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The current research unfolds the effect of block lengths, microdomain morphology and stereocomplexation on the mechanical properties of PLA-b-PCL-b-PLA triblock copolymers where PCL is involved to improve the poor extensibility of PLA. The linear triblock copolymers PLLA-b-PCL-b-PLLA and PDLA-b-PCL-b-PDLA (PLLA:poly (L-lactic acid) and PDLA:poly (D-lactic acid)) are made by two step ring opening polymerization and blended in a 1 : 1 ratio to achieve stereocomplex blends where the molecular weight of the terminal and the mid segment is tailored. The mechanical strength and elongation at break range from 13 MPa to 36 MPa and 540 to 950%, respectively, for the triblock copolymers with varied block lengths. Such wide-ranged mechanical properties are ascribed to the morphology of the self-assembled nanostructure of triblock copolymers as corroborated with the small angle X-ray scattering (SAXS) results. To render it industrially viable, the process of triblock copolymer synthesis is scaled up to ∼500 g batch followed by its processing using a twin-screw extruder to make a filament which is used for 3D printing of a mesh-type scaffold. The synthesized materials are tested for their biocompatibility by performing MTT assay using rat bone osteosarcoma (UMR-106) cells which renders them as potential biomaterials.

Bis(hydroxyethoxypropyldimethylsiloxy)-(triphenylsilyloxy)-heptaisobutyl open-cage silsesquioxane (2) was prepared from bis(dimethylsiloxy)-(triphenylsiloxy)-heptaisobutyl open-cage silsesquioxane (1), following our previous report of a one-pot procedure, from heptaisobutyl trisilanol cage silsesquioxane with triphenylchlorosilane and subsequent reaction with dimethylchlorosilane. The polymerization of 2 with a diisocyanate monomer, i.e. tolylene-2,4-diisocyante (3a), hexamethylenediisocyanate (3b), dicyclohexylmethane 4,4′-diisocyanate (3c) or methylenediphenyl 4,4′-diisocyanate (3d), produced hybrid polyurethanes (4) composed of isobutyl-substituted open-cage silsesquioxane in the main chains. The cast films of the resulting polyurethanes exhibited excellent optical transparency and surface hydrophobicity. The static contact angles of water for the cast films of the polymers were over 100°. In particular, the static contact angle of water for the cast film of 4b exhibited a significantly higher value of 121°, suggesting the higher accumulation of the open-cage silsesquioxane moieties in 4b on the surface. We applied them as surface modifiers in poly(methyl methacrylate) (PMMA) by surface segregation. The static contact angles of water for the hybrid PMMA films were more than 100°, suggesting that they were hydrophobic surfaces. We also applied the hybrid polyurethane presented here as a surface modifier for PMMA nanofibres by electrospinning using a chloroform solution of PMMA with 2 wt% content of 4a.

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.

A facile route was proposed to fabricate core–sheath microfibers, and the relationships among processing parameters, crystalline structures and the mechanical properties were investigated. The compression molded poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH)/poly(L-lactic acid) (PLLA) strip enhanced the spinnability of PHBH and the mechanical properties of PLLA as well. The core–sheath ratio of the fibers was determined by the prefab strip, while the PLLA sheath component did not completely cover the PHBH core component due to the weak interfacial tension between the melts of PHBH and PLLA. A rotational target was applied to collect aligned fibers, which were further drawn in a water bath. The tensile strength and the modulus of as-spun and drawn fibers increased with increasing the take-up velocities. When the take-up velocity was above 500 m/min, the jet became unstable and started to break up at the tip of the Taylor cone, decreasing the mechanical properties of the fibers. The drawing process facilitated the crystallization of PLLA and PHBH, and the tensile strength and the modulus increased linearly with the increasing the draw ratio. The crystal information displayed from wide-angle X-ray diffraction patterns and differential scanning calorimetry heating curves supported the results of the tensile tests.

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.

The effects of dyeing carriers on the color strength (K/S values) of poly( l -lactic acid) (PLLA) fibers were investigated, using the photochromic dye 1′,3′,3′-trimethyl-6-nitro-spiro(2H-1-benzopyran-2,2′-indole) (6-nitro BIPS). Both an organic solution (based on tetrachloroethylene) and an aqueous dispersion of the dye were applied to the PLLA fibers, and the resulting change in color of the PLLA samples irradiated by ultraviolet (UV) light was evaluated by spectrocolorimetry. In the case of aqueous dispersion processing, the uptake of 6-nitro BIPS on the PLLA fibers was expected to be increased when using o-phenylphenol as a carrier. The value was four times higher than that obtained using the organic solution. The energy diagrams associated with the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the 6-niro BIPS for the two dyeing processes were determined using photoelectron yield spectroscopy.

Multi-sb-PLAs with molecular weights of approximately 60,000 (MSB-60) and 130,000 (MSB-130) with various block lengths were synthesized. These have a structure in which di-block copolymers consisting of L - and D -blocks with the same length are connected with 1,12-dodecanediol (DMG), an initiator and hexamethylene diisocyanate (HMDI), a chain extender alternately. DSC analyses revealed that T g increases with the increase in the block length and the multi-sb-PLA with a lower molecular weight has higher T g at a constant block length. These are attributable to the higher concentration of DMG and HMDI in the multi-sb-PLA. T m increases with the increase in the block length and the molecular weight of multi-sb-PLA and those of MSB-60 and MSB-130 get close to a constant value at higher block length. The variation of T m seems to be attributable to change in the lateral dimension of lamella rather than that of the thickness. T c in the heating process from the amorphous solid decreases and that in the cooling process from the melt increases with the increase in the block length, indicating that the multi-sb-PLA with a long block has a wider temperature range of the crystallization.

Multi-stereoblock PLAs (multi-sb-PLA)s having the controlled block sequences between PLLA and PDLA were synthesized by the chain-extension of tri-stereoblock PLAs. These multi-sb-PLAs only crystallize into the stereocomplex without forming any traces of homo-chiral crystal. The effects of the block length and the total molecular weight on the isothermal crystallization behavior and the higher order structure of the multi-sb-PLAs were investigated. Observation of isothermal crystallization behavior revealed that the multi-sb-PLA with longer blocks and higher molecular weights started the crystallization at a lower temperature within a shorter period of time in a wider temperature range. The crystallization rate increases with increasing block length and the multi-sb-PLA with a longer blocks achieves higher degree of crystal. The multi-sb-PLA with a higher molecular weight forms more complete structure of the spherulite than that with a low molecular weight. Annealing of the amorphous multi-sb-PLA produced sc with two different lamellar thicknesses. One which melts at a higher temperature is a main sc phase with a lamellar thickness merely determined by the block length and the molecular weight regardless of the thermal history. The chains in the amorphous region only crystallized upon annealing and gradually grew with increasing annealing temperature giving some addition to the lamellar thickness of the samples detected by SAXS.

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.

A new and simple method of one-pot two-stage poly(lactic acid) (PLA) macromonomer synthesis has been developed. The first stage of the reaction is a direct polycondensation of lactic acid (LA) without a catalyst to PLA, and the second stage is a ring-opening addition of PLA to glycidyl methacrylate (GMA) to afford a PLA macromonomer with a methacryloyl polymerizable group (GMA-Macro). Both reactions are performed consecutively in one pot. This method produced GMA-Macro with high functionality in high yields and thus far seems the simplest and probably the cheapest way to prepare PLA macromonomers. Furthermore, the method is metal-free, offering considerable advantages for biomedical and pharmaceutical applications. GMA-Macro has been shown to be useful for the preparation of PLA graft copolymers in solution or in miniemulsion and of PLA comb polymers in solution. LA is a biobased renewable feedstock. Thus, this method provides a good opportunity to conduct ‘green polymer chemistry’.

A “green” and highly efficient route was proposed to fabricate ultrafine cellulose fibers. The processing steps include cellulose dissolution, gel preparation, melt-electrospinning and fiber coagulation. High DP cellulose can be easily dissolved in 1-butyl-3-methylimidazolium chloride (BmimCl) when the blend was stirred at 110 °C for 2 h. The maximum solubility can reach up to 16.7 wt%. A homogeneous ternary cellulose/BmimCl/ethanol or cellulose/BmimCl/water gel was made by the methods of crystallization and casting for the purpose of fixing the shape of the cellulose/BmimCl solution. After laser-heating and electrospinning, multiple jets were ejected from the gel tip and then frozen on a super cold target. Pure cellulose fibers without beads and blocks were achieved after coagulation. The results of WAXD and FTIR indicated that the regenerated cellulose fibers were amorphous and chemically stable. More importantly, this approach can be applied to other polysaccharides for the preparation of ultrafine fibers.

Triethoxysilyl-terminated poly(d-lactide)s (eSi-PDLA) were successfully prepared by hydrosilylation of allyl-terminated PDLAs (A-PDLA-ac) which were readily prepared by ring-opening polymerization of d-lactide and the following terminal protection by acetylation. Their acid-catalyzed hydrolysis produced hyper-conjugated PDLAs with terminal silanol coupling. Blend PLLA films containing eSi-PDLA (Mn = 2.1 kDa) in 5-25 wt.% were successfully prepared by the solution casting method. The blend films were found to take a nano-porous or micro-phase separation structure, being different from that of the blend PLLA films containing trimethoxysilyl-terminated poly(d-lactide) (mSi-PDLA) which exhibited particle distribution structure. This difference was reasonably attributed to the different rate of hydrolytic polycondensation of the trimethoxy- and triethoxy-silyl terminals. These results revealed that the competing sterecomplexation/ hyper-conjugation/phase separation can afford specific morphologies, allowing fine control of properties.

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.

The effect of additive on crystallization and mechanical properties of poly(lactic acid) (PLA) and poly(butylene succinate-co-adipate) (PBSA) blend was studied. PLA and PBSA were blended in a twin screw extruder, which incorporated poly(butylene adipate-co-terephthalate) (PBAT) as an additive in PLA/PBSA blend. The ratio of PLA/PBSA was 80/20. The contents of PBAT were varied from 0 to 50 wt%. The thermal properties and crystallization behavior of PLA/PBSA/PBAT blends were analyzed by differential scanning calorimetry. The effect of PBAT contents on non-isothermal crystallization kinetic of the composites was investigated by using Avrami equation. Tensile strength and impact performance of the PLA/PBSA/PBAT blends decreased when increasing PBAT contents. It can be noted that the addition of 20 wt% PBAT showed the maximum impact performance of the PLA/PBSA blends.

Blends comprising poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and talc were prepared via a solution casting method. The weight ratios of PLA to PBS (PLA/PBS) blends were 80:20 and 60:40, whereas the talc content was varied from 0 to 5.0 parts per hundred resin (phr). The crystallization halftime (t 1/2) of PLA/PBS (80:20) at 80 °C was higher than those of neat PLA, PBS, and PLA/PBS (60:40); this is due to its high PLA content. The t 1/2 value for neat PLA at 90 °C decreased when the talc content was increased, whereas the value for neat PBS gradually increased. These phenomena can be seen more clearly at 95 and 100 °C. This means that talc not only promotes PLA crystallization but also acts as a crystallization inhibitor for PBS. The isothermal crystallization kinetics and spherulitic morphology of these samples were investigated. The extent of talc loading showed a strong dependence on the isothermal crystallization rate and the extent of PLA crystallinity, whereas the contrary effect was observed for PBS due to the growth of large crystals. This suggests that talc not only promotes the crystallization of PLA but also inhibits the crystallization of PBS. The results are in agreement with the crystallization halftime and polarized optical microscopy analysis.

Bis maleimide-terminated poly-L-lactide (M-PLLA-M) and bis furan-terminated poly-D-lactide (F-PDLA-F) were synthesized by isocyanate coupling reactions of mono maleimide-terminated PLLA (M-PLLA) and mono furan-terminated PDLA (F-PDLA) that had been prepared by the ordinary ring opening polymerization of L- and D-lactides with N-(2-hydroxyethyl)-maleimide and furfurylamine as the initiators, respectively. Both the M-PLLA-M and F-PDLA-F were dissolved in CH2Cl2 in 1:1 ratio and subjected to the ordinary electrospinning where the initial polymer concentration was increased up to 20 wt% because of the prepolymer state of the solute and the fiber diameter could be retained in nanometer to submicron size. The molecular weight of the polymers was found to have increased from 1.0 × 104 to 2.5 and 4.5 × 104 after the electrospinning and post annealing, respectively, due to the spontaneous chain extension taking place by the terminal Diels-Alder reaction of M-PLLA-M and F-PDLA-F to form a stereoblock polylactide. The as-spun fibers were amorphous or partially semi-crystalline, whereas the annealed fibers become fully crystalline due to the formation of the stereocomplex showing a melting temperature above 200oC.

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.

Poly(L-lactic acid)s with molecular weights ranging from 500 to 43,000 were synthesized by the direct polycondensation of L-lactic acid. Both initial and total hydrolytic degradation rates in a buffer solution increased with decreasing Mw. Poly(L-lactic acid) with the lowest Mw showed a significantly high degradation rate. This may be due to its Tg lower than the temperature of degradation experiment at which the water molecules easily diffuse into the matrix. Although the hydrolytic degradation can be theoretically described by the first-order reaction, the weight loss of the low Mw poly(L-lactic acid) in the buffer solution deviated from the behavior predicted. The rate of the drug elution from the film showed a maximum at the first day, irrespective of the Mw of poly(L-lactic acid) suggesting that the drug dispersed near the film surface elutes most rapidly. The drug elution rate from the film with the highest Mw was not significantly different from those from low Mw films. This may be due to the similar degree of crystal to those of the low Mw film. These results indicate that the drug elution behavior is affected not only by the molecular weight but also the degree of crystal of the matrix poly(L-lactic acid).

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.

Poly(lactic acid) (PLA) was blended with baked shell powder increasing the content up to 10wt%, and the influence of mixing the powder on the physical properties of the obtained PLA compounds were investigated. The measurements for storage modulus E' revealed that the settled powder will promote the crystallization of PLA. Moreover not only the thermal decomposition but also the biodegradation in compost system for PLA were enhanced by the mixing the powder.

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.

Bacterial poly[( R )-3-hydroxybutyrate- co -( R )-3-hydroxyhexanoate] (PHBH) highly oriented films were prepared by the combination of roll and uniaxial drawing processes. The change in the higher-order structure of PHBH films was investigated by wide-angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS). Extended films, which show superior mechanical properties and high ductility, have complicated structures. By roll extension, both deformed and undeformed spherulites co-exist, the former inclined to the direction perpendicular to the film surface. The latter were destroyed by further uniaxial extension. The tie-molecules between uniaxially oriented lamellae were extended and transformed to the β-form with a planar zig-zag conformation. Three kinds of structures, c -axis parallel to the uniaxial drawing direction, c -axis inclining to the normal vector of the film surface, and the β-form between lamellae, are intermingled in the film.

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.

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.