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Different Molecular Weights (different + molecular_weight)
Selected AbstractsStudy on Flow Induced Nano Structures in iPP with Different Molecular Weight and Resulting Strength BehaviorMACROMOLECULAR SYMPOSIA, Issue 1 2010Achim Frick Abstract Polypropylene samples in a wide molecular weight range between approx. 100,kg/mol to 1 600,kg/mol were processed by injection molding to thin walled micro specimens with respect to study shear induced crystallization phenomena under high shear rate and subsequently possible self reinforcement effects. The specimens nano structures were investigated and related deformation behavior under tensile studied. Novel morphologies have been detect and their micromechanical mechanism interpret and summarized. [source] Antibacterial Activities of Chitosans and Chitosan Oligomers with Different Molecular Weights on Spoilage Bacteria Isolated from TofuJOURNAL OF FOOD SCIENCE, Issue 4 2002H.K. No ABSTRACT Seven bacteria were isolated from spoiled tofu and identified as Bacillus sp. (S08), B. megaterium (S10), B. cereus (S17, S27, S28, S32), and Enterobacter sakazakii (S35). In a paper disc test with 6 chitosans and 6 chitosan oligomers of different molecular weights, chitosans showed higher antimicrobial activity than did chitosan oligomers at a 0.1% concentration. Results of inhibitory effects of 6 chitosans on growth of Bacillus sp. (S08) failed to detect viable cells after incubation for 24 hrs at 37 C, even at 0.02% concentration. With B. megaterium (S10) and B. cereus (S27), a 3 to 4 log cycle reduction was found in the chitosan-treated group. The growth of Enterobacter sakazakii (S35) was completely suppressed in the presence of 0.04% chitosan except for 1 chitosan product. The minimum inhibitory concentration of chitosan differed with products and isolates, ranging from 0.005% to above 0.1%. [source] Processing, Morphology, and Mechanical Properties of Liquid Pool Polypropylene with Different Molecular WeightsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2005Claudia Stern Abstract Summary: The processability, morphology, and resulting mechanical properties of novel polypropylene (PP) samples of varying molecular weight () were studied. A series of homopolymer PP in a wide range from 101,000 to 1,600,000 g,·,mol,1 was polymerised in a liquid pool (LP) under defined conditions. The LP-PP with a well-known polymerisation history was manufactured into micro dumbbell specimens by means of a micro injection-moulding process. The morphology and mechanical properties of the samples were studied by light microscopy, transmission and scanning electron microscopy, and a quasi-static tensile test. Simulation of the filling behaviour of the molten polymer inside the mould shows that the shear rate increases as the molecular weight increases, up to a maximum shear rate of 750,000 s,1. In addition, the present crystallisation time of the high-molecular-weight PP samples is clearly lower than their retardation time; the long macromolecules do not have sufficient time to retard while cooling. As a result of the shear-induced crystallisation, a highly oriented crystalline structure is formed as a function of the acting shear rate. SEM and TEM investigations show the existence of an oriented shish kebab structure. The density of the shish kebab increases as the molecular weight increases. Evaluations of the shear rate and the morphological structure indicate a critical shear rate of about 300,000 s,1. Above this shear rate level, shish kebab structures are favourably formed. The shear-induced crystallisation and, therefore, the preferred formation of a highly oriented shish kebab structure lead, obviously, to unusual solid-state properties of the analysed LP-PP samples. With a tensile strength up to 100 N,·,mm,2 and an attainable strain at break of more than 30%, the mechanical performance is much higher than results ever reported in literature. True strain,stress behaviour of moulded the LP-PP samples of different molecular weight. [source] Grafting of functionalized silica particles with poly(acrylic acid)POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2006Jarkko J. Heikkinen Abstract Two different methods to graft silica particles with poly(acrylic acid) (PAA) were studied. In the first method PAA was reacted with 1,1,-carbonyldiimidazole to give functionalized PAA. The resulting activated carbonyl group reacted easily with 3-aminopropyl-functionalized silica at low temperatures. In the second method 3-glycidoxypropyl-functionalized silica particles were reacted directly with PAA by using magnesium chloride as a catalyst. Different molecular weights of PAAs were used in order to investigate the effect of molecular weight on grafting yields in both methods. The grafting yields were determined with thermogravimetric analysis (TGA). All products were also investigated with IR. The results showed that the yields of reactions performed at ambient temperature by using 1,1,-carbonyldiimidazole-functionalized PAA were the same as with a direct reaction of unfunctionalized PAA and 3-aminopropyl-functionalized silica performed at 153°C. Also in reactions between 3-glycidoxypropyl-functionalized silica and PAA the yields were satisfactory. Copyright © 2006 John Wiley & Sons, Ltd. [source] Physico-chemical properties of protein-bound polysaccharide from Agaricus blazei Murill prepared by ultrafiltration and spray drying processINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 1 2007Joo Heon Hong Summary This study was conducted to develop the powder material and investigate the various physico-chemical properties of protein-bound polysaccharide with different molecular weight from Agaricus blazei Murill using ultrafiltration and spray-drying process. Powder properties of the three spray-dried powders were very different based on their molecular weights. The inlet temperature had less influence than pump rate on particle size of spray-dried powders. The moisture content of powders was increased with increasing pump rate and decreasing inlet temperature. Among these powders, SD-1, the molecular weight of which is below 10 kDa, was less flowable by internal cohesion. The decomposition temperature for the powders was in the range of 200,400 °C and showed relatively good enough for their thermal stabilities. [source] Control of thermo reversible gelation of methylcellulose using polyethylene glycol and sodium chloride for sustained delivery of ophthalmic drugJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2010Mrinal Kanti Bain Abstract The effect of molecular weight of polyethyleneglycol (PEG) and sodium chloride (NaCl) on the gelation temperature of methylcellulose (MC) was studied with the objective to develop a MC based formulation for sustained delivery of ophthalmic drug. The gelation temperature of 1% MC was 60 ± 0.40°C. It was found that the gelation temperature of MC was reduced with the addition of 10% PEG and extent of reduction of gelation temperature was depended on the molecular weight of PEG at same PEG concentration of 10%. The gelation temperature of MC was reduced by 10.4 to 5.9°C with the increasing molecular weight of PEG starting from 400 to 20,000 (Mn) depending on the method of determination of gelation temperature. To reduce the gelation temperature of MC close to physiological temperature (37°C), 6% NaCl was added in the different MC-PEG combinations containing different molecular weight of PEG. It was observed that the drug release time increased from 5 to 8 h with the increase in molecular weight of PEG from 400 to 20,000 (Mn) and this was due to the maximum viscosity and gel strength of MC-PEG20000-NaCl ternary combination. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Role of Mn of PEG in the morphology and properties of electrospun PEG/CA composite fibers for thermal energy storageAICHE JOURNAL, Issue 3 2009Changzhong Chen Abstract As an aim toward developing novel class of form-stable polymer-matrix phase change materials for thermal energy storage, ultrafine composite fibers based on cellulose acetate and polyethylene glycol (PEG) with five different molecular weight (Mn) grades were prepared by electrospinning. The effects of Mn of PEG on morphology, thermal properties and mechanical properties of the composite fibers were studied by field emission scanning electron microscopy, differential scanning calorimetry, and tensile testing, respectively. It was found that the composite fibers were smooth and cylindrical shape, with the average diameters ranging from about 1000 to 1750 nm which increased with Mn of PEG. Thermal analysis results showed that the composite fibers imparted balanced thermal storage and release properties in different temperature ranges with the variation of Mn of PEG. Thermal cycling test indicated that the prepared composites had excellent thermal stability and reliability even they were subjected to 100 heating-cooling thermal cycles. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] The inhibition of blood coagulation by heparins of different molecular weight is caused by a common functional motif,the C-domainJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 5 2003R. Al Dieri Summary.,Background:,Heparins in clinical use differ considerably as to mode of preparation, molecular weight distribution and pharmacodynamic properties. Objectives:,Find a common basis for their anticoagulant action. Methods:,In 50 fractions of virtually single molecular weight (Mr), prepared from unfractionated heparin (UFH) and four low-molecular-weight heparins (LMWH), we determined: (i) the molar concentration of material (HAM) containing the antithrombin binding pentasaccharide (A-domain); (ii) the specific catalytic activity in thrombin and factor Xa inactivation; (iii) the capacity to inhibit thrombin generation (TG) and prolong the activated partial thromboplastin time (APTT). We also calculated the molar concentration of A-domain with 12 sugar units at its non-reducing end, i.e. the structure that carries antithrombin activity (C-domain). Results:,The antithrombin activity and the effects on TG and APTT are primarily determined by the concentration of C-domain and independent of the source material (UFH or LMWH) or Mr. High Mr fractions (>15 000) are less active, probably through interaction with non-antithrombin plasma proteins. Anti-factor Xa activity is proportional to the concentration of A-domain, it is Ca2+ - and Mr-dependent and does not determine the effect on TG and APTT. Conclusion:,For any type of heparin, the capacity to inhibit the coagulation process in plasma is primarily determined by the concentration of C-domain, i.e. the AT-binding pentasaccharide with 12 or more sugar units at its non-reducing end. [source] Stepwise fatigue crack propagation in poly(vinyl chloride)JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 1 2004T. E. Berna-Lara The kinetics and mechanism of fatigue crack growth in poly(vinyl chloride) (PVC) compounds of different molecular weight were studied. The fatigue crack propagation rate of all the PVC compounds followed the Paris law: da/dt = Af ,K. Fatigue crack propagation rate, as reflected by the pre-factor Af in the Paris law, was highly dependent on molecular weight of the resin, strain rate, and temperature. A stepwise mechanism of fatigue crack propagation was observed in all the PVC compounds. Steps were formed by discontinuous growth of the crack through a single craze in the shape of a narrow strip. Step length and lifetime were used to characterize fatigue crack propagation. J. Vinyl Addit. Technol. 10:5,10, 2004. © 2004 Society of Plastics Engineers. [source] Physical Hydrogels of Poly(vinyl alcohol) with Different Syndiotacticity Prepared in the Presence of Lactosilated Chitosan DerivativesMACROMOLECULAR BIOSCIENCE, Issue 9 2003Giancarlo Masci Abstract Poly(vinyl alcohol) (PVA) physical hydrogels were prepared by repeated freeze,thawing cycles using aqueous solutions of two PVA samples having different degrees of syndiotacticity, a-PVA and s-PVA with 55% and 61% of syndiotactic diads, respectively. The hydrogels were prepared in the presence of different amounts of lactosilated chitosan derivatives (LC) of different molecular weight. The PVA stereoregularity was found to have a dramatic effect on the amount of PVA incorporated into the hydrogels, leading to remarkable differences in the swelling degree and porosity of a-PVA and s-PVA hydrogels. A significant amount of LC was retained in the hydrogels after equilibrium swelling. The swelling of the a-PVA hydrogels was found to increase significantly by increasing the amount of LC while it was only slightly increased in the case of s-PVA hydrogels. The amount of LC released after equilibrium swelling was lower when chitosan derivatives with higher molecular weights were used. Increased initial concentrations of LC resulted in much higher porosity of the hydrogels. TGA and DSC studies showed that LC is stabilized by the incorporation in the PVA hydrogels. The melting temperature of the crystalline regions of PVA was not significantly influenced by LC. Conversely, the extension of the crystalline domains increased in the presence of LC. The retention of a chitosan derivative bearing , - D -galactose side chain residues makes these hydrogels potentially useful as scaffolds for hepatocytes culture. Scanning electron micrographs of PVA-LC hydrogels: (a) a-PVA; (b) a-PVA/LC150 80:20; (c) a-PVA/LC150 50:50. [source] Processing, Morphology, and Mechanical Properties of Liquid Pool Polypropylene with Different Molecular WeightsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2005Claudia Stern Abstract Summary: The processability, morphology, and resulting mechanical properties of novel polypropylene (PP) samples of varying molecular weight () were studied. A series of homopolymer PP in a wide range from 101,000 to 1,600,000 g,·,mol,1 was polymerised in a liquid pool (LP) under defined conditions. The LP-PP with a well-known polymerisation history was manufactured into micro dumbbell specimens by means of a micro injection-moulding process. The morphology and mechanical properties of the samples were studied by light microscopy, transmission and scanning electron microscopy, and a quasi-static tensile test. Simulation of the filling behaviour of the molten polymer inside the mould shows that the shear rate increases as the molecular weight increases, up to a maximum shear rate of 750,000 s,1. In addition, the present crystallisation time of the high-molecular-weight PP samples is clearly lower than their retardation time; the long macromolecules do not have sufficient time to retard while cooling. As a result of the shear-induced crystallisation, a highly oriented crystalline structure is formed as a function of the acting shear rate. SEM and TEM investigations show the existence of an oriented shish kebab structure. The density of the shish kebab increases as the molecular weight increases. Evaluations of the shear rate and the morphological structure indicate a critical shear rate of about 300,000 s,1. Above this shear rate level, shish kebab structures are favourably formed. The shear-induced crystallisation and, therefore, the preferred formation of a highly oriented shish kebab structure lead, obviously, to unusual solid-state properties of the analysed LP-PP samples. With a tensile strength up to 100 N,·,mm,2 and an attainable strain at break of more than 30%, the mechanical performance is much higher than results ever reported in literature. True strain,stress behaviour of moulded the LP-PP samples of different molecular weight. [source] New Strategy Targeting Well-Defined Polymethylene- block -Polystyrene Copolymers: The Combination of Living Polymerization of Ylides and Atom Transfer Radical PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 7 2009Jian-Zhuang Chen Abstract Well-defined polymethylene- block -polystyrene (PM- b -PS) diblock copolymers were synthesized via a combination of living polymerization of ylides and atom transfer radical polymerization (ATRP) of styrene. A series of hydroxyl-terminated polymethylenes (PM-OHs) with different molecular weight and narrow molecular weight distribution were prepared using living polymerization of ylides following efficient oxidation in a quantitive functionality. Then, the macroinitiators (PM-MIs (,=,1,900,15,000; PDI,=,1.12,1.23)) transformed from PM-OHs in ,,100% conversion initiated ATRPs of styrene to construct PM- b -PS copolymers. The GPC traces indicated the successful extension of PS segment ( of PM- b -PS,=,5,000,41,800; PDI,=,1.08,1.23). Such copolymers were characterized by 1H NMR and DSC. [source] The effect of polyoxypropylene-montmorillonite intercalates on polymethylmethacrylatePOLYMER COMPOSITES, Issue 1 2009Nehal Salahuddin Polymethylmethacrylate (PMMA)-layered silicate nanocomposites have been prepared by in situ polymerization of commercial type of methylmethacrylate monomer (MMA), for denture base material, into organoclay. Organoclay was prepared through an ion exchange process between sodium cations in montmorillonite and NH3+ groups in polyethertriamine hydrochloride and polyoxypropylene triamine hydrochloride with different molecular weight (5000, 440). X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been used to investigate the structure of the resulting composites. Both intercalated and exfoliated nanocomposites were obtained depending on the type and amount of organoclay. The thermal decomposition temperatures of the nanocomposites were found to be higher than that of pristine polymer. PMMA was strongly fixed to inorganic surfaces, due to cooperative formation of electrostatic bonding between NH3+ group and negatively charged surface of layered silicate and amide linkage between PMMA and polyethertriamine or polyoxypropylene triamine. The effect of the organoclay on the hardness, toughness, tensile stress, and elongation at break of the polymer was studied and was compared with pristine polymer. The hardness and Izod impact strength of PMMA-organoclay nanocomposites were enhanced with the inclusion of clay. Tensile properties appear to be enhanced at certain organoclay content. However, the water absorption is slightly higher than the pristine PMMA. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Preparation of poly(lactic acid)/poly(ethylene glycol)/organoclay nanocomposites by melt compoundingPOLYMER COMPOSITES, Issue 3 2006Shuichi Tanoue Poly(lactic acid) (PLA)/organoclay nanocomposites were prepared by melt compounding in a co-rotating twin screw extruder. Two types of commercialized organoclay (dimethyl benzyl stearyl ammonium ion and dimethyl distearyl ammonium ion intercalated between clay platelets named as Clay A and Clay B, respectively) and two grades of poly(ethylene glycol) (PEG) with different molecular weight (Mw = 2,000 and 300,000,500,000 named as PEG2k and PEG500k, respectively) were used in this study. The Young's modulus improved by the addition of organoclay to PLA matrix. The Young's modulus decreased with the addition of PEG to PLA/organoclay nanocomposites. The tensile strength and elongation of PLA/Clay B nanocomposites increased with the addition of PEG2k. The effect of the addition of PEG on d -spacing of PLA/organoclay nanocomposites is dependent upon the kind of organoclay. The sizes of clay agglomerations in PLA/PEG/organoclay nanocomposites are larger than those of PLA/organoclay ones in the same organoclay. Addition of PEG to PLA/organoclay nanocomposites during melt compounding will not be useful for the preparation of PLA/organoclay having fully exfoliated clay platelets. The shear thinning properties of the nanocomposites are independent of the addition of PEG. On the whole, PEG2k is good plasticizer for PLA/organoclay nanocomposites. POLYM. COMPOS. 27:256,263, 2006. © 2006 Society of Plastics Engineers [source] Layered silicate/epoxy nanocomposites: synthesis, characterization and propertiesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2004Nehal A. Salahuddin Abstract Novel epoxy-clay nanocomposites have been prepared by epoxy and organoclays. Polyoxypropylene triamine (Jeffamine T-403), primary polyethertriamine (Jeffamine T-5000) and three types of polyoxypropylene diamine (Jeffamine D-230, D-400, D-2000) with different molecular weight were used to treat Na-montmorillonite (MMT) to form organoclays. The preparation involves the ion exchange of Na+ in MMT with the organic ammonium group in Jeffamine compounds. X-ray diffraction (XRD) confirms the intercalation of these organic moieties to form Jeffamine-MMT intercalates. Jeffamine D-230 was used as a swelling agent for the organoclay and curing agent. It was established that the d001 spacing of MMT in epoxy-clay nanocomposites depends on the silicate modification. Although XRD data did not show any apparent order of the clay layers in the T5000-MMT/epoxy nanocomposite, transmission electron microscopy (TEM) revealed the presence of multiplets with an average size of 5,nm and the average spacing between multiplets falls in the range of 100 Å. The multiplets clustered into mineral rich domains with an average size of 140,nm. Scanning electron microscopy (SEM) reveals the absence of mineral aggregate. Nanocomposites exhibit significant increase in thermal stability in comparison to the original epoxy. The effect of the organoclay on the hardness and toughness properties of crosslinked polymer matrix was studied. The hardness of all the resulting materials was enhanced with the inclusion of organoclay. A three-fold increase in the energy required for breaking the test specimen was found for T5000-MMT/epoxy containing 7,wt% of organoclay as compared to that of pure epoxy. Copyright © 2004 John Wiley & Sons, Ltd. [source] Protein adsorption and platelet adhesion of polysulfone membrane immobilized with chitosan and heparin conjugatePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2 2003M.-C. Yang Abstract Polysulfone (PSF) membranes were treated with ozone to introduce peroxides, and then grafted with either acrylic acid or chitosan, followed by the immobilization of heparin. The effect of spacer arm on blood compatibility was investigated using three chitosans of different molecular weight [1170 (water soluble), 160,000, and 400,000] and similar degrees of deacetylation (75%). The hydrophilicity was evaluated by measuring the contact angle of water. Blood compatibility was evaluated using the activated partial thromboplastin time (APTT) as well as the adhesion of platelets. The protein affinity was determined by the absorption of human serum albumin (HSA) and human plasma fibrinogen (HPF). The results show that by the coupling of chitosan, the amount of heparin immobilized can be increased by four times. Water contact angle (from 78,° to 41,°) decreased with the increase of the amount of heparin immobilized, showing increased wettability. The heparinized PSF membrane showed longer APTT and decreasing platelet adhesion, compared to that of unmodified PSF membrane. The adsorption of HSA and HPF were reduced to 17 and 6%, respectively. This suggests that longer spacer binding to heparin can increase the opportunity of anti-coagulation on contacting blood. These results demonstrated that the hydrophilicity and blood compatibility of PSF membrane could be improved by chitosan and heparin conjugate. Copyright © 2003 John Wiley & Sons, Ltd. [source] Time-lapsed imaging for in-process evaluation of supercritical fluid processing of tissue engineering scaffoldsBIOTECHNOLOGY PROGRESS, Issue 4 2009Melissa L. Mather Abstract This article demonstrates the application of time-lapsed imaging and image processing to inform the supercritical processing of tissue scaffolds that are integral to many regenerative therapies. The methodology presented provides online quantitative evaluation of the complex process of scaffold formation in supercritical environments. The capabilities of the developed system are demonstrated through comparison of scaffolds formed from polymers with different molecular weight and with different venting times. Visual monitoring of scaffold fabrication enabled key events in the supercritical processing of the scaffolds to be identified including the onset of polymer plasticization, supercritical points and foam formation. Image processing of images acquired during the foaming process enabled quantitative tracking of the growing scaffold boundary that provided new insight into the nature of scaffold foaming. Further, this quantitative approach assisted in the comparison of different scaffold fabrication protocols. Observed differences in scaffold formation were found to persist, post-fabrication as evidenced by micro x-ray computed tomography (, x-ray CT) images. It is concluded that time-lapsed imaging in combination with image processing is a convenient and powerful tool to provide insight into the scaffold fabrication process. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Photoinduced Shuttling Dynamics of Rotaxanes in Viscous Polymer SolutionsADVANCED FUNCTIONAL MATERIALS, Issue 21 2009Dhiredj C. Jagesar Abstract The effect of external friction, caused by medium viscosity, on the photoinduced translational motion in a rotaxane-based molecular shuttle 1 is investigated. The shuttle is successfully operated in solutions of poly(methacrylonitrile) (PMAN) of different molecular weights in MeCN and PrCN. The viscosity of the medium is tuned by changing the PMAN concentration. The rheological behavior of the polymer solution gives insight into the structure of the polymer solution on the microscopic scale. In PrCN, the entanglement regime is reached at lower concentration than in MeCN. This is also reflected by the effect on the shuttling: in the PrCN/PMAN system, a larger viscosity effect is observed compared to MeCN/PMAN. The shuttle is found to be slowed down in the polymer solutions but is still active at high viscosities. The observed retardation effect on the kinetics of shuttling in MeCN/PMAN and PrCN/PMAN can be correlated to the PMAN concentration through the hydrodynamic scaling model. The Stokes,Einstein relationship proves inadequate to correlate the shuttling rates to macroscopic viscosity, but the dependence of the shuttling rate on the bulk viscosity fits well to a commonly observed power-law relationship. The viscosity effect on the shuttling is found to be weak in all cases. [source] Perpendicularly Aligned, Size-and Spacing-Controlled Nanocylinders by Molecular-Weight Adjustment of a Homopolymer Blended in an Asymmetric Triblock CopolymerADVANCED FUNCTIONAL MATERIALS, Issue 15 2006U. Ahn Abstract Perpendicularly arrayed and size-controlled nanocylinders have been prepared by simply blending an asymmetric polystyrene- block -polyisoprene- block -polystyrene triblock copolymer with polystyrene (the minority component) homopolymers of different molecular weights. The preference for perpendicular orientation or hexagonal ordering of the nanocylinders over a large area in the asymmetric block copolymer can be controlled by adjusting the molecular weight of the blended homopolymer, and the perfection of hexagonal ordering of the perpendicular cylinders can be tuned by using a substrate whose surface tension is much different from that of the majority component of the block copolymer. Such highly controlled nanostructured block-copolymer materials, which have been obtained by a simple method independent of film thickness and interfacial tension between the blocks and the substrates, have wide-ranging commercial potential, e.g., for use in membranes and nanotemplates with size-tunable pores, bandgap-controlled photonic crystals, and other nanotechnological fields demanding a specific nanosize and nanomorphology. [source] Controlled Degradability of Polysaccharide Multilayer Films In Vitro and In Vivo,ADVANCED FUNCTIONAL MATERIALS, Issue 11 2005C. Picart Abstract This article demonstrates the possibility of tuning the degradability of polysaccharide multilayer films in vitro and in vivo. Chitosan and hyaluronan multilayer films (CHI/HA) were either native or crosslinked using a water soluble carbodiimide, 1-ethyl-3-(3-dimethylamino-propyl)carbodiimide (EDC) at various concentrations in combination with N-hydroxysulfosuccinimide. The in-vitro degradation of the films in contact with lysozyme and hyaluronidase was followed by quartz crystal microbalance measurements, fluorimetry, and confocal laser scanning microscopy after labeling of the chitosan with fluorescein isothiocyanate (CHIFITC). The native films were subjected to degradation by these enzymes, and the crosslinked films were more resistant to enzymatic degradation. Films made of chitosan of medium molecular weight were more resistant than films made of chitosan-oligosaccharides. The films were also brought in contact with plasma, which induced a change in film structure for the native film but did not have any effect on the crosslinked film. The in-vitro study shows that macrophages can degrade all types of films and internalize the chitosan. The in-vivo degradation of the films implanted in mouse peritoneal cavity for a week again showed an almost complete degradation of the native films, whereas the crosslinked films were only partially degraded. Taken together, these results suggest that polysaccharide multilayer films are of potential interest for in-vivo applications as biodegradable coatings, and that degradation can be tuned by using chitosan of different molecular weights and by controlling film crosslinking. [source] Cytokeratin profiles of the thymus and thymomas: histogenetic correlations and proposal for a histological classification of thymomasHISTOPATHOLOGY, Issue 5 2000Aims Since cytokeratins (CKs) are useful as differentiation markers for histogenetic and classification studies, we investigated the CK profiles of the thymus and thymomas in an attempt to understand the histogenetic correlation and to propose a histological classification. Methods and results Nine thymuses and 34 thymomas were immunostained for various CKs of different molecular weights and involucrin. Based on cytomorphology and histoarchitecture, thymomas were classified into spindle cell (SC), small polygonal cell (SPC), mixed, organoid, large polygonal cell (LPC) and squamoid (SQ) thymomas for compiling CK profiles. The thymus was shown to comprise four epithelial compartments, each expressing a different CK profile. Different histological types of thymoma expressed different CK profiles. By correlating the CK profiles of the thymus and thymoma, SPC, SC and LPC thymomas appeared to be related to subcapsular, medullary and cortical cells, respectively. Organoid thymoma recapitulated the structure and CK profile of the normal thymus, while SQ thymoma acquired additional squamous type CK. The applicability and usefulness of the proposed histological classification were evaluated on 147 thymomas by correlating the results with their invasive behaviour. One hundred and thirty-nine cases (95%) could be classified and different histological types correlated strongly with their invasive behaviour. Conclusions The thymus is a complex epithelial organ composed of heterogeneous cell types giving rise to various related histological types of thymoma. The results of the CK profile study supports the proposed histological classification, which is pathologically applicable and clinically useful in correlating with invasiveness. This cytomorphological classification, supported by the CK expression patterns, is comparable to Müller-Hermelink classification and the new WHO histological classification except that a separate group of SPC thymoma expressing only CK14 and CK19 was identified and separated from mixed thymoma. [source] Preparation of tofu using chitosan as a coagulant for improved shelf-lifeINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 2 2004Hong Kyoon No Summary The potential of chitosan as a coagulant in commercial tofu preparation was investigated with six chitosans of different molecular weights using various treatments. The following optimum processing conditions for tofu preparation were proposed: chitosan with a molecular weight of 28 kDa; chitosan solution type, 1% chitosan/1% acetic acid; chitosan solution to soymilk ratio, 1 : 8; coagulation temperature, 80 °C; coagulation time, 15 min. However, the sensory quality of tofu was notably improved using a 1 : 1 mixture of 1% acetic acid and 1% lactic acid instead of 1% acetic acid alone as a chitosan solvent. Tofu prepared with chitosan had lower ash and higher protein content than those of commercial products tested. In storage tests, the chitosan-tofu had a longer shelf-life, about 3 days, than tofu made with CaCl2. This added shelf-life is significant in view of the magnitude (366 000 tonnes year,1) of tofu produced from commercial tofu plants (1407 plants as of 1998) in Korea. [source] Immobilisation of the BINAP Ligand on Dendrimers and Hyperbranched Polymers: Dependence of the Catalytic Properties on the Linker UnitADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009Jutta Abstract A series of immobilised Carbo-BINAP ligands has been synthesised using poly(propylene imine) (PPI) dendrimers as soluble supports. They contain up to 64 BINAP ligands at their periphery without an additional linking unit. Despite the high steric requirements of the ligand, all dendrimers could be completely functionalised, resulting in the immobilised systems in good yields. Furthermore, the immobilisation strategy that worked out for the fixation of AMINAP ligands with additional linking units as well as of Carbo-BINAP ligands without additional linking units on dendrimers has thus been extended to less regularly hyperbranched poly(ethylene imines) (PEI) as soluble supports. In that way it has been possible to attach on average 9, 26, and 138 Glutaroyl-AMINAP or Carbo-BINAP ligands to PEIs of different molecular weights. The catalytic properties of these systems in the copper-catalysed hydrosilylation of acetophenone were investigated. The dendritic PPI-bound Carbo-BINAP ligands displayed a strong dependence of enantioselectivity and activity on the generation of the dendrimer. For the Carbo-BINAP and Glutaroyl-AMINAP ligands immobilised on the hyperbranched polymers, however, activities and enantioselectivities comparable to those of the mononuclear catalysts were found. The macromolecular, immobilised BINAP ligands could be recycled several times without any observable loss of activity or enantioselectivity. [source] Rheological behavior and mechanical properties of high-density polyethylene blends with different molecular weightsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010Lu Bai Abstract The dynamic rheological and mechanical properties of the binary blends of two conventional high-density polyethylenes [HDPEs; low molecular weight (LMW) and high molecular weight (HMW)] with distinct different weight-average molecular weights were studied. The rheological results show that the rheological behavior of the blends departed from classical linear viscoelastic theory because of the polydispersity of the HDPEs that we used. Plots of the logarithm of the zero shear viscosity fitted by the Cross model versus the blend composition, Cole,Cole plots, Han curves, and master curves of the storage and loss moduli indicated the LMW/HMW blends of different compositions were miscible in the melt state. The tensile yield strength of the blends generally followed the linear additivity rule, whereas the elongation at break and impact strength were lower than those predicted by linear additivity; this suggested the incompatibility of the blends in solid state. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Competitive plasticization in ternary plasticized starch biopolymer systemJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010Deeptangshu S. Chaudhary Abstract Two plasticizers namely, glycerol and xylitol, based on their similar molecular diameter (, 6.3 Å) but different molecular weights (glycerol-92; xylitol-152) were selected were selected for studying the plasticization of starch biopolymer containing 70% amylopectin structure via glass transition measurements carried over a wide range of water activity. A standard calorimetry was used to determine the onset temperature of polymeric viscous flow. For both glycerol and xylitol, typical antiplasticization was evident at low plasticizer concentrations, whereas at higher concentration, there was significant reduction in glass transition temperature. Water activity isotherms showed that equilibrium moisture content of the starch biopolymer (no plasticizer) steadily increases up to 11%, however, for plasticized biopolymer, the moisture content was nearly double than that of biopolymer. We used a modified Gordon-Taylor model, using a new interaction parameter, to understand the competitive plasticization of glycerol and xylitol in presence of water, and determined 8 wt % water as a threshold amount of matrix water for strong three-way interactions: starch-plasticizer, plasticizer-plasticizer/water and starch-water. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Microencapsulation of doxycycline into poly(lactide- co -glycolide) by spray drying technique: Effect of polymer molecular weight on process parametersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Pradip Patel Abstract Poly(lactide- co -glycolide) (PLGA) polymers with three different molecular weights were prepared, and microparticles were produced by spray drying and water-in-oil-water (w/o/w) double emulsion techniques to encapsulate 86% of doxycycline (DXY), an antibiotic drug, for the use of periodontitis. Placebo and drug-loaded microspheres and pristine DXY were analyzed by Fourier transform infrared spectroscopy, which indicated no chemical interactions between DXY and PLGA. X-ray diffraction of drug-loaded microspheres confirmed the molecular level dispersion of DXY in PLGA. Scanning electron microscopy confirmed spherical nature and smooth surfaces of the microspheres. Mean particle size as measured by laser light scattering technique ranged between 10 and 25 ,m. In vitro release of DXY performed in 7.4 pH media continued up to 72 h and depended on molecular weight of PLGA and extent of DXY loading. Antimicrobial studies performed on one formulation and placebo microspheres suggested that drug concentrations during in vitro release are above the minimum inhibitory concentration (MIC) for Staphylococcus aureus growth. Overall, the release studies depended on the molecular weight of PLGA, extent of drug loading, and the method used to prepare microspheres. Statistical analyses of release data performed using the analysis of variance (ANOVA) method agreed well with experimental observations. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Chitosan-alginate films prepared with chitosans of different molecular weightsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 4 2001Xiao-Liang Yan Abstract Chitosan-alginate polyelectrolyte complex (CS-AL PEC) is water insoluble and more effective in limiting the release of encapsulated materials compared to chitosan or alginate. Coherent CS-AL PEC films have been prepared in our laboratory by casting and drying suspensions of chitosan-alginate coacervates. The objective of this study was to evaluate the properties of the CS-AL PEC films prepared with chitosans of different molecular weights. Films prepared with low-molecular-weight chitosan (Mv 1.30 × 105) were twice as thin and transparent, as well as 55% less permeable to water vapor, compared to films prepared with high-molecular-weight chitosan (Mv 10.0 × 105). It may be inferred that the low-molecular-weight chitosan reacted more completely with the sodium alginate (Mv 1.04 × 105) than chitosan of higher molecular weight. A threshold molecular weight may be required, because chitosans of Mv 10.0 × 105 and 5.33 × 105 yielded films with similar physical properties. The PEC films exhibited different surface properties from the parent films, and contained a higher degree of chain alignment with the possible formation of new crystal types. The PEC films exhibited good in vitro biocompatibility with mouse and human fibroblasts, suggesting that they can be further explored for biomedical applications. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 358,365, 2001 [source] Effect of Soluble Soybean Protein Hydrolysate-Calcium Complexes on Calcium Uptake by Caco-2 CellsJOURNAL OF FOOD SCIENCE, Issue 7 2008Y. Lv ABSTRACT:, Soybean protein hydrolysates (SPHs) bind with calcium, forming soluble SPH-calcium complexes via the carboxyl groups of glutamic and aspartic acid residues. However, their effect on calcium uptake is still unclear. In this study, Caco-2 cells were used to estimate the effect of SPH-calcium complexes with different molecular weights on calcium uptake in vitro. The changes in intracellular calcium ion concentration were measured by Fura-2 loading and expressed in fluorescence intensity. SPH-calcium complexes could promote calcium uptake. Improved fluorescence intensity was significantly different in SPH-calcium complexes (10 to 30 kDa), SPH-calcium complexes (3 to 10 kDa), and SPH-calcium complexes (1 to 3 kDa). The maximum levels of relative fluorescence intensity (18.3) occurred with SPH-calcium complexes (10 to 30 kDa). The effect of SPH-calcium complexes (10 to 30 kDa) on Ca2+ increase was determined to be concentration dependent in the range of 0.5 to 4 mg/mL. Our results indicate that soybean protein itself might be responsible for promoting calcium absorption. [source] Antibacterial Activities of Chitosans and Chitosan Oligomers with Different Molecular Weights on Spoilage Bacteria Isolated from TofuJOURNAL OF FOOD SCIENCE, Issue 4 2002H.K. No ABSTRACT Seven bacteria were isolated from spoiled tofu and identified as Bacillus sp. (S08), B. megaterium (S10), B. cereus (S17, S27, S28, S32), and Enterobacter sakazakii (S35). In a paper disc test with 6 chitosans and 6 chitosan oligomers of different molecular weights, chitosans showed higher antimicrobial activity than did chitosan oligomers at a 0.1% concentration. Results of inhibitory effects of 6 chitosans on growth of Bacillus sp. (S08) failed to detect viable cells after incubation for 24 hrs at 37 C, even at 0.02% concentration. With B. megaterium (S10) and B. cereus (S27), a 3 to 4 log cycle reduction was found in the chitosan-treated group. The growth of Enterobacter sakazakii (S35) was completely suppressed in the presence of 0.04% chitosan except for 1 chitosan product. The minimum inhibitory concentration of chitosan differed with products and isolates, ranging from 0.005% to above 0.1%. [source] Core,shell structure and segregation effects in composite droplet polymer blendsAICHE JOURNAL, Issue 4 2003Joël Reignier Core,shell morphology formation within the dispersed phase was studied for composite droplet polymer-blend systems comprising a high-density polyethylene matrix, polystyrene shell and different molecular weights of poly(methyl methacrylate) core material. The blends were prepared in the melt using an internal mixer, and the morphology was analyzed by electron microscopy. Changing the viscoelastic properties of the core in the dispersed phase dramatically affects PS-PMMA segregation within the dispersed composite droplet itself. A high-molecular-weight-PMMA core contains a large quantity of occluded PS inclusions, while the low-molecular-weight PMMA results in a perfectly segregated PS shell and PMMA core. These phenomena were attributed to the viscosity of the PMMA. Using the latter system, a direct microscopic study of the shell formation process demonstrates unambiguously that under conditions of perfect segregation, the onset of complete shell formation corresponds to a shell thickness that is close to two times the radius of gyration of polystyrene. Thus, the thinnest possible shell in such a system possesses a molecular-scale thickness. The system with the high-molecular-weight-PMMA core demonstrates an onset of complete shell formation that is displaced to higher concentrations due to the poor segregation effect. By counterbalancing the effects of viscosity ratio and interfacial effects on the composite droplet size, it is possible to generate perfectly segregated core,shell dispersed-phase morphologies of almost identical size with a controlled shell thickness ranging from 40 to 300 nm. [source] | |||||||||||||||||||||||||||||||