Skim and cream natural rubber particles: colloidal properties, coalescence and film formation

Cream and skim fractions of freshly tapped natural rubber latex have been studied using atomic force microscopy and scanning electric potential microscopy to elucidate the topology and charge properties in film formation. Elemental distribution maps of the particles have also been obtained using electron energy-loss imaging in a low-energy transmission electron microscope. The two rubber fractions are obtained by centrifugation. The cream fraction is stable while rapid coagulation occurs in the skim fraction. After removal of the coagulum, no further coagulation occurs and the remaining skim rubber particles are stable. The rubber particles from the cream rubber particles contain higher amount of adsorbed protein-phospholipid materials compared to those in the "self-cleaned" skim fraction. This difference in membrane property has a significant impact on the spreading of the cis-1,4-polyisoprene cores, their coalescence and film formation behavior. Coalescence of cream particles appears to be hindered by the membrane materials, forming a rough film that retains the topology of individual particles. Skim particles coalesce more readily, forming relatively smooth films.     

Surface heterogeneity of polystyrene latex particles determined by dynamic force microscopy

Atomic force microscopy (AFM) was employed to characterize the surface chemistry distribution on individual polystyrene latex particles. The particles were obtained by surfactant-free emulsion polymerization and contained hydrophilic quaternary ammonium chloride, sodium sulfonate, or hydroxyethyl groups. The phase shift in dynamic force mode AFM is sensitive to charge/chemical interactions between an oscillating atomic force microscope tip and a sample surface. In this work, the phase imaging technique distinguished phase domains of 50-100 nm on the surfaces of dried latex particles in ambient air. The domains are attributed to the separation of ion-rich and ion-poor components of the polymer on the particle surface.     

TiO2 colloidal suspension polydispersity analysed with sedimentation field flow fractionation and electron microscopy

Sedimentation field flow fractionation (SdFFF) operated at multi gravitational field is used to analyse a highly polydisperse TiO2 colloidal suspension. From the initial sample, time dependent eluted fractions are collected and submitted to electron microscopy (EM) shape and size analysis. To assess the accuracy of FFF in determining the average size of the different fractions, these are re-introduced into the channel by means of two different procedures, the on-channel concentration of the fractions and the direct re-injection of pre-concentrated fractions (DRI). Both methods appear accurate to determine the average size of every fraction, associated to a lower recovery in the case of DRI. The fractogram band spreading characteristics of the re-introduced fractions are correlated to the particle size distribution measured by EM. After density determination of fractionated particles, the fractogram is calibrated in terms of size and size distribution using data obtained from EM for each fraction. Quantitative analyses, based on particle counting showed high recovery (80-90%) of the eluted species. However, this loss limited the possibility to extend signal information to a quantitative one.     

P(St-AM)核壳聚合物微球的制备及其光子晶体膜

采用一步乳液聚合法,调节引发剂用量,制备了不同粒径的具有核壳结构的功能性聚(苯乙烯-丙烯酰胺)乳胶微球.用透射电子显微镜表征了乳胶微球的核壳结构和粒径,所制微球的粒径分别为195,217,234和255 nm.用红外光谱对微球的化学成分进行了表征,证实聚丙烯酰胺已包覆在聚苯乙烯外层.通过竖直沉积自组装法制备了聚合物微球的光子晶体薄膜.扫描电子显微镜表征了所制光子晶体膜的表面形貌,反射和透射光谱表征了光子禁带.结果表明,聚合物微球以面心立方紧密堆积,其(111)面与基底平行;微球粒径不同,光子晶体的光子禁带不同.制备了不同光子禁带的光子晶体,禁带分别位于473,515,574和630 nm,相应的薄膜分别呈蓝色、绿色、黄色和红色,对于光子晶体的拓展和应用具有重要的意义.     

Comparative chemical analysis of commercial creosotes and solvent refined coal-II materials by high resolution gas chromatography

The chemical composition of a commercially available creosote was compared to a direct coal liquefaction product, i.e., solvent refined coal-II fuel oil blend (SRC-II FOB) using high resolution gas chromatography (HRGC). In addition, hydrogenated products of these materials were studied. Samples were fractionated by chemical class on neutral alumina. Those fractions previously shown to be the most mutagenic and tumorigenic in laboratory bioassays of coal-derived materials were analyzed and compared by HRGC and gas chromatography/mass spectrometry (GC/MS). Individual components were tentatively identified and quantitated. Although similar chemical components were present in the creosote and SRC-II FOB fractions studied, the creosotes had higher concentrations of heavy molecular weight materials and a lower ratio of alkylated to parent polycyclic aromatic compounds than the coal liquefaction products. The creosote samples also had a significantly higher concentration of components which eluted in the polycyclic aromatic hydrocarbon (PAH) chemical class fraction. Amino-substituted PAH were present in both nonhydrogenated coal liquid and creosote materials. The creosote and SRC-II FOB crudes and nitrogen-containing polycyclic aromatic compound (NPAC) chemical class fractions expressed similar microbial mutagenicity. Based on chemical analysis data, the predicted tumorigenic potency of the creosote in laboratory bioassay systems would be equivalent to or greater than the SRC-II FOB.     

Fast gas chromatography characterisation of purified semiochemicals from essential oils of Matricaria chamomilla L. (Asteraceae) and Nepeta cataria L. (Lamiaceae)

The chemical composition of Matricaria chamomilla L. and Nepeta cataria L. essential oils was determined by GC-MS on an apolar stationary phase by comparison of the characteristic fragmentation patterns with those of the Wiley 275L database. The GC-MS chromatograms were compared with those obtained by fast GC equipped with a direct resistively heated column (Ultra Fast Module 5% phenyl, 5 mx 0.1 mm, 0.1 microm film thickness). Analytical conditions were optimised to reach a good peak resolution (split ratio=1:100), with analysis time lower than 5 min versus 35-45 min required by conventional GC-MS. The fast chromatographic method was completely validated for the analysis of mono- and sesquiterpene compounds. Essential oils were then fractionated by column chromatography packed with silica gel. Three main fractions with high degree of purity in E-beta-farnesene were isolated from the oil of M. chamomilla. One fraction enriched in (Z,E)-nepetalactone and one enriched in beta-caryophyllene were obtained from the oil of N. cataria. These semiochemical compounds could act as attractants of aphid's predators and parasitoids.     

L-丙交酯/ε-己内酯共聚物分子链结构非均匀性的研究

利用升温淋洗分级(TREF)和连续自成核退火热分级(SSA)等方法研究了L-丙交酯(LLA)和ε-己内酯(ε-CL)共聚物(PLC)分子链结构的非均匀性.合成了2种不同摩尔比的PLC共聚物,用TREF的方法,将同一个共聚物分级出3个级份.用核磁共振氢谱(1H-NMR)和凝胶渗透色谱(GPC)等方法对每个级份的分子结构进行了表征.结果表明,随着淋洗温度的升高,共聚物级份中的ε-CL单元的含量明显降低,而且级份的数均分子量增大,分子量分布指数降低.在SSA热分级研究中,发现PLC各级份间存在明显的分子链间和分子链内结构上的差异,这种链结构差异使得各个级份表现出不同的熔融行为.     

Synthesis of polyacrylate core-shell structure latex by radiation techniques

A series of poly(butyl acrylate-co-methyl methacrylate)/poly (ethyl acrylate-co-acrylic acid) interpenetrating polymer network (IPN) was synthesized in latex form by emulsion polymerization. The multiphase morphology of the latex particles was studied after two-stage polymerization by using transimission electron microscope (TEM), the result indicated that the morphology of the particles comprises gradient shell structure, cellular structure and core-shell structure. The change of morphology might stem from emulsion polymerization by radiation initiation or chemical initiation and the weight composition of poly(EA-co-MMA) seed latex which formed the core. By radiation techniques, we successfully synthesized poly( BA-co-MMA)/poly(EA-co-AA) latex of core-shell structure having (42-8)/(46-4) weight compositions. The PA core-shell structure latex applied to textile as a water proofing coating showed higher water-pressure and easier handling than that with PA homogeneous phase structure latex.     

Identification of estrogenic/anti-estrogenic compounds in diesel exhaust particulate extract

Diesel exhaust particulate extract (DEPE) was obtained from diesel exhaust particulates with Soxhlet extraction using dichloromethane. After separating DEPE into 11 fractions by liquid-liquid extraction, the neutral fraction (N) showed anti-estrogenic activity and the weak acid (phenol) fraction (WA(P)) showed estrogenic and anti-estrogenic activities by a yeast two-hybrid assay system expressing human estrogen receptor alpha. Both fractions were thoroughly fractionated by silica gel column chromatography and reversed-phase HPLC. In the WA(P) fraction, 3-methyl-4-nitrophenol and 2,6-dimethyl-4-nitrophenol were identified by LC-MS/MS as estrogenic compounds. This is the first study to identify 2,6-dimethyl-4-nitrophenol in DEPE and the first study to show that it is an estrogenic compound. In the N fraction, 1-hydroxypyrene was also identified by LC-MS/MS as an anti-estrogenic compound.     

The influence of fibre wall thickness on the undissolved residuals in CMC solutions

An industrial calcium sulfite pulp was fractionated in a hydrocyclone to four fractions that differed in dimensions and composition due to differences in density. The intention was to investigate whether the fibre dimensions had any influence on the properties of carboxymethyl cellulose (CMC) produced from the fractions and especially how the properties of the unreacted material differed. It was surprisingly found that the fraction containing thin-walled fibres gave CMC and dissolved residuals in the CMC-solution that had the lowest degree of substitution (DS). It was therefore believed that the thin-walled fibres were collapsed and more closely bound in the fibre network after drying of the pulp and that this impeded the chemical diffusion in the subsequent CMC-process, i.e. the diffusion of the CMC-chemicals into the cell wall was slower. There was thus a correlation between thinner fibres and a lower degree of substitution for CMC made from such fibres. It was also found that tick-walled fibres had a higher degree of substitution than the thin-walled fibres but that the highest degree of substitution was obtained if a mixture of thin- and thick-walled fibres were used.     

Preparation of subcellular fractions from granulation tissue by density gradient centrifugation

The 7000 g pellet of homogenized mature sponge-induced granulation tissue was fractionated by centrifugation in a stepwise sucrose gradient in order to study the synthesis and secretion of collagen and other components of this tissue on the subcellular level. As indicated by chemical and enzymatic assays, by electron microscopy and by incorporation experiments, the collagen-synthethesizing rough endoplasmic reticulum fraction was isolated free from the secretory vesicles (smooth endoplasmic membranes and Golgi elements) and fibrous extracellular matrix. Collagen differed from other proteins in the distribution among the subcellular fractions. In pulse-chase experiment the translocation of 14C-labelled collagen was demonstrated from the rough endoplasmic reticulum through the secretory vesicles to extracellular fibrillar collagen. This fractionation method will be used to study the modulation of collagen synthesis and secretion in the reparative tissue.     

Involvement of Hevea latex organelle membrane proteins in the rubber biosynthesis activity and regulatory function

Centrifugation of fresh Hevea rubber latex yields three distinct fractions. The sediment bottom fraction (BF) content of membrane-bound organelles is ca. 20 vol.-% of latex. Prolonged storage or delayed use of fresh latex will result in disintegration and loss of the bottom fraction. This is due to the osmotically sensitive BF rupture and its membrane debris being tightly bound to the top rubber particles (RP) phase. The BF membrane was found to be highly active for rubber biosynthesis (RB), in contrast to previous reports that describe RB only occurring on the RP surface. It was clearly shown that washed BF membrane (WBM) was much more active than fresh RP for RB activity. WBM was highly activated by SDS for RB in a biphasic manner, but SDS strongly inhibited the RP. Probably WBM micelle formation resulted in a highly increased active surface area for RB. C55-PP (UPP) was a very active allylic for WBM in RB function, but inactive for RP. Serial acetone extraction of WBM proteins showed a distinct profile of the fractions with different RB activity. WBM isolated proteins suspended in 2% sodium dodecyl sulfate (SDS) with an RB activity equal to that of intact WBM was with the 20% acetone protein fraction. The 60 and 80% fractions were inactive. Combining the 20 with 80% fractions showed a complete inhibition of RB activity. Complete RB loss was also found when WBM was mixed with the 80% fraction, indicating that WBM has both an enzyme system and a factor for regulation of the RB activity in a well controlled metabolic function for the latex RB process.     

Synthesis of water-soluble hyperbranched polymer and its application in acrylic latex

A water-soluble hyperbranched polymer (WHBP), obtained from a second generation of hyperbranched polyester and maleic anhydride, was studied. Its effects on the properties of acrylic latexes, which were based on emulsion polymerization of butyl acrylate (BA), methyl methacrylate (MMA), acrylic acid (AA) and WHBP, and latex film were discussed. The characteristics of WHBP were determined by nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared (FTIR) and gel permeation chromatography (GPC). Particle size and morphology of latex particles were confirmed by dynamic light scattering (DLS) and transmission electron microscope (TEM). The investigation showed that WHBP could be used in emulsion polymerization, and that latex of poly(BA-MMA-WHBP) was more stable than that of poly(BA-MMA-AA). The hardness of latex film increased from 2B to HB when WHBP was used.     

Low-energy-loss EFTEM imaging of thick particles and aggregates

Electron spectroscopy imaging is a powerful tool for the elucidation of colloidal particle morphology and microchemistry, but it normally requires the use of very thin samples, typically less than 50 nm, to avoid the effects of multiple scattering. This work shows that many aspects of the internal morphology of thick particles and aggregates and the chemical component distribution are revealed using low-energy-loss electron imaging in the transmission electron microscope, benefiting from multiple scattering as well as small but significant differences in the low-energy-loss spectra of aggregate constituents. Low-loss images reveal morphological details of thick aggregates made out of colloidal polymers (natural rubber and styrene-acrylic latex) and inorganic particles (silica, montmorillonite, and aluminum phosphate) at a spatial resolution close to that achieved in the bright-field images and much better than in the elemental maps, showing the advantages of the simultaneous use of low-loss images and standard thin-cut elemental maps.     

Viscoelastic properties of polystyrene and poly(methyl methacrylate) dispersions sterically stabilized by hydrophobically modified inulin (polyfructose) polymeric surfactant

Recently, steric repulsive forces induced by a new graft copolymer surfactant, which is based in inulin (polyfructose), have been described. Previous investigations by atomic force microscopy between solid surfaces covered with adsorbed surfactant indicated strong repulsive forces even at high electrolyte concentration, due to the steric repulsion produced by the surfactant hydration. In the present paper, the colloidal stabilization provided by this surfactant is studied by rheology. The measurements were carried out on sterically stabilized polystyrene (PS) and poly(methyl methacrylate) (PMMA) containing adsorbed surfactant (INUTEC SP1). Steady-state shear stress as a function of shear rate curves was established at various latex volume fractions. The viscosity volume fraction curves were compared with those calculated using the Doughtry-Krieger equation for hard sphere dispersions. From the experimental eta r-phi curves the effective volume fraction of the latex dispersions could be calculated and this was used to determine the adsorbed layer thickness Delta. The value obtained was 9.6 nm, which is in good agreement with that obtained using atomic force microscopy (AFM). Viscoelastic measurements of the various latex dispersions were carried out as a function of applied stress (to obtain the linear viscoelastic region) and frequency. The results showed a change from predominantly viscous to predominantly elastic response at a critical volume fraction (phi c). The effective critical volume fraction, phi eff, was calculated using the adsorbed layer thickness (Delta) obtained from steady-state measurements. For PS latex dispersions phi eff was found to be equal to 0.24 whereas for PMMA phi eff=0.12. These results indicated a much softer interaction between the latex dispersions containing hydrated polyfructose loops and tails when compared with latices containing poly(ethylene oxide) (PEO) layers. The difference could be attributed to the stronger hydration of the polyfructose loops and tails when compared with PEO. This clearly shows the much stronger steric interaction between particles stabilized using hydrophobically modified inulin.     

Identification of novel angiotensin-converting enzyme-inhibitory peptides from ovine milk proteins by CE-MS and chromatographic techniques

In this report, we present the use of CE-MS as complement to RP separation for the identification of novel angiotensin-converting enzyme-inhibitory (ACEI) peptides from a complex milk protein hydrolysate. As preliminary step, fast protein LC (FPLC) was used to isolate the different casein fractions from raw ovine milk. Enzymatic hydrolysis of these fractions was performed by using proteolytic enzymes of gastrointestinal origin. The most active hydrolysate, corresponding to kappa-casein hydrolyzed with pepsin, chymotrypsin, and trypsin, was fractionated by RP-HPLC and the peptides contained in the active fractions were sequenced by CE coupled to IT-MS (CE-MS). The use of CE-MS allowed the identification of short peptides with ACEI activity included in the scarcely retained fraction obtained by semipreparative RP-HPLC. Among the identified peptides, those with hydrophobic or positively charged residues at the C-terminal tripeptide were chemically synthesized to determine their ACEI activity. This procedure allowed us to identify four novel potent ACEI peptides from kappa-casein with sequences IAK, YQQRPVA, WQVLPNAVPAK, and HPHPHLSF. These active sequences could be obtained by enzymatic hydrolysis either of the individual kappa-casein fraction or the total casein fraction from ovine milk.     

On the interaction of HBT with pulp lignin during mediated laccase delignification—a study using fractionated pyrolysis-GC/MS

An analytical method using fractionated pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was developed and applied for characterizing the type of interaction between 1-hydroxybenzotriazole (HBT)-mediator and pulp lignin in laccase delignification of pulp. In fractionated pyrolysis, the sample is pyrolyzed at progressively increasing temperatures in order to study particular fractions of the sample and to minimize secondary pyrolysis effects. This makes it possible to determine whether a certain pyrolysis product originates from one chemical moiety or different chemical moieties in one molecule. In the present method, samples were fractionated by thermal desorption at 200 °C followed by pyrolysis at progressively increasing temperatures from 320 to 800 °C. The products formed in each fraction were separated in a capillary GC column and detected and identified using MS. The type of interaction between HBT and pulp lignin was studied by following the formation of nitrogen-containing products during fractionated pyrolysis of a residual lignin isolated from laccase/HBT-treated oxygen-delignified softwood kraft pulp. This residual lignin was found to contain approximately 2% HBT residue. Most (87%) of this residue was covalently linked to the residual lignin. The results also strongly suggest that the HBT residue is present in two chemically different forms.     

Qualitative and quantitative analysis of lipid extracts from rabbit meat by gas chromatography/mass spectrometry.

Analyses of lipid extracts from rabbit meat were carried out by gas chromatography/mass spectrometry (GC/mS) using both electron and chemical ionisation. Ten rabbit carcasses were randomly acquired on the market, from different farms; for each of them muscular tissues from hindleg and breast were analysed. The lipid fractions were extracted, separated and hydrolysed. The fatty acid fractions were derivatised by 2,2-dimethoxypropane. The GC/mS data obtained using electron ionisation (EI) did not allow the complete characterisation of the fatty acid fraction, and for this reason chemical ionisation (CI) was employed using acetonitrile as reactant gas. The data thus obtained show that, for both samples of rabbit tissue, the mean abundance ratio of plasma cholesterol lowering fatty acids and plasma cholesterol elevating fatty acids (PCL/PCE), taken as a parameter describing a desirable lipid uptake, is 2.2 +/- 0.3, significantly higher than the values reported for other meats (0.8-1. 8). These data, together with the high concentration of (n-6) fatty acids, provide a good indication of the high nutritional value of rabbit meat.     

Population balance modeling of aggregation and breakage in turbulent Taylor-Couette flow

An experimental and computational study of aggregation and breakage processes for fully destabilized polystyrene latex particles under turbulent-flow conditions in a Taylor-Couette apparatus is presented. To monitor the aggregation and breakage processes, an in situ optical imaging technique was used. Consequently, a computational study using a population balance model was carried out to test the various parameters in the aggregation and breakage models. Very good agreement was found between the time evolution of the cluster size distribution (CSD) calculated with the model and that obtained from experiment. In order to correctly model the left-hand side of the CSD (small clusters), it was necessary to use a highly unsymmetric fragment-distribution function for breakage. As another test of the model, measurements with different solid volume fractions were performed. Within the range of the solid volume fractions considered here, the steady-state CSD was not significantly affected. In order to correctly capture the right-hand side of the CSD (large aggregates) at the higher solid volume fraction, a modified aggregation rate prefactor was used in the population balance model.     

稀土顺1,4聚丁二烯的分子缠结与结晶

本文用电镜研究了经过分级得到的不同分子量及不同分子量分布的稀土顺1,4 聚丁二烯(Ln-PB)及镍顺1,4 聚丁二烯(Ni-PB)的低温结晶形态、结晶成核及生长机理。发现低分子量 PB以预现成核为主,而高分子量PB以大分子的缠结为中心的散现成核为主,得到两种不同片层缠结形态的PB球晶。其结晶形态及速率主要受高分子量中的大分子缠结影响。