Shear‐Induced Skin‐Core Structure of Molten Isotactic Polypropylene and the Formation of β‐Crystal

The study of crystallization behavior and crystalline morphology of polymer melt under shear flow is of great interest due to the strong effect of flow field on the final properties of polymer products in the practical processing. In this respect, the shearing hot stage provides a unique tool which monitors sensitively the changes in crystalline structure induced by precise experimental conditions. Herein, the impacts of both melting temperature and shear rate on the crystallization behavior of isotactic polypropylene (iPP) melt are investigated. Under static conditions, there are only random spherulite structures. Once shear is involved, the cylindrite‐layers appear near both surfaces of the sample, which is consistent with the skin‐core structure in the injection molded parts. Meanwhile, the β‐crystals can be developed and are related to the molecular orientation, depending on the applied melting temperatures and shear rates. More interestingly, the crystallinity of β‐crystal in the pure iPP can reach 15%. The above results indicate that the melting temperature and shear rate are important factors in determining the β‐form crystal development of iPP matrix.     

Rheology of 1‐butyl‐3‐methylimidazolium chloride cellulose solutions. I. Shear rheology

In this article, shear rheology of solutions of different concentrations obtained by dissolution of cellulose in the ionic liquid (IL) solvent 1‐butyl‐3‐methylimidazolium chloride ([Bmim]Cl) was studied by measuring the complex viscosity and dynamic moduli at different temperatures. The obtained viscosity curves were compared with those of lyocell solutions and melt blowing grade polypropylene melts of different melt flow rates (MFR). Master curves were generated for complex viscosity and dynamic moduli by using Carreau and Cross viscosity models to fit experimental data. From the Arrhenius plots of the shift factors with respect to temperature, the activation energies for shear flow were determined. These varied between 18.99 and 24.09 kCal/mol, and were compared with values for lyocell solutions and different polymeric melts, such as polyolefins, polystyrene, and polycarbonate. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Poly(Li‐2‐hydroxyethyl methacrylate)‐co‐poly(4‐vinyl pyridine): Molar mass effects on strong electrorheological response

Electrorheological (ER) fluids display remarkable rheological behavior, being able to convert rapidly and repeatedly from a fluid to a solid‐like when an external electric field (E) is applied or removed. In this study, electrical and ER properties of poly(Li‐2‐hydroxyethyl methacrylate)‐co‐poly(4‐vinyl pyridine), poly(Li‐HEMA)‐co‐poly(4‐VP), copolymeric salts (ionomers) were investigated. For this purpose six ionomers were synthesized with different molar masses. They were then ground‐milled for a few hours to obtain micron size ionomers. The particle sizes of the ionomers were determined by dynamic light scattering. Suspensions of ionomers were prepared in silicone oil (SO), at a series of concentrations (c = 5–30%, m/m). The gravitational stability of suspensions against sedimentation was determined at constant temperature (T = 25°C). Flow times of the suspensions were measured under no electric field (E = 0 kV/mm), and under an external applied electric field (E ≠ 0 kV/mm) strengths and a strong ER activities were observed for all the poly(Li‐HEMA)‐co‐poly(4‐VP)/SO suspensions. Further, the effects of suspension concentration, mole ratios of poly(HEMA) and poly(4‐VP), and the overall molar mass of the copolymers, shear rate, electric field strength, frequency, promoter, and temperature onto ER activities of ionomer suspensions were investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1065–1074, 2006     

Matrix‐Based Encapsulation of Construction Chemicals Using High‐Shear Agglomeration

Encapsulation of dry superplasticizers in matrix‐based encapsulation systems was investigated. As basic material, commercially available fly ash was granulated by high‐shear agglomeration. Due to a high variability of factors affecting the encapsulation process and later release of admixtures, the design‐of‐experiments method was applied to reduce the quantity of experiments. Statistical evaluation indicates that the particle characteristics of the agglomerates were mostly influenced by the binder viscosity during the investigations. The delayed admixture release was enhanced by high binder viscosity and low energy input during the agglomeration process due to a coating of the bigger superplasticizer particles by the smaller fly ash. These results will help to develop encapsulated construction chemicals with controlled admixture delivery for the future application in a wide range of different building materials.     

Power draw of a high‐Shear homogenizer

The power draw of a high‐shear rotor‐stator homogenizer has been characterized in laminar, transitional, and turbulent operation. The power draw is comprised of two components — that associated with mixing and that associated with a bushing and bearings in the device. In turbulent operation, the mixing power draw is influenced primarily by pumping mode (up‐ or down‐pumping), and to a lesser extent, by vessel baffling and other geometric parameters. Mixing power draw can be characterized in terms of power number across the Reynolds number spectrum if an empirical Froude number correction is applied.     

Mixing of Shear‐Thinning Fluids with Dual Off‐Centred Impellers

Mixing times for inelastic shear‐thinning fluids in stirred tanks have been experimentally investigated using a combination of two off‐centred impellers operating in both co‐ and counter‐rotating modes. A colour‐discolouration technique based on fast acid‐base reaction was used for the determination of the mixing times as well as to reveal the possible presence of caverns and dead regions. A statistical plan of experiments allowed determining the effects of the impeller position, the rotational speed, the flow behaviour index, the impeller type and their mutual interactions. A stronger influence of the impeller position on mixing times was observed for both rotating modes with fluids exhibiting pronounced shear‐thinning. It was also found that segregated regions could be readily destroyed by dual off‐centred impellers as compared with the single centred impeller configuration. Mixed flow impellers were shown to be less efficient in terms of mixing times than radial flow impellers. Results obtained under the best operating conditions were compared to steady stirring experiments showing the potential and drawbacks of the proposed scenarios.     

Model for the outer cavity of a dual‐cavity die with parameters determined by two‐dimensional finite‐element analysis

A coating die forms liquid layers of uniform thickness for application to a substrate. In a dual‐cavity coating die an outer cavity and slot improves flow distribution from an inner cavity and slot. A model for axial flow in the outer cavity must consider the ever‐present cross flow. A 1‐D equation for the pressure gradient for a power‐law liquid is obtained as a small departure from a uniform flow distribution and no axial flow. The equation contains a shape factor dependent on cavity shape, Reynolds number, and power‐law index. The shape factor for five triangular cavity shapes is obtained by finite‐element analysis and correlated for application to die design up to the onset of flow recirculation which arises at the junction of the cavity and outer slot. The performance of the combined cavity and slot is considered and the most effective design determined. © 2017 American Institute of Chemical Engineers AIChE J, 64: 708–716, 2018     

Thermal characterization of three‐component blends for hot‐melt adhesives

Traditional solvent‐based adhesives used in the footwear industry have been demonstrated as harmful to the workers' health and environment. Solvent‐free three‐component adhesives (hot‐melt adhesives or HMAs) for various applications including the leather and footwear industry are becoming more and more attractive. Thus, the formulation of a three‐component HMA was realized in this study. Thermogravimetry, differential scanning calorimetry, and the apparent strength of the adhesive bond were used to investigate the relationship between their properties and the polymer/wax/resin compositions. The thermal stability of HMA formulations was determined and compared with thermal traces based on an additive weight computation of the single components' thermal profiles. All HMA formulations showed a direct relationship between the glass‐transition temperature and the apparent adhesive shear strength at the leather–rubber interface. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2889–2901, 2001     

Melt rheology of poly(ϵ‐caprolactone)/poly(styrene‐co‐acrylonitrile) blends

Dynamic viscoelastic properties for miscible blends of poly(?‐caprolactone) (PCL) and poly(styrene‐co‐acrylonitrile) (SAN) were measured. It was found that the time–temperature superposition principle is applicable over the entire temperature range studied for the blends. The temperature dependency of the shift factors a_T can be expressed by the Williams–Landel–Ferry equation: log a_T = ?8.86(T ? T_s)/(101.6 + T ? T_s). The compositional dependency of T_s represents the Gordon–Taylor equation. The zero‐shear viscosities are found to increase concavely upward with an increase in weight fraction of SAN at constant temperature, but concavely downward at constant free volume fraction. It is concluded that the relaxation behavior of the PCL/SAN blends is similar to that of a blend consisting of homologous polymers. It is emphasized that the viscoelastic functions of the miscible blends should be compared in the iso‐free volume state. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2037–2041, 2001     

Evaluation of Norbornene‐Based Adhesives to Amine‐Cured Epoxy for Self‐Healing Applications

High adhesive strengths are essential in self‐healing polymers. In these novel materials, healing is triggered by crack propagation through embedded microcapsules in an epoxy matrix, which then release the liquid healing agent into the crack plane. Subsequent exposure of the healing agent to an embedded chemical initiator triggers ring‐opening metathesis polymerization (ROMP), bonding the crack faces closed. In order to improve self‐healing efficiencies in these systems, it is necessary to improve the adhesion of the polymerized healing agent with the epoxy matrix. In this study, the adhesive shear strength between different norbornene‐based healing agents and an amine‐cured epoxy resin was evaluated using single lap shear specimens. The healing agents tested include endo‐dicyclopentadiene (DCPD), 5‐ethylidene‐2‐norbornene (ENB) and DCPD/ENB blends. 5‐Norbornene‐2‐methanol (NBM) and 5‐norbornene‐2‐exo,3‐exo‐dimethanol (NBDM) were used as adhesion promoters because they contain hydroxyl groups which can form hydrogen bonds with the amine‐cured epoxy adherend. A custom synthesized norbornene‐based crosslinking agent was also added to improve the adhesion of the polymerized ENB by increasing its crosslink density after ROMP. The effects of catalyst loading, polymerization time and cure temperature on the adhesive bond strength are studied in detail.

     

Influence of block molecular weight on the properties of styrene‐ethylenebutylene‐styrene block copolymers

Styrene‐ethylene butylene‐styrene (S‐EB‐S) block copolymers with similar polystyrene contents and varying molecular weights (S‐EB‐S‐1, molecular weight: 8833‐41223‐8833; S‐EB‐S‐2, molecular weight: 15844‐70534‐15844; S‐EB‐S‐3, molecular weight: 26133‐111067‐26133) were used in this study. The domain size of the polystyrene phase marginally increases with an increase in polystyrene segmental weight as observed by atomic force microscopy. Dynamic mechanical measurements of these polymers were carried out over a wide range of temperatures and frequencies. These polymers exhibited three peaks: α, β, and γ in the tan δ‐temperature curve. With increase in the molecular weight of the S‐EB‐S polymers, the α‐transition temperature shifted to higher values, while the β‐ and γ‐transitions remained unaltered. Also, the elastic modulus and storage modulus decreased with increase in the molecular weight. The rheological behavior of the various S‐EB‐S polymers was studied using a Monsanto Processability Tester. These systems exhibited pseudoplastic flow behavior. The shear viscosity of these S‐EB‐S polymers decreased with an increase in the molecular weight from S‐EB‐S‐1 to S‐EB‐S‐3 polymers because of the wall slip and plug flow. The activation energy of the melt flow process was found to vary between 4 and 0.6 kcal/mol in the range of shear rates studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1621–1628, 2000     

Experimental fire analysis of steel‐to‐timber connections using dowels and nails

The paper describes and discusses the results of an extensive testing programme on the structural behaviour of timber connections under ISO‐fire. The results of reference tests performed at normal temperature are also presented. From the variety of timber connections multiple shear steel‐to‐timber connections with dowels and slotted‐in steel plates and connections with steel side plates and annular ringed shank nails were experimentally studied. Particular attention was given to the analysis of the efficiency of different strategies in order to increase the fire resistance of the timber connections. The test results showed that unprotected multiple shear steel‐to‐timber connections with dowels designed for normal temperature reached a fire resistance of about 30 min. A reduction of the load level applied during the fire did not lead to a significant increase of the fire resistance. By increasing the side timber members as well as the end distance of the dowels by 40 mm the connections reached a fire resistance of more than 70 min. Connections protected by timber boards or gypsum plasterboards showed a fire resistance of around 60 min. Thus, from a fire design point of view these strategies were favourable in order to increase the fire resistance of the connections significantly. Unprotected connections with steel side plates and annular ringed shank nails failed already after about 12 min due to large deformations of the nails and the steel side plates directly exposed to fire. By protecting the steel side plates using an intumescent paint the fire resistance of the connections was increased to around 30 min. The test results enlarged the experimental background of timber connections in fire significantly. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of 4,6‐Diazido‐N‐nitro‐1,3,5‐triazine‐2‐amine

4,6‐Diazido‐N‐nitro‐1,3,5‐triazine‐2‐amine (DANT) was prepared with a 35 % yield from cyanuric chloride in a three step process. DANT was characterized by IR and NMR spectroscopy (¹H, ¹³C, ¹⁵N), single‐crystal X‐ray diffraction, and DTA. The crystal density of DANT is 1.849 g cm⁻³. The cyclization of one azido group and one nitrogen atom of the triazine group giving tetrazole was observed for DANT in a dimethyl sulfoxide solution using NMR spectroscopy. An equilibrium exists between the original DANT molecule and its cyclic form at a ratio of 7 : 3. The sensitivity of DANT to impact is between that for PETN and RDX, sensitivity to friction is between that for lead azide and PETN, and sensitivity to electric discharge is about the same as for PETN. DANT′s heat of combustion is 2060 kJ mol⁻¹.     

Numerical simulation of viscous fingering of shear‐thinning fluids

The viscous fingering instability of miscible shear‐thinning fluids has been examined using a pseudo‐spectral numerical technique based on the Hartley transform. The instability was studied for a flow in a rectilinear Hele‐Shaw cell, and the shear‐thinning character of the fluids has been modelied using the Carreau equation. New mechanisms of viscous fingering not previously observed in the case of similar Newtonian flow displacements have been identified. These mechanisms, which are reminiscent of the fractal patterns observed in experimental studies, were interpreted in terms of the velocity‐dependent mobility of the flow.     

An Ab Initio Theoretical Study of 2,4,6‐Trinitro‐1,3,5‐Triazine, 3,6‐Dinitro‐1,2,4,5‐Tetrazine,and 2,5,8‐Trinitro‐Tri‐s‐Triazine

In order to evaluate 2,4,6‐trinitro‐1,3,5‐triazine (TNTAz), 3,6‐dinitro‐1,2,4,5‐tetrazine (DNTAz), and 2,5,8‐trinitro‐tri‐s‐triazine (TNTsTAz), the geometries of these compounds have been fully optimized employing the B3LYP density functional method and the AUG‐cc‐pVDZ basis set. The accurate gas phase enthalpies of formation have been obtained by using the atomization procedure and designing isodesmic reactions in which the parent rings are not destroyed. Based on B3LYP/AUG‐cc‐pVDZ calculated geometries and natural charges, the crystal structures have been predicted using the Karfunkel–Gdanitz method. Computed results show that there exists extended conjugation over the parent rings of these compounds. More energy content is reserved in DNTAz than in both TNTAz and TNTsTAz. The title compounds are much more sensitive than 1,3,5‐trinitrobenzene. The calculated detonation velocity of DNTAz reaches 9.73–9.88 km s⁻¹, being larger than those of CL‐20 and TNTAz. TNTsTAz has no advantage over the widely used energetic compounds such as RDX and HMX.     

Lecithin‐enhanced biotransformation of cholesterol to androsta‐1,4‐diene‐3,17‐dione and androsta‐4‐ene‐3,17‐dione

A biotransformation process using Mycobacterium sp was studied for androsta‐1, 4‐diene‐3,17‐dione (ADD) and androsta‐4‐ene‐3,17‐dione (AD) production from cholesterol. Cholesterol has a poor solubility in water (～1.8 mg dm^?3 at 25 °C), which makes it difficult to use as the substrate for biotransformation. Lecithin is a mixture of phospholipids of phosphatidylcholine (PC) and phosphatidylethanolamine (PE), which behave like surfactants and can form planar bi‐layer structures in an aqueous medium. Therefore, a small amount of lecithin (<1 g dm^?3) can be used to form stable colloids with cholesterol at a relatively high concentration (20 g dm^?3) in water. In this work, an energy density of 1000 J cm^?3 from sonication was provided to overcome the self‐association of cholesterol and to generate a stable lecithin–cholesterol suspension that could be used for enhanced biotransformation. The lecithin–cholesterol suspension was stable and could withstand typical autoclaving conditions (121 °C, 15 psig, 20 min). In contrast to conventional surfactants, such as Tween 80, that are commonly used to help solubilize cholesterol, lecithin did not change the surface tension of the aqueous solution nor cause any significant foaming problem. Lecithin was also biocompatible and showed no adverse effect on cell growth. Compared with the medium with Tween 80 as the cholesterol‐solubilizing agent, lecithin greatly improved the biotransformation process in regard to its final product yield (～59% w/w), productivity (0.127–0.346 g dm^?3 day^?1), ADD/AD ratio (6.7–8), as well as the long‐term process stability. Cells can be reused in repeated batch fermentations for up to seven consecutive batches, but then lose their bioactivity due to aging problems, possibly caused by product inhibition and nutrient depletion. © 2002 Society of Chemical Industry     

Enhancement of recombinant β‐D‐glucuronidase production under low‐shear modeled microgravity in Pichia pastoris

BACKGROUND: The effects of low‐shear modeled microgravity (LSMMG) on the production of recombinant proteins in a eukaryotic expression host have been investigated. The gene (GenBank Accession No.EU095019) derived from Penicillium purpurogenum Stoll (CGMCC 3. 3708) encoding β‐D ‐glucuronidase (EC 3.2.1.31, PGUS) was expressed in Pichia pastoris GS115. The behavior of P. pastoris growth and recombinant PGUS production during the methanol induction stage were examined in a high‐aspect ratio vessel (HARV) that could model the microgravity environment. RESULTS: The recombinant P. pastoris showed better growth under LSMMG than normal gravity (NG) during the methanol induction phase. It was also found that the efficiencies of PGUS production were enhanced 1.51 to 2.21‐fold under LSMMG compared with NG control at four different rotary speeds (P < 0.05), and 15 rpm was found to be the optimal for PGUS expression. Furthermore, the efficiency of PGUS secretion was also enhanced under LSMMG (all values above 30%). CONCLUSIONS: The LSMMG environment significantly enhances production and secretion of the recombinant PGUS expressed in P. pastoris GS115. Results suggest that simulated microgravity techniques could be used for the efficient production of recombinant proteins by microbial hosts. Copyright © 2010 Society of Chemical Industry     

Enzymatic Synthesis of 1‐Alkyl‐2‐hydroxy‐sn‐glycero‐2,3‐cyclic‐phosphate Using a Novel Lysoplasmalogen‐Specific Phopholipase D

Many phospholipase Ds (PLDs) are known to catalyze transphosphatidylation as well as hydrolysis of phospholipids. Transphosphatidylation of lysoplasmalogen (LyPls)‐specific phospholipase D (LyPls‐PLD), which catalyzes hydrolysis of ether lysophospholipids such as LyPls and 1‐hexadecyl‐2‐hydroxy‐sn‐glycero‐3‐phosphocholine (Lyso‐PAF), still remains unclear. This study aims to reveal the transphosphatidylation activity of LyPls‐PLD, that is, the production of cyclic ether lysophospholipid. The enzymatic reaction is conducted in a buffer system, and the reaction products of a novel LyPls‐PLD from Thermocrispum sp. are investigated using mass spectrometry (MS). MS analyses demonstrate the reaction products to consist of 100% 1‐hexadecyl‐2‐hydroxy‐sn‐glycero‐2,3‐cyclic‐phosphate (cLyPA) and choline from Lyso‐PAF; however, 1‐alkenyl‐2‐hydroxy‐sn‐glycero‐2,3‐cyclic‐phosphate from 1‐O‐1′‐(Z)‐octadecenyl‐2‐hydroxy‐sn‐glycero‐3‐phosphocholine and 1‐O‐1′‐(Z)‐octadecenyl‐2‐hydroxy‐sn‐glycero‐3‐phosphoethanolamine is not produced. These results are expected to help in elucidating the catalytic mechanism of LyPls‐PLD, that is, the rate‐limiting step, and indicate LyPls‐PLD to be useful for the one‐pot synthesis of cLyPA. Practical Applications: A novel phospholipase D, LyPls‐PLD, can exclusively synthesize cLyPA from Lyso‐PAF using a one‐step enzymatic reaction without an organic solvent. cLyPA could be expected to show bioactivities similar to those of cyclic phosphatidic acid, which promotes normal cell differentiation, hyaluronic acid synthesis, antiproliferative activity in fibroblasts, and inhibitory activity toward cancer cell invasion and metastasis.     

Poly(1,3‐disila‐1,3‐diphenyl‐2‐oxaindane)‐diphenylsiloxane‐poly(dimethylsiloxane) block copolymers

The heterofunctional condensation of 1,3‐dichloro‐1,3‐disila‐1,3‐diphenyl‐2‐oxaindane with dihydroxydiphenylsilane at various ratios of initial compounds in the presence of amines was carried out, and α,ω‐dihydroxy(1,3‐disila‐1,3‐diphenyl‐2‐oxaindane)‐diphenylsiloxane oligomers with various degrees of condensation were obtained. Corresponding block copolymers were obtained by heterofunctional polycondensation of synthesized α,ω‐dihydroxy(1,3‐disila‐1,3‐diphenyl‐2‐oxaindane)‐diphenylsiloxane oligomers with α,ω‐dichlorodimethylsiloxanes in the presence of amines. Thermogravimetry, gel permeation chromatography, differential scanning calorimetry, and wide‐angle X‐ray analysis were carried out on the synthesized block coplymers. Differential scanning calorimetry and wide‐angle X‐ray studies of these copolymers showed that their properties were determined by the ratio of the lengths of the flexible linear poly(dimethylsiloxane) and rigid poly(1,3‐disila‐1,3‐diphenyl‐2‐oxaindane)‐diphenylsiloxane fragments in the main macromolecular chain. Two‐phase systems were obtained with specific flexible and rigid fragment length values in synthesized block copolymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3462–3467, 2006     

1‐Amino‐1‐hydrazo‐2,2‐dinitroethene – a Hazard Warning

1‐Amino‐1‐hydrazo‐2,2‐dinitroethene ( 2 ) has been observed to spontaneously decompose with considerable violence during storage. Its preparation and handling should be regarded as potentially hazardous.