bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanisms of antioxidant action: Transformations involved in the antioxidant function of zinc dialkyl dithiocarbamates. I
Authors: Al‐Malaika S. , Marogi A. , Scott G. 
Published: April 2003

AbstractThe antioxidant mechanism of zinc dialkyl dithiocarbamate is examined in detail in model compounds. The kinetics of the reaction of zinc dialkyl dithiocarbamate with hydroperoxides were studied in inert and oxidizable substrates. A typical electron donor antioxidant and a base (CaCO3) were found to inhibit the peroxide decomposition. The oxidation products of the Zinc II complex appear to be quite different from those of the nickel II and iron III complexes. Two processes are involved in the antioxidant function of the zinc complex: The first is a free radical decomposition of the peroxides, which predominates at molar cumene hydroperoxide (CHP)/zinc diethyl dithiocarbamate (ZnDEC) ratios of 10 or less. At higher molar ratios an ionic reaction predominates, although there is a radical contribution at all ratios. Thiocarbamoyl disulfide does not seem to be formed as an intermediate from ZnDEC during the ionic process.
Shear modification of low density polyethylene
Authors: Teh J. W. , Rudin Alfred , Schreiber Henry P. 
Published: April 2003

AbstractA single screw extruder was used to impose different shear histories on a low density polyethylene with broad molecular weight distribution and high molecular weight tail that had very little long chain branching. This polymer exhibits relatively high melt elasticity and the viscoelastic properties of its melt are strongly affected by preshearing. Such changes are accomplished without significant changes in molecular weight distribution or chemical structure. Measured viscous and elastic properties of the melt are different from piston‐driven and screw extruder capillary rheometers. Shear modification effects in single screw extruders are enhanced by decreasing melt temperature, increased screw rotation speeds, and higher screw compression ratios. Melt elasticity can be cycled between high and relatively low values, for the particular polymer, by annealing or shearing the polymer melt.
Solute diffusion in swollen membranes. IV. Theories for moderately swollen networks
Authors: Peppas Nikolaos A. , Moynihan Humphrey J. 
Published: April 2003

AbstractA theoretical model was developed to describe solute transport through moderately swollen networks. The model is an extension of the previous analysis of Peppas and Reinhart (1983), and it describes the normalized effective diffusion coefficient of the solute through the network as a function of the equilibrium degree of swelling, Q, the hydrodynamic radius of the solute, rs, the number average molecular weight between crosslinks, M¯c, and a function f(ξ) of the mesh size ξ, which takes into consideration barriers due to crosslinks, entanglements, etc. For the development of this model, the Cohen–Turnbull (1958) free volume theory was modified to incorporate topological and mobility characteristics from de Gennes' analysis (1979).
Gas sorption and permeation of poly(γ‐methyl glutamate)
Authors: Tsujita Y. , Sumitomo T. , Nomura M. , Takizawa A. 
Published: April 2003

AbstractSorption, permeation, and diffusion behaviors of poly(γ‐methyl glutamate) were examined in the light of superstructure including conformation. Highly crystalline PMG, chloesteric twisted structure, low crystalline PMG, which are all composed of α helix, and β form PMG were prepared using cast solvent of chloroform, dichloromethane–dimethylformamide, and dimethylformamide and treating by formic acid, respectively. The large amount sorbed and the sorption capacity were interpreted by an existence of a microvoid in PMG cast film from chloroform. On the other hand, β form PMG had small amount sorbed. The sorption behavior was remarkably influenced by superstructure as well as conformation, while the effect of only conformation on the permeation behavior was recognized. A peculiar permeation was detected around 100°C for all the samples.
Polymerization of dicyclopentadiene: A new reaction injection molding system
Authors: Matějka Libor , Houtman Carl , Macosko Christopher W. 
Published: April 2003

AbstractDicyclopentadiene was polymerized by reaction injection molding (RIM) using a catalyst system based on WCl6 and diethylaluminium chloride. Ring opening polymerization results in formation of a crosslinked polymer with a high crosslink density. The kinetics of the fast exothermic reaction was followed by the adiabatic temperature rise method. In addition to the “adiabatic” polymerization, isothermal reactions were carried out in a thin mold. The properties of the cured samples were determined by dynamic mechanical measurements, solgel analysis, gas chromatography, mass spectrometry, DSC, and IR spectrometry. Gel fraction, glass transition temperature, content of the unreacted monomer, the modulus, and the degree of swelling were used to characterize the cured samples. The system shows very low critical conversion at the gel point (αc < 0.01) proving a chainwise mechanism of the polymerization. Possible participation of a cationic mechanism is discussed. We found the specific reaction temperature range (T = 100–140°C) for optimum properties of the cured samples. Deterioration of properties (decrease in the crosslinking density, etc.) at a high temperature is a result of a faster deactivation of catalytic centers and a reversibility of the exothermic ring opening polymerization. Reverse cyclodegradation is preferred at a higher temperature.
Thermal expansion properties of particulates based on the concept of mesophase
Authors: Theocaris P. S. , Varias A. G. 
Published: April 2003

AbstractThe determination of the cubic thermal expansion coefficient of a two‐phase particulate is presented in this paper. The model described is based on the well‐known Kerner's model and takes into account the existence of mesophase, which constitutes a boundary layer between inclusions and the matrix in the composite. This layer is assumed as created by the substance of matrix during the preparation procedure of the composite, and it includes areas of imperfections around and near the inclusions. The influence of this layer on the effective properties of the composite has been proved to be significant. In order to take into consideration the influence of mesophase a spherical shell with the average properties of this layer is interposed between the spherical inclusion and the matrix. The evaluation of the average elastic and thermoelastic properties and also of the extent of mesophase is succeeded by considering the two‐term unfolding model, introduced previously, for describing the change of the elastic modulus of the mesophase layer of fiber‐reinforced and particulate composites. The two‐term unfolding model was, in this paper, extended to incorporate the mode of variation of the thermal expansion coefficient and the bulk modulus in the mesophase. The model was applied to a polyurethane rubber filled with particles of sodium chloride, and its predictions were found to be in good agreement with the experimental data.
Properties of syndiotacticity‐rich poly(vinyl alcohol) thin film in water. II. Effect of the annealing temperature on the extension of thin film in water
Authors: Yamaura Kazuo , Matsuzawa Shuji 
Published: April 2003

AbstractThe effect of the annealing temperature on the extension of thin film of syndiotacticityrich poly(vinyl alcohol)(PVAVTFA) derived from vinyl trifluoroacetate is investigated in water. For the samples annealed at the temperature of above 125°C, the time of initiation of elongation and Young's modulus increase steeply with the elevation of annealing temperature, and the time required to maximum elongation and the maximum elongation ratio decrease quietly. The elongation ratio at break during the elevation of temperature of water decreases with the increase in the annealing temperature, that is, from 6.5 to 1.5. Reversely, the temperature at break increases from 85 to 97°C, but it is minimum at the annealing temperature of 125°C.
Chain extenders for polyesters. I. Addition‐type chain extenders reactive with carboxyl end groups of polyesters
Authors: Inata Hiroo , Matsumura Shunichi 
Published: April 2003

AbstractEffective chain extenders for linear polyesters were investigated among some bis‐heterocycles, which were capable of coupling carboxyl terminals of the polyesters through addition reaction. Consequently, 2,2′‐bis(2‐oxazoline), 2,2′‐bis(5,6‐dihydro‐4H‐1,3‐oxazine) and N,N′‐hexamethylenebis(carbamoyl‐2‐ oxazoline) were found to be the most effective chain extenders. Starting from a poly(ethylene terephthalate) (PET) having intrinsic viscosity ([η]) of 0.66 and carboxyl content (CV) of 46 eq/106 g, one could obtain polyesters with [η] of above 1.0 and CV of below 5 eq/106 g in the presence of the chain extenders. Typical reaction condition for the coupling of PET was heating PET under atmospheric nitrogen above its melting temperature with 0.5 mol % of a chain extenders only for several minutes. Bis‐2‐thiazolines showed no effect under the condition investigated, while in case of bis‐2‐imidazolines definite degradation was observed. Bis‐N‐acylaziridines and bisiminocarbonates resulted in some gell formation, indicative of side reactions.
Fatigue mechanism of fiber‐reinforced polypropylene swollen by oil
Authors: Iisaka K. , Namai Y. 
Published: April 2003

AbstractFatigue mechanism was investigated for the fiber‐reinforced polypropylene (FRPP) swollen by a small amount of oil. The curves of applied cyclic stress (S) vs. logarithm of cycles to failure (N) shifted into smaller values of S and N, respectively, by adding oil into the polymer and with increasing a test temperature. The endurance limiting stress (σe) for the swollen FRPP, defined as the stress at a long lifetime, became much the same as the one for the swollen unfilled polypropylene, though the former was considerably larger than the latter for the breaking strength measured in standard bending test. The activation energy and the activated volume, which have been determined by the Eyring's model from the S–N curves at higher stress levels, suggest that the introduction of a small amount of oil into the polymer lowers a motional unit associated with a fatigue process from 30 to several repeat units. The major decrease in σe by swelling can be explained in terms of the crack–nucleation theory. It is indicated that this decrease yields from the change in the stress–concentration factor.
Carboxymethyl‐cellulose‐grafted with dextrin synthesis and solution rheology
Authors: Sikkema D. J. 
Published: April 2003

AbstractCarboxymethyl cellulose grafted with dextrin (CMC‐g‐dextrin) products are easily accessible by reacting freshly prepared CMC with the acid alcoholysis product from starch and glycerol monochlorohydrin. The success of the grafting reaction depends on adjusting the alkalinity of the grafting reaction mass prior to addition of the dextrin chlorohydrin reagent. In all, less NaOH should be applied than theoretically necessary for all chlorine substitution. In some cases the products show interesting rheology at very low shear, but rather CMC‐like rheology or more Newtonian behavior than CMC at shearing rates over a few reciprocal seconds. These results reinforce the credibility of the view that natural polysaccharide gums with unusual rheologies derive their special properties from their well‐defined substitution pattern rather than from their overall degree of substitution with (oligo)saccharide units.
Solvent power effect on graessley's time constant in concentrated polystyrene solutions
Authors: Quadrat Otakar , Mikeŝov´ Jana , Prokopová Eva 
Published: April 2003

AbstractResults of our measurements of polystyrene solutions and those reported in the literature demonstrate the common dependence of Graessley's relaxation time on the product of concentration and molecular weight, irrespective of the solvent power and its viscosity, and of temperature. Such behavior is in agreement with the conclusions reached in our previous paper, namely, that the shear stress dependence of viscosity of this polymer in solvents differing considerably in viscosity and solvent power may be unified by plotting relative viscosity against the product of velocity gradient and Rouse's relaxation time.
Effects of poly(methyl methacrylate‐co‐n‐butyl acrylate) on the properties and processing behavior of poly(vinyl chloride)
Authors: Lee Yu‐Der , Cheng Kung‐Chun 
Published: April 2003

AbstractRandom copolymers of methyl methacrylate/n‐butyl acrylate with a BA content of 0–50% and M̄v = 0.16–4.04 × 106 were synthesized and evaluated as a processing aid (PA) for poly(vinyl chloride) (PVC). Their effects on the processability and properties of PVC were investigated with respect to the composition, molecular weight, and the amount of the copolymer added. It was found that the fusion rate of PVC could be improved (i) by increasing the amount of the copolymer used, (ii) by increasing the butyl acrylate content in the copolymer, and (iii) by lowering the molecular weight of the copolymer. The effect of molecular weight, composition, and amount of copolymer on the ultimate mechanical properties of PVC was investigated. The presence of copolymer did not affect the impact strength. However, the tensile strength and elongation at break were improved, particularly at high temperature (125°C). It was also found that the “plate out” phenomenon of PVC could be significantly reduced in the presence of the processing aid.
The behavior of spiral angle ϕ and the angle of crystallite dispersion α of normal cottons with stress
Authors: Kalyanaraman A. R. 
Published: April 2003

AbstractIt is well known that the cotton fiber consists of microfibrils which in turn do have crystalline and amorphous regions. The crystallites are arranged in the form of helices, and with stress the helical configuration changes. This paper examines the configurational changes that occur in the helix and makes it clear that the amorphous regions of the microfibrils are the source of these changes.
Matrix resins based on bismaleimide–1,2‐polybutadienes
Authors: Gupta Alka D. , Kumar Devendra 
Published: April 2003

AbstractImproved thermally stable matrix resins have been obtained by the incorporation of 1,2‐polybutadiene in 4,4′‐bismaleimidodiphenylmethane. The thermal curing was performed at 185–195°C for 2.5 h and at 230–235°C for 45 min to give tough crosslinked polymers. The thermal curing reaction was monitered using FT‐IR and differential scanning calorimetry. Thermogravimetric analysis of the cured resins have shown improved thermal stability up to 490–480°C both in air and nitrogen atmospheres. The char yield obtained in nitrogen at 800°C was in the range of 50–49%. Graphite cloth laminates were prepared and tested. The laminates showed improved tensile strength over to parent bismaleimide. 1,2‐Polybutadiene was hydrogenated using 10% palladized‐charcoal. The resulting polymer was characterized by using IR and 1H‐NMR, which showed reduction of 15% pendent vinyl double bonds.
Chemical engineering aspects of reactive dyeing
Authors: Sada Eizo , Kumazawa Hidehiro , Ando Tetsuo 
Published: April 2003

AbstractThe process of dyeing with reactive dyes was formulated on the basis of diffusion of dye species in the pores of polymer phase accompanied by fixation reaction with fiber substrate on the pore wall incorporating hydrolysis of dye species. The effect of the hydrolysis on the fractional fixation was numerically analyzed under various levels of bath ratio and degree of mixing in the dyebath. The simulation model was presented to yield the unlevelness arisen from lack of uniformity of degree of mixing in the dyebath.
Shrinkage and retractive force of drawn isotactic polypropylene during heating
Authors: De Candia F. , Romano G. , Vittoria V. , Peterlin A. 
Published: April 2003

AbstractThe semi‐crystalline isotactic polypropylene was drawn to λ = 6,7,8,9,11 and the drawn samples heated to temperatures between 40 and 160°C. The shrinkage of the sample with λ = 7 and 11 was measured as function of time and temperature. The effect of shrinkage is higher with the smaller draw ratio as if the drawing increased the thermal stability of the sample. With fixed ends the drawn samples were heated at a constant rate and the retractive stress observed. It increases with λ and the heating rate. At the same drawing ratio λ, the curves of the retractive stress show a maximum and subsequently drop to a substantially smaller value that increases with the draw ratio and the distance of the highest temperature of the heating from the melting point of the sample. The cooling curve of the first run almost coincides with the heating and cooling curve of the next runs if one does not surpass the maximum temperature of heating of the first run. The time dependence of the retractive stress after an inital maximum decays more rapidly to the limiting value σ∞ (T) the higher the temperature of the experiment. The limiting value σ∞ (T) rapidly decreases with T and increases with λ.
Uniaxial orientation of linear low density polyethylene
Authors: Pezzutti Jose L. , Porter Roger S. 
Published: April 2003

AbstractOnly a few reported studies have involved the uniaxial orientation of LDPE and even less on LLDPE. It is our purpose to report on characteristics of uniaxially oriented films of LLDPE that contribute to property development. The LLDPE has been coextruded at 25 and at 80°C layered as ribbons within longitudinally split billets of HDPE. The LLDPE so drawn was characterized by thermal analysis, birefringence, elastic recovery, and wide angle X‐ray measurements. As a result, we can conclude that the drawing of LLDPE at the lower temperature produces a relatively high content of monoclinic crystals; the orientation behavior of LLDPE is similar to that of HDPE. The molecular network formed by entanglements and crystals reduces the draw to a maximum below 15.
Radiation‐induced emulsion polymerization of vinyl acetate in a pilot plant reactor I. Recycle flow reactor
Authors: Challa R. R. , Drew J. H. , Stannett V. T. , Stahel E. P. 
Published: April 2003

AbstractA number of successful radiation polymerization of vinyl acetate in emulsion have been carried out in a modular stainless steel flow pilot plant. In a recycle mode, the system was utilized for extremely accurate kinetic measurements and experimental verification of model restrictions such as plug flow, lack of post irradiation effects and differential reactor behavior. Experimental conditions were explored to minimize contaminant, primarily oxygen, inhibition, and the tendency for this formulation, essentially an adhesive, to build up on the reactor walls. Industrial scaleup of such a prototype system appears attractive.
Preparation of polymer latex films by a flash casting technique
Authors: Chainey M. , Wilkinson M. C. , Hearn J. 
Published: April 2003

AbstractConventional film casting methods have proved unsuitable for the preparation of thin (10–100 μ) films from surfactant‐free polymer latices. A flash casting technique has been devised and successfully employed to cast films from a wide range of surfactant‐free homopolymer, copolymer and core‐shell polymer latices. Essentially, the method involves spraying the latex at a specially designed hotplate, the surface of which is coated with a thin layer of PTFE. The hotplate is maintained at a temperature between 393 and 473 K. When sufficient thickness of film has been built up, the hotplate is switched off and allowed to cool to the temperature at which the film is to be removed. For homogeneous latex films, the optimum temperature range for removal lies in the region of the glass transition temperature of the polymer concerned. Where this is below ambient, the appropriate cooling mixture is placed in a slush bath, situated to the rear of the hotplate, thereby cooling the hotplate to the correct temperature. The film is removed by gently peeling it from the surface. The surfaces of the films appeared smooth to the naked eye, but the sprayed surfaces of freshly prepared poly(n‐butyl methacrylate) films were rough when examined by scanning electron microscopy. The surfaces smoothed out on ageing, resembling those of solvent‐cast films after one months storage.
Effect of silicon comonomers on thermal degradation of polystyrene
Authors: Gupta D. C. , Sharma R. C. 
Published: April 2003

AbstractThe thermal degradation of the following organosilicon copolymers: styrene–vinylmethyl‐diacetoxysilane, styrene‐2‐methacryloyloxypropoxytrimethyl silane, styrene–(dimethyl) siloxane–methylvinylsiloxane) diol and hexamethyl cyclotrisiloxane–styrene–hexamethyl cyclotrisiloxane was investigated. The techniques of thermogravimetry, thermomechanical analysis, and differential scanning calorimetry (DSC) were used. The initial decomposition temperature for all the copolymers except styrene–siloxane block copolymers was less than that for polystyrene irrespective of the nature of the silicon comonomer. Integral procedural decomposition temperature of copolymers was higher than that for polystyrene except styrene‐2‐methacryloyloxy propoxytrimethyl silane copolymers which were showing lower (IPDT) values. Styrene–siloxane copolymers were found to be most thermally stable. Variation in the glass transition temperature and probe displacement under stress is related to the polarity of the silicon moiety in the styrene copolymers.
Radiation‐induced graft copolymerization of methacrylic acid onto polypropylene fibers VI. Dyeing behavior
Authors: Mukherjee A. K. , Gupta B. D. 
Published: April 2003

AbstractThe dyeing behavior of polypropylene‐g‐polymethacrylic acid fibers prepared by graft copolymerization of methacrylic acid onto polypropylene fibers by gamma‐ray irradiation was evaluated for their dyeability characteristics using two basic dyes, rhodamine B and methylene blue. An increase in the dye uptake and moisture regain with the increase in graft content was observed. Such behavior has been attributed to the hydrophilicity imparted to polypropylene fiber by the presence of polar carboxyl groups in polymethacrylic acid grafts. The dependence of rate of dyeing on the percentage graft was evaluated. The diffusion coefficient of the fiber showed an increase with the increase in graft content and has been related to the structural changes occurring during grafting.
Study on the curing behavior of resol. IV. Comparison of the curing behavior of resols prepared with either sodium hydroxide or barium hydroxide
Authors: Fukuda Akinori , Hasegawa Kiichi , Horiuchi Hikaru 
Published: April 2003

AbstractCuring behaviors of two kinds of resols prepared by the reaction of phenol (1 mol), formaldehyde (1.2 mol), and either sodium hydroxide (0.02 mol) or barium hydroxide (0.01 mol), were examined at 120°C by means of Curelastometer, IR spectroscopy, THE extraction, and GPC. Gelling and curing speeds of the resol prepared with barium hydroxide as catalyst (BR) were faster than with sodium hydroxide (NR). The amount of hydroxymethyl groups in BR also decreased more rapidly with an increase in the cure time than that in NR by IR spectrometry. Similar results were confirmed by THF extraction and GPC. It is recognized in the curing of both resols that relatively higher molecular weight compounds gel rapidly and that, after major components in the resol have changed to gel, low molecular weight compounds still remain in the resol as sol state. It is inferred from GPC that NR differs from BR in the molecular weight of the compounds which exist prior to gel formation, namely, the molecular weight of the compounds in BR is smaller than that in NR.