Mechanical properties of films of poly(vinyl alcohol) derived from vinyl trifluoroacetate

In order to study the influence of the stereoreguralities of polymer chains on the mechanical properties of films of poly(vinyl alcohol) (PVA)_(VTFA) derived from vinyl trifluoroacetate, the strength of the film was measured. In the case of undrawn PVA_(VTFA) films, Young's modulus and strength at break were the smallest at the annealing temperature of about 100°C. It is considered to be due to the melt of small microcrystals and the increase in mobility of chains in amorphous parts. Young's moduli of undrawn PVA_(VTFA) films were in the range of 1.50–3.75 GPs and the values were higher than that (0.17–0.36 GPa) of undrawn film of commercial PVA with the low concentration of syndiotacticity and the high concentration of head-to-head bounds. In the case of drawn, annealed PVA_(VTFA) films, the maximum Young's modulus was about 20 GPa.     

Effect of diethylene glycol content and annealing temperature on the structure and properties of poly(ethylene terephthalate)

The effect of 2,2′-oxydiethanol (diethylene glycol, DEG) content (ranging from 2 to 15 mol %) and of the annealing temperature (in the range from 100 to 260°C) on the density, calorimetric, dynamic- and static-mechanical and small angle X-ray scattering (SAXS) behavior of undrawn and drawn samples (granules, films, and bristles) of poly(ethylene terephthalate) (PET) has been studied. The known dependences on the annealing temperature are confirmed. Some discrepancies with earlier investigations of the dependences on the DEG content are established: constant values for the SAXS intensity and long spacing, for the lamellar thickness and for the volume fraction crystallinity a_c. These discrepancies are explained by the variation of the glass transition temperature (T_g) and melting temperature (T_m) of the materials with different DEG contents. The previous hypothesis of the segregation of the comonomer (DEG) units into the amorphous regions is confirmed.     

Dielectric and EMW absorbing properties of PDCs-SiBCN annealed at different temperatures

Polymer derived SiBCN ceramics (PDCs-SiBCN) were prepared from polyborosilazane and then annealed at 1200–1800 °C in N₂. Effects of annealing temperature on the microstructure, phase composition, dielectric and wave-absorbing properties of ceramics were investigated. Results showed that nano-sized SiC grains were formed in amorphous SiBCN after annealing and the content and crystallization degree of SiC gradually intensified with annealing temperature increasing. The permittivity, dielectric loss and electrical conductivity of PDCs-SiBCN gradually increased as the temperature rose due to the formation of conductivity network of SiC grains and the increase of nano-grain boundary. The increased content of SiC (as the dipole) and interface between SiC nano-grains and amorphous SiBCN phase led to a higher polarization ability and higher dielectric loss. The RC gradually decreased with the annealing temperature increasing, demonstrating the annealed ceramics had the superior wave-absorbing ability and high annealing temperature was conducive to the improvement of wave-absorbing property.     

Effect of annealing on transport properties of organic vapours in drawn polyethylene

Drawing of quenched polyethylene at 60°C transforms the spherulitic sample into a material with fibrous structure. As a consequence, the sorption and still more the diffusion of C₂Cl₄ vapours are drastically reduced. Annealing at 120 and 125°C increases the crystallinity and hence reduces the amount of the amorphous component. In spite of that, it enormously increases the transport properties. It restores the sorption per unit volume of amorphous component to a value which, corresponding to completely relaxed amorphous component, is even higher than that of the starting undrawn but quenched material. The diffusion constant after annealing is a little smaller than in the undeformed original sample and shows the same small dependence on concentration in striking contrast with the drawn material. One concludes that the restoration by annealing of the sorption and diffusion coefficients for drawn polyethylene to the values of the undrawn material is a consequence of the complete relaxation of polyethylene chains, in particular of tie molecules, in the amorphous component which completely overcompensates the effects of a reduced amorphous fraction and the increase in crystal perfection.     

Long Spacing in Polyblock Poly(ether ester)s—Origin and Peculiarities

Abstract

Poly(ether ester)s (PEE) based on poly(butylene terephthalate) (PBT) as hard segments and poly(ethylene glycols) (PEG) with different molecular weight as soft segments are studied by means of WAXS and SAXS in the drawn and undrawn state after annealing at various temperatures (T_a ). The repeatedly reported strong increase of the long spacing L with T_a is confirmed once again. In the same time the directly measured by WAXS crystallite size of PBT remains insensitive to T_a and the increase of L with T_a is the stronger, the higher the PEG content. It is concluded therefore that the rise in L is due to the expansion of the amorphous intercrystalline layers rather than to crystal thickening, the latter being the case of semicrystalline homopolymers.

The observed much stronger increase of L with T_a in undrawn samples than in drawn ones is explained by melting of less perfect crystallites at higher T_a and dephasing processes in the amorphous regions. The conclusions drawn seem to be valid for other segmented polyblock copolymers and suggest some specific features of the block copolymers in comparison to homopolymers.     

Enhancing mechanical properties of aromatic polyamide fibers containing benzimidazole units via temporarily suppressing hydrogen bonding and crystallization

The copolymerization modified poly(p‐phenylene terephthalamide) containing 2‐(4‐aminophenyl)?5‐aminobenzimidazole (PABZ) units in the main chain was synthesized and the corresponding poly‐p‐phenylene‐benzimidazole‐terephthalamide (PBIA) fibers were prepared by wet spinning. The HCl, the by‐product released during polymerization, can complex with PABZ units to prevent the formation of hydrogen bonding between PABZ units, resulting in amorphous PBIA fibers and a lower glass transition temperature (T_g). Therefore, for the purpose of gaining strong hydrogen bonding and high orientation degree at the same time in PBIA fibers, two‐step drawing–annealing processing was adopted. The as‐spun PBIA/HCl complex fibers were drawn first at 280°C, higher than the T_g of the PBIA/HCl complex fibers and lower than the decomplexed temperature of HCl, which temporarily suppresses the formation of hydrogen bonding and crystallization. Subsequently, the fibers were annealed to reform hydrogen bonding between PABZ units and crystallization via decomplexation of HCl at 400°C. However, when the drawing is above the decomplexed temperature of HCl, the decomplexation of HCl begins to occur which leads to the reform of hydrogen bonding and crystallization, and the tensile strength of the drawn‐annealed PBIA/HCl complex fibers decreases with a decrease in the HCl content of fibers. The tensile strength of two‐step drawn‐annealed fibers increased by approximately 15% compared to that of one‐step drawn PBIA/HCl complex fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42482.     

Effects of Annealing Temperature on the Structure and Capacitive Performance of Nanoscale Ti/IrO2–ZrO2 Electrodes

Electrodes consisting of coating of the Iridium oxide–Zirconium oxide (70%IrO₂–30%ZrO₂) binary oxide were formed on Ti substrates by thermal decomposition and annealing at 340°C–450°C. The effects of the annealing temperature on the structure, surface morphology, surface composition, and capacitive performance of the coatings were investigated using X‐ray diffraction analysis (XRD), transmission electron microscopy (TEM), scanning electron microscopy, X‐ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). The XRD and TEM analyses showed that 360°C is greater than but very close to the crystallization temperature of the 70%IrO₂–30%ZrO₂ oxide coating. The 70%IrO₂–30%ZrO₂ oxide coatings annealed at this temperature consisted of an amorphous matrix containing a few IrO₂ nanocrystalline particles (diameter of 1–2 nm). The degree of crystallinity of the coatings was approximately 13.2%. EIS analysis showed that the electrode annealed at 360°C exhibited the highest specific capacitance, which was much higher than that of the electrode annealed at 340°C (which had a purely amorphous structure) as well as those of the electrodes annealed at 380°C and 400°C (which had higher degrees of crystallinity). On the basis of the obtained results, the following conclusion can be drawn: oxide coatings prepared at temperatures slightly higher than the crystallization temperature of the oxide and containing conductive nanocrystalline particles exhibit the best capacitive performance. We suggest that this phenomenon can be explained by the fact that the electronic conductivity of the coating is greatly improved by the presence of the homogeneously distributed conductive nanocrystalline particles in the amorphous matrix. Furthermore, the protonic conductivity and loose atomic configuration of the amorphous structure of the electrode are not adversely affected by the annealing treatment.     

Higher order structures and mechanical properties of bacterial homo poly(3-hydroxybutyrate) fibers prepared by cold-drawing and annealing processes

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, 2₁ 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.     

DSC studies on polyester-polyamide biconstituent fibers

The melting and crystallization behaviour of undrawn poly(ethylene terephthalate)-nylon 6 biconstituent fibers (BCF) have been investigated by DSC measurements. A decrease of the internal ΔT between the temperature of the glass transition and the temperature of the cold crystallization has been found. Changes of the temperature of the melt crystallization of the two components depending on the blend ratios (e.g. the phase morphology) have been also observed. These effects have been explained by an interface physical interaction which changes the degree of order of the molecules inside the phases. A relation between the decrease in ΔT of the PETP component and the maximum draw ratio λ_max of the BCF has been established. It is supposed that the change in ΔT causes the occurrence of local tensions and the initial formation of microcracks in the PETP phase which lead to a decrease of λ_max.     

Structure and properties of drawn tapes of high-density polyethylene/ethylene copolymer blends. I

A series of undrawn and drawn tapes has been prepared from HDPE, as well as, blends consisting of 90% HDPE and 10% ethylene copolymers. The influence of both the molecular irregularity of ethylene copolymers and resultant crystallization behavior on structure and mechanical properties of these blends has been investigated using differential scanning calorimetry, wide-and small-angle X-ray diffraction, mechanical response at small and large strains, and dynamic mechanical thermal analysis. The tensile drawing study of un-drawn tapes shows enhanced strain hardening and a consistent reduction in natural, as well as, maximum achievable draw ratio with an increase in molecular irregularity of ethylene copolymers. It has been confirmed that blends are partially miscible in the amorphous, as well as, in the crystalline phase through cocrystallization. The lateral crystallite thicknesses, crystallinity, and amorphous phase orientation of blends consistently decreases with an increase in molecular irregularity of ethylene copolymers because of a large-scale change in crystallization and drawing behavior of HDPE component in the blends. There is a distinct possibility that the molecular network exerts an important influence on physical and mechanical properties of undrawn and drawn tapes. © 1996 John Wiley & Sons, Inc.     

Structure and properties of ethylene—methacrylic acid copolymers and their sodium salts: Dielectric and proton magnetic relaxation studies

Dielectric and proton magnetic relaxation data have been obtained for an ethylene-methacrylic acid copolymer (containing about 4 mole% methacrylic acid units) and its 53% ionised sodium salt. The degrees of crystallinity and percentage ionisation of the samples investigated were estimated by infra-red methods. The dielectric results were obtained principally in the frequency range 100 Hz to 10 kHz and at temperatures ranging from 80° to – 120°. A few results are also reported at frequencies down to 0·1 Hz and up to 100 MHz. For the acid copolymer, two dielectric loss regions are observed and these are correlated with the reported mechanical β′- and γa-processes respectively. The partly ionised copolymer exhibits three dielectric relaxation regions which correlate with the mechanical α-, β- and γa-relaxations respectively. In addition, a dielectric peak appears at about —40° in the presence of absorbed water, a result similar to that found in the polyamides. The proton magnetic relaxation results were obtained by pulse methods which yielded the spin-lattice relaxation times T₁ (at 30 MHz) and T_1p (at kilohertz frequencies) as a function of temperature from ?180° to 100°. Two components were generally observed for T_1p. For the acid copolymer the β′- and γ-processes have been observed from these results, as well as a lower-temperature (δ) process which has not been detected by the mechanical or dielectric methods. For the sodium salt the γ- and δ-processes are also found, in addition to a high-temperature process in the region of the merged α- and β-processes. The present data are consistent with previous assignments for the β′-, α-, β- and γ-processes. The ‘water’ relaxation appears to involve some rotation of water molecules, or of ionic segments to which water molecules are attached, in the proposed ionic domains. The δ-process is ascribed to the rotations of methyl groups present in the methacrylic acid units.     

Preparation and magnetic properties of iron titanium oxide nanotube arrays

FeTi alloy was prepared by a vacuum smelting method, iron titanium oxide nanotube arrays have been made directly by anodization of the FeTi alloy. Morphologies and microstructures of the samples were characterized by scanning electron microscope, transmission electron microscope, and X-ray diffractometer. Influences of temperature and H₂O concentration on the morphologies of the nanotube arrays have been discussed in detail. Magnetic properties of the samples have also been investigated. The as-prepared samples were amorphous. When annealed at 500 °C and 550 °C, pesudobrookite Fe₂TiO₅ was obtained. At 600 °C, there were mixed Fe₂TiO₅, rutile TiO₂, and α-Fe₂O₃. Magnetic performance of the nanotube arrays exhibited high sensitivity to temperature and changed interestingly upon annealing. The values of the coercivity and remanence were 340 Oe and 0.061 emu/g respectively for the sample annealed at 550 °C.     

Annealing of drawn crystalline polymers

The annealing of drawn samples mobilizes the almost fully extended amorphous tie molecules which try to assume the thermodynamically required random conformations. The sample shrinks if annealed with free ends which permits the crystal blocks on different microfibrils and connected by almost fully extended taut tie molecules to move towards the position they had before plastic deformation. Hence the annealed sample has irretrievably lost most of its high axial elastic modulus which in the sample as drawn was caused by the high fraction of taut tie molecules. With fixed ends no shrinkage is possible so that the partial relaxation of interfibrillar taut tie molecules still lets them connect far away blocks. If their fraction is large enough so that in spite of the high surface to volume ratio which drastically depresses the crystallization temperature they can crystallize they do so after cooling to room temperature. The new axial crystalline bridges restore the high elastic modulus of the material before annealing, partially stabilize the sample against shrinkage during a new annealing, but also cause the dead bend effect which is the consequence of the replacement of flexible taut tie molecules in still amorphous conformation by rigid crystalline bridges. The drawing or extrusion at high temperature produces some annealing effects comparable with those of cold drawn material annealed with fixed ends.     

Crystallization and orientation behaviors in isotactic polystyrene and poly(2,6-dimethylphenylene oxide) blends

The crystallization and orientation behavior in the miscible iPS/PPO blends were studied aiming at producing oriented materials consisting of iPS crystals and amorphous PPO chains. Oriented films of iPS/PPO blends were prepared by drawing the melt-quenched blend films. The films were heat-treated under constraint at the drawing temperature so as to crystallize the molecular chains of iPS in the oriented state. The crystallinity and the crystal orientation in the drawn annealed films were studied by the wide-angle X-ray diffraction (WAXD), and the orientation behaviors of molecular chains were analyzed by polarized FTIR spectroscopy. WAXD diagrams show the presence of the highly oriented crystalline structure of iPS in the drawn annealed films of pure iPS and iPS/PPO=7/3 blend. The polarized FTIR spectra of drawn annealed films suggest that the molecular orientation of the amorphous chains of PPO and iPS is markedly relaxed by the heat treatment, although the orientation of iPS with 3₁ helical structure was retained during the oriented crystallization. It was concluded that the drawn annealed samples of the iPS/PPO=7/3 blend consist of highly oriented iPS crystals and nearly isotropic amorphous materials. The mechanical properties of the oriented iPS/PPO blends were measured not only in the stretching direction but also perpendicular to the stretching direction. It was shown that the ultimate strength in the perpendicular direction is 4-5 times higher in the drawn annealed film of iPS/PPO=7/3 blend than in the drawn annealed iPS. The improvement in the vertical strength in the blend is discussed in relation to the structural characteristics of the iPS/PPO blend.     

Dielectric and dynamic mechanical relaxation behaviour of poly(ethylene 2,6-naphthalene dicarboxylate). II. Semicrystalline oriented films

The dielectric and dynamic mechanical behaviour of bi-stretched non-treated and annealed semicrystalline poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) films are studied as a function of different morphologies obtained by thermal treatments at temperatures close to the melting temperature of a semicrystalline film. Differential scanning calorimetry (DSC) shows that the glass transition temperatures do not change significantly with the thermal treatment for bi-stretched films. However, the melting temperatures and the degree of crystallinity increase with the value of annealing temperature. Both dielectric relaxation spectroscopy (DRS) and dynamic mechanical analysis (DMA) display three relaxation processes. In order of decreasing temperature, can be observed: the α-relaxation due to the glass transition, the β^∗-process assigned to cooperative molecular motions of the naphthalene groups which aggregate and the β-relaxation due to local fluctuations of the carbonyl groups. The α-relaxation process shifts to higher temperatures for the 250 and 260 °C treated bi-stretched semicrystalline samples compared to the sample thermally treated at 240 °C according to DRS data but shifts to lower temperatures according to the DMA measurements for the three annealed samples. This discrepency results from the different sensitivity of each methods with regards to the release of orientation. At a fixed frequency the temperature associated to β^∗-relaxation is lower for the non-treated bi-stretched semicrystalline samples than for the treated ones using DMA but no difference can be seen in DRS. The associated apparent activation energies are rather high which suggest cooperative motions. It is assumed that the orientation of the samples prevents coupling between the naphthalene groups due to the stretched chain configuration in the amorphous phase. The activation energy for the β-process given by DRS is independent of the thermal treatment and the value agrees with those found for poly(ethylene terephthalate) (PET) and amorphous PEN. Evidence of the decrease of orientation in the sample with thermal treatment can be seen via the onset of mobility, both by DRS and DMA. Thus, the orientation induces a greater change of properties compared to the crystalline samples obtained from the thermal treatment of an amorphous sample. Finally, a three phase model is proposed since there is evidence of a rigid amorphous phase present in PEN biaxially stretched samples which was favoured by the dependence of dielectric relaxation strengths on the degree of crystallinity for the β^∗- and α-relaxation.     

Thermal properties of ethylene ionomers

The annealing effect of ethylene ionomers annealed at various temperatures and for various periods was studied by differential scanning calorimetry. Two endothermic melting peaks were observed for all the ethylene ionomers annealed. The melting peak at the lower temperature, which was assigned to bundlelike crystal owing to a Hoffman-Weeks relationship, shifted to a higher temperature with the annealing temperature and period, indicative of recrystallization. There is physical cross-linking consisting of ionic aggregates, such as multiplets and clusters in ethylene ionomers. The crystallization kinetics of ethylene ionomers was fundamentally similar, but different from that of low-density polyethylene. Crystallization and recrystallization suggested a mobile ethylene chain in both amorphous regions and ionic aggregates even in the presence of cross-linking.     

Post-deposition annealed MoO3 film based high performance MSM UV photodetector fabricated on Si (100)

Molybdenum oxide (MoO₃) films were prepared on Si (100) at room temperature using radiofrequency (RF) magnetron sputtering technique. The films were annealed in the presence of air at different temperatures from 100 to 550 °C. The as-prepared films were amorphous as revealed by the X-ray diffraction analysis. Post-deposition annealing of MoO₃ film enhanced its crystalline structure, showing β-MoO₃ phase at 100 °C and a mixture of α-MoO₃ and β-MoO₃ phases at 300 °C. The crystallinity of α-MoO₃ improved with increasing the annealing temperature to 500 °C, however, the β-MoO₃ phase became amorphous. The film was dissolved at 550 °C as no diffraction peak of MoO₃ was detected at this temperature. The band gap of MoO₃ was evaluated through ultraviolet–visible spectroscopy. The results showed a decrease in the band gap from 3.70 to 3.39 eV with increasing the annealing temperature to 500 °C. The film with optimum crystalline quality was used to fabricate a metal-semiconductor-metal (MSM) photodetector device. The photo-detection characteristics of the film were studied after the deposition of Nickel contacts on MoO₃ using a metal mask having interdigitated electrodes. The fabricated device exhibited a high current gain and sensitivity under 365 nm UV illumination. The responsivity of the device under UV light was 0.41 A/W at 7 V. The rise and decay time of UV photodetector were 0.32 and 0.23 s respectively. These findings suggested that the MoO₃ film with dominant orthorhombic α-phase can potentially be used for the photodetector application.     

Annealing effect on the microstructure of poly(vinyl chloride)

The effect of annealing on the microstructure of commercial grade poly(vinyl chloride) was investigated by calorimetric, X-ray and viscoelastic measurements. The degree of crystallinity increases with increasing annealing temperature from above the glass transition temperature up to 130°C, at which point the degree of crystallinity takes on a maximum value. Also, the crystal melting temperature increases with increasing annealing temperature. Thermal analysis and X-ray study suggest that the crystallite of poly (vinyl chloride) decomposes by thermal degradation when annealed, above 170°C. The isothermal crystallization process is analyzed using Avrami's equation employing the degree of crystallinity as a function of annealing time at various annealing temperatures. The crystallization rate has a maximum value at around 140°C. It is expected that the crystalline texture grows in the shape of a lineal-like habit, judging from the magnitude of Avrami's constant and from a study of the X-ray intensity distribution. The α_f-transition was observed to occur at temperatures 5 to 10°C lower than the crystalline melting temperatures for annealed specimens of poly(vinyl chloride) using a dynamic spring analysis. The α_f-transition may be attributed to thermal molecular motions with a long time scale, resulting from the cross-link points introduced by the small crystallites.     

Effects of mechanical drawing on the structure and properties of peek

This study examines the effects of crystallinity and temperature on the mechanical properties of PEEK. Crystallinity in PEEK Increases with annealing temperature up to a maximum of 28 percent with a melting point at 335°C. A minor melting peak also occurs about 10°C above the annealing temperature. In cold drawing the samples exhibited a yield stress and necking followed by homogeneous drawing. The yield stress increases with crystallinity, but there is no change in the modulus. The extension in the necking process also increases with crystallinity, however there is only a slight increase in extension-to-break since necking is compensated by the final amount of homogeneous drawing. The yield stress of PEEK when drawn at T_g (145°C) is significantly lower than at room temperature indicating a reduction in mechanical properties at temperatures approaching T_g. After mechanical drawing the minor melting peak disappears and on heating the material undergoes cold crystallization near the onset of T_g. There is evidence that this minor crystalline component might contribute to the yield stress changes with annealing history. Cold drawing induces crystallization of amorphous PEEK but decreases crystallinity and generates microscopic voids in crystalline PEEK, The various effects of crystallinity on mechanical properties could be important in determining the stress response of PEEK as the matrix in composites.     

Structure and properties of poly(ethylene terephthalate) crystallized by annealing in the highly oriented state: 2. Melting behaviour and the mosaic block structure of the crystalline layers

The melting behaviour of drawn poly(ethylene terephthalate) bristles has been studied by means of differential scanning calorimetry. In addition the wide-angle X-ray diffraction pattern were analysed. For comparison some of the experiments were also carried out with undrawn samples. The differences in the melting curves of drawn and undrawn PET originate from the different crystallization kinetics. The density defect ($\text{?}{}^{\mathrm{id}}{}_{\mathrm{c}}\text{? ?1}{}_{\mathrm{c}}$) between the ideal crystal density ?^id_c and the effective density $\text{?1}{}_{\mathrm{c}}$ of the crystalline layers is a result of lattice vacancies introduced by the grain boundaries of the mosaic blocks. The relatively low ultimate crystallinity of PET is supposed to be caused by the hindrance of crystal growth of fibre direction during isothermal crystallization.