Largely enhanced molecular orientation and mechanical property of injection-molded high-density polyethylene parts via the synergistic effect of polyamide 6 in situ microfibrillar and intense shear flow

The high-density polyethylene (HDPE)/polyamide 6 (PA6) in situ microfibrillar composites (HAM-C) were fabricated by the “extrusion-hot stretch-quenching” technique, in which PA6 microfibrillar had diameters lying in the range 0.55 to 1.05 μm. Then the HAM-C and pure HDPE were processed by multi-melt multi-injection molding (MMMIM). The effect of PA6 in situ microfibrillar and secondary melt penetration on the crystalline morphologies and mechanical properties was investigated using a variety of characterization techniques including differential scanning calorimetry (DSC), rheological experiments, scanning electron microscopy (SEM), synchrotron two-dimensional small-angle X-ray scattering (SAXS), and tensile testing. It was found that PA6 microfibrillar not only acted as a heterogeneous nucleation agent, but also prolonged the relaxation time of HDPE matrix by suppressing the mobility of HDPE molecular chains. It was revealed, from observing the morphologies, that the presence of PA6 microfibrillar not only facilitated the formation of transcrystalline superstructures on its surface, but also induced much more oriented crystals nearby as a result of the amplified local shear field. Furthermore, SAXS results confirmed that the degree of orientation of the injection-molded HAM-C part (HAM-M) was largely enhanced. Finally, the tensile testing showed that the tensile strength and Young’s modulus of the HAM-M sample were enhanced by 38.8 and 54.6 %, respectively, when compared with pure HDPE parts. This work provides a promising way to tailor the crystalline structure of the injection-molded parts.     

Sephadex-bound histamine in the catalysis of ester hydrolysis

Ester hydrolysis by Sephadex-bound catalysts was studied in a flow-through system. Three different immobilized preparations were synthesized and used: histamine-, coimmobilized histamine-octylamine-, and octylamine-Sephadex; octylamine-Sephadex was used as a reference. Immobilization was carried out using water-soluble carbodiimide, which gave amide linkages between carboxymethyl Sephadex and the groups attached. It was found that the coimmobilized histamine-octylamine preparation was three times more efficient than immobilized histamine alone in the hydrolysis of the esterp-nitrophenylcaproate, whereas hardly any difference was found in the hydrolysis of the less hydrophobic substratep-nitrophenylacetate. We attribute this enhancement of the hydrolysis ofp-nitrophenylcaproate to local enrichment of the substrate on the histamine-octylamine matrix caused by the presence of hydrophobic octyl groups.     

Thermal decomposition of polymethylmethacrylate synthesized with anionic catalysts

TG and DTA data are used to show that the thermal decomposition of polymethylmethacrylate (PMMA) synthesized with anionic catalysts depends on the nature of the catalyst. It is found that the thermal stability of PMMA obtained by using anionic amide catalysts is higher than that of radical PMMA and of PMMA obtained with other anionic catalysts, and depends on the temperature of polymerization and on the molecular weight of the polymer.     

Preparation and characterization of cationic pH-sensitive SiO2/polymer core-shell nanoparticles with amino groups in the shell

Silica/poly(styrene-N,N′-dimethylaminoethyl methacrylate) (SiO₂/P(St-DMAEMA)) cationic pH-responsive core-shell particles with a narrow size distribution and diameter of less than 200 nm were synthesized by emulsion polymerization. The effects of the St/DMAEMA molar ratio, SiO₂ core size, monomer amount, and cross-linking degree on the morphology and pH-responsiveness of the core-shell particles were investigated by transmission electron microscopy, dynamic light scattering, and conductometric titration. The results showed that core-shell particles with only one SiO₂ core could be obtained when the cross-linker divinyl benzene (DVB) was used, and the diameter of the core-shell particles increased with the size of the SiO₂ core and the total amount of monomer. It was observed that the amount of surface amino groups, zeta potential, and volume swelling ratio of the core-shell particles were significantly affected by the St/DMAEMA molar ratio, and a high volume swelling ratio was achieved at pH 4 and a DVB content of 3 mol%. The zeta potential was observed to be a function of pH, and the particles were positively charged when the pH value was below approximately 7.2.     

Effect of intermediate coupling in angular distribution of Auger electrons

A general expression for angular distribution of Auger electrons in the intermediate coupling scheme is obtained. It is shown that the intermediate coupling can lead to an anisotropy of the Auger line which is isotropic in the pure LS-coupling     

Relaxation properties and structures of polymer nanocomposites based on modified organoclays

Nanocomposite materials composed of HDPE and new guanidine-containing organoclays have been investigated. The basic changes in the relaxation properties of HDPE after the addition of guanidine-containing organoclays that vary in composition and content have been found. It has been shown that, depending on their structures and affinities for the polymer, guanidine-containing modifiers of montmorillonite have different effects on the structure and relaxation properties of the polymer.     

Thermal analysis of polymer layered silicate nanocomposites

It has been shown, for three different polymer layered silicate (PLS) nanocomposite systems, how differential scanning calorimetry (DSC) can identify the different reactions of homopolymerisation and of crosslinking that occur in the intra- and extra-gallery regions of these nanocomposites, respectively, and hence how DSC can be used to assess the cure conditions for optimising their nanostructure. The PLS nanocomposites are based upon: (i) diglycidyl ether of bisphenol-A (DGEBA) cured with a polyoxypropylene diamine; (ii) DGEBA cured with an –NH₂ terminated hyperbranched polymer (HBP); and (iii) tri-glycidyl p-amino phenol (TGAP) cured with a diamine. In each case, the existence of both intra- and extra-gallery reactions in the DSC cure curves, and whether they occur simultaneously or sequentially, and in what order, are identified and correlated with the nanostructure as observed by small angle X-ray scattering and transmission electron microscopy. In particular, it is shown that the intra-gallery reaction must precede the extra-gallery for significant exfoliation to occur. In accordance with this scenario, the TGAP/diamine system displays the greatest degree of exfoliation, the DGEBA/diamine system the least, with the DGEBA/HBP system intermediate. For those systems in which significant exfoliation occurs, the DSC cure curves also allow the optimum cure conditions, such as the isothermal cure temperature, to be determined.     

Controlling the properties of HDPE in the presence of low-molecular-mass additives of various types

To develop materials with new mechanical and improved rheological properties on the basis of common polyolefins, ultrahigh-molecular-weight PE and HDPE of medium molecular masses, the polymers have been modified with low-molecular-mass additives: crystalline organic disulfides (dithiaalkanes), liquid oligomer phenylmethylsiloxane, and oligooxypropylene glycol. It has been shown that the studied disulfide additives at low concentrations (up to 10% of the mass of PE) have no significant effect on the content and quality of the crystalline phase of HDPE. (The degree of crystallinity, enthalpy, and melting temperature change weakly.) In this case the plasticity of the modified PE improves: the tensile modulus and dynamic modulus decrease, whereas the elongation at break increases. In the presence of organic disulfides, the effective viscosity of the PE melt decreases. Unlike oligomeric phenylmethylsiloxane and oligooxypropylene glycol, dithiaalkanes are inert to the components of metallocomplex catalysts. Thus, the modification of PE with the aforementioned additives may be performed via their addition to the final polymer or in the course of the synthesis of the polymer.     

The Effect of Arg on the Structure Perturbation and Chaperone Activity of α-Crystallin in the Presence of the Crowding Agent,Dextran

α-Crystallin is a protein that is expressed at high levels in all vertebrate eye lenses. It has a molecular weight of 20 kDa and is composed of two subunits: αA and αB. α-Crystallin is a member of the small heat shock protein (sHsps) family that has been shown to prevent protein aggregation. Small molecules are organic compounds that have low molecular weight (<800 Da). Arginin (Arg) is a small molecule and has been shown to prevent protein aggregation through interaction with partially folded intermediates. In this study, the effect of Arg on the chaperone activity of α-crystallin in the presence of dextran, as a crowding agent, against ordered and disordered aggregation of different target proteins (α-lactalbumin, ovotransferrin, and catalase) has been investigated. The experiments were done using visible absorption spectroscopy, ThT-binding assay, fluorescence spectroscopy, and CD spectroscopy. The results showed that in amorphous aggregation and amyloid fibril formation, both in the presence and absence of dextran, Arg had a positive effect on the chaperone action of α-crystallin. However, in the presence of dextran, the effect of Arg on the chaperone ability of α-crystallin was less than in its absence. Thus, our result suggests that crowding interior media decreases the positive effect of Arg on the chaperone ability of α-crystallin. This is a very important issue, since we are trying to find a mechanism to protect living cells against the toxic effect of protein aggregation.     

Lariat ethers in the chiral recognition of amino acid esters:electrospray ionization mass spectrometry investigation

The ability of the crown ethers (1–4), containing the ortho- or para- methoxyphenoxy-methyl substituents in their structure, to chiral recognition in reference to amino acid esters has been investigated by electrospray ionization mass spectrometry (ESI-MS). The method allows registering the diastereomeric complexes between the studied crowns as hosts and the protonated alanine, phenylglycine and phenylalanine methyl esters as guests in the gas phase. ESI-MS experiments using isotopically labeled guests provide robust and reproducible results, indicating a moderate degree of chiral discrimination in the series of the studied crown ethers. ESI-MS experiments using achiral amine as a reference yielded the results comparable with the previous method. It has been found that (S)-enantiomers of the crowns bind predominately (S)-enantiomers of the amino acid esters, and vice-versa. It has been shown that the chiral ortho-substituted crown (S)-1 demonstrates the more pronounced values for chiral discrimination as compared with the para-substituted crown (S)-2. This fact indicates the interrelationship between the chiral recognition and the lariat nature of crown 1. Increasing the size of the cavity and the presence of a flat aromatic moiety in crowns 3 and 4 strengthens their complexing ability, simultaneously weakening the enantioselectivity of the complexation.     

Microstructure and melting in fractions of polyethylene characterized with the aid of a novel folded-chain-lamella model

Folded-chain-lamellae are considered as “cooperative units” with frozen matter flow and with a locally heterogeneous atomistic order the degree of which is reversibly regulated by surface-melting or surface crystallization. A consequent thermodynamic treatment of restricted micro-phase equilibrium in semicrystalline fractions of polyethylene of different molecular weights can be shown to deliver a characterization of such nonequilibrium states by relating additional internal variables to parameters of the microstructure (DSC-measurements, electron-micrographs, SAXS). What appears to be very satisfactory is the conclusion that the excess situation produced by noncrystallizable defects in the semicrystalline samples is clearly related to the original state of order in the melt: Approximative invariance of penetration is directly elucidating that any matter flow in the regime of the chains of sufficient length is frozen during folded-chain crystallization. Molecular-weight effects in semicrystalline fractions of polyethylene can be interpreted on these lines.     

Infrared study of hydration and association of functional groups in a perfluorinated Nafion membrane,Part 1

A perfluorosulfonic acid Nafion membrane has been studied with infrared spectroscopy. Infrared spectra of the membrane in acid form at the different degree of hydration were analysed in details and the conclusions about the state of sulfonic groups within clusters were drawn. The results indicate that in swollen samples in acid form hydrate structures involving dissociated sulfonic groups and water molecules are formed. These structures are analogous to those found in polystyrenesulfonic acid. With progressive drying of the Nafion membrane the network of hydrate structures breaks up and functional groups are transformed into their undissociated forms.     

DNA methylation ratio variability may impede clinical application of cancer diagnostic markers

Hypermethylation at promoter regions of tumour suppressor genes is diagnostic for many cancers. Many genomic regions that may be the targets for clinical diagnostic assays have been identified through use of measuring systems reliant on bisulphite conversion, but few of these promising markers are in clinical use. The comparability of a widely used DNA methylation measuring system involving bisulphite conversion was evaluated by supplying three experienced centres with methylated DNA reference material mixtures that were independently prepared and characterised by mass spectrometry and high-pressure liquid chromatography. A replication scheme was designed to evaluate reproducibility of key analytical steps within and between laboratories by regression analysis. In general, methylation was underestimated and methylation ratio values were highly variable. The difference in methylation ratio between CpG sites was the key contributor to variable results. The CpG site effect followed a similar pattern at all centres and at all methylation levels examined indicating that sequence context had a major effect on methylation ratio measurement using the bisulphite conversion process. The magnitude of underestimation combined with the variability of measurements between CpG sites compromises the concept of measuring genomic regional methylation by averaging the methylation ratios of many CpG sites. There were no significant differences in replicate bisulphite conversions or sample work-up and instrument analysis at each centre thus making this technique suitable for comparative intralaboratory investigations. However, it may not be suitable for a routine diagnostic assay without extensive standardisation efforts.     

Thermally stimulated discharge current (TSDC) characteristics in β-phase PVDF–BaTiO3 nanocomposites

β-phase polyvinylidene fluoride (PVDF)–BaTiO₃ nanocomposite samples have been prepared by solution mixing method. XRD data represent that the crystallinity of PVDF decreases with increase in loading level of BaTiO₃ nanoparticles. DSC curve represents that the melting point of PVDF is lightly affected by loading concentration of BaTiO₃. The morphology and microstructure of PVDF and PVDF embedded by BaTiO₃ nanofillers were investigated by using inverted contrast microscopy (ICM) and scanning electron microscopy (SEM). FTIR interferrometry is proven that PVDF and BaTiO₃ are not chemically interacting; therefore, interaction of BaTiO₃ is van der Waals type of interaction. The thermally stimulated discharge current (TSDC) of PVDF and PVDF–BaTiO₃ nanocomposites sample was characterized by single peak. The observed TSDC peak is discussed on the basis of dipolar and interfacial polarization.     

Dependence of the basic properties of meso-nitro-substituted derivatives of β-octaethylporphyrin on the nature of substituents

Spectrophotometric titration is used to study the basic properties of a series of porphyrins with a continuously increasing degree of macrocycle deformation resulting from the introduction of strong electron-withdrawing substituents: 2,3,7,8,12,13,17,18-octaethylporphyrin (I), 5-nitro-2,3,7,8,12,13,17,18-octaethylporphyrin (II), 5,15-dinitro-2,3,7,8,12,13,17,18-octaethylporphyrin (III), 5,10,15-trinitro-2,3,7,8,12,13,17,18-octaethylporphyrin (IV), and 5,10,15,20-tetranitro-2,3,7,8,12,13,17,18-octaethylporphyrin (V). It is found that the values of logK _b (total basicity constants) obtained for the investigated compounds consistently diminish with an increase in the number of meso-substituents: 11.85 (I) > 10.45 (II) > 10.31 (III) > 10.23 (IV) > 9.56 (V). It is shown that two opposing factors, the steric and electronic effects of the substituents, change the basic properties of the above series of compounds.     

Preparation and evaluation of PANI/PTT electromagnetic shielding fabric by in-situ chemical polymerization

To prepare the flexible and stretchable electromagnetic shielding (EMS) fabric with environmental stability, this paper uses polytrimethylene terephthalate (PTT) fabric as substrate, the aniline monomer as raw material, hydrochloric acid (HCl) as the doping agent, ammonium persulfate (APS) as the oxidant to produce polyaniline (PANI)/PTT electromagnetic shielding fabric by in-situ chemical polymerization. It studies the influence of APS and HCl concentration on the surface electrical resistance and the absorption loss of electromagnetic shielding fabric. It can be observed that an increasing APS and HCl facilitate the absorption and spread of PANI into PTT fabric to form a conductive network, and improve the absorption loss efficiency, while the excess APS and HCl will hinder the PANI polymerization. The high electrical conductivity and absorption loss of the PANI/PTT fabric are obtained at the concentration of An 0.4 M, APS 0.4 M, HCl 1.25 M, and polymerization reaction time 120 min. Meanwhile, in-situ polymerization of PANI does not introduce new impurities and destroy the molecular structure of PTT.     

Determination of cyanide using a chemiluminescence system composed of permanganate,rhodamine B,and gold nanoparticles

We describe a new chemiluminescence (CL) system based on the oxidation of rhodamine B (RhoB) with alkaline potassium permanganate in the presence of gold nanoparticles (Au-NPs) and anionic detergent sodium dodecyl sulfate. Free RhoB is weakly chemiluminescent when oxidized with permanganate at alkaline pH values. However, a remarkably strong enhancement of CL is observed in the presence of Au-NPs, probably due to a strong interaction between RhoB and the NPs. The possible mechanism was studied via recording the CL emission. It is also found that the intensity of CL gradually decreases in the presence of cyanide due to its interaction with the Au-NPs. The relation between the decreased CL intensity and cyanide concentration was exploited to develop a method for the determination of cyanide in the 0.01–0.5 μM concentration range, with a detection limit of 2.8 nM. The method was used to determine cyanide in spiked water, urine, and serum. Figure

Alkaline permanganate-rhodamine B-SDS CL reaction is dramatically enhanced by gold nanoparticles. Based on the inhibiting effect of cyanide on this system, a sensitive CL method was developed for its determination     

Extraction and separation of60Co and65Zn halides from H2SO4 with TBP and amberlite LA-2

A systematic study is presented on the extraction of⁶⁰Co and⁶⁵Zn bromides and chlorides from H₂SO₄ with tri-n-butyl phosphate (TBP) and Amberlite LA-2. It has been found that the presence of a little HBr or HCl enhances the extraction of the two isotopes with both solvents. The extractions of⁶⁰Co and⁶⁵Zn have been studied as functions of the acidity (HBr, HCl or H₂SO₄) in the aqueous phase, and of the diluent and solvent concentrations in the organic phase. The presence of water-miscible alcohols or acetone enhances extraction. A suggested extraction mechanism is presented in the light of the obtained results.     

Miscibility and crystallization behaviors of stereocomplex-type poly(l- and d-lactide)/poly(methyl methacrylate) blends

Stereocomplex-poly(l- and d-lactide) (sc-PLA) and poly(methyl methacrylate) (PMMA) blends were prepared by solution blending at PMMA loadings from 20 to 80 mass%. The miscibility and crystallization behaviors of the blends have been studied in detail by differential scanning calorimeter. The single-glass transition temperatures (T _g) of the blends demonstrated that the obtained system was miscible in the amorphous state. It was observed that the crystallization peak temperature of sc-PLA/PMMA blends was marginally lower than that of neat sc-PLA at various cooling rates, indicating the dilution effect of PMMA on the sc-PLA component to restrain the overall crystallization process. In the study of isothermal crystallization kinetics, the reciprocal value of crystallization peak time ( \( t_{\text{p}}^{ - 1} \) ) decreased with increasing PMMA content, indicating that the addition of non-crystalline PMMA inhibited the isothermal crystallization of sc-PLA at an identical crystallization temperature (T _c). Moreover, the negative value of Flory–Huggins interaction parameter (χ ₁₂ = ?0.16) of the blend further indicated that sc-PLA and PMMA formed miscible blends.     

Crystallization behavior,tensile behavior and hydrophilicity of poly(vinylidene fluoride)/poly(vinyl pyrrolidone) blends

Binary polymer blends of hydrophobic poly(vinylidene fluoride) (PVDF) and hydrophilic poly(vinylpyrrolidone) (PVP) were prepared by melt blending. The crystallization behavior, mechanical properties and hydrophilicity of the binary blends were investigated using Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffractometry (WAXD), differential scanning calorimeter (DSC) scanning, non-isothermal crystallization kinetics, successive self-nucleation and annealing (SSA) fractionation, tensile tests and contact angle tests. The analysis of FTIR, WAXD, DSC scanning, non-isothermal crystallization kinetics and SSA fractionation showed that the addition of PVP greatly influenced the crystallization behavior of the sample. As the PVP content increased, the crystallization temperature, crystallization rate, degree of crystallinity, and the amount of thick lamellaes decreased gradually. Meanwhile, PVP favored the formation of β-phase of PVDF. The results of tensile test revealed that the addition of PVP increased the elongation at break of the sample, and lowered the yield stress. Besides, the result of contact angle test indicated that the hydrophilicity of PVDF was remarkably improved in the presence PVP. The relationship between crystallization behavior and the tensile behavior, hydrophilicity were discussed.