Wide-angle X-ray Diffraction Data Research Articles

The Crystallization Morphology and Conformational Changes of Polypropylene Random Copolymer Induced by a Novel β-Nucleating Agent.

The crystal morphology and conformational changes during crystallization of a polypropylene random copolymer (PPR) are the basis for understanding its crystallization process. In this work, novel rare-earth β-nucleating agent WBN-28 was directly added into PPR to induce β-crystallization. The results of differential scanning calorimetry (DSC) showed that it has an excellent β-crystal-induced effect. The β-crystal content could surpass 85%, calculated from wide-angle X-ray diffraction (WAXD) data. The morphology of the β-crystal and α-crystal was intuitively observed via a polarizing optical microscope (POM). The β-crystallites were interconnected to naturally develop plate-like crystalline regions possessing a certain size, and the α-crystallites with sufficient thicknesses possessed a cross-hatched phenomenon. The bundle-like supramolecular structure of the β-crystal induced by WBN-28 was further observed via a scanning electron microscope (SEM). The conformational changes in the crystallization process of PPR were resolved via high-resolution infrared spectroscopy to understand its β-crystallization in depth. The conformational changes during the crystallization of PPR were found to be different from those of the isotactic polypropylene homopolymer (PPH); they had their own characteristics. This will provide guidance for understanding the β-crystallization of PPR in depth.

Determination of the Degree of Crystallinity of Poly(2-methyl-2-oxazoline).

A new method for purification of 2-methyl-2-oxazoline using citric acid was developed and living cationic ring-opening polymerization of 2-methyl-2-oxazoline was carried out. Polymerization was conducted in acetonitrile using benzyl chloride—boron trifluoride etherate initiating system. According to DSC data, the temperature range of melting of the crystalline phase of the resulting polymer was 95–180 °C. According to small-angle X-ray scattering and wide-angle X-ray diffraction data, the degree of crystallinity of the polymer was 12%. Upon cooling of the polymer melt, the polymer became amorphous. Using thermogravimetric analysis, it was found that the thermal destruction of poly(2-methyl-2-oxazoline) started above 209 °C.

Synthesis and Physical Properties of Biodegradable Nanocomposites Fabricated Using Acrylic Acid-Grafted Poly(butylene carbonate-co-terephthalate) and Organically-Modified Layered Zinc Phenylphosphonate

A set of novel biocompatible aliphatic–aromatic nanocomposites, including numerous acrylic acid-grafted poly(butylene carbonate-co-terephthalate) (g-PBCT) and organically-modified layered zinc phenylphosphonate (m-PPZn), were successfully synthesized via polycondensation and transesterification. A primary covalent linkage was produced between the biocompatible polymer and the inorganic reinforcements. Fourier transform infrared spectroscopy and 13C-nuclear magnetic resonance spectra demonstrated the successful grafting of acrylic acid into the PBCT (g-PBCT). Both wide-angle X-ray diffraction data and X-ray photoelectron spectroscopy analysis showed that the g-PBCT polymer matrix was intercalated into the interlayer spacing of the m-PPZn and was chemically interacted with the m-PPZn. The addition of m-PPZn in the g-PBCT matrix significantly improved its storage modulus. A slight increase in thermal stability was observed in all the g-PBCT/m-PPZn composites. Both results are attributed to the presence of covalent bond between g-PBCT and m-PPZn.

Morphologies and Structure of Brain Lipid Membrane Dispersions.

This study aims to explore the variety of previously unknown morphologies that brain lipids form in aqueous solutions. We study how these structures are dependent on cholesterol content, salt solution composition, and temperature. For this purpose, dispersions of porcine sphingomyelin with varying amounts of cholesterol as well as dispersions of porcine brain lipid extracts were investigated. We used cryo-TEM to investigate the dispersions at high-salt solution content together with small-angle (SAXD) and wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) for dispersions in the corresponding salt solution at high lipid content. Sphingomyelin forms multilamellar vesicles in large excess of aqueous salt solution. These vesicles appear as double rippled bilayers in the images and as split Bragg peaks in SAXD together with a very distinct lamellar phase pattern. These features disappear with increasing temperature, and addition of cholesterol as the WAXD data shows that the peak corresponding to the chain crystallinity disappears. The dispersions of sphingomyelin at high cholesterol content form large vesicular type of structures with smooth bilayers. The repeat distance of the lamellar phase depends on temperature, salt solution composition, and slightly with cholesterol content. The brain lipid extracts form large multilamellar vesicles often attached to assemblies of higher electron density. We think that this is probably an example of supra self-assembly with a multiple-layered vesicle surrounding an interior cubic microphase. This is challenging to resolve. DSC shows the presence of different kinds of water bound to the lipid aggregates as a function of the lipid content. Comparison with the effect of lithium, sodium, and calcium salts on the structural parameters of the sphingomyelin and the morphologies of brain lipid extract morphologies demonstrate that lithium has remarkable effects also at low content.

High-Electric-Field-Induced Hierarchical Structure Change of Poly(vinylidene fluoride) as Studied by the Simultaneous Time-Resolved WAXD/SAXS/FTIR Measurements and Computer Simulations

A high electric field was applied cyclically to poly(vinylidene fluoride) films, during which the simultaneous and time-resolved measurements of the two-dimensional wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and transmission-type Fourier transform infrared (FTIR) spectra were performed using a synchrotron X-ray radiation system. The inversion of the CF2 dipole moments caused by the alternate change of the electric field vector direction was detected to occur around ±80–100 MV/m as estimated by the electric-field-strength dependence of the IR band intensity. On the other hand, the WAXD peaks were found to show the maximal intensities at 0 and ±250–300 MV/m. In these regions, the 001 reflection of the β form and the 002 reflection of the δ form changed the intensities remarkably and periodically. These experimental data were interpreted, not by the idea of a simple inversion motion of the rigid polar chains (the planar zigzag chains of the form β and the TGTG̅ chains of the α and δ forms) but by the more complicated couplings between the rotation and tilting motions of the chain segments, the cooperative T-G conformational exchanges, and the associated inversion motion of the CF2 dipoles. The idea of the cooperative chain motions was supported by the density functional theory calculations performed under the external electric field. Different from the remarkable changes of the WAXD and FTIR data, the SAXS patterns did not show the detectable changes in these processes, indicating that the above-mentioned cooperative structural changes should occur in the crystalline regions with the stacked lamellar structure kept unchanged.

The colloidal structure of a cellulose fiber

We present a small angle X-ray scattering (SAXS) study of the colloidal structure of regenerated cellulose fibers, air-gap spun from an ionic liquid solution. Based on the data, and a different interpretation of the anisotropic SAXS pattern, we propose a slightly different colloidal structure of the fibers, than what is commonly assumed for regenerated cellulose fibers. Fibers with two different degrees of orientation, as produced by different draw ratios, DR = 2 and 15, respectively, are analyzed. The 2D SAXS pattern is highly anisotropic with striking cross-like pattern, having scattering predominantly perpendicular and parallel to the fiber axis. This cross-like pattern suggest a colloidal structure with oriented crystalline lamellae of ca. 10 nm thickness, embedded within a continuous matrix of amorphous cellulose. The lamellae are oriented with their normal parallel with the fiber axis. Complementary wide angle X-ray diffraction data confirm that the lamellae normal direction corresponds to the cellulose chain direction (c-direction) in the monoclinic cellulose crystal (Cellulose II).Graphic abstract

Fabrication and properties of polyimide copolymer fibers containing pyrimidine and amide units

Polyimide (PI) fibers containing pyrimidine and amide moieties were fabricated by the copolymerization of 2,5-bis(4-aminophenyl)pyrimidine (PRM) and 4,4′-diaminobenzanilide (DABA) with 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) via a two-step method. The effects of chemical structure of PI fibers, i.e., various molar ratios of PRM/DABA, on their thermal property, crystallinity, orientation factor, microvoid defects, and mechanical property, were investigated in detail. The glass transition temperatures (Tg) of all PI fibers ranged from 282 to 310 °C, and the temperatures at 5% weight loss (T5%) under N2 and air atmosphere were respectively within 548–584 °C and 482–540 °C, demonstrating the excellent thermal stability and thermal oxidation stability of all fibers. The wide-angle X-ray diffraction data illustrated that the co-PI fibers had lower crystallinity than the homo-PI fibers due to a marked decrease in molecular order packing by copolymerization. However, the co-PI fibers possessed higher degrees of orientation relative to the homo-PI fibers. In particular, the co-PI fiber with PRM/DABA = 5/5 showed the highest orientation factor, fc = 0.872. Moreover, the small-angle X-ray scattering results, i.e., decrease in microvoid size, revealed that DABA incorporation helps to reduce the defects in PI fibers. When the PRM/DABA molar ratio was 5/5, the co-PI fiber possessed an optimal tensile strength and initial modulus of 3.43 and 136.92 GPa, respectively.

A Synchrotron in situ X-ray Study on the Multiple Melting Behaviors of Isomorphous Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(HB-co-HV)) with Middle HV Content

The multiple endothermic peaks without observable recrystallization phenomenon of isomorphous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-co-HV)] with the middle HV content of 19.4 mol% and 28.7 mol% were confirmed by differential scanning calorimetry (DSC), and the evolutions of crystal structure and lamellar morphology in the heating and melting process were tracked by in situ synchrotron wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) techniques. The emergence of asymmetric features of both the diffraction peaks and scattering curves indicates the coexistence of different lamellar crystals with varied unit cell parameters. Based on the in situ WAXD and SAXS measurements, we calculated the evolutions of the unit cell parameters a and b as well as the long period and lamellar thickness upon heating. The comparative analysis of WAXD and SAXS data confirms that the multiple endothermic peaks of P(HB-co-19.4%HV) and P(HB-co-28.7%HV) result from the melting of different lamellae rather than the melting/recrystallization. The thinner, unstable uniform lamellae with HV counits total inclusion melt first and the thicker, stable sandwich lamellae with HV counits partial inclusion melt last. In addition, the large second melting peak in P(HB-co-19.4%HV), differing from that of samples with HV content of 28.7 mol% and 36.2 mol%, is due to the unique state of HV content leading to a transition of sandwich lamellae to uniform lamellae. The present study establishes the relationship between the different lamellae structure and multiple melting behaviors of isomorphous copolymer.

Crystallization and Enzymatic Degradation of Maleic Acid-Grafted Poly(butylene adipate-co-terephthalate)/Organically Modified Layered Zinc Phenylphosphonate Nanocomposites

Biodegradable nanocomposites were successfully synthesized using the maleic acid-grafted poly(butylene adipate-co-terephthalate) (g-PBAT) and organically modified layered zinc phenylphosphonate (m-PPZn), containing covalent linkages between g-PBAT and m-PPZn. Differential scanning calorimetry, wide-angle X-ray diffraction (WAXD), and transmission electron microscopy (TEM) were used to determine the crystallization behavior and morphology of g-PBAT/m-PPZn nanocomposites. The isothermal crystallization kinetics of g-PBAT/m-PPZn nanocomposites was determined using the Avrami equation. It was found that the half-time for the crystallization of the neat g-PBAT matrix is larger than that of g-PBAT/m-PPZn nanocomposites. This result suggests that the incorporation of m-PPZn can improve the crystallization rate of nanocomposites. The WAXD and TEM data illustrate that most of the m-PPZn layered materials are partially intercalated or exfoliated in the g-PBAT matrix. As the enzyme, lipase from Pseudomonas sp. was used for the enzymatic degradation tests. The degradation rates of the neatly fabricated g-PBAT copolymers using the heat pressing technique increase in the order of g-PBAT-80 > g-PBAT-50 > g-PBAT-20. The growing degradation rate of g-PBAT-80 is due to the growing amount of the adipate acid group and the increasing chain flexibility of the polymer backbone. Moreover, the increasing loading of m-PPZn enhances the weight loss of nanocomposites, suggesting that the existence of m-PPZn enhances the degradation of g-PBAT copolymers. The degradation rate of the freeze-drying samples containing a highly porous structure is greater than those prepared using the heat pressing technique.

A Study on Blend Ratio-dependent Far-IR and Low-frequency Raman Spectra and WAXD Patterns of Poly(3-hydroxybutyrate)/poly(4-vinylphenol) Using Homospectral and Heterospectral Two-dimensional Correlation Spectroscopy.

An intensive analysis of far-infrared (far-IR), low-frequency Raman, and wide angle X-ray diffraction (WAXD) data has been performed by two-dimensional correlation spectroscopy (2D-COS) as a function of the blend ratio of poly(3-hydroxybutyrate)/poly(4-vinylphenol) (PHB/PVPh). Homospectral 2D-COS revealed that a weak band at 128 cm-1 in the far-IR spectra appeared more clearly in the 2D correlation spectra. Heterospectral 2D-COS (far-IR/low-frequency Raman and far-IR/WAXD) provided very important results that were hardly detected in the conventional 2D-COS. A far-IR peak at 130 cm-1 in the heterospectral 2D-COS had negative correlations with the peaks in the low-frequency Raman spectra at 81, 100, and 110 cm-1 and WAXD profile 8.78 and 11.01°. These results indicated that those peaks have different origins; the 130 cm-1 peak comes from the intermolecular C=O···H-O hydrogen bond between PHB and PVPh, while those for low-frequency Raman and WAXD peaks are the features of PHB crystalline structure.

A Facile Synthesis of Itaconic Acid Based Biodegradable Co-polyesters: An In-Vitro Anticancer Evaluation and Controlled Drug Delivery System

A series of aliphatic co-polyesters were prepared via one-step polycondensation reaction of itaconic acid, 1,4-cyclohexane dimethanol and diols using titanium tetraisopropoxide (TTIP) as a catalyst. The chemical structure of the repeating units present in the polymer chains were confirmed by FTIR, 1H and 13C NMR spectral data. The glass transition temperature (Tg), melting temperature (Tm) and decomposition temperature (Td) of the co-polyesters were evaluated by Differential Scanning Calorimetry (DSC). The biodegradability of the synthesized co-polyesters would be qualitatively studied by hydrolytic degradation at different pH followed by studying the change in surface morphology of the co-polyesters before and after degradation using Scanning Electron Microscope (SEM) images and the extent of crystallinity would also be studied using wide angle X-ray Diffraction (W-XRD) data. In-vitro anticancer activity of the synthesized co-polyesters were tested against human breast cancer (MCF-7) cell lines, all the co-polyesters show good IC50 value at lower concentration but among them PICMCD [Poly (1,4-cyclohexanedimethanol itaconate-co-1,4-cyclohexane diol itaconate)] has higher toxicity on MCF-7 cells. The drug delivery property of the co-polyesters would be investigated on tamoxifen citrate using spray down tablet coating process and PICMCD found to be a potential drug carrier.

The formation of Gluconacetobacter xylinum cellulose under the influence of the dye brilliant yellow

The structural characteristics of the nascent fibril produced by Gluconacetobacter xylinum (G. xylinum) have been studied under the influence of the cellulose binding dye brilliant yellow (BY) by wide angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR) and 13C solid-state nuclear magnetic resonance. BY is found to be more effective at reducing crystallinity than fluorescent brightener 28 (FB28), pontamine fast scarlet 4 (S4B) and other dyes previously studied. Under static cultivation conditions, increasing concentrations of brilliant yellow in the growth media from 20, 50, 100 to 250 μM, result in decreasing cellulose crystallinity from 73 to 18%, respectively, as compared to 82% exhibited by the control. FTIR data indicate that the presence of BY is most effective at suppressing intra-molecular hydrogen bonding. After boiling in 70 vol% aqueous EtOH solution for 12 h, the extracted dye-altered cellulose becomes more ordered, which may be due to the extraction of BY from the BY-cellulose complex. FTIR data indicate that compared to control cellulose, the reclaimed brilliant yellow-altered cellulose contains more cellulose Iβ, where the FB28 and S4B altered cellulose remains principally Iα. Based on WAXD and NMR data we propose a dye-cellulose complex structure associated with BY. This model supports the hypothesis that microfibrils assemble through the hydrogen bonding of formed mini-sheets that consist of stacked glucan chains linked by van der Waals forces.

X-ray Crystal Structure Analysis of Poly(3-hydroxybutyrate) β-Form and the Proposition of a Mechanism of the Stress-Induced α-to-β Phase Transition

The crystal structure of poly(3-hydroxybutyrare) β crystal form has been analyzed on the basis of two-dimensional X-ray diffraction data. The all-trans zigzag chains are packed in the hexagonal unit cell of a = b = 9.22 A, c (chain axis) = 4.66 A, and γ = 120° with the space group P3221. The upward and downward chains are statistically located at one lattice site at 50% probability. By combining the thus-analyzed structure information of the β-form with the previously reported structure information of the α-form, the geometrical relation between these two crystalline phases has been clarified in detail. The tension-induced α-to-β phase transition affects the higher-order structural change, as known from the small-angle X-ray scattering (SAXS) data collected in the tensile deformation process. By analyzing all experimentally obtained wide-angle X-ray diffraction and SAXS data, the following transition model has been proposed: the high tension to the oriented sample causes the increase of the long period of...

Synthesis, mechanical properties and biodegradation of various acrylic acid-grafted poly(butylene succinate-co-terephthalate)/organically modified layered zinc phenylphosphonate nanocomposites

A new series of biodegradable aliphatic-aromatic nanocomposites containing various acrylic acid-grafted poly(butylene succinate-co-terephthalate) (PBST) and organically modified layered zinc phenylphosphonate (m-PPZn) were successfully synthesized through the transesterification and polycondensation having the covalent linkages between polymer and inorganic materials. Fourier transform infrared (FTIR) and 13C-nuclear magnetic resonance (NMR) spectra demonstrate the successful grafting of acrylic acid to PBST (g-PBST). Both wide-angle X-ray diffraction and transmission electron microscopy data show that the g-PBST polymer matrix was intercalated into the interlayer spacing of m-PPZn. The additional m-PPZn into g-PBST matrix significantly enhanced the storage modulus as compared with that of neat g-PBST. The reduction in thermal stability was observed in all g-PBST/m-PPZn systems, which is probably caused by more nucleation to form more tiny and imperfect crystals. The biodegradations of neat g-PBST copolymers and g-PBST/m-PPZn nanocomposites were investigated using lipase from Pseudomonas sp. The degradation rates of the neat g-PBST copolymers increased in the order of g-PBST-70 > g-PBST-50 > g-PBST-30. The faster degradation rate of g-PBST-70 is a result of a higher content of succinic acid unit and chain flexibility of polymer backbone. Furthermore, the weight loss increased by increasing the loading of m-PPZn, suggesting that the existence of m-PPZn improved the degradation of the g-PBST copolymers.

Influence of Boron Nitride Nanosheets on the Crystallization and Polymorphism of Poly(l-lactide).

This work reports on the impact of delaminated boron nitride nanosheets (BNNSs) on the crystallization behavior and crystalline structure of melt-crystallized poly-L-lactic acid (PLLA). Wide-angle X-ray diffraction and scanning electron microscopy data revealed that the addition of lower loadings of BNNSs (∼0.5 wt %) resulted in the highly dispersed PLLA nanocomposites, whereas the higher loading of BNNSs (≥1 wt %) leads to the agglomerated nanocomposites. It is shown that the presence of lower loadings of the BNNSs (∼0.5 wt %) induces the formation of ordered α form when crystallizing from the melt at a cooling rate of 10 °C/min, but the mixture of α' and α forms is formed in the presence of higher loading of BNNSs (≥1 wt %). Polarized optical microscopy images revealed that the crystallization rate of PLLA was significantly enhanced in the presence of lower loading of BNNSs (∼0.5 wt %) as corroborated by the increasing number of tiny spherulites. The strong interaction between the highly dispersed BNNSs and PLLA chains induces the conformationally ordered α form, and the various experimental techniques revealed that crystallization of PLLA occurred rapidly with the narrow distribution of crystal size and degree of crystal perfection in highly dispersed nanocomposites. Furthermore, the thermal conductivity of PLLA/BNNSs nanocomposites was found to increase significantly with BNNSs loading.

Generation of versatile titania-silica nano-vehicles using dual templates exploiting as tunable drug releaser

In a new approach, a series of nanoporous TiO2-SiO2 systems (NTSn (n = 1–5)) were synthesized with various Ti/Si ratios via one step hydrothermal process in the presence of P123 and tetrabutylammonium bromide (TBAB) as dual templating agents. Then, simvastatin (SV) as a model drug was incorporated into the prepared mesoporous matrixes (NTS@SV). Wide-angle X-ray diffraction data (WAXRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, N2 adsorption-desorption isotherms, field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and zeta potential (ζ) measurement were used for the characterization of the prepared samples. It was found that the variation of Ti percent and attendance of both TBAB & P123 in the synthesis condition led to high pore volume (0.6–1.2 cm3 g-1), high surface area (187–656 m2 g-1), a wide range of pore sizes (5–13 nm) and surface zeta potential charge (−16 to −24 mV) of the prepared samples. These diversities made wide opportunities for new NTS@SV to exhibit the vast drug-release profiles in simulated gastric fluid (SGF, pH = 1.2) and simulated intestinal fluid (SIF, pH = 6.8) at 37 °C. In vitro drug release indicated that the sample prepared in the presence of both TBAB and P123 with Ti/Si = 1 represented maximum release of SV (ζ = −18 mV) equal to 77 and 100% in SGF and SIF media, respectively. SH-SY5Y cell viability was tested against the toxic background of parkinsonian toxin 6-OHDA upon cell exposure to NTS3@SV. Results demonstrated cell exposure to NTS3@SV neutralized 6-OHDA toxicity and enhanced cell survival significantly.

Strategy to improve PA6 performances by melt compounding

PA6 is widely used for packaging and engineering applications. Literature reports that organically modified nanoclays can improve its flame resistance, thermo-mechanical and gas barrier properties. This study aims at showing a new approach to effectively disperse an unmodified nanoclay (MMT) in PA6 by melt compounding polymeric matrix and clay in the presence of dipentaerythritol (DPE). The prepared composites have been studied in terms of composition and thermal characteristics; moreover, by using a combination of wide and small angle X-ray diffraction data and transmission electron microscopy observations it has been possible to draw the conclusion that a good dispersion of MMT platelets is obtained. The reason has been imputed to probable interactions between DPE, PA6 and clay. On the other hand, the nanoclay can prevent the DPE separation by crystallization. This synergistic effect between DPE and MMT has been observed for balanced amounts of additive and clay. Final properties, in particular barrier properties, are notably enhanced.

Micromechanical analysis of molecular orientation in high-temperature creep of polycarbonate

The molecular orientation of bisphenol-A polycarbonate (PC) was determined by the in-situ wide-angle X-ray diffraction (WAXD) measurement during high-temperature creep. The resulting creep and WAXD data were used to analyze the coupled deformation of macro-continuum and micro-structure. A four elements viscoelastic model was introduced to fit the creep results and describe the time-dependent orientation in creep. The delayed elastic stress was regarded as an assessment of molecular orientation, and two dashpots in the model were used to analyze the physical meanings of retardation time, which helped to understand the mechanism of molecular orientation and the role of free volume and stress on the viscoelastic parameters. A threshold range of free volume was proposed to interpret the change regularity of retardation time, delayed elastic modulus and coefficient C. The delayed elastic stress can be successfully used in assessing the orientation. Our work provides a deeper insight into the evolution of molecular orientation induced by high-temperature creep.

Effects of chemical structure on gas transport properties of polyethersulfone polymers

Compared to polysulfone (PSF), the effects of chemical structure on gas separation performance of polyethersulfone (PES) are rarely in-depth studied. To explore the potential of various PES polymers as gas separation membranes, PES containing four different backbone structures have been synthesized. They are polyphenylsulfone (PPSU), poly trimethyl benzene ethersulfone (TPESU), polyethersulfone (PESU) and hydrophilic polyethersulfone (HPESU). Both wide-angle X-ray diffraction (XRD) and positron annihilation life-time spectroscopy (PALS) data indicate that PPSU and TPESU have bigger d-space, pore size and fractional free volume (FFV) values than PESU and HPESU. Among the four PES, PPSU stands out with the highest O2 and CO2 permeability of 1.61 and 9.13 Barrer at 35 °C, respectively, because the two additional aryl groups in PPSU contributes to high segmental motions. HPESU has the lowest gas permeability but shows the highest CO2/N2 and CO2/CH4 selectivity of 34.9 and 34.6, respectively, possibly because of the affinity between its polyethylene oxide units and CO2. The addition of trimethyl benzene groups into TPESU not only increases all gas permeability but also increases selectivity of some gas pairs. It has the highest O2/N2 selectivity of 6.0 and the 2nd highest CO2/CH4 selectivity of 33.8. Its O2 and CO2 permeability are 1.33 and 5.74 Barrer at 35 °C, respectively. In contrast, PESU has low gas permeability and average selectivity because of its linear ethersulfone chain structure. In addition, the diffusivity ratio between Henry and Langmuir modes as a function of chain structure has been investigated. The diffusivity ratio is always smaller than 32%. This study may provide useful insights to design better PES polymers for gas separation.

Effect of injection molding parameters on crystallinity and mechanical properties of isotactic polypropylene

The effects of injection molding parameters namely mold temperature, melt temperature and injection speed on crystallization and mechanical properties of isotactic polypropylene were studied. The specimens were molded as per the Taguchi design of experiment and analyzed for signal to noise ratio and for analysis of variance test. The crystallinity and crystal sizes were determined by wide angle X-ray diffraction data. The specimens were tested for tensile, impact, flexural, stress relaxation and dynamic mechanical properties. It was observed that mold temperature was the most influential injection molding parameter governing the crystallinity and other mechanical properties. It was observed that increase in crystallinity is favorable from tensile and flexural strength point of view but impact properties deteriorate with increase in crystallinity. At high injection speed β-phase changes to α-phase due to shear induced orientation of polymer chains. It is interesting to notice that stress relaxation occurred in elastic as well as in plastic regions has the similar trends and can be modeled by the same decay model proposed in this paper.