bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of the SPME-GC-MS technique to study the thermal degradation of isotactic polypropylene: Effects of temperature and reaction time, and analysis of the reaction mechanism
Authors: Bortoluzzi Janina H. , Cristiano Rodrigo , Gallardo Hugo A. , Carasek Eduardo , Soldi Valdir 
Published: August 2014

AbstractCommercial fibers covered with poly(dimethylsiloxane) were used to pre-concentrate (solid phase microextraction technique) products evolved from the thermal degradation of isotactic polypropylene. Although the analysis by GC-MS indicated the formation of more than one hundred evolved products (ca. forty were identified), only twenty nine formed at 470°C (the temperature of maximum degradation rate for isotactic polypropylene) were analyzed. The main compounds identified were 2,4-dimethyl-1-heptene, 2-methyl-1-pentene, 2,3-dimethyl hexane, n-pentane and 1,3,5-trimethyl cyclohexane. The analysis at 470°C, using different degradation times, also indicated that the compounds 2-methyl-1-pentene and 2,4- dimethyl-1-heptene (major products) were formed at 15 and 25 minutes, respectively. The mechanism proposed for the formation of the major compounds was based on radical formation through chain cleavage (allyl and secondary radicals), followed by a chain decomposition process via hydrogen radical addition or cyclization to a thermodynamically stable six-membered ring.
Chain Extender and Diisocyanate Amount Effects on the Thermal, Mechanical and Wettability Properties of Some Polyurethane Elastomers
Authors: Vlad Stelian , Oprea Stefan 
Published: August 2014

AbstractThe aim of this study was to investigate the effect of chain extender and diisocyanate amount on the thermal, mechanical and wettability properties of some polyurethanes. The chain extender nature caused the increase of the thermal stability due to the higher stability of the double and triple bonds respectively in contrast to simple bonds. Tg of the polyurethanes based on PCL/MDI decreased when the unsaturated grade from chain extenders increased. The double and triple bonds content from polyurethane structure was responsible for this behavior. The hard segment contents and the chain extenders nature also influenced the wettability. The results showed that the thermal, mechanical and wettability properties of the final products might be controlled by fine control of the amount of the MDI and the nature of the chain extenders
First approach on transfection ability of novel amphiphilic water soluble degradable poly(ε-caprolactone)-g-poly(Llysine) copolymers
Authors: Nottelet Benjamin , Vendrell Julie , Coudane Jean , Vert Michel 
Published: August 2014

AbstractThe potential of novel amphiphilic water soluble and degradable poly(ε- caprolactone)-g-poly(L-lysine) as carriers for DNA transfection has been investigated. Two graft copolymers having the same proportion of lysine units but different structures have been synthesized following two grafting techniques. The chemical composition of these copolymers, their expected architectures and their behaviour in aqueous solutions have been studied. The benefits resulting from the use of these degradable polycationic structures as well as their ability to form polyplexes are discussed. Finally, preliminary transfection assays of MCF-7 cells by pRL-TK plasmid using poly(ε-caprolactone)-g-poly(L-lysine) copolymers as carriers are reported.
Polypropylene + Polystyrene Blends with a Compatibilizer. Part I. Morphology and Thermophysical Properties
Authors: Brostow Witold , Holjevac Grguric Tamara , Olea-Mejia Oscar , Rek Vesna , Unni Jaykumar 
Published: August 2014

AbstractVarious concentrations of polypropylene (PP) and polystyrene (PS) blends were prepared with styrene-ethylene/butylene-styrene block copolymer (SEBS) added as a compatibilizer between the two main polymers. We have investigated the effect of SEBS on processing, morphology and thermophysical properties of the blends. The compatibilizing agent improves the blend morphology since smaller particles of the dispersed PS phase in the PP matrix blends are obtained; adding more than 5 % SEBS has no further effect on the blends. The presence of SEBS lowers the crystallinity of the PP-rich phase - as reflected in the enthalpy of fusion and also in the enthalpy of crystallization.
Characterization of acrylic copolymer latex modified by fluorine, silicon, and epoxy resin
Authors: Xiong Pingting , Guan Rong , Lu Deping , Chen Peizhi , Hongzhi Huang Ling Shen 
Published: August 2014

AbstractThe ever-increasing demand of waterborne heavy-duty coatings for high resistance to many aggressive environment factors and low-surface energy has spurred the ongoing development of acrylic latex modified by fluorine, silicon, and epoxy resin. The morphology of the latex particles were characterized by means of light scattering and transmission electron microscopy (TEM). The stability measurements of modified latex and films showed that the resultant acrylic copolymers containing fluorine, silicon and epoxy resin represented very good resistance to organic solvent, acid and base, water and heat. From contact angle measurements and atomic force microscopy (AFM), a dense and gradient film with surface energy as low as 16.1 mN/m was obtained.
High density polyethylene/boron carbide composites for neutron shielding
Authors: Yasin Tariq , Khan Muhammad Nasir 
Published: August 2014

AbstractComposites of high density polyethylene with three different amounts of modified boron carbide namely: 7 phr (parts per hundred parts of resin), 15 phr and 24 phr have been prepared. These composites show excellent thermal neutron shielding properties which increase with the increase of boron content in the composites matrix. Moreover, the effects of boron carbide on the mechanical properties, the effect of thermal oxidative aging on mechanical properties and swelling of composites in different solvents have also been studied in these composites.
Review on the thermo-oxidative degradation of polymers during processing and in service
Authors: Gijsman Pieter 
Published: August 2014

AbstractDuring processing as well as in service life, polymers degrade. For the majority of polymers this is due to oxidative processes. In this review the mechanism of the thermo-oxidative degradation of the most important (unstabilized) polymers as well as the factors determining the degradation rates are discussed.
The effect of extraction condition on gel spun super denier PVA fiber structure and properties
Authors: Yumin Xia , Zhixin Wang , Huigong Tang 
Published: August 2014

AbstractThis paper is directed towards PVA monofilament with good mechanical properties and super denier, which was produced with the gel spinning technique, first used by K. YAMAURA, used to strengthen the concrete. The structure and properties of PVA fiber were affected especially by extraction conditions, including the temperature, the solvent content and the duration of the extraction, all of which were studied and the optimum parameters were selected.
Biodegradable poly(vinyl alcohol-lactic acid-aspartic acid) copolymers
Authors: Tudorachi Nita , Lipsa Rodica 
Published: August 2014

AbstractThe aliphatic polyesters: polylactides (PLA), polyglycolides (PGA), poly( -caprolactone) (PCL) as well as their copolymers especially, poly(lactide-coglycolide) (PLGA), poly(vinyl alcohol) (PVA), chitosan, dextran and starch occupy first place among biodegradable, biocompatible and non-toxic polymers. PVA, with different molecular weights, hydrolysis degree, tacticity, crystallinity, and due to the abundance of pendant hydroxy groups in the backbone is capable of several grafting and cross-linking. The present study concerns the synthesis of graft copolymers poly(vinyl alcohol) with lactic acid (LA) and aspartic acid (Asp). The modification reaction of poly(vinyl alcohol) with lactic and aspartic acid was achieved by solution polycondensation using dioxane/water (3/1) as solvent mixture, different molar ratios PVA/LA/Asp and manganese acetate as catalyst: Mn(CH3COO)2 4H2O. The copolymers were characterized by FTIR, 1H-NMR, thermal stability (DSC, TG), elemental analysis, wide angle X-ray diffraction (WAXD). The average particle size and zeta potential for aqueous dispersions of copolymers, solubility in organic solvents and biodegradation testing on agar-agar medium inoculated with a fungus Chaetomium globosum class MO5 stock, were studied.
Thixotropy of aqueous solution of fluorocarbon-modified poly(acrylic acid)
Authors: Hu Hongqi , Li Lin , Chen Mingcai 
Published: August 2014

AbstractThe rheological properties of the aqueous solution of 1H,1H,11Hperfluoroundecyl acrylate -modified poly(acrylic acid) were studied. It was found that the solutions show different viscosity dependence on shear time at different pH and shear rates. At lower pH and moderate shear rates, the viscosity of the solutions shows a great increase with time. At pH 5.0 and above, it exhibits thixotropy at any shear rate, i.e., the viscosity decreases with time at constant shear rates. If the shearing stops, the viscosity of the solutions can be recovered to some extent. These phenomena are interpreted to be due to the intermolecular hydrophobic association: the construction of the association leads to an increase of the viscosity, the destroying of the association leads to a decrease of the viscosity. The pH-induced conformational change and the shearing-induced chain elongation jointly influence the intermolecular hydrophobic association.
Infrared study of the photochemical behaviour of aromatic poly(ether urethanes): effect of various stabilizers
Authors: Mendikute G. , Irusta L. , Fernández-Berridi M.J. 
Published: August 2014

AbstractThe influence of various additives on poly(ether-urethane) UV stability is evaluated. The extent of the photo degradation has been studied by FTIR spectroscopy. The photo-stabilizer 2-hydroxy-benzophenone decreases the photooxidation on both hard and soft segment, whereas the effect of the phenolic antioxidant 2,6-di-t-butyl-4-hydroxytoluene is more significant on the soft segment. However, the effect of the nickel chelate, 2,2’-thiobis(4-t-octylphenolate)-nbutylamine of nickel, depends on the polyurethane nature.
Effect of rosemary extract on the radiation stability of UHMWPE
Authors: Zaharescu Traian , Jipa Silviu , Artenie Mariş Dan , Mariş Maria , Kappel Wilhelm 
Published: August 2014

AbstractThis paper presents the assay on the radiochemical degradation of UHMWPE films containing rosemary. Three concentrations of natural polyphenolic extract were selected: 0, 0.25 and 0.50 % (w/w). FTIR and UV-VIS spectra were recorded and the variation in the characteristic bands was followed. The accumulation of carbonyl and hydroperoxyl structures was attempted for all samples including neat specimen. The contribution of additive to the protection of UHMWPE against oxidative degradation is discussed in relation with polyphenol concentration and irradiation dose. The spectral information is correlated with the results of chemiluminescence investigation. The increase in the additive concentration brings about significant longer induction times that are determined by the slower accumulation of primary intermediates, hydroperoxides. The antioxidant efficiency of rosemary extract is also revealed by the variation in carbonyl and hydroxyl indexes.
Fabrication and properties of PVDF/expanded graphite nanocomposites
Authors: Li Yuchao , Li R. K. Y. , Tjong S. C. 
Published: August 2014

AbstractPoly(vinylidene fluoride) (PVDF) nanocomposites filled with various expanded graphite (EG) contents were prepared via melt-mixing followed by hotpressing. The structure, electrical, and thermal properties of resulting nanocomposites were investigated. X-ray diffraction results indicated that the EG additions do not lead to structural changes of PVDF. Differential thermal calorimetry measurements revealed that EG act as a nucleating agent for PVDF molecular chains. The crystallization temperature shifted to higher temperature with increasing EG content. DMA results showed that the storage modulus and glass transition temperature can be enhanced by adding EG. The nanocomposites were found to exhibit a small percolation threshold of 6.3 vol% due to the large aspect ratio of graphite nano-sheets. A great enhancement of dielectric constant is also found as EG concentration approaches percolation threshold. Both the electrical conductivity and dielectric constant of PVDF/EG nanocomposites can be well described by the percolation theory.
Preparation and characterization of carbamoylethyl hemicelluloses
Authors: Ren Jun-Li , Peng Feng , Sun Run-Cang , Zhang Xun-Li 
Published: August 2014

AbstractThe reaction of hemicelluloses, isolated from wheat straw, with acrylamide in alkaline aqueous solution was investigated. The degree of substitution (DS, up to 0.65) of the products could be obtained by adjusting the molar ratios of reagent to xylose unit in hemicelluloses (1.0-10.0) and the molar ratios of catalyst to xylose unit in hemicelluloses (0.5-1.6). Changes in the structure of hemicelluloses were verified by FT-IR and 1H and 13C NMR spectroscopies. The results showed that carbamoylethyl groups surely were grafted onto the main chain of hemicelluloses. Moreover, it was also found that the saponification of carbamoylethyl groups to carboxyl groups occurred in alkaline medium. The behavior of modified hemicelluloses was monitored by means of thermo gravimetry (TG) and differential thermal analysis (TGA). It was found that the products had a lower thermal stability than the native hemicelluloses.
Rheological properties of conductive polymer composite (CPC) filled with double percolated network of carbon nanoparticles and boron nitride powder
Authors: Droval Guillaume , Feller Jean-François , Salagnac Patrick , Glouannec Patrick 
Published: August 2014

AbstractIn this study, double percolated network of carbon nanoparticles and ceramics powder is used to uncouple electrical and thermal conductivity of polymer composite. The influence of ceramic powders on morphological properties of a biphasic conductive polymer composite (CPC) is investigated by means of rheological measurements. The biphasic materials studied are blends of a thermally conductive polymer phase (syndiotactic poly(styrene) (sPS) filled with boron nitride (BN)) with an electrically conductive polymer phase (high-density poly(ethylene) (hdPE) filled with nano-structured carbon black (NCB)) into a cocontinuous structure. The elastic modulus (with viscous modulus) was found to be the most sensitive rheological property to accurately detect the co-continuous morphology in our system. It was found to be at 40% v/v of hdPE-NCB, which can be interpreted as the phase inversion.
The thermal behaviors of Ag/polyamidoamine nanocomposites
Authors: Peng Zheng , Zhang Jianmin , Diao Jianzhi , Mei Shigang 
Published: August 2014

AbstractAg/polyamidoamine nanocomposites were produced by photoreduction of relevant metallic salts in polyamidoamine methanol solutions under room temperature and ambient pressure. The obtained products were characterized by FTIR, XRD, TEM, TGA and DSC techniques. The results showed that Ag nanoparticles were quite uniform in size with a diameter of about 15 nm, and the amount of Ag nanoparticles could well affect the thermal stability and the glass transition temperature of polyamidoamine. As the mass ratio of Ag nanoparticles to polyamidoamine increased, the glass transition temperatures were increased, while the weight loss ratios were decreased. TGA curves indicated that the loading of Ag nanoparticles mainly influences the high temperature thermal stability of polyamidoamine. Moreover, the multistage decomposition profile of DTG curves suggested that the Ag/polyamidoamine nanocomposites of higher silver loading might contain some intermediate Ag+/polyamidoamine type of composites.
The polymeric crystallinity effect on the responses of bone marrow stromal cells
Authors: Yi Qiangying , Wen Xiantao , Li Li , He Bin , Wu Yao , Nie Yu , Gu Zhongwei 
Published: August 2014

AbstractThe cell-material interaction is an important factor to be considered in the applications of biomaterials. The properties of biomaterials, for example crystallinity, would change the cell behaviors such as proliferation, differentiation, morphology and so on. In this article, the research was focused on the relationship between the crystallinity of polymeric substrates and the cell responses. Two kinds of biodegradable poly(L-lactide) (PLLA) films with different crystallinity were prepared and used as substrates for cell behavior study. The PLLA films were fabricated with crystallinity of 19% and 69% through solution casting and isothermal processing, respectively. The crystallinity of PLLA films was characterized by DSC and XRD. The surface morphologies of PLLA films with different crystallinity were observed by SEM. Bone marrow stromal cells (MSCs) isolated from the marrow of new born male Sprague Dawley rats were cultured on the films. The cell morphology, proliferation, total protein amount and alkaline phosphatase (ALP) activities were tested. The results showed that the crystallinity of PLLA films affected the behavior of MSCs greatly.
One pot synthesis and characterization of industrially important graft copolymer (GOH-g-ACM) by using peroxymonosulphate/ mercaptosuccinic acid redox pair
Authors: Srivastava Arti , Mishra Vivek , Kumar Singh Shailendra , Kumar Rajesh 
Published: August 2014

AbstractGuar gum-g-polyacrylamide is a graft copolymer which is used for many industrial applications. This paper outlines the details of synthesis of guar gum -gacrylamide by using potassium peroxymonosulphate/ mercaptosuccinic acid redox pair in an inert atmosphere and their characterization by infrared spectroscopy, UV analysis and study of swelling and thermal properties. Grafting characteristics: %G, %E, %C, %A and %H were determined by using Fanta’s definition; rate of grafting was also calculated. On studying the effect of reaction conditions on grafting characteristics, it was found that the optimum concentration of peroxymonosulphate, mercaptosuccinic acid, hydrogen ion, acrylamide and guar gum for maximum % of grafting were 8.0×10-3, 3.2×10-3, 8.0×10-3, 16.0×10-2 mol dm-3 and 60.0×10-2 g dm-3 respectively. The optimum time duration and temperature of reaction were found to be 120 min and 40 °C respectively. During the study [H+] variation showed prompt changes on grafting characteristics. It was found that after 310 °C the polyacrylamide grafted guar gum was thermally more stable than pure guar gum.
Barrier and physical properties of polypropylene/highbarrier ethylene vinyl alcohol copolymer blends compatibilized with a sodium ionomer
Authors: Ares Ana , Abad María J , Barral Luis , García-Garabal Sandra 
Published: August 2014

AbstractThe aim of this work is to investigate the properties of the PP/EVOH films for their potential use in the packaging industry. Besides, the barrier properties, the mechanical parameters and the morphology of the PP/EVOH films have been studied as function of their composition and the processing technique used for their manufacture. In these applications, the package is frequently in contact with humidity environments and for this, it is necessary to know how environments with different humidity contents, affect the O2 permeability of the polymer material. For these reasons, the influence of the moisture in the values of permeability was evaluated too. The data showed that the oxygen transmission rate (O2TR) decreased with the amount of EVOH, and if the copolymer mass is maintained constant, the O2TR diminished with the quantity of the ionomer in the compositions. Besides, the films obtained by extrusion and following unidirectional stretching, presented better barrier properties to the oxygen molecules than the compression moulded films. When the ionomer is added to the compositions the permeability is reduced even for the films maintained in wet atmosphere. The micrographs obtained by SEM showed that the films have a biphasic structure, where the EVOH particles are dispersed in the PP matrix.
Toughening of PBT/PC blends with epoxy functionalized core-shell modifiers
Authors: Zhang Fangfang , Sun Shulin , Liu Xiaoyun , Zhang Lixia , Zhang Huixuan 
Published: August 2014

AbstractCore-shell modifiers of MB-g-GMA have been synthesized by emulsion polymerization technique. For these modifiers, the core is made up of the crosslinked poly(butadiene) and the shell is methyl methacrylate (MMA) and glycidyl methacrylate (GMA) copolymer. These modifiers were used to toughen poly(butylene terephthalate) (PBT)/bisphenol A polycarbonate (PC) blends. The mechanical properties showed that the addition of 15% MB-g-GMA had a very good influence on the notched Izod impact strength and elongation at break of the PBT/PC blends. DMA results showed PBT was partially miscible with PC and the addition of MB-g-GMA further improved the miscibility of PBT and PC. DSC tests further testified the introduction of MB-g-GMA improved miscibility between PBT and PC. Scanning electron microscopy (SEM) displayed a very good dispersion of MB-g-GMA particles in PBT/PC blend. Transmission electron microscopy (TEM) proved MB-g-GMA particles were enveloped by a thin layer of PC, PBT and PC showed co-continuous structure or dispersed phase which depended on the content of MB-g-GMA. SEM results showed shear yielding of the matrix and cavitation of rubber particles were the major toughening mechanisms.
Selective recognition of methotrexate by molecularly imprinted polymers
Authors: Curcio Manuela , Parisi Ortensia Ilaria , Cirillo Giuseppe , Spizzirri Umile Gianfranco , Puoci Francesco , Iemma Francesca , Picci Nevio 
Published: August 2014

AbstractThe aim of this study is the preparation of molecularly imprinted polymers with high selectivity for metotrexate (MTX), a useful antineoplastic drug widely employed in clinical trials. Methacrylic acid, 2-(dimethylamino)ethyl methacrylate and a mixture of them were tested as functional monomers in order to optimize the performance of imprinted materials. The specificity and the selectivity of imprinted polymers was tested by performing rebinding experiments in water at pH 7.4. The best results were obtained by employing both functional monomers in the polymeric feed. In this way, each monomer interacts with complementary functionalities on template molecule, stabilizing the prepolymerization complex and minimizing the repulsive effects (due to the ionization of functional groups) in the rebinding media.
Piezoresistive polymer composites based on EPDM and MWNTs for strain sensing applications
Authors: Ciselli Paola , Lu Lan , Busfield James J.C. , Peijs Ton 
Published: August 2014

AbstractElastomeric composites based on Ethylene-Propylene-Diene-Monomer (EPDM) filled with multi-wall carbon nanotubes (MWNTs) have been prepared, showing improved mechanical properties as compared to the pure EPDM matrix. The results have been discussed using the Guth model. The main focus of the study was on the electrical behavior of these conductive polymer composites (CPCs), in view of possible sensor applications. A linear relation has been found between conductivity and deformations up to 10% strain, which means that such materials could be used for applications such as strain or pressure sensors. Cyclic experiments were conducted to establish whether the linear relation was reversible, which is an important requirement for sensor materials.