The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Mitsuhiro Shibayama - One of the best experts on this subject based on the ideXlab platform.
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diffusion behavior of methanol molecules confined in cross linked Phenolic Resins studied using neutron scattering and molecular dynamics simulations
Macromolecules, 2018Co-Authors: Yasuyuki Shudo, Atsushi Izumi, Katsumi Hagita, Takeshi Yamada, Kaoru Shibata, Mitsuhiro ShibayamaAbstract:The dynamics of methanol confined in highly cross-linked Phenolic Resins was investigated using incoherent quasielastic neutron scattering (QENS) and atomistic molecular dynamics (MD) simulations. The QENS analysis for a deuterated Phenolic resin and both deuterated and nondeuterated methanol indicated the presence of resin dynamics induced by methanol invasion and confined diffusion of the methanol molecules. QENS results suggested that methanol had a diffusion coefficient of 1.6 × 10–6 cm2/s, which is 1 order of magnitude smaller than the bulk value (2.3 × 10–5 cm2/s). The MD trajectories also showed that the methanol diffusion was limited by the resin network, consistent with QENS results in terms of the diffusion coefficient and diffusion-like behavior.
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large scale molecular dynamics simulation of crosslinked Phenolic Resins using pseudo reaction model
Polymer, 2016Co-Authors: Yasuyuki Shudo, Atsushi Izumi, Toshio Nakao, Katsumi Hagita, Mitsuhiro ShibayamaAbstract:Abstract We constructed and characterized a network structure of crosslinked Phenolic Resins using a large-scale atomistic molecular dynamics simulation with a pseudo-reaction algorithm. The atomic configuration of the reaction products was controlled by the reaction probabilities and initial molecular structures. The crosslinked structure obtained from phenols as initial molecules agreed well with experimental results in terms of the branching structure of the Phenolic units and the methylene linkages, molecular weight distributions, densities, and scattering functions at various reaction conversions. The calculated structure factor for Phenolic Resins indicated inhomogeneous crosslinking, which expanded as the reaction proceeded after gelation. Voronoi tessellation analysis of the change in the occupation volume of the Phenolic units after crosslinking indicated that the initial molecular configuration influenced the resulting crosslinked structure. The experimental molecular weight distribution before gelation and the scattering function were well reproduced by a large-scale simulation with 232,000 atoms.
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cross link inhomogeneity in Phenolic Resins at the initial stage of curing studied by 1h pulse nmr spectroscopy and complementary saxs waxs and sans wans with a solvent swelling technique
Polymer, 2016Co-Authors: Atsushi Izumi, Toshio Nakao, Yasuyuki Shudo, Mitsuhiro ShibayamaAbstract:Abstract The cross-link inhomogeneity of Phenolic Resins at the initial stage of curing in a temperature range of 110–130 °C was investigated through structural analysis of the network structure evolution mechanism using 1 H-pulse nuclear magnetic resonance spectroscopy and complementary small- and wide-angle X-ray and neutron scattering methods. Two types of Phenolic Resins, PR06 and PR12, were prepared with stoichiometrically insufficient and sufficient amounts of cross-linker, respectively, via curing of a novolac-type Phenolic resin oligomer with hexamethylenetetramine as the curing agent. Their network structures comprised three different structural domains because of the cross-link inhomogeneity: the high-cross-link-density domain (HXD), the low-cross-link-density domain (LXD), and the interface region between these domains. Percolation of the HXD occurred at the beginning of the curing. Intradomain reactions inside both HXD and LXD proceeded as the dominant reactions accompanying minor interdomain reactions between the HXDs, resulting in no significant change in the spatial location and size of the HXDs and LXDs. Intradomain reactions inside the LXD involved reactions with dangling chains, which would not affect the average mesh size of the domain significantly. These behaviors of the network structure evolution mechanism at the initial stage of the curing are a general feature of Phenolic Resins that does not depend on the amount of cross-linker. The difference between the amount of the cross-linker present in PR06 and PR12 was manifested as a difference in the degree of cross-linking in the percolated HXDs, i.e., the HXD of PR12 exhibited a tightly cross-linked, well-developed network structure since the beginning of the curing process; however, that of PR06 exhibited a loosely cross-linked network structure, with the degree of cross-linking increasing as the curing proceeded.
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gelation and cross link inhomogeneity of Phenolic Resins studied by small and wide angle x ray scattering and 1h pulse nmr spectroscopy
Polymer, 2015Co-Authors: Atsushi Izumi, Toshio Nakao, Mitsuhiro ShibayamaAbstract:Abstract The gelation mechanism and cross-link inhomogeneity of Phenolic Resins prepared via polycondensation of phenol and formaldehyde under acidic conditions were studied using small- and wide-angle X-ray scattering and 1 H-pulse nuclear magnetic resonance spectroscopy. The solvent-swelling technique was applied for both measurements at the initial stage of gelation to enhance the local fluctuations of the cross-link density. The change in the static and dynamic structures obtained through observations of the X-ray scattering functions and the spin–spin relaxation functions, respectively, during the polycondensation reaction indicates the presence of two different mechanisms for the formation and growth of the inhomogeneity that depend on the amount of cross-linker. (i) When there is a stoichiometrically insufficient amount of the cross-linker, inhomogeneous domains with a loosely cross-linked network appear at the initial stage of gelation. The intradomain reactions become dominant in the growth of the inhomogeneous domain and the degree of cross-linking in the domain increases by bridging two unreacted sites in the network structure via the cross-linker. (ii) When there is a stoichiometric amount of the cross-linker, inhomogeneous domains with a tightly cross-linked network appear at the initial stage of gelation. The interdomain reactions become dominant in the growth of the domain and the size of the domain increases by incorporating new polymer chains into the domain via the cross-linker.
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gelation and cross link inhomogeneity of Phenolic Resins studied by 13c nmr spectroscopy and small angle x ray scattering
Soft Matter, 2013Co-Authors: Atsushi Izumi, Toshio Nakao, Mitsuhiro ShibayamaAbstract:The gelation mechanism and cross-link inhomogeneity of Phenolic Resins prepared via polycondensation of phenol and formaldehyde under acidic conditions were studied by using 13C-NMR spectroscopy and small-angle X-ray scattering. The structural analysis of the gelation process indicated the presence of two different mechanisms of the formation and growth of the inhomogeneity that depend on the initial formaldehyde-to-phenol molar ratio: (i) when there is an insufficient amount of a cross-linker at the initial stage of gelation, inhomogeneous domains with a loosely cross-linked network appear and the degree of cross-linking in the domain increases with the reaction time. (ii) When there is a sufficient amount of a cross-linker at the initial stage of gelation, inhomogeneous domains with a tightly cross-linked network appear, followed by an increase in the size of the domains.
Atsushi Izumi - One of the best experts on this subject based on the ideXlab platform.
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diffusion behavior of methanol molecules confined in cross linked Phenolic Resins studied using neutron scattering and molecular dynamics simulations
Macromolecules, 2018Co-Authors: Yasuyuki Shudo, Atsushi Izumi, Katsumi Hagita, Takeshi Yamada, Kaoru Shibata, Mitsuhiro ShibayamaAbstract:The dynamics of methanol confined in highly cross-linked Phenolic Resins was investigated using incoherent quasielastic neutron scattering (QENS) and atomistic molecular dynamics (MD) simulations. The QENS analysis for a deuterated Phenolic resin and both deuterated and nondeuterated methanol indicated the presence of resin dynamics induced by methanol invasion and confined diffusion of the methanol molecules. QENS results suggested that methanol had a diffusion coefficient of 1.6 × 10–6 cm2/s, which is 1 order of magnitude smaller than the bulk value (2.3 × 10–5 cm2/s). The MD trajectories also showed that the methanol diffusion was limited by the resin network, consistent with QENS results in terms of the diffusion coefficient and diffusion-like behavior.
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large scale molecular dynamics simulation of crosslinked Phenolic Resins using pseudo reaction model
Polymer, 2016Co-Authors: Yasuyuki Shudo, Atsushi Izumi, Toshio Nakao, Katsumi Hagita, Mitsuhiro ShibayamaAbstract:Abstract We constructed and characterized a network structure of crosslinked Phenolic Resins using a large-scale atomistic molecular dynamics simulation with a pseudo-reaction algorithm. The atomic configuration of the reaction products was controlled by the reaction probabilities and initial molecular structures. The crosslinked structure obtained from phenols as initial molecules agreed well with experimental results in terms of the branching structure of the Phenolic units and the methylene linkages, molecular weight distributions, densities, and scattering functions at various reaction conversions. The calculated structure factor for Phenolic Resins indicated inhomogeneous crosslinking, which expanded as the reaction proceeded after gelation. Voronoi tessellation analysis of the change in the occupation volume of the Phenolic units after crosslinking indicated that the initial molecular configuration influenced the resulting crosslinked structure. The experimental molecular weight distribution before gelation and the scattering function were well reproduced by a large-scale simulation with 232,000 atoms.
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cross link inhomogeneity in Phenolic Resins at the initial stage of curing studied by 1h pulse nmr spectroscopy and complementary saxs waxs and sans wans with a solvent swelling technique
Polymer, 2016Co-Authors: Atsushi Izumi, Toshio Nakao, Yasuyuki Shudo, Mitsuhiro ShibayamaAbstract:Abstract The cross-link inhomogeneity of Phenolic Resins at the initial stage of curing in a temperature range of 110–130 °C was investigated through structural analysis of the network structure evolution mechanism using 1 H-pulse nuclear magnetic resonance spectroscopy and complementary small- and wide-angle X-ray and neutron scattering methods. Two types of Phenolic Resins, PR06 and PR12, were prepared with stoichiometrically insufficient and sufficient amounts of cross-linker, respectively, via curing of a novolac-type Phenolic resin oligomer with hexamethylenetetramine as the curing agent. Their network structures comprised three different structural domains because of the cross-link inhomogeneity: the high-cross-link-density domain (HXD), the low-cross-link-density domain (LXD), and the interface region between these domains. Percolation of the HXD occurred at the beginning of the curing. Intradomain reactions inside both HXD and LXD proceeded as the dominant reactions accompanying minor interdomain reactions between the HXDs, resulting in no significant change in the spatial location and size of the HXDs and LXDs. Intradomain reactions inside the LXD involved reactions with dangling chains, which would not affect the average mesh size of the domain significantly. These behaviors of the network structure evolution mechanism at the initial stage of the curing are a general feature of Phenolic Resins that does not depend on the amount of cross-linker. The difference between the amount of the cross-linker present in PR06 and PR12 was manifested as a difference in the degree of cross-linking in the percolated HXDs, i.e., the HXD of PR12 exhibited a tightly cross-linked, well-developed network structure since the beginning of the curing process; however, that of PR06 exhibited a loosely cross-linked network structure, with the degree of cross-linking increasing as the curing proceeded.
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gelation and cross link inhomogeneity of Phenolic Resins studied by small and wide angle x ray scattering and 1h pulse nmr spectroscopy
Polymer, 2015Co-Authors: Atsushi Izumi, Toshio Nakao, Mitsuhiro ShibayamaAbstract:Abstract The gelation mechanism and cross-link inhomogeneity of Phenolic Resins prepared via polycondensation of phenol and formaldehyde under acidic conditions were studied using small- and wide-angle X-ray scattering and 1 H-pulse nuclear magnetic resonance spectroscopy. The solvent-swelling technique was applied for both measurements at the initial stage of gelation to enhance the local fluctuations of the cross-link density. The change in the static and dynamic structures obtained through observations of the X-ray scattering functions and the spin–spin relaxation functions, respectively, during the polycondensation reaction indicates the presence of two different mechanisms for the formation and growth of the inhomogeneity that depend on the amount of cross-linker. (i) When there is a stoichiometrically insufficient amount of the cross-linker, inhomogeneous domains with a loosely cross-linked network appear at the initial stage of gelation. The intradomain reactions become dominant in the growth of the inhomogeneous domain and the degree of cross-linking in the domain increases by bridging two unreacted sites in the network structure via the cross-linker. (ii) When there is a stoichiometric amount of the cross-linker, inhomogeneous domains with a tightly cross-linked network appear at the initial stage of gelation. The interdomain reactions become dominant in the growth of the domain and the size of the domain increases by incorporating new polymer chains into the domain via the cross-linker.
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gelation and cross link inhomogeneity of Phenolic Resins studied by 13c nmr spectroscopy and small angle x ray scattering
Soft Matter, 2013Co-Authors: Atsushi Izumi, Toshio Nakao, Mitsuhiro ShibayamaAbstract:The gelation mechanism and cross-link inhomogeneity of Phenolic Resins prepared via polycondensation of phenol and formaldehyde under acidic conditions were studied by using 13C-NMR spectroscopy and small-angle X-ray scattering. The structural analysis of the gelation process indicated the presence of two different mechanisms of the formation and growth of the inhomogeneity that depend on the initial formaldehyde-to-phenol molar ratio: (i) when there is an insufficient amount of a cross-linker at the initial stage of gelation, inhomogeneous domains with a loosely cross-linked network appear and the degree of cross-linking in the domain increases with the reaction time. (ii) When there is a sufficient amount of a cross-linker at the initial stage of gelation, inhomogeneous domains with a tightly cross-linked network appear, followed by an increase in the size of the domains.
Toshio Nakao - One of the best experts on this subject based on the ideXlab platform.
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large scale molecular dynamics simulation of crosslinked Phenolic Resins using pseudo reaction model
Polymer, 2016Co-Authors: Yasuyuki Shudo, Atsushi Izumi, Toshio Nakao, Katsumi Hagita, Mitsuhiro ShibayamaAbstract:Abstract We constructed and characterized a network structure of crosslinked Phenolic Resins using a large-scale atomistic molecular dynamics simulation with a pseudo-reaction algorithm. The atomic configuration of the reaction products was controlled by the reaction probabilities and initial molecular structures. The crosslinked structure obtained from phenols as initial molecules agreed well with experimental results in terms of the branching structure of the Phenolic units and the methylene linkages, molecular weight distributions, densities, and scattering functions at various reaction conversions. The calculated structure factor for Phenolic Resins indicated inhomogeneous crosslinking, which expanded as the reaction proceeded after gelation. Voronoi tessellation analysis of the change in the occupation volume of the Phenolic units after crosslinking indicated that the initial molecular configuration influenced the resulting crosslinked structure. The experimental molecular weight distribution before gelation and the scattering function were well reproduced by a large-scale simulation with 232,000 atoms.
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cross link inhomogeneity in Phenolic Resins at the initial stage of curing studied by 1h pulse nmr spectroscopy and complementary saxs waxs and sans wans with a solvent swelling technique
Polymer, 2016Co-Authors: Atsushi Izumi, Toshio Nakao, Yasuyuki Shudo, Mitsuhiro ShibayamaAbstract:Abstract The cross-link inhomogeneity of Phenolic Resins at the initial stage of curing in a temperature range of 110–130 °C was investigated through structural analysis of the network structure evolution mechanism using 1 H-pulse nuclear magnetic resonance spectroscopy and complementary small- and wide-angle X-ray and neutron scattering methods. Two types of Phenolic Resins, PR06 and PR12, were prepared with stoichiometrically insufficient and sufficient amounts of cross-linker, respectively, via curing of a novolac-type Phenolic resin oligomer with hexamethylenetetramine as the curing agent. Their network structures comprised three different structural domains because of the cross-link inhomogeneity: the high-cross-link-density domain (HXD), the low-cross-link-density domain (LXD), and the interface region between these domains. Percolation of the HXD occurred at the beginning of the curing. Intradomain reactions inside both HXD and LXD proceeded as the dominant reactions accompanying minor interdomain reactions between the HXDs, resulting in no significant change in the spatial location and size of the HXDs and LXDs. Intradomain reactions inside the LXD involved reactions with dangling chains, which would not affect the average mesh size of the domain significantly. These behaviors of the network structure evolution mechanism at the initial stage of the curing are a general feature of Phenolic Resins that does not depend on the amount of cross-linker. The difference between the amount of the cross-linker present in PR06 and PR12 was manifested as a difference in the degree of cross-linking in the percolated HXDs, i.e., the HXD of PR12 exhibited a tightly cross-linked, well-developed network structure since the beginning of the curing process; however, that of PR06 exhibited a loosely cross-linked network structure, with the degree of cross-linking increasing as the curing proceeded.
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gelation and cross link inhomogeneity of Phenolic Resins studied by small and wide angle x ray scattering and 1h pulse nmr spectroscopy
Polymer, 2015Co-Authors: Atsushi Izumi, Toshio Nakao, Mitsuhiro ShibayamaAbstract:Abstract The gelation mechanism and cross-link inhomogeneity of Phenolic Resins prepared via polycondensation of phenol and formaldehyde under acidic conditions were studied using small- and wide-angle X-ray scattering and 1 H-pulse nuclear magnetic resonance spectroscopy. The solvent-swelling technique was applied for both measurements at the initial stage of gelation to enhance the local fluctuations of the cross-link density. The change in the static and dynamic structures obtained through observations of the X-ray scattering functions and the spin–spin relaxation functions, respectively, during the polycondensation reaction indicates the presence of two different mechanisms for the formation and growth of the inhomogeneity that depend on the amount of cross-linker. (i) When there is a stoichiometrically insufficient amount of the cross-linker, inhomogeneous domains with a loosely cross-linked network appear at the initial stage of gelation. The intradomain reactions become dominant in the growth of the inhomogeneous domain and the degree of cross-linking in the domain increases by bridging two unreacted sites in the network structure via the cross-linker. (ii) When there is a stoichiometric amount of the cross-linker, inhomogeneous domains with a tightly cross-linked network appear at the initial stage of gelation. The interdomain reactions become dominant in the growth of the domain and the size of the domain increases by incorporating new polymer chains into the domain via the cross-linker.
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gelation and cross link inhomogeneity of Phenolic Resins studied by 13c nmr spectroscopy and small angle x ray scattering
Soft Matter, 2013Co-Authors: Atsushi Izumi, Toshio Nakao, Mitsuhiro ShibayamaAbstract:The gelation mechanism and cross-link inhomogeneity of Phenolic Resins prepared via polycondensation of phenol and formaldehyde under acidic conditions were studied by using 13C-NMR spectroscopy and small-angle X-ray scattering. The structural analysis of the gelation process indicated the presence of two different mechanisms of the formation and growth of the inhomogeneity that depend on the initial formaldehyde-to-phenol molar ratio: (i) when there is an insufficient amount of a cross-linker at the initial stage of gelation, inhomogeneous domains with a loosely cross-linked network appear and the degree of cross-linking in the domain increases with the reaction time. (ii) When there is a sufficient amount of a cross-linker at the initial stage of gelation, inhomogeneous domains with a tightly cross-linked network appear, followed by an increase in the size of the domains.
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structural analysis of cured Phenolic Resins using complementary small angle neutron and x ray scattering and scanning electron microscopy
Soft Matter, 2012Co-Authors: Atsushi Izumi, Toshio Nakao, Hiroki Iwase, Mitsuhiro ShibayamaAbstract:The structure of cured Phenolic Resins prepared by compression molding of a deuterated Phenolic resin oligomer and nondeuterated hexamethylenetetramine as a curing agent was investigated using complementary small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and scanning electron microscopy (SEM). Cured thermosetting Resins have been considered to have an inherent inhomogeneity of the cross-links with sizes ranging from tens to hundreds of nanometers based on SEM observations of fracture surfaces. However, such spatial inhomogeneity has not been observed for the Phenolic Resins by either SANS or SAXS. The present observation with SANS and SAXS indicates that the Phenolic Resins have an inhomogeneity associated with internal fractal interfaces between voids and Phenolic Resins, with a fractal dimension equal to 2.5–2.6 in the range of 3–1600 nm. The presence of voids in Phenolic Resins with sizes ranging from tens to hundreds of nanometers is clearly confirmed by an evaluation of the difference in scattering length densities between the SANS and SAXS functions and by SEM observations of etched surfaces prepared by focused-ion beam milling. Therefore, it can be concluded that (i) cross-links are randomly distributed over the range and (ii) the spatial inhomogeneity of the cross-links in that range is very small and negligible in comparison with the inhomogeneity associated with the internal fractal interfaces in terms of the fluctuations of the neutron and X-ray scattering length densities.
I R Harrison - One of the best experts on this subject based on the ideXlab platform.
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small angle x ray scattering saxs in carbonized Phenolic Resins
Carbon, 1994Co-Authors: Anunay Gupta, I R HarrisonAbstract:Abstract Small-Angle X-ray Scattering (SAXS) has been used as an analytical tool to study the development of microstructure with increasing Heat Treatment Temperature (HTT) of a carbonized Phenolic resin, which is often used as matrix in commercial carbon-carbon composites. Processing parameters — heating rate and maximum heat treatment temperature — were the primary variables of interest. Results from SAXS have led to the consideration of a model for microstructure development in carbonized Phenolic Resins. Local density variations on the 10 A-100 A scale seem to be the predominant feature of these carbonized Resins in the temperature range studied (450–900°C). Heat treatment results in a gradual destruction of crosslinks, which leads to clustering of the aromatic units. These clusters enclose pores, the high concentrations of which give rise to scattering maxima in SAXS data. Concentration and dimensions of pores are sensitive both to the heating rate used and the maximum carbonization temperature.
Masakatsu Asami - One of the best experts on this subject based on the ideXlab platform.
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Phenolic Resins 100 years of progress and their future
Reactive & Functional Polymers, 2013Co-Authors: Kazuhisa Hirano, Masakatsu AsamiAbstract:Abstract Phenolic Resins have been under continuous development as an important thermosetting resin material since the first successful trial production of the synthetic resin in Japan in 1911. Sumitomo Bakelite Co., Ltd. traces its origin to the birth of this material (i.e. the successful trial production) and has been developing synthetic and composite production technologies since that time for adaptation to various applications. Phenolic resin molding compounds, which have been among the major applications of Phenolic Resins since their inception, exhibit highly favorable characteristics in terms of strength, heat-resistance, long-term reliability and cost, and therefore have been used in a wide range of applications from kitchen parts to components for electronic appliances and automobiles. In particular, Phenolic resin molding compounds are gathering attention as a lightweight solution to replace metals in automotive applications, among others applications, and we are investigating these applications while making a vigorous research effort toward further improving the mechanical properties of these materials. This new research and development is founded on detailed prediction and analysis of the hardened structures in Phenolic Resins. This report outlines the history of Phenolic Resins, which were invented in 1907 and brought to Japan, along with the associated technology, as a result of personal ties between Dr. Leo Hendrik Baekeland and Dr. Jokichi Takamine; the widening application of Phenolic Resins in recent years; showcase applications based on green sustainable chemistry; and examples of new analysis methods (chemical analysis) and structural analysis. We hope this report will encourage the research and development of plastics in the new century and the development of commercial products [1] .
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Phenolic Resins—100 years of progress and their future
Reactive & Functional Polymers, 2013Co-Authors: Kazuhisa Hirano, Masakatsu AsamiAbstract:Abstract Phenolic Resins have been under continuous development as an important thermosetting resin material since the first successful trial production of the synthetic resin in Japan in 1911. Sumitomo Bakelite Co., Ltd. traces its origin to the birth of this material (i.e. the successful trial production) and has been developing synthetic and composite production technologies since that time for adaptation to various applications. Phenolic resin molding compounds, which have been among the major applications of Phenolic Resins since their inception, exhibit highly favorable characteristics in terms of strength, heat-resistance, long-term reliability and cost, and therefore have been used in a wide range of applications from kitchen parts to components for electronic appliances and automobiles. In particular, Phenolic resin molding compounds are gathering attention as a lightweight solution to replace metals in automotive applications, among others applications, and we are investigating these applications while making a vigorous research effort toward further improving the mechanical properties of these materials. This new research and development is founded on detailed prediction and analysis of the hardened structures in Phenolic Resins. This report outlines the history of Phenolic Resins, which were invented in 1907 and brought to Japan, along with the associated technology, as a result of personal ties between Dr. Leo Hendrik Baekeland and Dr. Jokichi Takamine; the widening application of Phenolic Resins in recent years; showcase applications based on green sustainable chemistry; and examples of new analysis methods (chemical analysis) and structural analysis. We hope this report will encourage the research and development of plastics in the new century and the development of commercial products [1] .
