Increasing Stirring Rate Research Articles

Microencapsulation of a sunlight-curable silicon-based resin in the presence of polyvinylpyrrolidone

PurposeThe purpose of this investigation is to develop a facile method to encapsulate a sunlight-curable silicone-based resin into a melamine–urea–formaldehyde (MUF) shell in the presence of polyvinylpyrrolidone (PVP) as an emulsifier. These microcapsules can be used in self-healing coating formulations.Design/methodology/approachMUF microcapsules containing a sunlight-curable core (methacryloxypropyl-terminated polydimethylsiloxane, MAT-PDMS) have been fabricated by means of in situ polymerisation of an oil-in-water emulsion using PVP as an efficient and environmentally advantageous stabiliser. The effects of agitation rate and PVP concentration on the microencapsulation process have been investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The chemical structure and thermal stability of the microcapsules have been studied using Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The solvent resistance of the microcapsules has been determined as well.FindingsIt has been revealed that the pH of the reaction mixture remained almost constant during the reaction, which simplified the process. It has also been observed that the microencapsulation yield improved and the microcapsules’ surface morphology became smoother when a high PVP content was used. With an increase in stirring rate from 600 to 1,200 rpm, the surface roughness and the average particle size decreased. The mean diameter of the prepared microcapsules ranged from 32.1 to 327.1 µm depending on the synthesis conditions. It was demonstrated that the microcapsules had a high capacity for MAT-PDMS encapsulation (more than 88 Wt.%). The solvent stability of the microcapsules against different polar, semi-polar and non-polar solvents was also evaluated.Research limitations/implicationsThis research is limited to the encapsulation of a hydrophobic and sunlight curable liquid (such as MAT-PDMS) by means of in situ polymerisation of amino resins.Practical implicationsThe results can be used by researchers working on the fabrication of microcapsules for applications such as drugs, electrophoretic inks, electrophoretic displays, intumescent fire-retardant coatings and self-healing materials.Social implicationsIn self-healing coatings, healing agents which can be cured by UV irradiation or sunlight are envisaged attractive because they are catalyst-free, environmentally friendly and relatively inexpensive. PVP is an environmentally friendly emulsifier. The prepared microcapsules can be used in self-healing coatings to help in reducing maintenance costs for buildings and steel structures.Originality/valueThe novel aspect of this work is the development of a sunlight-curable silicone-based resin that was encapsulated in a MUF shell in the presence of PVP. A simple method was used to fabricate MUF microcapsules containing MAT-PDMS without the need to control pH during the reaction. Conventional methods for the preparation of amino resin microcapsules require an intensive and precise pH control to obtain favourable microcapsules. MAT-PDMS can be cured by sunlight and is catalyst-free, environmentally friendly and relatively inexpensive.

Development of erosion-corrosion mechanisms for the study of steel surface behavior in a sand slurry

In this study, dry sand impact and linear polarization resistance (LPR) monitoring techniques were used to study the detrimental effects of the sand size on surface morphology of the mild steel. An electrochemical mechanism was developed to measure the resistance of the metal coupons rotating in a slurry of 4wt% NaCl and 5wt% sand. Scanning probe microscopy (SPM) and hardness testing of the eroded coupons were conducted to elaborate their surface topography. In-depth analysis revealed that not only the larger particles but smaller particles as well caused significant erosion-corrosion of the steel coupons. It was noticed that hardness and density of the erodent particles were reasonably high to induce the plastic deformation and micro-structures at the metal surface. The LPR measurements revealed high coupon resistance in the fine sand slurry than in the coarse sand slurry. The localized corrosion and erosion-corrosion attacks on the metal surface were also supplemented with the stirring rate and the presence of NaCl in the solution. The corrosion rate was sharply increased with an increase in stirring rate above 500rpm.

Dependence of size and morphology on shear flow for PS-based amphiphilic block copolymer micelles in aqueous solution

This contribution focuses on the impact of shear flow on size and nanostructure of PS-based amphiphilic block copolymer (BC) micelles by varying the stirring rate and copolymer composition. The results show that the vesicles formed from diblock copolymer (di-BC) of PS-b-PAA remain with vesicular morphology, although the average size decreases, with the increase of stirring rate. However, the multi-compartment micelles (MCMs) formed from tri-block copolymer (tri-BC) of PS-b-P2VP-b-PEO are quite intricate, in which the copolymer first self-assembles into spheres, then to clusters, to large compound micelles (LCMs), and finally back to spheres, as stirring rate increases from 100 r/min to 2200 r/min. Formation mechanism studies manifest that vesicles form simultaneously as water is added to the di-BC solution, termed as directassembly, and remain with vesicular structure in the flowing process. While for the PS-b-P2VP-b-PEO copolymer, spherical micelles at initial stage can further assemble into clusters and LCMs, termed as second-assembly, due to the speeding-up-aggregation of the favorable stirring. As a result, an invert V-relationship between tri-BC micelle dimension and stirring rate is observed in contrast to the non-linear decreasing curve of di-BC vesicles. It is by investigating these various amphiphilic BCs that the understanding of shear dependence of size and morphology of micelles is improved from self-assembly to second-assembly process.

Preparation and formation mechanism of size-controlled lignin nanospheres by self-assembly

Lignin has recently attracted much attention due to their renewable nature. Here we focused on a simple self-assembly method for fabricating size and shape uniform enzymatic hydrolysis lignin (EHL) nanospheres, without chemical modification of lignin. EHL was dissolved in tetrahydrofuran at different initial concentrations and subsequently self-assembly with adding water under magnetic stirring for fabricating the nanospheres. The self-assembled structure, process parameters and formation mechanism of the nanospheres were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic light scattering (DLS), fourier transform infrared spectroscopy (FTIR), and UV–vis absorption spectra. Results showed that the nanospheres were formed through a layer-by-layer self-assembly approach from inside to outside based on π–π interactions, which enabled the formation of nanospheres in the size range of 190–590nm. Increasing the pre-dropping EHL concentration resulted in an increase of the average diameter and yield of the nanospheres. The nanospheres have good stability, and their average diameters had no significant change after 30days. The chemical structural features of the nanospheres had not produced a significant change in the preparation process. High preparation temperature brought about the formation of the gaps at the surface of the nanospheres due to the effect of volatile speed of solvent. Moreover, the average diameter of the nanospheres decreased with an increase of stirring rate or the dropping speed of water. The proposed EHL nanospheres are eco-friendly, cost-effective and therefore a promising candidate for biomass based carrier.

The fouling behavior in microfiltration of activated sludge suspension from submerged membrane bioreactors (SBR)—The boundary flux and sub boundary fouling rate index

The boundary flux (Jb) and sub boundary fouling rate index (α) in constant pressure microfiltration of activated sludge suspension from SBR were determined using TMP-step method. Effects of mixed liquor suspended solids concentration (MLSS), stirring rate and the mean pore size of the membrane on Jb and α were also analyzed using the factorial experiment method. Results showed that the influence sequence of operating conditions on Jb was as follows: mean pore size of the membrane > stirring rate > MLSS concentration. Specially, the effect of shifting mean membrane pore size from 0.01 µm to 0.1 µm or from 0.01 µm to 0.22 µm on Jb was almost six times or twice as much as that of increasing stirring rate from 100 rpm to 300 rpm in the tested MLSS concentration range. The fact that the membrane with lager pore size was easy to be internally fouled at the initial filtration period was confirmed by analyzing α and morphologies of fouled membranes.

Manufacturing of functionally graded Ni–ZrO2 composite coating controlled by stirring rate of the electroplating bath

For the first time, functionally ZrO2 content graded Ni–ZrO2 composite coating has been successfully co-electrodeposited from a bath with gradually increasing stirring rate. For this, different composite coatings were electroplated in the same bath with different stirring rates to find the optimum stirring rate in which the maximum content with uniform distribution of ZrO2 particles in the coating can be achieved. To produce ZrO2 content graded Ni–ZrO2 composite coating, the stirring rate was continuously increased from 0 to optimum value. The results showed that functionally graded Ni–ZrO2 composite coating has been successfully electroplated with continuous gradient distribution of Zirconia content in the coating using controlling of bath stirring rate. With increasing of ZrO2 particles content, the microhardness increases from the interface towards the surface of the coating. This could provide a high wear resistance with high adhesion of the coating to the substrate.

Insight of anode reaction for CWS (coal water slurry) electrolysis for hydrogen production

Mechanism of CWS (coal water slurry) electrolysis was investigated by using anode reaction kinetics. The results indicated that the activation energies of electrode reaction reduce with the increase in activity of carbon materials. According to the electrode reaction kinetics, the direct oxidation of CWS electrolysis occurred easily under lower concentration of electrolyte and higher concentration of CWS. On the contrary, the indirect oxidation of CWS electrolysis took place. Because of the high oxygen evolution potential of water electrolysis in H2SO4 solution (1.23 V), the direct oxidation of CWS electrolysis mainly occurred under water decomposition potential (0.5–1.23 V). As NaOH solution was used as electrolyte, it was difficult to distinguish direct and indirect oxidation under the low potential (0.4 V). With increasing stirring rate, the electrode reaction activation energies of GWS (graphite water slurry) electrolysis increased slightly and were always lower than 40 kJ/mol. The results indicated that GWS electrolysis was controlled by diffusion and the increase in stirring rate could not reduce the polarization.

Synthesis of poly(propylene carbonate) from highly active, inexpensive achiral (Salph)Co(III)X as initiator and bis(triphenyl phosphine) iminium as co‐initiator

ABSTRACTCopolymerization of carbon dioxide with racemic propylene oxide has been investigated in the presence of an inexpensive achiral (Salph)Co(III)X [Salph is N,N′‐bis(3,5‐di‐tert‐butylsalicylidene) phenylenediimine and X is pentaflorobenzoate] as initiator and [PPN]+Cl− ([PPN] is bis(triphenylphosphine) iminium) as co‐initiator. Effects of monomer‐to‐initiator ratio, initiator/co‐initiator ratio, and reaction conditions like stirring rate, temperature, and pressure of CO2 on the molecular weight, yield, and selectivity of poly(propylene carbonate) over propylene carbonate have been studied. The initiator used in the study has been found to be highly active at milder conditions of pressure and temperature, giving a product with maximum Mw of 14.8 × 103 g/mol at 25 bar and 50°C. The conversion increases with an increase in stirring rate and then becomes almost constant at 1100 rpm and above, indicating that the reaction is no longer limited by mass transfer. The molecular weight Mw of the polymer has been found to increase with increasing monomer‐to‐initiator ratio up to 3000:1, but it starts decreasing with a further increase in monomer‐to‐initiator ratio, giving a polymer of lower Mw. The activity of the initiator is considerably affected by pressure, temperature, time, and amount of co‐initiator. The polymeric product has low polydispersity (near unity) with negligible formation of polypropylene oxide. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43099.

Effects of Rotating Magnetic Field on Microstructure and Properties of Bi-Containing Hypereutectic Al-Si Alloy

In the present paper, based on Bi-containing hypereutectic Al-20%Si alloy, a rotating magnetic field was used, the microstructures of the alloy have been observed and analyzed by optical microscope and scanning electronic microscope, and its wear-resisting property was measured. The influence mechanism of rotating magnetic field on the microstructures and properties of the alloy has been discussed. Research results show that exerting a rotating magnetic field in the hypereutectic Al-20%Si alloy drastically decreases the amount of primary Si phase, only some tiny bulk Si exist and the amount of needle eutectic Si increase. The dendrite-like primary α-Al appears at the same time. With the increase of stirring rate of rotating magnetic field, the change way of eutectic Si shape is coarse needle→tiny needle→coarse needle; the rotating magnetic field can change the nonuniform distribution of Bi induced by Bi local decentralization. With the increase of stirring rate of rotating magnetic field, the change way of Bi shape in upper part microstructures of the alloy is large bulk→short rodlike→big globular→small globular, Bi local decentralization is changed into uniform distribution; In addition, exerting a rotating magnetic field in the hypereutectic Al-20%Si alloy can increase wear-resisting property of the alloy.

Stealth Amphotericin B nanoparticles for oral drug delivery: In vitro optimization

PurposeAmphotericin B (AmB) is an effective anti-fungal and anti-leishmanial agent. However, AmB has low oral bioavailability (0.3%) and adverse effects (e.g., nephrotoxicity). The objectives of this study were to improve the oral bioavailability by entrapping AmB in pegylated (PEG) poly lactide co glycolide copolymer (PLGA–PEG) nanoparticles (NPs). The feasibility of different surfactants and stabilizers on the mean particle size (MPS) and entrapment efficiency were also investigated. Materials and methodsNPs of AmB were prepared by a modified emulsification diffusion method employing a vitamin E derivative as a stabilizer. Physicochemical properties and particle size characterization were evaluated using Fourier Transform Infra-Red spectroscopy (FTIR), differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. Moreover, in vitro dissolution profiles were performed for all formulated AmB NPs. ResultsMPS of the prepared spherical particles of AmB ranged from 26.4±2.9 to 1068±489.8nm. An increased stirring rate favored AmB NPs with a smaller MPS. There was a significant reduction in MPS, drug content and drug release, when AmB NPs were prepared using the diblock polymer PLGA–PEG with 15% PEG. Addition of three emulsifying agents poly vinyl pyrrolidone (PVP), Vitamin E (TPGS) and pluronic F-68 to AmB formulations led to a significant reduction in particle size and increase in drug entrapment efficiency (DEE) compared to addition of PVP alone. FTIR spectroscopy demonstrated a successful loading of AmB to pegylated PLGA–PEG copolymers. PLGA–PEG copolymer entrapment efficiency of AmB was increased up to 56.7%, with 92.7% drug yield. After a slow initial release, between 20% and 54% of AmB was released in vitro within 24h phosphate buffer containing 2% sodium deoxycholate and were best fit Korsmeyer–Peppas model. In conclusion, PLGA–PEG diblock copolymer with 15% PEG produced a significant reduction (>70%) in MPS with highest drug content. The percentage of PEG in the copolymer and the surfactant/stabilizer used had a direct effect on AmB release in vitro, entrapment efficiency and MPS. These developed formulations are feasible, effective and improved alternatives to other carriers for oral delivery of AmB.

Synthesis and Self-assembly Behavior of Photo-responsive Diblock Copolymers with Different Hydrophilic/Hydrophobic Ratios

A series of diblock copolymers, poly(ethylene oxide)-block-poly{6-(4-(4-ethoxyphenylazo) phenoxy) hexyl methacrylate} (PEO-b-PMA6AB2), with different hydrophilic/hydrophobic ratios were synthesized by reversible addi- tion-fragmentation chain transfer (RAFT) polymerization. The structures and properties of diblock copolymers were charac- terized by 1 H NMR and gel permeation chromatography (GPC). The self-assembly method was as follows: block copolymers were dissolved in tetrahydrofuran (THF) at first, and then by adding water at the rate of 2.5 μL/s, the aggregates self-assembled when the critical micelle concentration (CMC) was reached. Field emission transmission electron microscope (FETEM), scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), optical microscope, particle size analyzer, UV-Vis absorption spectroscope and fluorescence emission spectroscope were used to study the mor- phology and size of the aggregates and their stimuli-responsive behavior. The SEM and FETEM results showed that poly- meric micelles and large compound micelles (LCM) coexisted in the aqueous solution. Furthermore, it was found that the size of the self-assembly reduced with the decrease of initial concentration and the increase of stirring rate, and the distribution tended to be uniform. Meanwhile, the morphology of large compound micelles turned to be different, changing from common sphere to peanut shape or rod-like shape when the hydrophilic/hydrophobic ratio was 2.3. By encapsulating Nile Red into the aggregates, the peanut shape and rod-like shape were captured by fluorescence microscope. UV-Vis absorption spectra of the self-assembly revealed that the photo-responsive behavior of azobenzene moieties in the aggregates was reversible but re- stricted to some extent. The change on fluorescence intensity of Nile Red encapsulated in the diblock copolymer aggregates indicated that the alternative irradiation of UV and visible light induced the release of Nile Red resulted from the photoisom- erization of the azobenzene moieties. In addition, the photo-responsive study showed that large compound micelles self-assembled from BCP-S3-0.82 could dissociate under the irradiation of UV light. Other large compound micelles assem- bled from the rest of block copolymers also dissociated, but the extent of the dissociation was not as remarkable as BCP-S3-0.82, which had the maximal hydrophobic ratio. Keywords RAFT; amphiphilic block copolymer; azobenzene moiety; hydrophilic/hydrophobic ratio; self-assembly; mi- celles

Factors Affecting Fines Flocculation Performance with Cofactor-Polyethylene Oxide

In literature, neutral polyethylene oxide (PEO) flocculated fines at low shear rates, while with cofactor (CF) addition, the formed CF-PEO complex showed larger ability to bridge fines, producing flocs. In this work, some process factors were found having significant effects on fines flocculation. Increases in CF to PEO ratio at constant PEO enhanced the bridging bonds, causing increases in flocculation initial rate (efficiency), amplitude (floc size), and fastness (a decrease in characteristic time). On the other hand, an increase in stirring rate (shear rate) in flocculation vessel caused decreases in initial rate and amplitude, and an increase in the fastness. All runs showed transient flocculation; the amplitude increased with time, reached maximum at equilibrium, and then started to decrease showing deflocculation. In brief, the CF to PEO ratio and the shear rate were found important parameters in mill operation, having significant effects on flocculation efficiency, fastness, and floc size.

Semibatch reaction crystallization of salicylic acid

Reaction crystallization of salicylic acid has been investigated by experiments and modeling. In the experimental work, dilute hydrochloric acid has been added to an agitated aqueous solution of sodium salicylate in 1L scale, and product crystals have been characterized by image analysis. The results show that the product crystal number mean size at first increases with increasing agitation rate but then gradually decreases again at further increase in stirring rate. At lower stirring rate, larger crystals are obtained when the feeding point is located close to the agitator instead of being located out in the bulk solution. The mean crystal size increases with decreasing feeding rate and with decreasing reactant concentrations. There is a decrease in mean size with increasing feed pipe diameter. These trends in the experimental results show great similarity with previous results on benzoic acid. The experimental results have been examined by a population balance model accounting for meso and micro mixing, and crystal nucleation and growth rate dispersion. It is found that the crystallization kinetic parameter estimation is quite complex, and the objective function hyper surface contains many different minima. Hence, parameter estimation has to rely on a combination of mathematical optimization strategies and a scientific understanding of the physical meaning of the parameters and their relation to current theories. As opposed to our previous work on benzoic acid, it has not been possible to find a set of kinetic parameters that provides for a good description of all experimental data.

Rate and Mechanism of Reduction-Dissolution of Chromite in Liquid Slags

AbstractThe dissolution of chromite from the Bushveld Complex of South Africa in liquid slags was studied in the temperature range 1550° to 1665°C under argon gas. The slag compositions were similar to those of ferrochromium production and stainless steel making. Empirical relations between the slag composition and the dissolution of chromite were established through the use of a statistical model. The dissolution process was investigated by using the rotating cylinder technique and measured by the chemical analysis of the samples taken from the melt and the SEM-EDAX analysis of the reacted chromite cylinder samples. The chromite grains were depleted in iron and chromium as the dissolution progressed, leaving behind an alumina and magnesia rich spinel. The experimental data was evaluated by using kinetic models and mass transfer coefficients of chromium, iron and oxygen ions through the phase boundary between the solid chromite cylinder and the liquid slag were determined.The dissolution of chromite in liquid slags increases with increasing stirring rate. SEM-EDAX studies on the reacted chromite cylinders showed that coring took place within the chromite grains subjected to dissolution for sufficient length of time. Chromium and iron concentrations in the chromite were decreasing from the centre towards the surface of the grains while aluminum and magnesium contents were increasing at the edges compared to the centre of the chromite grains. Furthermore, the slag rich in alumina and magnesia diffuses in bulk into the chromite with a net result of increase in the concentration of these elements.The rate of dissolution of chromite in liquid slags was found to be controlled by the mass transfer of oxygen ions (O2−) through the liquid phase boundary between the solid chromite and the liquid slag. The activation energy for the mass transfer of O2− ions was calculated as 30.61 kCal/mol (128.07 kJ/mol).

Solvent extraction of copper from chloride solution II: Cuprous oxidation by oxygen coupled with simultaneous cupric solvent extraction

This study was conducted as part of the development of a novel process for copper recovery from copper sulfide concentrates by chloride leaching, simultaneous cuprous oxidation and cupric solvent extraction to transfer copper to a conventional sulfate electrowinning circuit, and hematite precipitation to reject iron. The kinetics of cuprous and ferrous oxidation by oxygen and cupric solvent extraction were studied as a function of reaction time, stirring rate, oxygen pressure and extractants. The concentration of Cu(I)+Fe(II) decreased linearly with reaction time while the copper extraction increased with reaction time. The rate of cuprous and ferrous oxidation increased with increasing stirring rate and it was proportional to the partial pressure of oxygen. The cuprous and ferrous oxidation by oxygen was enhanced with the addition of organic solution. During the simultaneous cuprous oxidation and cupric solvent extraction, the aqueous solution pH first decreased sharply with time, then remained constant and finally increased, which was determined by the generation of H+ ions (cupric and ferric solvent extraction) and consumption of H+ ions (cuprous and ferrous oxidation by oxygen). The iron extraction increased as the oxidation reaction generated more ferric ions and raised the pH to a higher value. Simultaneous cuprous oxidation and cupric solvent extraction is feasible to transfer copper to the conventional sulfate electrowinning circuit from a chloride leaching system. The optimum copper solvent extraction conditions in chloride solution were proposed.

Impact of operating conditions on the flux changing rate during dead-end microfiltration process

Dead-end microfiltration experiments with the activated sludge suspension from submerged membrane bioreactors were performed to determine the critical flux, which is a very significant factor to indicate the membrane fouling in microfiltration process. In this study, the critical permeation fluxes were measured by successive variations of transmembrane pressure (step by step technique) under different operating conditions (temperatures, stirring rate and concentrations of the mixed liquor suspended solid [MLSS]) using polyvinylidene fluoride membranes with a pore size of 0.1 μm. A study of the impact of various operating conditions on the fouling rate when the critical flux is achieved was especially made. The experiments revealed that: the increase in stirring rate leads to a decrease in the rate of fouling; the fouling rate decreased with the increase in temperature when it was less than a certain values, after that, it increased with the continuous increase in temperature, while the variation of the concentration of the MLSS has a negative influence on the membrane fouling. The results obtained from the experiments can provide reliable information to the optimization of operating conditions to alleviate membrane fouling.

Effects of pCO2 on the Removal of Fluoride from Wastewater by Calcite

AbstractFree-drift batch reactor experiments using calcite (limestone, CaCO3) were used to study fluoride removal through precipitation as fluorite (CaF2) from solutions with concentrations reflective of an industrially contaminated site. The influence of CO2 partial pressure (pCO2), stirring rate, and fluoride concentration were investigated in this paper. Equilibrium modeling shows that in wastewaters with high fluoride concentrations (∼2,000 mg/L), the flux of CO2(g) to CO2(aq) could not keep up with the consumption of CO2(aq), resulting in an initial disequilibrium with experimental pH reaching equilibrium quickly, while fluoride removal lagged. Increasing stirring rate significantly decreased the extent of disequilibrium and the time at which the CaCO3-fluoride-CO2 system attained equilibrium due to the increased rate of transport of dissolved CO2 to the CaCO3 surface, and simultaneously the rate of transport of the dissolved CaCO3 to the bulk solution. Optimal fluoride removal occurs at pCO2∼10−0.5...

Control of liquid crystallinity of amyloid-forming systems

Many proteins are known to be capable of forming amyloid fibrils, long thin fibrils that, if they possess sufficiently large aspect ratios and volume fractions, have been shown to form liquid crystals in several protein systems. However, denatured proteins exhibit polymorphism as they aggregate, and external factors affect which type of structure forms. Here we demonstrate the ability to form liquid crystalline phases in three different protein systems, without the need for the prior formation of fibrils, by the use of mechanical shear during the aggregation step to modify the aggregation process. It is shown that the rate of stirring affects the aspect ratio of the amyloid fibrils formed in vitro, and hence the ability to form liquid crystalline phases, as predicted by theory. A shift is observed with increasing stirring rate from the large spherulitic structures (structures formed via suprafibrillar aggregation under highly acidic conditions) to the alignment of amyloid fibrils into a nematic liquid crystal phase in insulin, β-lactoglobulin (BLG) and hen egg white lysozyme (HEWL). Because the stirring modifies the fibril formation, above a threshold stirring rate, the aspect ratio of insulin and BLG fibrils drops below the point at which liquid crystal-like phases can form. However, in the case of HEWL, the decrease in the fibril aspect ratio at higher stirring rates is still sufficiently small to enable liquid crystalline phases to form. The overall phase behaviour can be rationalised within the Onsager model for liquid crystallinity.

Preparation and characterization of ethyl menthane carboxamide microcapsules using PLA

AbstractUsing polylactic acid (PLA) as wall and ethyl menthane carboxamide (EMC) as core substance, microencapsulated EMC (MEMC) agents were prepared based on solvent evaporation method. The structure and morphology of MEMC were analyzed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and laser particle size analyzer. The MEMC agents had a mean diameter of about 10–20 μm. Moreover, the thermal properties of the MEMC agents were measured by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The melting point and thermal stability were improved due to the encapsulation of PLA resin. In addition, polyvinyl alcohol (PVA) and PLA concentration, stirring rate, and oil/water ratio were investigated for their effects on the particle size. As demonstrated by experimental results, the diameters of the microcapsules decreased with increasing stirring rate and oil/water ratio, and increased with increasing PLA concentration. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Design and construction of microcapsules containing rejuvenator for asphalt

Microcapsules containing rejuvenator are a promising chemical powder product applied in asphalt concrete to prolong its service life. However, the size, thermal stability and mechanical properties of microcapsules are strictly demanded to suit the natural instincts and the actual application conditions of asphalt. The objective of this work was to fabricate and characterize the physicochemical properties of novel microcapsules containing rejuvenator by an in-situ polymerization method using methanol–melamine–formaldehyde (MMF) prepolymer as shell material. It was found that the average size of microcapsules could be successfully controlled in the range of 23.5 to 5.0 μm with increasing stirring rates from 1000 to 6000 r·min− 1. The average size was mainly determined by the core material dispersion rates in an oil-in-water emulsion. Shell thickness and shell density were increased by adding more MMF prepolymer in the fabrication process. Thermal stability results indicated that the decomposition temperatures of microcapsule samples (core/shell ratios of 2/1, 1/1, 1/2 and 1/3) were higher than the melting temperature of asphalt (180 °C). Lower prepolymer dropping rate is responsible for the better homogeneity of the sample which results in achieving a correct thermal decomposition as the investigation in this case shows an improvement of the stability. The hardness and Young's modulus results measured by nanoindentation indicated that the MMF-shell microcapsules had an elastic–plastic deformation. The size and shell thickness were two main influencing factors of micromechanical properties of the microcapsules containing rejuvenator.