Effect of annealing on the viscoelastic and viscoplastic responses of low-density polyethylene

Two series of tensile tests with constant crosshead speeds (ranging from 5 to 200 mm/min) and tensile relaxation tests (at strains from 0.03 to 0.09) were performed on low-density polyethylene in the subyield region of deformations at room temperature. Mechanical tests were carried out on nonannealed specimens and on samples annealed for 24 h at the temperatures T = 50, 60, 70, 80, and 100 degreesC. Constitutive equations were derived for the time-dependent response of semicrystalline polymers at isothermal deformations with small strains. A polymer is treated as an equivalent heterogeneous network of chains bridged by temporary junctions (entanglements, physical crosslinks, and lamellar blocks). The network is thought of as an ensemble of mesoregions linked with each other. The viscoelastic behavior of a polymer is modeled as a thermally induced rearrangement of strands (separation of active strands from temporary junctions and merging of dangling strands with the network). The viscoplastic response reflects sliding of junctions in the network with respect to their reference positions driven by macrostrains. Stress-strain relations involve five material constants that were found by fitting the observations.

The viscoelastic and viscoplastic behavior of low-density polyethylene

Three series of tensile tests with constant cross-head speeds (ranging from 5 to 200 mm/min), tensile relaxation tests (at strains from 0.03 to 0.09) and tensile creep tests (at stresses from 2.0 to 6.0 MPa) are performed on low-density polyethylene at room temperature. Constitutive equations are derived for the time-dependent response of semicrystalline polymers at isothermal deformation with small strains. A polymer is treated as an equivalent heterogeneous network of chains bridged by temporary junctions (entanglements, physical cross-links and lamellar blocks). The network is thought of as an ensemble of meso-regions linked with each other. The viscoelastic behavior of a polymer is modelled as thermally-induced rearrangement of strands (separation of active strands from temporary junctions and merging of dangling strands with the network). The viscoplastic response reflects mutual displacement of meso-domains driven by macro-strains. Stress-strain relations for uniaxial deformation are developed by using the laws of thermodynamics. The governing equations involve five material constants that are found by fitting the observations. Fair agreement is demonstrated between the experimental data and the results of numerical simulation.

Synthesis of chitosan-stabilized gold nanoparticles in the absence/presence of tripolyphosphate

Gold nanoparticles were prepared by reducing gold salt with a polysaccharide, chitosan, in the absence/ presence of tripolyphosphate (TPP). Here, chitosan acted as a reducing/stabilizing agent. The obtained gold nanoparticles were characterized with UV-vis spectroscopy and transmission electron microscopy. The results indicated that the shape and size distribution of gold nanoparticles changed with the molecular weight and concentration of chitosan. More interestingly, the gelation of chitosan upon contacting with polyanion (TPP) can also affect the shape and size distribution of gold nanoparticles. By adding TPP to chitosan solution before the reduction of gold salt, gold nanoparticles have a bimodal size distribution, and at the same time, polygonal gold particles were obtained in addition to spherical gold nanoparticles.

Nonradiative energy transfer study on the interface of compatibilized linear low density polyethylene/poly(methyl methacrylate) blends

Blends of chromophore-labeled LLDPE and chromophore-labeled PMMA compatibilized by block copolymer of hydrogenated polybutadiene and methyl methacrylate (PHB-b-PMMA) were studied by nonradiative energy transfer (NRET) technique. The ratio of fluorescence intensity of the donor at 336 nm and the acceptor at 408 nm (I-D/I-A) decreased with an increase in block copolymer content. At about 8 wt.-% block copolymer content I-D/I-A reached a minimum value, indicating the interdiffusion of LLDPE chains and PMMA chains in the interface is strongest. The influence of temperature on the interdiffusion of polymer chains in the interface was also examined. Samples quenched in liquid nitrogen from 140 degrees C showed lower energy transfer efficiencies than those annealed from 150 degrees C to room temperature.

A DYNAMIC LASER LIGHT-SCATTERING STUDY OF CHITOSAN IN AQUEOUS-SOLUTION

The solution behavior of four chitosans (91% deacetylated chitin) with different molecular weights in 0.2M CH3COOH/0.1M CH3COONa aqueous solution was investigated at 25 degrees C by dynamic laser light scattering (LLS). The Laplace inversion of the precisely measured intensity-intensity time correlation function leads us to an estimate of the line-width distribution G(Gamma), which could be further reduced to a translational diffusion coefficient distribution G(D). By using a combination of static and dynamic LLS results, i.e. Mw and G(D), we were able to establish a calibration of D = k(D)M(-alpha D) with k(D) = (3.14 +/- 0.20) X 10(-4) and alpha(D) = 0.655 +/- 0.015. By using this calibration, we successfully converted G(D) into a molecular weight distribution f(w)(M). The larger alpha(D) value confirms that the chitosan chain is slightly extended in aqueous solution even in the presence of salts. This is mainly due to its backbone and polyelectrolytes nature. As a very sensitive technique, our dynamic LLS results also revealed that even in dilute solution chitosan still forms a small amount of larger sized aggregates that have ben overlooked in previous studies. The calibration obtained in this study will provide another way to characterize the molecular weight distribution of chitosan in aqueous solution at room temperature. (C) 1995 John Wiley & Sons, Inc.

MOLECULAR CHARACTERISTICS AND CRYSTALLINE-STRUCTURE OF ETHYLENE-DIMETHYLAMINOETHYL-METHACRYLATE COPOLYMERS

The relationship between molecular and crystalline structural characteristics of the ethylene -dimethylaminoethylmethacrylate copolymers (EDAM) was investigated and related to melt flow index MI and average gross content of DAM comonomer, in comparison with low density polyethylene (LDPE) produced by the common high-pressure radical polymerization process. Although the average molecular weight and its distribution are influenced predominantly by the polymerization conditions, DAM-content seems not to depend significantly on molecular weight according to the GPC-FT/IR measurement. Comonomer sequence distributions were determined quantitatively with the C-13-NMR spectra entirely assigned by DEPT and H-1-C-13 COSY techniques. The result suggests the alternating copolymerization tendency and surprisingly coincides with the simulation out-puts based on the assumption of continuous complete mixing reactor model, using Mayo-Lewis equation and the same Q-e values as previously reported on different types of copolymers such as EVA and St.DAM (VA;vinylacetate, St;styrene). It was confirmed by WAXD and SAXS analyses that the crystallinity X(c) and the thickness of lamellar crystal l(c) decreased with increasing DAM-content, whereas the a-lattice and b-lattice dimensions enlarged. X(c) and l(c) can definitely be correlated to the heats of fusion and crystallization measured by DSC. The average size of spherulites measured with light scattering photometry tends to be enlarged with decreasing molecular weight (increasing MI) and DAM-content.

First molluscan TNFR homologue in Zhikong scallop: Molecular characterization and expression analysis

Tumor necrosis factor receptors (TNFRs) are a superfamily of proteins characterized by the unique cysteine-rich domain (CRD) and their important roles in diverse physiological and pathological events such as inflammation, apoptosis, autoimmunity and organogenesis. The first member of the molluscan TNFR family, designated as CfTNFR, was identified from Zhikong scallop Chlamys farreri by expressed sequence tag (EST) and rapid amplification of cDNA ends (RACE) approaches. The full-length cDNA of CfTNFR was of 1334 bp, consisting of a 5' UTR of 17 bp, a 3'UTR of 69 by with a poly (A) tail, and an open reading frame (ORE) of 1248 by encoding a polypeptide of 415 amino acids with a theoretical isoelectric point of 8.33 and predicted molecular weight of 47.07 kDa. There were a signal peptide, a CRD, a transmembrane region and a death domain in the deduced amino acid sequence of CfTNFR, suggesting that it was a typical type 1 membrane protein. The high identities (22-40%) of CfTNFR with other TNFR superfamily members indicated that CfTNFR should be a member of TNFR superfamily, and moreover, it should be the first death domain-containing TNFR found in invertebrates. Phylogenetic analysis revealed that CfTNFR was closely related to TNFR-like proteins from Strongylocentrotus purpuratus, Drosophila melanogaster and Ciona intestinalis, and they formed a separate branch apart from vertebrate TNFRs. The spatial expression of CfTNFR transcripts in healthy and bacteria challenged scallops was examined by quantitative real-time PCR. CfTNFR transcripts could be detected in all tested tissues, including haemocytes, gonad, gill, mantle and hepatopancreas, and significantly up-regulated in the tissues of gonad, gill, mantle and hepatopancreas after Listonella anguillarum challenge, indicating that CfTNFR was constitutive and inducible acute-phase protein involved in immune defence. The present results suggested the existence of the TNFR-like molecules and TNF-TNFR system in low invertebrates, and provided new insights into the role of CfTNFR in scallop innate immune responses to invading microorganisms. (C) 2009 Elsevier Ltd. All rights reserved.

Antimicrobial activity of hydroxylbenzenesulfonailides derivatives of chitosan, chitosan sulfates and carboxymethyl chitosan

Chitosan, carboxymethyl chitosan (CIVICS) and chitosan sulfates (CSS) with different molecular weight were modified by reacting with 4-hydroxyl-5-chloride-1,3-benzene-disulfo-chloride or 2-hydroxyl-5-chloride-1,3 -benzene-disulfo-chloride to give 12 kinds of new hydroxylbenzenesulfonailides derivatives of them. The preparation conditions of the derivatives were discussed in this paper, and their structures were characterized by FT-IR and C-13 NMR spectroscopy. The solubility of the derivatives was measured in the experiment. In addition, their antimicrobial activities against four bacteria and five crop-threatening pathogenic fungi were tested in the experiment. Besides, the rule and mechanism of their antibacterial activities were discussed in this paper. (C) 2009 Published by Elsevier B.V.

Preparation, characterization and antifungal properties of 2-(alpha-arylamino phosphonate)-chitosan

In this paper, 20 kinds of different 2-(alpha-arylamino phosphonate)-chitosan (2-alpha-AAPCS) were prepared by different Schiff bases of chitosan (CS) reacted with di-alkyl phosphite in benzene solution. The structures of the derivatives (2-alpha-AAPCS) were characterized by FT-IR spectroscopy and elemental analysis. In addition, the antifungal activities of the derivatives against four kinds of fungi were evaluated in the experiment. The results indicated that all the prepared 2-alpha-AAPCS had a significant inhibiting effect on the investigated fungi when the derivatives concentration ranged from 50 to 500 mu g mL(-1). Furthermore, the antifungal activities of the derivatives increased with increasing the molecular weight and concentration. And the antifungal activities of the derivatives were affected by their dimensional effect and charge density. Besides, the rule and mechanism of the antifungal activities of them were discussed in this paper. (C) 2009 Elsevier B.V. All rights reserved.

Salt-assisted acid hydrolysis of chitosan to oligomers under microwave irradiation

The effect of inorganic salts such as sodium chloride on the hydrolysis of chitosan in a microwave field was investigated. While it is known that microwave heating is a convenient way to obtain a wide range of products of different molecular weights only by changing the reaction time and/or the radiation power, the addition of some inorganic salts was shown to effectively accelerate the degradation of chitosan under microwave irradiation. The molecular weight of the degraded chitosan obtained by microwave irradiation was considerably lower than that obtained by traditional heating. Moreover, the molecular weight of degraded chitosan obtained by microwave irradiation assisted under the conditions of added salt was considerably lower than that obtained by microwave irradiation without added salt. Furthermore, the effect of ionic strength of the added salts was not linked with the change of molecular weight. FTIR spectral analyses demonstrated that a significantly shorter time was required to obtain a satisfactory molecular weight by the microwave irradiation-assisted inorganic salt method than by microwave irradiation without inorganic salts and conventional technology. (C) 2005 Elsevier Ltd. All rights reserved.

Synthesis and antifungal properties of sulfanilamide derivatives of chitosan

Sulfanilamide derivatives of chitosan (2-(4-acetamido-2-sulfanimide)-chitosan (HSACS, LSACS), 2-(4-acetamido-2-sulfanimide)-6-sulfo-chitosan (HSACSS, LSACSS) and 2-(4-acetamido-2-sulfanimide)-6-carboxymethyl-chitosan (HSACMCS, LSACMCS)) were prepared using different molecular weights of chitosan (CS), carboxymethyl chitosan (CMCS) and chitosan sulfates (CSS) reacted with 4-acetamidobenzene sulfonyl chloride in dimethylsulfoxide solution. The structures of the derivatives were characterized by FT-IR spectroscopy and elemental analysis, which showed that the substitution degree of sulfanilamide group of HSACS, HSACSS, HSACMCS, LSACS, LSACSS and LSACMCS were 0.623, 0.492, 0.515, 0.576, 0.463 and 0.477, respectively. The solubility of the derivatives (pH < 7.5) was higher than that of chitosan (pH < 6.5). The antifungal activities of the derivatives against Aiternaria solani and Phomopsis asparagi were evaluated based on the method of Jasso et al. in the experiment. The results indicated that all the prepared sulfanilamide derivatives had a significant inhibiting effect on the investigated fungi in the polymer concentration range from 50 to 500 mu g mL(-1). The antifungal activities of the derivatives increased with increasing the molecular weight, concentration or the substitution degree. The sulfanilamide derivatives of CS, CMCS and CSS show stronger antifungal activities than CS, CMCS and CSS. (C) 2007 Elsevier Ltd. All rights reserved.

The preparation and antioxidant activity of the sulfanilamide derivatives of chitosan and chitosan sulfates

Chitosan (CS) and chitosan sulfates (CSS) with different molecular weight (Mw) were reacted with 4-acetamidobenzene sulfonyl chloride to obtain sulfanilamide derivatives of chitosan and chitosan sulfates (LSACS, HSACS, LSACSS, HSACSS). The preparation conditions such as different reaction time, temperature, solvent, and the molar ratio of reaction materials are discussed in this paper. Their structures were characterized by FTIR spectroscopy and elemental analyses. The antioxidant activities of the derivatives were investigated employing various established in vitro systems, such as hydroxyl-radical (OH) superoxide anion (O-2(center dot-)) scavenging and reducing power. All kinds of the compounds (HCS, LCS, HCSS, LCSS, HSACS, LSACS, HSACSS, LSACSS) showed stronger scavenging activity on hydroxyl radical than ascorbic acid (Vc). The inhibitory activities of the derivatives toward superoxide radical by the PMS-NADH system were obvious. The experiment showed that the superoxide radical scavenging effect of sulfanilamide derivatives of chitosan and chitosan sulfates was stronger than that of original CS and CSS. All of the derivatives were efficient in the reducing power. The results indicated that the sulfanilamide group were grafted on CS and CSS increased the reducing power of them obviously. (c) 2007 Elsevier Ltd. All rights reserved.

The preparation and antioxidant activity of 2-[phenylhydrazine (or hydrazine)-thiosemicarbazone]-chitosan

Chitosan (CS) with two different molecular weight were modified by reacting with methyl hydrazine-dithiocarboxylate and methyl phenylhydrazine-dithiocarboxylate to give 2-(hydrazine-thiosemicarbazone)-chitosan (2-HTCHCS, 2-HTCLCS) and 2-(phenylhydrazine-thiosemicarbazone)chitosan (2-PHTCHCS, 2-PHTCLCS). The structure of the derivatives was characterized by FT-IR spectroscopy and elemental analysis. The antioxidant activities of the derivatives were investigated employing various established systems, such as hydroxyl radical (*OH)/superoxide anion (O-2(center dot-)) scavenging/reducing power and chelating activity. All of the derivatives showed strong scavenging activity on hydroxyl radical than chitosan and ascorbic acid (Vc), and IC50 of 2-HTCHCS, 2-HTCLCS, 2-PHTCHCS and 2-PHTCLCS was 0.362, 0.263, 0.531 and 0.336 mg/mL respectively. The inhibitory activities of the derivatives toward superoxide radical by the PMS-NADH system were strong. The results showed that the superoxide radical scavenging effect of 2-[phenylhydrazine (or hydrazine)-thiosemicarbazone]-chitosan were higher than that of chitosan. The derivatives had obviously reducing power and chelating activity. The data obtained from vitro models clearly establish the antioxidant potency of 2-[phenylhydrazine (or hydrazine)-thiosemicarbazone]-chitosan. (C) 2010 Elsevier B.V. All rights reserved.

光致聚合物中单体及粘结剂对全息性能的影响

研究了单体及粘结剂等成份对全息光致聚合物薄膜光存储性能的影响。在相同引发条件下．以丙烯酰胺作为单体时，光聚物的衍射效率明显高于以丙烯酸和N羟甲基丙烯酰胺作为单体时光聚物的衍射效率。向丙烯酰胺中加入少量N-羟甲基丙烯酰胺，可以改善膜表面的光学质量．降低散射光强度，并提高膜的保存时间。在聚乙烯醇膜中单体聚合程度明显优于在聚乙烯吡咯烷酮中的程度，在大分子量的聚乙烯醇中的衍射效率及感光灵敏度高于在小分子量中的衍射效率和感光灵敏度，而且大分子量的聚乙烯醇能够制备厚膜，这是实现全息海量存储的一个重要因素。

A NOVEL PLASMINOGEN-ACTIVATOR FROM SNAKE-VENOM - PURIFICATION, CHARACTERIZATION, AND MOLECULAR-CLONING

A novel plasminogen activator from Trimeresurus stejnegeri venom (TSV-PA) has been identified and purified to homogeneity. It is a single chain glycoprotein with an apparent molecular weight of 33,000 and an isoelectric point of pH 5.2. It specifically activates plasminogen through an enzymatic reaction. The activation of human native GIu-plasminogen by TSV-PA is due to a single cleavage of the molecule at the peptide bond Arg(561)-Val-(562). Purified TSV-PA, which catalyzes the hydrolysis of several tripeptide p-nitroanilide substrates, does not activate nor degrade prothrombin, factor X, or protein C and does not clot fibrinogen nor show fibrino(geno)lytic activity in the absence of plasminogen. The activity of TSV-PA was readily inhibited by phenylmethanesulfonyl fluoride and by p-nitrophenyl-p-guanidinobenzoate. Oligonucleotide primers designed on the basis of the N-terminal and the internal peptide sequences of TSV-PA were used for the amplification of cDNA fragments by polymerase chain reaction. This allowed the cloning of a full-length cDNA encoding TSV-PA from a cDNA library prepared from the venom glands. The deduced complete amino acid sequence of TSV-PA indicates that the mature TSV-PA protein is composed of 234 amino acids and contains a single potential N-gIycosylation site at Asn(1G1). The sequence of TSV-PA exhibits a high degree of sequence identity with other snake venom proteases: 66% with the protein C activator from Aghistrodon contortrix contortrix venom, 63% with batroxobin, and 60% with the factor V activator from Russell's viper venom. On the other hand, TSV-PA shows only 21-23% sequence similarity with the catalytic domains of u-PA and t-PA. Furthermore, TSV-PA lacks the sequence site that has been demonstrated to be responsible for the interaction of t-PA (KHRR) and u-PA (RRHR) with plasminogen activator inhibitor type 1.