Showing papers on "Thermoplastic published in 2016"

Three-dimensional printing of continuous-fiber composites by in-nozzle impregnation.

Abstract: We have developed a method for the three-dimensional (3D) printing of continuous fiber-reinforced thermoplastics based on fused-deposition modeling. The technique enables direct 3D fabrication without the use of molds and may become the standard next-generation composite fabrication methodology. A thermoplastic filament and continuous fibers were separately supplied to the 3D printer and the fibers were impregnated with the filament within the heated nozzle of the printer immediately before printing. Polylactic acid was used as the matrix while carbon fibers, or twisted yarns of natural jute fibers, were used as the reinforcements. The thermoplastics reinforced with unidirectional jute fibers were examples of plant-sourced composites; those reinforced with unidirectional carbon fiber showed mechanical properties superior to those of both the jute-reinforced and unreinforced thermoplastics. Continuous fiber reinforcement improved the tensile strength of the printed composites relative to the values shown by conventional 3D-printed polymer-based composites.

Lignin-Based Thermoplastic Materials

Abstract: Lignin-based thermoplastic materials have attracted increasing interest as sustainable, cost-effective, and biodegradable alternatives for petroleum-based thermoplastics. As an amorphous thermoplastic material, lignin has a relatively high glass-transition temperature and also undergoes radical-induced self-condensation at high temperatures, which limits its thermal processability. Additionally, lignin-based materials are usually brittle and exhibit poor mechanical properties. To improve the thermoplasticity and mechanical properties of technical lignin, polymers or plasticizers are usually integrated with lignin by blending or chemical modification. This Review attempts to cover the reported approaches towards the development of lignin-based thermoplastic materials on the basis of published information. Approaches reviewed include plasticization, blending with miscible polymers, and chemical modifications by esterification, etherification, polymer grafting, and copolymerization. Those lignin-based thermoplastic materials are expected to show applications as engineering plastics, polymeric foams, thermoplastic elastomers, and carbon-fiber precursors.

Infrared thermography of welding zones produced by polymer extrusion additive manufacturing

Abstract: In common thermoplastic additive manufacturing (AM) processes, a solid polymer filament is melted, extruded though a rastering nozzle, welded onto neighboring layers and solidified. The temperature of the polymer at each of these stages is the key parameter governing these non-equilibrium processes, but due to its strong spatial and temporal variations, it is difficult to measure accurately. Here we utilize infrared (IR) imaging – in conjunction with necessary reflection corrections and calibration procedures – to measure these temperature profiles of a model polymer during 3D printing. From the temperature profiles of the printed layer (road) and sublayers, the temporal profile of the crucially important weld temperatures can be obtained. Under typical printing conditions, the weld temperature decreases at a rate of approximately 100 °C/s and remains above the glass transition temperature for approximately 1 s. These measurement methods are a first step in the development of strategies to control and model the printing processes and in the ability to develop models that correlate critical part strength with material and processing parameters.

Bio-based polycarbonate as synthetic toolbox

Abstract: Completely bio-based poly(limonene carbonate) is a thermoplastic polymer, which can be synthesized by copolymerization of limonene oxide (derived from limonene, which is found in orange peel) and CO2. Poly(limonene carbonate) has one double bond per repeating unit that can be exploited for further chemical modifications. These chemical modifications allow the tuning of the properties of the aliphatic polycarbonate in nearly any direction. Here we show synthetic routes to demonstrate that poly(limonene carbonate) is the perfect green platform polymer, from which many functional materials can be derived. The relevant examples presented in this study are the transformation from an engineering thermoplastic into a rubber, addition of permanent antibacterial activity, hydrophilization and even pH-dependent water solubility of the polycarbonate. Finally, we show a synthetic route to yield the completely saturated counterpart that exhibits improved heat processability due to lower reactivity.

All‐Polystyrene 3D‐Printed Electrochemical Device with Embedded Carbon Nanofiber‐Graphite‐Polystyrene Composite Conductor

Abstract: Carbon nanofibres (CNFs) and graphite flake microparticles were added to thermoplastic polystyrene polymer with the aim of making new conductive blends suitable for 3D-printing. Various polymer/carbon blends were evaluated for suitability as printable, electroactive material. An electrically conducting polystyrene composite was developed and used with commercially available polystyrene (HIPS) to manufacture electrodes suitable for electrochemical experiments. Electrodes were produced and evaluated for cyclic voltammetry of aqueous 1,1’-ferrocenedimethanol and differential pulse voltammetry detection of aqueous Pb2+ via anodic stripping. A polystyrene/CNF/graphite (80/10/10 wt%) composite provides good conductivity and a stable electrochemical interface with well-defined active geometric surface area. The printed electrodes form a stable interface to the polystyrene shell, give good signal to background voltammetric responses, and are reusable after polishing.

Preparation of starch/acrylonitrile-butadiene-styrene copolymers (ABS) biomass alloys and their feasible evaluation for 3D printing applications

Abstract: With debranching and plasticization of starches, we have successfully prepared thermoplastic starches (TPS) with high processibility by a twin-screw extruder. Afterwards, the TPS have blended with appropriate amounts of acrylonitrile-butadiene-styrene copolymers (ABS), compatibilizers, impact modifiers, and pigments to compound in a twin-screw extruder, manufacturing TPS/ABS biomass alloys. Finally, we have prepared white and black filaments, whose diameters of 1.75 mm, for additive manufacturing (AM) with TPS/ABS biomass alloys by a single-screw extruder as well as proper mold and also executed their measurement of physical properties. In addition, their feasible evaluation for 3D printing applications has also been made. Experimental results reveal that physical properties of lab-made white and black filaments (i.e. mechanical properties, thermal resistance, flowability, and emissions of volatile organic compounds (VOCs)) are superior to those of commercial ABS filaments and the shaping samples for 3D printing have also been successfully fabricated, preliminarily demonstrating that they are potential biomass polymeric materials with excellent physical performances and high processibility for 3D printing utilizations.

Reinforced fused-deposition modeling

Abstract: An apparatus for manufacturing an object includes an extrusion head having an extrusion needle for extruding thermoplastic material associated with one or more fiber strands. The apparatus may further include a turn-table, a more robotic arm for moving the extrusion head and needle, thermoplastic filament and fiber strand spools and thermoplastic filament and fiber strands. A controller is provided for directing the robotic arm, extrusion head and the turn-table. Further, a method for manufacturing an object includes generating a design for the object that substantially satisfies desired structural properties of the object and generating a sequence for extruding one or more beads of thermoplastic material to manufacture the object according to the design, in which the one or more beads of thermoplastic material are associated with one or more fiber strands. The one or more beads of thermoplastic material and the associated one or more fiber strands are then extruded according to the sequence.

Controlled Chain Walking for the Synthesis of Thermoplastic Polyolefin Elastomers: Synthesis, Structure, and Properties

Abstract: Thermoplastic elastomers are attractive materials because of their ability to be melt-processed, reused, and recycled, unlike chemically cross-linked elastomers such as rubber. We report the synthesis and mechanical properties of polyolefin-based thermoplastic elastomer block copolymers. A simple one-pot procedure is employed, using a living arylnaphthyl-α-diimine Ni(II) “sandwich” complex to generate high crystallinity hard blocks from 1-decene and low crystallinity soft blocks from ethylene. Various block structures are accessed, ranging from a diblock up to a heptablock copolymer. Statistical copolymers of 1-decene and ethylene are also synthesized for comparison. All resulting polymers behave as elastomers, with properties that modulate with hard and soft block composition, block architecture, and polymerization solvent. Triblock copolymers demonstrate strain at break values up to 750%, with elastic strain recoveries up to 85%. Interestingly, statistical copolymers demonstrate strain at break values u...

Impact damage tolerance of thermoset composites reinforced with hybrid commingled yarns

Abstract: This paper examines the potential of low-cost thermoplastic fibres in improving the impact damage resistance and damage tolerance of thermoset (glass-epoxy) composites. Polypropylene (PP) fibres, commodity fibres without any surface modifications, have been incorporated at tow-scale with the aid of air jet commingling process. Glass-PP hybrid yarns with varying proportion of PP fibres (0–35%) are converted into several non-crimp cross-ply laminates and a plain-woven laminate. Damage resistance in terms of damage area and depth are assessed for low energy (20–50 J) as well as high energy (500 J) drop-weight impacts; damage tolerance is assessed through Compression after Impact (CAI) tests. Overall density of the composite laminate has reduced by 16% due to the introduction of PP fibres; at the same time total absorbed energy has increased by 22% during a high velocity impact test due to a toughing mechanism by PP fibres. Non-crimp laminates absorbed more energy at low velocity impacts in comparison to woven laminates, possibly due to extensive tow-level delaminations. On the other hand, a much larger dent depth was observed in the woven laminate after low energy impact. Compression after Impact (CAI) tests indicated that woven laminates retained 83% of compressive strength while non-crimp laminates retained 50–60%, depending on proportion of thermoplastic fibres, and standard glass fibre laminates retain around 45%. Fibre damage has been significantly reduced during impact loading in case of hybrid laminates due to the cushioning effect offered by lower modulus PP fibres.

Thermoplastic Micro-Forming of Bulk Metallic Glasses: A Review

Abstract: Bulk metallic glasses are a fascinating class of metallic alloys with an isotropic amorphous structure that is rapidly quenched from liquid melts. The absence of a crystalline micro-structure endows them with a portfolio of properties such as high strength, high elasticity, and excellent corrosion resistance. Whereas the limited plasticity and hence poor workability at ambient temperature impede the structural application of bulk metallic glasses, the unique superplasticity within the supercooled liquid region opens an alternative window of so-called thermoplastic forming, which allows precise and versatile net-shaping of complex geometries on length scales ranging from nanometers to centimeters that were previously unachievable with conventional crystalline metal processing. Thermoplastic forming not only breaks through the bottleneck of the manufacture of bulk metallic glasses at ambient temperature but also offers an alluring prospect in micro-engineering applications. This paper comprehensively reviews some pivotal aspects of bulk metallic glasses during thermoplastic micro-forming, including an in-depth understanding of the crystallization kinetics of bulk metallic glasses and the thermoplastic processing time window, the thermoplastic forming map that clarifies the relationship between the flow characteristics and the formability, the interfacial friction in micro-forming and novel forming methods to improve the formability, and the potential applications of the hot-embossed micro-patterns/components.

Role of the polymer phase in the mechanics of nacre-like composites

Abstract: Although strength and toughness are often mutually exclusive properties in man-made structural materials, nature is full of examples of composite materials that combine these properties in a remarkable way through sophisticated multiscale architectures. Understanding the contributions of the different constituents to the energy dissipating toughening mechanisms active in these natural materials is crucial for the development of strong artificial composites with a high resistance to fracture. Here, we systematically study the influence of the polymer properties on the mechanics of nacre-like composites containing an intermediate fraction of mineral phase (57 vol%). To this end, we infiltrate ceramic scaffolds prepared by magnetically assisted slip casting (MASC) with monomers that are subsequently cured to yield three drastically different polymers: (i) poly(lauryl methacrylate) (PLMA), a soft and weak elastomer; (ii) poly(methyl methacrylate) (PMMA), a strong, stiff and brittle thermoplastic; and (iii) polyether urethane diacrylate-co-poly(2-hydroxyethyl methacrylate) (PUA-PHEMA), a tough polymer of intermediate strength and stiffness. By combining our experimental data with finite element modeling, we find that stiffer polymers can increase the strength of the composite by reducing stress concentrations in the inorganic scaffold. Moreover, infiltrating the scaffolds with tough polymers leads to composites with high crack initiation toughness KIC. An organic phase with a minimum strength and toughness is also required to fully activate the mechanisms programmed within the ceramic structure for a rising R-curve behavior. Our results indicate that a high modulus of toughness is a key parameter for the selection of polymers leading to strong and tough bioinspired nacre-like composites.

Thermosetting epoxy resin/thermoplastic system with combined shape memory and self-healing properties

Abstract: A novel and facile strategy was proposed to construct a thermosetting/thermoplastic system with both shape memory and self-healing properties based on commercial epoxy resin and poly(-caprolactone)-PCL. Thermoplastic material is capable of re-structuring and changing the stiffness/modulus when the temperature is above melting temperature. PCL microfiber was used as a plasticizer in epoxy resin–based blends, and served as a 'hard segment' to fix a temporary shape of the composites during shape memory cycles. In this study, the electrospun PCL membrane with a porous network structure enabled a homogenous PCL fibrous distribution and optimized interaction between fiber and epoxy resin. The self-healing capability is achieved by phase transition during curing of the composites. The mechanism of the shape memory effect of the thermosetting (rubber)/thermoplastic composite is attributed to the structural design of the thermoplastic network inside the thermosetting resin/rubber matrix.

About the thermomechanical behaviour of a carbon fibre reinforced high-temperature thermoplastic composite

Abstract: Novel high-temperature thermoplastic polymers offer potential advantages over thermoset ones and represent a promising alternative in advanced composite applications. This work proposes to determine the thermal properties and resistance of unidirectional carbon fibre reinforced thermoplastic polyimide composite and to characterize the influence of temperature on its mechanical behaviour and properties, including tensile properties, interlaminar shear strength and failure mechanisms. Characterization is performed on composite tapes and on ring-shaped specimens manufactured using a heated-head thermoplastic filament winding process. Results show that the thermal degradation of such composite material occurs at temperature higher than 400 °C. The glass transition temperature is approximately 250 °C. The tensile strength is higher than 1200 MPa in the fibre direction on a temperature range varying from −50 to 250 °C. The material has also an outstanding fatigue strength under tension in this material direction. At 200 °C, the fatigue strength for a high number of cycles (2·10 6 ) is still approximately 50% of the static strength. One of the weak point of this composite laminate is the relatively low interlaminar shear strength at high temperature.

Pultrusion of fibre reinforced thermoplastic pre-impregnated materials

Abstract: Fibre reinforced thermoplastic pre-impregnated materials produced continuously by diverse methods and processing conditions were used to produce composites using pultrusion. The processing windows used to produce these materials and composites profiles were optimized by using the Taguchi/DOE (Design of Experiments) methods. Those composites were then submitted to mechanical testing and microscopy analysis. The obtained results were compared with the expected theoretical ones predicted from the Rule Of Mixtures (ROM) and with those of similar engineering conventional available materials. The results obtained shown that produced composites have adequate properties for applications in common and structural engineering markets.

Analysis of the mechanical behaviour of flax and glass fabrics-reinforced thermoplastic and thermoset resins

Abstract: This paper aims at comparing the mechanical behaviour of different composite materials constituted of twill flax and glass fabrics-reinforced liquid thermoplastic and thermoset resins. The main obj...

Modeling of continuous ultrasonic impregnation and consolidation of thermoplastic matrix composites

Abstract: Ultrasonic propagation was used to provide heat and pressure in order to perform impregnation and consolidation during production of thermoplastic matrix composites. For this purpose, a new experimental set-up, integrating a laboratory filament winding machine with a horn and a compaction roller, was developed. The heat transfer phenomena occurring during continuous impregnation and consolidation were simulated solving by finite element (FE) analysis the energy balance equations in 2D accounting for the heat generated by ultrasonic waves, the melting characteristics of the matrix and the movement of the thermoplastic commingled roving. The temperature distribution in the composite, predicted by the numerical simulations, was validated by temperature measurements during the production of E-glass/polypropylene cylinders, with the optimized parameters obtained by the FE analysis. The ultrasonic consolidated composite cylinders were characterized by low void content and a shear modulus comparable with that obtained by the micromechanical analysis.

Controlling of the interfacial shear strength between thermoplastic resin and carbon fiber by adsorbing polymer particles on carbon fiber using electrophoresis

Abstract: In order to control the interfacial adhesion between carbon fibers and thermoplastic resins, poly(methyl methacrylate) (PMMA) particles have been adsorbed on the carbon fiber surfaces using an electrophoresis process. The amount of PMMA particles adsorbed on the modified carbon fibers was varied using the electrophoresis technique performed in polymer colloids for a short time. Additionally, the interfacial shear strength between the modified carbon fiber and the resin was controlled by a modification of the present process. An improved interaction and a strengthened surface adhesion between the carbon fiber coated with particles and the PMMA resin were observed.

Shape Memory Composites Based on Electrospun Poly(vinyl alcohol) Fibers and a Thermoplastic Polyether Block Amide Elastomer.

Abstract: The present study aimed at developing new thermally responsive shape-memory composites, that were fabricated by compacting mats of electrospun poly(vinyl alcohol) (PVA) fibers and sheets of a thermoplastic polyether block amide elastomer (PEBA). This design was based on the expectation that the combination of the rubber elasticity of the PEBA matrix and the mechanical switching exploitable through the reversible glass transition temperature (Tg) of the PVA filler could be combined to create materials that display shape memory characteristics as an emergent effect. Dynamic mechanical analyses (DMA) show that, upon introduction of 10–20% w/w PVA fibers, the room-temperature storage modulus (E′) increased by a factor of 4–5 in comparison to the neat PEBA, and they reveal a stepwise reduction of E′ around the Tg of PVA (85 °C). This transition could indeed be utilized to fix a temporary shape and recover the permanent shape. At low strain, the fixity was 66 ± 14% and the recovery was 98 ± 2%. Overall, the dat...

‘Two way’ shape memory composites based on electroactive polymer and thermoplastic membrane

Abstract: A practical and facile strategy was proposed to fabricate composites that not only use the properties of individual components (commercial electroactive polymer and thermoplastic resin) to their advantage, but also produce synergy effect of ‘two way’ shape memory properties. In this design, electroactive polymer is treated as soft segment which provides actuation force via converting electrical energy to dynamic energy. Thermoplastic material serves as ‘hard segment’ to help with fixation of temporary shape thanks to its re-structuring and stiffness/modulus changing abilities through the reversible transitional temperature. Compared with traditional one way and two way shape memory materials, this composite material has the capability of changing shape without pre-programming. High shape recover property (99 ± 0.3%.) has been obtained due to the rubber elasticity of electroactive polymer matrix. Many features could be brought up based on this design, such as accurate control over deformation by changing strength of applied electric field as well as tailorable stimulus temperature and mechanical properties.

Preparation and Characterization of Low-Density Polyethylene/Thermoplastic Starch Composites

Abstract: In this study, sago starch was physically blended with low-density polyethylene (LDPE) via the melt blending process followed by injection molding to produce LDPE/sago starch (LPS) composites. The sago starch content was varied from 5 to 30 wt% of LDPE. The addition of starch to LDPE reduced the melt flow rate (MFR), the tensile strength, and impact strength, whereas the tensile modulus, flexural strength, and flexural modulus increased. To improve poor mechanical properties of the LPS, LDPE/glycerol thermoplastic starch (LPGTS) or LDPE/2:1 mixture of glycerol and urea thermoplastic starch (LPMTS) was used in this study. The effect of compatibilizer (maleic anhydride) on properties of the LPMTS specimens was also investigated. The LPS, LPGTS, LPMTS, and maleic anhydride treated LPMTS (LPMTSM) samples were analyzed for the MFR, mechanical properties (tensile, flexural, and impact tests), thermal (TGA and DSC), and morphological properties. As a result, the incorporation of plasticizers or compatibilizer into LPS caused the considerable improvement in MFR and mechanical properties. Moreover, the presence of compatibilizer produced better properties for the LPMTSM sample than for the other samples, indicating better dispersion and homogeneity of starch to the matrix. In addition, thermal stability, DSC, and phase morphology were carried out for different LPS samples.

Carbonized Lignin as Sustainable Filler in Biobased Poly(trimethylene terephthalate) Polymer for Injection Molding Applications

Abstract: Light weight and sustainability are the key drivers in the development of novel biobased thermoplastic compounds for automotive applications. This paper reports the engineering properties of thermoplastic compound consisting of a novel bioresourced carbon filler in combination with partially biobased poly(trimethylene terephthalate). The bioresourced carbon filler, which was derived from lignin residue of cellulosic ethanol production, has a clear advantage in terms of density compared to glass fiber and other minerals, and shows potential for weight reduction with 7% lower density at 20% filler content. Polymer processing conditions were optimized in terms of thermomechanical properties, and use of a reactive chain extender additive was studied for improving the performance of the compound. At the optimized conditions, good dimensional stability, 89% increase in heat deflection temperature, 60% increase in flexural modulus, and 14% increase in flexural strength was attained in comparison to neat PTT poly...