bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and superstructure of carbon fibres
Authors: Ruland W. 
Published: March 2011

AbstractThe structure of carbon fibres consists of stacks of carbon layers oriented parallel to the fibre axis. From X‐ray wide‐angle scattering studies (WAXS) one obtains various structural parameters characterizing the perfection of the stacking and the orientation of the layers. The latter is quantitatively related to the tensile modulus of the fibres. Small‐angle scattering studies (SAXS) are used to determine size, shape and orientation of microvoids. For carbon fibres with high heat treatment temperatures (HTT), a correlation between microvoid content and elongation at break is observed which indicates an optimum value for the microvoid content. Electrochemical intercalation is used to obtain information on the accessibility of the carbon layer structure.
Modern aspects of multicomponent copolymerization, quantitative theory
Authors: Kuchanov Semen I. 
Published: March 2011

AbstractIt is proposed to consider multicomponent copolymerization at high, monomer conversions proceeding from the theory of dynamic systems. A general approach based on such a consideration is suggested. This approach permits to make theoretical predictions of some fundamental properties of multicomponent copolymers taking data of only binary systems. The efficiency of this approach is clearly shown while predicting clarity and heat resistance of some terpolymers.
Complex formation and dynamics in polymer melts
Authors: Stadler Reimund , Freitas Liane De Lucca 
Published: March 2011

AbstractThe viscoelastic properties of polymer chains with a few number of pairwise associating functional groups are studied as a function of polymer molecular weight, degree of substitution and polymer concentration. As a model system, polybutadienes of narrow molecular weight distribution are used as starting materials. These polymer chains are modified by introducing few 1,2,4‐triazolidine‐3,5‐dione (urazole) groups U. These form defined dimeric hydrogen bond complexes U + U → U2.
Stabilisation of polymers by catalytic antioxidants
Authors: Scott Gerald 
Published: March 2011

AbstractTwo types of catalytic antioxidant are now recognised. The first involves the catalytic destruction of hydroperoxides to non‐radical products and the second consists of “stable” redox couples with the ability to remove both alkyl (CB‐A) and alkylperoxyl (CB‐D) radicals in autoxidising systems. The conditions under which both types of antioxidant can operate effectively are reviewed and the limitations to their activity are outlined.
Some aspects of polyethylene photooxidation
Authors: Gugumus François 
Published: March 2011

AbstractThe hydroperoxides produced by thermal oxidation of LDPE films were used to study their photolysis. Product analysis, kinetics of hydroperoxide decomposition and product formation as well as experiments with model compounds point to new mechanisms of hydroperoxide photolysis. Intermolecular as well as intramolecular decomposition mechanisms are proposed. In polyethylene, these reactions are essentially non‐initiating. In addition, it is confirmed that ketones such as those formed by oxidation of polyethylene do not have a significant initiating effect. Reactions of excited charge‐transfer complexes polyethylene‐oxygen are proposed to account for initiation of photo‐oxidation. One of these reactions yields trans‐vinylene groups and hydrogen peroxide whose direct decomposition or subsequent photolysis will generate hydroxyl radicals. It is found that this reaction is quenched very efficiently by small amounts of HALS (Hindered Amine Light Stabilizers) and by amines in general. It is postulated that quenching is due to energy transfer from the charge‐tranfer complex polymer‐oxygen to a charge‐transfer complex HALS‐oxygen or amine‐oxygen. The data available so far support such a mechanism.
Quantum effects in molecular dynamics and fracture kinetics of polymers
Authors: Slutsker A. I. 
Published: March 2011

AbstractMolecular dynamics in crystallites of a number of polymers, such as polyethylene, nylon‐6, poly‐(vinyl alcohol), was studied at temperatures ranging from 4.2 to 400 K using the X‐ray diffraction technique. Thermal expansion of the lattice was measured by the temperature‐induced displacements of diffraction maxima. The thermal expansion coefficient was found to grow from 0 to ∼10−4 K−1, this fact being the evidence of the quantum statistics in the vibrational dynamics of straightened molecules over the whole temperature range. Characteristic temperatures of vibrations were estimated. The kinetics of fracture was studied using highly ‐ oriented nylon‐6 and KEVLAR‐49 fibers. Tensile strength (σr) was measured as a function of loading rate σ and temperature (T) in the range from 4.2 to 400–600 K. The observed specific features of the σr(σ) and σr(T) curves at low temperatures correspond to tunnel scission of stressed chain molecules.
Stabilization of low density polyethylene with sterically hindered derivatives of 4‐hydroxybenzoic acid
Authors: Seiffarth K. , Baeseler M. , Dahlmann J. 
Published: March 2011

AbstractIn comparison with other commercial light stabilizers, sterically hindered 4‐hydroxybenzoates are found to possess only a weak power, if they are used for low density polyethylene (LDPE). It is known that these benzoates exhibit significant synergistic effects together with 2‐hydroxybenzophenones and hindered amine light stabilizers in light stabilization of high‐density and linear low‐density polyethylene. The light stabilizing efficiencies of the above mentioned stabilizers and mixtures of them in different weight ratios are determined by weathering in a Xenotest 150 unit. Only small synergistic effects of about 15 −30% are found for light stabilizing LDPE. The effects can be explained by the stabilizing efficiency of sterically hindered 4‐hydroxybenzoates during processing. Combining of light stabilizing structure components like 2‐hydroxy‐benzophenone resp. 2, 2, 6, 6‐tetramethylpiperidine with sterically hindered 4‐hydroxybenzoates in one stabilizer molecule only, from the first mentioned combination, results a powerful light stabilizer. Its efficiency is the sum of the powers of the single structure components.
The role of air in the radiolytic degradation of polycarbonate
Authors: Gupta Mool C. , Pandey Rajbahadur R. 
Published: March 2011

AbstractBisphenol A polycarbonate (PC) was irradiated with Co‐60 γ‐rays at room temperature in presence of air or nitrogen. Changes were followed by IR and NMR spectroscopy as well as GPC, X‐ray diffraction, melting temperature, DTA, and isothermal TG. The changes observed include chain scission, chain branching/cross‐links, decrease in thermal stability, crystallinity and scission of the product. However, there are some differences in samples irradiated in presence of air as opposed to those irradiated in nitrogen, but many changes are similar. Air accelerates the radiolytic degradation of PC. The radiochemical yield of chain scission, G(s), increased to 0.20 from 0.13; the chain branching/cross‐links are less numerous as compared to those after irradiation in nitrogen the thermal stability decreases along with the temperature of that rate of maximum mass loss, crystallinity and the melting temperature. The chemical products in both air and nitrogen irradiations are almost identical. The formation of these products could be explained by multiple pathways‐free radical formation and by ring as well as side chain attack. The studies suggest that Fries' rearrangement is not an important pathway during the radiolytic degradation as compared with photodegradation.
Ageing characteristics of styrene‐butadiene rubber containing some sulfanilyl derivatives
Authors: Abdel‐Bary E. M. , Makar S. M. , Mousa A. N. 
Published: March 2011

AbstractStyrene‐butadiene rubber (SBR) mixtures containing some sulfanilyl derivatives have been prepared. The effect of the latter compounds on the rate of vulcanization of SBR formulations as well as the ageing characteristics of corresponding vulcanizates were evaluated. In all cases, the efficiency of the compounds under investigation was correlated with their chemical structure. It was found that vulcanizates containing sulfanilyl thiourea compounds deteriorate to a lesser degree than those containing N‐isopropyl‐N'‐phenyl‐1, 4‐phenylenediamine (IPPD) as conventional antioxidant. In addition, the effect of the type of carbon black on the efficiency of such compounds as antioxidants was evaluated.
Mechano‐ions produced by mechanical fracture of solid polymers
Authors: Sakaguchi Masato , Kashiwabara Hisatsugu 
Published: March 2011

AbstractIt is said that the free radical caused by C‐C‐bond scission, homogeneous scission, is produced by mechanical degradation. In addition to free radicals, ionic species are produced due to the mechanical destruction of the polymers. Studies in our group concerning this problem are summarized. When the polymers were ground with tetracyanoethylene (TCNE) powder in a vibration glass ball mill in vacuum in the dark at 77 K, the TCNE anion radical (TCNE\documentclass{article}\pagestyle{empty}\begin{document}$ \bar . $\end{document}) was detected by electron spin resonance (ESR) method. The TCNE\documentclass{article}\pagestyle{empty}\begin{document}$ \bar . $\end{document} is formed by the abstraction of electrons by TCNE from the anion produced by a heterogeneous bond scission of carboncarbon bonds in the polymer main chain. The identification of TCNE\documentclass{article}\pagestyle{empty}\begin{document}$ \bar . $\end{document} was carried out by the spectral simulation on the basis of an anisotropic hyperfine tensor including a forbidden transition term. Several polymers were examined; polyethylene, polypropylene, poly(tetrafluoroethylene) and poly(vinylidene fluoride). The ratio of ionic species and free radicals is discussed.
The impact of external conditions on the structure of perfluorinated ion‐exchange membranes, determined by means of Mössbauer spectroscopy
Authors: Chibirova F. Kh. , Timashov S. F. 
Published: March 2011

AbstractTo ascertain the changes taking place in their submicrostructure after accelerated tests under the conditions of chlorine electrolysis, perfluorinated ion‐exchange sulfocationic membranes hydrolyzed by different techniques were investigated by means of Mössbauer spectroscopy on a Fe57 nucleus introduced into a membrane as a Fe3+ counter‐ion and precipitated into its submicropores in the form of superparamagnetic hydroxide particles. Information on the submicroporosity of the investigated polymeric membranes was thus obtained. Different techniques of membrane hydrolysis and the processes of both the passage of current (I ∼ 0.3 A/cm2) through them and of precipitation have been established to change radically the characteristic size of submicropores in the membrane, as well as their size distribution. Thermal treatment in air at T ≈︁ 423 K is shown to be accompanied by the Fe3+ ← Fe2+ ion reduction in the membrane.
Modification of polyolefins by antioxidants and stabilisers
Authors: Scott Gerald 
Published: March 2011

AbstractThe limitations of conventional antioxidants and stabilisers in polymers are associated with their migration into contacting fluids. This leads to toxicity in packaging and medicinal applications and loss of effectiveness in many engineering uses of polymers. Reactive processing procedures are being increasingly used to chemically attach antioxidants to polymers and the most successful of these involve the synthesis of bound antioxidant concentrates which can be used as macromolecular adducts for normal polymers. Present evidence suggests that a polymer modified by substantial concentration of antioxidants loses its physical identity and can be used in a range of other polymers. Future developments in which the additives are 100% bound to the polymer substrate are discussed.
Orientational drawing of polymers and their blends
Authors: Kuleznev Valeri N. , Vlasov Stanislav V. , Pirogovskaya M. 
Published: March 2011

AbstractPecularities of deformation of two‐phase blends is considered depending on drawing conditions and mechanical properties of each phase.Significant anisotropy of mechanical properties of polymer blends film can take place because of particle orientation of dispersed polymer. This significant anisotropy exists also when there is no orientation of macromolecules in each phase. Possibility is demonstrated to regulate properties of each phase in polymer blends by addition of selective plasticizer which can act only on one polymer phase in two‐phase polymer mixture.
Localization of oxidation in polypropylene
Authors: Billingham N C 
Published: March 2011

AbstractWe review some of the available evidence to suggest that the oxidation of polypropylene is not a homogeneous process but is localised at several levels. Optical microscopy of oxidised polymer shows regions of high oxidation on the micron scale, sometimes associated with uneven distribution of catalyst residues. Atactic polymer is shown to oxidise more rapidly than isotactic and to be redistributed in the isotactic polymer during melt crystallization. Atactic polymer is shown by GPC to undergo random scission with the formation of terminal carbonyl groups; in contrast, the oxidation of isotactic polymers is non‐random. Finally, evidence is discussed to show that both the initiation of oxidation by peroxide decomposition and its termination by radical recombination follow complex kinetics.
Stabilization and modification op polyolefins used in medical articles
Authors: Gorelik B. A. , Sokolova L. A. , Grigoriev A. G. , Koshelev S. D. , Semenenko E. I. , Matiushin G. A. , Rychla L. 
Published: March 2011

AbstractThe thermo and radiation aging of polyolefins and their blends were studied. It was shown that near the inversion point of phase there is the most marked interaction between continuous and dispersed components of blend. This interaction results in an improvement of blend stability higher than expected. The investigation of the influence of supermolecular structure of PP stability revealed the small spherulite samples are more stable under irradiation in air than large spherulite ones. The possibility of obtaining composites of polyolefins and silicon liquids urns shown.
Photoinitiated crosslinking of polyethylene
Authors: Zamotaev P. V. 
Published: March 2011

AbstractThe main types of polyethylene (PE) crosslinking photoinitiators were examined. It was shown that the aromatic ketones and quinone are the best types of the photoinitiators for practical usage. The quantum yields of initiators' photoreduction and the crosslinking yields per one initiator molecule at the different stages of PE photochemical crosslinking were measured. The photoinitiators effectiveness dependence on their chemical structure was considered. The influences of the UV‐irradiation intensity, temperature, photoinitiators' concentration, some copolymers, polyfunctional monomers, peroxides additives on the photocrosslinking and photooxidation processes in PE were investigated.
The latest achievements in the field of degradation and stabilization of vinyl chloride (CO)polymers
Authors: Minsker K. S. 
Published: March 2011

AbstractThe achievements of the past years are associated, in the first place, with solution of the problems of the abnormally low stability and the new ways of effective stabilization of vinyl chloride (VC) (co)‐polymers. A generalized approach to the quantitative description of the degradation of VC polymers, taking into account the short‐ and long‐range effects of neighbouring groups, which are fundamental for the chemistry of the halogen‐containing polymers, has been elaborated. The principal effects of the polymer phase state and the solvent nature on the degradation rate of VC (co)polymers have been elucidated. This fact predetermines different approaches to the stabilization of the polymer products in creation of rigid and plasticized compositions, including those in solutions.
Vinyl chloride polymers and their use in polymer blends
Authors: Braun Dietrich , Böhringer Bertram 
Published: March 2011

AbstractA short introduction to polymer‐polymer miscibility and to the prediction of the miscibility of polymers is given. The four main types of polymer‐modified poly(vinyl chloride) (plastification, impact modification, processing aids and heat deflection temperature modification) are explained by examples. The thermal stability of poly(vinyl chloride) in such blends is discussed; the effectivity of tin‐stabilizers may be higher in such blends than in pure poly(vinyl chloride).
Transport of organic vapors and liquids in poly(vinyl chloride)
Authors: Berens Alan R. 
Published: March 2011

AbstractThis paper reviews research since 1980 on the equilibria and kinetics of transport of small organic molecules in rigid and plasticized PVC. The forms of both the solubility isotherms and the sorption kinetics are shown to change as the PVC/penetrant system undergoes a glass‐rubber transition with an increase of either temperature or penetrant concentration. The isotherms are of “dual‐mode” form (concave to the activity axis) for the glassy state, and show an inflection to Flory‐Huggins form when the penetrant concentration exceeds Cg, the transition composition at the experimental temperature. The solubility at a given penetrant activity is governed primarily by the PVC/penetrant interaction parameter, χ. Sorption kinetics are Fickian for conditions producing small changes of concentration in either the glassy or rubbery state. For sorption into initially unplasticized PVC, kinetics are anomalous if the final penetrant concentration is between about Cg/2 and Cg, and Case II if Cg is exceeded. The magnitude of the Fickian diffusion coefficients depends largely on the geometric factors of molecular size and shape of the penetrant; this dependence is much steeper in the glassy than in the rubbery state. Recent results show that carbon dioxide displays both high diffusivity and substantial solubility in PVC under high pressure; this combination makes compressed CO2 uniquely useful in accelerating the absorption of low‐molecular‐weight additives into PVC.
Estimation of the degree of fusion of rigid PVC from thermal analysis measurements
Authors: Teh J.W. , Rudin A. , Cooper A.A. , Batiste J.L.H. 
Published: March 2011

AbstractPVC that has been processed exhibits two endothermic peaks in DSC heating curves. These endotherms are separated by a temperature. Tc, which is characteristic of the maximum temperature reached in prior processing. The relative value of the lower temperature endotherm has been proposed as a measure of degree of gelation of unplasticized PVC. This measure is not exact, however, because it does not reflect the extent of breakdown of primary PVC particles. An alternative DSC measurement technique is proposed that reflects the degree of fusion more accurately. The nature of the various endotherms that are observed is a subject of speculation in this article.
Fire performance of poly(vinyl chloride) and its relation to fire hazard
Authors: Hirschler Marcelo M. 
Published: March 2011

AbstractThis paper discusses the most important parameters in terms of fire hazard and shows how PVC fares in relation to other polymers. The fire properties specifically addressed are: ignitability, flammability, flame spread, rate and amount of heat release, mass loss rate, smoke release and toxicity. Hydrogen chloride decay is also commented on, because it affects the toxicity of PVC smoke. The individual parameter most relevant to fire hazard is heat release. The two most useful tools for measuring rate of heat release (viz. the OSU and Cone calorimeters) are described. Results obtained from them are discussed.Smoke can best be measured by combined parameters from rate of heat release calorimeters, rather than in the traditional static NBS smoke chamber.Toxic hazard is being addressed by recognition that most smokes are of similar toxicity, so that the mass loss rate will, generally, govern the toxicity of smoke.Not all fire tests are equally good representations of the probable consequences of a full‐scale fire. Fire hazard assessment is best carried out based on those test results most relevant to real fires; they can be obtained from small and full‐scale experiments and fire models.The fire performance of PVC is excellent; PVC products generally represent low fire hazard in a scenario.
Rheological aspects in degradation and stabilization of poly(vinyl chloride)
Authors: Gonnu M. , Verney V. , Michel A. 
Published: March 2011

AbstractViscoelastic properties of PVC depend on temperature because of the existence of a physical temporary network. The main consequence of gel state within the range of usual processing temperatures is a heterogeneous dispersion of stabilizers. PVC is most sensitive to the dehydrochlorination in the state of the intermediate flow between particulate and molecular flow because of radicals arised from polymer chain scission caused by shear stress.
Properties of poly(vinyl chloride) blends with polycarbonates and chlorinated polyethylene
Authors: Braun D. , Böhringer B. , Herth J. 
Published: March 2011

AbstractThe miscibility of polycarbonates derived from Bisphenol A or 2,5,2′,5′‐tetramethyl‐Bisphenol A with poly(vinyl chloride), chlorinated poly(vinyl chloride), and vinyl chloride‐vinylidene chloride copolymers has been investigated. In miscible blends a shift of the position of the carbonyl absorption in the IR spectra indicates dipolar interactions between the polymers. The miscibility of chlorinated polyethylenes and reduced poly(vinyl chloride)s among each others demonstrates besides the importance of polar groups the influence of their distribution within the polymer chains for the compatibility of the polymers. The investigations on the miscibility have been carried out by differential scanning calorimetry, and by casting films with microscopical observation of the resulting structures.
Factors affecting dimensional stability of exterior vinyl products
Authors: Rabinovitch Elvira B. 
Published: March 2011

AbstractDimensional stability problems such as warpage, bowing, buckling and other changes in shape and size may occur when exterior building products (siding, windows) are heated by the sun. This paper describes the effects of material properties such as coefficient of thermal expansion, heat deflection temperature and heat buildup, caused by the sun, on dimensional stability of exterior building products. This paper also discusses the effect of profile design, such as thickness and width, on dimensional performance.
Study of poly(vinyl chloride) by inverse gas chromatography
Authors: Hattam P. , Cheng W. , Du Q. , Munk P. 
Published: March 2011

AbstractInverse gas chromatography (IGC) was used to investigate PVC to determine what information can be gathered using the technique. Standard IGC using a column of PVC‐coated support was performed at 120°C. The polymer‐solvent interaction coefficients for 25 probes were obtained and the polymer solubility parameter was determined. A 50/50 blend of PVC/poly(∈‐caprolactone) was studied to determine the polymer‐polymer interaction coefficient B23 and the solubility parameter of the blend. A nonstandard analysis using bulk, suspension‐polymerized PVC as the column packing was performed at 40°C, and the retention behavior compared with a computer simulation of Langmuir type adsorption.
Relaxation properties of plasticised poly(vinyl chloride) and PVC blends
Authors: Suvorova A.I. 
Published: March 2011

AbstractThe temperature‐frequency dependence of dielectric parameters for several PVC‐plasticizer systems and PVC blends was obtained. Kinetic and activation parameters and α‐relaxation spectra were estimated. The increase of the polar group number and size in the plasticizer molecules results in the narrowing of the relaxation spectra and in the increase of inner mobility of PVC segments. It was found for PVC‐ABS and PVC‐Paraloid blends that all relaxation characteristics depend on the miscibility of components. The results were also confirmed by the cloud point data.