研究者詳細 - 堀田　篤

論文 - 堀田　篤

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The property of adhesion and biocompatibility of silicon and fluorine doped diamond-like carbon films

Toyonaga M., Hasebe T., Maegawa S., Matsumoto T., Hotta A., Suzuki T.

Diamond and Related Materials （Diamond and Related Materials） 119 2021年11月

ISSN 09259635

Application of nickel‑titanium (NiTi) alloys to medical implant devices is increasing due to their unique characteristics. However, many reports show adverse effects of corrosion of the alloys due to implantation in human body. To ensure good biocompatibility in the human body, fluorine-doped amorphous carbon (a-C:H:F) coating is a promising candidate. Generally, a-C:H:F coating shows poor adhesion on metallic alloys, so that silicon-incorporated interlayer is introduced between a-C:H:F and metallic alloys. However, this membrane design has a risk of delamination at the outermost interface (a-C:H:F//interlayer), and also there is a practical problem that coating time becomes long because the deposition process in multiple stages is required. Here we develop silicon and fluorine doped amorphous carbon (a-C:H:Si:F) film which exhibits high adhesion and excellent biocompatibility. One of the a-C:H:Si:F films “C2H2-doped”, which was deposited using a mixture of TMS, C2H2 and C3F8, showed higher adhesive strength than a-C:H:F with Si-interlayer and the same number of adhesive platelets and leukocytes as a-C:H:F. This result demonstrated that a single film with both adhesion of Si-interlayer and biocompatibility of a-C:H:F was fabricated. Furthermore, this a-C:H:Si:F coating can be anticipated as an effective film coating method in a practical point of view, because the film deposition is completed in one process.

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Controlling the switching temperature of biodegradable shape memory polymers composed of stereocomplex polylactide / poly(<inf>D,L</inf>-lactide-co-ε-caprolactone) blends

Hashimoto K., Kurokawa N., Hotta A.

Polymer （Polymer） 233 2021年10月

ISSN 00323861

We synthesized new biodegradable shape-memory polymers (SMPs) by blending synthesized poly(D,L-lactide-co-ε-caprolactone) (PLCL) and stereocomplex polylactide (sc-PLA) to be used as biomaterials for medical devices. PLCL copolymers (Mn ∼80,000) with various monomer ratios (LA:CL) were synthesized by the bulk ring-opening polymerization. The glass transition temperature of the resulting PLCL copolymers could be well controlled from −3 °C to 60 °C, agreeing well with the values by the Gordon-Taylor equation, confirming the homogeneous random distribution of LA and CL monomers in the synthesized PLCL. The synthesized PLCL and sc-PLA were eventually blended for the fabrication of biodegradable SMPS. The PLCL/sc-PLA blend samples possessed the sc-PLA crystallinity of ∼13%, which effectively worked as crosslinkings, exhibiting shape-memory behavior with various switching temperatures (30.5°C–62 °C) and shape-recovery ratios realized by adjusting the CL ratio of the PLCL copolymers: a lower CL ratio resulted in a higher switching temperature and a higher shape-recovery ratio.

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Finite element analysis of blood clots based on the nonlinear visco-hyperelastic model

Tashiro K., Shobayashi Y., Ota I., Hotta A.

Biophysical Journal （Biophysical Journal） 120 （ 20 ） 4547 - 4556 2021年10月

ISSN 00063495

Mechanical thrombectomy has become the standard treatment for patients with an acute ischemic stroke. In this approach, to remove blood clots, mechanical force is applied using thrombectomy devices, in which the interaction between the clot and the device could significantly affect the clot retrieval performance. It is expected that the finite element method (FEM) could visualize the mechanical interaction by the visualization of the stress transmission from the device to the clot. This research was aimed at verifying the constitutive theory by implementing FEM based on the visco-hyperelastic theory, using a three-dimensional clot model. We used the visco-hyperelastic FEM to reproduce the mechanical behavior of blood clots, as observed in experiments. This study is focused on the mechanical responses of clots under tensile loading and unloading because in mechanical thrombectomy, elongation is assumed to occur locally on the clots during the retrieval process. Several types of cylindrical clots were created by changing the fibrinogen dose. Tensile testing revealed that the stiffness (E0.45-value) of clots with fibrinogen could be more than three times higher than that of clots without fibrinogen. It was also found that the stiffness was not proportional to the fibrinogen dose. By fitting to the theoretical curve, it was revealed that the Mooney-Rivlin model could reproduce the hyperelastic characteristics of clots well. From the stress-relaxation data, the three-chain Maxwell model could accurately fit the experimental viscoelastic data. FEM, taking the theoretical models into account, was then carried out, and the results matched well with the experimental visco-hyperelastic characteristics of clots under tensile load, reproducing the mechanical hysteresis during unloading, the stress dependence on the strain rate, and the time-dependent stress decrease in the stress-relaxation test.

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Article mechanical property of polypropylene gels associated with that of molten polypropylenes

Ouchi T., Yamazaki M., Maeda T., Hotta A.

Gels （Gels） 7 （ 3 ） 2021年09月

This study aims to understand the fundamental mechanical relationship between polypropy-lene (PP)-gels and solid PPs without solvent through mechanical and thermal analyses, by which the mechanical similarities between molten PPs and PP gels were found, leading to the reliable estimate of the mechanical properties of semi-crystalline gels. The gelation of syndiotactic and isotactic polypropylenes (sPP and iPP) was found when PPs were dissolved in 1,2,3,4-tetrahydronaphthalene (tetralin). Interestingly, it was found that the storage modulus of sPP-gel became higher than that of iPP-gel at low PP concentration (<~40 wt%). The result was distinctly different from the result of neat solid PPs (without solvent), where the modulus of solid sPP is generally significantly lower than that of solid iPP. Such inversion behavior in the mechanical property of semi-crystalline gels had not been reported and discussed before. By further investigation of the storage moduli of neat sPP and iPP, it was found that the storage modulus of sPP became higher than that of iPP above the melting points of PP, which was similar to the behavior of the storage moduli observed in the diluted PP-gels. Such similarity between PP-gels and PP melts was also observed within iPP samples with different molecular weights.

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Antithrombogenic poly(2-methoxyethyl acrylate) elastomer via triblock copolymerization with poly(methyl methacrylate)

Kurokawa N., Endo F., Bito K., Maeda T., Hotta A.

Polymer （Polymer） 228 2021年07月

ISSN 00323861

For the development of blood-contacting biomedical devices, preventing platelet adhesion and avoiding subsequent thrombosis through antithrombogenic surface are vitally important. Poly (2-methoxyethyl acrylate) (PMEA) is a synthetic viscous polymer with an excellent antithrombogenic property, which has already been used as an antithrombogenic coating for biomedical purposes. The PMEA coating, however, can be easily broken due to its liquid-like feature, since the glass transition temperature (Tg) of PMEA is at −25οC. Solidifying PMEA has, therefore, been desperately desired for the improvement of the stability of PMEA coating. Also, once solidified, PMEA could be utilized not only for coating but also for structural materials for medical devices, expanding the application range of PMEA. In this study, PMEA was first solidified by triblock copolymerization with poly (methyl methacrylate) (PMMA) to obtain thermoplastic elastomers with excellent antithrombogenicity. We synthesized PMMA-PMEA-PMMA triblock copolymers with different volume fractions of PMMA (fMMA) by atom transfer radical polymerization (ATRP). The synthesis and the chemical structures of the new triblock copolymers were characterized and confirmed by proton nuclear magnetic resonance (1H NMR) analyses and gel permeation chromatography (GPC). The synthesized elastomeric triblocks were then compression-molded at 180οC to obtain solid transparent films. The tensile property was measured and the drastic change from the soft-elastomer phase to the hard-plastic phase was clearly observed by varying fMMA. It was found that the new triblocks possessed significantly higher tensile strengths than the other solidified PMEA by the previous studies. The platelet adhesion test revealed that the number of adherent platelets on the triblocks with fMMA of 0.12 and 0.40 was almost the same as that on pure PMEA, indicating that the synthesized triblocks possessed excellent antithrombogenicity similar to liquid PMEA. Further investigation on hydrated water and microphase-separated structures eventually revealed that the new triblock copolymers with a sufficient amount of intermediate water or with microphase separation on the surface resulted in excellent antithrombogenicity.

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Fabrication of Gd-DOTA-functionalized carboxylated nanodiamonds for selective MR imaging (MRI) of the lymphatic system

Yano K., Matsumoto T., Okamoto Y., Kurokawa N., Hasebe T., Hotta A.

Nanotechnology （Nanotechnology） 32 （ 23 ） 2021年06月

ISSN 09574484

Magnetic resonance imaging (MRI) contrast agents with the particle diameter of around 3-10 nm hold the potential to be selectively uptaken by lymphatic vessels and be filtered in the kidney for final excretion. However, there are no existing MRI contrast agents based on gadolinium (Gd) complexes within the size of this range, and thus the selective imaging of the lymphatic system has not yet been achieved. In our previous report, we succeeded in fabricating nano-scale MRI contrast agents by complexing ordinary contrast agents (Gd-diethylenetriaminepentaacetic acid (DTPA)) with carboxylated nanodiamond (CND) particles to conquer this problem. However, DTPA has recently been reported to release Gd ions in the course of time, leading to the potential danger of severe side effects in the human body. In this study, we utilized cyclic-chained DOTA as an alternative chelating material for DTPA to fabricate CND-based MRI contrast agents for the selective lymphatic imaging. The newly fabricated contrast agents possessed the diameter ranging from 3 to 10 nm in distilled water and serum, indicating that these particles can be selectively uptaken by lymphatic vessels and effectively filtered in the kidney. Furthermore, the DOTA-applied CND contrast agents exhibited stronger MRI visibility in water and serum compared to DTPA-applied CND contrast agents. These results indicate that DOTA-applied CND contrast agents are promising materials for the selective MR imaging of lymphatic systems.

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Degradation of thermoresponsive laponite/PEG-b-PLGA nanocomposite hydrogels controlled by blending PEG-b-PLGA diblock copolymers with different PLGA molecular weights

Maeda T., Kitagawa M., Hotta A.

Polymer Degradation and Stability （Polymer Degradation and Stability） 187 2021年05月

ISSN 01413910

The thermoresponsive gelation behavior and the degradation behavior of the nanocomposites consisting of poly(ethylene glycol)-b-poly(lactic acid-co-glycolic acid) (PEG-b-PLGA) diblock copolymers and clay nanoparticles (laponite) (laponite/PEG-b-PLGA nanocomposites) were studied by changing the blend ratio of the PEG-b-PLGA diblock copolymers using different PLGA molecular weights of 800 g/mol and 1600 g/mol: PEG-b-PLGA (1000-800, Diblock0.8k) and PEG-b-PLGA (1000-1600, Diblock1.6k). It was found that each gelation temperature was in the temperature range between 25°C and 37°C, when the PEG-b-PLGA concentration and the laponite concentration were kept at 3–4 wt% and 1 wt%, respectively. The degradation rate at 37°C was found to be effectively regulated by the Diblock1.6k/Diblock0.8k blend ratio (DR). In detail, after 15 days of the degradation experiments, the weight loss was decreased by ∼14% when DR changed from DR=0/100 to DR=100/0. It was, therefore, confirmed that DR was the key parameter to control the degradation behavior of the laponite/blended PEG-b-PLGA nanocomposites.

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Mechanical, thermal, and microstructural analyses of thermoplastic poly(2-methoxyethyl acrylate)-based polyurethane by RAFT and polyaddition

Tazawa S., Maeda T., Hotta A.

Materials Advances （Materials Advances） 2 （ 5 ） 1657 - 1664 2021年03月

Mechanical and thermal properties of the newly synthesized solid poly(2-methoxyethyl acrylate) (PMEA)-based polyurethane (PU) were studied. The obtained PMEA-based PUs with various molecular weights were thermoplastic, synthesized by reversible addition-fragmentation chain transfer (RAFT) and polyaddition. Dynamic mechanical analysis (DMA) revealed that the storage modulus and the melting temperature of PMEA-based PU significantly increased from 1.5 × 104 Pa to 2.3 × 105 Pa and from 25 °C to 73 °C, respectively, as the molecular weight of PMEA-based PU increased. This enhancement in the properties could be due to the formation of an ordered structure in PMEA-based PU, studied using small-angle and wide angle X-ray scattering (SAXS, WAXS). Glass transition temperature, 5% weight-reduction temperature, and the amount of intermediate water of PMEA-based PU were also analyzed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). This journal is

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Gadolinium-Complexed Carboxylated Nanodiamond Particles for Magnetic Resonance Imaging of the Lymphatic System

Yano K., Matsumoto T., Okamoto Y., Bito K., Kurokawa N., Hasebe T., Hotta A.

ACS Applied Nano Materials （ACS Applied Nano Materials） 4 （ 2 ） 1702 - 1711 2021年02月

MRI contrast agents with a size of 3-10 nm are considered to be an effective pathway for selective MR lymphatic imaging. In our previous study, we fabricated nanosized MRI contrast agents (Gd-DTPA-ND) with the condensation of nanodiamond (ND) particles and gadolinium chelates (Gd-DTPA). However, these Gd-DTPA-ND particles formed microscale aggregates in distilled water, exceeding the size required for selective lymphatic MR imaging. In this study, carboxylated nanodiamond (CND) particles were utilized as alternative platforms for condensation with gadolinium complexes. The carboxyl groups introduced by oxidation were expected to induce hydrophilicity with a negative charge on the ND surface, resulting in the high dispersity of gadolinium-complexed CND particles. The fabricated Gd-DTPA-CND particles possessed a hydrodynamic diameter of around 4-5 nm without any signs of aggregation in distilled water and human serum. Furthermore, the T1-weighted image of Gd-DTPA-CND particles in distilled water and human serum presented strong contrast, indicating the excellent MRI visibility of the particles. Therefore, the Gd-DTPA-CND particles can become practical MRI contrast agents for the achievement of selective MR imaging of the lymphatic system.

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Structures and mechanical properties of electrospun cellulose nanofibers/poly(ε-caprolactone) composites

Taniguchi H., Kurokawa N., Inukai S., Hotta A.

Journal of Applied Polymer Science （Journal of Applied Polymer Science） 137 （ 42 ） 2020年11月

ISSN 00218995

© 2020 Wiley Periodicals, Inc. Poly(ε-caprolactone) (PCL) is one of the ecofriendly biodegradable polymers with excellent moldability but with rather low mechanical properties especially for the industrial and biomedical use. In this research, to overcome the problem, the two types of cellulose nanofibers, the cellulose acetate nanofibers (CA-NF) and the cellulose nanofibers (C-NF), were composited into PCL for the enhancement of the mechanical properties of PCL. CA-NF were prepared by electrospinning and converted into C-NF afterward by deacetylation. It was found that the Young's modulus of the CA-NF/PCL composite at the fiber concentration of 35 wt% significantly increased by ~3 times as compared with that of neat PCL, whereas C-NF/PCL of the same fiber concentration also increased by ~4.5 times. It was also found that the Young's moduli of CA-NF/PCL nearly reached the theoretical values calculated by the equation suggested by Tsai, but that the Young's moduli of C-NF/PCL could not reach the theoretical values. It indicates that CA-NF possessed better compatibility with PCL than C-NF, agreeing well with the fracture-surface analyses of the two composites by the scanning electron microscopy.

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Synthesis of Thermoplastic Poly(2-methoxyethyl acrylate)-Based Polyurethane by RAFT and Condensation Polymerization

Tazawa S., Maeda T., Nakayama M., Hotta A.

Macromolecular Rapid Communications （Macromolecular Rapid Communications） 41 （ 19 ） 2020年10月

ISSN 10221336

© 2020 Wiley-VCH GmbH Thermoplastic solid poly(2-methoxyethyl acrylate) (PMEA)-based polyurethane (PU) is synthesized through the reversible addition−fragmentation chain transfer (RAFT) polymerization and the condensation polymerization, using hydroxyl-terminated RAFT reagents and diisocyanate, respectively. Neat PMEA is a promising antithrombogenic liquid used in the medical fields. The thermoplastic property of the solid PMEA-based PU due to hydrogen bonding is confirmed by the dynamic mechanical analysis (DMA) at temperature below 72 °C. The antithrombogenic property of PMEA-based PU is also analyzed by the platelet adhesion test. The number of platelets on PMEA-based PU is 17 cells per unit area, which is smaller than that on the fluorinated diamond-like carbon (F-DLC), a well-known highly antithrombogenic material. It is concluded that a newly synthesized PMEA-based PU exhibits thermoplastic characteristics with excellent antithrombogenicity.

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Evaluation of Crystallinity and Hydrogen Bond Formation in Stereocomplex Poly(lactic acid) Films by Terahertz Time-Domain Spectroscopy

Hirata J., Kurokawa N., Okano M., Hotta A., Watanabe S.

Macromolecules （Macromolecules） 53 （ 16 ） 7171 - 7177 2020年08月

ISSN 00249297

Copyright © 2020 American Chemical Society. Stereocomplex poly(lactic acid) (sc-PLA) crystallites exhibit higher mechanical strength and thermal stability than PLA homocrystallites. In sc-PLA, a hydrogen bond that governs the physical properties is formed between two enantiomeric PLA chains during crystallization. Therefore, the investigation of this hydrogen bond is essential for a better understanding of the properties of sc-PLA. Here, we report on the terahertz spectroscopy of sc-PLA films with low crystallinities. The dielectric function in the terahertz regime allows us to estimate the crystallinity of sc-PLA because various intra- and intermolecular vibration modes lie in the terahertz frequency range. By comparison with X-ray diffraction measurements, the validity of the crystallinity evaluation based on terahertz spectroscopy is verified. Furthermore, a remarkable red-shift of the peak in the imaginary part of the dielectric function occurs as the crystallinity increases. By comparison with Fourier transform infrared spectroscopy, it is considered that this red-shift is caused by the anharmonic nature of the vibrational potential corresponding to the intermolecular libration mode of the sc-PLA crystallites. The hydrogen bond formation associated with the sc-PLA crystallization increases the anharmonicity of the vibrational potential of sc-PLA, and then the red-shift of the peak occurs. Our findings suggest that structural changes due to the stereocomplexation can be sensitively probed by terahertz spectroscopy.

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Thermophysical Property Measurements of Tetrabutylphosphonium Oxalate (TBPOx) Ionic Semiclathrate Hydrate as a Media for the Thermal Energy Storage System

Miyamoto T., Koyama R., Kurokawa N., Hotta A., Alavi S., Ohmura R.

Frontiers in Chemistry （Frontiers in Chemistry） 8 2020年07月

© Copyright © 2020 Miyamoto, Koyama, Kurokawa, Hotta, Alavi and Ohmura. With increasing global power demand, thermal energy storage technology could play a role ensuring a sustainable energy supply in power generation from renewable energy sources and power demand concentration. Hydrates have high potential as phase change materials (PCMs) for the use as a thermal energy storage medium. To develop thermal energy storage technology using a hydrate-based material, further investigation of thermophysical properties and the selection of a suitable hydrate are required. Tetrabutylphosphonium oxalate (TBPOx) ionic semiclathrate hydrate contains oxalic acid in salt form, as a guest compound, which is classified as carboxylic acid group with low environmental impact. In the present study, the phase equilibrium temperature and the dissociation heat of TBPOx hydrate were measured. The highest equilibrium temperature of the solid hydrate formed was 9.4°C at the mass fraction 0.35 of TBPOx in aqueous solution. The largest dissociation heat was 186.0 ± 0.5 kJ·kg−1 at the mass fraction of 0.35. Comparing with other PCMs with close phase equilibrium temperatures, TBPOx hydrate is superior in safety and sustainability. These results indicate that TBPOx hydrate would be suitable as the thermal storage medium for the general air conditioning systems.

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Mechanical properties of poly(ε-caprolactone) composites with electrospun cellulose nanofibers surface modified by 3-aminopropyltriethoxysilane

Inukai S., Kurokawa N., Hotta A.

Journal of Applied Polymer Science （Journal of Applied Polymer Science） 137 （ 17 ） 2020年05月

ISSN 00218995

© 2019 Wiley Periodicals, Inc. To enhance the reinforcement effects of regenerated cellulose nanofibers (RC-NF) in poly(ε-caprolactone) (PCL), we synthesized RC-NF-3-aminopropyltriethoxysilane (APS), the surface-modified RC-NF by APS. The RC-NF were fabricated by the saponification of electrospun cellulose–acetate nanofibers. The surface modification by APS was confirmed by the X-ray photoelectron spectroscopy (XPS). To enhance the mechanical property of PCL, the RC-NF and the RC-NF-APS were separately compounded into PCL by compression molding. It was found that, when the fiber concentration of RC-NF-APS was 17 wt %, the Young's modulus at room temperature increased from 698.0 to 744.7 MPa, whereas the storage modulus at 55 °C almost increased from 180 to 220 MPa. The micrographs of the fracture surface of the composites revealed that the surface modification prevented the pull-out of RC-NF from PCL. It was concluded that the mechanical properties of the composites were enhanced due to the improvement of the compatibility between RC-NF and PCL by the surface modification with APS. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48599.

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Fabrication of radiopaque drug-eluting beads based on Lipiodol/biodegradable-polymer for image-guided transarterial chemoembolization of unresectable hepatocellular carcinoma: Fabrication of radiopaque DEBs by Lipiodol/biodegradable-polymer for TACE of HCC

Okamoto Y., Hasebe T., Bito K., Yano K., Matsumoto T., Tomita K., Hotta A.

Polymer Degradation and Stability （Polymer Degradation and Stability） 175 2020年05月

ISSN 01413910

© 2020 Elsevier Ltd New radiopaque/biodegradable drug-eluting beads (DEBs) for transarterial chemoembolization (TACE) were fabricated using Lipiodol and polycaprolactone (PCL) (Lipiodol/PCL beads) through a microfluidic device. TACE is the most extensively-applied therapy for unresectable hepatocellular carcinoma (HCC). DEBs are embolic microspheres with sustained and tumor-selective drug-delivery characteristics for tumor-feeding arteries. As the conventional DEBs are not radiopaque by themselves and not biodegradable, it is difficult to monitor bead localization and attenuation through CT images after DEB-TACE procedures, and the complication after non-target embolization becomes potentially more serious. In this work, we found that our new biodegradable Lipiodol/PCL lost 63.5% of their weight 11 days after immersion, simultaneously releasing 0.94 μg of miriplatin (a lipophilic platinum-based anticancer drug) from the Lipiodol/PCL beads in 11 days. We also found that the degradation speed could be controlled from 18.2% to 63.5% of the weight loss in 11 days by changing the molecular weight of PCL and the ratio of Lipiodol/PCL. The mean diameter of the bead could be well controlled by changing the flow-rate ratio of the microfluidic device. Regarding the radiopacity in vitro, the Lipiodol/PCL beads were clearly visualized through CT imaging, with a mean attenuation of over 5600 HU. Furthermore, it was found from the radiopacity experiments in vivo, that the embolization by the Lipiodol/PCL beads in the rabbit vessel was clearly recognized through CT images, indicating high potential of the newly synthesized biodegradable beads to improve the current TACE procedures by providing refined locational information on drug and embolic particles.

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Equilibrium temperature and dissociation heat of tetrabutylphosphonium acrylate (TBPAc) ionic semi-clathrate hydrate as a medium for the hydrate-based thermal energy storage system

Koyama R., Hotta A., Ohmura R.

Journal of Chemical Thermodynamics （Journal of Chemical Thermodynamics） 144 2020年05月

ISSN 00219614

© 2020 The hydrate-based thermal energy storage system is one of the most effective supplemental technologies to stabilize the energy supply for renewable energies. The system is expected to solve the global energy-management issues related to energy-demand increase and energy supply chain. In fact, this eco-friendly technology requires prospective hydrate candidates for the thermal energy storage media, followed by the extensive investigation of the thermophysical properties of the selected hydrates. In this study, to satisfy these requirements, the equilibrium temperature and the dissociation heat of tetrabutylphosphonium acrylate (TBPAc) ionic semi-clathrate hydrate were studied. It was found that the highest equilibrium temperature was 14.4 °C at the mass fractions from 0.37 to 0.40. It was also found that the largest dissociation heat was (210.4 ± 5.3) kJ kg−1 at the mass fraction 0.39. These values indicate that TBPAc hydrate could be a new promising thermal-storage medium for the general or data-centre air-conditioning systems. The experimental results of this study also revealed an underlying tendency between the thermophysical properties of the tetrabutylphosphonium (TBP) + carboxylate salt hydrates and the molar mass of the guest anion in salt.

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Regenerated cellulose nanofibers fabricated through electrospinning and saponification of cellulose acetate as reinforcement of polylactide composites

Kurokawa N., Hotta A.

Cellulose （Cellulose） 26 （ 13-14 ） 7797 - 7808 2019年09月

ISSN 09690239

© 2019, Springer Nature B.V. Cellulose-acetate nanofibers (CA-NF) and regenerated cellulose nanofibers (RC-NF) were separately compounded as reinforcement materials for enhancement of the mechanical property of polylactide (PLA). PLA has a great potential as an alternative to widely-used plastics such as polystyrene and poly(ethylene terephthalate), which are made from petroleum. PLA is well known for its biodegradability and renewability, but the mechanical property of PLA is not sufficient for industrial applications. In this study, CA-NF were successfully fabricated by electrospinning using 20 wt% cellulose-acetate solution with acetone/N,N-dimethylacetamide (6/4, wt/wt) mixture solvent, and RC-NF were synthesized by subsequent saponification, as reinforcement materials for PLA composites. The Young’s modulus of CA-NF/PLA composites increased linearly from 1670 to 1840 MPa with the increase in the nanofiber concentration to 15 wt%. In contrast, the Young’s modulus of RC-NF/PLA composites rapidly increased to ~ 1840 MPa at the relatively low nanofiber concentration of 5.0 wt%. Above 5.0 wt%, the Young’s modulus became stable and almost constant. RC-NF exhibited better reinforcing efficiency due to the excellent mechanical property of RC-NF, although the interfacial compatibility of RC-NF for PLA matrix was relatively poor as compared with that of CA-NF.

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SANS study on the nano-crystalline network structure of elastic physical gels made of syndiotactic polypropylene

Endo F., Kurokawa N., Tanimoto K., Iwase H., Maeda T., Hotta A.

Soft matter （Soft matter） 15 （ 27 ） 5521 - 5528 2019年07月

The structure-property relationship of an elastic physical gel, obtained by simply quenching syndiotactic polypropylene (sPP)/decahydronaphthalene solution with liquid nitrogen, was investigated based on small-angle neutron scattering (SANS) analysis. The SANS analysis revealed that sPP nanocrystals with a constant radius of 4-5 nm existed in the sPP gels regardless of the sPP concentration, whereas the correlation length of the nanocrystals drastically decreased from ∼130 to ∼20 nm upon increasing the sPP concentration from 2 to 12 wt%. The volume fraction and the number density of the sPP nanocrystals increased monotonously with the increase in the sPP concentration. The rheological properties and the melting behavior of the quenched sPP gels were highly consistent with the number density of the nanocrystals calculated from the SANS analysis, strongly suggesting that the sPP nanocrystals actually worked as crosslinking points by inducing elasticity in the quenched sPP gels.

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Thermophysical properties of trimethylolethane (TME) hydrate as phase change material for cooling lithium-ion battery in electric vehicle

Koyama R., Arai Y., Yamauchi Y., Takeya S., Endo F., Hotta A., Ohmura R.

Journal of Power Sources （Journal of Power Sources） 427 70 - 76 2019年07月

ISSN 03787753

© 2019 Elsevier B.V. Management for the temperature increase of lithium-ion batteries in electric vehicles (EV) is required for safety and energy efficiency. As a cooling medium for lithium-ion batteries, one suitable candidate is trimethylolethane (TME) hydrate, which may be utilized as a phase change material (PCM). This hydrate has a large dissociation heat and will form/dissociate at approximately 30 °C under atmospheric pressure conditions. A cooling system which uses TME hydrate can have a high performance with regards to the efficiency and the stability of heat transfer process. However, in previous studies, the equilibrium temperature and the dissociation heat of TME hydrate have been reported only for a TME mass fraction of 0.625. Since TME hydrate forms in an aqueous solution, it is necessary to know how these thermophysical properties change for a range of TME mass fractions. Therefore, in this study, the equilibrium temperatures and the dissociation heats were measured respectively by the visual observation method and differential scanning calorimetry measurements for TME mass fraction range from 0.20 to 0.80. The highest equilibrium temperature was 29.6 °C at the mass fraction of 0.60. For the cooling system, the largest dissociation heat was 190.1 kJ kg−1, also at the mass fraction of 0.60.

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Controlling the size of spherulite and the degradation of poly(butylene succinate-co-adipate) by solvent and gel preparation temperature

Yamazaki H., Kamitabira S., Maeda T., Hotta A.

Polymer Degradation and Stability （Polymer Degradation and Stability） 162 106 - 111 2019年04月

ISSN 01413910

© 2019 Elsevier Ltd The size of spherulites observed in the poly(butylene succinate-co-adipate) (PBSA) gel was found to be effectively controlled by the careful selection of the types of solvent and the gel preparation temperature. Additionally, the degradation behavior of the PBSA dried-gels with different sizes of spherulites was studied. By using different solvents, such as toluene (TOL), o-dichlorobenzene (o-DCB), and cyclohexanone (CHN), the diameter of the spherulites could be changed from 16.7 μm to 186.2 μm, while the gel preparation temperature was kept constant at 28 °C. The gel preparation temperature was then changed from −50 °C to 28 °C using CHN, and it was found that the diameter of the spherulites changed from 25.2 μm to 186.2 μm. Regarding the degradation behavior, the PBSA dried-gel with relatively smaller spherulites (∼20 μm in diameter) exhibited higher weight loss of over 80% at the immersion time of 6 days, while the PBSA dried-gels with relatively larger spherulites (∼186 μm in diameter) presented lower weight loss of below 30% at the immersion time of 6 days. It was therefore concluded that the degradation rate became lower with the increase in the size of spherulites.

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