bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fracture behavior of exposed HDPE specimens with an embrittled layer due to UV‐exposure
Authors: Hoekstra H. D. , Breen J. 
Published: April 2003

AbstractThe applicability of fracture mechanics was studied on UV‐exposed HDPE Charpy specimens. The failure distribution of the stress at failure measured in three‐points bending tests showed a bifurcation in failure processes. At high stresses yielding occurs, resulting in large strain at failures. At lower stresses crack propagation causes low strain at failures. Due to the bifurcation in failure processes the ductile‐brittle transition temperature of exposed specimens is hard to determine.Specimens notched after exposure showed a decrease in the critical stress intensity values. The effective notch depth of exposed specimens was found to be larger than the thickness of the oxidized layer measured by FT‐IR and density measurements.
Radiation induced degradation of polymers ‐an approach by using liquid paraffins as a model system
Authors: Katsumura Yosuke 
Published: April 2003

AbstractParaffins, n‐hexadecane and squalane, were employed as a model of polymers and radiation induced reactions in the polymers have been simulated. After vacuum irradiation, products were identified and their yields were determined by a variety of techniques. In the presence of the aromatic additives, the reduction of the degradation, so called protection effect, was clearly observed. Both energy and charge transfer play important roles in the protection effect. The same system was adapted to the irradiation under aerated condition in order to clarify the radiation induced oxidation. Furthermore, corresponding experiments using polypropylene were also performed and validity of the model system and phase effect were discussed. On the basis of the above results, it was revealed that the model experiment is valuable to understand the radiation induced reactions in polymers, especially amorphous phase of the polymers.Recently, the same model system has been extended to the thermal degradation at the temperature ranges of 300 ‐ 400°C. When radiation was introduced, both a significant acceleration of the degradation and an enhancement of H2 evolution were clearly observed. This is suggesting a potential application of radiations to the degradation of polymers at elevated temperatures.
The preparation and performance of “Cage” diphosphites as secondary antioxidants in the stabilization of polyolefins
Authors: Klender G. J. , Elnagar H. Y. 
Published: April 2003

Abstract“Cage” diphosphites, a new family of phosphorus antioxidants, are discussed in regard to their preparation, properties, and effectiveness in polyolefins, particularly, with phenolic stabilizers, in respect to their ability to control melt flow and color during processing. These trivalent phosphorus compounds have two different types of phosphite functionalities in their structure. One phosphorus is part of an eight membered (1,3,2‐dioxaphosphocine) ring system while the other is part of a tricyclic cage of carbon and oxygen atoms. This structures can contribute to improved hydrolytic stability over rather similar aryloxy‐alkoxy phosphites and show competitive stabilization effectiveness in the processing of polyolefins. The possible modes of formation and of hydrolysis are discussed.
Deactivation processes of 2‐hydroxyphenyl‐1,3,5‐triazines — polymeric and monomeric UV absorbers of the benzotriazole and triazine class
Authors: Keck Jürgen , Stüber Guido J. , Kramer Horst E. A. 
Published: April 2003

AbstractIn the 2‐hydroxyphenyl‐1,3,5‐triazines, the intramolecular hydrogen bond is stronger than in the corresponding 2‐hydroxyphenylbenzotriazoles. Compounds with only one aryl group in the 2‐hydroxyphenyl‐1,3,5‐triazine series show proton‐transferred fluorescence with large Stokes shift and high quantum yield. No such fluorescence is observed, in contrast, for compunds with three aryi groups bearing no electrondonating groups on the aryl moieties. When the hydrogen atom of the intramolecular hydrogen bond is replaced by CH3, the respective derivative shows fluorescence with a normal Stokes shift.Various copolymers of MA‐TIN 1 (2‐[2‐hydroxy‐3‐tert.‐butyl‐5‐(O‐[2‐hydroxy‐3‐(2‐methylpropenoyloxy)propyl]‐2‐carbonyloxyethyl)phenyl]benzotriazole), and MA‐TZ 1 (2,4‐Bis(2,4‐dimethyl‐phenyl)‐6‐[2‐hydroxy‐4‐(2‐hydroxy‐3‐[2‐methylpropenoyloxy])propoxyphenyl]‐1,3,5‐triazine) with styrene, methyl methacrylate, and methacrylic acid have been synthesized by radical polymerization. The absorption spectra in the longwavelength UV region appear unchanged compared to those of the monomeric UV absorbers indicating that the stabilizer chromophores are conserved intact in the polymer. Both the monomeric and the polymeric stabilizers exhibit a strongly Stokesshifted, temperature‐dependent, low‐quantum‐yield, proton‐transferred fluorescence. This may be taken as evidence that the intramolecular hydrogen bond, which is essential for the photostability of this type of UV absorber, remains intact also in the copolymers. Activation energies of the radiationless deactivation process can be evaluated from the temperature dependence of this fluorescence. These energies lie between 4 and 5 kJ/mol for most of the benzotriazole and triazine stabilizers investigated.Fluorescence‐decay measurements with crystalline MA‐TIN 1 at different temperatures reveal a close correspondence of the temperature dependence between decay times and relative quantum yields. The radiationless process is thence concluded to originate from the proton‐transferred level S1'. The decay time at room temperature is estimated at 70 ps, close to the value for crystalline TIN P (2‐(2‐hydroxy‐5‐methylphenyl)benzotriazole). The proton‐transferred fluorescence of MA‐TIN 1 exhibits a biexponential decay profile whereas solid TIN P, in contrast, displays only one single lifetime.
Oxidizability of lactams and lactam‐based polyamides
Authors: Lánská Božena 
Published: April 2003

AbstractIn the chain oxidation of N‐alkylamides with molecular oxygen, propagation is the ratedetermining step under conditions when the oxidation rate is independent of oxygen pressure. The oxidizability of lactams and lactam‐based polyamides correlates with the energy of the formation of N‐alkylamide radical by abstraction of hydrogen from the methylene group adjacent to nitrogen. While for lactams this energy depends on the number of carbons in the lactam ring, for N‐alkylamides and polylactams such dependence is not observed.
Percolation concept as applied to the degradation of elastomer networks
Authors: Ono Katsumichi 
Published: April 2003

AbstractThe kinetics of the degradation of elastomer networks are most conveniently disscussed by the stress relaxation which is due to the time change of the effective number of the network chain caused by thermo‐oxidative scission and/or crosslinking reaction. However, this view is only correct in the initial stage of the oxidation. In the later stage, several number of elastically effective network chains simultaneously lose their effectiveness by the scission of only one network chain. In order to explain the network behavior in the course of degradation, we introduced a percolation concept to the degradation of the network chain. The important parameter of this concept is the critical exponent. We determined the critical exponent in the vicinity of gel to sol transition of ealstomer network by comparing the tensile modulus of DCP vulcanized rubber and the gel fraction. The experimentally determined critical exponent was in good agreement with the value which was calculated for the 3D percolation. From this point of view, we can construct a universal curve for the degradation. All the experimental stress relaxation curves fall in this universal curve by taking the critical point of degradation as a standard state.
Use of EPR to image nitroxyl radicals in hals stabilized polymers
Authors: Lucarini Macro , Pedulli Gian Franco 
Published: April 2003

AbstractAn X‐band EPR‐Imaging apparatus which allowed us to determine the distribution of nitroxyl radicals within solid samples of polymeric materials containing hindered amine stabilizers, is described. It is shown that EPR Imaging represents a powerful tool for investigating the growth and decay of nitroxyls formed in polymers irradiated under air for long periods. Since the variations of the radical concentration can be monitored both in time and in the space, this technique provides valuable information not easily attainable by means of other methods.
Ethylene‐vinyl acetate (EVA) encapsulants for photovoltaic modules: Degradation and discoloration mechanisms and formulation modifications for improved photostability
Authors: Pern F. J. 
Published: April 2003

AbstractLong‐term photothermal stability is needed for the polymeric encapsulants made of ethylenevinyl acetate (EVA) copolymer used in crystalline‐silicon (c‐Si) based photovoltaic (PV) modules. Severe browning of EVA was observed in late 1980s on Carrisa Plains PV arrays installed with reflecting mirrors and resulted in large losses of the power output. The EVA browning crisis prompted NREL scientists in 1990 to investigate the problems and search for solutions. The key degradation mechanisms and discoloration factors were investigated by using a variety of film samples, including field‐degraded EVA samples and two commercial EVA formulations, regular‐cure A9918 and fast‐cure 15295, that were laminated, cured, and subjected to accelerated environmental exposures. Chemical, thermogravimetric, absorption/transmission, colorimetric, and fluorescence analyses were employed to characterize the EVA samples. Current‐voltage (I‐V) measurements were used to determine the electrical performance characteristics of solar cells. The results show that photothermal degradation is greater than thermal degradation and that the EVA A9918 discolors earlier and faster than EVA 15295. The UV absorber, Cyasorb UV 531,TMin commercial formulations decomposes photochemically and its decomposition rate is directly related to the temporal evolution of discoloring polyenic chromophores. In general, the loss rate of the UV absorber and the progress of EVA discoloration from light yellow to brown follow a sigmoidal pattern. Physically, UV‐filtering glass superstrates that remove UV ≤ 350 nm effectively reduce the discoloration rate of both commercial EVA formulations. Chemically, the EVA discoloration rate is affected by a number of factors, but more strongly by the formulation additives and curing conditions, in which additives and curinggenerated chromophores and their concentrations show a synergistic discoloring effect. Photobleaching reactions are responsible for the non‐discolored but degraded EVA because of oxidative destruction of the curing‐generated chromophores in the presence of oxygen. By using specifically selected stabilizers and curing agents in the new formulations, a large reduction in the chromophore generation by curing has been achieved and resulted in significant improvement of the photostability against discoloration.
Photo‐oxidation mechanisms of poly(2,6‐dimethyl‐1,4‐phenylene oxide).
Authors: Scoponi Macro , Ghiglione Chiara 
Published: April 2003

AbstractA re‐examination of the photo‐oxidation mechanism of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) at both long and short irradiation wavelengths under accelerated conditions is reported. The formation rate of poly‐2,6‐dimethylphenoxy (PDMP) radicals, have been observed by esr spectroscopy, while benzylic‐type radicals have been detected by spin trapping experiments using nitrosodurene under UV irradiation conditions. The changes of FTIR spectra obtained under accelerated photo‐oxidative conditions show the formation of primary oxidation products such as aromatic aldehydes and quinones. The direct formation of radical cations and superoxide anions by a photo‐induced electron‐transfer reaction is suggested under our conditions. In addition, some results on the of photo‐oxidation PPO/PS blends as a function of polystyrene tacticity are also reported. In the case of syndiotactic polystyrene the blend photostability shows some differences in comparison with the blend containing atactic polystyrene. This effect has been ascribed to the absence of excimers in syndiotactic polystyrene which are not revealed by fluorescence measurements. Finally, the chemical modification of PPO with bromine gave a bromomethylated PPO with different amounts of CH2 Br groups, which has been used for further substitution reactions with alkoxy sodium salts of 4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) and 4‐hydroxy‐1,2,2,6,6‐pentamethylpiperidine (PMPP). The accelerated photo‐oxidation of a modified copolymer PPO‐PMPP containing a 60% PMPP moieties as side groups and its blends with pure PPO has been followed by FTIR and esr spectroscopies. Some comparisons with a commercially available hindered amine light stabilizers (HALS) and a modified copolymer PPO‐PMPP are also reported under the same photo‐oxidative conditions.
The effects of desolvation methods of the recrystallized MgCl2‐alcohol adduct on catalyst characteristics and the bulk density of polyethylene
Authors: Chung Jin Suk , Han Jae Hyuck , Cho Han Suk , Lee Wha Young , Park Hong Man 
Published: April 2003

AbstractThe MgCl2 supports for an ethylene polymerization catalyst were prepared by the recrystallization method using methanol as a solvent. The effects of different desolvation methods of the recrystallized MgCl2‐alcohol adduct on the morphological characteristics of the catalysts were examined. The desolvation method greatly affects the characteristics of the catalyst. The prepared catalysts had different Ti/Mg ratios with respect to both surface content and entire catalyst particles. Considering Ti distribution and activity profiles, not only the polymerization conditions but also the Ti distribution on the catalyst appear to be an important factor which affects the bulk density of the polymers.
Zähigkeit und Relaxationsverhalten von Polymethylmethacrylat, Polystyrol und Polycarbonat
Authors: Grellmann Wolfgang , Lach Ralf 
Published: April 2003

AbstractInnovative Kunststoffanwendungen, die die speziellen Eigenschaften polymerer Werkstoffe gezielt ausnutzen, erfordern vertiefte Kenntnisse über festigkeits‐ und zähigkeitsbestimmende Mechanismen. Das sich in Abhängigkeit von der Temperatur ändernde Werkstoffverhalten von PMMA, PS und PC wurde bei dynamischer Beanspruchung mittels instrumentierter Kerbschlagbiegeprüfung bestimmt. Mit der verformungsbestimmten Rißöffnungsverschiebung δ und dem energiebestimmten J‐Integral stehen Kenngrößen der Fließbruchmechanik zur Verfügung, die eine strukturbezogene Quantifizierung der temperaturabhängigen mikromechanischen Prozesse erlauben. Die J‐Integralwerte zeigen für PMMA bei 50°C und für PC bei −60°C ein durch einen energiedissipativen Prozeß verursachtes Maximum. Dieses Maximum steht, wie sich aus der Interpretation der Frequenzabhängigkeit des mechanischen Verlustfaktors ergibt, mit der Neben(β)‐Relaxation in Beziehung. Dabei initiiert die β‐Relaxation Scherdeformationsmechanismen, die ihrerseits die lokale Zähigkeitserhöhung bewirken. Ab −25°C führt für PC ein spannungsinduzierter Scherfließprozeß zu einer erheblichen Zähigkeitssteigerung. Durch die Einbeziehung lichtmikroskopischer Untersuchungen des stabilen Rißfortschritts auf der Bruchfläche können Morphologie‐Zähigkeits‐Korrelationen abgeleitet werden.
Thermostable block copolymers, 2. Preparation and characterization of soluble blockcopolyimides
Authors: Sychra Marcel , Gruber Heinrich 
Published: April 2003

AbstractNew poly(amide‐imide)‐poly(imide) block copolymers (PAI‐PI‐BCPs) were prepared by polycondensation of amino‐terminated PAI‐blocks with anhydride‐terminated PI‐blocks. For the syntheses of the blocks with molecular weights from 2000 to 15000 only commercially available monomers were used, e.g. trimellitic acid anhydride chloride, benzophenone tetracarboxylic acid dianhydride, 4,4′‐diaminodiphenylmethane, 2,4‐toluenediamine and 4,4′‐diaminodiphenylsulfone. The BCPs were shown to have better solubility compared to the pure, insoluble PIs with only minor decrease of the thermostability. Thus, BCPs with good mechanical properties, thermostabilities up to 480°C (thermogravimetric analysis, 5% weight loss) and good solubility in dimethylacetamide and other polar aprotic solvents were obtained.
Synthesis of aromatic poly(ether ketone)s with ferrocene units in the main chain
Authors: Tunca Ümit 
Published: April 2003

AbstractAromatic poly(ether ketone)s with ferrocene units in the main chain were prepared by direct polycondensation of 1,1′‐ferrocenedicarboxylic acid with diphenyl ether or 1,4‐diphenoxybenzene using various catalysts such as trifluoromethanesulfonic acid (triflic acid), a combination of methanesulfonic acid/P2O5 (Eaton's reagent) or a combination of triflic acid/P2O5. Polycondensations at room temperature for 24 h gave poly(arylene ether ketone)s with inherent viscosities up to 40 mL g−1. Monoacylation of diphenyl ether with ferrocenecarboxylic acid was studied in detail in order to show the efficiency of polymer formation employing Eaton's reagent as catalyst and solvent.
Pervaporation membranes made of functionalized block copolymers
Authors: Schauer Jan , Lochmann Lubomír , Janata Miroslav , Bleha Miroslav 
Published: April 2003

AbstractPervaporation membranes were prepared with the separation layer made of various block copolymers. These copolymers were either unsubstituted hydrogenated polystyrene‐block‐polyisoprene or its derivatives substituted with Si(CH3)3, CH2OH, or COOCH3 groups in the polystyrene block. Composite membranes with a separation layer made of the unsubstituted copolymer preferentially transported water in pervaporation of aqueous solutions of ethanol or 1,4‐dioxane. Composite membranes with a separation layer made of the copolymer with COOCH3 groups also preferentially transported water in pervaporation of aqueous solutions of ethanol and in pervaporation of aqueous solutions of 1,4‐dioxane if the concentration of 1,4‐dioxane was low in the feed mixture. Composite membranes with a separation layer made of the trimethylsilylated copolymer transported preferentially ethanol or 1,4‐dioxane. Membranes with a separation layer containing hydroxymethyl groups exhibited high permeability but no selectivity.
Block and graft copolymers with polysiloxane and poly(N‐acyliminoethylene) sequences
Authors: Simionescu Cristofor I. , Rusa Mariana , David Geta , Pinteala Mariana , Harabagiu Valeria , Simionescu Bogdan C. 
Published: April 2003

AbstractA series of polysiloxane/poly(N‐acetyliminoethylene) (PSiO/PNAI) block and graft copolymers were synthesized by the initiation of 2‐methyl‐2‐oxazoline (Me‐OZO) polymerization with functional polysiloxane prepolymers. The copolymerization products were characterized by IR‐ and 1H NMR spectroscopy, elemental analysis, DSC and thermogravimetry. The insertion of both hydrophobic and hydrophilic sequences in the macromolecular structure induces a behavior characteristic of amphiphilic compounds. Their solution and solid state behavior evidenced peculiarities which make them able to act as nonionic emulsifiers, surface modifiers, gels, etc.
Compared properties of aromatic polyamides containing silicon in the main chain
Authors: Sava Ion , Szesztay Marta , Bruma Maria , Mercer Frank , Schulz Burkhard 
Published: April 2003

AbstractTwo series of aromatic polyamides incorporating silicon together with phenylquinoxaline or with hexafluoroisopropylidene groups have been synthesized and their properties have been characterized and compared with those of related polymers. These polymers are easily soluble in polar amidic solvents such as N‐methyl‐2‐pyrrolidinone and dimethylformamide, and in tetrahydrofuran, and can be cast into thin, transparent films from solution. The polyamides have weight‐ and number‐average molecular weights in the range of 10 000–40 000 and 3 000–6 000, respectively, and polydispersities in the range of 3–10. They show glass transition temperatures in the range of 236°C–275°C and decomposition temperatures above 400°C. The polymer films have low dielectric constants in the range of 3.26–3.68, and good mechanical properties (tensile strength 74–100 MPa, tensile modulus 180–386 MPa), thus being comparable with other high performance dielectrics.
Biological degradation of cellulose acetate films: Effect of plasticizer
Authors: Jiang L. , Hinrichsen G. 
Published: April 2003

AbstractBiodegradation of plasticized cellulose acetate (PCA) was established with a standard municipal solid waste (ED 73). The relative percent weight loss of the specimen was measured, and the aerobic biodegradation was evaluated in a controlled aerobic composting system that was designed to capture CO2 produced by microbiological metabolism. Infrared spectra (FTIR), mechanical properties and molecular weight of degraded PCA films indicate that the lower molecular weight fractions, such as plasticizer and lower substituted fractions of PCA, are biodegraded and removed preferentially from the PCA.
A study of particle initiation in vinyl chloride emulsion polymerization using response surface experimentation
Authors: Lazor John T. 
Published: April 2003

AbstractVinyl chloride monomer was polymerized in an emulsion system in the presence of a redox catalyst and relatively low concentrations of emulsifier. The effects of sodium bisulfite, potassium persulfate, and commercial sodium lauryl sulfate concentrations on particle initiation were determined by response‐surface experimentation. A regression equation was developed which describes the number of particles per unit volume initiated in this vinyl chloride emulsion system. At subcritical emulsifier concentrations, the number of particles initiated was dependent primarily upon the emulsifier and sodium bisulfite concentrations and to a lesser degree upon the persulfate concentration. As the critical micelle concentration was approached, an apparent change in the particle initiation mechanism was observed, in that the sodium bisulfite concentration ceased to have an effect. In this system the change occurred at a concentration of 0.005% emulsifier.
The force‐temperature behavior of swollen cellulose model filaments
Authors: Passaglia Elio , Koppehele H. P. 
Published: April 2003

AbstractThe force as a function of temperature at constant length for cellulose model filaments swollen in water shows a maximum the temperature of which decreases with increasing orientation. At an orientation achieved by a prestretch of 80%, no more maximum exists, and the force decreases monotonically with increasing temperature. This behavior cannot be attributed to changes in the entropy and enthalpy of elongation with temperature, but is due rather to changes in the degree of swelling. When corrections are made for this, the positive force‐temperature coefficient observed for some of the curves becomes negative. The equilibrium stress‐strain curves are linear up to elongations of 5%. The‐oretical evaluation of these curves is not possible with the present state of theory. Filaments with predominantly a skin structure show a minimum in the force‐temperature curves; this is the more common behavior.
Preparation of porous membranes
Authors: Harper B. G. 
Published: April 2003

AbstractA new method for preparing plastic membranes with very small pores is described. The method involves dissolving two or more film‐forming polymers in a common solvent. A thin layer of the resulting solution is spread on a smooth surface and the solvent is allowed to evaporate. One of the polymers is then extracted from the resulting film with a selective solvent. The selective permeability of ethyl cellulose was altered considerably using polyethylene glycol as the second polymer. The apparatus for determining the permeability of these films is described. Pictures of the membranes at different stages in their preparation are shown. Electron micrographs demonstrating the effect of this treatment on ethyl cellulose are presented.