An investigation on dispersion state of graphene in polypropylene/graphite nanocomposite with extensional flow mixing

Graphene nanoplatelets (GNP) have attracted considerable attention because of their excellent mechanical, thermal and electrical properties. Many researchers have tried to exfoliate GNP directly from graphite (Gr) in polymer by shear flow mixing process with twin-screw extruder, internal mixer and so on. By usual shear mixing, however, exfoliation of Gr into GNP is very difficult because of inefficiency process. Therefore, we focused on the extensional flow for exfoliating to GNP from Gr. In this study, the mixing effect of pure extensional flow for exfoliating into GNP was investigated by comparing with shear flow. Primary, PP/Gr masterbatch pellets were extruded by capillary rheometer equipped with orifice die (i.e. extensional flow) and capillary die (i.e. shear flow). Then, mixing effect was discussed by morphological and rheological analysis. As the results, extensional flow can exfoliate into few layer GNP with keeping larger sure face area by comparing shear flow and storage modulus G’ was improved as the extensional stress is higher.The 32nd International Conference of the Polymer Processing Society, PPS-32, 25–29 July 2016, Lyon, Francejournal articl

Development of a new segment to improve the dispersion of a nanofiller by extensional flow in a co-rotating twin-screw extruder

Extensional flow has been recognised as a more effective process than shear flow for improving the dispersion of nanofillers in polymeric materials. One of the production processes of nanocomposites is melt extrusion with a co-rotating twins-crew extruder (TSE), which is superior in terms of productivity and mixing performance. Then, we focused on “Blister Disk (BD)” having new segments which have many holes to generate the extensional flow in TSE. The purpose of this study is to optimize BD geometry (i.e. hole numbers, hole diameter and disk width) for improving the dispersion of nanocomposites. Primary to interpreting the mixing effect of BD, the extensional flow state (i.e. extensional stress and pressure loss) at the hole entrance of BD was investigated with a 3D FEM analysis. Secondly, the mixing performance of the BD segment was evaluated by morphology observation (microscopy and TEM), rheological analysis and electric conductivity for polypropylene (PP) and carbon nanotube (CNT) nanocomposite. These experimental results were correlated with the results of the FEM analysis. The dispersion state of CNTs was improved with a decreasing hole area of BD and the disk width didn’t affect the dispersion of CNT significantly. Also, it was found that the dispersion state of CNT can be controlled by a pressure drop at the BD segment.journal articl

Influence of contents rate and dispersion of carbon nanotubes on interfacial adhesion between continuous fiber reinforced thermoplastics and injection resin

Fiber reinforced plastics have been expected as an alternative of metal materials in order to reduce the lightweight of the automotive and the environmental loading. Carbon fiber reinforced thermoplastics (CFRTP) have been studied from the view point of reducing cycle time and recycling of polymer materials. Prepreg compression molding (PCM) enables to provide the excellent mechanical property. However, PCM is difficult to form complex shape. On the other hand, hybrid injection molding (HIM) has attracted attention because HIM makes it possible to form complex shape. However, the mechanical property of molded parts are affected by the interlaminar shear strength between continuous fiber reinforced thermoplastics and injection molded parts. Some researchers reported interlaminar shear strength improve by use of carbon nanotubes (CNTs). Therefore, we aimed at improving interfacial adhesion by preparing a film with CNT added in matrix and inserting the film at the interface of hybrid injection molded parts. We conducted short beam test on specimens inserted films. When CNT/PP film was used, the interfacial shear strength was improved compared to when no film was used. When the CNT was in the low dispersion state, the interfacial shear strength rose gently up to 1.0 wt% and dropped greatly at 3.0wt%. On the other hand, when the CNT was in the highly dispersed state, the interfacial shear strength rose up to 0.5 wt%, and thereafter dropped. When the CNT content was 1.0 wt%, the CF entered deep into interface at low dispersion. However, the interface was smooth and entry of CF could not be confirmed on the peeled surface at high dispersion. There is an optimum value for the content and dispersibility of CNT in the film.journal articl

Creep properties of biofiller- and fire retardant-filled polypropylene composites

Biofillers, lignocellulosic and cellulosic fillers have the potential to significantly improve the mechanical properties of polypropylene (PP) and reduce its carbon footprint by reducing the amount of petroleum-derived polymer used. In addition, the realization of fire retardancy of biofiller-filled PP composites is an important key topic to enhance their applications; ammonium polyphosphate (APP) is an effective fire retardant (FR). In this study, to ensure the reliability of biofiller- and FR-filled PP composites, the creep properties were investigated in terms of the filler and FR content and filler type. In particular, the influence of APP addition into polymer composites on the creep properties has not been studied thoroughly. Two biofillers, wood flour (WF) and cellulose filler (CeF), with similar particle sizes and aspect ratios were used in this study. The creep test was conducted at a temperature of 80℃ in an accelerated test. Furthermore, the creep strain curves were modelled by the Burgers model of the viscoelastic constitutive equation to analyse the creep deformation behaviour. The incorporation of biofillers into the PP matrix significantly decreased the creep strain and improved the creep-rupture life with increasing filler content. Moreover, the creep-rupture life was longer for WF-filled PP composites than for CeF-filled PP composites. On the other hand, we found that incorporation of FR increased the creep rate at steady state and decreased the creep-rupture life of biofiller-filled PP composites, although the instantaneous creep strain decreased.journal articl

Influence Of Nanofiber Loading and Moulding Conditions on The Joining Strength of Thermoplastic Composites Fabricated by Injection Over-Moulding Process

An over-moulding process has promised a novel technology for joining lightweight thermoplastic composites with metal or polymer composite parts. Specifically, the substrate parts (metal or textile composites) are put into a mould of the injection moulding machine and melt polymer is injected onto substrate parts. This over-moulding process provides great benefits in terms of fast welding and moulding at the same time. However, the interfacial joining strength of over-moulded parts is still unreliable, and it has a strong dependence on surface treatment of substrate and moulding conditions. The key topic of this joining process is to achieve a reliable joining strength. In this study, we focused on using cellulose nanofiber (CNF) to interconnect between substrate and injection part by purpose of mechanical interlocking in nanoscale. Furthermore, joining strength was determined by single-lap shear test to examine the effect of presence of nanofiber. The single-lap joint consists of plain weave carbon fibre (CF) reinforced polypropylene (PP) composites (CFRPP) as substrate part and pure PP as over-injection polymer. To place the cellulose nanofiber at the interface, CF wovens and PP sheets were stacked alternately, and CNF contained PP sheet was placed at outer layer. The CFRPP substrate was obtained by heating press, pure PP was injected onto the substrate at the side of presence of CNF. This study was investigated on the influence of process conditions (i.e., injection temperature and runner route) and CNF content ratio (up to 3.0 wt%) on the shear strength as joining strength. Furthermore, the fracture morphology was observed through scanning electron microscope (SEM).journal articl

The optimization of Blister Disk geometry for mixing performance in co-rotating twin-screw extruder

Extensional flow has been taken notice as the more efficient solution for improving the dispersion of nanocomposites than shear flow. One of the production processes of nanocomposites is melt extrusion with co-rotating twin-screw extruder (TSE) which is superior in terms of productivity and mixing performance. Then, we focused on “Blister Disk” which had many small holes for generating the extensional flow. However, the influences on the mixing performance by changing the geometry of Blister Disk have not been investigated as far as we know. Therefore, the objective of this study is the optimization of Blister Disk geometry (e.g. hole numbers, hole diameter and disk length) for improving the dispersion of nanocomposites. Primary, the extensional flow state was investigated at the Blister Disk with FEM analysis. Secondly, to validate the simulation results experimentally, the polypropylene reinforced multi-walled carbon nanotube (PP/CNT nanocomposite) was used as the model of nanocomposite, and the dispersion state of CNT was investigated by morphological observation. As the result of these experiments, the better dispersion state of CNT was obtained as total permeation area and shorter hole length of Blister Disk was smaller because extensional and shear stress were increased.The 30th International Conference of the Polymer Processing Society, PPS-30, 6–12 June 2014, Cleveland, Ohio, USAjournal articl

An influence of nanofiller size on the joining strength of injection overmolded component by insert of nanofiller-filled thermoplastics films at interface

Injection overmolding process is promising process for fabrication of thermoplastic composites which has excellent mechanical properties and complex shapes. Concretely, the continuous fiber-reinforced thermoplastic composites are fabricated by stamping process as substrate. Followed by the melt polymer is overmolded onto the substrate by injection molding for fabrication the ribs and bosses. Therefore, in this process, joining strength between two materials is a major factor in the mechanical strength of a product. As the new approach to improve the joining strength, nanofiber-filled thermoplastic film is inserted between the substrate and overmolded polymer for reinforcing the interface directly in nanoscale. In our previous works, we revealed that multi-walled carbon nanotubes (MWCNTs) filled polypropylene (PP) films could improve the interlaminar shear strength. However, it is still unclear cause why interlaminar shear strength increased by adding the films. In this study, to clarify the influence of nanofiller size on the adhesion strength, two kinds of nanofillers, CNTs and vapor grown carbon fibers (VGCFs) were used. As a quantitative evaluation method of adhesive strength, a tensile overlay shear strength test was performed. As a result, it improved the joining strength at CNT contents of 0.5wt% of CNTs film the best. CT scan images confirmed that CNT tangled with polymer chains. This indicated that entanglement between CNTs and injection resin has effect on the adhesion. By diffraction scanning calorimetry (DSC) data, the crystallinity of nanofiller-filled thermoplastic film was lower than PP film and it was considered that addition of nanofiller distracted crystallization PP. Therefore, although the crystallinity of substrate surface decreased by adding nanofibers, CNT contents of 0.5wt% was the best contents for joining strength. Consequently, the relationship between crystallinity and joining strength requires detailed investigation, such as focusing on crystallization behavior during cooling.37th International Conference of the Polymer Processing Society (PPS-37), 11–15 April 2022, Fukuoka City, Japanjournal articl

Selective Reinforcement of Joining Interface Using Nanofibers in Single-Lap Joints of Thermoplastic Composites Fabricated by The Injection Overmolding Process: Creep Deformation Behaviour

An injection overmolding process enables molding and welding at the same time: a discontinuous fiberreinforced thermoplastic is injected onto the thermoformed continuous fiber-reinforced thermoplastic composites for the fabrication of complex shape parts, namely, ribs and bosses. Since the joining strength is significantly influenced by process parameters, such as resin temperature and molding pressure during the overmolding process, achieving reliable joining strength is important for increasing the load bearing capacity. The nanofibers have great potential to increase the toughness of fiber reinforced composites as secondary reinforcement. Furthermore, selective reinforcement is allowed by nanofiber addition in the matrix onto the fiber surface or interlaminar region of laminated composites. Thus, we previously proposed the selective addition of nanofillers at the joining interfaces to increase the joining strength. In this study, we attempt to reveal the effect of cellulose nanofiber (CNF) addition on creep properties for long-term use under constant load. The shear creep test was conducted under various loads and various temperatures using a self-designed fixture. Furthermore, the debonded surface of a single lap joint was observed by optical microscopy and scanning electron microscopy. We discovered that 1.0 wt% CNF addition increased the creep failure time and decreased the creep strain at the same load. Furthermore, the creep rate was significantly decreased by CNF addition regardless of temperature.journal articl

The improvement in functional characteristics of eco-friendly composites made of natural rubber and cellulose

We investigated the efficient use of cellulose to resolve the problem of the depletion of fossil resources. In this study, as the biomass material, the green composite based on natural rubber (NR) and the flake-shaped cellulose particles (FSCP) was produced. In order to further improvement of functional characteristics, epoxidized natural rubber (ENR) was also used instead of NR. The FSCP were produced by mechanical milling in a planetary ball mill with a grinding aid as a cellulose aggregation inhibitor. Moreover, talc and mica particles were used to compare with FSCP. NR and ENR was mixed with vulcanizing agents and then each filler was added to NR compound in an internal mixer. The vulcanizing agents are as follows: stearic acid, zinc oxide, sulfur, and vulcanization accelerator. The functionalities of the composites were evaluated by a vibration-damping experiment and a gas permeability experiment. As a result, we found that FSCP filler has effects similar to (or more than) inorganic filler in vibration-damping and O2 barrier properties. And then, vibration- damping and O2 barrier properties of the composite including FSCP was increased with use of ENR. In particular, we found that ENR-50 composite containing 50 phr FSCP has three times as high vibration-damping property as ENR-50 without FSCP.journal articl

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