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A simple, inexpensive method is described for the measurement of specific volumes of thermoplastic melts during extrusion at low shear stresses. Data for several polyolefins agree closely with specific volumes obtained by dilatometry or compression measurements on static melts. Data can be obtained at a variety of temperatures more rapidly than by dilatometry. The method described yields specific volumes essentially at atmospheric pressure, but extension to higher pressures and the measurement of compressibilities is possible, with more complicated apparatus. Simultaneous measurements can be also made of apparent shear rates, and these can be converted to absolute shear rates, and viscosities, by application of standard techniques. The simple procedure described does not permit the concurrent measurement of useful apparent shear and volume viscosities because the initial state of the system reflects operational as well as polymer properties. It is suggested that an extension of the present method would provide such data.

Solid‐phase microextraction (SPME) technique with poly(dimethylsiloxane)‐coated fiber has been employed for the rapid determination of sixteen polycyclic aromatic hydrocarbons (PAHs) present in natural water. The method is solvent‐less with the analytes being adsorbed and then desorbed thermally at the injector port of a gas chromato‐graph (GC) prior to mass spectrometric (MS) analysis in selective ion monitoring (SIM) mode. The influences of the injector port temperature, desorption time and initial oven temperature on the thermal desorption of PAHs from the fiber were investigated. Then the optimum SPME conditions were applied for the qualitative and quantitative determination of PAHs in environmental samples. The recoveries of the 16 PAHs being spiked into sea water at 50 ng/mL level were 75.3%. The levels of PAHs in the Singapore coastal sea water are between 0.02–8.50 ng/mL using SPME(PDMS).

The corresponding states correlation with the surface tension (γ) of polymers after Patterson et al. has been modified by considering the molecular weight (M) dependence of the equation-of-state parameters, which may be estimated by either the Flory-Orwoll-Vrij (FOV) theory or the cell model (CEM). It has been found that the corresponding states principle-cum-FOV predicts the γs of polystyrene melts over a wide range of M satisfactorily. However, its CEM counterpart is rather irrelevant to the present system of interest. Indeed, the three classical linear equations proposed for the variations of γ with M are intimately correlated with the foregoing models, and hence, facilitating the predictions of the γs of polymer end groups. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 697–703, 1998

A microwave-assisted solvent extraction (MASE) technique was developed for the quantitative extraction of gasoline- and diesel-range petroleum hydrocarbons (PHs) from soil and marine sediment samples. The influence of different extracting solvents, extraction temperature and duration of extraction on the recoveries of PHs was evaluated using a two-level orthogonal array design (OAD) with a OA8(27) matrix. Gas chromatographic-mass spectrometry (GC-MS) in multiple selective ion monitoring (MSIM) mode was used for the analysis of the PHs in environmental samples. The spiking range of the PHs in the environmental samples was between 1 to 1000 μg/g. Good recoveries (>80%) could be obtained for most of the PHs using the optimum MASE conditions. The limit of detection (LOD) achieved by the GC-MS-MSIM was 0.02 μg/g. A preliminary survey for the levels of PHs in marine sediment and soil samples from different parts of Singapore was carried out using the method.

A method for the determination of polycyclic aromatic hydrocarbons (PAHs) in air particulates using microwave-assisted solvent extraction (MASE) coupled to a microwave extraction system (MES) is proposed. During the period of August to October, 1994, Singapore was enveloped by haze caused by forest fires in Sumatra, Indonesia. Air sampling were carried out during September and October; the determination of ambient air PAH levels in Singapore was undertaken. PAH analysis by GC-MS provided excellent sensitivity, linearity of quantitation, peak identification. This technique was evaluated using certified reference materials (CRMs) HS-4 and HS-6. Good recoveries of PAHs (>73.3%) were obtained for both CRMs. The MASE technique using MES is suitable for the determination of PAH levels in ambient air with no clean-up step required.

Solid phase extraction (SPE) with appropriate solid sorbents has been commonly used in the routine extraction of organic pollutants in water. The elution of analytes from the solid sorbents normally takes place by organic solvents under an applied vacuum. In this study, a microwave-assisted solvent elution technique was developed for the elution of analytes from C18 membrane disks during microwave irradiation from a microwave extraction system (MES). Several parameters, namely, elution solvent, elution temperature, duration of elution and the volume of solvent which may affect the elution efficiency of microwave-assisted solvent elution (MASE) technique towards organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), phthalate esters (PAEs), organophosphorus pesticides (OPs), fungicides, herbicides and insecticides from the membrane disk were investigated. Good recoveries above 75% were obtained for most of the organic pollutants using the optimum SPE-MASE technique. The effect of sodium chloride and humic acid on the recoveries on the target analytes were also investigated.

C 18 -impregnated disks for solid-phase extraction were evaluated for the extraction of organochlorine pesticides (OCPs) from water samples, and stability of the pesticides in storage. Good recoveries from different water samples were obtained. Microwave-assisted solvent extraction (MASE) was employed for the extraction of marine sediments spiked with OCPs. Factors affecting the efficiency of MASE were also investigated. Recoveries of 17 OCPs and 2 OCP surrogates were in the range 70.6–93.1% with mean deviation between 2.0 to 8.0%.

A novel approach is developed to estimate the interaction energy density, B, of polymer solutions by the melting point depression method using a crystallizable molecule as the probe. It rests on the classical Flory-Huggins lattice model of polymer solutions, and considers the polymer-solvent interaction parameter to be concentration dependent. The ternary system dimethyl terephthalate (DMT)/bis(2-ethylhexyl)adipate (DOA)/poly(vinyl chloride) (PVC) is chosen for the present study. The data of B for the three possible binary interactions are reported as the functions of composition at elevated temperatures. For a plasticized PVC resin containing 20 vol % DOA, the B is estimated to be 6 MJ m -3 , which is approximately 2 MJ m -3 higher than the B value cited in the literature for the PVC mixed with almost 100% DOA. The thermodynamic stability of the ternary system is discussed.

In the present study, a microwave-assisted solvent extraction (MASE) technique using a microwave extraction system (MES) has been developed for the extraction of polycyclic aromatic hydrocarbons (PAHs) from marine sediment. The optimum MASE conditions can be obtained by performing the mixed-level orthogonal array design (OAD) procedure. A comparison between the Soxhlet extraction method and the MASE technique showed that although both techniques gave comparable results on certified reference materials (CRM) HS-4 and HS-6, the MASE technique allows the use of less solvent and is also time-saving and cost-effective without affecting its extraction efficiency. The optimum MASE technique was coupled to two analytical techniques: high-performance liquid chromatography (HPLC) with both ultraviolet (UV) and fluorescence detectors and gas chromatography-mass spectrometry (GC-MS) for the qualitative and quantitative screening of PAHs in CRM and “real world” samples. Recoveries of PAHs from two CRMs were all above 73.3%. The concentration of PAHs in marine sediment collected from primary industrial areas was between 0.03 and 0.35 μg/g on a dry weight basis.

Orthogonal array design (OAD) using two-level OA8(27) matrix was employed for the optimization of solid-phase microextraction (SPME) conditions for the determination of 4-nonylphenol (4-NP) in water. The parameters under consideration for the optimization of SPME conditions include: injector port temperature, initial oven temperature, desorption time, and pH. The effect of dissolved humic substances on the extraction efficiency of SPME for the determination of 4-NP was also investigated. The method is capable of parts per billion detection limit with a %RSD of 6.5%. Thus, the SPME approach is suitable for analytical determination of 4-NP in environmental water samples compared to conventional liquid-liquid extraction (LLE) technique. © 1996 John Wiley & Sons, Inc.

Sample preparation techniques for the determination of 4-nonylphenol in water and sediments were optimized using two-level orthogonal array design (OAD). Comparison between the use of cartridge-based solid-phase extraction and membranous disk-based extraction was made for water samples. For sediment samples, microwave-assisted solvent extraction (MASE) was employed. A comparison between MASE and classical soxhlet extraction of spiked samples was also carried out. 4-Nonylphenol was determined using high performance liquid chromatography (HPLC) coupled to both ultraviolet and fluorescence detection

The swelling behavior of the networks of natural rubber, an epoxidized natural rubber, low-density polyethylene, polystyrene, and poly(methyl methacrylate) are studied in six classes of solvents at 60°C. The data of the swelling coefficient are successfully treated by a modified version of the empirical equation proposed by Gee, as to determine the solubility parameter of a polymer, δ2. It is found that increasing the temperature would decrease the δ2's of these polymers with a common rate of 0.02 (J/mL)1/2/K. A semiempirical model is proposed to rationalize the present finding satisfactorily. © 1995 John Wiley & Sons, Inc.

A two-level orthogonal array design (OAD) to optimize the solid phase extraction of organochlorine pesticides is described. Parameters including eluting solvents, SPE cartridges packed with C18-bonded silica from different manufacturers, duration of air drying, pH, salinity and humic acid have been examined using OAD. This systematic approach was then used to optimize the relevant parameters required for off-line solid phase extraction of organochlorine pesticides from water. The optimized parameters were employed to perform extraction of the pesticides from natural waters.

Allyl esters of palm olein, palmitic, and oleic acids were synthesized by transesterification and esterification methods using KOH and absolute H2SO4 as catalysts, respectively. Three allyl esters, namely, allyl palmitate, allyl epoxystearate, and epoxidized allyl ester of palm olein, were successfully polymerized in the presence of t-butyl perbenzoate at 120°C to obtain oligomers with the average number of backbone atoms approximately equal to the number of skeletal atoms of the long-dangling side chains. The kinetic data of polymerization were conformed to the rate equation proposed by other workers. No oxirane cleavage was detected during the chain reaction. The melting behavior of these comb-shaped polymers was compared with that of their respective allylic monomers. The polymer of epoxidized allyl ester of palm olein exhibits a glass transition temperature at 204.4 K. The critical molecular weights of the polymers of allyl esters investigated are predicted to be not lower than 104.

The kinetics of thermal oxidative degradation of natural rubber (NR) have been studied by Wallace plasticity measurements. On the basis of the Kotliar's model of random chain scission, an expression was derived to interpret the kinetic data collected over a range of temperatures from 80 to 160°C. It has been shown that the kinetic parameter resulting from the present analysis, indeed refers to a diffusion-controlled reaction with an overall activation energy estimated to be 135 ± 6 kJ · mol−1. In addition, the implications of plasticity retention index, which measures the oxidizability of NR, are discussed.

Background: Ingestion of flour contaminated with dust mite may trigger severe anaphylaxis in tropical and sub-tropical regions. Aims: This study aimed to evaluate environmental factors that affect dust mite propagation in the tropics. Materials & Methods: Dust mites were introduced to a variety of flour samples and incubated at two different environmental conditions. Results: It was found that dust mites populations flourished best in wheat flour compared to other varieties of flour, and at ambient temperatures with high humidity instead of the air conditioned environment. Conclusion: Dust mite infestation of flour is dependent on the presence of wheat and high ambient temperature in the tropics.

The thermodynamic interaction parameter, χφ, for a low-density polyethylene in p-xylene, ethylbenzene, and n-octane has been determined over a range of segment fraction, φ2, from 0.2 to 0.7 using the melting point depression method. Taking advantage of a unique feature of polyethylene, a new procedure has been proposed for evaluating the equilibrium melting points from data obtained by differential scanning calorimetry. The experimental χφ-φ2 relations conform well to the recent equation-of-state theory of polymer solutions. The exchange parameters of the model X 12 and Q 12 are accessible by a nonlinear leastsquares algorithm. Apparently, the observed small values of χφ for the foregoing dispersion force interactions are originated from the negative contribution of the effective interaction energy as concluded by the present findings.

A Study of Temperature Dependence of Thermodynamic Interactions in Polymer Solutions of Infinite Dilution by Equation-of-State Theory

Based on the Saito's model for random chain scission, a novel procedure is developed to determine the activation energy of polymer degradation process. Basically, this is a simple viscometric technique which yields reliable results. In fact, it is superior to the existing viscometry which has been widely used to study the kinetics of random scission. The present method is successfully applied to the thermal degradation of natural rubber, polycarbonate, and poly(tetramethylene oxide) in bulk.

The theory and methodology of a five-level orthogonal array design for the optimization of analytical procedures were developed. In the theoretical section, the construction and characteristics of the OA25(56) matrix are described in detail while orthogonality is proved by means of a fourth-order polynomial model. Next, the assignment of experiments in the OA25(56) matrix is illustrated, followed by the data analysis strategy, in which significant/non-significant influence for each factor is quantitatively evaluated by the analysis of variance (ANOVA) technique including the percentage contribution, and the differences among five levels for each factor that has a significant influence are determined by Duncan's multiple F-test. Finally, the response surface methodology for the OA25(56) matrix is developed by using the equations obtained from the proof on orthogonality. In the application section, the reaction system for selenium determination by differential-pulse polarography, as a practical example, is employed to demonstrate the application of the OA25(56) matrix in the area of analytical chemistry.

The theory and methodology of a mixed-level orthogonal array design for the optimization of analytical procedures is described. Firstly, the method of construction of a mixed-level orthogonal array design is discussed in detail, followed by the assignment of experiments and the data analysis strategy in the design. The optimization of the parameters involved in the high-performance liquid chromatographic determination of polycyclic aromatic hydrocarbons is then employed to demonstrate the practical application of the proposed mixed-level orthogonal array design in the area of analytical chemistry.

The weight-average molecular weight is estimated by an extrapolation technique based on a linear relation between the viscosity-average molecular weight Mv and a Mark–Houwink–Sakurada constant. This method may also be used to assess the unperturbed dimensions of polymers. If the Mv data are known with high accuracy, then the straight line may be stretched to reach the number-average molecular weight confidently. The slope of the linear plot is associated with the molecular weight distribution and as such can be utilized to compute the polydispersity index.

A simple, inexpensive glass viscometer can be constructed to time the rate at which a rod falls into a liquid held in a concentric closed-end glass cylinder. This equipment can be used to measure absolute values of apparent viscosities of Newtonian and non-Newtonian fluids. Calibration is not required. The technique is an adaptation of a method used previously with polymer melts at elevated temperatures. The present article describes the modifications needed for lower-viscosity fluids, such as paints, and validates the flow analysis with results of study of a characterized Newtonian fluid.

A new semi-empirical equation proposed by us recently for evaluating the intrinsic viscosity of polymer solutions from the viscometric data of moderately concentrated solutions is successfully extended to the higher concentration region in which the critical concentration can be determined. Values of viscometric parameters for various polymer-diluent systems are reported by the present analysis. It is shown that the critical concentration can be used to estimate the unperturbed parameter and its physical significance is discussed.

Two novel procedures have been established to estimate the intrinsic viscosity and the Huggins constant accurately. It is shown that these numerical methods are superior to the existing models, namely the Huggins, Nagy–Kelven–Tudos, and Reilly–Van Der Hoff–Ziogas equations. This finding is attributed to the more even distribution of errors in the dependent variables of the present analyses. The viscometic data of a poly(vinyl chloride) sample in tetrahydrofuran are analyzed by the foregoing five approaches whose accuracies are compared in terms of their variances of estimates.

A linear expression is derived from Tobolsky's equation related to the dead-end polymerization method to determine the rate constant for the initiator dissociation. This novel graphical method applies remarkably well to the kinetic data collected by dilatometry from the polymerization of methyl methacrylate initiated by 2,2′-azobisisobutyronitrile and benzoyl peroxide in toluene at 60°C. Results obtained for these two initiators are consistent with those published in the literature. Applicability of the method is confined to at least 5% and at most 13% decomposition of initiator. However, these limiting values are sensitive to the experimental techniques employed. The effects of induced decomposition of benzoyl peroxide and thermal polymerization of methyl methacrylate are shown to be negligible in the present investigations.

A rigorous statistical method is established to compute the rate constants of the bimolecular decomposition of redox catalysts used to initiate polymer chains. Results obtained for the systems styrene-dimethylaniline-benzoyl peroxide and acrylamide-thio-glycollic acid-potassium bromate compare favorably with those reported by other workers. The merits of this error-in-variable technique, which outperforms conventional nonlinear least-square analysis and the dead-end polymerization method, are discussed.

The phase-separation process in segmented copolymers is treated by first-order kinetics which couples with the Fox equation to derive an expression for describing the change of soft segment Tg with the annealing time. Kinetic data of five commercial polyurethanes have been analyzed. The studies conclude that the phase-segregation mechanisms involve two elementary steps which can be characterized by two discrete relaxation times. It has been shown quantitatively that a polyether-based polyurethane (ET) recovers its original domain structure faster than a polyester soft-segment material. The average activation energy of the demixing process of an ET polyurethane is found to be about 23 kJ.mol−1 and is not influenced by hydrogen bonding.

A semiempirical equation is developed to compute the unperturbed parameter from the critical concentration of polymer solutions derived from the viscometric and kinetic data. This equation gives satisfactory results for various vinyl polymers including poly(vinyl chloride), polystyrene and poly(methyl methacrylate) among others that follow the Schulz molecular weight distribution function. It is found that the segments of a Gaussian polymer chain are associated with an equal number of foreign segments near its center of mass, when the polymer solution has attained a uniform segment density at the critical concentration. The effect of molecular weight distribution on the present studies is significantly large that it merits an empirical treatment. Defects of the model is also discussed.

A novel method developed to evaluate the unperturbed parameter Kθ from the viscometric data of dilute polymer solutions can be considerably simplified by making the reasonable assumption that the Huggins' constant under theta conditions, kHθ, is equal to ½ for a number-average degree of polymerization of over about 2000. Two linear equations are derived pertaining to the present analysis, one to deal with the experimental data, and the other specially to estimate the intrinsic viscosity [η]θ which corresponds to κHθ. All calculations were done by the linear least-squares method. The Kθ was computed by the Mark–Houwink–Sakurada equation. It is shown that reliable results on Kθ can be obtained for polystyrene and poly(vinyl acetate).

The classical expression for estimating the polymer-solvent interaction parameter χ from melting point data of the solvent is refined by considering χ to be concentration-dependent. Differential scanning calorimetry (DSC) measurements are performed on blends of cis-polyiso-prene-dimethyl terephthalate (DMT) and trans-polyisoprene–DMT. It is found that the presence of DMT would not affect the DSC events of the polyisoprenes appreciably. However, in both cases, the melting point of DMT decreases, and the rate of depression increases with increasing proportions of polymer. These DSC data are analyzed by the proposed procedure. The results on the interaction energy density parameter are presented as a function of the blend concentration, and rationalized by the specific interactions between different moieties on the component molecules. The limitations of the present technique are discussed.

L'equation de copolymerisation integree est convertie en forme plus accessible. Comparaison de la methode EVM du titre avec la methode NLD (nonlinear least squares)

Capillary extrusion flow curves of four anionic and five polydisperse polystyrenes have been measured at five temperatures between 170 and 237°C. The non‐Newtonian flow curves of the narrow distribution polymers can be represented by a common master curve in terms of the viscosity ratio (η/η0) and the product of shear rate and a relaxation time. The polydisperse polymers do not yield a single flow curve. Current molecular and semiempirical models do not yield master curves which fit the experimental plots. Exceptions are Pao's model for monodisperse polymers and an empirical relation presented in this article which fits the data of the five commercial polymers studied. The existence of a general theory which represents experimental polymer flow curves satisfactorily has yet to be demonstrated. An acceptable model should predict rheological parameters correctly and should also show why experimental data for polymer melts scatter rather severely. Such scatter often reflects lack of control of an important e...

A three-parameter equation is put forward to evaluate the [η] of polymer solution from a wide range of concentrations, up to a relative viscosity of 100. The equation is tested by viscometric data of polystyrene, poly(vinyl chloride), poly(1-vinylnaphthalene), poly(2-vinylnaphthalene), and poly(4-vinylbiphenyl) at different temperatures and in a variety of solvents including mixed solvents. A statistical method is employed to analyze the experimental data. It is found that the values of [η] obtained by the new equation are consistently lower than those derived from the Huggins equation. However, the discrepancy is not more than 3% on average, and it does not affect the values of Mark-Houwink constants significantly. Other parameters of the equation are also computed.

A novel viscometer was devised to measure flow curves of polymer melts over a wide range of shear rates. The apparatus comprises a concentric cylinder viscometer with the inner moving piston driven axially at set speeds. Immersion depth of the moving piston increases continuously during the course of an experiment. An Instron or similar piston-operated capillary viscometer can be easily modified for this purpose.

Both the rate constant of initiator dissociation, kd, and the chain transfer constant, Cx, are determined by monitoring the rates of monomer and transfer agent conversions in a chain polymerization. Statistical analysis that takes into account the errors of experimental variables has been used to treat the kinetic data for the polymerization of styrene initiated by benzoyl peroxide (Bz2O2) in carbon tetrachloride at 60°C. Values of kd and Cx produced by this error-in-variable method (EVM) are in accordance with those reported in literature. More important, the EVM algorithm always results in the smallest standard deviations of estimates, and hence, it is superior to the usual least-squares calculations. Other distinct features of the method are outlined. The initiator efficiency for Bz2O2 is estimated to be 0.72 under the present conditions.

A new approach pertaining to the hole and lattice theories of polymeric systems is developed to interpret the universal inverse relationship between the glass transition temperature (Tg) and the difference in thermal expansion coefficients for liquid and glassy polymers (δ α). The success of this particular theoretical consideration rests upon the familiar hypothesis of the iso-free volume state at Tg and the entropy contribution to the hole-polymer segment interaction energy. Based on the experimental data available, we have established the free volume fraction at Tg, vg = 0.025, which is identical with the assessment of the empirical Williams-Landel-Ferry (WLF) equation for the temperature-dependence shift factor aT. However, appreciably higher values of vg are reported by other contemporary models. The present findings justify an alternative form of the WLF equation with the product Tg, δ α playing the role of δ α. The universality of this novel expression is demonstrated, by means of statisti...

The general validity of four single-point methods for intrinsic viscosity ([η]) determination is verified to be unacceptable even for dilute polymer solutions. Also, a direct method based on a truncated version of Huggins equation is shown to be less practical in that it involves advanced experimentation and is valid only at sufficiently low concentrations. In view of the shortcoming and sophistication of the above procedures, an effective approach is introduced to resolve these problems. This novel computation expresses the Huggins coefficient in terms of [η], and the associated equations are calibrated against the polymer system of interest. This procedure is tested using various polymer solutions with results compatible with those acquired by other means. The advantage of the proposed technique is discussed.

A linear equation is proposed to quantify the glass transition behavior of miscible polymer blends in terms of the polymer-polymer interaction density parameter whose values are obtainable from the melting point depression method. This practical model is successfully applied to four series of binary polyblends containing poly(hydroxy ether) of biphenol A, poly(vinyl chloride), poly(vinylidene fluoride), and poly(2,4-dimethyl-1,4-phenylene oxide) as the common components. Each of these groups of polymer systems exhibits a distinct type of intermolecular interaction that can be characterized by the two coefficients of the model equation. In connection with the present analysis, three novel expressions are introduced for describing the glass transition temperature—composition relations of the polymer systems of interest.

A polystyrene melt has been extruded through successive capillaries arranged to produce converging and diverging flow patterns through the twin orifices. Applied pressure at fixed mass flow rate through the combined dies is equal to the sum of the pressure drops in the single capillaries in both flow modes. The Bagley end correction was found to apply to each die in the sequence. Bagley plots were linear with a particular upper capillary at given apparent shear rate in the lower die. No effect of shear history could be detected on the viscous behavior of the polymer, but preshearing in converging flow produced a slight reduction in die swell.

The assumptions involved in the analysis of flow of polymer melts in a closed end falling coaxial cylinder viscometer(1–3) are examined and it is shown that true values of shear rate and shear stress at the wall of the moving cylinder can be obtained by assuming classical Poiseuille flow. Flow curves obtained with a variety of apparatus geometries, driving loads and polymers are consistent with those of other measurement techniques. This apparatus, which is a simple modification of a capillary extrusion rheometer, provides measurements of apparent viscosity at much lower shear rates than can be obtained with the former viscometers. A quantitative measurement of end correction effects is provided by the present analysis. End effects, which are formally similar to those in capillary extrusion, were measured for several polystyrenes and polyethylenes. On a examine les hypotheses qu'implique l'analyse de l'ecoulement de polymeres en fusion dans un viscosimetre comprenant un cylindre coaxial a extremites fermees et tombant; on a constate qu'on peut obtenir les vraies valeurs du taux de cisaillement et de l'effort de cisaillement sur la paroi du cylindre en mouvement en supposant qu'il s'agit de l'ecoulement classique de Poiseuille. Les courbes d'ecoulement qu'on a obtenues, en employant differentes formes geometriques de l'appareil et charges de poussee ainsi que divers polymeres, ont bien concorde avec celles qui resultent de l'utilisation d'autres methodes de mesure. Ledit appareil, qui est un simple modification d'un rheometre a extrusion capillaire, permet d'obtenir des mesures de la viscosite apparente a des taux de cisaillement bien plus faibles que dans le cas des viscosimetres prealablement employes. L'analyse actuelle fournit une mesure quantitative des effets finals de correction; on a mesure, dans le cas de plusieurs polystyrenes et polyethylenes, les effets finals qui sont formellement semblables a ceux qu'on rencontre dans le cas de l'extrusion capillaire.

The flow behavior of a polystyrene and a polyethylene melt has been studied during extrusion through successive capillaries arranged to produce converging and diverging flow patterns through the two orifices. Laminar flow and flow instability regions were included in the experiments.

An inexpensive, accurate falling coaxial cylinder viscometer is described. Viscosities can be measured at shear stresses at least as low as 103 dynes per cm2 and flow curves can be obtained with shear thinning fluids. Data for a polystyrene and a polyethylene polymer coincide with those from other techniques and with corresponding literature values. The lower Newtonian viscosities pf both polymers were experimentally accessible, and it is shown that estimation of ηo by extrapolation from viscosities in the non-Newtonian region may be subject to errors of uncertain magnitude. Shear history of the sample affects the Newtonian and low shear viscosities of high molecular weight polymer melts. On decrit un viscosimetre non-coǔteux dans lequel on peut determiner avec exactitude le temps de chute d'un cylindre coaxial dans un fluide. On peut mesurer des viscosites correspondent a des efforts de cisaillement aussi faibles que 103 dynes au centimetre carre et peut obtenir des courbes d'ecoulement pour des fluides dont la viscosite est reduite par le cisaillement. Les resultats obtenus dans le cas de deux polymeres (polystyrene et polyethylene) concordent avec ceux qui proviennent d'autres methodes et avec les valeurs correspondantes qui ont ete publiees. On a pu determiner experimentalement les viscosites newtoniennes plus faibles des deux polymeres et demontre que l'estimation de ηo par extrapolation des viscosites dang le secteur non-newtonien peut ětre sujette a des erreurs dont l'importance est aleatoire. Le degre de cisaillement auquel ont ete soumis les echantillons affecte les viscosites newtoniennes et a cisaillement faible des polymeres fondus qui possedent un poids molceulaire eleve.

The specific volumes of anionic polystyrenes with molecular weights between 9,000 and 700,000 have been measured at 170–237°C. The volumes attributable to end groups differ between anionic and thermally initiated polystyrenes. Uncertainties in average molecular weights of short chain polymers have a critical influence on conclusions as to the influence of molecular weight and temperature on polymer melt density and related phenomena.

This article considers possible erxors in experiment or analysis and alternative methods of data treatment for a falling coaxial cylinder viscometer. The viscometer uses a weighted rod falling into a polymer melt contained in a closed end concentric cylinder. Flow relations can be solved for non-Newtonian fluid response in steady, simple shearing flow. Although the rod fall is found not to be steady, as assumed, this produces negligible error in the computed flow curves. Consistent flow curves which were independent of apparatus geometry were obtained by a method in which instantaneous rod velocities were estimated graphically from raw data and an end correction was taken into account. On considere, dans le present travail, les erreurs qui peuvent se glisser dans les experiences ou analyses et la methodes alternatives du traitement des donnees dans le cas d'un viscosimetre base sur la chute d'un cylindre coaxial. Dam le dit viscosimetre, on laisse tomber une tige alourdie par un poids dans un polymere en fusion qui se trouve dans un cylindre ferme et concentrique. On peut resoudre les equations d'ecoulement relatives a la reaction d'un fluide non-newtonien engage dans un ecoulement stable et a cisaillement simple. Bien qu'on constate que la chute de la tige n'est pas aussi reguliere qu'on le supposait, l'erreur resultante dans les courbes d'ecoulement calculees est negligeable. On a obtenu des courbes consistantes d'ecoulement, qui ne dependaient pas de la geometrie de l'appareillage, en utilisant une methode dans laquelle on a evalue graphiquement les velocites instantanees de la tige, a partir de donnees brutes, et tenu compte d'une correction finale.