bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of free‐radical emulsion polymerization of methyl methacrylate by oxygen injection. I. Modeling study
Authors: Louie Brian M. , Chiu Wen Yen , Soong David S.
Published: April 2003

Oxygen injection has been proposed as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model is developed to describe the system behavior with and without oxygen injection. Because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight.
Molecular weight distribution control in a semibatch “living” anionic polymerization. I. Theoretical study
Authors: Couso D. A. , Alassia L. M. , Meira G. R.
Published: April 2003

A method to produce homopolymers of preestablished molecular weight distribution (MWD), through “living” anionic polymerizations carried out in homogeneous semibatch reactors is proposed and theoretically justified. In the direct form of the technique, very fast reactions are assumed, and the monomer and “killing” agent feed flows are obtained from the knowledge of the desired MWD, the system spreading function, the total reaction time, the initial reaction volume, and the reagent concentrations. Alternatively, by controlling a reactor outlet flow instead of the “killing” agent feed, an external deactivation of the “living” ends can be implemented. The method can be extended to slow reactions, to more elaborated mechanisms, and to take into account the unwanted deactivation of “living” ends by impurities in the monomer solution feed.
Foam extrusion characteristics of thermoplastic resin with fluorocarbon blowing agent. III. Foam sheet extrusion of polystyrene and low‐density polyethylene
Authors: Yang Heng‐Huey , Han Chang Dae
Published: April 2003

An experimental study was conducted on the extrusion of polystyrene and low‐density polyethylene foam sheets, using fluorocarbon blowing agents and a tubular die. The effects of the type and concentration of blowing agent, die temperature, and takeoff speed on foam extrusion characteristics were investigated. They are foam density, tensile modulus, and cell morphology. It has been found that die temperature greatly influences the open cell fraction and foam density and that the takeoff speed greatly influences cell orientation, which, in turn, has a profound influence on the tensile modulus of the foam sheets produced.
Equilibrium disperse dye sorption by drawn polypropylene films
Authors: Yonetake Koichiro , Nagamatsuya Kotoku , Masuko Toru
Published: April 2003

Isotactic polypropylene (PP) films drawn at various temperatures ranging from 100 to 155°C have been dyed at 80°C with p‐aminoazobenzene (PAAB) or C.I. Disperse Yellow 7 (Y‐7). The equilibrium dye sorption (M0) of PAAB obtained for these films decreased with an increase in draw ratio (λ) of the films. The M0 values of Y‐7, however, increased with increasing in λ similarly the crystallinities of these films increased slightly with draw ratios. By use of fine structural data of these films, the change in M0 of Y‐7 for drawn PP films were analyzed in terms of a mosaic‐block structural model. The increase in M0 with increasing in λ was thus ascribed to enhanced sorption by the amorphous side region between crystalline cores located parallelly in the direction to the molecular axis. The side regions of the drawn systems become rich in interfibrillar tie chains in a higher range of λ. The side region seem to have a strong affinity particularly to a long rodlike dye molecule such as Y‐7; this feature is probably associated with the amount of the amorphous chains having extended chain conformation, the fraction of which increases during drawing.
Copolymers of ethylene with butene‐1 and long chain α‐olefins. I. Decene‐1 as long chain α‐olefin
Authors: Seppälä Jukka Veli
Published: April 2003

The possibility was studied of using decene‐1 as comonomer with ethylene in a slurry type polymerization with Ziegler–Natta catalysts. Under the reaction conditions used decene contents remained at the 2 wt% level in ethylene/decene‐1 copolymers. When additionally butene‐1 was present in the polymerization, decene‐1 contents were significantly higher. A synergistic effect was identified in the reactivities of butene‐1 and decene‐1 in terpolymerization with ethylene. The comonomer reactions were determined and comonomer contents measured by 13C‐NMR spectroscopy. Decene‐1 content had an effect on the polymer density and crystallinity, but virtually no effect on melting temperature. With high comonomer contents an additional melting range was identified in DSC curves at about 100°C.
Physical properties of barium titanate‐filled rubber‐modified epoxies
Authors: Tse Mun‐Fu
Published: April 2003

Rubber‐modified epoxies (RME) filled with different levels of barium titanate (BaTiO3) have been characterized by using DSC, TGA, and TMA. The presence of the filler does not affect the glass transition temperature or the activation energy of pyrolysis; however, it does change other thermal properties. The dielectric constant increases markedly, but the dissipation factor remains fairly constant with increasing BaTiO3 loading. The polymers, in MEK, exhibit slightly different degrees of swelling and their sol fractions vary. Mechanical properties, such as stress‐strain relation, friction, abrasion, scratch hardness, and scrape adhesion of the polymers, will be described.
Optimization of batch polymerization processes—narrowing the MWD. I. Model simulation
Authors: Louie Brian M. , Soong David S.
Published: April 2003

Several control strategies for the free‐radical polymerization of methyl methacrylate are analyzed with a detailed constitutive model incorporating the gel and glass effects. Optimal temperature history, photoinitiation intensity variation, and programmed monomer and solvent additions, employed alone and in combination, represent cases simulated by this model. Solvent addition is selected for further experimental studies, due to some attractive features. The product molecular weight distribution is narrowed, while the molecular weight averages are maintained high. Model predictions of the solvent injection history exhibit a strong sensitivity to the constitutive equations for describing the gel and glass effects.
Synthesis of a novel polyesterimide
Authors: Dolui Swapan Kumar , Pal Dhananjay , Maiti Sukumar
Published: April 2003

A new polyesterimide has been synthesized from trimellitic acid anhydride, diaminodiphenylsulfone, and bisphenol‐A following three different routes. Solubility behavior in different solvents, solution viscosity, density, crystallinity, and thermal and electrical properties of the polyesterimide have been discussed. Results indicate that the polyesterimide thus prepared has medium thermal stability.
Fracture behavior of short fiber reinforced thermoplastics I. Crack propagation mode and fracture toughness
Authors: Jang B. Z. , Lieu Y. K.
Published: April 2003

The fracture behavior of several short glass fiber reinforced thermoplastics has been studied. The fracture toughness of these materials may be related to local crack propagation mode, which is found to be highly rate dependent. At low test rates the crack growth in the reinforced polymers tend to follow a fiber avoidance mode, creating a greater area of new surfaces, which in conjunction with greater degree of interfacial debonding and fiber pullout friction leads to a higher fracture resistance. An increase in loading rate in general results in a more straight and flat crack path, as well as a lesser extent of fiber debonding and pullout. Therefore the fracture toughness is reduced although the frequency of fiber breakage is increased. The fracture behavior of these short fiber reinforced polymers appears to be dictated by the matrix properties when the loading rate is high.
The turbulent drag reduction by graft copolymers of guargum and polyacrylamide
Authors: Deshmukh S. R. , Chaturvedi P. N. , Singh R. P.
Published: April 2003

Commercial guargum is known to be a shear stable drag reducing agent. However, the aqueous solutions of guargum start degrading within 8 hrs. of their preparation and after 65 hrs., they degrade completely. In the present investigation, the graft copolymers of guargum and polyacrylamide have been prepared. It has been shown that the purification and grafting enhance the drag reduction effectiveness and biodegradation resistance considerably in guargum.
Dynamic mechanical properties and adhesive strengths of epoxy resins modified with liquid rubber. I. Modification with ATBN
Authors: Takemura Akio , Tomita Bun‐Ichiro , Mizumachi Hiroshi
Published: April 2003

The dynamic mechanical properties and the adhesive strengths of Epikote 828 and Epikote 828‐ATBN blend systems were investigated. The ATBN blend systems were proved to be completely incompatible with the dynamic mechanical measurement and also fitted well with Takayanagi's model which was designed for completely incompatible two‐phase systems. The epoxy resin had a nonreacted part when cured at room temperature. The blending of ATBN reduced the nonreacted part of the epoxy resin, and made contributions to the adhesive strengths. In the case of tensile test of crosslap specimens using aluminium as adherends, the adhesive strengths of ATBN blend systems were almost 1.5‐fold of those of epoxy resin without blending of ATBN. As for wood adherends, the maximum of the adhesive strengths was found at 60°C for epoxy resin without blending of ATBN, and at 0°C for ATBN blend systems. The facts meant that there were mutual interactions between the adhesive strengths and the viscoelastic behavior of the adhesive polymers in the two‐phase systems as observed in completely miscible polymer blends. There was not pronounced distinction between epoxy resins without blending of ATBN and ATBN blend system, as to the shear adhesive strengths.
Effect of plasma treatment on the structure and allied textile properties of mulberry silk
Authors: Nadiger G. S. , Bhat N. V.
Published: April 2003

Studies on the effect of nitrogen plasma on morphology and textile properties of mulberry silk fibers and fabrics have been conducted. The changes in the morphological structure have been monitored by transmission electron microscopy, X‐ray diffraction, and internal reflection infrared spectroscopy. The changes in some of textile properties such as wettability, drying rate, and crease recovery owing to plasma treatment have also been investigated. It has been found that the surface of mulberry silk gets etched away, even affecting the crystalline region. This behavior is opposite to our findings on tassar silk. Therefore, an explanation of this differential behavior of mulberry with tasar on the basis of amino acid linkages vis‐à‐vis bonding, wettability, drying rate, and water retention capacity has been attempted. These results have been used to arrive at an understanding of internal structure of mulberry.
Phase behavior of polycarbonate blends with selected halogenated polymers
Authors: Woo E. M. , Barlow J. W. , Paul D. R.
Published: April 2003

Bisphenol A polycarbonate is shown to be miscible with a vinylidene chloride based polymer containing 13.5% by weight of vinyl chloride. On the other hand, polycarbonate is found to be immiscible with poly(vinyl chloride), poly(vinylidene fluoride), and polyepichlorohydrin.
Dynamic mechanical properties of some nylons and their blends
Authors: Ong Eng Seong , Kim Yunghoon , Williams H. Leverne
Published: April 2003

The dynamic mechanical properties of nylons 6, 11, 12, 66, 610, 612, and 666 are compared. The spectra are very similar with peaks in the loss curves at about −120, −40, and 85°C. The similarity suggests that attempts to determine whether the nylons could in fact be incompatible when blended might not be successful. Calculations based in turn on calculated cohesive energy densities and interaction parameters also suggest that only nylon, 6 and 66 would be compatible. By using the nature of the major loss peak at the glassy transition which is high and narrow for nylons 11 and 12 and broader and shorter for nylons 6, 66, and 666, it is possible to deduce that nylons 6 and 12 are somewhat incompatible but that the other combinations are most likely dynamically compatible.
Dynamic mechanical and impact properties of PP/SEBS blend
Authors: Gupta A. K. , Purwar S. N.
Published: April 2003

Studies on impact behaviour of the blend of isotactic polypropylene (PP) with styrene‐b‐ethylene‐co‐butylene–b‐styrene triblock copolymer (SEBS) in the composition range 0–25 wt % SEBS at three temperatures, viz., ambient, −30°C, and −190°C, are presented. Dynamic mechanical properties on a torsion pendulum in the temperature range −100−100°C are also studied for this blend at various compositions. Scanning electron microscopic studies of the impact‐fractured surfaces are presented to illustrate the differences in the mode of fracture at the three temperatures of impact tests. Choice of the three temperatures for impact tests was such that the effect of shear yielding mechanism of toughening of PP at ambient temperature remains suppressed at −30°C, whereas at the lowest temperature (i.e., −190°C) the elastomeric role of the inclusion SEBS is suppressed. The observed considerably large difference in impact toughening at ambient temperature and at −;30°C seems not entirely accountable by the prevalence of shear yielding or crazing mechanisms in the respective temperature regions. A third mechanism, viz., viscoelastic energy dissipation, is invoked to account for the observed large difference of impact toughening at these two upper temperatures. Correlation of peak area of dynamic mechanical loss peaks occurring below the impact test temperature with the impact strength is also shown. This suggests greater significance of viscoelastic energy dissipation mechanism in the toughening of this blend at ambient temperature than at −30°C.
Photoregulated sorption of dyes to polymers I. The effect of polymers on some photochemical properties of acid yellow 38
Authors: Petrak K. , Douglas P. , Leyshon L. L.
Published: April 2003

The effect of polymers [gelatin, dextran, poly(vinyl alcohol), polyvinylimidazoles] on the photochemical and thermal isomerization of the water‐soluble bisazo dye, Acid Yellow 38, has been studied. The absorption spectrum curve of the cis AY38 isomer was obtained using the method of Fischer. We have shown that the rate of thermal cis–trans isomerization of AY38 is first order and independent of pH from 6 to 9. An activation energy of 84 ± 4 kJ mol−1 has been calculated for this process. The effect of added polymers on the rate of this conversion is relatively small. The quantum yields for the trans‐cis and cis–trans conversions have been estimated to be 0.15 ± 0.01 and 0.34 ± 0.03, respectively, for irradiation at 380 nm. Only polyvinylimidazoles were found to influence the behavior of the dye to any degree. For quaternized polyvinylimidazole the polymer/dye ratio determined solution turbidity, wavelength of maximum absorption, molar absorptivity, and the degree of conversion at photoequilibrium. The effect of polymer was interpreted in terms of increased dye/dye interactions due to high local concentration of the dye bound to polymer. The charge neutralization and crosslinking by the dye due to ionic interactions are seen to be the cause of polymer/dye complex precipitation. Precipitation occurs over a narrow [polymer]/[dye] ratio range.
A study on blends of nylon‐6 and nylon‐66
Authors: Verma Anu , Deopura B. L. , Sengupta A. K.
Published: April 2003

Blending of nylon‐6 and nylon‐66 was carried out by coextrusion in the whole range of compositions with particular emphasis on small amounts of one polymer in the other. Most significant improvement in properties is achieved at low blend compositions in which the minor component remains amorphous while severely affecting the crystallization behavior of the major component. The nylon‐6‐rich blends crystallize predominantly in the γ‐crystalline form, whereas the nylon‐66‐rich blends exhibit low crystallinity. Because of this property, the blends are more easily drawable, giving rise to a more highly oriented structure with improved tensile properties and uniformity. High tenacity and modulus are observed in drawn blends containing 70% nylon 6 and 30% nylon‐66.
Synthesis and properties of copolypyromellitimides
Authors: Yang Chin‐Ping , Hsiao Sheng‐Huei
Published: April 2003

Copolyamic acids with different proportions of diamine component were prepared by polymerizing different molar ratios of diamines—benzidine (B)/4,4′‐diaminodiphenyl ether (E) and p‐phenylene diamine (P)/4,4′‐diaminodiphenyl methane (M)—with pyromellitic dianhydride (PMDA) in dimethylacetamide (DMAc) at room temperature. Diamine component can be arranged in regular sequence through various reaction processes, such as alternating, block, and partial block copolymers. In addition, it can also be arranged in random sequence to obtain random copolymers. Thermal cyclodehydration of polyamic acids results in the corresponding polyimides. Polymers are characterized by viscosity, thermal stability, crystallinity, and mechanical strength. It was found that an increase in the proportion of more flexible diamine component (such as E and M) incorporated in polymer chain results in copolyimides with better mechanical strength and causes a fall in viscosity of copolyamic acids and a decrease in thermal stability and crystallinity of copolyimides. Within the copolymers of the same composition, the thermal stability, crystallinity, and mechanical strength of ordered polymers are superior to those of random polymers. The results of viscosity measurements imply that the anhydride‐terminated prepolymer is easily destroyed by water in the solution, so that the ultimate viscosities of alternating and block copolyamic acids are inferior to those of random ones, but this phenomenon can be improved through the preparation of the partial block copolymers.
Dynamic mechanical properties and adhesive strengths of epoxy resins modified with liquid rubber. II. Modification with CTBN
Authors: Takemura Akio , Shiozawa Kimihide , Tomita Bun‐Ichiro , Mizumachi Hiroshi
Published: April 2003

The dynamic mechanical properties and the adhesive strengths of epoxy resins‐CTBN blend systems and epoxy resins‐CTBNX blend systems were investigated.

Both CTBN blend and CTBNX blend systems were proved to be partially compatible with the dynamic mechanical measurement. In the case of CTBN blend systems, the more blending of CTBN, the more the compatibility increased. On the other hand, CTBNX‐20 was more compatible than CTBNX‐30 but less than CTBNX‐40. In any case, the blending of CTBN or CTBNX reduced the nonreacted part of the epoxy resins cured at room temperature.

The adhesive strengths were evaluated as a function of the storage modulus with altering temperature and altering rubber content. Both procedures were proved to be equal.
Dielectric properties of an epoxy resin and its composite I. Moisture effects on dipole relaxation
Authors: Reid Jonathan D. , Lawrence William H. , Buck Richard P.
Published: April 2003

Dipole relaxation dielectric loss behavior of a fiberglass–epoxy composite has been studied as a function of moisture uptake. A single widely distributed loss peak, centered at −16°C for 10 kHz measurement, is observed in the dry composite. Very low moisture concentrations (<0.1%) interact with the composite, through either dipole pairing or by inducing chemical changes, to decrease loss intensity. At moisture concentrations from 0.1 to 1.4%, loss peak intensity generally increases with moisture uptake. Over this moisture concentration range water dipoles presumably relax in phase with the epoxy segments or side groups upon which they adsorb. Arrhenius relaxation activation energy decreases, and improved loss peak definition at increasing moisture concentrations is interpreted as indicating resin plasticization by adsorbed moisture. At moisture concentrations above 1.4%, the appearance of a second loss peak suggests formation of a new colloidal or weakly adsorbed moisture phase, as well as the saturation of primary adsorption sites.
Lower critical solution temperature behavior of ethylene propylene copolymers in multicomponent solvents
Authors: Irani C. A. , Cozewith C.
Published: April 2003

The lower critical solution temperature (LCST) locus for ethylene‐propylene copolymers has been determined as a function of pressure in a variety of single and multicomponent solvents. The lower critical end‐point temperature (LCEP), which is the intersection of the LCST locus with the vapor‐pressure curve, was found to be predictable from the solvent density as previously established for single‐component solvents by Charlet and Delmas.1 Dissolving a low‐molecular hydrocarbon gas such as propylene in an alkane has a dramatic effect on lowering the LCEP, and can reduce phase‐separation temperatures to levels at which this technique becomes attractive as a practical method for polymer recovery from diluents such as those used in solution polymerizations. Temperatures considerably above the LCEP are needed to minimize the residual polymer concentration in the solvent in the two‐liquid‐phase region. The solvent critical temperature must be approached for essentially complete elimination of the polymer from the solvent phase. The LCST locus was found to be a linear function of pressure for all of the systems investigated, and the slope of the line, d(LCST)/dP, could be well correlated as a function of solvent density and critical temperature. From the relationship between the LCEP and solvent density and the correlation for d(LCST)/dP, the location of the LCST locus can be readily predicted from a knowledge of solvent properties.
Melt viscosity and electrical conductivity of carbon black‐PVC composite
Authors: Noguchi Tsutomu , Nagai Tohru , Seto Jun'etsu
Published: April 2003

The effect of the structure of carbon black aggregates on the melt behavior and electrical conductivity of carbon black‐vinylchloride‐vinylacetate copolymer systems was analyzed. As the amorphous carbon aggregates are roll‐milled, they become cylindrical, then, as the milling time is prolonged, spherical. During milling, polymer adsorption and dispersivity increases in the same manner, causing the viscosity of the composite to decrease. It was established that during a certain milling time, conductivity rises to a peak, after which it falls. We attribute this phenomenon to there being an optimum aspect ratio and degree of dispersion of the cylindrical carbon aggregates. A model explaining the relationship between milling time and change in conductivity is proposed. When oxidized carbon black was dispersed into the copolymer, it was found that it disperses better than unoxidized carbon black, although the conductivity of the resulting composite is lower.
Latex interpenetrating polymer networks based on acrylic polymers. II. The influence of the degree of network compatibility on morphology
Authors: Hourston D. J. , Satgurunathan R. , Varma H.
Published: April 2003

Two latex interpenetrating polymer networks, one prepared from a pair of supposedly compatible polymers and the other from an incompatible pair, were investigated using transmission electron microscopy and dynamic mechanical analysis. From the results, it was proposed that both interpenetrating polymer networks consisted of latex particles with essentially coreshell morphologies. Evidence for a core‐shell structure was more marked for the materials synthesised from the incompatible polymers. The other polymer pair showed indications of a significant amount of mixing.
Mathematical analysis of transport properties of polymer films for food packaging. VI. Coupling of moisture and oxygen transport using langmuir sorption isotherms
Authors: Howsmon Gregg J. , Peppas Nikolaos A.
Published: April 2003

Deterioration of food products stored in flexible packaging materials can be attributed to the presence of both water and oxygen in the environment surrounding the food. Mathematical models for the simultaneous permeation of moisture and oxygen through the packaging polymeric film and subsequent adsorption on the food surface are presented for the case of competitive adsorption of the two diffusing species. These models are then used to predict internal packaging conditions over time for selected food products. Oxygen and moisture permeation are treated as independent phenomena, and the competition is regarded as occuring on a surface described by the Langmuir adsorption isotherm. It is found that for certain polymer physical properties and relative surface coverages, water and oxygen molecules can dislodge each other from the food surface and, even for situations where the initial partial pressure of oxygen is less than the external partial pressure, can cause an outward flow of the more weakly adsorbed material. This theory is then extended to incorporate varying external conditions of storage.
Relationship between phenolic adhesive chemistry and adhesive joint performance: Effect of filler type on fraction energy
Authors: Ebewele Robert O. , River Bryan H. , Koutsky James A.
Published: April 2003

The performance of adhesive bonded joints depends on many factors, one of which is the adhesive formulation. The effects of organic and inorganic fillers upon the fracture toughness of phenol–resorchinol–formaldehyde adhesive in hard maple joints were explored in this study. Analytical techniques (DSC, IR, SEM, and GPC), and solubility studies were employed to relate physical effects to chemical effects of teh fillers. The resin showed two distinct stages of cure: (1) a low temperature exotherm associated with resorcinol and paraformaldehyde and (2) a high temperature endotherm associated with the base resin. Filler was found not to affect the cure. Fillers did have a profound effect on the morphology of the wood‐adhesive interphase and upon the bulk adhesive properties. These effects, revealed in both SEM and fracture toughness studies, are discussed at lenghth.
Rheological characterization of dextran‐enzymatic synthesis media
Authors: Tecante A. , C. A. López‐Munguia , García‐Rejón A.
Published: April 2003

The bacteria Leuconostoc mesenteroides (strain NRRL‐B512) has been used for the fermentative production of the polysaccharide dextran from sucrose. The polysaccharide production was carried out via a four‐step process involving (1) production of the enzyme dextransucrase (DS), (2) bacteria removal from the culture broth, (3) enzyme purification by gel permeation chromatography, and (4) enzymatic synthesis of dextran in a cell‐free reaction medium.

The enzymatic reaction was followed measuring the change in rheological properties of the reaction medium with time at different initial substrate concentrations. The influence of other parameters, such as temperature, addition of acceptor molecules (maltose), and enzyme purity, were also considered.

The microbial extracellular polysaccharide is responsible for the non‐newtonian character of the reaction media. At low shear rate values the flow behavior was newtonian, whereas at higher shear rates the reaction media exhibited a marked shear‐thinning behavior. The Carreau equation appears to fit fairly well the experimental data over several decades of shear rate. The reaction media showed elastic behavior as well.
Calculation of temperature and pressure dependence of heat capacities in polymer melts
Authors: Hartmann Bruce , Balizer Edward
Published: April 2003

A new PVT equation of state PV5 = T1/2 − ln V where P = P/B0, and T = T/T0, was used to calculate the temperature and pressure dependence of Cp − Cν for polymer melts. The results are in the form of universal master curves in terms of reduced variables. As a function of temperature, a maximum in Cp – Cν is predicted, while as a function of pressure a minimum is predicted. Supplementing the PVT equation with experimental Cp (T) data from the literature, Cp/Cν was also found to have a maximum as a function of temperature. Two useful approximations were also found. One is related to the Nernst–Lindemann equation for Cp – Cν and the other is the approximate constancy of RT0/B0V0.
Solvent‐vapor‐induced crystallization of branched polydisperse polycarbonate
Authors: Daniewska I. , Dobkowski Z. , Członkowska‐Kohutnicka Z.
Published: April 2003

Preliminary results on the investigation of solvent‐vapor‐induced crystallization of polycarbonate/PC/ are presented. The influence of solvent solubility parameters δs on the sphrulite radius R and crystallinity degree α is taken into account. It has been found that both R and α depend on δs for PC samples of different molecular characteristics.
Effect of catalyst residues on the degradation of rigid foam polyurethane
Authors: Abu‐Zeid M. E. , Nofal E. E.
Published: April 2003

Immediately after heating rigid foam polyurethane (PU) at 165°C, it degrades in accordance with the degradation mechanisms suggested by Abu‐Zeid et al. in earlier publications. However, after three days all photoacoustic spectra (PAS) bands indicative of PU degradation almost disappeared, and the samples were found to resist both UV and thermal degradation for a wide range of temperatures and UV dosages. Residual catalysts left from PU polymerization were found to be the main cause of its degradation. When these residues were consumed in the process of solid repolymerization, PU becomes immune to heat and UV degradation.
Swelling of cotton in ethylene diamine: Variation of the spiral angle and the angle of crystallite dispersion with stress
Authors: Kalyanaraman A. R.
Published: April 2003

The swelling of cotton in ethylene diamine is well known. This paper analyzes the variation of the spiral angle and the angle of crystallite dispersion with variation in applied stress to a bundle of EDA‐treated fibers. EDA treatment causes regular variation in the spirality of cotton. The variation in the angle of crystallite dispersion is irregular signifying the onset of decrystallization. Mechanical deformation of cotton fibers involves extension and compression of crystallite helices. The present analysis seems to point out that EDA treatment of cotton fibers cause a kind of order in the mechanical deformation of the fibers by aligning the helices and disordering the crystallites.
Characterization of polyisobutylene‐based model urethane networks
Authors: Miyabayashi Toshio , Kennedy J. P.
Published: April 2003

Polyisobutylene‐based model urethane networks have been prepared by crosslinking liquid α, ω‐di(hydroxyl)polyisobutylenes, i.e., PIB‐diols carrying exactly two CH2OH functions, Fn = 2.0 ± 0.1, and rather narrow molecular weight distributions, Mw/Mn = 1.5−1.6, with tritriphenylmethyl isocyanate \documentclass{article}\pagestyle{empty}\begin{document}$$\rm{HC}\ (\hskip-6pt\hbox{---}p\rm{C}_6\rm{H}_4\hbox{---}\rm{NCO})_3$$\end{document}. Networks prepared with Mn = 1400 and 7500 PIB‐diols, and with 90/10 and 80/20 mixtures of these PIB‐diols (bimodal networks), have been characterized by extraction, by the Flory–Rehner swelling method, and by the Mooney–Rivlin equilibrium modulus method, and tested by stress–strain measurements. Mc values of the Mn = 1400 PIB‐diol network obtained by swelling (1550) and by equilibrium modulus studies (1500) were in excellent agreement with the Mn of the prepolymer. Also the C2 parameter was negligible in comparison to C1, suggesting the absence of interchain entanglements. This is the first hydrocarbon‐based polyurethane network that exhibits a negligible C2 value by stress–strain measurements of unswollen samples. The Mc values of the Mn = 7500 PIB‐diol were also in good agreement with the Mn of the prepolymer; however, C2 was larger than C1, indicating interchain entanglements. Evidence for strain‐induced toughening was observed with both networks prepared with the Mn = 1400 and 7500 PIB‐diols. The ultimate properties of the two bimodal networks did not show improvement over those of the individual constituents; however, the Mn's of the constituents were not very different.
Gas transport in partially fluorinated low‐density polyethylene
Authors: Kiplinger C. L. , Persico D. F. , Lagow R. J. , Paul D. R.
Published: April 2003

Low‐density polyethylene film was subjected to direct fluorination on one surface by exposure to a dilute fluorine gas stream for various periods of time. Various analyses indicate partial fluorination of a thin surface layer. The permeability coefficients for He, CO2, and CH4 were measured at 35°C. The permeability of He was not changed by fluorination; whereas, values for CO2 and CH4 were decreased by as much as two orders of magnitude. The selectivity of transport for gas pairs of different molecular size was greatly improved, suggesting applications of this technique for membrane separation processes.
Improvement in properties of poly(vinyl acetate): Emulsion with dibasic acids
Authors: Verma S. K. , Bisarya S. C.
Published: April 2003

We report an attempt to graft cis (maleic and citraconic) and trans (e.g., fumaric and mesaconic) unsaturated dibasic acids onto poly(vinyl acetate) in emulsion system, in the presence of an initiator and a small quantity of vinyl acetate. The resulting emulsions showed better adhesiveness, higher shear strength, and varied viscosity, and yielded relatively translucent films with faster drying properties. Grafting in the case of these acids was poor, but the cis acids were better grafted than the trans acids. Furthermore, saturated acids (e.g., oxalic and succinic acid) and an inorganic acid (boric acid) were only physically incorporated in the poly(vinyl acetate) emulsion (PVAc emulsion); the resulting product also showed similar improvement in the end properties.
Swelling of particulate polymers enmeshed in poly(tetrafluoroethylene)
Authors: Errede L. A. , Stoesz J. D. , Sirvio L. M.
Published: April 2003

It was demonstrated that swelling of cross‐linked polymers can be monitored much more conveniently and reproducibly after that polymer has been comminuted to a fine powder, and then fabricated mechanically into a tough microporous composite film consisting of the particulate matter (> 80%) enmeshed in poly(tetrafluoroethylene) [PTFE; < 20%]. The latter component provides the physical integrity that affords ease of handling and ensures permanent entrapment of the particles even after 100 cycles of swelling and desiccation to the original dry state. The PTFE microfiber network, however, does not affect adversely either the physicochemical properties of the particles or the permeability to fluids. Kinetic studies in 10 replicates have shown that the void space (0.3 to 0.6 mL/g of composite) is filled by capillary action within the first few minutes of contact with the liquid, and that swelling to the equilibrium state (2 to 90 mL/g of composite) usually occurs within 0.5 to 2 hours thereafter, depending primarily upon the surface to volume ratio of the particles. The magnitude of swelling at equilibrium, however, is depended only on the thermodynamic state of the gelled polymer in excess liquid, and is reproducible usually within 0.2%.
Specific‐enzyme release of cellulose‐bound drugs, experimental and theoretical study
Authors: Lapicque F. , Dellacherie E.
Published: April 2003

Various polymeric prodrugs of pholcodine were prepared by covalently linking a substrate ester of the hydroxylic drug to cellulosic derivatives. The ester derivatives of the drug were chosen so that the resulting insoluble cellulosic prodrugs became substrates of α‐chymotrypsin. The hydrolysis of such compounds was studied for various spacer arms in conditions simulating the intestinal medium. A theoretical model was developed to describe the enzymatic catalysis of this hydrolysis, taking into account the adsorption of the enzyme onto the polymer, the hydrolysis reaction, and the enzyme denaturation. The resulting equations using independently determined parameter values such as the Langmuir adsorption constants, the enzyme denaturation constants, and the initial hydrolysis rate constant successfully correlated with the experimental data.
Sorption and transport of CO2 in PVF2/PMMA Blends
Authors: Chiou J. S. , Paul D. R.
Published: April 2003

The sorption and transport of CO2 in miscible PVF2/PMMA blends are reported at 35°C as a function of pressure from 1 to 25 atm. Significant plasticization by CO2 is evident for all blend compositions. This effect induced further crystallization of PVF2 for some blends, altered the shape of sorption isotherms for blends with a glassy amorphous phase, and resulted in permeabilities which increased with pressure for all compositions. Modified sorption and transport models to account for plasticization are used to analyze the data. The effect of crystallinity on observed behavior has been accounted for using approximate models to allow comparison of responses of sorption and transport with blend composition.
Improvements in the stress‐strain behavior of urethane rubbers by bimodal network formation
Authors: Kim C. S. Youn , Ahmad J. , Bottaro J. , Farzan M.
Published: April 2003

Urethane rubbers find increasing application as binders for composites. Typical examples are solid propellants. The rubber networks are formed by end linking hydroxy‐terminated prepolymers with tri‐ or higher functional isocyanates. A recent trend in solid propellant technology is the replacement of the traditional low‐energy binders with “energetic” binders containing nitro, nitrato, or azido groups. Since these energetic polymers create relatively short interchain lengths between the cross‐link points, the binders give notoriously poor mechanical properties. Our study demonstrates that significant improvements in the stress‐strain behavior are attained with bimodal modifications of the energetic binders, that is, by blending these energetic short chains with very long chains prior to curing into rubbers.

Molecular aspects of the improvement have been examined in terms of polymer types, crosslinkers, viscoelastic factors, and solid filler content. Results indicate that the improvement is primarily due to the extent of nonaffine deformation of the bimodal rubber network.
The SCOPE dynamic model for emulsion polymerization I. Theory
Authors: Dougherty Eugene P.
Published: April 2003

The SCOPE dynamic process model has been developed to treat batch and semibatch emulsion copolymerizations. This computer‐based model treats jacketed reactors of arbitrary size. It consists of a coupled set of ordinary differential and algebraic equations that describe material balances for the reacting species and energy balances for both the reactor and the cooling water jacket. The model also includes a feature that allows for proportional integral derivative (PID) control of the monomer emulsion and cooling water feed rates to a reactor temperature set point. The model is based largely upon the kinetic theories developed by Smith, Ewart, and Harkins to treat emulsion homopolymerizations. The SCOPE model improves upon and expands the classic theories by taking advantage of recent theoretical developments in emulsion polymerization. Such phenomena as diffusion‐controlled termination and radical desorption—important for predicting accurate polymerization rates—are included in the model. More modern theories of particle nucleation, including both homogeneous and micellar mechanisms, have been incorporated into the model to predict accurate particle size distributions. SCOPE also extends the classic theories to treat the emulsion copolymerization of an arbitrary number of monomers. Output from the model includes species concentrations, residual monomer levels, particle size distributions, molecular weight distributions, instantaneous and cumulative copolymer compositions, and reactor temperatures as a function of time. The SCOPE model can be used to evaluate various process control strategies and to study the effects of process dynamics on polymer properties. In Part II, SCOPE model predictions are compared with experimental data for styrene‐methyl methacrylate copolymerizations.
The SCOPE dynamic model for emulsion polymerization II. Comparison with experiment and applications
Authors: Dougherty Eugene P.
Published: April 2003

Paper I provides the underlying theoretical framework for the SCOPE dynamic model of emulsion copolymerization. The present paper compares the model predictions for styrenemethyl methacrylate copolymerizations with experimental measurements made at a variety of polymerization conditions. The SCOPE model predicts conversion–time profiles reasonably well over wide ranges of initiator concentration, monomer concentration and monomer composition. In addition, the model accurately predicts number average molecular weights and copolymer compositions over the entire range of monomer composition. Like previous investigations of this system, the present study suggests that free radical desorption from polymer particles plays a dominant role on the copolymerization kinetics: Simple case II Smith‐Ewart kinetics do not apply. The model for this system was applied to understand how changing reaction conditions could effect polymer properties such as particle size and molecular weight distributions. The power of the SCOPE model is illustrated by using it to predict conversion profiles, temperature profiles and copolymer properties for some large‐scale versions of these recipes.
High‐strength–high‐modulus polyimide fibers I. One‐step synthesis of spinnable polyimides
Authors: Kaneda Takaho , Katsura Toshio , Nakagawa Kanji , Makino Hiroshi , Horio Masao
Published: April 2003

Polyimides with aromatic links are synthesized usually in two steps, but a series of aromatic polyimides with large molecular weights sufficient to produce strong fibers were prepared in one step by the reaction of 3,3′, 4,4′‐biphenyltetracarboxylic dianhydride (BPDA) with various aromatic diamines. The one‐step polycondensation was possible even when BPDA was replaced to some extent by pyromellitic dianhydride, which is a basic component in the conventional two‐step method. The copolyimides based on BPDA and mixtures of aromatic diamines were also synthesized in similar manner. For the one‐step polycondensation, phenol and some of its derivatives were found to be suitable solvents, while the typical solvent employed in the two‐step method, such as N‐methyl‐2‐pyrrolidone, could not be used because of the precipitation of low‐molecular weight polyimides. p‐Hydroxybenzoic acid proved to be a very efficient accelerator for the conversion of polyamic acids to polyimides.
Permeation of solutes in water‐swollen poly(vinyl alcohol‐co‐itaconic acid) membranes
Authors: Higuchi Akon , Iijima Toshiro
Published: April 2003

Partition and permeability coefficients of urea, NaCl, and saccharose in water‐swollen poly(vinyl alcohol‐co‐itaconic acid) membranes with various water contents (0.25 ⩽ H ⩽ 0.86) were measured. Partition coefficients and permeability ratios in freezing and nonfreezing water were estimated based on a parallel permeation model. It was suggested that at 25°C the permeation of saccharose in the nonfreezing water was nearly zero due to its negligible partition coefficient, while NaCl and urea were found to be able to permeate even the nonfreezing water. The activation energies of diffusion for three solutes were found to increase with the decrease of water content of the membranes. Since the fraction of nonfreezing water increased with the decrease of water content of the membranes, it is assumed that the increased activation energy of diffusion is due to the fact that the diffusion in nonfreezing water needs higher activation energy than in the pure bulk water.
Structure and molecular properties of saponified starch–graft‐polyacrylonitrile
Authors: Rodehed Cenita , Rånby Bengt
Published: April 2003

The Mn3+ initiation system has been used to prepare starch‐g‐polyacrylonitrile copolymers. Both granular native starch and water‐swollen gelatinized starch have been used as substrate. Conversion of monomer, graiting ratio, and percent add‐on tend to increase with increasing amounts of monomer charged. The amount of homopolymer formed is extremely low, a p proximately 1%. The efficiency, measured as conversion, is consistently higher with gelatinized starch as Substrate. The molecular weight of the grafta on gelatinized starch is approximately eight times higher than those on granular starch. Granular starch has a correspondingly higher frequency of grafta. Solubility measurements of starch, polyacrylonitrile, and grafted starch were carried out in dimethylsulfoxide (DMSO) at 348 K. Starch and polyacrylonitrile were totally soluble in DMSO under the chosen conditions. The solubilities of grafted samples were independent of the state of the substrate before grafting and of molecular weights of the grafted chains, but were found to be correlated to percent add‐on. Starch‐g‐polyacrylonitrile samples, with gelatinized starch as substrate, were saponified in aqueous sodium hydroxide eolution. The water retention value increased linearly with increasing add‐on. The saponified polyacrylonitrile, branches alone had a water retention value that was three times higher than that of the original copolymer.
Effect of diethylene glycol content and annealing temperature on the structure and properties of poly(ethylene terephthalate)
Authors: Seganov I. , Schultz J. M. , Fakirov S.
Published: April 2003

The effect of 2,2′‐oxydiethanol (diethylene glycol, DEG) content (ranging from 2 to 15 mol %) and of the annealing temperature (in the range from 100 to 260°C) on the density, calorimetric, dynamic‐ and static‐mechanical and small angle X‐ray scattering (SAXS) behavior of undrawn and drawn samples (granules, films, and bristles) of poly(ethylene terephthalate) (PET) has been studied. The known dependences on the annealing temperature are confirmed. Some discrepancies with earlier investigations of the dependences on the DEG content are established: constant values for the SAXS intensity and long spacing, for the lamellar thickness and for the volume fraction crystallinity ac. These discrepancies are explained by the variation of the glass transition temperature (Tg) and melting temperature (Tm) of the materials with different DEG contents. The previous hypothesis of the segregation of the comonomer (DEG) units into the amorphous regions is confirmed.
The effect of particle concentration on the rheology of polydimethylsiloxane filled with fumed silica
Authors: Kosinski L. E. , Caruthers J. M.
Published: April 2003

The effects of particle concentration on the shear‐rate‐dependent viscosity, stress relaxation, and stress growth function were investigated for various molecular weight polydimethylsiloxane (PDMS) fluids filled with colloidal fumed silica. Shear‐rate‐dependent stress relaxation was observed for all dispersions, and a significant stress growth overshoot was observed when the PDMS molecular weight was just greater than the entanglement molecular weight. The rate of stress—relaxation and the type of stress growth are primarily determined by the previous shear rate history and the PDMS molecular weight, while particle concentration only affects the quantitative details of the filled fluid's rheology. The observed effects of particle concentration are consistent with a molecular deformation process, where the silica particles interact via the entanglements of the polymer adsorbed on the surface of the fumed silica.