bluuebunny/crossref_metadata_2025 huggingface dataset:
Mie scattering from sphere structures in polymer blends
Authors: Uemura Yukikazu , Chikaishi Kazuhiro , Yamazaki Takashi
Published: April 2003

Polymer blends of transparent poly(methyl methacrylate) and polystyrene become opaque due to light scattering at the boundaries of the two polymers. The polymer blend is light brown when it is illuminated by white light. The coloring depends on the spherical domain structures existing in the polymer blend. The coloring was analyzed by using the rigorous Mie theory. The Mie results were compared with the semiempirical results previously reported by the authors. The wavelength dependence of theoretical scattering efficiencies on radii of scattering spheres from 0.05 to 1.2 μm was obtained for polystyrene spheres in poly(methyl methacrylate) matrix, and vice versa. The scattering at the short wavelength region is stronger than at the long wavelength region. The scattering efficiencies become almost constant in the visible wavelength region for sufficiently large spheres.
The chemistry and development of tannin/urea–formaldehyde condensates for exterior wood adhesives
Authors: Pizzi A.
Published: April 2003

Novolak‐like materials were prepared by condensation of urea–formaldehyde resins with resorcinol and/or resorcinolic A‐rings of polyflavonoids such as condensed tannins. The copolymers formed were used as thermosetting and cold‐setting exterior‐grade wood adhesives. Condensation of tannins with small amounts of urea–formaldehyde resins can prevent the water deterioration normally experienced by the latter resins. Conversely, urea–formaldehyde resins improve crosslinking and strength of wood tannin–formaldehyde networks.
Plasma polymerization of tetrafluoroethylene. II. Capacitive radio frequency discharge
Authors: Morosoff N. , Yasuda H. , Brandt E. S. , Reilley C. N.
Published: April 2003

The plasma polymerization of tetrafluoroethylene (TFE) is studied in a capacitively coupled system with internal electrodes using radio frequency (13.56 MHz) power. The emphasis is on identifying conditions that are compatible with continuous coating of plasma polymer on a substrate moving through the center of the interelectrode gap. At high pressure (500 mTorr), deposition of plasma polymer is primarily on the electrodes rather than on a substrate placed midway between electrodes. Glow is observed in only part of the interelectrode gap at low powers and fills the gap only at high power levels. The use of a magnetic field effects barely discernible changes. Low‐pressure (below 100 mTorr) operation is more favorable for deposition of a substantial portion of the plasma polymer on a substrate placed midway between electrodes. The plasma polymer deposited at low pressure is characterized by ESCA and deposition rate data and compared to that deposited in an inductively coupled system. The polymers formed in both systems are broadly similar and completely different from conventional poly(TFE). Subtle system‐dependent differences are identified. The known susceptibility of fluorine‐containing polymers (including plasma polymer) to a high‐power plasma has been used as a probe of plasma power density within the interelectrode gap in the capacitively coupled system. Without magnets the most active zone of the plasma is in the center of the interelectrode gap. The use of a magnetic field moves this active zone closer to the electrodes and leads to a more efficient coupling of energy to a polymerizing glow discharge.
Composition analysis of crosslinked styrene–ethylene dimethacrylate and styrene–divinylbenzene copolymers by Raman spectroscopy
Authors: Štokr J. , Schneider B. , Frydrychová A. , Čoupek J.
Published: April 2003

A method for the determination of composition and content of pendent double bonds in untreated samples of styrene–ethylene dimethacrylate and styrene–divinylbenzene copolymers from Raman spectra has been developed. By computer treatment of spectra it was shown that Raman spectra are sensitive to the distribution of components in the studied copolymers.
Pilot‐plant process for starch xanthide encapsulated pesticides
Authors: Stout E. I. , Shasha B. S. , Doane W. M.
Published: April 2003

A small pilot‐plant batch process for the encapsulation of pesticides with crosslinked starch xanthate (starch xanthide) has been developed. Multipound quantities of several encapsulated pesticides have been prepared that have slow‐release properties. Products were made from starch xanthates of varying degrees of substitution (0.1 to 0.3) and with various crosslinking agents (H2O2, NaNO2, NaOCl, NaClO2, and FeCl3). Recovery of the pesticides as the encapsulated product ranged from 62% to nearly 100%. In a single experiment, processing water was recycled without apparent problems.
Reverse osmosis characteristics of cellulose acetate butyrate membranes
Authors: Ohya Haruhiko , Akimoto Naoyuki , Negishi Yoichi
Published: April 2003

Cellulose acetate butyrate membranes were cast from five different formulations. The pure water flux through the membrane increased with evaporation period. The separation of 4000 ppm NaCl aqueous solution remained unchanged until it reached a critical flux; at that point, separation decreased inversely proportional to the flux. Scanning electron microscope photography of the membranes corresponding to each evaporation period is reported.
Morphology and mechanical behavior of poly(vinyl chloride)/poly(butadiene–co–acrylonitrile) latex interpenetrating polymer networks
Authors: Sionakidis J. , Sperling L. H. , Thomas D. A.
Published: April 2003

A series of poly(vinyl chloride)/poly(butadiene–co–acrylonitrile) interpenetrating polymer networks (IPNs), all having 50/(25–25) weight compositions, was synthesized in latex form. The latex particles were studied after each step of the two‐staged polymerization and after molding or casting. Transmission electron microscopy together with dynamic mechanical spectroscopy suggest a graded composition within the latexes, in which the poly(vinyl chloride) seed latex network I forms a core that is partially penetrated by the poly(butadiene–co–acrylonitrile) network II, yielding increased amounts of poly(butadiene–co–acrylonitrile) in the shell of the latex particles.
Phenolic and tannin‐based adhesive resins by reactions of coordinated metal ligands. II. Tannin adhesive preparation, characteristics, and application
Authors: Pizzi A.
Published: April 2003

The accelerating effect due to bivalent metal ions observed in simple phenol–formaldehyde reactions are also observed in tannin–formaldehyde resins. Tannin steric hindrance prevents the retarding effect of trivalent metallic ions on tannin–formaldehyde reactions. Small amounts of metal ions do not significantly increase flavonoid B‐ring participation to the crosslinking of tannin–formaldehyde networks. Improved plywood strength and shorter pressing times are obtained by the addition of metal ions to tannin/formaldehyde resins. These results are due to faster curing promoted by the presence of the metal ions.
Characterization of transport across cellulose acetate membranes in the presence of strong solute–membrane interactions
Authors: Burghoff H.‐G. , Lee K. L. , Pusch W.
Published: April 2003

Certain organic solutes, including phenol, undergo anomalous enrichment when hyperfiltered through cellulose acetate membranes: the solute concentration is higher in the permeate than in the feed solution. A number of existing theoretical approaches describing hyperfiltration phenomena are presented and their merits and limitations upon application to the transport of phenol discussed. A new two‐parameter transport relationship is derived based on an extension of the solution–diffusion model. The enrichment, or negative solute rejection by the membrane, is predicted to occur whenever the pressure‐induced solute permeation velocity exceeds that of water. By acknowledging and incorporating the effect of pressure on the chemical potential of the solute, the present extended solution–diffusion model relationship successfully describes hyperfiltration data of phenol in homogeneous and asymmetric cellulose acetate membranes provided the contribution of convective flow to the overall solute transport is insignificant. In addition to the transport parameters of the extended solution–diffusion model, the transport parameters of the phenomenological, Kedem–Spiegler, and combined viscous flow–frictional relationship are evaluated from hyperfiltration data obtained with 0.05 and 0.1 wt % phenol feed solutions and homogeneous cellulose acetate membranes of different acetyl content.
The effect of dyes and dyeing on the mechanical properties of polymeric materials
Authors: Ugbolue S. C. O. , Aula S. M.
Published: April 2003

The effect of reactive and disperse dyes and dyeing on the mechanical properties of cotton and polyester fibers, respectively, has been studied. It is observed that reactive dye (Procion Brilliant Red MX‐2B) and disperse dye (Dispersol Red B‐2B) caused a decrease in the tensile strength of the fiber which was often accompained by a decrease in the extensibility and general improvement in the tensile stiffness of the fibers. A linear relationship exists between percent disperse dye on the fiber and the square root of time of dyeing for poly(ethylene terephthalate) fibers in the initial region of dye uptake.
Surface characterization of plasma‐treated poly‐p‐xylylene films
Authors: Nowlin T. E. , Smith D. Foss
Published: April 2003

Plasma‐treated poly‐p‐xylylene films have been characterized by neutron activation oxygen analysis, internal reflection (IRS) and transmission infrared spectroscopy, transmission electron microscopy (TEM), and surface contact angle measurements. The results indicate that an oxygen plasma roughens the surface and that oxygen is incorporated into the surface. Oxygen is not detected in the bulk of the sample. The infrared transmission spectra exhibited no carbonyl band, but the relative band intensities changed, indicating a change in ring substitution by a loss of chlorine in the chlorinated poly‐p‐xylylenes. The IRS spectra of the surface of films treated with oxygen plasma did contain carbonyl bands at 1730 and 1640 cm−1. Argon and helium plasmas generally decreased the water contact angle measured on plasma‐treated poly‐p‐xylylene surfaces more than oxygen or nitrogen plasma treatments. Regardless of the plasma utilized, the water contact angles increased with time after the treatment but did not recover to the original level. IRS spectra of the surface of films treated with argon plasma contained carbonyl bands at 1730 and 1695 cm−1. The adhesion of a polyurethane thermosetting material to a poly‐p‐xylylene surface is greatly improved if a plasma treatment is used prior to the application of the polyurethane. The degree of improvement in adhesion was dependent on the type of plasma and the treatment time.
Polyparaxylylene electrets usable at high temperatures
Authors: Raschke C. R. , Nowlin T. E.
Published: April 2003

Thin coatings of various polyparaxylylenes were transformed into electrets by corona charging them and then overcoating with more polyparaxylylene to protect the charge layer. For such electrets, the extrapolated ten‐year use temperature depended on the thermo‐oxidative stability of the polyparaxylylene layer and was greater than 100°C for the most stable electrets. The voltage levels and surface charge densities were always greater than or equal to those of charged Teflon electrets, similar to those used in commercial devices.
Comparison of laboratory techniques for evaluating the fracture toughness of glassy polymers
Authors: Ting R. Y. , Cottington R. L.
Published: April 2003

Several test methods were employed to determine polymer fracture toughness (𝒢Ic, the opening‐mode strain energy release rate) at room temperature. The materials used included DGEBA epoxies and those modified by the addition of CTBN elastomers. Double‐cantilever beam specimens were used to determine the fracture toughness both of bulk resins and of an adhesive layer bonded between two aluminum half‐beams. The adhesive fracture toughness of a 0.025‐cm bond was slightly less than the bulk 𝒢Ic value, attributed to the bond thickness effect. Fracture toughness of bulk resins was also evaluated by using both rectangular and round compact tension specimens. The results, when compared with those obtained with the bulk double‐cantilever beams, are quite acceptable. The thickness of compact tension specimens, ranging from 0.64 to 1.0 cm, might not give pure plane‐strain conditions, and thus some plane‐stress contribution to 𝒢Ic should be expected for the tougher materials. Izod impact tests were also carried out to determine sample fracture toughness at high loading rate.
Catalytic effect of hydrogen chloride on the degradation of poly(vinyl chloride)
Authors: Owen Eryl D. , Pasha Ishrat , Moayyedi Faezeh
Published: April 2003

The distribution of polyenes which results from the chemical dehydrochlorination of poly(vinyl chloride) has been studied in dichloromethane (DCM) and tetrahydrofuran (THF) solvents. A higher percentage of longer polyenes is formed in DCM than in THF. On the addition of trifluoroacetic acid to DCM solutions of the polyenes, new species are formed with strong absorptions in the region 500–800 nm. The absorptions are probably due to polyenylic ions formed by protonation of the polyenes, and the interrelated changes in their intensities can be explained by the migration of short polyene sequences along the polymer chain with the formation of longer sequences. The species are extremely photosensitive and are bleached in a few seconds with light from a medium‐pressure mercury lamp. The relevance of these experiments to the effect of HCl on the polyene distribution and on the rate of photocrosslinking is discussed.
Preparation and surface modification of poly(vinylbenzyl chloride) latices
Authors: Chonde Y. , Liu L‐J. , Krieger I. M.
Published: April 2003

Monodisperse stable latices with reactive methyl chloride surface functionalities were prepared in the presence of mixed surfactants using vinylbenzyl chloride in various ways: as a homopolymer, crosslinked with divinylbenzene, copolymerized with styrene, and overpolymerized onto uniform polystyrene latices. In homopolymerization of vinylbenzyl chloride, the effect of monomer content and concntration and type of surfactant are reported. Nucleophilic displacement of the surface chloride by sulfite ions was accomplished by reaction with aqueous sodium sulfite, without change in latex particle size. Also discussed are ways to control the amount of water‐soluble polyelectrolyte produced as a result of the sulfonation reaction.
Studies on the semirigid chain polyamide—poly(1,4‐phenyleneterephthalamide)
Authors: Jingsheng Bao , Anji You , Shengqing Zhang , Shufan Zhang , Chang Hu
Published: April 2003

In this article, the polycondensation of terephthaloyl chloride and p‐phenylenediamine was systematically studied, including the liquid–crystalline state of the solution and the spinning of poly(1,4‐phenyleneterephthalamide) (PPTA). High‐molecular‐weight PPTA with εinh = 5–7 was prepared and the main factors influencing the solution polycondensation of 1,4‐phenylenediamine with terephthaloyl chloride were studied in detail. Experimental results showed that the water content of the reaction system, reactant concentration, and volume ratio of mix solvents have a great influence on the inherent viscosity of the poly(1,4‐phenyleneterephthalamide) obtained. The highest εinh was obtained at 0.3M/liter reactant concentration in a mixed solvent ratio HMPA/DMAC of 4/1 (by volume), at 0.35M/liter reactant concentration in a mixed solvent of HMPA/NMP = 7/3, and at 0.5M/liter of reactant concentration in a mixed solvent of HMPA/THF = 9/1. The water content must be controlled to less than 100 ppm in the polymerization system. In the early stage of the polycondensation process, the εinh of the polymer obtained increased rapidly with time. The system gelled within 2 or 3 min, while the monomer conversion reached about 100%. However, the reaction of polycondensation continued after gelation and the εinh of the polymer increased appreciably. We have studied the viscosity behavior at 20–155°C for the anisotropic solution of PPTA in 100% sulfuric acid (εinh of PPTA 2.5–4.9). Experimental results showed that, at low concentrations the viscosity of isotropic solution increases with the increase of polymer concentration to reach a maxium near the critical polymer concentration, beyond which the solution changes to an anisotropic liquid–crystalline solution. The appropriate spinning region was obtained as shown in the phase diagram determined by viscosity, degree of depolarization anisotropy, and region of thermal depolymerization. Fibers of PPTA with high modulus and high tenacity were obtained by dry‐jet wet spinning. The fibers obtained have a tenacity of ∼22 g/denier, a modulus of ∼600 g/denier, and elongation at break ∼3.5%.
Polyester chain scission by selective chemical site attack
Authors: Hogsed M. J. , Carlson B. A. , Maerov S. B.
Published: April 2003

Tribenzylamine moieties copolymerized into poly(ethylene terephthalate) (PET) are selectively cleaved by mild hypochlorous acid oxidation to give dibenzylamines plus aldehyde and/or carboxyl groups. When either 3,3′‐dicarboxytribenzylamine (DCTBA) or 4,4′‐DCTBA were used, molecular weight was reduced, consistent with a mechanism where only two of the three carbon–nitrogen bonds which cleave can give polyester backbone scission. When copolymerized 3,5 DCTBA was cleaved, no chain scission resulted, but about one‐third of the nitrogen content was lost, again consistent with the random statistical oxidative attack at each of the three carbon–nitrogen bonds. Borane ester, B[(CH2)10CO2Me]3, copolymerized into PET, lost molecular weight progressively after melt spinning, drawing, and boil off of the resulting fibers. Chain scission resulted from rapid oxidation of borane bonds to borate esters followed by hydrolytic cleavage to boric acid and/or intermediate boronic acids.
Evaluation of number‐average molecular weight of poly(tetrafluoroethylene) irradiated with γ rays
Authors: Takenaga Mitsuru , Yamagata Kyozo
Published: April 2003

The number‐average molecular weight of poly(tetrafluoroethylene) (PTFE) irradiated from a 60Co source in air at room temperature has been estimated from the experimental results of tensile creep measurements and electron microscopy. The viscoelastic method which makes use of the maximum relaxation time was used for samples with low radiation doses. The mean chain length of highly irradiated samples, which can form fully extended chain crystals upon crystallization from the melt, was obtained from the bandwidth distribution on micrographs of the fracture surfaces. The dependence of the average molecular weight on the radiation dose is derived on the basis of a statistical treatment in which effects of cages in the process of chain scission and of molecules evolved out of the specimen, together with random decomposition of polymer backbone chains, are considered. Good agreement between the experimental and calculated results is attained over a wide range of radiation doses.
Mechanical behavior of gradient polymers
Authors: Martin G. C. , Enssani E. , Shen M.
Published: April 2003

Gradient polymers are multicomponent networks which contain a spatial gradient in the concentration of the components in the blend. In this study, the properties of a system of gradient polymers consisting of a rubbery addition to a glassy matrix [poly(methyl methacrylate)] and a glassy addition to a rubbery matrix [poly(2‐chloroethyl acrylate)] were investigated. Dynamic mechanical spectroscopy was used to characterize the compatibility of the polymers. The PMMA matrix gradients were found to be incompatible, while the PCIEA matrix gradients and the interpenetrating network exhibited compatibility. The tensile properties and the fracture strength of the polymers were measured and interpreted in terms of the composition and the deformation mechanism of the materials.
Cryogenic crushing of polystyrene
Authors: Vivatpanachart Somsak , Nomura Hiroyasu , Miyahara Yutaka
Published: April 2003

Atactic and isotactic polystyrene powders were fractured with a ball mill at −196°C. The molecular weight distributions at various milling times measured by GPC show an initial asymmetric broadening and then a gradual returning to the original narrow bell‐shaped distribution. Analysis of molecular weight distributions suggests a preferential chain scission near the chain ends. X‐ray diffraction spectra of isotactic polystyrene samples show that after 24 hr of milling, the semicrystalline polystyrene was completely transformed into an amorphous polymer. DSC thermogram of the milled isotactic polystyrene reveals several crystallization peaks preceding melting when the samples were heated.
Polymer purification through solvent addition: Physical implications and modeling of separation units
Authors: Carrà S. , Morbidelli M. , Santacesaria E. , Niederjaufner G.
Published: April 2003

Addition of solvents may ease removal of small amounts of volatile residues from polymeric materials. Enhanced separation thus obtained is due to the influence of the solvent on the vaporpolymer–liquid equilibria and to its influence on the increase of the diffusion rate of the impurities. The problem has been examined through a mathematical model describing the behavior of the units employed in the purification. Examples of applications are illustrated in which prediction of the behavior of purification units are performed from small‐scale apparatus experiments.
Storage hardening and “abnormal” groups in guayule rubber
Authors: Angulo–Sanchez J. L. , Jimenez–Valdez L. L. , Campos–Lopez E.
Published: April 2003

The hardening process of natural (Hevea brasiliensis) rubber, that takes place when this rubber is stored in dry conditions over long periods of time, has been correlated with the presence of reactive “abnormal” groups directly grafted on the polymeric chain and in the serum of the latex. In the present work, natural Hevea (HR) and Guayule (Parthenium argentatum) rubber (GR) were stored under accelerated conditions and the changes in Mooney viscosity and molecular weight measured. The results showed that while HR undergoes hardening, GR keeps its Mooney viscosity constant, as does a constant viscosity (CV) Hevea rubber. These results are explained by the absence of functional “abnormal” groups that sustain the hardening reactions.
Kinetics of dielectric‐loss microwave degradation of polymers: Lignin
Authors: Chan R. Wai‐Chun , Krieger Barbara B.
Published: April 2003

The rate of product formation as well as detailed product composition were measured in the rapid pyrolysis of a 1.3‐cm cylindrical pellet of lignin, a major component of biomass. Volume heating by dielectric‐loss microwave heating resulted in rapid weight loss with an apparent rate coefficient of 1–5 min−1. Char yield was surprisingly low (33%) owing to the rapid heating rate and high temperature of the pellet. Total gas yield was 38%, of which 12% were simple hydrocarbons and H2 (both weight percent, of original lignin). Product composition showed extensive secondary reaction at high temperatures evidenced by the significant yields of C2H2,H2, and condensed aromatics as well as the typical lignin cracking products such as phenols. Poor coupling of microwave energy to lignin required large power settings in order to initiate reaction. Once initiated, the reaction rate was difficult to control because of the exothermic nature of the reactions. Additives of a suitable composition to increase coupling may be a possible solution to this problem and may result in more favorable economics.
Copolymerization of styrene with acrylamide derivatives in an emulsifier‐free aqueous medium
Authors: Kawaguchi Haruma , Sugi Yoshishige , Ohtsuka Yasuji
Published: April 2003

Acrylamide derivatives were copolymerized with styrene in an emulsifier‐free aqueous medium, and the copolymerization mode and the characteristics of the resulting latices were compared with those of a styrene–acrylamide copolymerization system. In their copolymerization mode, N‐(hydroxymethyl)acrylamide and N,N‐dimethylacrylamide resembled acrylamide, and their heterogeneous copolymerization course was divided into three stages on the basis of the main reaction locus. Copolymerization of styrene–methacrylamide did not resemble that of the others. The interfacial property and reactivity of acrylamides affected not only the polymerization mechanism but also the latex properties, e.g., particle size, distribution of acrylamides units in the latex, etc. The narrowest distribution of particle size was obtained in styrene–N‐(hydroxymethyl)acrylamide copolymerization at a monomer ratio of 10:1. Delayed addition of styrene into the aqueous solution of N‐(hydroxymethyl)acrylamide prepolymerized to some extent was found to be effective in preparing a latex with nearly monodisperse and large particles.
Photoconductivity of poly(vinyl alcohol) films with Fe3+ complexes and ESR study of their structures
Authors: Sumita Osao , Fukuda Atsuo , Kuze Eiichi
Published: April 2003

We have studied whether photoconductivity is observed in polymer films containing the first transition metal complexes. Polymers investigated were poly(vinyl alcohol) (PVA), polyacrylamide, poly(acrylic acid), poly(vinyl pyrrolidone), and polyethylene glycol. Transition metal salts used were CrCl3, MnCl2, FeCl3, CoCl2, NiCl2, FeBr3, Fe(NO3)3, Fe2(SO4)3, and Fe(ClO4)3. Only in the PVA–FeCl3 film was relatively large photoconductivity due to the photoreduction of Fe3+ observed. ESR spectra indicate that an Fe3+ ion is chelated with two in‐plane OH residues of PVA and coordinated with three Cl−ions on the meridian. UV irradiation causes an electron transfer from Cl− to Fe3+. The produced chlorine atom extracts an electron from the oxygen of a neighboring OH residue. The unpaired electron thus formed can move from one oxygen to another through hydrogen bonding. In other words, the photoconductivity is due to holes produced in the network of PVA hydrogen bonding by the reduction of Fe3+. Finally, we have tried to explain why the photoconductivity is observed only in the PVA–FeCl3 film.
Effects of structural features of cotton cellulose on enzymatic hydrolysis
Authors: Focher B. , Marzetti A. , Cattaneo M. , Beltrame P. L. , Carniti P.
Published: April 2003

Textile cotton wastes were treated with γ rays and 18% NaOH and 70% ZnCl2 solutions and were subjected to enzymatic hydrolysis. The untreated and treated samples were characterized both before and after hydrolysis by means of parameters concerning molecular structure (degree of polymerization), supermolecular structure (x‐ray diffraction), accessibility, and reactivity (moisture regain, enzyme adsorption, and solubility in FeTNa). These parameters were correlated to kinetic parameters of the hydrolysis reaction. The Vmax and Km values were evaluated from Lineweaver–Burk plots at different temperatures. The Vmax/Km ratio, analogous to the specificity constant, proved to be less sensitive to experimental errors and more suitable for a comparison of the kinetic behavior of the samples. The modifications of both supermolecular structure and morphology of cellulose were of primary importance to attain high yields and rates of hydrolysis. Furthermore, the structural and morphologic parameters chosen to characterize the samples can be correlated to the kinetic parameters of enzymatic hydrolysis, in particular to Km values.
Thermomechanical analysis of Tg and T > Tg transitions in polystyrene
Authors: Keinath Steven E. , Boyer Raymond F.
Published: April 2003

Phenomenological softening points were measured on a series of 13 anionic, nearly monodisperse, atactic polystyrenes using a DuPont 943 thermomechanical analyzer (TMA) in a penetration mode. Although TMA cannot identify the nature of the “transition” observed as such, the results obtained support the evidence for the Tg, Tll, and T′ll transition in polystyrene discussed in recent literature. Tg and Tll were found to vary with molecular weight in a systematic manner, while T′ll could only be observed at very high molecular weight. The technique appears to be quite useful in offering rapid and reproducible information on the various transitions in the liquid state of polystyrene.
Simulation of molecular weight distribution and cyclic oligomer formation in the polymerization of nylon 6
Authors: Gupta Santosh K. , Naik C. D. , Tandon Pravin , Kumar Anil
Published: April 2003

The reversible polymerization of nylon 6 including ring opening, polycondensation, polyaddition, and cyclization reactions as well as the reaction with monofunctional acids was simulated for an isothermal batch reactor at 235°C. The cyclic oligomer concentrations, the molecular weight distributions, and its moments have been computed using a chain length‐dependent equilibrium constant for the cyclization reaction. Even though the cyclization step does not influence the monomer conversion considerably, it does effect the molecular weight distribution and its moments.
Manufacture of ultrahigh‐modulus poly(oxymethylenes) by die drawing
Authors: Hope P. S. , Richardson A. , Ward I. M.
Published: April 2003

A stable experimental die drawing process has been operated for poly(oxymethylene) over a range of temperature. Rods possessing room‐temperature Young's moduli up to 23 GPa were produced using a homopolymer grade, the values obtained from a copolymer being somewhat lower. This compares favorably with the best modulus achieved by hydrostatic extrusion but is rather lower than that produced by conventional drawing; reasons for this are discussed. A stable die drawing process has also been operated for glass fiber‐reinforced poly(oxymethylene), but extensive macroscopic void formation occurred in the products under all conditions, reducing their potential for practical application.
Morphology and properties of poly(vinyl chloride)–polyurethane blends
Authors: Wang Carl B. , Cooper Stuart L.
Published: April 2003

The objective of this research was to study the morphology and properties of PVC–polyurethane blends. Studies on blends of a segmented polyether polyurethane with PVC were carried out utilizing differential scanning calorimetry, Rheovibron, stress–strain, infrared peak position studies, and infrared dichroism experiments. This thermodynamically incompatible system was made kinetically compatible by precipitation from tetrahydrofuran (THF) solutions. THF–dioxane solution casting and melt processing produced an incompatible system. The compatible polyurethane–PVC system contains a well‐mixed PVC–polyether matrix phase as evidenced by Tg shifts, orientation characteristics, and infrared peak position changes. The aromatic urethane segments which exhibit microphase separation in the pure polyurethane are not solubilized by blending with PVC by any of sample preparation methods used in this study.
The effect of network structure on moisture absorption of epoxy resins
Authors: Diamant Y. , Marom G. , Broutman L. J.
Published: April 2003

An investigation of the effect of modifying the network structure on moisture absorption of epoxies was performed. The network was modified by crosslinking the epoxides with various mono/diamine proportions, resulting in decreasing density and increasing free volume. It was discovered, however, that concomitant effects, i.e., the formation of a two‐phase structure, and changes in resin polarity and in resin–water affinity predominated. Thus, compositions with higher chain molecular weights between crosslink points yet exhibited lower diffusion coefficients. Also, when drastic swelling conditions (such as a water‐boil treatment) were employed, moisture absorption was facilitated by penetration via newly formed microcracks.
Combustion and pyrolysis of poly(ethylene terephthalate). II. A study of the gas‐phase inhibition reactions of flame retardant systems
Authors: Day M. , Suprunchuk T. , Wiles D. M.
Published: April 2003

A device to measure the flammability limits of the gaseous pyrolysis products of polymeric materials has been developed and applied to a study of untreated and flame‐retarded poly(ethylene terephthalate). The results indicate that phosphorus‐containing compounds, like bromine‐containing compounds, are capable of inhibiting the gas‐phase free radical combustion reactions of the pyrolysis products obtained from poly(ethylene terephthalate).
Fundamental analysis of the dynamics, mass transfer, and coagulation in wet spinning of fibers
Authors: White James L. , Hancock Tony A.
Published: April 2003

New models are developed to analyze the wet spinning process. These involve a formulation of simultaneous overall mass, force, and solvent mass transfer balances. In the first‐order model, internal concentration gradients and mass transfer resistance within the fiber are neglected. It is equivalent to the Kase–Matsuo melt spinning model. In the second‐order model, concentration gradients and diffusion within the fiber are included. Comparison is made with an experimental study of wet spinning nylon‐66 fibers. The first‐order model seriously underpredicts final fiber diameter under conditions of specified spinline tension and spinning efflux. The second‐order model gives better agreement between theory and experiment.
Stress relaxation behavior of biaxially oriented poly(ethylene terephthalate)
Authors: Hawthorne James M.
Published: April 2003

The stress relaxation behavior of biaxially oriented semicrystalline poly(ethylene terephthalate) was studied by thermomechanical analysis. Experimental techniques were developed for thin films. Relaxation moduli were measured as a function of stress, time, and temperature. The relaxation modulus was shown to be independent of stress over the range tested. Rate of loss of the relaxation modulus was found to be a nonlinear function of time and temperature up to about 100°C, encompassing the Tg for the polymer. Over the temperature range of 100–120°C it was primarily temperature‐dependent. An empirical time—temperature superposition showed that significant losses in modulus can occur at very short times. At temperatures above the Tg these losses can result in significantly reduced film physical properties.
Effect of tensile strain rate on the mechanical properties of constrained‐uniaxially and simultaneous‐biaxially drawn poly(ethylene terephthalate) sheets
Authors: Yokouchi Mitsuru , Mori Junichiro , Kobayashi Yasuji
Published: April 2003

The dependency of the mechanical properties (Young's modulus, yield strength, breaking strain, and breaking energy) of preoriented poly(ethylene terephthalate) (PET) sheets on the tensile deformation speeds was examined and discussed in relation to changes of density and birefringence. The procedures for preorientation were constrained‐uniaxially (CU) and simultaneous‐biaxially (SB) drawings at 65°C. The performance characteristics of the present tensile testing at room temperature were obtained over a wide range of extension rates (1.7 × 10−4−13.1 m/s = 0.29–2.3 × 104%/s) without changing the mode of deformation and the shape of the test pieces. The CU drawn PET is strain‐rate‐independent and mechanically superior in structure in the preextended direction with draw ratio λ > 2.5. In the SB drawn PET such a structure comes into existence at λ > 3, which has, furthermore, no dependency on draw direction (mechanically isotropic). The draw ratio of the latter case corresponded to the birefringence (−Δn/d) of about 5 × 10−2. These results imply a possibility of producing the strain rate (from low to impact speeds) independent, anisotropy‐free, and mechanically superior molded products of PET if adequate extrusion or blow molding methods which induce multiaxial orientation with −Δn/d > 5 × 10−2 are developed.
Chemistry of miscible polycarbonate–copolyester blends
Authors: Smith W. A. , Barlow J. W. , Paul D. R.
Published: April 2003

Blends of polycarbonate and the copolyester based on 1,4‐cyclohexanedimethanol and a mixture of terephthalic and isophthalic acids are known to be completely miscible. This study was concerned with various chemical events which may occur in this system, particularly during melt processing. Degradation reactions were studied by both TGA and dilute viscometry techniques, and some indications of component interaction were noted. The residual titanium catalyst from the copolyester formation was found to produce color formation by interaction with phenolic end groups in the polycarbonate and to promote interchange reactions. Both events could be suppressed by deactivation of the residual catalyst with appropriate additives. An indication of the extent of interchange reactions was obtained by following the crystallizability of the copolyester component using differential scanning calorimetry.
The effect of moisture on the dielectric relaxations in wood
Authors: Handa Takashi , Fukuoka Masayoshi , Yoshizawa Shuji , Kanamoto Tetsuo
Published: April 2003

The dielectric constant ϵ′ and the loss factor ϵ″ of moistened wood were measured over a wide range of moisture content (MC), 0–40 wt% in the temperature range −196 to 0°C, and in the frequency range 30 Hz to 1 M Hz. Three relaxations were observed depending on the MC and frequency. The first ϵ″ peak at −103°C (30 Hz) in oven‐dried wood is known to be due to the methylol rotation in the amorphous regions. A new ϵ″ peak (second peak), which appeared for MC >0.6 wt% at −110 to −40°C (30Hz) depending on the MC, is assigned to the local mode motions of the complexes between moisture and polar groups in the wood system; it is enhanced as the overall loosening of the initial hydrogen bond network is promoted by the extended hydration due to further sorption of moisture. The peak temperatures and the activation energies for these relaxations changed complexly depending on the MC. At MC > 10 wt%, a novel ϵ″ peak (third peak) was disclosed around −40°C (30 Hz) as a shoulder of the ionic conduction. This novel peak may be attributed to the water frozen in wood on the basis of the peak temperature, relaxation strength vs. MC, the activation energy, and the fact that the peak is not observed for the sorption of various polar organic solvents. This suggests that some of the moisture sorbed by wood may probably exist in a frozen state at low temperatures, even at a MC well below the commonly accepted fiber saturation point.
High‐conversion diffusion‐controlled polymerization of styrene. I
Authors: Marten F. L. , Hamielec A. E.
Published: April 2003

A kinetic model based on the free volume theory has been proposed for the polymerization of styrene. The model, which is capable of describing the course of polymerization in both bulk and solution, accounts for diffusion‐controlled termination and propagation and gives a limiting conversion.
Combustion and pyrolysis of poly(ethylene terephthalate). III. The effect of tris(2,3‐dibromopropyl) phosphate on the products of pyrolysis
Authors: Day M. , Parfenov V. , Wiles D. M.
Published: April 2003

The influence of the flame retardant chemical tris(2,3‐dibromopropyl) phosphate, and the related chemical species, tripropyl phosphate and 2,3‐dibromopropanol, on the products of pyrolysis of poly(ethylene terephthalate), has been examined as a function of chemical concentration. The species containing phosphourus only and bromine only had little effect on the composition and concentration of the pyrolysis products. The tris(2,3‐dibromopropyl) phosphate had a significant effect upon the pyrolysis product distribution, and is capable of influencing the decomposition reactions of poly(ethylene terephthalate).
Polyelectrolytes as secondary calibration standards for aqueous size‐exclusion chromatography
Authors: Bose A. , Rollings J. E. , Caruthers J. M. , Okos M. R. , Tsao G. T.
Published: April 2003

The effect of the ionic strength of the solvent on the size‐exclusion chromatography of narrow molecular weight dextrans and monodisperse sodium polystyrene sulfonates has been investigated. In both NaOH and NaCl solutions the elution volume of the sodium polystyrene sulfonates increased as the ionic strength was increased, while the elution volume of the dextrans decreased slightly as the ionic strength was increased. The elution data for various ionic strength solvents could not be described by the traditional universal calibration procedure of plotting the product of the intrinsic viscosity and the molecular weight vs. the elution volume. By using a modified calibration procedure which includes excluded volume effects, the elution data can be described for NaOH solution of moderate and high ionic strength. This modified calibration technique was unable to describe the elution data for very low ionic strength NaOH solutions and for the NaCl solutions. Possible explanations of the inability of straightforward size exclusion chromatographic calibration techniques to quantitatively described all the observed elution behavior are discussed.
Crystallization of crystalline/crystalline blends: Polypropylene/polybutene‐1
Authors: Siegmann Arnon
Published: April 2003

The crystallization, from molten blends, of polypropylene (PP) and polybutene‐1 (PB), two highly crystallizable, polymers, their interaction in the amorphous phase, and the resulting tensile mechanical properties were studied. The crystallization was followed by DSC, showing two separate PP and PB crystallization processes which are affected each by the presence of the other component. The crystallization temperature of PP is significantly affected only in PB rich blends whereas that of PB is affected in the whole composition range. The PP crystalline phase, acting as a nucleating agent, increases the PB crystallization temperature whereas the PP amorphous phase, acting as a high viscosity polymeric diluent, reduces the PB crystallization temperature. The first effect is dominant at low PP content, and the second one becomes increasingly effective with increasing PP content in the blend. The interaction between the two polymers in the amorphous phase was studied by applying dynamic mechanical analysis, in which a single glass transition was observed for the blends and its temperature was found to vary with the blends' composition. Tensile mechanical properties of blends were found to be more sensitive to thermal treatments, such as isothermal crystallization or annealing at elevated temperatures, than single component systems. Such thermal treatments enable better structured blends to be formed, resulting in mechanical properties with no abrupt changes in the whole composition range.
Grafting onto wool. XX. Graft copolymerization of vinyl monomers by use of redox initiators. Comparison of monomer reactivities
Authors: Misra B. N. , Singha A. S. , Sharma R. K.
Published: April 2003

Methyl methacrylate (MMA) and ethylacrylate (EA) have been graft copolymerized onto Himachali wool in aqueous medium by using a ferrous ammonium sulfate–hydrogen peroxide (FASH2O2) system as redox initiator. Percentage of grafting has been determined as functions of concentration of monomer, molar ratio of [FAS]/[H2O2], time and temperature. Percentage of grafting is found to depend upon the molar ratio of [FAS]/[H2O2]. An attempt has been made to compare the reactivities of the acceptor monomer (MMA and EA) with that of the donor monomer (VAc) toward grafting onto wool.
Rheological properties of polyethylenes modified with dicumyl peroxide
Authors: Lem Kwok‐Wai , Han Chang Dae
Published: April 2003

Low‐ and high‐density polyethylenes were modified using dicumyl peroxide. The modified polyethylenes were subjected to steady and oscillatory shearing flows. The viscous and elastic properties determined with a cone‐and‐plate rheometer are correlated to the molecular weight of the materials, which was determined with the aid of size exclusion chromatographic analysis. It was found that both the melt viscosity and elasticity increase with the amount of dicumyl peroxide used, and shear‐thinning behavior becomes more intense. The Bueche master curve of viscosity is constructed by using a relaxation time based on the weight‐average molecular weight for both virgin and modified resins.
Environmental degradation of some polymer blends. Blends of polystyrene with acrylonitrile butadiene styrene, poly(vinyl chloride), and polybutadiene and blends of polybutadiene with poly(vinyl chloride)
Authors: Kolawole E. G. , Agboola M. O.
Published: April 2003

One class of polymer/additive which has become increasingly important is polymer blends. In this study the ultimate tensile strength, elongation at break, and the modulus of acrylonitrile–butadiene–styrene, poly(vinyl chloride), polybutadiene and polystyrene and their blends have been studied over an entire binary composition range. We have correlated these mechanical properties to their degradation behavior under natural and accelerated weathering by measurement of various indices during thermal and natural weathering. It was found that during natural weathering the presence of polystyrene in acrylonitrile–butadiene–styrene (ABS) improved the weatherability of ABS; the converse was true when the blends were heated in an air oven at 100°C. It was also found that the weatherability of PB was improved in the presence of polystyrene and large improvement in the rigidity was observed. Similarly, from a measurement of carbonyl index, it was found that PVC has a stabilizing effect on PB. In many cases, the 50:50 composition of the polymers gave the best compromise of good mechanical properties, heat stability, and outdoor weathering. The mechanisms of possible interactions between the degrading polymers are discussed.
Mechanical properties of blends containing HDPE and PP
Authors: Bartlett D. W. , Barlow J. W. , Paul D. R.
Published: April 2003

The mechanical properties of binary blends of high‐density polyethylene and polypropylene are quite good compared to those for blends of some other immiscible pairs. The property relationships observed depend strongly on the process used to fabricate the blends as shown by comparisons of specimens made by injection and compression molding with widely varied cooling rates in the latter. Strength and modulus may show additive behavior or have positive or negative deviations, depending on the process conditions; however, measures of ductility like impact strength or elongation at break always show negative departures from additivity and exhibit minima in some cases. Addition of an appropriate ethylene–propylene elastomer greatly improves the ductility of these blends but with a corresponding decrease in strength and modulus. The presence of weld lines has a serious detrimental effect on mechanical properties of these blends.
Kinetics of emulsion copolymerization. II. Effect of free radical desorption on the rate of emulsion copolymerization of styrene and methyl methacrylate
Authors: Nomura M. , Yamamoto K. , Horie I. , Fujita K. , Harada M.
Published: April 2003

The rate coefficient for radical desorption from the polymer particles is derived for an emulsion copolymerization system, assuming, for simplicity, that only monomer radicals can desorb from the particles. The effect of free radical desorption on the rate of emulsion copolymerization and the copolymer composition is theoretically analyzed, using the rate coefficient for radical desorption developed in this paper and a mathematical reaction model proposed earlier by the present authors for an emulsion copolymerization system where the average number of total radicals per particle does not exceed 0.5. The validity of the analysis is demonstrated experimentally using the seeded emulsion copolymerization of styrene (ST) and methyl methacrylate (MMA). Radical desorption from the particles does not affect the copolymer composition, but the desorption of MMA—monomer radicals plays an important role in determining the rate of emulsion copolymerization, while the desorption of ST—monomer radicals from the particles can be neglected from a kinetic point of view.