Continuous Multistep Encapsulation Process for the Generation of Multiple Emulsions

Multiple emulsions (ME) are of interest as carrier of active ingredients that can be released in a controlled way. ME are thermodynamically unstable with a strong tendency to coalesce or flocculate, resulting in a complex emulsion generation and stabilization process. Typical encapsulation procedures utilize individual batch operation steps for the ME production. In this work, a multistep membrane encapsulation process is proposed to allow the generation of ME in a continuous shear‐sensitive processing through different membrane stages. The stages combine the premix generation, followed by the internal phase production, and the final ME encapsulation step. For each step, a tailored membrane with different surface properties is used and combined into the continuous process.     

Shear stability of inverse latexes during their polymerization process

The shear‐stability of inverse latexes (IL) during their polymerization process is studied. The IL is made of water droplets containing a copolymer of acrylamide and dimethyl‐aminoethyl‐methylenechloride emulsified in a paraffin oil. It is found for the first time that the shear stability of the ILs is a nonmonotonic function of the monomer conversion. At low conversions the shear stability increases as the conversion increases, but at a certain conversion value it reaches a local maximum and then decreases with conversion. Moreover, at the final stage of the conversion, the shear stability can increase again. A proper interpretation of this behavior is proposed and related to the combined effects of the polymer properties, fractal aggregation, and coalescence. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1380–1384, 2015     

Processing,rheology, and storage stability of recycled EVA/LDPE modified bitumen

The optimum processing conditions for the manufacture of polymer‐modified bitumens (PMBs), as well as the rheological properties of the final polymer‐bitumen blends, strongly depend on the characteristics of the mixing device used. The present work is focused on the comparison among the kinetics of the mixing process and the rheological properties and microstructural characteristics of PMBs manufactured in two different mixers. Thus, blends of 60/70 penetration grade bitumen and recycled EVA/LDPE were processed in both high and low‐shear devices. Knowledge on the evolution of shear viscosity and microstructure with time, as well as on the mechanical properties of the final polymer‐bitumen blends, was gained from rheological and modulated DSC tests, and optical microscopy. The results obtained demonstrate that processing in the high‐shear device yields a significant decrease in the time needed for the polymer‐bitumen blend to reach the final stage of the manufacturing process, as well as an important reduction in bitumen oxidation and enhanced properties in a wide range of in‐service temperatures. However, polymer‐bitumen blends manufactured in the high‐shear device are not stable during its storage at high temperature. POLYM. ENG. SCI., 47:181–191, 2007. © 2007 Society of Plastics Engineers     

Processing of short‐fiber reinforced polypropylene. I. Influence of processing conditions on the morphology of extruded filaments

An experimental investigation of the processing of glass fiber reinforced polypropylene is presented. Final fiber orientation distribution, fiber distribution in filament sections, rheological properties, final fiber length distribution and surface morphology were analyzed. This analysis was done taking into account the quantity of fibers and their interactions and flow conditions. The final fiber orientation increased when shear rate increased and fiber concentration decreased. Moreover, inhomogeneities in fiber distribution increased as the concentration of fibers decreased. The density profile showed a significant variation with fiber concentration, but it was not dependent on the shear rate applied. The viscosity showed a linear dependence with shear rate. The average fiber length and the breadth of this distribution decreased with the increasing fiber concentration and extrusion rate. The extruded filament surface showed minor roughness when the shear rate increased or when the fiber concentration decreased. The results of this experimental characterization give useful information to determine the influence of the processing variables on the final properties of short‐fiber reinforced polypropylene and constitutes the first part of a more ambitious project that also includes the development of a modeling strategy of the processing behavior for short‐fiber composites.     

Herschel‐Bulkley rheological parameters of a novel environmentally friendly lightweight biopolymer drilling fluid from xanthan gum and starch

This article summarizes a concise investigation on the effect of concentration of the four main components of a novel lightweight drilling fluid, i.e., glass bubbles, xanthan gum, starch, and clay, to the Herschel‐Bulkley rheological model parameters. The three parameters of Herschel‐Bulkley model, i.e., yield stress, fluid consistency, and fluid index were calculated by fitting the experimental data of shear stress as a function of rate of shear to the model. Results indicate that the increment of the amount of four main components increase the yield stress of the final fluid as the flow resistance is increased. Furthermore, the result also showed that the calculated fluid consistency of the drilling fluid appears to be strongly dependent on the presence of glass bubbles, xanthan gum, and clay. However, the fluid consistency appears not to be affected by the presence of starch. It is also concluded that the presence of glass bubbles, xanthan gum, and clay in the fluid tends to determine the final fluid to behave as pseudoplastic. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of poly(vinyl chloride) latexes using a dual surfactant system: The effect in the particle size distribution

The control of the average particle size and size distribution in the emulsion polymerization of vinyl chloride monomer is an important parameter to determine, not only the latex characteristics, but also the properties of the final dispersion powder in several industrial applications. It is possible to manipulate the particle size distribution (PSD) by applying a mixture of an anionic surfactant‐fatty alcohol before the start of the free radical polymerization. Contrary to the procedures of the miniemulsion and the derivative diffusional swelling techniques, no kind of high shear is applied to the monomer and/or surfactant mixtures. In fact, the concentration and selection of the anionic surfactant, together with the fatty‐alcohol, can play an interesting role on the final PSD of the polymer's particles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermomechanical reactive blending of silicone rubber and LLDPE: Effects of processing parameters

To prepare thermoplastic elastomers based on linear low density polyethylene (LLDPE) and silicone rubber (SR) the reactive blending of the two polymers was carried out at different processing conditions. Effects of mixing parameters such as temperature, shear rate, mixing time, and sequence of feeding the ingredients, upon the yield and rate of interfacial reaction, have been evaluated by following the variation of mixing torque and also by determination of the reacted fraction of silicone rubber. The yield and rate of the reaction increased by increasing the temperature of mixing, shear mixing rate, and the time of mixing. Changing the sequence of feeding the ingredients also changed the yield of the reaction. First feeding of polyethylene increased the yield of reaction. According to the obtained results, interfacial reaction between two phases is limited by chemical kinetics of the reaction and by rate of mass transfer during melt mixing. The order of interfacial reaction between these two polymers under thermomechanical conditions was found to be about 1.1. Rheological studies on the blends performed by using rheomechanical spectroscopy showed a distinct rheological behavior with a non‐Newtonian characteristic and higher dynamic viscosity at low frequencies for the blends prepared at high temperature and shear rate. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 155–161, 2005     

Effect of ingredients on oxidative stability of fish oil‐enriched drinking yoghurt

The oxidative stabilities of fish oil‐enriched milk and fish oil‐enriched drinking yoghurt were compared by following the development of lipid oxidation in plain milk, plain yoghurt and yoghurt to which ingredients present in drinking yoghurt were added one by one. All samples were enriched with 1 wt‐% fish oil. After 3 weeks of storage, development of peroxide values, volatile secondary oxidation products and fishy off‐flavors were much more pronounced in the milk compared to any of the yoghurt samples, irrespective of any added ingredients used to prepare flavored drinking yoghurt. Thus, pectin, citric acid or glucono‐delta‐lactone did not affect the oxidative stability of fish oil‐enriched yoghurt emulsions. Furthermore, the fruit preparation and added sugar did not lead to increased antioxidative activity. It is concluded that yoghurt as the dairy component in the fish oil‐enriched emulsion was responsible for the remarkably high oxidative stability and was able to protect the n‐3 PUFA against oxidative deterioration. It should be considered that this strong antioxidative effect of yoghurt might mask potential antioxidative effects of the other ingredients in the drinking yoghurt.     

Orientated crystallization in discontinuous aramid fiber/isotactic polypropylene composites under shear flow conditions

Melt blends of short aramid fibers (AF) and isotactic polypropylene (iPP) are subjected to shear at 145°C and the structural evolution and final morphology are examined by in situ synchrotron X‐ray scattering/diffraction and high‐resolution scanning electron microscopy, respectively. The results indicate that the presence of short AFs significantly enhances the crystallization of iPP. It is argued that shear flow in this system exerts a twofold orientating action, namely, on the bulk iPP molecules and on the short AFs. The resultant crystalline morphology reflects the combined effects of crystallization on orientated iPP molecules to facilitate a shish kebab morphology and at the interface of the aligned fibers, to form transcrystallinity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1113–1118, 2005     

Experimental study on the mechanical behavior and failure mechanism of 3d MWK carbon/epoxy composites under quasi‐static loading

Quasi‐static tensile, out‐of compression, in‐plane compression, three‐point‐bending and shear tests were conducted to reveal the mechanical behavior and failure mechanisms of three‐dimensional (3D) multiaxial warp‐knitted (MWK) carbon/epoxy composites. The characterization of the failure process and deformation analysis is supported by high‐speed camera system and Digital Image Correlation. The results show that tensile, bending, out‐of‐plane compression, in‐plane compression stress–strain response exhibit obvious linear elastic feature and brittle fracture characteristics, whereas the shear response exhibits a distinct nonlinear behavior and gradual damage process. Meanwhile, 3D MWK carbon/epoxy composites have good mechanical properties, which can be widely used in the fields of engineering. In addition, the failure for tension behaves as interlayer delaminating, 90/+45/−45° interface debonding and tensile breakage of 0° fibers; the damage for out‐of‐plane compression is mainly interlaminar shear dislocation together with local buckling and shear fracture of fibers; the failure pattern for in‐plane compression is 90° fiber separating along fiber/matrix interface as well as 0/+45/−45° fiber shear fracture in the shear plane. The main failure for bending is fiber/matrix interface debonding and fibers tearing on the compression surface, 0° fibers breakage on the tension surface as well as fiber layers delaminating. Although the shear behavior is characterized by a gradually growing shear matrix damage, 90/+45/−45° interface debonding, +45/−45° fibers shear fracture, and final 0° fiber compression failure. POLYM. COMPOS., 37:3486–3498, 2016. © 2015 Society of Plastics Engineers     

Effect of selective localization of carbon nanotubes in pa6 dispersed phase of PP/PA6 blends on the morphology evolution with time,part 2: Relaxation of deformed droplets after cessation of flow

The relaxation of carbon nanotube (CNT)‐filled PA6 droplets in PP matrix was studied after cessation of simple shear flows. The morphology evolutions of blends with various CNT contents in PA6 were probed by optical microcopy over time. It was shown that the retraction of deformed droplets accelerates with increasing CNT content in PA6. As evidenced by linear rheological measurements, gradual formation of elastic structures within the droplets was found responsible for such observations. The pre‐shearing flow was varied to investigate the effects of different flow histories on the kinetics of relaxation. By increasing the shear‐rate of the flow prior to relaxation, the relaxation kinetics slowed down to some extent. The slowed‐down kinetics was attributed to the partial rupture of the elastic structures within PA6. This idea was evidenced by performing the startup of steady shear flow experiments on PA6/CNT nanocomposites. The final morphology of the blends after the melt blending process was analyzed. The average droplet size was found to increase with increasing the CNT content. Also, the distribution of the droplet sizes became broader as a result of the increased viscosity and elasticity ratios. POLYM. ENG. SCI., 56:51–60, 2016. © 2015 Society of Plastics Engineers     

Butyl Acrylate/Vinyl Acetate Emulsion‐Based Pressure‐Sensitive Adhesives: Empirical Modelling of Final Properties

The influence of the amounts of acrylic acid, chain transfer agent and anionic stabilizer on polymer microstructural properties and final adhesive performance of BA/VAc emulsion‐based PSAs on stainless‐steel and high‐density polyethylene substrates was investigated using a Box‐Behnken experimental design for 15 runs. The resulting data were empirically modelled. For each final adhesive property (i.e., loop tack, shear and peel strength), different models were found to fit the data. Similar models for loop tack and peel strength were found to be adequate for different PSA thicknesses on the same substrate. AA and SDS had significant effects on loop tack as did the AA‐SDS and CTA‐SDS two‐factor interactions. Quadratic peel strength models were found to adequately describe the data for SS substrate cases with a noticeable absence of any interaction parameters. The shear strength models were similar regardless of the substrate or thickness of the adhesive (e.g. in all models, AA and CTA, as well as their second‐order interactions, were the significant factors).     

Curing Viscosity of HTPB‐Based Binder Embedding Micro‐ and Nano‐Aluminum Particles

Aluminum is used as a metal fuel in energetic materials for the improvement of propulsion performance and density. Both nano‐sized and micrometer‐sized activated powders represent valuable options in order to improve metal combustion properties, each possessing advantages and drawbacks. These ingredients bear peculiar properties (namely, higher specific surface, coatings, or surface characteristics) which generate high mixing viscosity once suspended in a polymer as well as altered mechanical properties of the final product. Four different powders dispersed in a polymer binder are taken into consideration and the evolution of viscosity in time during the curing process is investigated. The suspending medium is represented by a mixture of hydroxyl‐terminated polybutadiene (HTPB), isophorone diisocyanate (IPDI) and dioctyl adipate (DOA). Viscosity was measured for 5 h on samples under isothermal curing at 60 °C. Non‐isothermal DSC kinetic analyses were also performed using the Kissinger method. It was found that, for the test conditions, a size reduction of metal particles slowed down the increment rate of curing viscosity while some peculiar coatings, such as fatty acids, introduced opposite trends.     

Effect of Melt‐Memory on the Crystal Polymorphism in Molded Isotactic Polypropylene

The influence of γ‐quinacridone as a β‐crystal nucleating agent in injection molded isotactic polypropylene (iPP) is discussed. Samples are injection molded and characterized via polarized‐light optical microscopy and X‐ray diffraction. Mold‐filling simulation is used to understand the shear and cooling processes during sample preparation. The cooling rate associated with the quench near the mold wall is estimated to be greater than 600 K s^?1 using simulation, confirming previous studies that β‐crystal growth is not supported at that cooling rate. The non‐nucleated samples form β‐crystals at a distance of 100–300 µm from the skin and in the core of the sample, which is not expected based on quiescent cooling data. Since the mold‐filling simulation does not predict shear in the core, the formation of the β‐crystals formed in this region is attributed to shear‐induced crystallization effects in the injection unit of the molding machine that are not modeled in flow simulation, as they are typically excluded from any molding simulation analysis. This “melt‐memory” effect has shown to be significant, and it is suggested that the prediction of final properties of injection moldings requires understanding and knowledge of the entire shear history of the material including that of the injection unit.     

Preparation and linear rheological behavior of polypropylene/MMT nanocomposites

Maleic anhydride grafted low isotactic homopolypropylene elastomer (LiPP‐g‐MAH) is used as a compatibilizer in the melting mixing of polypropylene (PP) and clay. The microstructures of the composites of PP/clay (PPCN) are investigated using a wide‐angle X‐ray diffractometer (WAXD) and transmission electron microscope (TEM) as well as parallel rheometer, which show that PPCN with different phase morphologies have been obtained. It is found that the weight ratio of LiPP‐g‐MAH to clay and the weight content of LiPP‐g‐MAH in PPCN have a strong effect on the final dispersibility of the clay. The rheological response to small amplitude oscillatory shear (SAOS) shows that the storage modulus (G′) at the low frequencies is greatly sensitive to the microstructures in comparison with WAXD measurements. The investigation further indicates that the virgin clay particles, intercalated silicate crystallites, and exfoliated layers may coexist in the matrix at the same time, resulting in the great enhancement of G′ plateau at low frequency region.     

Preparation and chemical reactions of rigid cross‐linked poly(vinyl chloride) foams modified by epoxy compounds

A novel method to prepare semi‐interpenetrating polymer network rigid cross‐linked poly(vinyl chloride) (c‐PVC) foams with improved shear toughness in the absence of anhydride components is reported. The cross‐linked network structure in the c‐PVC foams was composed of polyurea network modified by epoxy structure. The cellular morphology was characterized by scanning electron microscopy. Tensile, compressive, and shear properties of the foams were studied. The obtained c‐PVC foams showed high shear properties compared with the comparative samples with the same density and cellular morphology. Possible reactions during the preparation of c‐PVC foams were studied by means of Fourier transform infrared spectrometry and nuclear magnetic resonance measurements through the model experiments. The results showed that allophanate structure resulting from the reaction between isocyanate compounds and epoxy compounds formed in the molding step, which was included into the final cross‐linked network in the cross‐linking step. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40567.     

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.     

Measurement of Mechanical Strength of Glass‐to‐Metal Joints

Three different test geometries were used to apply shear loading to fracture glass‐to‐metal joints typical of seals intended for use in planar solid oxide fuel cells (SOFCs): asymmetric compression; symmetric compression; and four‐point asymmetric bending. The measured apparent shear strengths were found to differ by an order of magnitude depending on the test configuration employed. In particular, the apparent shear strength measured in the asymmetric compression test was very low. Conversely, the highest apparent shear strengths were measured using the symmetric compression test and the four‐point asymmetric bend test gave an intermediate result. It is shown, by finite element modelling, that these differences are caused by differences in the normal stresses transverse to the joint. The locus of failure was always along the glass/metal interface in all test geometries. It is concluded that mechanical test procedures used to characterize glass‐ceramic seals in SOFC stacks need to be selected and interpreted with great care.     

Optimal cure steps for product quality in a tire curing process

Numerical algorithms and computer programs have been developed to determine optimal cure steps in a tire curing process. A dynamic constrained optimization problem was formulated with the following ingredients: (1) an objective function that measures product quality in terms of final state of cure and temperature history at selected points in a tire; (2) constraints that consist of a process model and temperature limits imposed on cure media; (3) B‐splines representation of a time‐varying profile of cure media temperature. The optimization problem was solved using the complex algorithm along with a finite element model solver. Numerical simulations were carried out to demonstrate the procedure of determining optimal cure steps for a truck/bus radial tire. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2063–2071, 1999     

Influence of processing conditions on the morphological and mechanical properties of compatibilized PP/LCP blends

The main aim of this work is to study the influence of the application of different processing conditions on the morphological and mechanical properties of thermoplastic/LCP blends, in which the viscosity ratios are inferior to unity and decrease with increasing temperature. The way the microstructure evolves along the extruder determines the final morphology and thus, the mechanical performance of the systems. In the present case, the mechanical properties are related with the degree of fibrillation in the final composites. The best degree of fibrillation was obtained for low screw speeds and temperatures and for intermediate outputs. The use of high screw speeds and processing temperatures results in a decrease of the viscosity ratio, in the former case via an increase in the viscous dissipation, at the regions of higher shear rates (kneading‐elements). The application of a lower processing temperature is advantageous for deformation, break‐up, and fibrillar formation because of the higher viscosity ratios and higher shear stresses involved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007