Mechanical properties and structure of the zone‐drawn poly(L‐lactic acid) fibers

The zone‐drawing (ZD) method was applied three times to the melt‐spun poly(L ‐lactic acid) (PLLA) fibers of low molecular weight (M_v = 13,100) at different temperatures under various tensions. The mechanical properties and superstructure of the ZD fibers were investigated. The resulting ZD‐3 fiber had a draw ratio of 10.5, birefringence of 37.31 × 10⁻³, and crystallinity of 37%, while an orientation factor of crystallites remarkably increased to 0.985 by the ZD‐1. The Young's modulus and tensile strength of the ZD‐3 fiber respectively attained 9.1 GPa and 275 MPa, and the dynamic storage modulus was 10.4 GPa at room temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 991–996, 1999     

Dynamic mechanical and dielectrical properties of poly(vinyl alcohol) and poly(vinyl alcohol)‐based nanocomposites

In this article we report on the investigation of the dynamics of poly(vinyl alcohol) (PVA) and PVA‐based composite films by means of dielectric spectroscopy and dynamic mechanical thermal analysis. Once the characterization of pure PVA was done, we studied the effect of a nanostructured magnetic filler (nanosized CoFe₂O₄ particles homogeneously dispersed within a sulfonated polystyrene matrix) on the dynamics of PVA. Our results suggest that the α‐relaxation process, corresponding to the glass transition of PVA, is affected by the filler. The glass‐transition temperature of PVA increases with filler content up to compositions of around 10 wt %, probably as a result of polymer–filler interactions that reduce the polymer chain mobility. For filler contents higher than 10 wt %, the glass‐transition temperature of PVA decreases as a result of the absorption of water that causes a plasticizing effect. The β‐ and γ‐relaxation processes of PVA are not affected by the filler as stated from both dynamic mechanical thermal analysis and dielectric spectroscopy. Nevertheless, both relaxation processes are greatly affected by the moisture content. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1968–1975, 2001     

Correlation between the tensile properties and network draw ratio of CO2‐laser‐heated drawn poly(ethylene terephthalate) fibers

Low‐orientation and amorphous poly(ethylene terephthalate) fibers were drawn continuously with heating by carbon dioxide (CO₂) laser radiation. The tensile properties were examined in terms of the birefringence and network draw ratio, which was estimated from the strain shift of true stress–strain curves. Two drawing forms, neck drawing with a draw efficiency (the ratio of the network draw ratio to the actual draw ratio) of about unity and flow drawing with a draw efficiency of about zero, were found to be stable in the continuous drawing process. Meanwhile, any draw‐efficiency value between zero and unity could be obtained in the batch‐drawing process. The object whose orientation was estimated by the network draw ratio differed from that estimated by birefringence. Two linear relationships were found, between the network draw ratio and tensile strength and between the birefringence and initial modulus. The true stress at breaking increased with the network draw ratio of the CO₂‐laser‐heated drawn fibers, and when the draw ratio exceeded 5.0, it became higher than that for batch‐drawn fibers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2322–2331, 2003     

Formation of poly(vinyl alcohol)–iodine complexes in solution

The effect of the dissolved state of poly(vinyl alcohol) (PVA) molecules in water on the color development due to PVA–iodine complexes was investigated at each given PVA and iodine concentration using two kinds of syndiotactic-rich PVA (S-PVA) which are unstable in water because of the formation of intermolecular hydrogen bonds and form the complex easily. In the reaction mixtures prepared by mixing PVA solutions and an iodine solution, the color development was constant and independent of standing time of the PVA solution before the addition of iodine up to a certain time, after which it decreased with the standing time. The color development obtained with use of the PVA solution allowed to stand for a fixed time was higher for S-PVA with a lower s-(diad)%. In the case of the reaction mixture prepared by dissolving PVA in an iodine solution, the color development was higher for S-PVA with a higher s-(diad)%. The initial ratio of the I₅⁻/I₃⁻ and the rate of decrease in the ratio of I₅⁻/I₃⁻ were larger than those in the preceding case. The color development decreased for the PVA with an s-(diad) % of 58, whereas it increased for the PVA an s-(diad) % of 61.3 with increasing propanol content, an inhibitor of gelation. From these results, the aggregates of PVA molecules have been assumed to play an important role in forming the complexes. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1701–1709, 1997     

Microstructure and mechanical properties of hot‐air drawn poly(ethylene terephthalate) fibers

Hot‐air drawing method has been applied to poly(ethylene terephthalate) (PET) fibers in order to investigate the effect of strain rate on their microstructure and mechanical properties and produce high‐performance PET fibers. The hot‐air drawing was carried out by blowing hot air controlled at a constant temperature against an as‐spun PET fiber connected to a weight. As the hot air blew against the fibers weighted variously at a flow rate of about 90 ℓ/min, the fibers elongated instantaneously at a strain rate in the range of 2.3–18.7 s⁻¹. The strain rate in the hot‐air drawing increased with increasing drawing temperature and applied tension. When the hot‐air drawing was carried out at a drawing temperature of 220°C under an applied tension of 27.6 MPa, the strain rate was the highest value of 18.7 s⁻¹. A draw ratio, birefringence, crystallite orientation factor, and mechanical properties increased as the strain rate increased. The fiber drawn at the highest stain rate had a birefringence of 0.231, degree of crystallinity of 44%, tensile modulus of 18 GPa, and dynamic storage modulus of 19 GPa at 25°C. The mechanical properties of fiber obtained had almost the same values as those of the zone‐annealed PET fiber reported previously. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1703–1713, 1999     

Preparation of water‐soluble,syndiotacticity‐rich,low molecular weight poly(vinyl alcohol) microfibrils in high yields with the low‐temperature polymerization of vinyl pivalate in tetrahydrofuran and saponification

To prepare water‐soluble, syndiotacticity‐rich poly(vinyl alcohol) (PVA) microfibrils for various industrial applications, we synthesized syndiotacticity‐rich, low molecular weight PVA by the solution polymerization of vinyl pivalate (VPi) in tetrahydrofuran (THF) at low temperatures with 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN) as an initiator and successive saponification of poly(vinyl pivalate) (PVPi). Effects of the initiator and monomer concentrations and the polymerization temperature were investigated in terms of the polymerization behaviors and molecular structures of PVPi and the corresponding syndiotacticity‐rich PVA. The polymerization rate of VPi in THF was proportional to the 0.91 power of the ADMVN concentration, indicating the heterogeneous nature of THF polymerization. The low‐temperature solution polymerization of VPi in THF with ADMVN proved to be successful in obtaining water‐soluble PVA with a number‐average degree of polymerization (P_n) of 300–900, a syndiotactic dyad content of 60–63%, and an ultimate conversion of VPi into PVPi of over 75%. Despite the low molecular weight of PVA with P_n = 800, water‐soluble PVA microfibrillar fibers were prepared because of the high level of syndiotacticity. In contrast, for PVA with P_n = 330, shapeless and globular morphologies were observed, indicating that molecular weight has an important role in the in situ fibrillation of syndiotacticity‐rich PVA. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1103–1111, 2002     

Preparation and fluorescent properties of poly(vinyl alcohol) bearing coumarin

A novel water‐soluble fluorescent material was prepared via ring‐opening reaction between 4‐methyl‐7‐(2,3‐expoxypropoxy) coumarin (MEC) and poly(vinyl alcohol) (PVA). The fluorescent behaviors of this material (PVA–MEC) in solution, solid and film were studied in detail. The results showed that the fluorescence of PVA–MEC arose from isolated dye molecules and had a good film forming ability. In addition, the effects of acid/base environments on PVA–MEC were studied and the results showed that it was less affected by environment than 7‐HMC. Moreover, relative fluorescence intensity of PVA–MEC had an excellent linear response in the temperature range of 0–60°C. These observations suggest that PVA–MEC is an excellent fluorescent macromolecular material with a convenient method of preparation and had a good water‐soluble ability. Copyright © 2007 John Wiley & Sons, Ltd.     

Changes in superstructure and mechanical properties of poly(ethylene‐2,6‐naphthalate) fibers with critical necking tension

Poly(ethylene‐2,6‐naphthalate) fibers were zone‐drawn under a critical necking tension (σ_c) defined as the minimum tension needed to generate a necking at a given drawing temperature (T_d). In the zone drawing under σ_c, the neck was observed from 110 to 160 °C. The superstructure in a neck zone induced at each T_d was studied. The σ_c value decreased exponentially with increasing T_d and dropped to a low level at a higher T_d. The draw ratio increased rapidly with T_d increasing above 90 °C, but the birefringence and degree of crystallinity decreased gradually. To study the molecular orientation in the neck zone, we measured a dichroic ratio (A_‖/A_?) of a C? O band at 1256 cm^?1 along a drawing direction in the neck zone with a Fourier transform infrared microscope. A_‖/A_? at T_d = 110 °C increased rapidly in the narrow neck zone, and that at T_d = 140 °C increased in the edge of the wide neck zone. Wide‐angle X‐ray diffraction patterns of the fibers obtained at T_d = 130 °C and lower showed three reflections due to an α form, but those at T_d = 140 and 150 °C had reflections due to the α form and a β form. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1629–1637, 2001     

Solid‐state 13C and 129Xe NMR study of poly(vinyl alcohol) and poly(vinyl alcohol)/lactosilated chitosan gels

Dry and hydrated poly(vinyl alcohol) (PVA) gels with 55% (a‐PVA) and 61% (s‐PVA) syndiotacticity and related PVA/lactyl chitosan (LC) blends have been investigated with ¹²⁹Xe and cross‐polarization/magic‐angle‐spinning ¹³C NMR techniques. Although the dry gels exhibit two broad ¹²⁹Xe resonances in the slow‐to‐intermediate exchange limit, both hydrated gels show three resonances. The corresponding dry blends exhibit two signals, the chemical shifts and line widths of which change with respect to those of pure PVA, whereas one (a‐PVA/LC) or two (s‐PVA/LC) signals appear in the spectra of the hydrated blends. A comparative analysis of the data demonstrates that LC rearranges the domains of the polymeric matrix in both the dry and hydrated blends according to the syndiotacticity of the PVA chains. Information on the molecular motions of the amorphous and swollen polymeric domains in the kilohertz range has been obtained from an analysis of the spin‐lattice relaxation times. These data indicate that the dynamics and arrangement of the PVA chains in the gels are strongly affected by their tacticity and the addition of the copolymer LC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3123–3131, 2003     

Structure and mechanical properties in drawn poly(l‐lactide)/clay hybrid films

Films composed of poly(l ‐lactide) (PLLA)/organophilic montmorillonite hybrids (PLACHs) have been prepared via a melt‐compounding process, which is followed by uniaxial drawing at 90°C in air. In addition, an enhancement of the mechanical properties of these drawn PLACH films, which is expected to differ depending on the drawn ratios, is also estimated by dynamic viscoelastic measurements. Three different organoclay concentrations in the hybrid of 3, 5, and 9 wt% were investigated. The structural parameters for the PLLA crystallites in the drawn films, such as the c‐axis orientation function (f_PLLA) and crystallite size, were measured by X‐ray diffraction, and their drawn ratio (λ) and clay concentration dependence were examined from a textural viewpoint. Another orientation function (f_clay) of the organoclay particles was obtained by transmission electron microscopy (TEM). The values of f_PLLA and crystallinity for PLLA sharply increased with λ for λ < 3, although f_clay was unchanged during the initial stage of elongation. In the high‐λ region (>5), the organoclay particles in the PLACHs started orienting themselves parallel to the draw direction. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of water‐soluble perylenediimide‐functionalized polymer through esterification with poly(vinyl alcohol)

A new material has been prepared by covalent attachment of a perylene derivative, N‐(carboxyphenyl)‐N′‐(8‐pentadecyl)perylene‐3,4:9,10‐bis(dicarboximide) (PDI‐COOH), to poly(vinyl alcohol) (PVA) by esterification. The perylenediimide (PDI)‐modified PVA polymers are soluble in water and dimethylsulfoxide (DMSO). This solubility is conferred to the insoluble perylene derivative by the water‐soluble polymer. The materials have been characterized by hydrogen‐nuclear magnetic resonance, Fourier transform infrared spectra, X‐ray diffraction, and X‐ray photoelectron spectroscopy confirming the covalent attachment of the PDI to the polymer chains. The significant changes in the crystalline parameters and the thermal stability observed for the polymer after the esterification also confirm the covalent linkage with PDI. In addition, the PDI‐modified PVA shows good fluorescence both in solution (quantum yield ～0.2–0.25) and in solid suggesting that the PDI retains largely its photochemical and photophysical properties after immobilization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3613–3622, 2010     

Oriented crystallization of poly(L‐lactic acid) in uniaxially oriented blends with poly(vinylidene fluoride)

This article describes the oriented crystallization of poly(L ‐lactic acid) (PLLA) in uniaxially oriented blends with poly(vinylidene fluoride) (PVDF). Uniaxially drawn films of PLLA/PVDF blend with fixed ends were heat‐treated in two ways to crystallize PLLA in oriented blend films. The crystal orientation of PLLA depended upon the heat‐treatment process. The crystal c‐axis of the α form crystal of PLLA was highly oriented in the drawing direction in a sample cold‐crystallized at T_c = 120 °C, whereas the tilt‐orientation of the [200]/ [110] axes of PLLA was induced in the sample crystallized at T_c = 120 °C after preheating at T_p = 164.5–168.5 °C. Detailed analysis of the wide‐angle X‐ray diffraction (WAXD) indicated that the [020]/ [310] crystal axes were oriented parallel to the drawing direction, which causes the tilt‐orientation of the [200]/ [110] axes and other crystal axes. Scanning electron microscopy (SEM) suggested that oriented crystallization occurs in the stretched domains of PLLA with diameters of 0.5–2.0 μm in the uniaxially drawn films of PVDF/PLLA = 90/10 blend. Although the mechanism for the oriented crystallization of PLLA was not clear, a possibility was heteroepitaxy of the [200]/[110] axes of the α form crystal of PLLA along the [201]/[111] axes of the β form crystal of PVDF that is induced by lattice matching of d₁₀₀(PLLA) ≈ 5d₂₀₁(PVDF). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1376–1389, 2008     

Synthesis and characterization of novel photoactive polymer poly(vinyl alcohol)‐graft‐poly(vinyl naphthalene)

A copolymer of poly(vinyl naphthalene) grafted onto poly(vinyl alcohol) has been synthesized with nitroxide‐mediated controlled radical polymerization. By separating the processes of the generation of grafting sites and polymerization, we can avoid the formation of the homopolymer. Because of its architecture, the polymer is soluble in water, despite the high content of hydrophobic groups. The naphthalene chromophores tend to aggregate, forming hydrophobic microdomains in an aqueous solution. Those aggregates exist in a very constrained environment that leads to extraordinarily large redshifts of both the absorption and emission of the polymer. The polymer acts as an efficient photosensitizer in photoinduced electron transfer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2675–2683, 2006     

Effect of poly(ethylene oxide) on the structure and properties of poly(vinyl alcohol)

To improve the drawability of poly(vinyl alcohol) (PVA) thermal products, poly(ethylene oxide) (PEO), a special resin with good flexibility, excellent lubricity, and compatibility with many resins, was applied, and the Fourier transform infrared spectroscopy, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WXRD) were adopted to study the hydrogen bonds, water states, thermal properties, crystal structure, and nonisothermal crystallization of modified PVA. It was found that PEO formed strong hydrogen bonds with water and PVA, thus weakened the intra‐ and inter‐hydrogen bonds of PVA, changed the aggregation states of PVA chains, and decreased its melting point and crystallinity. Moreover, the interactions among PVA, water, and PEO retarded the water evaporation and made more water remain in the system to plasticize PVA. The existence of PEO also slowed down the melt crystallization process of PVA, however, increased the nucleation points of system, thus made more and smaller spherulites formed. The weakened crystallization capability of PVA and the lubrication of PEO made PVA chains to have more mobility under the outside force and obtain high mechanical properties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1946–1954, 2010     

Preparation and properties of poly(vinyl alcohol)–vermiculite nanocomposites

A vermiculite (VMT) dispersion in water was blended with aqueous poly(vinyl alcohol) (PVA). The properties of the PVA–VMT nanocomposites greatly depended on the preparation procedure because of the chemical reactions and physical interactions involved. The samples were prepared in two steps to investigate the properties of the PVA–VMT nanocomposites. The VMT was first pretreated and delaminated with hydrochloric acid. The delaminated VMT was then added to the PVA solution with various mixing times. The structure and properties of the films were investigated. From X‐ray diffraction and transmission electron microscopy, the VMT layers were found to be well dispersed individually in the PVA–VMT blends. The effect of the VMT content on the thermal behavior of the PVA–VMT blends was also studied with differential scanning calorimetry. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 749–755, 2003     

Electrostatic Forces Induce Poly(vinyl alcohol)‐Protected Copper Nanoparticles to Form Copper/Poly(vinyl alcohol) Nanocables via Electrospinning

Summary: Copper/poly(vinyl alcohol) (PVA) nanocables have been successfully obtained by electrospinning a PVA‐protected copper nanoparticle solution. The molar ratio of copper ions to PVA (in terms of VA repeating units) plays an important role in the formation of copper/PVA nanocables. The average diameter of the copper cores and PVA shells is about 100 and 400 nm, respectively. The structures of the copper/PVA nanocables are characterized by transmission electron microscopy (TEM) and their formation is confirmed by scanning electron microscopy (SEM).

TEM image of a copper/PVA nanocable.     

Oxygen‐barrier properties of cold‐drawn polyesters

The improvement of oxygen‐barrier properties of glassy polyesters by orientation was examined. Poly(ethylene terephthalate) (PET), poly(ethylene naphthalate), and a copolymer based on PET in which 55 mol % of the terephthalate was replaced with bibenzoate (PET‐BB55) were oriented by constrained uniaxial stretching. In a fairly narrow window of stretching conditions near the glass‐transition temperature, it was possible to achieve uniform extension of the polyesters without crystallization or stress whitening. The processes of orientation and densification correlated with the conformational transformation of glycol linkages from gauche to trans. Oxygen permeability, diffusivity, and solubility decreased with the amount of orientation. A linear relationship between the oxygen solubility and polymer specific volume suggested that the cold‐drawn polyester could be regarded as a one‐phase densified glass. This allowed an analysis of oxygen solubility in accordance with free‐volume concepts of gas permeability in glassy polymers. Orientation was seen as the process of decreasing the amount of excess‐hole free volume and bringing the nonequilibrium polymer glass closer to the equilibrium (zero‐solubility) condition. Cold drawing most effectively reduced the free volume of PET‐BB55. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 862–877, 2002     

Segmental orientations and deformation mechanism of a poly(ether‐block‐amide) film

Simultaneous measurements of microscopic infrared dichroism, mesoscale deformation, and macroscopic stress have been made for a microphase‐separated film of poly(ether‐block‐amide) 4033 during uniaxial stretching at temperatures between 30 and 91 °C, well below the melting point of the hard polyamide‐12 (PA) domains. Before the onset of dramatic microstructural alterations, the true stress–strain relationship on the mesoscale can be described with an interpenetrating network model, and poly(tetramethylene oxide) (PTMO) soft segments undergo affine deformation. Beyond a threshold strain at which stress from the soft network becomes larger than that from the hard network, plastic deformation occurs in the hard PA domains, and this is accompanied by the downward derivations of the true stress and molecular orientation of PTMO blocks from the model predictions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1161–1167, 2005     

Well‐defined amphiphilic poly(p‐dioxanone)‐grafted poly(vinyl alcohol) copolymers: Synthesis and micellization

A series of amphiphilic biodegradable and biocompatible poly(p‐dioxanone)‐grafted poly(vinyl alcohol) (PVA) copolymers with well‐defined structure were obtained by a three‐step synthesis based on the “grafting from” concept. The first step (protection step), called the partial silylation of PVA hydroxyl groups, was accomplished by 1,1,1,3,3,3‐hexamethyldisilazane and catalyst chlorotrimethylsilane in dimethyl sulfoxide using THF as cosolvent. The second step was the ring‐opening polymerization of p‐dioxanone (PDO) initiated from the remaining OH groups of the partially silylated PVA. Finally, a deprotection step was followed: the silylether group was deprotected easily under very mild conditions. The synthetic conditions of the first two steps were investigated, and the structures of polymers formed in each step were characterized by various analytical methods. The results showed that the molecular structure of the PVA‐g‐PPDO could be controlled easily by the degree of silylation and the feed ratio. In addition, the micellization of amphiphilic PVA‐g‐PPDO copolymers in water was proved by fluorescence spectra and dynamic light scattering, and the relationship between structural parameters of copolymers and micellar properties was studied preliminarily. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010