites have better heat transfer capacity with an increase in the draw ratio (λ). In addition, the composites also have the characteristics of low density and low electrical conductivity. These researches will provide a new idea for the preparation of all‐polymer composites with high thermal properties.Highlights A hot drawing process was introduced to increase the crystallinity of UHMWPE fiber for improving thermal conductivity. High crystallinity facilitates the reduction of phonon scattering and the transmission of thermal energy by phonons. The obtained polymer composites exhibit an ultra‐high in‐plane thermal conductivity.

Revealing pore size distribution in cellulose and lignin-cellulose man-made fibers – effect of draw ratio and lignin content

There are limited methods available for measurement of the porosity of cellulose fibers, even more so for obtaining a pore size distribution. Conventional pore analysis methods require dry samples, with intact pores. However, pores in cellulose fibers collapse when dried from water and thus present a challenge for sample analysis. Furthermore, the pore collapse is partially irreversible which should be accounted for in the analysis. In this study, analysis of pore structure was carried out in the wet state with thermoporometry and also for critical point dried samples, analyzed with N2 sorption. This study determines the effect of fiber lignin content and certain spinning parameters on the pore size distribution of spun fibers before and after drying. It could also be concluded that solvent exchange, drying from a non-polar solvent will result in an altered pore size distribution, with a total pore volume greater than if dried from water, however not representative of the never-dried state. It is concluded that thermoporometry together with the water retention value (WRV) measurement is a powerful combination to acquire insights to the pore size distribution of spun fiber.

Scanning WAXS microscopy of regenerated cellulose fibers at mesoscopic resolution.

In this work, regenerated cellulose textile fibers, Ioncell-F, dry-wet spun with different draw ratios, have been investigated by scanning wide-angle X-ray scattering (WAXS) using a mesoscopic X-ray beam. The fibers were found to be homogeneous on the 500 nm length scale. Analysis of the azimuthal angular dependence of a crystalline Bragg spot intensity revealed a radial dependence of the degree of orientation of crystallites that was found to increase with the distance from the center of the fiber. We attribute this to radial velocity gradients during the extrusion of the spin dope and the early stage of drawing. On the other hand, the fiber crystallinity was found to be essentially homogeneous over the fiber cross section.

Effect of drawing and heat‐setting process on aggregate structure of Poly(ethylene terephthalate) industrial fiber in large‐scale spinning production

AbstractIt is a vital route to develop new fiber products with various physical‐mechanical properties by which their aggregation structure can be changed via controlling the spinning process parameters. In this study, five groups fiber samples had been obtained by changing the spinneret drawing ratio, two stages drawing ratio and two stages heat‐setting rate. The aggregation structure of the poly(ethylene terephthalate) (PET) industrial fibers from different spinning process was analyzed by combination use of thermal analysis, two‐dimensional wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and Infrared Spectroscopy (IR) measurements. It was found that, increasing the spinneret drawing ratio and two stages drawing ratio promoted the orientation and crystallinity within a certain range. For the subsequent two stages heat‐setting process, the disorientation of the amorphous chain is simulated by reducing the relaxation rate and heat setting temperature. Finally, a concise three‐dimensional structure model was established to explain the relationship between aggregation structure and property. These results have important reference for the structure and property analysis of polyester industrial fiber.

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.