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The thermally sensitive polymer, poly ( l -lactic acid) PLLA, is first printed to a high-resolution object using an advanced 3D printing technology, called melt electrowriting (MEW). The MEW processing conditions are systematically investigated to manufacture PLLA scaffolds with adjustable filament diameter and pore size for the application of bone tissue engineering. To this end, the relationships among the rheological behavior of the molten polymer, the electro-hydrodynamics of the jet, and the processing parameters (applied voltage, collection speed, and flow rate) are illuminated. The scaffold with relatively high deposition accuracy and crystallinity of PLLA is achieved when the printing speed was set slightly above the critical translation speed. The MEW PLLA scaffold with filament diameter of 40 μm and pore size of 200 μm is evaluated with KUSA-A1 cells to prove its in vitro potential. This is a milestone work for MEW since it supplies one of the best strategies to design and manufacture an essential biobased polymer for tissue engineering.

The electrodynamics of the polymer melt as well as its effects on fiber spinnability in the framework of laser-heated melt electrospinning was investigated. We challenge the classic views in the aspects of the molten Taylor-cone, the thinning process, and the jet deformation. A temperature-voltage phase diagram was constructed to distinguish the regimes of the bending, the whipping, and the break-up of the jet. These jet kinematics are significantly dependent on the molten Taylor-cone, the jet thinning, and the forces exerted on the jet. The surface tension restricts the growth of the jet while it can be safely neglected after jet initiation. Jet breaks up periodically at the tip of Taylor-cone if the polymer viscosity is too low or the elongation rate is not high enough to stretch the jet. The elongation rate for each segment of the jet keeps almost constant at a certain melt temperature, while the elongation rate increases and the solidification point of the jet shifts from the Taylor-cone to the target with increasing melt temperature. An analytic equation is proposed to estimate the jet diameter along the spinline before jet solidifies. Additionally, the experiment of coiling proved that the electrical and the elastic as the dominant forces for bending are gradually replaced by the inertial and the viscous forces for whipping.

Biodegradable polymer yarns of polymer blends of poly(lactic acid) (PLA) and poly(butylene succinate-co-adipate) (PBSA) reinforced with natural fiber were prepared by a micro braiding technique. The biodegradation of the micro-braid yarn was studied by field tests. The yarn are prepared from polymer blends of PLA:PBSA with ratios of 100:0, 90:10, and 85:15 (wt%) by a single screw extruder. Braided samples were prepared using jute as a braided core fiber. The mechanical property analysis showed tensile strength of polymer yarn with jute fiber higher than polymer yarn without jute. Biodegradation of micro-braiding yarn with and without jute fiber was studied by buried under controlled conditions compared with cellulose. The field biodegradation test was carried out for 28 days with period of 7 days sampling. It was found that humidity and soil temperature affected the biodegradability of polymers. Analysis of samples confirmed that buried at low temperature position showed higher degradation than at high temperature. High humidity enhanced the degradability due to hydrolysis reaction. Micro-braided polymer yarns of PLA:PBSA (85:15) and PLA:PBSA (85:15)/jute showed similar biodegradability confirmed that the mechanism of biodegradation from surface of the yarn was priority.

The higher-order structure and the formations of SC and HC of the PLLA/PDLA blend melt-electrospun fibers collected on a rotating target were investigated. The diameter of the fiber decreased and the orientation factor increased with increasing take-up velocity. The formation of SC was promoted with decreasing fiber diameter and with increasing take-up velocity. The fiber collected on the fixed target was amorphous and did not show the molecular orientation to any particular directions indicating that the stretching of the fiber by the electrostatic force did not give much molecular orientation to the fiber. On the other hand, the stretching of the fiber by applying the mechanical taking-up gave a significant degree of the molecular orientation to the fiber direction. The crystalline orientation of HC of the annealed fiber was higher than that of SC.

Bacterial poly(3-hydroxybutyrate-co-hydroxyhexanoate) (PHBH) biaxially oriented films were prepared by combination of the roll and biaxial drawing processes. Compression molded films, which consisted of large spherulite aggregation, were roll drawn up to ×1.4 and further biaxially drawn up to 3.0×3.0. The tensile modulus and the break elongation decreased while the tensile strength increased as the biaxial draw ratio increased. Biaxially drawn films showed two kinds of structures: one in which the c-axis was almost perpendicular to the film surface and the other in which the c-axis was at an incline compared to the normal film surface. The correlation among the processing conditions, higher-order structures, and mechanical properties was investigated using wide-angle X-ray diffraction, small-angle X-ray scattering, and tensile measurements. Open image in new window

Structure of poly(dioxanone) (PPDX) fibers produced through a two-step melt-spinning process with an additional short-period annealing above the melting temperature of PPDX was investigated and the effect of annealing on the degradation behavior was discussed. The morphological study carried out by etching the fibers using a phosphate or permanganate solution suggested that the fibers take a skin–core structure, and both the skin layer and the core region consist of a bundle of microfibrils. The micro-beam X-ray diffraction analysis revealed that the short-period annealing in the production process only slightly promotes the crystallization in the skin layer but contributes to increasing the packing of amorphous chains near the skin, which seems to be the controlling factor of the hydrolytic degradation behavior of the fibers.

Poly(tetrafluoroethylene) (PTFE) fiber with a superior mechanical property was prepared directly from its emulsion by the novel manufacturing process. The PTFE emulsion turned into a paste when a high shear flow was applied and the paste was extruded through a nozzle into a strand consisting of fine PTFE particles. The diameter of the strand was reduced stepwise by applying the die-drawing process through a conical die at a low temperature. The strand was further die-drawn down at elevated temperatures into fine PTFE fibers with a highly oriented crystalline structure. The crystalline orientation factor of the PTFE fiber reached very close to unity. Although the fibers obtained have a very high tensile modulus, the tensile strength was not as high as that expected from the crystalline orientation, suggesting that the presence of some defects in the PTFE fiber formed in the instantaneous deformation.

A new electrospinning set-up is described for continuous aligning of poly(L-lactide) yarn. It comprises a slowly rotating grounded `funnel' target and a winder placed right up to the funnel. A charged polymer jet is ejected from a nozzle. The electrospun fibers are first accumulated on the mouth plane of the funnel to form a web. The web is then pulled upward and guided to a winder on which twisted fibers are continuously wound as a bundle. Each filament of the bundle is slanted at about 45 relative to the collecting direction, and its average diameter is 6.0+/-1.9 mu m. The drawn fiber shows improved tensile properties as a result of the increased molecular orientation. The morphologies of the twisted fibers before and after drawing are compared.

Thin fibers having diameters ranging from 25 nm to 2 micro-m were successfully electrospun from solutions of polylactides (PLA) having different molecular weights both in entangled and aligned fiber forms. The latter aligned fibers were collected with a new target comprising a rotor around which several fins were attached. Low viscosity of the solutions resulted in formation of beads or beads-on-strings, while high viscosity gave homogeneous fibers at optimum conditions. The resultant aligned fibers were drawn to 2 - 3 times at various optimum temperatures. WAXD of the drawn fibers revealed smectic nature of the PLA chain arrangement in spite of crystal orientation supported. The mechanical properties of the PLA fibers were also improved after drawing.

Solution-spun PLLA⁄PDLA blend fibers were obtained by the laboratory size spinning machine. The fibers obtained were drawn to various ratios at temperatures ranging from 80 to 140°C and subsequently annealed at 200°C under tension. Solution-spun fibers were highly crystallized during the coagulation process in the solution spinning and only the a-form homo-crystal of PLLA and PDLA were detected. Drawing of the fiber at temperatures between 80°C and 160°C did not promote the stereocomplexation between PLLA and PDLA. The drawn fiber seems to have two homo-crystal phases, one easily transformed to the streocomplex upon annealing at an elevated temperature and the other stayed either homo-crystal or melted during annealing and froze into the amorphous phase. The fibers drawn to higher ratios at higher temperatures, which showed a large melting peak of the homo-crystal at higher temperature region, kept homo-crystal phase even upon annealing at 200°C. On the other hand, the fibers drawn to lower ratios at lower temperatures, which show the single melting peak of homo-crystal at a lower temperature region, changed the structure from oriented homo-crystal to the oriented stereocomplex upon annealing. Due to the small content of oriented stereocomplex crystal and larger content of unoriented amorphous phase, the fibers annealed at an elevated temperature have fairly poor mechanical property.

Poly(L-lactic acid) fibers were prepared by the melt electro-spinning process using CO2 laser irradiation. A grounded metallic flat plate and a grounded metallic rotating blade were used to collect the electrospun fibers. The fiber structure was investigated by polarizing optical microscopy, scanning electron microscopy and X-ray diffraction. The average fiber diameters were decreased with laser output power applied, and the fiber diameters collected on the flat collector were smaller than those collected on the rotating collector. The polarized light micrograph observation under crossed-nicol clearly showed an optical anisotropy of the as-spun fibers. The X-ray diffraction patterns of the annealed fibers showed a crystal orientation. Although the uniaxial drawing of the fibers up to x 2 enhanced the crystalline orientation, the crystal modification was unchanged.

Montmorillonites (MMT) treated with various organic amines were added to the acrylic rubber in the polymerization process. Effects of the kind of organic amines, the contents of added MMT, and the method of the addition of MMT to the acrylic rubber on the dispersion state of MMT in the matrix and on the mechanical property of the obtained rubber were studied. As a result, the remarkable improvement of the mechanical property was achieved when 5 wt% of MMT organically treated with the laurylamine was added, although the deterioration of the mechanical property was observed at higher MMT contents. On the other hand, the mechanical property of the sample, to which MMT was added in the solution state, was improved gradually with the MMT content without showing a significant deterioration. Although the addition of organically treated MMT having a hydrophobic surface was added in the aqueous emulsion polymerization system, an excellent dispersion state was achieved when 5 wt% of MMT treated with laurylamine was added. Moreover, comparing with the friction property, the heat resistance, and the water resistance of the acrylic rubber added with MMT to those of the acrylic rubber added with the white carbon, it was proved that the addition of MMT significantly improve various physical and practical properties of the acrylic rubber.

A new target collector was designed for taking up aligned nanofibers by electrospinning. The collector consists of a rotor around which several fins were attached for winding electrospun filaments continuously in large amounts. The alignment of the nanofibers wound on the collector was affected by the electrospinning conditions, such as the needle-to-collector distance and the applied voltage, but not by the rotation speed of the collector. At a voltage of 0.5 kV · cm -1 , about 60% of the fibers were found to be aligned within an angle of ± 5° relative to the rotational direction of the collector. The fiber alignment was improved to 90% by drawing the fiber bundle 2-3 times at 110°C. The drawing was also effective for crystal orientation of the fibers as revealed by WAXD. The drawn fibers show improved mechanical properties.

Montmorillonites organically treated with various alkylamines were filled to the acrylic rubber and various properties including mechanical, oil resistance, and abrasion were investigated. Montmorillonite tended to exfoliate after the organic treatment and uniformly dispersed in the acrylic rubber. This uniform dispersion of the filler resulted in the improvement of the mechanical property. Number of carbon atoms in the alkylamine used for the organic treatment increased the swelling with oil at high temperature. Abrasion wear rate of the acrylic rubber was reduced when organically treated montmorillonite was well dispersed in the matrix.

Poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) with high molecular weights were melt mixed in a special procedure into a blend which produced the stereocomplex without indicating any trace of the occurrence of the homo-crystal. The granular blend with high stereocomplex content was obtained by mixing PLLA and PDLA at a temperature between Tms of the homo-crystal and the stereocomplex. This blend produced the stereocomplex consistently even in the repeated melting-solidifying processes. The formation of the block-copolymer of L- and Dlactic acids suspected to occur during the blending at high temperature may act as either the nucleating agent of the stereocomplex crystal or the compatibilizing agent for PLLA and PDLA. The blend obtained was melt-spun into amorphous fibers. Some of the drawn fibers showed very broad WAXD reflections from the alpha-form crystal, which immediately transformed to the stereocomplex in the annealing process at elevated temperatures without relaxing the molecular orientation. The annealing under tension seemed to extend the tie molecules between lamella of the stereocomplex and the change in the structure significantly reflected the mechanical property.

Zirconium oxide (ZrO2) particles are dispersed in polystyrene (PS)/poly(butyl methacrylate) (PBMA) and PS/poly(methyl methacrylate) (PMMA) blend melts with bicontinuous structure. ZrO2 particles enter exclusively into PBMA phase in PS/PBMA blend, while the particles exist in both phases in PS/PMMA blend. The main cause for the exclusive localization in PBMA phase is the lowest entropy loss of the most flexible PBMA chains among the three polymers due to adsorption onto ZrO2 particles. In PBMA phase, spherical aggregates of ZrO2 particles are formed at a concentration of 11 vol%, while ZrO2 particles make linear arrays at 21 vol% and branches at 29 vol%. These arrays and branches give very high second-plateau in G' at low frequencies. In PS/PMMA blend melt, linear arrays and branches appear in both phases even at 4.4 vol%, and network structure is formed at 11 vol%. Due to the structural difference, the PS/PMMA/ZrO2 composite gives much higher second-plateau than that of PS/PBMA/ZrO2, when compared at the same vol% of ZrO2. A peculiar network structure is observed in PS/ZrO2 composite at a low concentration of 4.4 vol%. The low value of G' close to that of the matrix at intermediate frequencies with a small number of spherical aggregates indicates very weak adsorption of PS chains to ZrO2 particles.

Bacterial poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)(PHBH) highly oriented films were prepared by the combination of roll and uniaxial drawing processes. Compression molded films, which is rather brittle, turned to be ductile after roll drawing up to x 2, and the films were further uniaxially drawn to a draw ratio as high as 1000 %. The PHBH film with the tensile strength of 178 MPa and the modulus of 1.4 GPa were obtained. The roll drawn PHB film showed a slight crystalline orientation of Alpha-form. The orientation advanced with uniaxial draw ratio and the formation of Beta-form crystal was observed. Relations among the processing conditions, higher order structures and mechanical properties were investigated using wide-angle X-ray diffraction, differential scanning calorimetry, and tensile measurements.

Poly(lactic acid) (PLA) is a biobased polymer made from biomass having high mechanical properties for engineering materials applications. However, PLA has certain limited properties such as its brittleness and low heat distortion temperature. Thus, the aim of this study is to improve toughness of PLA by blending with poly(butylene succinate-co-adipate) (PBSA), the biodegradable polymer having high toughness. Polymer blends of PLA and PBSA were prepared using a twin screw extruder. The melt rheology and the thermal property of the blends were examined. Further the blends were fabricated into compression molded parts and melt-spun fiber and were subjected to tensile and impact tests. When the PBSA content was low, PBSA phase was finely dispersed in the PLA matrix. On the other hand, when the PBSA content was high, this minor phase dispersed as a large droplet. Mechanical properties of the compression molded parts were affected by the dispersion state of PBSA minor component in PLA matrix. Impact strength of the compression molded parts was also improved by the addition of soft PBSA. The improvement was pronounced when the PBSA phase was finely dispersed in PLA matrix. However, the mechanical property of the blend fibers was affected by the postdrawing condition as well as the PBSA content. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41856.

Biodegradable poly[(R)-3-hydroxybutyrate| (P(3HB)) fibers with high tensile strength of 1.32 GPa were processed from ultra-high-molecular-weight P(3HB) by a method combining cold-drawing and two-step-drawing procedures at room temperature. The distribution of molecular structures in a mono-filament was analyzed by micro-beam X-ray diffraction with synchrotron radiation. It was revealed that the P(3HB) fiber has a new core-sheath structure consistent with two types of molecular conformations: a 2 1 helix conformation in the sheath region and a planar zigzag conformation in the core region.

Influence of surface treatment and crosslinking density on the rheological and mechanical properties of silicone resin filled with silica particles was investigated. Although addition of particle in the liquid silicone matrix increased the storage modulus G' and the complex viscosity |η*| especially at a low frequency region, surface treatment of particle suppressed such tendency. On the other hand, surface treatment increased the storage modulus E' and the tensile modulus E of crosslinked elastomers. Particle unfilled silicone elastomer showed an increasing storage modulus with temperature at a rubbery region behaving as an entropy elastomer and highly particle filled elastomers showed a decreasing storage modulus indicating an enthalpy elastic character. However silicone elastomers with small particle content changed their character from entropy elastic to enthalpy elastic with increasing crosslinking density.

The mono-filaments (> 10 m in length) of chitosan and the blends of chitosan-collagen, chitin-collagen and chitin-silk fibroin were wet-spun. The mono-filaments were chemically N-modified with each of n-fatty acid anhydrides, intra-molecular carboxylic anhydrides, fragrant aldehydes and transition metal ions. The mono-filament was aligned on a straight line with the mono-filament of silk fibroin or poly(ethylene terephthalate) (PET), and a bundle of one to three mono-filaments was coated with a medium of sericin (Se), chitosan or N-acylchitosan to give rise to novel silk-mimic filament composites. The filaments coated with a medium of sericin exhibited 26-27 denier for the titer, 2.46-3.36 gf.denier -1 for the tenacity and 11.8-25.0% for the elongation. The apparent density (denier.μm -1 in the filament diameter) of the filament composites was about 3-4 times higher than that of the mono-filaments. Portion of fragrant aldehydes in Schiff's base was slowly hydrolyzed at room temperature by contacting with atmospheric moisture in the open air, and released from the fragrant filaments and composites. The filament composites coated with a chitosan medium were thrombogenic, and those coated with N-acylchitosans were antithrombogenic.

The damage imposed on SiOx deposited nylon 6 films as a result of abrasion with a cotton cloth and Gelboflex testing was examined by evaluating the rate at which copper plates, which were enveloped by the damaged films, were corroded by H2S. Abrasion with a cotton cloth caused some micro-cracking of the SiOx layer and the permeation rate of H2S approached that of the uncoated nylon 6 film. Damage to the SiOx layer by twisting and crushing progressed gradually with the number of Gelboflex test cycles and correspondingly the corrosion rate of the copper plates increased. Comparison of the corrosion rates of the copper plates kept in the pouches made of various commercial films with those obtained for the damaged SiOx deposited nylon 6 films showed a clear relationship between the H2 permeation rate of the films and the corrosion rate of the copper plates by H2S.

Silica/poly (vinyl alcohol) (PVA) layers with various PVA ratios were coated on nylon 6 films by sol-gel method. Damage of Silica/PVA layer on the nylon 6 film caused by elongation was examined by an atomic force microscope (AFM) and scanning electron microscope (SEM) observations and measurements of water vapor permeation rate. At 1% elongational strain, pure silica layer no longer follows the deformation of nylon film and the linear cracks perpendicular to the stretching direction were produced. Consequently water vapor permeability of silica coated films increased drastically. However, critical elongational strain at which linear cracks were produced increased with PVA ratio in silica/PVA layer and only mild deterioration of barrier property was observed. Such durability of silica/PVA layer to the elongational strain is due to the flexibility of silica/PVA layer which can follow the deformation of nylon film. Further PVA seems to fill the micropores of silica prepared by sol-gel method.

Dynamic viscoelastic properties, steady shear and biaxial extensional flow behaviors have been investigated for melts of potassium titanate whisker filled polyoxymethylene. A second plateau appears in the low frequency region of the storage modulus G', and the plateau value increases with whisker content. Addition of the whisker also increases the steady shear viscosity and the low strain rate asymptote of the biaxial extensional viscosity. The upturn of biaxial extensional viscosity from the low strain rate asymptote decreases by the addition of whisker due to suppression of polymer chain extension. Change in whisker dispersion and orientation in the melts was observed with scanning electron microscopy after quenching the samples in biaxial extensional flow. The degree of whisker orientation to the flow direction decreases with increasing strain rate in the range where the strain rate is much greater than the rate of whisker orientation and it is smaller than or comparable with the relaxation rate of the matrix chain. It is suggested that the matrix does not have enough power to orient the whisker in this range of strain rate.

The changes in the barrier properties due to the damage imposed on the SiOx deposited nylon 6 films accompanying various deformations such as bending and elongation were examined by evaluating the corrosion rate of the copper plates by H2S kept in the pouches made of the damaged films. After application of elongational deformation of as high as 2% or less, only slight corrosion of the copper plates, almost similar to those of the copper plates kept in the pouches made of undeformed films, was observed. After application of elongational deformations of 3% or more, the corrosion of the copper plates was more distinct and proceeded significantly with time, Bending deformation given to the SiOx deposited nylon films also deteriorated the barrier property to H2S when the radius of curvature at the bent part was small. Comparison of the corrosion rates of the copper plates kept in the pouches made of films deformed in various ways and undeformed commercial films shows a clear relationship between the H2 permeation rate of the films and the corrosion rate of the copper plates by H2S.

Silicate layer was prepared on the nylon 6 film by sol-gel method. Effect of reaction conditions on the various properties, such as layer thickness, surface morphology and the water vapor permeation rates were examined. Increasing sol-gel reaction time gives a increasing silicate layer thickness. However because of the roughness of the surface produced due to the 3-dimensional siloxane network formation in sol-gel reaction system occurred at a longer reaction time, the water vapor permeation rate was high. Addition of DMF in sol-gel reaction system controlled the drying of coated film and suppressed the shrinkage of silicate layer resulting in the smooth crack-free layers. When UV was irradiated on the sol-gel reaction system, the surface of the coated film was rather smooth and the coated film gave a fairly high barrier to water vapor, although the thickness of the layer was rather small.

The deformation and shape recovery of a soft polymer droplet in an immiscible polymer matrix with higher viscosity were directly observed from two directions after application of large double-step shear strains. After application of the first-step strain γ1 (|γ1|=5), the deformed droplet changes its shape, starting from a flat ellipsoid to a rodlike shape then to a dumbbell, an ellipsoid of revolution, and finally back to a sphere. When a large second-step strain γ2 is applied in the same or opposite direction to the first strain during the recovery, the shape of the droplet and the orientation angle depend on both γ2 and the shape during the recovery. Just after application of γ2 (0

Poly(butylene succinate) copolyesters with terephthalic acid (T) were melt-spun into monofilaments, subsequently were drawn with draw ratio of 2-6 times. The structure and properties of these drawn fibers were examined by wide angle X-ray scattering, differential scanning calorimetry, tensile test and scanning electron microscope (SEM). The enzymatic degradation of these fibers was performed in a buffer solution with Rhizopus delemar lipase at 37°C and evaluated by weight loss, SEM observation and tensile strength retention. The copolyester with 17 mol % of T component (T-17) fiber drawn with draw ratio of 6 times at 40°C showed the much higher degradation rate than poly(butylene succinate) and the copolyester with 52 mol % of T component (T-52) fibers. Tensile strength of T-17 fiber was decreased appreciably at the initial stage of the enzymatic degradation. The degradation rate of T-17 fiber was remarkably decreased with increasing the draw ratio of the fibers due to the increase in crystallinity and the development of orientation in the amorphous region.

Dynamic viscoelasticity and tribological properties of epoxy resins cured using four curing agents with various chain length were studied. Viscoelastic functions of the resins were similar in form and the glass transition temperature Tg decreased with increasing chain length of the curing agent. Hence, these epoxy samples showed simialr viscoelastic properties in a temperature range in reference to Tg. Changes in the velocity and the applied pressure in the tribological tests affected the temperature of the friction interface. Observation of the wearing behavior revealed that there were three different temperature ranges in reference to Tg. At temperatures below Tg-100°C all the samples showed a fairly low coefficient of friction, leaving flake like wear particles. At temperatures above Tg-100°C, the coefficient of friction increased with temperature. In an intermediate temperature range about 20 to 100°C less than Tg, roll debris came out. At temperatures near and higher than Tg, samples were severely damaged and the wear rate was extremely high.

Change in fiber orientation in glass fiber filled polypropylene (PP/GF) melts was observed with scanning electron microscopy after quenching the samples in biaxial extensional flow. The upturn of biaxial extensional viscosity from the low strain rate asymptote decreases by the addition of glass fibers, due to suppression of polymer chain extension. When the binder of glass fibers is immiscible with the matrix, fiber dispersion becomes worse and there appears a very small upturn in the biaxial viscosity. It has been found that there is an appropriate range of strain rate where the glass fibers orient well to the flow direction. This range corresponds to the range where the strain rate is much greater than the rate of fiber orientation and it is smaller than or comparable with the relaxation rate of the matrix chain. In this range, the degree of fiber orientation decreases with increasing the strain rate. It is suggested that the fibers take time to orient and cannot follow the fast flow in this range where the matrix does not have enough power to orient the fibers.

The interfacial tension between a poly (isobutylene) (PIB) and a poly (dimethylsiloxane) (PDMS) was obtained by an improved imbedded fiber retraction method from the observation of the PDMS (or PIB) droplet shape in the PIB (or PDMS) matrix after application of the step shear strain. The interfacial tension was also obtained from the observation of the PDMS (or PIB) droplet shape during the steady shear flow. We compared the values of interfacial tension obtained by these methods with the value determined by the pendant drop method. It was found that these values agree fairly well when the viscosity ratio of the droplet to the matrix is around unity.

Tensile properties and the phase morphologies of ABS resins with various rubber particle sizes and graft ratios of SAN are examined. Large rubber particles disperse well in ABS resins irrespective of the graft ratio. On the other hand, the graft ratio affects the dispersion state of the small rubber particle, particles with high graft ratio disperse well and those with low graft ratio tend to coalesce into large aggregates. These differences of the morphology strongly alter the deformation mechanism, such as craze formation and cavitation in the rubber particles. The effects of mixing of ABS resins with various graft ratio and particle size on the mechanical properties and phase morphology are also discussed.

We observed the stress relaxation and shape recovery of a dispersed droplet phase after application of step shear strains in a polystyrene/polycarbonate blend melt. A polystyrene makes a droplet phase in a polycarbonate matrix of higher viscosity. The orientation angle of the droplet is independent of the initial radius. The angle does not change during stress relaxation and is nearly equal to the angle given by the affine deformation. The shape recovery of the droplets leads to the decay of the relaxation modulus at long times. The stress relaxation slows down at long times for large strains, reflecting the retarded shape recovery of the droplets. Calculated time dependences of the relaxation modulus based on the rate equations by Doi and Ohta [J. Chem. Phys. 95, 1242–1248 (1991)] do not agree with the observed slowing down of the stress relaxation. A force balance equation developed by Cohen and Carriere [Rheol. Acta 28, 223–232 (1989)] explains the retarded shape recovery of the droplet from a prolonged ellipsoid of revolution to a sphere.

Dynamic viscoelasticity of ethylene-co-methacrylic acid copolymer (EMAA) and its ionomers (EMAA-Zn and EMAA-Na) has been measured in the melt state. The time-temperature superposition principle is applicable to data of angular frequency dependences of storage modulus (G') and loss modulus (G") for EMAA very well from 140°C to 200°C. On the other hand, data for ionomers give two separated master curves with different temperature dependences of shift factor, one from the data obtained in the range of 140°C-170°C and the other in the range of 180°C-200°C. Even at 200°C, the moduli G' and G" are still much higher than those of EMAA. These results indicate that a structure change in EMAA ionomers occurs between 170°C and 180°C. The free volume fraction (fr) and the thermal expansion coefficient (αf) in the range of 180°C-200°C are larger than those in the range of 140°C-170°C for EMAA ionomers. This implies that in higher temperature range, some hydrocarbon chains depart from cross-links of ion aggregates and move much more freely.

Tranilast, N- (3, 4-dimethoxycinnamoyl) anthranilic acid), which suppresses the fibro blast hyperpalsia, and poly (e-caprolactone) (PCL), a biodegradable polyester with a low melting point, were blended and melt spun to produce the drug releasing biodegradable fibers.Thermal analyses, polarized optical microscope observation, and WAXD analyses revealed that tranilast existed as crystal in PCL solid at room temperature and dissolved in molten PCL at an elevated temperature. This tranilast acted either as a crystal nucleating agent or an impurity which obstracted the crystallization of PCL depending on the tranilast content and the thermal history.Melt-spun fibers of PCL/tranilast blends had mechanical properties which deteriorated with increasing tranilast contents. The drug release rate decreased with increasing draw ratio. This seems to be attributable to high crystallinity of drawn fibers.

We improved the imbedded fiber retraction (IFR) method as a simple method to obtain the interfacial tension between polymer melts. A force balance equation for a fiber in an immiscible matrix by Cohen and Carriere is solved for a more realistic fiber shape at later stage of retraction. Moreover, unknown hydrodynamic coefficient in the balance equation is determined theoretically as 0.125. The interfacial tension between polystyrene (PS) and poly (methy methacrylate) (PMMA) is measured by the improved IFR (IIFR) method as well as the breaking thread method and dynamic viscoelasticity method. In dynamic viscoelasticity method, we determine the interfacial tension by fitting the Palierne theory with dynamic viscoelastic data. The interfacial tension obtained from the three methods agrees fairly well and is found to be about 1.6 mNm＾ at 180°C and 1.4mNm＾ at 200°C.

Polymer blend is one of the materials which has shown a highest growth rate in the polymer industries. One of the key factors to obtain the polymer blends with superior performance is to control the phase morphology and higher order structure of the blends. Sea-island morphology in the incompatible blends has to be controlled in the flow fields during shaping process. Even in the compatible blends, control of the crystalline higher order structure has to be carried out in the processing, if at least one of the component is crystalline. This report presents some of the researches related to the processability and the mechanical properties of polymer blends, including the researches on “PLLA/PDLA blend fibers”, “Polymer blends which involve a liquid crystalline polymer as a component”, and “Observation of deformation and recovery of minor phase in an incompatible polymer blend”.

The deformation and recovery of a poly(isobutylene) droplet with a lower viscosity embedded in a poly(dimethyl siloxane) matrix are directly observed from two directions after application of a large step shear strain. The droplet shape and recovery time strongly depended on the magnitude of the applied strain. Just after application of a large strain, a droplet deforms almost affinely to a flat ellipsoid. It then changes into a rodlike shape, a dumbbell, and to an ellipsoid of revolution, and finally to a sphere. Model calculations show that the primary driving force for the shape recovery is the interfacial energy in order to reduce the surface area of the deformed droplet.

Silicon monoxide (SiO) amorphous layer was deposited on the biaxially oriented nylon 6 films in a vacuum evaporator. This deposited layer tightly attaches to the nylon film. SiO deposited nylon 6 films thus obtained are transparent and show a high barrier to the water vapor and oxgen. Wettability of the SiO surface of the film to the water, ink, and the adhesives are satisfactory for the gravure printing and lamination with polyolefin films. It was found that the gloss of nylon film, which reflects the surface roughness of the film, affects the uniformity of SiO deposited layer on the nylon film and barrier property of the deposited films. Permeabilities of the water vapor and oxygen through the SiO deposited nylon films were fairly high just after the deposition, especially when the deposited layer was thin, and then decreased to lower equilibrium values. These equilibrium values are surprisingly low comparing with other high barrier films such as nylon and polypropylene films coated with poly (vinylidene chloride). Further the SiO vacuum deposition was continuously carried out on the running nylon film. We found that the thickness of the silicon oxide layer on the nylon film and the water permeability are strongly related to the running velocity of the nylon film and the applied electric current to the heater.

The tribological properties of blends of polyamide 6 (PA 6) with the polyolefins including high density polyethylene (HDPE), low density polyethylene (LDPE), and polypropylene (PP) at various blend ratios and maleic anhydride (MAH) content were investigated and the wear morphology at the sliding interface was discussed. Tribological properties such as coefficient of friction and the specific wear rate against stainless steel disks were measured by using a pin-on-disk type tribological test apparatus. The wear surface of the polymer samples and the metal disks were observed by SEM and polarized microscope. Tribological properties obtained were related to the choice of polyolefins, blend ratio of PA 6/polyolefins and MAH content. Tribological results were explained through mechanisms such as the transfer of polymer films onto the metal disks and wear debris at the interface between polymer and metal. It was found that the unique tribological properties of PA 6/LDPE and PA 6/PP blends, lower coefficient of friction than those of the parent polymers, were mainly caused by the formation of roll debris of LDPE and PP which reduces the true contact area. Furthermore, very high wear rates of the blends with lower PA 6 contents were due to an abrasion effect of worn PA 6 particles at the interface.

Tribological and morphological properties, and crystalline structure of polyamide 6 (PA6) in polyamide 6/maleic anhydride grafted high density and low density polyethylene (MAH-g-HDPE, LDPE) blends were investigated.Introduction of MAH into HDPE and LDPE greatly decreased the PE particle size in PA6 matrix and converted the crystalline structure of PA6 from α to γ form. Pure LDPE showed highest and HDPE showed lowest coefficient of friction and frictional wear. PA6 showed intermediate values. Although both the coefficient of friction and the frictional wear of HDPE tended to increase with MAH grafting ratio, those of PA6/HDPE blends decreased with MAH grafting ratio and reached to those of HDPE. PA6/LDPE blends showed an opposite tribological behavior, increasing coefficient of friction and wear with MAH content.When α form of PA6 was dominant in PA6/HDPE blends, the coefficient of friction and the frictional wear were almost constant, and these decreased with γ content. Although the coefficient of friction of PA6/LDPE blends had almost constant value irrespective of γ/α ratio, the frictional wear increased with γ/α ratio. These differences are due to the different way of formation of the transferred film onto the counter metal surfaces.

ポリアミド6 (PA6) と, 無水マレイン酸 (MAH) 変性した (グラフト率0～0.8wt%) 高密度ポリエチレンおよび低密度ポリエチレンとのブレンド (ブレンド比10～30wt%) を2軸混練押出機で調製し, 射出成形した. ブレンドポリマーの種類, ブレンド比, ならびに変性率の差によるモルフォロジーと摺動特性の変化を評価し, 機械的特性との関連を調べた. PA6/HDPEおよびLDPEブレンドは, それぞれトライボロジー特性の傾向が異なっていることから, その挙動が発現する機構も相違すると考えられた. これはMAHのグラフトによるマトリックス中の分散粒子径変化などによってもたらされるブレンドの機械的性質の変化 (引張りおよび曲げ剪断の強度とそれらの降伏応力) で定性的に説明される.

Tribological properties such as the coefficient of friction and the specific wear rate of the model polymer blends consist of two different epoxy resin matrices and high density polyethylene (HDPE) fibers unidirectionally dispersed in the matrix to a stainless steel disk were investigated by using a pin-on-disk type friction tester. Further the morphology of the abraded surfaces were studied by SEM photomicrographs. When the modulus of the matrix epoxy resin is high, both the coefficient of friction and the specific wear rate monotonically decreased with HDPE fiber contents to those of neat HDPE. On the other hand, when the modulus of the matrix is low, HDPE or HDPE/epoxy resin mixture covers the sample surface resulted in the sudden drop of the coefficient of friction and in the specific wear rate lower than those of both epoxy resin and neat HDPE. It was further found that the HDPE fiber so oriented to the friction direction that HDPE can more efficiently make the lubrication film onto the metal surface reduces the coefficient of friction of the model polymer blends.

サーモトロピック液晶性コポリエステル (LCP) をビスフェノールAポリカーボネート (PC) にLCP/PC=20/80 (wt/wt) で溶融ブレンドした. 溶融ブレンドの際の機械的要因, 及びPCの分子量がブレンド繊維内のLCP成分の分散性及び形状に与える影響, またブレンド繊維の力学的性質に与える影響について検討した. 少量成分であるLCPの分散状態は溶融ブレンドに使用したニーダのローター回転速度, 及びPCの分子量の増大とともにより良好となった. これらのブレンド物から得られた繊維内のLCP成分はブレンド繊維の繊維軸方向に伸長されているが, その形状はブレンド直後のLCP成分の平均粒径に依存した. ブレンド繊維の力学的性質もLCP成分のアスペクト比と直線的な関係を示した, しかしながら, LCP成分の補強効果は繊維の弾性率に顕著に現れたが, LCP/PC界面での接着性の欠如のため, 引張強度に対しては負の効果となって現れた.