Keiichi Kuboyama

Oxygen permeability and free volume hole size in ethylene-vinyl alcohol copolymer film: temperature and humidity dependence

Abstract Relationship between oxygen permeability and free volume hole size evaluated from ortho -positronium lifetime in ethylene–vinyl alcohol copolymer (EVOH) was studied as functions of temperature and relative humidity. As the relative humidity rises at room temperature, the permeability first decreases and then increases. This behavior is attributed to the effects of pore filling and plasticization by water molecules. Linear correlations are obtained on the plots of logarithmic permeability versus reciprocal free volume hole size for EVOH at different temperatures and humidities as well as for different polymers including EVOH at room temperature, suggesting that the free volume hole size plays a crucial role in the oxygen permeation in EVOH and other polymers.

Photoinduced alignment of polymerisable liquid crystals on photoreactive polymers containing 2,6-bis(benzylidene)-1-cyclohexanone units in the main chain

ABSTRACT Photoreactive polymers containing 2,6-bis(benzylidene)-1-cyclohexanone (bisBC) units were synthesised and investigated as a photoalignment layer for polymerisable liquid crystals (PLCs) and liquid crystalline polymers (LCPs). The liquid crystalline materials were aligned homogeneously on the photoalignment layers in a wide range of irradiation dose of linearly polarised UV light (LPUVL). Specifically, for the photoalignment layer baked at 80°C, order parameters of the liquid crystalline materials were low due to the disturbance of oriented-photoreactive polymer caused by the contact with the solvent of liquid crystalline materials. However, the liquid crystalline materials were aligned homogeneously even at low irradiation doses on the thermally cured photoalignment layer baked at 180°C. In addition, the liquid crystalline materials were aligned perpendicular to the LPUVL electric field. The alignment mechanism is discussed by comparing the retardation of photoalignment layer with anisotropic polarisabilities of model molecules calculated by density functional theory (DFT). It is suggested that the liquid crystalline materials aligned along the unreacted chromophores in the photoreactive polymer. GRAPHICAL ABSTRACT

High-Pressure Analysis of the Multiple Melting Endotherms of Poly(ethylene succinate) and Poly(butylene succinate)

The origin of the multiple melting peaks in two linear polyesters, poly(ethylene succinate) (PES) and poly(butylene succinate) (PBS), of isothermally crystallized samples was investigated by differential scanning calorimetry (DSC) at atmospheric pressure and high-pressure differential thermal analysis (HP-DTA) at elevated pressures. In PES, the DSC melting curves showed three endothermic peaks at slow heating rates, which decreased to two with increasing heating rates. The HP-DTA curves showed that the area (qualitative) and peak height of the high-temperature peak decreased with increasing pressure and merged with the low-temperature peak at pressures above 450 MPa. This behavior supported the melting, recrystallization, and remelting model for the observed multiple melting endotherms. In PBS, the DSC melting curves were similar to those seen in PES. The HP-DTA curves were also similar to PES up to 400 MPa, but above this pressure the area and the peak height of the high-temperature peak and the temperature difference between the high- and low-temperature peaks remained unchanged. This observation suggested that the two peaks in PBS were due to the melting of two populations of crystals with different lamellar thickness originally present in the sample. The multiple melting behavior in isothermally crystallized PBS is proposed to incorporate both the melting of two populations of crystals and melting, recrystallization, and remelting.

Photo-induced alignment behaviour of polymerisable liquid crystals on bisazide in a polymer matrix

ABSTRACT Photo-reactive bisazide in a polymer matrix containing acryloyl groups on the side chain was investigated as a photoalignment layer for polymerizable liquid crystals (PLC). We found the thin film of bisazide (2,6-bis(4-azidobenzylidene)-4-methyl-1-cyclohexanone) in a polymer matrix, irradiated by linearly polarised ultraviolet light (LPUVL), was able to homogeneously align PLC. The LPUVL irradiation dose changed the orientation direction of the PLC on the thin film of bisazide in the polymer matrix. In addition, the direction of the slow axis for the retardation of the photoalignment layer changed from parallel to perpendicular to the LPUVL electric field with the irradiation dose. From these results, it was suggested that the PLC was likely to be aligned along the slow axis of the retardation of the photoalignment layer. We concluded that the key mechanism that changed the direction of the slow axis in a plane was the photoreaction of azide–acrylate at low irradiation dose and that of bis(benzylidene)cyclohexanone at high irradiation dose. Although the photoalignment as a result of a simple photo cross-linking was previously little known except for photo-dimerisation, we revealed that the photoaddition of azide–acrylate is able to achieve the photoalignment. GRAPHICAL ABSTRACT

Thermoplastic Vulcanizate Based on Poly(lactic acid) and Acrylic Rubber Blended with Ethylene Ionomer

ABSTRACT A new thermoplastic vulcanizate (TPV) was developed by meltblending of poly(lactic acid) (PLA), acrylic rubber (ACM), and ethylene-methacrylic acid with sodium ions (EMAA-Na). The PLA/ACM/EMAA-Na blend showed low-yield strength, low modulus, and excellent strain recovery. It also demonstrated an increase in complex viscosity and decrease in melting temperature due to the interfacial reaction between the PLA and the ACM phases. The Fourier transform infrared spectroscopy results indicate that EMAA-Na can interact with both PLA and ACM, and that the Na+ ions act as a catalyst for the interfacial reaction between PLA and ACM, while PLA does not react with ACM without EMAA-Na. Moreover, the tensile strength at break of the PLA/ACM/EMAA-Na blend was observed to be extremely improved by the addition of hexamethylenediaminecarbamate (HMDC) due to the increasing of the cross-link density inside the rubber phase. The morphology of the PLA/ACM/EMAA-Na blend with HMDC was finer than that of PLA/ACM/EMAA-Na without HMDC. From the results, it is suggested that the interfacial reaction between the PLA and the ACM phases, the cross-linking in the ACM phase, and the finer morphology improved the mechanical properties of the blend.

Thermoplastic Elastomer by Terpolymer Reactive Blending of Polyamide-6, Ethylene-1-Butene Rubber and Ethylene Ionomer

Reactive blending of polyamide-6 (PA6), maleic anhydride grafted ethylene-1-butene copolymer (EB-g-MAH) and ethylene-methacrylic acid ionomer partially neutralized by sodium ions (EMAA-Na) was performed to obtain a heat and oil resistant thermoplastic elastomer (TPE). The strain at break of the PA6/EB-g-MAH (40/60) was clearly higher than that of the PA6/EB (40/60). Addition of 2 wt% of EMAA-Na to the PA6/EB-g-MAH (38/60) blend induced an increase of the tensile modulus. TEM images confirmed that the PA6 was the matrix phase in the PA6/EB-g-MAH (40/60) blend, while the EB rubber phase was the matrix in the PA6/EB (40/60) blend. It was considered that the reaction between amino end groups of PA6 and maleic anhydride in EB-g-MAH induced the significant change of blend morphology. The PA6/EB-g-MAH/EMAA-Na blend showed similar morphology with the PA6/EB-g-MAH blend, and the EMAA-Na was expected to be located within the EB-g-MAH phase. It was found that ionic aggregates were formed in the EB-g-MAH phase by neutralization of the hydrated EB-g-MAH with sodium ions. The change of the mechanical properties by addition of EMAA-Na was due to the ionic aggregate formation which acted as physical crosslinks in the EB-g-MAH phase.

Shear effect on morphology of poly(butylene terephthalate) /poly(styrene-co-acrylonitrile) blends

Abstract The shear flow effect on the morphology of poly(butylene terephthalate)(PBT)/poly(styrene‐co‐acrylonitrile)(SAN) was studied by a parallel plate type shear apparatus. In PBT/SAN = 20/80 blend, particle size of dispersed domains was governed by both break‐up and coalescence processes, and it was much affected by shear rate. The minimum particle size was observed at a certain shear rate. This phenomenon can be explained by the shear matching effect of PBT and SAN; that is, the viscosity ratio of PBT to SAN changed with shear rate and the finest morphology was obtained at the appropriate viscosity ratio. Similar behavior was also observed for PBT/SAN = 70/30 (PBT was the matrix), even though the particle size was larger than that of PBT/SAN = 20/80. For PBT/SAN = 10/90 blend, the sample showed a complicated appearance during shearing. A translucent region correlated to the fine morphology was observed more than twice with increasing shear rate. This phenomenon could not be explained by the viscosity matching effect only. It was affected by small changes in the balance of breaking‐up and coalescence effects.

Thermoplastic elastomer by reactive blending of poly(butylene succinate) with ethylene-propylene-diene terpolymer and ethylene-1-butene rubbers

Poly(butylene succinate) (PBS) was melt blended with maleic anhydride–grafted ethylene-propylene-diene terpolymer (EPDM-MAH) and maleic anhydride–grafted ethylene-1-butene copolymer (EB-MAH) to obtain thermoplastic elastomers (TPEs) containing a biodegradable polyester. PBS/EB-MAH blend showed lower modulus and excellent strain recovery compared to PBS/EPDM-MAH blend due to the smaller rubber particle size. Tensile strength of PBS/EPDM-MAH blend was found to be significantly improved by annealing because of the increased interfacial reaction between PBS matrix phase and EPDM dispersed phase and the increased cross-linking in EPDM. As the result, it was found that the annealing process is effective for the improvement of the mechanical properties of PBS/MAH-grafted rubber blends.

Photoalignmentability of silsesquioxane-containing citraconimide and its solvent-induced surface enrichment in PMMA matrix

ABSTRACT Photo-reactive polymer of silsesquioxane-containing citraconimide (SQ-CI) was synthesised and evaluated as a photoalignment layer for polymerisable liquid crystals (PLC). A generation mechanism of the anisotropy by the linearly polarised ultraviolet light was discussed by comparing optical retardation of SQ-CI with theoretical calculations using density functional theory. In addition, the SQ-CI and poly(methyl methacrylate) were blended for a model of unification of photoalignment layer and protection layer in liquid crystal display. The orientation of PLC on the blend film was dominated by the solvent used for the sample preparation of PMMA/SQ-CI blend. We found that the SQ-CI was enriched at surface of the blend film prepared from the ?-butyrolactone solution, while not in the case of the film prepared from cyclopentanone solution. The surface enrichment in the film prepared from ?-butyrolactone solution does not follow the conventional mechanism which is that the lower surface free energy component segregates to the blend surface, because the surface free energy of SQ-CI is higher than that of PMMA. Based on the result of solvent-annealing effect and photoalignmentability, we concluded that the mechanism of surface enrichment was explained due to the difference of affinity between the polymer and the solvent. Graphical Abstract

PMMA/TEMPO-oxidized cellulose nanofiber nanocomposite with improved mechanical properties, high transparency and tunable birefringence

Recently, cellulose nanofibers (CNFs) have been developed as a very popular renewable and biodegradable nanofiller material for polymer nanocomposites. However, achieving good dispersion in a polymer matrix for effective reinforcement is still a challenge because CNFs are hydrophilic, whereas most polymers are hydrophobic. In this study, we report the poly(methyl methacrylate)/2,2,6,6-tetramethylpiperidyl-1-oxyl oxidized CNFs (PMMA/TOCN) nanocomposites, which show good dispersion, improved mechanical properties, excellent transparency, as well as controllable birefringence using a simple surface-modification procedure of TOCN with amine-functionalized poly(ethylene glycol). Studies conducted using transmission electron microscopy and fourier transform infrared spectroscopy showed that TOCNs were homogenously dispersed in the PMMA matrix without aggregation due to the successful surface modification of TOCN. Moreover, the nanocomposites were highly transparent and the transmittance in the visible region was as high as approximately 90%. In addition, we firstly discovered that the birefringence of the nanocomposite could be controlled by the amount of TOCN added, even achieving zero birefringence. More importantly, the tensile strength and Young’s modulus of PMMA were significantly improved with the addition of TOCN. Such well-dispersed TOCN-based nanocomposites with high transparency, controllable birefringence and enhanced mechanical properties exhibit great potential for the applications in the optical devices and in the engineering field.