Biocompatible water-in-oil emulsion as a model to study ascorbic acid effect on lipid oxidation

A biocompatible water-in-oil (W/O) emulsion has been used as a model to study the effect of ascorbic acid (AA) on the oxidation of the oil (glycerol trioleate, GTO) continuous phase. The model system consisted of 3 wt % water dispersed in GTO containing 0.5 wt % sodium oleate (NaO)/oleic acid (OA) mixture (NaO/OA = 20/80 mol/mol %) as a stabilizer. To study the ascorbic acid effect on GTO light-promoted oxidation, we added aqueous solutions of ascorbic acid to GTO in place of distilled water. Results obtained as peroxide values show that ascorbic acid activity depends on its concentration and it is affected by the characteristics of the W/O interface. In the presence of ascorbyl palmitate (AP) or sorbitan trioleate (Span 85) in the continuous phase, ascorbic acid activity increases in the first few hours of oxidation. The effect of ascorbic acid has been related to emulsion structure by calculating characteristic parameters of the droplet size distributions by means of optical microscopy.     

聚乳酸/聚己内酯/聚(ε-己内酯-L-丙交酯)共聚物三元共混体系的结构与性能

通过开环共聚合,合成了3种不同单元比例的ε-己内酯(ε-CL)与L-丙交酯(L-LA)的共聚物P(CL-co-LA)。通过熔融共混制备了聚乳酸(PLA)/聚己内酯(PCL)/P(CL-co-LA)三元共混材料,研究了P(CL-co-LA)对共混材料微观形貌、热性能以及力学性能的影响。 结果表明,共聚物P(CL-co-LA)作为PLA/PCL不相容体系的界面增容剂,减小了PCL分散相的尺寸,改善了PLA/PCL共混体系的相容性,提高了共混材料的韧性。 固定m(PLA):m(PCL):m(P(CL-co-LA))=80:20:10时,以P(CL49/LA51)(其中数字代表摩尔分数(%))作为界面增容剂效果最佳,共混材料的断裂伸长率可达到(210±30)%。     

Phase morphology of iPP/aPS/SEP blends

Supermolecular structure and phase morphology of the ternary isotactic polypropylene/atactic polystyrene/poly(styrene-b-ethylene-co-propylene) (iPP/aPS/SEP) compression molded blends with 100/0, 90/10, 70/30, and 50/50 iPP/aPS weight ratios and with different amounts of added SEP compatibilizer were studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). SEP significantly reduced the size of dispersed aPS particles that enabled better spherulitization in the iPP matrix. Furthermore, iPP spherulites in ternary blends with 90/10 iPP/aPS weight ratio became larger in comparison with the pure iPP. TEM revealed that the SEP formed continuous interface layer around the dispersed aPS particles even when only 2.5 wt.% of SEP was added. Particle size distribution was distinctly bimodal. When the SEP content was increased to 10 wt.%, joining together smaller and bigger aPS and SEP particles formed dispersed aggregates. Additionally, both amorphous components (aPS and SEP) influenced crystallization process of iPP matrix and so modified, to some extent, its final supermolecular structure. SEP compatibilizer did not significantly affect crystallite orientation. The increase of crystallite sizes, which was more affected by the addition of aPS than by the addition of SEP, seemed to be influenced by the solidification effect rather than by the phase morphology of the blends.     

Preparation of novel W/O gel-emulsions and their application in the preparation of low-density materials

A series of novel and stable water in oil (W/O) gel-emulsions was created by utilizing a new cholesteryl derivative, a low-molecular mass gelator (LMMGs), as a stabilizer. In the emulsions, n-heptane, n-octane, n-nonane, n-decane, tertiary butyl methacrylate (t-BMA), methyl methacrylate (MMA), or styrene can be used as a continuous phase, water as a dispersed phase, and the stabilizer in the continuous phase is only 2% (w/v). Importantly, the gel-emulsions could be prepared by simple agitation of the mixtures at room temperature, while heating, cooling, and addition of a cosolvent or other additional component are unnecessary. SEM and optical microscopy studies revealed the foam-like structures of the gel-emulsions. Rheological measurements demonstrated that the gel-emulsions are mechanically stable and exhibit typical viscoelastic properties. Surprisingly, the storage modulus, G', and the yield stress of the gel-emulsions with the alkanes as continuous phase decrease along with increasing the volume ratio of the dispersed phase, water, a property different from those of conventional gel-emulsions reported in the literature. From the viewpoint of application, the gel-emulsions as prepared are superior to others due to their simplicity in preparation, less amount of stabilizer needed, and the nonionic nature of the stabilizer, which must benefit practical applications. Furthermore, porous polymer monoliths could be prepared by polymerizing gel-emulsions with organic monomers as a continuous phase.     

反应条件对乳液法自组装合成氧化锰纳米粒子结构、形貌和尺寸的影响

通过改变反应物物质的量比、分散相与连续相体积比、反应体系温度和煅烧后处理温度,研究了反应条件对乳液法自组装合成氧化锰纳米粒子结构、形貌和尺寸的影响.结果表明:当高锰酸钾与油酸物质的量比在1∶5～1∶1之间时,形成蜂窝状纳米粒子和空心纳米粒子;当分散相(油酸)与连续相(水)的体积比为4∶200时,形成良好的空心球纳米结构;反应体系温度升高不利于产物的洗涤;不同温度的煅烧后处理不仅影响氧化锰纳米粒子的形貌,而且影响其结晶度和晶型.     

Microencapsulation of hydrophilic solid powder as a flame retardant with epoxy resin by using interfacial reaction method

Microencapsulation of Bistetrazol · diammonium (BHT · 2NH₃) as a hydrophilic powdery flame retardant was tried by the interfacial reaction method in reverse emulsion. In this microencapsulation method, water droplets containing BHT · 2NH₃ and hydrazine as gelation agent for epoxy resin were dispersed in the continuous phase of corn oil. When epoxy resin was added to the continuous phase, BHT · 2NH₃ as a core material was microencapsulated by the reaction of epoxy resin with hydrazine on the interface between the surface of water droplet and the continuous phase. The content of the core material from 70 to 85%, and the microencapsulation efficiency from 89 to ca 100% were able to be attained under the experimental conditions adopted here. Copyright © 2009 John Wiley & Sons, Ltd.     

Complexation and rate of polymerization of acrylic acid and methacrylic acid in the presence of poly(4-vinylpyridine) in dilute methanol solution

A 1:1 hydrogen-bonded complex was formed between acrylic acid (AA) or methacrylic acid (MA) and the pyridine group of poly(4-vinylpyridine) (P4VP) in dilute solutions. A shift of infrared absorption of the hydrogen-bonded acid O? H to a lower energy direction and an upfield shift of acid proton in the NMR were observed when the monomers were added with pyridine. The equilibrium constants of the 1:1 complexation with P4VP measured by using a semipermeable membrane were 0.58 and 0.26 for AA and MA, respectively, at 25°C in methanol. The bromometrically measured initial rate of radical polymerization showed only a slight enhancement in the presence of P4VP, the rate being maximum at the 4VP unit:monomer mole ratio of 0.25 and 0.5 for AA and MA, respectively, in dilute methanol solution at 60°C.     

Rheological,mechanical and morphological properties of thermoplastic vulcanizates based on NR‐g‐PMMA/PMMA blends

Graft copolymer of natural rubber and poly(methyl methacrylate) (NR‐g‐PMMA) was prepared using semi‐batch emulsion polymerization technique via bipolar redox initiation system. It was found that the grafted PMMA increased with the increase of methyl methacrylate (MMA) concentration used in the graft copolymerization. The NR‐g‐PMMA was later used to prepare thermoplastic vulcanizates (TPVs) by blending with PMMA through dynamic vulcanization technique. Conventional vulcanization (CV) and efficient sulphur vulcanization (EV) systems were studied. It was found that the CV system provided polymer melt with lower shear stress and viscosity at a given shear rate. This causes ease of processability of the TPVs via extrusion and injection molding processes. Furthermore, the TPVs with the CV system showed higher ultimate tensile strength and elongation. The results correspond to the morphological properties of the TPVs. That is, finer dispersion of the small vulcanized rubber particles were observed in the PMMA matrix. Various blend ratios of the NR‐g‐PMMA/PMMA blends using various types of NR‐g‐PMMA (i.e. prepared using various percentage molar ratios of NR and MMA) were later studied via dynamic vulcanization by a conventional sulphur vulcanization system. It was found that increasing the level of PMMA caused increasing trend of the tensile strength and hardness properties but decreasing level of elongation properties. Increasing level of the grafted PMMA in NR molecules showed the same trend of mechanical properties as in the case of increasing concentration of PMMA used as a blend component. From morphological studies, two phase morphologies were observed with a continuous PMMA phase and dispersed elastomeric phase. It was also found that more finely dispersed elastomeric phase was obtained with increasing the grafted PMMA in the NR molecules. Copyright © 2005 John Wiley & Sons, Ltd.     

An unusual reaction polymerization in nitric acid medium

We are investigating an unusual reaction that occurs when methyl methacrylate (MMA) is kept in contact with concentrated nitric acid¹ (65% HNO₃, sp. gr. 1.41). Polymer of high molecular weight is formed, showing about one unit of methacrylic acid (MAA) per unit of MMA, when equilibrium is reached. The reaction depends on the temperature, the molar ratio MMA:HNO₃, and the reaction time. Although we also found polymer at temperatures in the range 50–70°C,² in this paper we only report the results when the temperature was kept between 25 and 40°C. Methacrylic acid (MAA) was found to homopolymerize under those mild conditions; its behavior was investigated. Although we also observed that polymer is formed with sulfuric acid (96%) and that acrylic acid polymerizes with both nitric and sulfuric acid at 20–30°C, we are limiting this article to the observed polymerizing action of nitric acid on methyl methacrylate and on methacrylic acid. Work proceeds on this matter in this laboratory.     

新型乳液聚合制备疏松PMMA树脂及成粒机理

采用以水相为分散相、甲基丙烯酸甲酯 (MMA) 环己烷混合物为连续相的新型乳液聚合制备PMMA树脂 .发现 ,在未加乳化剂和加入少量Tween2 0乳化剂时 ,均可制备由初级粒子凝聚而成、无明显皮膜结构的疏松PMMA粒子 ,初级粒子粒径小于环己烷存在下MMA悬浮聚合得到的PMMA粒子的初级粒子 .根据聚合体系相构成、PMMA在MMA 环己烷混合液的溶解性及PMMA粒子粒径分布和形态的演变 ,提出了在分散水滴内乳液聚合形成初级粒子 生长 凝聚的新型乳液聚合成粒机理     

Hydrocarbon formation in the pyrolytic decomposition of methacrylate copolymers

A series of methyl methacrylate (MMA)–methacrylic acid (MAA) copolymers containing up to 50% methacrylic acid and the respective homopolymers were reproducibly pyrolyzed at 900°C and the fragments identified by gas chromatography (GC) or GC–mass spectroscopy. It was shown that PMMA and the MMA portions of blocky or random copolymers yielded 99% MMA, while a large portion (50–60%) of the MAA broke down to give a wide variety of hydrocarbons via decarboxylation and/or anhydride formation. Both unsaturated aliphatic and aromatic hydrocarbons, as well as the minor products of the MMA decomposition, support free-radical processes for these decompositions. It was also shown that the copolymers readily complex oxygenated solvents (which did not affect decomposition) and metal ions (which markedly affected the products).     

Lecithin organogels used as bioactive compounds carriers. A microdomain properties investigation

Organogels were obtained by adding small amounts of water to a solution of lecithin in organic solvents. Either isooctane or isopropyl palmitate and isopropyl myristate were used as the continuous organic phase of the gels. EPR spectroscopy using both DSA membrane-sensitive and lipophilic spin probes was applied to define the dynamic structure of the surfactant monolayer and the continuous oil phase of lecithin organogels. It was found that by increasing the water quantity, an increase of the polar head area per lecithin molecule was induced, and as a consequence the total interface expanded. It was found that the use of esters as organic solvents induced a decrease of the size of the dispersed structures. The interconnection of the aqueous microdomains and their dynamics were monitored by both static and time-resolved fluorescence quenching spectroscopy using Ru(bipy)32+ as fluorophore and Fe(CN)63- as quencher. It was found that the rates of inter- and/or intra-micellar exchange of water molecules were very slow because they appeared quite immobilized close to the lecithin polar heads. According to the results of the dynamic studies, appropriate organogels were formulated and used to incorporate model bioactive compounds with medicinal or cosmetic interest such as caffeine and theophylline. When these systems were tested for trans-membrane diffusion, they showed a 24 h permeation of 20% and 35%, respectively.     

Controlled (Co)Polymerization of Methacrylates Using a Novel Symmetrical Trithiocarbonate RAFT Agent Bearing Diphenylmethyl Groups

Herein, we report a novel type of symmetrical trithiocarbonate chain transfer agent (CTA) based diphenylmethyl as R groups. The utilization of this CTA in the Reversible Addition-Fragmentation chain Transfer (RAFT) process reveals an efficient control in the polymerization of methacrylic monomers and the preparation of block copolymers. The latter are obtained by the (co)polymerization of styrene or butyl acrylate using a functionalized macro-CTA polymethyl methacrylate (PMMA) previously synthesized. Data show low molecular weight dispersity values (Đ < 1.5) particularly in the polymerization of methacrylic monomers. Considering a typical RAFT mechanism, the leaving groups (R) from the fragmentation of CTA should be able to re-initiate the polymerization (formation of growth chains) allowing an efficient control of the process. Nevertheless, in the case of the polymerization of MMA in the presence of this symmetrical CTA, the polymerization process displays an atypical behavior that requires high [initiator]/[CTA] molar ratios for accessing predictable molecular weights without affecting the Đ. Some evidence suggests that this does not completely behave as a common RAFT agent as it is not completely consumed during the polymerization reaction, and it needs atypical high molar ratios [initiator]/[CTA] to be closer to the predicted molecular weight without affecting the Đ. This work demonstrates that MMA and other methacrylic monomers can be polymerized in a controlled way, and with “living” characteristics, using certain symmetrical trithiocarbonates.     

Mono- or narrow disperse poly(methacrylate-co-divinylbenzene) microspheres by precipitation polymerization

Precipitation copolymerizations of five mono-vinyl methacrylic monomers including methyl methacrylate (MMA), butyl methacrylate (BMA), dodecyl methacrylate (DMA), glycidyl methacrylate (GMA), and hydroxyethyl methacrylate (HEMA) with divinylbenzene (DVB), in a wide range of comonomer composition, were carried out in acetonitrile to form mono- or narrow disperse crosslinked copolymer microspheres. In addition, two divinyl methacrylic monomers, ethylene glycol dimethacrylate (EGDMA) and triethylene glycol dimethacrylate (TEGDMA), were also copolymerized with DVB, and optionally a third comonomer (GMA or HEMA), to yield similar microspheres in acetonitrile. The possibility of creating porosity was explored for some of the copolymer particles. All these microspheres have clean surfaces due to the absence of any added steric or ionic stabilizer, and they are in the size of the micrometer range, varying from 1 to 7 µm, depending on the type and content of the methacrylic comonomer. Particle size distribution, surface morphology, internal texture, and porosity properties of these particles were studied by a Coulter Multisizer, a scanning electron microscope, a transmission electron microscope, and an Autosorb-1. The effects of comonomers on microsphere formation and morphology are described. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2899–2907, 1999     

Freeze–thaw stability of water-in-oil emulsions

Factors influencing water-in-oil emulsion stability during freeze/thaw-cycling, namely interfacial crystallization vs. network crystallization and the sequence of crystallization events (i.e., dispersed vs. continuous phase or vice versa), are assessed. We show that destabilization is most apparent with a liquid-state emulsifier and a continuous oil phase that solidifies prior to the dispersed phase. Emulsions stable to F/T-cycling are obtained when the emulsifier crystallizes at the oil–water interface or in emulsions where the continuous phase crystallizes after the dispersed aqueous phase. The materials used are two food-grade oil-soluble emulsifiers – polyglycerol polyricinoleate (PGPR) and glycerol monostearin (GMS) and two continuous oil phases with differing crystallization temperatures – canola oil and coconut oil. Emulsion stability is assessed with pulsed field gradient NMR droplet size analysis, sedimentation, microscopy and differential scanning calorimetry. This study demonstrates the sequence of crystallization events and the physical state of the surfactant at the oil–water interface strongly impact the freeze–thaw stability of water-in-oil emulsions.     

SOME ASPECTS OF MORPHOLOGIES AND INTERFACES IN COPOLYMER/HOMOPOLYMER BLENDS

Based on a series of morphological studies of blends of homopolymer (Homo) and a variety of block and graft copolymers (Cop), the nature of phase separation, interface, emulsification and inner morphology of copolymer-dispersed phase etc. in the blends are discussed. In the cases of Cop AB/Homo A/Homo B systems, in which one homopolymer forms matrix, it is observed that the dispersed homopolymer phase is exclusively associated with Cop AB, i.e. no Homo A-Homo B interface exists. This phenomenon is believed to be caused by minimizing the interfacial energy of the systems. Meanwhile, preferential solubilization or anchoring of the like chains of copolymer into homopolymer matrix leads to stabilization of the dispersed phase in the matrix. In addition, regular variation of the inner morphology of the dispersed copolymer phase with the composition and molecular parameters of the component polymers is observed. When the two components have comparable proportions, alternating concentric shells are the most common feature which is associated with minimizing the interfacial energy in the Cop/Homo systems.     

Encapsulation of Jojoba and Andiroba Oils by Miniemulsion Polymerization. Effect on Molar Mass Distribution

Summary: This paper aims to study the encapsulation of jojoba and andiroba oils via miniemulsion polymerization. The effect of different hydrophilic monomers (acrylic or methacrylic acid), co-stabilizers (hexadecane, jojoba oil or andiroba oil) and initiator concentrations were evaluated. Results indicated the formation of particles with nanocapsule morphology when either hexadecane or jojoba oils were used. When andiroba oil was used no phase separation could be detected in polymer particles and molar mass distributions showed a shoulder of intermediate molar masses between those of the oil and of the pure polymer.     

Blends of low-density polyethylene with nylon compatibilized with a sodium-neutralized carboxylate ionomer

An ethylene-methacrylic acid copolymer partially neutralized with sodium (Na-EMAA) was successfully used to compatibilize Nylon 6 (Ny6) and low-density polyethylene (LDPE) blends. The phase morphology and thermal behavior of these blends were investigated over a range of compositions using a variety of analytical techniques. The addition of small amounts (0.5 phr) of Na-EMAA improved the compatibility of Ny6/LDPE blends as evidenced by a significant reduction in dispersed phase sizes. TGA measurements demonstrated an improvement in thermal stability when Na-EMAA was added to either LDPE or Ny6. DSC results of Ny6/Na-EMAA binary blends showed that with increasing Na-EMAA content, the crystallization temperature of Ny6 phase decreased indicating that Na-EMAA retarded crystallization of Ny6. TGA and DSC results indicate that chemical reactions might have taken place between Ny6 and Na-EMAA, a hypothesis confirmed by the Molau test.     

Nonionic Microemulsion: Mechanism of Formation and Percolation

A series of microemulsions, both W/O and O/W, based on nonionic surfactants of the form (NP(EO)_n), were prepared using the titration method. Mixing a constant weight of surfactant with a constant volume of the dispersed phase and an initial volume of continuous phase produces an emulsion, which is titrated to clarity with another surfactant (cosurfactant). Plotting (a) the volume of cosurfactant necessary to transform an emulsion into a microemulsion containing a fixed volume of dispersed phase and constant weight of surfactant versus (b) different initial continuous-phase volumes yields a straight line. Extrapolating from experimentally determined values for the cosurfactant volume to the value corresponding to a zero-volume continuous phase allows the determination of the surfactant molar composition and the average number of ethylene oxides (EO) per nonylphenol adsorbed at the interface. Using a surfactant with the same number of ethylene oxides yields a single-surfactant microemulsion. Measurement of surfactants transmittance in the oil and water phases demonstrates that microemulsification occurs when the surfactant interfacial film is equally soluble in the two phases. Surface pressure measurements reveal that oil penetration impedes formation of O/W microemulsions with n-tetradecane or n-hexadecane as dispersed phase. Conductance, particle size, and transmittance measurements show that above a certain dispersed-phase volume percolation of the microemulsion occurs.     

Comparison of Pickering and network stabilization in water-in-oil emulsions

We compared the efficacy of Pickering crystals, a continuous phase crystal network, and a combination thereof against sedimentation and dispersed phase coalescence in water-in-oil (W/O) emulsions. Using 20 wt % water-in-canola oil emulsions as our model, glycerol monostearate (GMS) permitted Pickering-type stabilization, whereas simultaneous usage of hydrogenated canola oil (HCO) and glycerol monooleate (GMO) primarily led to network-stabilized emulsions. A minimum of 4 wt % GMS or 10 wt % HCO was required for long-term sedimentation stability. Although there were no significant differences between the two in mean droplet size with time, the free water content of the network-stabilized emulsions was higher than Pickering-stabilized emulsions, suggesting higher instability. Microscopy revealed the presence of crystal shells around the dispersed phase in the GMS-stabilized emulsions, whereas in the HCO-stabilized emulsion, spherulitic growth in the continuous phase and on the droplet surface occurred. The displacement energy (E(disp)) to detach crystals from the oil-water interface was ～10(4) kT, and was highest for GMS crystals. Thermal cycling to induce dispersed phase coalescence of the emulsions resulted in desorption of both GMS and GMO from the interface, which we ascribed to solute-solvent hydrogen bonding between the emulsifier molecules and the solvent oil, based on IR spectra. Overall, Pickering crystals were more effective than network crystals for emulsion stabilization. However, the thermal stability of all emulsions was hampered by the diffusion of the molten emulsifiers from the interface.