Solid-state Drawing Research Articles

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.

Monofilaments of isosorbide-based tetrapolyesters with enhanced (bio)degradability prepared by a solid-state drawing process: Synthesis and struture-property relations

To enhance the degradation rate of poly (butylene adipate-co-terephthalate) (PBAT) in the natural environment and to investigate the effect of modified monomers on the molding and structure of copolyester fibers, a series of isosorbide modified PBAT (PBIAT) tetrapolyesters were synthesized and monofilaments were prepared by solid-state drawing in this work. The experimental results revealed that the introduction of isosorbide formed a partial block structure in the molecular chain, and that a significant improvement in the properties of heat resistance and degradability of the copolyester was observed with the introduction of isosorbide. In the research of fiber forming and structure-property relationship by isosorbide, it was found that although the monofilament orientation process was affected by the V-shape structure of isosorbide, the change of the crystal structure under stress was similar to that of polybutylene terephthalate (PBT). The PBIAT monofilaments showed a decrease in the strength at break affected by the introduction of isosorbide but they still met the requirements for textile applications.

Tailoring Structure-Dominated Mechanical Properties of Poly(L-Lactide Acid) Monofilaments via Controllable Molecular Relaxation

Controllable mechanical properties of highly performed Poly (L-lactide acid) (PLLA) monofilaments with oriented molecular structure could widen their applications, especially in biomedical field. Herein, different heat treatments were applied to regulate the degree of molecular relaxation of oriented PLLA monofilaments to tune their mechanical properties. These filaments were manufactured by melting spun and solid-state drawing processes. Then, they were processed by different heat treatments, including annealing, normalizing, and quenching. As the cooling time extension, an obvious molecular orientation loss in filaments happened and increased regularly, and it could reach up to about 35.1% maximumly. However, molecules only in crystal phase were limitedly affected. As a result, mechanical performances of these filaments exhibited a corresponding change after heat treatments. Young’s modulus and elongation at break were promoted after all kinds of post-processes and increased with longer cooling time gradually. But breaking strength showed a contrast change. It means that different heat treatments could be effective avenues to control mechanical properties of oriented PLLA materials by altering the orientation structure.

Self-Reinforced PTLG Copolymer with Shish Kebab Structures and a Bionic Surface as Bioimplant Materials for Tissue Engineering Applications.

Green and biodegradable materials with great mechanical properties and biocompatibility will offer new opportunities for next-generation high-performance biological materials. Herein, the novel oriented shish kebab crystals of a novel poly(trimethylene carbonate-lactide-glycolide) (PTLG) vascular stent are first reported to be successfully fabricated through a feasible solid-state drawing process to simultaneously enhance the mechanical performance and biocompatibility. The crystal structure of this self-reinforced vascular stent was transformed from spherulites to a shish kebab crystal, which indicates the mechanical interlocking effect and prevents the lamellae from slipping with a significant improvement of mechanical strength to 333 MPa. Meanwhile, it is different from typical biomedical polymers with smooth surface structures, and the as-obtained PTLG vascular stent exhibits a bionic surface morphology with a parallel micro groove and ridge structure. These ridges and grooves were attributed to the reorganization of cytoskeleton fiber bundles following the direction of blood flow shear stress. The structure and parameters of these morphologies were highly similar to the inner surface of blood vessels of the human, which facilitates cell adhesion growth to improve its proliferation, differentiation, and activity on the surface of PTLG.

Poly-lactic acid self-reinforcing composites with improved toughness utilising solid-state drawn oriented tape

With the increasing white pollution problem and the enhancement of people’s awareness of environmental protection, the bio-based and biodegradable polymers have received unprecedented attention. Poly-lactic acid (PLA) is considered as one of the most potential alternatives to petroleum-based polymer materials. However, Due to its inherent brittleness and the difficulties of post-disposal and recycling caused by traditional processing methods, PLA has not been fully accepted by the market. To overcome the issues, self-reinforcing PLA composites (SRPLA) were prepared with different PLA grades as the matrix and the reinforcement respectively. High toughness SRPLA were prepared by hot pressing using PLA3052 casting films as the matrix and PLA6202 oriented tapes fabricated by solid state drawing as the reinforcement. In addition, the toughening mechanism was analyzed. Mechanical tests showed that the strength, modulus and elongation at break were increased by 124.3%, 114% and 145.2% respectively compared with pure PLA hot pressed film. Particularly, the tensile toughness of SRPLA is more than 200% that of pure PLA. The interface debonding and tape pullout were the main toughening mechanisms.

Effect of Post-Drawing Thermal Treatment on the Mechanical Behavior of Solid-State Drawn Poly(lactic acid) (PLA) Filaments

In this work, two commercial extruded filaments for 3D printing obtained from different NatureWorks PLA resins (Ingeo™ Biopolymer 3D850 and Ingeo™ Biopolymer 4043D) were solid-state drawn at varying temperatures and subsequently heat treated by annealing. The aim was to analyze the effect of post-processing of industrial fibers (solid-state drawing and annealing treatment) with varied composition (PLA grades with different contents of D-isomer) on the mechanical performance and thermal stability of the obtained PLA fibers. Morphological, thermal, and mechanical characterizations were performed for the undrawn filaments and drawn fibers, both before and after heat treatment. Drawn fibers presented a fibrillar core–shell structure, and their mechanical properties were greatly improved with respect to undrawn filaments in accordance with their higher crystallinity. The resin with the higher content of D-isomer (4043D) resulted in lower crystallinities with a subsequent decrease in mechanical properties. After heat treatment, drawn fibers exhibited completely different behaviors depending on the PLA resin, with 3D850 fibers being much more stable than 4043D fibers, which underwent molecular orientation upon drawing rather than crystallization. The solid-state drawn fibers obtained herein are comparable to commercial fibers in terms of mechanical properties.

Regulating mechanical performance of poly (l-lactide acid) stent by the combined effects of heat and aqueous media

Annealing process has been applied to the development of thermoforming polymer braided stent and treating its basic constitute monofilaments, especially for Poly (l-lactide acid) (PLLA) condensed by lactic acid monomer made from the plant starch. In this work, high performance monofilaments were produced by melting spun and solid-state drawing methods. Inspired by the effects of water plasticization on semi-crystal polymer, PLLA monofilaments were annealed with and without constraint in vacuum and aqueous media. Then, the co-effects of water infestation and heat on the micro-structure and mechanical properties of these filaments were characterized. Furtherly, mechanical performance of PLLA braided stents shaped by different annealing methods was also compared. Results showed that annealing in aqueous media generated more obvious structure change of PLLA filaments. Interestingly, the combined effects of aqueous phase and thermal effectively increased the crystallinity, and decreased the molecular weight and orientation of PLLA filaments. Therefore, higher modulus, smaller strength, and elongation at the break for filaments could be obtained, which could furtherly realize better radial compression resistance of the braided stent. This annealing strategy could provide new perspectives between anneal and material properties of PLLA monofilaments, and provide more suitable manufacturing technics for polymer braided stent.

High-performance and durable fibrous poly(glycolic acid)/poly(butylene adipate-co-terephthalate) blends by reactive compatibilization and solid-state drawing

The application of poly(glycolic acid) (PGA) is limited by its inherent brittleness and easy to hydrolysis. Herein, we demonstrate an effective strategy to make fibrous PGA/poly (butylene adipate-co-terephthalate) (PBAT) blends with high strength, toughness and better hydrolysis resistance by reactive compatibilization and subsequent solid-state drawing. The enhanced chain entanglement due to the compatibilization restricts the chain relaxation during drawing process, leading to a predominance of stress-induced orientation. Meanwhile, it also facilitates the immobilization and transformation of extended chains into rigid amorphous fraction (RAF). As a consequence, the combination of strong interfacial bonding, high orientation and abundant RAF results in superior comprehensive properties of the fibrous PGA/PBAT blends, e.g., the drawn compatibilized PGA/PBAT exhibit a tensile strength as high as 700 MPa and a tensile toughness of 385 MJ/m3. Moreover, the tensile strength retention of the drawn compatibilized PGA/PBAT is 20 % higher than uncompatibilized sample after hydrolysis for 5 days. Therefore, this work provides a feasible strategy to make robust and durable fibrous PGA-based blends, which may broaden the application range of PGA.

Optimization of thermoelectric properties of carbon nanotube veils by defect engineering.

Carbon nanotubes (CNTs), with their combination of excellent electrical conductivity, Seebeck coefficient, mechanical robustness and environmental stability are highly desired as thermoelectric (TE) materials for a wide range of fields including Internet of Things, health monitoring and environmental remediation solutions. However, their high thermal conductivity (κ) is an obstacle to practical TE applications. Herein, we present a novel method to reduce the κ of CNT veils, by introducing defects, while preserving their Seebeck coefficient and electrical conductivity. Solid-state drawing of a CNT veil embedded within two polycarbonate films generates CNT veil fragments of reducing size with increasing draw ratio. A successive heat treatment, at above the polycarbonate glass-to-rubber transition temperature, spontaneously reconnects the CNT veils fragments electrically but not thermally. Stretching to a draw ratio of 1.5 and heat repairing at 170 °C leads to a dramatic 3.5-fold decrease in κ (from 46 to 13 W m-1 K-1), in contrast with a decrease in electrical conductivity of only 26% and an increase in Seebeck coefficient of 10%. To clarify the mechanism of reduction in thermal conductivity, a large-scale mesoscopic simulation of CNT veils under uniaxial stretching has also been used. This work shows that defect engineering can be a valuable strategy to optimize TE properties of CNT veils and, potentially, other thermoelectric materials.

Dielectric polymer composites with ultra-high thermal conductivity and low dielectric loss

Polymer based dielectric materials with simultaneously high thermal conductivity and low dielectric loss are highly desirable in various applications like energy storage, thermal management and electronic packaging. Polymer dielectrics generally benefit from good electrical insulation, high breakdown strength, high toughness and low density but suffer from very low thermal conductivity (0.1–0.5 W m −1 K −1). Herein we propose a new strategy to overcome this compromise; solid-state drawing of ultra-high molecular weight polyethylene (UHMWPE) films doped with a small amount of nanodiamonds (NDs). The resulting orientation of UHMWPE macromolecules and the nanofiller significantly improves the thermal conductivity along the stretching direction, while the dodecane surface functionalization of the NDs endows a robust interface between the matrix and filler, which minimizes the thermal resistance and dielectric loss. Our composites film (2 wt% NDs) shows an ultra-high thermal conductivity of 60 W m −1 K −1 in the drawing direction and very low dielectric loss, both at low and high electric field. More generally, herein we demonstrates that the interfaces introduced by the nanofillers do not necessarily cause an increase in dielectric loss at high electric field and a decrease in thermal conductivity, providing a new direction for the design of novel polymer based dielectric and functional materials.

Development of drawn polypropylene-based blends and composites

We developed highly oriented polypropylene tapes with solid-state drawing, and studied the effect of additives—two grades of talc, low-density polyethylene (LDPE), and an amorphous poly-alpha-olefin (APAO). The PP compounds were prepared in a co-rotating twin-screw extruder, and sheet films were extruded. The specimens cut out from the sheet films were drawn in a tensile testing machine, and the drawing temperature of 130 °C was maintained by the heating chamber of the tensile testing machine. A draw ratio of λ=10 was set. We investigated the work of drawing and prepared DSC and tensile tests. Both types of talc acted as strong nucleating agents and increased the tensile strength and modulus of the tapes. APAO reduced the crystalline melting enthalpy only to a small extent. Both APAO and LDPE reduced the tensile strength and modulus and increased the strain at break of the tapes.

Improvement on the Mechanical Performance and Resistance Towards Hydrolysis of Poly(glycolic acid) via Solid-state Drawing

Improvement on the Mechanical Performance and Resistance Towards Hydrolysis of Poly(glycolic acid) via Solid-state Drawing

Fabrication of high-performance HDPE/CWPF blend film via the assistance of OBC and solid-state drawing

To achieving highly efficient reuse of commingled waste plastic films (CWPF) in high-density polyethylene (HDPE), elastomer-olefin block copolymer (OBC) was adopted to improve the compatibility between CWPF and HDPE, and solid-state drawing was further used to improve the mechanical properties of the blends. The results showed that OBC could form core-shell structure with CWPF, as a bridge layer to simultaneously connect CWPF and HDPE, and form epitaxial crystallization induced by HDPE crystals, thereby greatly enhancing the compatibility between CWPF and HDPE, and improving the tensile strength, elongation at break and impact strength of HDPE/CWPF blend. In the subsequent solid-state drawing, depending on the fluidity of OBC at the drawing temperature of 100 °C, more CWPF were covered, efficiently reducing the defects caused by CWPF along the transverse direction (TD) and increasing the elongation at break of the stretched sheet along this direction. With the increase of draw ratio, lamellae in fibril along TD and shish-kebab-like structure along the flow direction (FD) formed, greatly improving the tensile strength of the blend along both TD and FD. And the long period (Lp), amorphous region (La) and lateral dimension (Llateral) decreased, but lamella thickness (Lc) increased. This work provides good bases for obtaining novel and low-cost HDPE based material as well as high-effect recycling of CWPF.

Ultrarobust, hierarchically anisotropic structured piezoelectric nanogenerators for self-powered sensing

Despite significant efforts to develop piezoelectric nanogenerators (PENGs), scalable manufacture of polymeric PENGs with highly sensitive and stable piezoelectric output remains a great challenge. Here, we propose a noncovalent assembly-mediated solid-state drawing strategy for the electrical treatment-free fabrication of high-performance PENGs with hierarchically anisotropic structure. Along with the stress-induced anisotropic alignment of glycine modified-molybdenum disulfide nanosheets, the strong intermolecular interactions and confinement between 2D nanosheets and polyvinylidene fluoride (PVDF) dipoles can aggressively induce the self-polarized β-phase transition of PVDF in a favorable direction. The resulted nanocomposite without extra electrical treatment exhibits remarkable piezoelectric performance (d33 =24.9 pC N-1) and extraordinary mechanical performance (tensile strength of 213.3 MPa, toughness of 85.8 MJ m-3), far surpassing most reported polymeric piezoelectric materials. Taking these advantages, the PENGs-based self-powered physiological sensors show highly sensitive and stable output signals, satisfying the requirements of tiny and large human motions monitoring. This work opens an avenue toward large-area compliant and low-energy manufacturing of diverse energy harvesting devices and self-powered sensory systems.

Influence of Dispersion and Orientation on Polyamide-6 Cellulose Nanocomposites Manufactured through Liquid-Assisted Extrusion.

In this study, the possibility of adding nanocellulose and its dispersion to polyamide 6 (PA6), a polymer with a high melting temperature, is investigated using melt extrusion. The main challenges of the extrusion of these materials are achieving a homogeneous dispersion and avoiding the thermal degradation of nanocellulose. These challenges are overcome by using an aqueous suspension of never-dried nanocellulose, which is pumped into the molten polymer without any chemical modification or drying. Furthermore, polyethylene glycol is tested as a dispersant for nanocellulose. The dispersion, thermal degradation, and mechanical and viscoelastic properties of the nanocomposites are studied. The results show that the dispersant has a positive impact on the dispersion of nanocellulose and that the liquid-assisted melt compounding does not cause the degradation of nanocellulose. The addition of only 0.5 wt.% nanocellulose increases the stiffness of the neat polyamide 6 from 2 to 2.3 GPa and shifts the tan δ peak toward higher temperatures, indicating an interaction between PA6 and nanocellulose. The addition of the dispersant decreases the strength and modulus but has a significant effect on the elongation and toughness. To further enhance the mechanical properties of the nanocomposites, solid-state drawing is used to create an oriented structure in the polymer and nanocomposites. The orientation greatly improves its mechanical properties, and the oriented nanocomposite with polyethylene glycol as dispersant exhibits the best alignment and properties: with orientation, the strength increases from 52 to 221 MPa, modulus from 1.4 to 2.8 GPa, and toughness 30 to 33 MJ m−3 in a draw ratio of 2.5. This study shows that nanocellulose can be added to PA6 by liquid-assisted extrusion with good dispersion and without degradation and that the orientation of the structure is a highly-effective method for producing thermoplastic nanocomposites with excellent mechanical properties.

Experimental Investigation of Polypropylene Composite Drawn Fibers with Talc, Wollastonite, Attapulgite and Single-Wall Carbon Nanotubes.

Isotactic polypropylene (PP) composite drawn fibers were prepared using melt extrusion and high-temperature solid-state drawing at a draw ratio of 7. Five different fillers were used as reinforcement agents (microtalc, ultrafine talc, wollastonite, attapulgite and single-wall carbon nanotubes). In all the prepared samples, antioxidant was added, while all samples were prepared with and without using PP grafted with maleic anhydride as compatibilizer. Material characterization was performed by tensile tests, differential scanning calorimetry, thermogravimetric analysis and Fourier transform infrared spectroscopy. Attapulgite composite fibers exhibited poor results in terms of tensile strength and thermal stability. The use of ultrafine talc particles yields better results, in terms of thermal stability and tensile strength, compared to microtalc. Better results were observed using needle-like fillers, such as wollastonite and single-wall carbon nanotubes, since, as was previously observed, high aspect ratio particles tend to align during the drawing process and, thus, contribute to a more symmetrical distribution of stresses. Competitive and synergistic effects were recognized to occur among the additives and fillers, such as the antioxidant effect being enhanced by the addition of the compatibilizer, while the antioxidant itself acts as a compatibilizing agent.

Tensile properties and fracture behavior of carbon nanotube-sheets/carbon fibers epoxy-impregnated bundle composites

An interesting technique for modifying carbon fiber-reinforced polymer matrix composites is through hybridization with carbon nanotubes (CNTs). Carbon nanotubes sheets/carbon fibers offer potential benefits of nanoscale reinforcement to the well-established fibrous composites by creating multiscale hybrid micro-nano composites. In this study, the tensile properties of high tensile strength polyacrylonitrile (PAN)- and high modulus pitch-based carbon fiber-reinforced polymer matrix composites incorporating CNT sheets (CNT-sh/CFs/Ep-H: CNT sheets/carbon fibers/epoxy hybrid composites) were investigated. To fabricate CNT sheets, CNT was vertically grown on a quartz glass plate by chemical vapor deposition. A solid-state drawing and winding technique was applied to transform the vertically aligned CNT array into horizontally aligned CNT sheets. The tensile modulus of the CNT-sh/CFs/Ep-H was higher than that of the composite in the as-received state (CFs/Ep: carbon fibers/epoxy bundle composite). The tensile strength of the CNT-sh/PAN-based CF/Ep-H was lower than that of the PAN-based CF/Ep, whereas the tensile strength of the CNT-sh/pitch-based CF/Ep-H was higher than that of the pitch-based CF/Ep.

Orientation of Polylactic Acid-Chitin Nanocomposite Films via Combined Calendering and Uniaxial Drawing: Effect on Structure, Mechanical, and Thermal Properties.

The orientation of polymer composites is one way to increase the mechanical properties of the material in a desired direction. In this study, the aim was to orient chitin nanocrystal (ChNC)-reinforced poly(lactic acid) (PLA) nanocomposites by combining two techniques: calendering and solid-state drawing. The effect of orientation on thermal properties, crystallinity, degree of orientation, mechanical properties and microstructure was studied. The orientation affected the thermal and structural behavior of the nanocomposites. The degree of crystallinity increased from 8% for the isotropic compression-molded films to 53% for the nanocomposites drawn with the highest draw ratio. The wide-angle X-ray scattering results confirmed an orientation factor of 0.9 for the solid-state drawn nanocomposites. The mechanical properties of the oriented nanocomposite films were significantly improved by the orientation, and the pre-orientation achieved by film calendering showed very positive effects on solid-state drawn nanocomposites: The highest mechanical properties were achieved for pre-oriented nanocomposites. The stiffness increased from 2.3 to 4 GPa, the strength from 37 to 170 MPa, the elongation at break from 3 to 75%, and the work of fracture from 1 to 96 MJ/m3. This study demonstrates that the pre-orientation has positive effect on the orientation of the nanocomposites structure and that it is an extremely efficient means to produce films with high strength and toughness.

Oriented polylactic acid/graphene oxide nanocomposites with high mechanical and thermal properties

Oriented polylactic acid (PLA)/graphene oxide (GO) nanosheets tapes were prepared via uniaxial solid state drawing. The effect of various drawing conditions, including drawing ratio (DR), temperature (DT), and speed (DS) on mechanical, thermal, structural, and barrier properties were studied. Structural studies showed oriented structure for the drawn tapes with aligned polymer chains and GO nanosheets. Differential scanning calorimetry revealed improved glass transition temperature (Tg) and crystallinity (Xc) after drawing. In addition, Tg and Xc were increased more by increasing DR and DT. The highest Tg and Xc were achieved for 3/70/50 tape with values of 73°C and %22, respectively. Higher thermal stabilities and enhanced barrier properties were achieved after drawing, especially at the higher DR. Finally, tensile testing revealed simultaneous improvement in stiffness and toughness due to strain hardening for all the drawn tapes. The strength and elastic modulus were increased after increasing DR, DS, and DT and reached the highest values of 149 MPa and 3.6 GPa for 3/70/50. Overall, the properties were controllable by the processing conditions.

Poly(l-lactic acid) monofilaments for biodegradable braided self-expanding stent

Although poly(l-lactic acid) (PLLA) is the widely used material for bioresorbable stents, publications on PLLA braided stents are still lacking. In this paper, the PLLA monofilaments were prepared via melt spinning and solid-state drawing. The total draw ratios are from 2.8 to 30.8. The properties of the monofilaments, such as crystallinity, elastic modulus, elongation at break, were characterized. Due to the relatively good mechanical properties, PLLA monofilaments with draw ratio of 16.8 were used to braid carotid stents. The curve of the radial force of the braided PLLA stent almost overlaps with that of a Carotid Wallstent with similar parameters, which indicates that the braided PLLA stent can provide adequate support to the carotid lesion.