High Melt Viscosity Research Articles

Properties of compression molded ultra‐high molecular weight polyethylene products pretreated by eccentric rotor extrusion

AbstractLow processing efficiency and fusion defects limit the application of ultra‐high molecular weight polyethylene (UHMWPE) in artificial joint implants. These problems result from the high melt viscosity of UHMWPE. Here, we use an eccentric rotor extruder (ERE) based on elongational flow to pretreat UHMWPE. Compression molded UHMWPE is obtained without and with ERE pretreatment (EP‐UHMWPE). The processing efficiency of EP‐UHMWPE is improved compared with direct compression molded UHMWPE. This is because the preheating time can be omitted during the molding process, and the residence time of UHMWPE in the extruder is less than 90 s. The mechanical properties and friction resistance of EP‐UHMWPE are significantly improved compared with those of direct compression molded UHMWPE. The yield strength increases from 21 MPa to 23 MPa, the tensile strength increases from 36 MPa to 46 MPa, the elongation at break increases from 610% to 700%, and the abrasion loss decreases from 1.73 mg/1000 r to 0.93 mg/1000 r when UHMWPE is subjected to ERE pretreatment. We attribute these improvements to the elongational flow enhancing the orientation and disentanglement of UHMWPE molecular chains, which in turn improves particle fusion. The molecular weight is well maintained when subjected to ERE pretreatment. UHMWPE components pretreated by ERE have good prospects in artificial joint implants. © 2019 Society of Chemical Industry

Effects of thermal binders on chemical stabilities and tabletability of gabapentin granules prepared by twin-screw melt granulation

The effect of thermal binders on the physicochemical properties of gabapentin, a thermally labile drug, in granules prepared using twin-screw melt granulation was investigated in this study. Hydroxypropyl cellulose (HPC), a thermoplastic high molecular-weight binder, was compared against conventional low molecular-weight semi-crystalline thermal binders PEG 8000 and Compritol. Both the chemical degradation and polymorph form change of gabapentin were analyzed. The effects of particle size and molecular weight of HPC on the properties of granules were also studied. To overcome the high melt viscosity of HPC, higher barrel temperatures and higher specific mechanical energy were required to attain suitable granules. As a result, higher levels of gabapentin degradant were observed in HPC-based formulations. However, gabapentin form change was not observed in all formulations. Smaller particle size and lower molecular weight of HPC led to faster granule growth. The tabletability of granules was insensitive to the variations in particle size and molecular weight of HPC. Gabapentin crystal size reduction, HPC size reduction, and HPC enrichment on granule surface were observed for HPC-based granules.

Thermoplastic prepreg with partially polymerized matrix: Material and process development for efficient part manufacturing

Extensive use of thermoplastic composites has been restricted by processing challenges emerging from high melt viscosities. We demonstrate the feasibility of thermoplastic prepreg with partially polymerized poly(methyl methacrylate) (PMMA) matrix and carbon fiber reinforcement. The low viscosity pre-polymer resin allowed part consolidation at low temperature and pressure. The chemical kinetics and rheology of PMMA polymerization were characterized, and an aging study was conducted to assess pre-polymer stability. Prepregs were fabricated using lab-scale methods, and a fabrication map was constructed to determine the optimal extent of polymerization for the prepreg. The prepregs were tested for tack and drape at ambient temperature, and thermoformed for microstructural and chemical analysis. The results show that auto-acceleration drives both the rate of polymerization and viscosity evolution, while refrigeration delays pre-polymer out-time effects. The thermoformed laminates exhibited near-zero porosity. This work establishes material and process development guidelines for reactive thermoplastic prepreg, and highlights potential advantages of the proposed prepreg.

Evaluation of internal morphology and engineering properties of graphite-filled UHMWPE nanocomposites produced using a novel octa-screw kneading extruder

Abstract Ultra-high molecular weight polyethylene (UHMWPE) is a very attractive polymer employed as a high performance material, while filler-reinforced composites have demonstrated its feasibility in various applications. Melt-mixing in an extruder is a key process in the development of polymer nanocomposites. Due to its high melt viscosity, dispersion of fillers is considered as a challenge in UHMWPE nanocomposites preparation process. In this work, we have prepared graphite-filled UHMWPE nanocomposites using a novel octa-screw melt kneading extruder. The engineering properties as well as the morphology of kneaded nanocomposites were characterized using tensile tester, friction and wear tester, scanning electron microscopy, optical profilemeter, polarized optical microscope, thermogravimetric analysis, differential scanning calorimetry, etc. The experimental results suggested good dispersion of graphite in the UHMWPE nanocomposites, demonstrating the excellent capability of the octa-screw extruder in compounding the graphite-filled nanocomposites. The yield strengths of the nanocomposites increase by 10% (from 21.6 MPa to 23.8 MPa) with the addition of 2% graphite. When the filler percentage was increased to 20%, the yield strengths improved from 21.6 to 27.4 MPa (an increase of 26.8%) for the graphite-filled composites. Furthermore, the crystallinity of UHMWPE nanocomposites increased with the content of graphite fillers, while the pyrolysis temperature of the composites increased with the content of graphite fillers.

New strategy towards flame retardancy through design, synthesis, characterization, and fire performance of a chain extender in polyamide 6 composites

A novel flame‐retardant chain extension agent (9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide)‐3,5‐triglycidyl isocyanurate defined as DOPO‐TGIC was synthesized, and its chemical structure was well characterized and confirmed. The effect of DOPO‐TGIC as a synergistic agent on the flame retardancy, rheology, thermal and mechanical properties of polyamide 6/aluminum diethylphosphinate (PA6/AlPi) composites were investigated in details. The results demonstrated that PA6/AlPi/DOPO‐TGIC composites (1.6 mm) successfully passed UL‐94 V‐0 rating with the limiting oxygen index value of 30.5% when the total loading amount of AlPi/DOPO‐TGIC was 10 wt%. In order to achieve the equal flame‐retardant level, the individual AlPi was required 14 wt%. The incorporated DOPO‐TGIC improved the complex viscosity of PA6/AlPi/DOPO‐TGIC composites due to the chain extending reaction between epoxide groups in DOPO‐TGIC and the terminal groups of PA6 matrix. The mechanical performance of PA6/AlPi/DOPO‐TGIC composites was also improved compared with that of PA6/AlPi composites. DOPO‐TGIC stimulated to the formation of more sufficient and compact char layer during combustion. The higher melt viscosity and compact char layer of PA6 composites effectively constrained the volatilization of flammable gases, thus the heat release was reduced. Consequently, the introduction of DOPO‐TGIC simultaneously enhanced the flame retardant and mechanical properties of PA6/AlPi/DOPO‐TGIC composites compared with that of PA6/AlPi composites. POLYM. ENG. SCI., 59:E206–E215, 2019. © 2018 Society of Plastics Engineers

Processability improvement of a 4-vinlyguiacol derived benzoxazine using reactive diluents

High melting temperature and viscosity of most benzoxazine monomers are challenging problems in processing, especially for preparation of composites. The present work introduces the “reactive diluent” concept to improve the processability of benzoxazines. A benzoxazine monomer having a vinyl group is first synthesized from 4-vinylguaiacol (4VG), and then dissolved in a reactive diluent, styrene or methyl methacrylate. The resulting solutions show low viscosity (less than 2 mPa s), and exhibit high reactivity during free radical and ring-opening polymerizations, successively. Furthermore, the solutions are applied to fabricate cotton fabrics reinforced composites. Both of them possess high glass transition temperature and excellent mechanical properties, which have potential applications as structural components.

H2O-content and temperature limit the explosive potential of rhyolite magma during Plinian eruptions

Recent rhyolite eruptions on Earth have demonstrated their capacity to produce a multitude of hazards, including ash formation lasting months and impacting the large reaches of the southern hemisphere. Nevertheless, the underlying mechanisms driving these eruptions are not yet fully understood. Magmatic volatiles, especially H2O, dictate whether volcanic eruptions proceed explosively or effusively. Experimental evidence for the role played by H2O in driving explosive fragmentation is rare, in particular in the eruption of rhyolitic magma. Here we show that when hydrous rhyolitic obsidians from Chaitén Volcano (Chile) are experimentally heated above their glass transition temperatures at ambient 1 atm-conditions, two different behaviors result, depending on starting H2O concentration and temperature: obsidians vesiculate to stable or quasi-steady state foams when H2O is ≤1 wt.% for a wide range of temperatures (728–1032°C), but will explode within just tens of seconds (<30 s) of the foaming process when H2O is 1.4 wt.% and T is >874°C. Explosive activity occurs above Chaitén's estimated eruption temperature but, for lower temperatures, only foaming occurs. Whether a foaming sample remains coherent or explodes depends on two interrelated factors, the Peclet number (Pe), a dimensionless ratio of diffusive and viscous timescales, and the timescale or rate of decompression, which is dictated in part by the H2O-vapor pressure gradient between bubbles and atmosphere. At or above 1.4 wt.% H2O, and for a range of permissible Chaitén eruption temperatures (∼780–825°C), Pe is large (>10), meaning viscous deformation aiding vapor expansion is the dominant mode of growing bubbles. Consequently, vesiculation can proceed rapidly due to high initial overpressure and low melt viscosity, until the point is reached that the melt deforms at a rate greater than its relaxation rate, resulting in fragmentation. Below 1.4 wt.% H2O and for temperatures equal to or lower than Chaitén's eruption, decompression and deformation rates, inferred from experimental clast expansion and bubble growth behavior, are at least an order of magnitude smaller than the explosive cases, which is insufficient for critical melt-rupturing. Pe estimations highlight the first order influence of temperature and H2O content on physical degassing behavior. Since the starting H2O content and temperature dictate many the parameters that govern bubble growth—pressure gradient, melt viscosity, and chemical diffusivity—our experiments shed light on what limits fragmentation in natural eruptions and offer an alternative explanation for H2O contents measured in Plinian fall deposits from Chaitén and other rhyolite centers. In essence, pyroclastic obsidian H2O contents could reflect temperature and P-H2O limitations on fragmentation. Furthermore, since foam expansion under low-P, high-T-H2O conditions can foster strain rates in excess of the melt's relaxation rate and thus drive fragmentation, we contend that, in addition to rapid magma ascent (and high magma supply rates), rapid clast expansion under low pressure conditions may also be important for explosive magma fragmentation.

Preparation and thermal property of ultrahigh molecular weight polyethylene composites filled by calcium carbonate modified with long chain

Ultrahigh molecular weight polyethylene (UHMWPE) is an excellent property polymer, but its poor processability due to high melt viscosity limits the more wide-ranging application. To improve the processability of UHMWPE composites filled by calcium carbonate (CaCO3), a novel method is reported to modify CaCO3. PE wax coated on the surface of CaCO3 (PEW@CaCO3) can be prepared by acrylic acid–modified CaCO3 (AA-CaCO3) and PE wax. The crystallization and melting behavior of UHMWPE and its composites filled by CaCO3, AA-CaCO3, and PEW@CaCO3 was compared by differential scanning calorimetry. The processability of UHMWPE composites was characterized by torque rheometer. The effect of CaCO3, AA-CaCO3, and PEW@CaCO3 on the crystallization and processability of UHMWPE was discussed.

Advances in Temporary Bonding and Debonding Technologies for use with Wafer-Level System-in-Package (WLSiP) and Fan-Out Wafer-Level Packaging (FOWLP) Processes

AbstractToday's complex fan-out wafer-level packaging (FOWLP) processes include the use of redistribution layers (RDL) and reconstituted wafers with epoxy mold compound (EMC) for use in heterogeneous integration [1]. Wafer-level system-in-package (WLSiP) uses fan-out wafer-level packaging (FOWLP) to build the system-in-package (SiP) by attaching know-good die (KGD) in a chip-first process to a tape laminated temporary carrier. If the dies are attached in a die-up configuration (active area facing up) and then over-molded with EMC, contact pads on the embedded die are exposed during the backside grind process. During the RDL build, the temporary carrier supplies mechanical support for the thinned substrate. In a die-down configuration with the active area facing down (eWLB), the temporary carrier is removed after the molding process thus exposing the contact pads for RDL build and solder ball mount.The ideal chip attachment scheme should minimize lateral movement of the die during over-mold (die shift) and also minimize vertical deformation of the bonding material. Thermal release tape provides a convenient way to attach die to a carrier prior to over-molding with EMC. However, not all bonding materials are suitable for presentation in tape form, so the material used in the tape may not be the optimal choice. An alternative method is to directly apply temporary bonding material to the carrier substrate. This enables the use of bonding materials with higher melt viscosity and improved thermal stability, resulting in less vertical deformation during die placement, and reduced die shift during over-molding. The bonding material will ideally have high adhesion to the EMC wafer to prevent delamination in the bond line during downstream processing. Stack stress and warpage is a major concern which causes handling and alignment problems during processing. The bonding material and carrier will need to be specifically suited to minimize the effects of stress in the compound wafer.Such material must balance rigidity with warp to prevent lateral die shift and deformation induced by coefficient of thermal expansion (CTE) mismatch between the carrier and EMC material [2]. Bonding materials must also have enough adhesion to the EMC material to overcome such stress without bond failure for an associated debond path (such as laser or mechanical release). In this experiment, we will examine a thermoplastic bonding material in combination with different release materials, addressing die shift, and deformation after EMC processing. Successful pairs will then undergo carrier release using either mechanical release or laser ablation release technology.

Graphene/carbon black/natural rubber composites prepared by a wet compounding and latex mixing process

ABSTRACTThe extensively used latex mixing approach to prepare graphene can improve the graphene dispersion but meets some challenges in the preparation of high content carbon black filled rubber system like a rubber tire. Owing to the high melt viscosity of the rubber/graphene masterbatch, the dispersion of carbon black is not perfect during twin-roll mixing and some aggregates will be formed. Here we proposed a wet compounding process, combined with ultrasonically assisted latex mixing, named as the WCL method to prepare reduced graphene oxide/carbon black/natural rubber (rGO/CB/NR) composites. The morphological observations confirmed that both graphene and carbon black can be evenly dispersed in the rubber composites. The incorporation of rGO also improves the hardness, thermal conductivity and anti-aging properties of the composites. The rGO/CB/NR composites prepared by the WCL method possess better mechanical properties compared to conventional latex mixing. The entanglement-bound rubber tube model was utilised to understand the reinforcing mechanism.

Laser-matter interactions in additive manufacturing of stainless steel SS316L and 13-93 bioactive glass revealed by in situ X-ray imaging

Laser-matter interactions in laser additive manufacturing (LAM) occur on short time scales (10−6–10−3 s) and have traditionally proven difficult to characterise. We investigate these interactions during LAM of stainless steel SS316L and 13-93 bioactive glass powders using a custom built LAM process replicator (LAMPR) with in situ and operando synchrotron X-ray real-time radiography. This reveals a wide range of melt track solidification phenomena as well as spatter and porosity formation. We hypothesise that the SS316L powder absorbs the laser energy at its surface while the trace elements in the 13-93 bioactive glass powder absorb and remit the infra-red radiation. Our results show that a low viscosity melt, e.g. 8 mPa s for SS316L, tends to generate spatter (diameter up to 250 μm and an average spatter velocity of 0.26 m s−1) and form a melt track by molten pool wetting. In contrast, a high viscosity melt, e.g. 2 Pa s for 13-93 bioactive glass, inhibits spatter formation by damping the Marangoni convection, forming a melt track via viscous flow. The viscous flow in 13-93 bioactive glass resists pore transport; combined with the reboil effect, this promotes pore growth during LAM, resulting in a pore size up to 600 times larger than that exhibited in the SS316L sample.

Effect of configuration in intermediate materials on textile processability by TFP technology

Continuous fiber reinforced thermoplastic (c-FRTP) has been focused on because of not only the excellent specific rigidity and strength but also the recyclability and the secondary workability due to a feature of the thermoplastic resin as the matrix. However, unlike the thermosetting resin, it is very difficult to impregnate thermoplastic resin into continuous fiber bundles because of its high melt viscosity. In order to solve this problem, various intermediate materials have been developed. On the other hand, Tailored Fiber Placement (TFP) is a textile manufacturing technology for continuous fiber preforming. Compared to other textile manufacturing processes, the continuous fiber material can be placed in any direction according to the requirement. From this characteristic, it is possible to change the local fiber orientation in the fiber reinforced composite material, so that mechanical properties of reinforcing fibers can be utilized to maximum. Applying fibrous intermediate material for c-FRTP to TFP technology, the high cycle c-FRTP molding with optimized fiber orientation can be achieved. However, in order to prepare a preform of c-FRTP, textile processability (flexibility) is needed for fibrous intermediate materials as dry fiber. Therefore, to develop fibrous intermediate material with both better impregnation property and flexibility for TFP technology is required. In this study, the effect of fabrication condition of newly developed fibrous intermediate material called PCY (Partially Impregnated Commingled Yarn) on preforming by TFP technology was investigated. The textile processability was evaluated by measuring the deformation resistance of various PCYs. The unidirectional (UD) preforms were prepared using PCY with better textile processability and impregnation property. In order to investigate the effect of stitch yarn on impregnation property during molding, the impregnation state was quantified by cross-sectional observation of various specimens. In addition, a tensile test using UD specimen was carried out to investigate the effect of stitch yarn on mechanical properties.

Thermoplastic vs. thermoset epoxy carbon textile composites

The main advantage of thermoplastic resins compared to thermoset counterpart are: increased toughness, better recyclability, and mainly the ability to deliver fast manufacturing processes. However, available thermoplastic resins (TP) have higher melt viscosity than thermoset ones. Due to high viscosity, the infusion process with conventional thermoplastic resins could lead to inappropriate impregnation of the fiber bundles. Recently, a thermoplastic epoxy resin (TP-EP) was developed with both advantages of thermoset and thermoplastic resins. The TP-EP couples the workability of thermoset, formability and recyclability of thermoplastic. The purpose of the present research is to comparatively assess the mechanical features of thermoplastic and thermoset epoxy carbon textile composites. As main outcome, the composite with highly polymerized thermoplastic epoxy has better mechanical performance than the conventional thermoset epoxy textile composite.

Hexa-[4-(glycidyloxycarbonyl) phenoxy]cyclotriphosphazene chain extender for preparing high-performance flame retardant polyamide 6 composites

The effects of phosphazene based epoxy resin hexa-[4-(glycidyloxycarbonyl) phenoxy]cyclotriphosphazene (CTP-EP) as a synergistic agent on fire retardancy, thermal and mechanical properties of polyamide 6/aluminum diethylphosphinate (PA6/AlPi) composites were investigated. AlPi and CTP-EP presented an obviously synergistic flame retardant effect for the PA6 matrix. The PA6/AlPi/CTP-EP composites with a thickness of 1.6 mm successfully passed UL-94 V-0 rating with the limiting oxygen index value of 31.0% when the loading amount of AlPi/CTP-EP (mass fraction of 97/3) was 11 wt%. The incorporated CTP-EP improved the complex viscosity of PA6/AlPi/CTP-EP composites due to the chain extending reaction between the epoxide groups of CTP-EP and the terminal groups of PA6 matrix. The CTP-EP stimulated the formation of more sufficient and compact char layer during combustion. The higher melt viscosity and more compact char layer of PA6 composites further inhibited the volatilization of flammable gases, thus the ignition time of PA6/AlPi/CTP-EP composites was prolonged and the released heat was reduced. The introduction of CTP-EP simultaneously enhanced the flame retardant and mechanical properties of PA6/AlPi/CTP-EP composites compared with that of PA6/AlPi composites.

Fabrication‐controlled morphology of poly(butylene succinate) nano‐microcellular foams by supercritical CO2

Poly(butylene succinate) urethane ionomer (PBSUIs) foams with nano‐microcellular morphology were fabricated using supercritical CO2 (sc‐CO2) at different parameters. Effect of urethane ionic group (UIG) content (ranged from 1% to 5%) on the rheology and crystallization of PBSUIs were evaluated by intrinsic, dynamic rheological, X‐ray diffraction, and differential scanning calorimetry measurements. The results show that the complex viscosity of PBSUIs vastly improved, while their intrinsic viscosity and crystallinity decreased. They also evidenced that CO2 promoted the formation of crystallites in the amorphous and increased the Xc of PBSU and PBSUIs foams. Scanning electron microscope was employed to explore the influences of UIG content and foaming parameters on the morphologies of PBSUIs microcellular foams, and it revealed that UIG content was the dominated factor. The cell size and cell densities of PBSUIs microcellular foams were smaller than 5.0 micrometers and higher than 1.5 × 1010 cells/cm3, respectively, even foamed at diverse variations of foam temperature and pressure. Interestingly, PBSUIs with 3% and 5% UIG content achieved microcellular foams in nano‐cells, high‐stretched elliptical shape. The mechanism was ascribed that these PBSUIs with high melt viscosities could retard the CO2 bubbles to merge during the foam process and induce the cells to stretch and orient in depressururization direction. This study proposed a novel method for fabricating PBS nano‐microcellular foams.

Decoupling Study of Melt Polycondensation of Polycarbonate: Experimental and Modeling of Reaction Kinetics and Mass Transfer in Thin Films Polycondensation Process

AbstractDuring the melt polycondensation process of polycarbonate, reaction and mass transfer are deeply coupled owing to relatively high melt viscosity. In this work, the polycondensation reaction kinetics and mass transfer behavior of volatile phenol are decoupling studied in detail by using thin‐film experiments with 250–280 °C, 10–1000 Pa and 0.085–0.68 mm film thickness. A realistic apparent rate model coupled the reaction kinetics with thermodynamic equilibrium and diffusion behavior is developed to describe the polycondensation process, while the diffusion characteristic of small molecule (phenol) is further obtained based on penetration theory. The obtained polycondensation equilibrium constant ranges from 0.3 to 0.55, while the activation energy and pre‐exponential factor of temperature‐dependent diffusion coefficients of phenol are 87.9 kJ mol−1 and 5.08 × 102 m2 s−1, respectively. It is also observed that the overall apparent rate of polycarbonate (PC) polycondensation process increases with higher temperature, lower pressure, and thinner film thickness. Coupling the reaction kinetics with mass transfer, the predictions of the realistic apparent rate model are in quite satisfactory agreement with experimental data.

Extrusion-based additive manufacturing process for producing flexible parts

The processing of elastomers through fused deposition modeling (FDM) is challenging task due to low column strength and high melt viscosity. Ethylene vinyl acetate (EVA) is an elastomer which is widely used for fabricating flexible objects. However, the potential of this material has not been explored in the FDM process. Pre-fabricated EVA filament cannot be processed in standard filament feed extrusion mechanism of commercial FDM machine due to buckling of the filament. However, development of pellet-based extrusion additive manufacturing (AM) may eliminate the issues caused by elastomer filament. The current study demonstrates the development of pellet-based AM system for processing EVA material. The developed system is compatible with the three-axis CNC milling machine, which provides high precision positioning to the deposition path and required power for screw rotation. Details about hardware and software related to the developed system have been presented. Flexible parts using EVA pellets have been fabricated successfully, which shows the capability of the developed extrusion AM system. Experiments have been performed for tuning process parameters. Further, mechanical characterization has been done to analyze the dimensional accuracy, flexibility, strength and hardness of printed parts. Obtained results show that EVA demonstrates approx. 300–550% higher elongation as compared to ABS and PLA materials, which indicates EVA can be used to make highly flexible parts. The outcome of this study will be helpful to the engineers for the development of low-cost flexible parts for those applications where customized flexible parts are needed in short span of time.

Effect of Aspect Ratio on Electrical, Rheological and Glass Transition Properties of PC/MWCNT Nanocomposites.

Since the discovery of carbon nanotubes (CNT), significant research works have focused on the application of CNT as conductive filler to polymer nanocomposites which can be used in several fields such as electrostatic dissipation (ESD), electrostatic painting and electromagnetic interference shielding (EMI-shielding). However, the main challenge in the large-scale manufacturing of this technology is the poor electrical conductivity of polymer nanocomposites produced by injection molding process. This study aims to investigate the effect of CNT aspect ratio in improving the electrical conductivity of injection molded nanocomposites. In this work, three types of multiwall carbon nanotubes with different lengths were melt-mixed with polycarbonate in a twin screw extruder followed by injection and compression molding. Results show that nanocomposites with higher CNT aspect ratio exhibit higher electrical conductivity. Longer nanotubes form a stronger conductive network during secondary agglomeration which can withstand the high shear forces during injection molding. Higher melt viscosity and storage modulus were observed in nanocomposites with higher CNT aspect ratio which is attributed to the effective constriction of polymer chains by longer nanotubes. It was also found that Tg of the composites increased with nanotube aspect ratio and the addition of CNT causes degradation which leads to the general Tg depression of polycarbonate.

Development of air-jet textured and twisted carbon fibre–polyamide 6,6 hybrid yarn for the production of thermoplastic composite materials

Recently, fibre-reinforced thermoplastic composite materials have been used widely in the automotive and aerospace industries because of their fracture toughness and recycling. Despite such superior properties, these materials have a weak side: high melt viscosity and low thermal resistance. The high melt viscosity of such materials makes the homogeneous wetting process difficult. This property leads to problems with the machinery and equipment at the mass production lines, and thus costs increase. Reinforcing the fibre and matrix mixed in the solid state and consolidating them helps to solve this problem. This creates a new type of semi-finished material for thermoplastic composites - hybrid yarn. The main aim of the current study was to solve the problem with high melt viscosity of thermoplastic composite materials by mixing the reinforcing fibre and matrix in the intermingling and twisting process and consolidating them. Fabricated hybrid yarns can be processed by using different textile surface forming techniques (weaving, knitting, etc.).

New application for aromatic Schiff base: High efficient flame-retardant and anti-dripping action for polyesters

Bonding aryl groups with carbon-nitrogen double bond is a critical structural factor for the self-crosslinking of Schiff bases at high temperature. In this study, a novel aromatic Schiff base “5-(benzylidene-amino)-isophthalic acid dimethyl ester (BA)” has been designed as a self-crosslinking monomer for poly(ethylene terephthalate) (PET) based copolyesters (BAnPETs). The cross-linking behaviors, flame retardancy and non-dripping performance of BAnPETs have been investigated by simultaneous thermal analysis (TG-DSC), dynamic rheology, limiting oxygen index (LOI), UL-94 vertical burning and cone calorimetry tests. It is found that BA units can cross-link during combustion resulting in high melting viscosity and enhance char forming for BAnPETs, which endows the copolyesters with excellent flame retardancy and non-dripping behavior. Incorporating of BA with a low content (only 7.7 mol%), the LOI value of copolyester increases from 22.0% to 31.0%, and at the same time it achieves V-0 rating in the UL-94 vertical burning test. The mode action of Schiff bases on flame retardation and anti-dripping of copolyesters also has been investigated, and the results show that the aromatic Schiff base groups can lead copolyesters to form nitrogen-containing cross-linkable networks and further transform into compact char layer during combustion. The char layer which acts as an effective barrier, cuts off oxygen, hinders the volatilization of combustible gas and isolates unburned polymer from fire resource. This work suggests that using Schiff base as a self-crosslinkable monomer is a new and effective way for fire-safe polymeric materials.