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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.

The effect of polyethylene glycol (PEG) on the mechanical and thermal properties of poly(lactic acid) (PLA)/poly(butylene succinate) (PBS) blends was examined. Overall, it was found that PEG acted as an effective plasticizer for the PLA phase in these microphase-separated blends, increasing the elongation at break in all blends and decreasing the Tg of the PLA phase. Significant effects on other properties were also observed. The tensile strength and Young's modulus both decreased with increasing PEG content in the blends. In contrast, the elongation at break increased with the addition of PEG, suggesting that PEG acted as a plasticizer in the polymer blends. Scanning electron microscope images showed that the fracture mode of PLA changed from brittle to ductile with the addition of PEG in the polymer blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43044.

To achieve appropriate efficacy of paclitaxel (PTX) used in drug eluting stents, uniform PTX coating on the stent and increased initial release of PTX leading to immediate therapeutic level of the drug are required. The present study investigated whether either restriction of crystal growth though sonication and subsequent liquid nitrogen cooling, or formation of anhydrous PTX crystals through heating microcrystals after seeding and crystal growth could increase PTX initial release coated on a fully-bioabsorbable poly(L-lactic acid) stent. The sonication and subsequent liquid nitrogen cooling of the growing PTX crystals could prevent stable attachment of the crystals onto the stent surface. In addition, the initial PTX release from the stent applied sonication during the crystal growth process followed by heating showed five times as high as the stent without heating, which indicated the heating improved the PTX release from the stent at early phase. These results suggested that PTX was changed into an anhydrous soluble form.

A first clinically-used, fully-bioabsorbable poly(L-lactic acid) (PLLA) stent was coated with microcrystals of paclitaxel (PTX), antiproliferative agent through seeding and/or crystal growing technique to investigate the drug properties on the stent surface and drug release behavior from the stent. PTX particles subject to only seeding process was peeled off after stent compression, while less PTX was coated on the stent subject to only crystal growth without seeding. PLLA stent with both processes could stably maintain an increased amount of PTX on its surface. The maximum amount of initial release (10 μg/cm2) was found in the sample only with seeding, which decreased to 3 μg/cm2 or below after one week. Also in the PLLA stent only with crystal growth, release amount decreased after one week. In the PLLA stent with seeding and crystal growth, formation of needle-like PTX crystals on the surface resulted in decreased initial release and lower solubility after hydration in phosphate buffered solution compared to other types of stent with different procedures. It is suggested that both seeding and crystal growth are required for stable application of PTX on fully-bioabsorbable PLLA stent and needle-like crystals containing water have lower aqueous solubility resulting in decreased PTX release.

This study attempted to visualize reversible X-ray radiation by using a poly-(l-lactic acid) (PLLA) composite fiber with an average diameter of 150 μm. The fiber contains photostimulable phosphor (PSP) BaFCl:Eu(2+) particles that are subsequently dyed with the photochromic spiropyran dye (1,3,3-trimethylindolino-6'-nitrobenzopyrylospiran) (6-nitro BIPS).

Equimolar blend of poly( l -lactic acid) (PLLA) and poly( d -lactic acid) (PDLA) was melt spun into fibers and the relations among the processing conditions, crystalline structures, thermal properties, and mechanical properties were investigated. Drawing and annealing were performed in order to obtain fiber mainly consisting of the stereocomplex crystal phase. Fibers drawn at various temperatures exhibited either amorphous, highly oriented homo crystal, or the mixture of homo and stereocomplex with a fairly low orientation depending on the drawing temperature. Annealing of the drawn fibers at an elevated temperature higher than the melting temperature of homo crystal increased the stereocomplex content significantly. The fractions of the homo and the stereocomplex crystals strongly depended on the higher-order structure of the drawn fibers and the annealing temperature.

The higher order structure of stereocomplex-type poly(lactic acid) melt-spun fibers of an equimolar blend of poly(L-lactic acid) and poly(D-lactic acid) was analyzed with wide-angle X-ray diffraction (WAXD) and birefringence measurements. Two different crystalline structures were observed in the fibers: α-form homocrystals and stereocomplex crystals. The weight fractions of the two crystals were estimated with the WAXD integrated intensity data. The crystalline orientation factors were obtained from the WAXD measurements. Well-oriented homocrystals formed during a drawing process at the crystallization temperature of the homocrystal. Drawing above this temperature caused the stereocomplex crystal to be formed. The crystalline orientation tended to be lower with increasing drawing temperatures. Through the combination of the intrinsic birefringence and the fractions of the α-form homocrystals and stereocomplex crystals, the birefringence of the amorphous phase was evaluated. The amorphous birefringence stayed positive and decreased with increasing drawing temperature.

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.

Solution-grown lamellar crystals of poly(p-dioxanone) (PPDX) have been crystallized isothermally from butane-1,4-diol at 100°C. The crystal structure of PPDX has been determined by interpretation of X-ray fiber diagrams of PPDX fibers and electron diffraction diagrams of lozenge-shaped chain-folder lamellar crystals. The unit cell of PPDX is orthorbombic with space group P2 1 2 1 2 1 and parameters: a=0.970 nm, b=0.74 mm, and c (chain axis) = 0.682 nm. There are two chains per unit cell, which exist in an anti parallel arrangement.

Pure bacterial homo poly(3-hydroxybutyrate) (PHB) fibers were prepared by melt spinning, followed by cold-drawing in an amorphous state at a temperature just above its glass transition temperature. Cold drawn fibers obtained were further drawn at higher temperatures, followed by annealing at various temperatures under tension. Relations among the processing conditions, higher order structures and mechanical properties were investigated using wide- and small-angle X-ray diffractions (WAXD and SAXD, respectively), birefringence, differential scanning calorimetry (DSC), and tensile measurements. PHB has two different crystalline forms, 2 1 helix conformation (α-form) and planar zigzag conformation (β-form). A single broad reflection of β-form was detected even in a PHB fiber drawn once at a temperature just above its T g immediately after quenching and it tended to be stronger after 2nd drawing at higher temperatures. Annealing under low temperature and high tension facilitates the occurrence of β-form. It is suggested that the β-form crystal is formed not only from the tie chains between α-form lamella, but also from completely free amorphous chains. Changes in the amount of two types of crystals were analyzed using the WAXD integrated intensity. Birefringence of these fibers shows negative and positive values, depending on process conditions. Changes in higher order structure on the mechanical properties are also discussed.

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.

The effect of addition of a small amount of poly(D-lactic acid) (PDLA) on the melt rheology of poly(L-lactic acid) (PLLA) was investigated. PDLA added to PLLA produces a stereocomplex which stays unmelted even above Tm of PLLA. Because of the imbalanced contents of component polymers, the stereocomplex does not grow into a large crystallite but rather acts as a crosslinking point of PLLA chains resulting in the apparent introduction of the long chain branching as well as in the apparent increase in molecular weight. Such changes in the molecular structure give rise to the change in the melt rheology depending on the content and the molecular weight of PDLA. The addition of low Mw PDLA significantly affects the shear rheology of PLLA melts while high Mw PDLA does not give such a significant effect. However, the addition of PDLA with high and low Mw’s gives a strong strain hardening character to PLLA melt even at a very low PDLA content.

The phase behaviors for the blends of poly(3-hydroxypropionate) (PHP), poly(L-lactide) (PLLA), poly(D-lactide) (PDLA), and poly(D,L-lactide) (PDLLA) with catechin were investigated by differential scanning calorimetry. In PLLA/catechin, PDLA/catechin, and PDLLA/catechin blends, two glass transitions were detected when the catechin content was ≥40 wt %, whereas in PHP/catechin blends only one glass transition was observed over the whole range of blend compositions. The former and the latter results should reflect the inhomogeneous and the homogeneous nature of the blends, respectively, in the amorphous phase. These different phase behaviors should arise from the differences in the chemical structures between PHP and PLLA/PDLA/PDLLA, which dominates the strength and the number of intermolecular hydrogen-bonding interactions between the ester carbonyl groups of polyesters and the phenol groups of catechin. As detected by FTIR spectroscopy, in comparison with PHP, the steric hindrance of side-chain methyl groups of PLLA, PDLA, and PDLLA might restrain the formation of hydrogen bonds between their ester carbonyl groups and the phenol hydroxyl groups of catechin, even weakening the strength of such hydrogen bonds. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3565–3573, 2004

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.

Thermal property and crystallization behavior of PLLA blended with a small amount of PDLA (1–5 wt%) were studied. PDLA molecules added in PLLA formed stereocomplex crystallites in the PLLA matrix. When the blend was cooled to a temperature below Tm of PLLA, stereocomplex crystallites acted as nucleation sites of PLLA and enhanced the crystallization of PLLA significantly (heterogeneous nucleation). Such crystallization enhancement was not observed when the blend with lower PDLA content was cooled from 240 °C at which both PLLA crystal and the stereocomplex disappeared. Low molecular weight PDLA isolated in the matrix of PLLA did not form a stereocomplex crystallite with a large surface area enough to act as a nucleation site. On the other hand, high molecular weight PDLA chains formed a large stereocomplex crystallite. With increasing PDLA content, stereocomplex crystallites were more easily formed and they acted as nucleation sites. PLLA crystal near the stereocomplex crystallites has an incomplete structure and showed a melting peak at a lower temperature than pure PLLA crystal.

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 effect of the mixing condition in a mill-type mixer on the thermal property and the crystal formation of the poly(l-lactide)/poly(d-lactide) blends is investigated. The blends melt-mixed at 200 and 210 °C under application of a high shear flow tend to show a single melting peak of the stereocomplex crystal (SC) in the differential scanning calorimetry first and second heating processes without indicating the trace of the melting of homo-chiral crystal. The mixing at an elevated temperature causes a serious thermal degradation. Further kneading of the blends at an elevated temperature higher than Tm of SC causes the transesterification between the same enatiomeric chains forming block copolymers of l- and d-chains. This block copolymer acts as a nucleating agent of SC and the compatibilizing agent between poly(l-lactide) and poly(d-lactide) and promotes the formation of SC. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45489.

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

Bacterial homo poly(3-hydroxybutyrate) (PHB) was melt spun into fibers and the relations among the processing conditions, crystalline structures, and the mechanical properties were investigated. WAXD patterns of PHB fibers indicate a broad reflection which cannot be assigned to any plane in the orthorhombic system of PHB, although most strong reflections can be assigned to the planes in the orthorhombic system. It has been reported that the broad reflection is assigned to be β-zigzag form, which occurs by the stretching of the amorphous tie molecules between lamellae. When annealed under high tension, this broad reflection tended to be stronger, while it became significantly weak when annealed without tension. These results suggest that the annealing without tension makes the amorphous tie molecules crystallized into orthorhombic form, while annealing under high tension makes the molecules in the amorphous region stretched and increased the fraction of the β-zigzag form.

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.

We observed shape recovery of a deformed droplet in an immiscible polymer matrix under large step strains using stereo microscopes from two directions. On application of a large step strain, a soft spherical droplet in a matrix with higher viscosity deformed to a flat ellipsoid. The stretch ratio of major axis of the flat ellipsoid was 5/4 times larger than that predicted from the affine deformation. The flat ellipsoid changed into a rod-like shape and then to a dumbbell, to an ellipsoid of revolution, and finally back to the sphere. The orientation angle between the major axis and shear direction did not change during the course of this shape recovery and was independent of the initial radius of the droplet. The time needed for the whole shape recovery got longer as the initial radius and the strain were increased. For a given step strain, the normalized interfacial area plotted against the stretch ratio fell onto a master curve irrespective of the initial radius of the undeformed droplet. It is shown that the deformed droplet reforms to the sphere after it passes through various shapes by reducing the interfacial area.

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.

A series of acylated chitosans were synthesized by reacting chitosan with hexanoyl, decanoyl, and lauroyl chlorides. The chemical structures of these polymers were characterized by elemental analysis, IR, 1H-NMR, 13C-NMR, and GPC. These results suggested that the degree of substitution was 4 per monosaccharide ring. These acylated chitosans exhibited an excellent solubility in organic solvents such as chloroform, benzene, pyridine, and THF and transparent films were obtained from these solutions. Dynamic mechanical analyses (DMA) showed that all acylated chitosans have two phase transitions in the solid state. The first transition at −10, −42, and −40°C are attributable to the glass transition (Tg) of H-, D-, and L-chitosans, respectively. The second one around 88°C may be attributed to the transition related to the structure formed by the side chains. WAXS analyses indicate that these polymers form a layered structure in solid state and the layer spacing d increases linearly with increasing the length of side chains.

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.

The biodegradable poly (L-lactic acid) (PLLA) stents, made of a cylindrical knitted structure of PLLA monofilament, were implanted into the coronary arteries of 8 pigs by 8 Fr guiding catheters. Follow-up coronary angiography was performed and the standard optical microscopic observations of the cross section of the stented segments were carried out after implantation.Coronary angiographies and the histological examinations revealed that no acute closure was observed immediately after implantation and the patency of stented arteries of PLLA stent segments was wider. The %stenosis was lower than any other biodegradable stents already reported. These results are attributable to the lower degradation rate of PLLA which keeps its strength of the stent to hold the arteries from the inside for a longer period of time.It was further observed that the overlapping portions of the knitted structure tend to press and injure the internal wall of the blood vessel resulting in the growth of neo-intimal hyperplasia. The modified PLLA stents whose overlapping portions were flattened by compression at higher temperature give less %stenosis.

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.

High polymers of poly(butylenesuccinate) (PBS) and poly(butylenesuccinate-co-L-lactide) (PBSL) were melt-spun by the on-line spinning and drawing technique. The PBS fibers were drawn 4 - 12 times, while the PBSL fibers were drawn 4 - 40 times. The structcre and properties of these drawn fibers were studied by tensile test, WAXS, birefringence, and SEM. It was revealed that the tensile strength and modulus of the PBS and PBSL fibers mcreased with increasing craw rato while then tensile clongation was kept significantly high because of the low glass transition temperature of both polymers The molecular orientation of these fibers were comparable with that of the ordinary synthetic fibers such as Nylon 6 as judged by birefringence. Both PBS and PBSL fibers were found to be degraded quickly by enzymatic hydrolysis using a lipase originated from Pseudomonas, while they were little degraded in phosphate buffer (pH 7.0). The inclusion of a small amount of L-lactic acid units into the PBS sequences gave little effect on the degradability and mechamcal properties of these fibers.

Fourier-transform infrared spectra (FTIR) measurement was made on zinc and sodium ionomers (EMAA-Zn and EMAA-Na) of ethylene-co-methacrylic acid copolymer. It was found that the asymmetry stretching vibration peak of C-O bond of COO- group in ion aggregates of EMAA-Na appeared at lower wavenumber, compared with EMAA-Zn. This means that complete and stable ion aggregates exist in EMAA-Na. Differential scanning calorimetry (DSC) measurement showed that endotherm peak (T1) in lower temperature range resulted from melting of subcrystallites of crystalline ethylene in EMAA and EMAA ionomers. Tensile properties and dynamic viscoelasticity of EMAA greatly changed with the introduction of ionic groups.

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.