Melt viscosity of acrylic copolymers

The melt flow behavior of methyl methacrylate (MMA) copolymerized with methyl acrylate (MA) was measured and analyzed in terms of the molecular structure of the copolymers. Measurement was done by using a capillary rheometer in the shear rate range from 6 × 10⁰ to 3 × 10³ s^?1 and in temperatures from 160°C to 280°C. The Newtonian flow pattern appeared in lower shear rate and higher temperature regions. However, with increasing shear rate at lower temperature, viscosity decreased to a constant slope on a logarithmic scale. The melt fracture arose at the critical shearing stress point S_c of 6 × 10⁶ dyn/cm². A die swell also appeared in the shear rate range larger than 1 × 10⁶ dyn/cm², and its maximum value was two times larger than that of the capillary diameter. The decrease in viscosity with increasing shear rate is explained in terms of the apparent energy of activation in flow E. E also decreases with increasing shear rate. The exponential relation of E to η is maintained in the higher shear rate. The lowering of viscosity in lower shear rate, however, is attributed to not only the change in E but also the change in the volume of flow unit. The melt viscosity increases in inverse proportion to the MA content in the copolymers which form more flexible chains. Syndiotactic form of MMA has increased viscosity, caused by the rigidifying of segmented chains, rather than the strengthening of intermolecular interaction.     

Characterization of the aging behavior of raw epoxidized natural rubber with a rubber processing analyzer

Tests of the strain sweep, frequency sweep, and stress relaxation for raw epoxidized natural rubber were carried out with a rubber processing analyzer. The results showed that the complex viscosity, η*, decreased with the prolongation of the aging time in the region of Newtonian flow, but in the region of non‐Newtonian flow, the decrement of η* with a rising shear rate decreased with the prolongation of the aging time. The torque (S′) response from the strain sweep indicated that aging brought about an obvious decrease in the increment of S′ with rising strain in the linear viscoelastic region and a small increase in the slope of the plateau on the curve of the S′ response in the nonlinear viscoelastic region. The stress relaxation rate constants k and b, calculated according to the equations S_t = S₀e^?kt and S_t = S₁t^?b (where S_t, S₀, and S₁ are the stresses at relaxation time t, t = 0, and t = 1, respectively), increased, and the stress relaxation time obtained directly from the rubber processing analyzer shortened with the prolongation of the aging time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1277–1281, 2006     

Lower Newtonian viscosities of polystyrene

A falling coaxial cylinder viscometer was used to measure the melt flow behaviour of a commercial polystyrene with Mw 260,000. The shear stress region extended down to 0.6 × 10⁴ dynes/cm² and shear rates were as low as 3 × 10^?2 sec^?1 at 186°C. The shear rate-shear stress plots were linear at low shear stresses with slopes (differential viscosities) of 3.3 × 10⁵ poises at total shear less than 120 units and decreasing differential viscosity with higher total shear. The flow curves at relatively low total shear were initially dilatant and became pseudoplastic with increasing shear stress. The inflection point represents a Newtonian apparent viscosity, which agrees fairly well with literature values for polystyrenes of the same Mw. Newtonian apparent viscosity is characteristic of a point value of shear stress and shear rate and is not necessarily a plateau region. Observation of a Newtonian region with decreasing shear stress or shear rate does not prove that this flow regime persists unchanged to zero values of the experimental parameter. The existence and magnitude of the Newtonian apparent viscosity reflects shear history of the polymer as well as its constitution and molecular weight distribution.     

Stress growth and relaxation of a molten polyethylene in a modified weissenberg rheogoniometer

A Weissenberg rheogoniometer was modified^1-3 to improve sample temperature uniformity and constancy (to within ±0.5°C) and to give a quicker response to normal thrust changes (estimated gap change ≤0.1 μm/kg thrust; gap angle = 8.046°; gap radius = 1.2 cm; servomechanism replaced by an open-loop cantilever spring of 10 kg/μm stiffness). Low-density polyethylenes (IUPAC samples A and C, melt index at 190°C = 1.6) at 150°C were used in step-function shear rate experiments. Inspection of marked sectors in the samples showed substantial uniformity of shear at values of ? = 0.1, 2, and 5 sec^?1; for ? = 10 sec^?1 and S ≤ 2 shear units (S = ?t), the shear was highly nonuniform at and near the free boundary. Using selected premolded samples A, scatter in seven replicate tests at ? = 1.0 sec^?1 did not exceed ±6% for N₁(t) and ±5% for σ(t) (N₁ = primary normal stress difference; σ = shear stress; t = time of deformation from the initiation of experiment at zero time). N₁(t) and σ(t) data agreed with Meissner's¹; for ? = 0.1, 2.0, 5.0, and 10.0 sec^?1, torque maxima occurred at S = 6 shear units, and thrust maxima occurred in the range of 10 to 20 shear units. σ(t) and N₁(t) data do not satisfy the van Es and Christensen⁴ test for rubber-like liquids with strain rate invariants included in the memory function. On cessation of shear (after a shear strain S at constant shear rate ?), initial values of ?dσ(t)/dt and ?dN₁(t)/dt were found to depend strongly on S, in some cases passing through maxima as S was increased. After shearing at ? = 0.1 sec^?1 for 500 sec, such that stresses became constant, stress relaxation data satisfied Yamamoto's⁵ equation of dN₁(t)/dt = ?2?σ(t).     

Mechanical properties of drawn poly(methyl methacrylate) filled with ultrafine particles

The elastic and yield properties of drawn poly(methyl methacrylate) (PMMA) filled with ultrafine SiO₂ are described as functions of filler content and size. The drawn PMMA composites were made by uniaxially drawing to x4.0 at 100°C and at a rate of 20 mm/min. Four compliance values, i.e., S₃₃, S₁₁, S₁₃, and S₄₄ were determined. These values decreased with filler content and decreasing filler size. The relative compliance values S^de/S^do(S^de is the compliance of drawn PMMA composites and S^do is that of drawn unfilled PMMA) are almost equivalently changed with changes in filler content. The elastic properties of drawn PMMA composites are thus reinforced isotopically. This is characteristic of PMMA which has a large side group. The yield behavior of drawn PMMA composites have similar filler size and content dependence to those of elastic properties except that the transverse yield stresses become more brittle with filler content. The anisotropy in yield stress is relatively larger than that of elastic properties. This is probably because the anti-reiforcing effect, such as fibrillation becomes prominent with increasing filler content in the perpendicular direction.     

A study of low shear viscosity of polymer melts

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 η_o 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.     

Melt viscosities of molten poly(ethylene terephthalate) calculated from modified Bueche-Harding equation

The semiempirical Bueche-Harding equation was successfully modified to allow the calculation of experimentally verified melt viscosities of molten poly(ethylene terephthalate) (PET) for shear stresses > 9.65 × 10⁵ dynes/cm² by accounting for the definite Newtonian region in the flow behavior of PET for shear stresses lE; 9.65 × 10⁵ dynes/cm². Melt viscosity values calculated from the modified Bueche-Harding equation agreed within ±12% of the values calculated from the equations based on experimental data.     

Effect of supercritical carbon dioxide on morphology development during polymer blending

Supercritical carbon dioxide (scCO₂) was added during compounding of polystyrene and poly(methyl methacrylate) (PMMA) and the resulting morphology development was observed. The compounding took place in a twin screw extruder and a high‐pressure batch mixer. Viscosity reduction of PMMA and polystyrene were measured using a slit die rheometer attached to the twin screw extruder. Carbon dioxide was added at 0.5, 1.0, 2.0 and 3.0 wt% based on polymer melt flow rates. A viscosity reduction of up to 80% was seen with PMMA and up to 70% with polystyrene. A sharp decrease in the size of the minor (dispersed) phase was observed near the injection point of CO₂ in the twin screw extruder for blends with a viscosity ratio, ηPMMA/ηpolystyrene, of 7.3, at a shear rate of 100 s^?1. However, further compounding led to coalescence of the dispersed phase. Adding scCO₂ did not change the path of morphology development; however, the final domain size was smaller. In both batch and continuous blending, de‐mixing occurred upon CO₂ venting. The reduction in size of the PMMA phase was lost after CO₂ venting. The resulting morphology was similar to that without the addition of CO₂. Adding small amounts of fillers (e.g. carbon black, calcium carbonate, or nano‐clay particles) tended to prevent the de‐mixing of the polymer blend system when the CO₂ was released. For blends with a viscosity ratio of 1.3, at a shear rate of 100 s^?1, the addition of scCO₂ only slightly reduced the domain size of the minor phase.     

Superstructure and mechanical properties of nylon 66 microfiber prepared by carbon dioxide laser‐thinning method

Nylon 66 microfibers were obtained by a carbon dioxide (CO₂) laser‐thinning method. A laser‐thinning apparatus used to continuously prepare microfibers consisted of spools supplying and winding the fibers, a continuous‐wave CO₂‐laser emitter, a system supplying the fibers, and a traverse. The diameter of the microfibers decreased as the winding speed increased, and the birefringence increased as the winding speed increased. When microfibers, obtained through the laser irradiation (at a power density of 8.0 W cm^?2) of the original fiber supplied at 0.23 m min^?1, were wound at 2000 m min^?1, they had a diameter of 2.8 μm and a birefringence of 46 × 10^?3. The draw ratio calculated from the supplying and winding speeds was 8696×. Scanning electron microscopy showed that the microfibers obtained with the laser‐thinning apparatus had smooth surfaces not roughened by laser ablation that were uniform in diameter. To study the conformational transition with winding speed, the changes in trans band at 936 cm^?1 and gauche band at 1136 cm^?1 were measured with a Fourier transform infrared microscope. The trans band increased as the winding speed increased, and the gauche band decreased. Young's modulus and tensile strength increased with increasing winding speed. The microfiber, which was obtained at a winding speed of 2000 m min^?1, had a Young's modulus of 2.5 GPa and tensile strength of 0.6 GPa. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 802–807, 2006     

Electrical properties of diphenyldiacetylene annealed under elevated pressure

A unique class of conjugated compounds composed of the derivative of condensed polycyclic aromatic compound with the phenyl group and diphenyldiacetylene oligomer was synthesized by annealing of diphenyldiacetylene under elevated pressure. The effect of annealing pressure on the conductivity of the compounds was studied. The total conductivity of the compound decreased with a decrease of frequency, approaching a constant value (dc conductivity: C_dc). The dc conductivity of the compound increased from below 10^?15 to 10 S cm^?1 with increasing annealing pressure. The dc conductivity of the oligomer was below 10^?15 S cm^?1 and that of the derivative increased from 10^?8 to 10 S cm^?1 with decreasing H/C (H/C:0.45–0.04). The conduction of the conjugated compound was electronic. The temperature coefficient of those dc conductivities was positive, with an approximately linear relation between In (C_dcT^0.5) and (1/T)^0.25, where T is the temperature. The ac conductivities C_ac were proportional to temperature and frequency f and had the following equation C_ac = Tf^S, S = 0.67–0.75. These results showed that the conduction mechanism can be explained by the hopping in a manifold of states at the Fermi level. © 1994 John Wiley & Sons, Inc.     

Rheological behavior of SAN/PC blends under extremely high shear rate

Extremely high shear rate processing was applied to the compound system of acrylonitrilestyrene copolymer/polycarbonate (SAN/PC). The viscosity was measured against the shear rate up to 10⁷ s^?1. The first non-Newtonian region, the second Newtonian region and second non-Newtonian region were observed in the compound system. The occurrence of these regions are very similar to those in the parent polymers, SAN and PC. For the calculation of the viscosity-shear rate curve, a concentric multilayer model was proposed. It gives good agreement between the calculated value and the measured one. A new mechanism for the occurrence of the non-Newtonian, second Newtonian, and second non-Newtonian regions was proposed. Nuclear spin–spin relaxation time measured on SAN, T₂, seems to be consistent with the consideration that the occurrence of non-Newtonian region, second Newtonian region, and second non-Newtonian region are caused, respectively, by the disentanglement, near saturation of disentanglement associated with snapping of macromolecules, and reentanglement through recoiling of snapped macromolecules, and further snapping of the macromolecules, which is inconsistent with the proposed explanation.     

Isothermal transient current studies in cellulose acetate films

Step voltage transient current studies have been made in cellulose acetate films as a function of filed and thickness. A logarithmic plot (Scherr-Montroll plot) of the transient current vs. time gives a knee at a time t_T, which is interpreted as the transit time of the charge carrier. The value of the carrier mobility has been estimated to be 3.9 × 10^?9 cm².V^?1.S^?1 in cellulose acetate film. The carrier mobility in iodine-doped (2% w/w) cellulose acetate film has also been determined from Scher-Montroll plot and is found to be 3.3 × 10^?7 cm².V^?1.S^?1.     

Comparison of hydrodynamic and rheological properties of dilute solutions of a styrene-hydrogenated butadiene copolymer in aliphatic solvents by light scattering and viscometric techniques

Dilute solution of a styrene-hydrogenated butadiene copolymer, a viscosity index improver, were studied by static and dynamic light-scattering techniques. In n-hexane (a model solvent for paraffinic oils) and a mineral base oil, aggregation is observed below 30°C. In cyclohexane (a model solvent for napthenic oils) only isolated polymers are present in the whole temperature range. Kinematic viscometric measurements from 20 to 60°C in the mineral oil show a continuous increase of the intrinsic viscosity together with a decrease of k_H, the Huggins coefficient, from 2.5 to 0.5. At shear rates between 5000 and 40000_s^?1, a large shear thinning is observed at room temperature for the polymer in the mineral base oil. This effect progressively disappears as the temperature increases and the suspension becomes Newtonian near 100°C. All results can be interpreted in terms of micelle formation. © 1994 John Wiley & Sons, Inc.     

Photochemical grafting of acrylated azo dyes onto polymeric surfaces. VII. Kinetics and mechanism of dye-sensitized photoinitiation of some diacrylates

Photoinitiated grafting and graft polymerization of liquid mixtures, adsorbed onto polypropylene, polycaprolactam, and poly(ethylene terephthalate) films, containing one of four acryloxy-substituted aromatic diazenes and one of four diacrylate comonomers, in the presence of 1,2-diphenyl-2,2-dimethoxyethanone as photoinitiator, were investigated kinetically at 30 ± 2°C. Irradiation was carried out polychromatically, with impinging photoenergy from 2.1 × 10^?8 to 20.5 × 10^?8 einstein s^?1 cm^?2; in some of the runs the ultraviolet radiation was filtered. The ratio R between the molar concentration of photoinitiator and the sum of concentrations of dye and diacrylate varied between 0.005 and 0.095; the ratio M between the molar concentration of dye and diacrylate varied between 0.005 and 0.046. The moles of dye and diacrylate n initially deposited per unit apparent polymeric surface S varied between 2 and 74 μmol cm^?2. No selective effect was shown by the presence of dyes in the comonomer mixture. The surface density of grafted molecules at the end of the grafting process was not affected by the photoinitiator concentration (for 0.030 < R < 0.095), by diacrylate or dye concentrations, or by the kind of polymer substrate. This parameter, on the contrary, clearly depended on n/S, and linearly up to n/S ? 30 μmol cm^?2. Quantum efficiencies for the two consecutive kinetic processes of grafting and graft polymerization (Φ₁ and Φ₂, respectively) were evaluated. The dependency of Φ₁ on R, as well as of Φ₂ on n/S, are critically discussed on the basis of the proposed mechanism involving grafting of an oligomeric chain (Φ₁ values up to the order of 10²) followed by a step-by-step graft polymerization (Φ₂ limiting values of the order of unity). The sensitizing effect of acryloxy-substituted aromatic diazenes on both Φ₁ and Φ₂ is evidenced.     

An empirical model relating the molecular weight distribution of high-density polyethylene to the shear dependence of the steady shear melt viscosity

An empirical model has been developed to relate molecular weight distribution to the shear dependence of the steady shear viscosity in high-density polyethylene melts. It uses a molecular weight, M_c, which partitions molecular weights into two classes; those below M_c contribute to the viscosity as they do at zero shear, and those above M_c contribute to the viscosity as though they were of molecular weight M_c at zero shear. Each individual molecular weight species contributes on the basis of its weight fraction. M_c is proposed to be a unique function of the shear rate. Using this method of treating the molecular weight distribution, and the zero shear relation for relating η0 to molecular weight, the calculated steady shear viscosities at various shear rates for polyethylene samples of widely varying polydispersities agree well with experimental results. The model makes no judgment on the existence or importance of entanglements in non-Newtonian behavior since it has no specific parameters involving an entanglement concept. Use of the model suggests that for the samples studied, only the upper portion of the molecular weight distribution contributes toward the experimentally observed decrease of steady shear viscosity with shear rate for shear rates of up to 10,000 sec^?1. The lower molecular weight species are assumed to behave in a Newtonian manner.     

Effects of extrusion conditions on rheological behavior of acrylonitrile–butadiene–styrene terpolymer melt

The influence of temperatures and flow rates on the rheological behavior during extrusion of acrylonitrile–butadiene–styrene (ABS) terpolymer melt was investigated by using a Rosand capillary rheometer. It was found that the wall shear stress (τ_w) increased nonlinearly with increasing apparent shear rates and the slope of the curves changed suddenly at a shear rate of about 10³ s^?1, whereas the melt‐shear viscosity decreased quickly at a τ_w of about 200 kPa. When the temperature was fixed, the entry‐pressure drop and extensional stress increased nonlinearly with increasing τ_w, whereas it decreased with a rise of temperature at a constant level of τ_w. The relationship between the melt‐shear viscosity and temperature was consistent with an Arrhenius expression. The results showed that the effects of extrusion operation conditions on the rheological behavior of the ABS resin melt were significant and were attributable to the change of morphology of the rubber phase over a wide range of shear rates. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 606–611, 2002     

Rheological and rheo-optical properties of high molecular weight syndiotactic and atactic polyvinylalcohol solutions

The rheological and rheo-optical properties of solutions of high molecular weight polyvinylalcohol (PVA) with different syndiotactic diad contents in dimethylsulfoxide (DMSO) were investigated in terms of tacticity, molecular weight, and degree of saponification. Tacticity played a significant role in rheological behavior. Over the frequency range of 10^?1 to 10² rad/s PVA with syndiotactic diad content of ～53% (atactic PVA) exhibited almost Newtonian flow behavior whereas PVA with syndiotactic diad content of ～63% (syndiotactic PVA) exhibited Bingham flow behavior. On the plot of storage modulus (G′) against loss modulus (G″) atactic PVA gave slopes of ～2 while syndiotactic PVA gave slopes of ～1. With syndiotactic PVA, an increase of shear rate notably increased flow birefringence (Δn_f) at shear rates higher than 5 sec^?1. On the other hand, only a slight increase in Δn_f was observed in the case of atactic PVA. The effects of molecular weight and degree of saponification were discussed as well.     

ESR studies of solvent penetration into polymer-blend-like material: Particles formed from poly(methyl methacrylate) and polyisobutylene

Solvent penetration into nonaqueous dispersions (NAD) of poly(methyl methacrylate) (PMMA) sterically stabilized by PIB were studied by ESR spectroscopy. These colloidal particles were exposed to dilute solution of spin probe 3-carbomoyl 2,2,5,5-tetramethyl 3-pyrolin-1-yloxy and the bimodal distribution of ESR spectra of this probe molecules were carefully monitored as a function of time. Fickian type diffusion of spin probes into the particles was observed and a spherical model was employed to obtain the diffusion coefficients (D) in various solvents. D values were found around 10^?15 cm²/s, and interpreted as the parameter, inversely proportional to the apparent viscosity of the environment inside the colloid particle. Maximum amount of diffused solvent molecules (M_∞) into the PMMA particle was found inversely proportional to polymer-solvent interaction through the solubility parameters. The interconnected network of PIB was found to be responsible for the penetration of spin-probe (i.e., solvent) molecules into the glassy PMMA phase and/or PIB-PMMA interface.     

Effects of drawing conditions on the properties of optical fibers made from polystyrene and poly(methyl methacrylate)

Monofilaments possessing various degrees of birefringence were obtained by changing the drawing rate, the molten polymer temperature, and the molecular weight of polystyrene (PS) and poly(methyl methacrylate) (PMMA). The “brittle-toductile” transition point of optically pure PS was found in the range of birefringences of ?0.6 · 10^?3 to ?2.6 · 10^?3. Both the height and position of this point are influenced by M?_w, molecular weight distribution, and polymer melt temperature. The birefringence of PS is higher by two orders of magnitude than that of PMMA in which this transition point has not been observed. The mechanical and optical properties depend not only on the average amount of orientation characterized by the birefringence but on what portion of the relaxation spectrum of the polymer is preferentially oriented. During the drawing of PS and PMMA monofilaments crazes are formed in the centre of the fibers and do not reach the surface.     

Melt rheology of nanometre‐calcium‐carbonate‐filled acrylonitrile–butadiene–styrene (ABS) copolymer composites during capillary extrusion

The melt flow properties during capillary extrusion of nanometre‐calcium‐carbonate‐filled acrylonitrile–butadiene–styrene (ABS) copolymer composites were measured by using a Rosand rheometer to identify the effects of the filler content and operation conditions on the rheological behaviour of the sample melts. The experiments were conducted under the following test conditions: temperature varied from 220 to 240 °C and shear rate ranged from 10 to 10⁴ s^?1. The filler volume fractions were 0, 10, 20, 30, 40 and 50%. The results showed that the shear flow did not strictly obey the power law under the test conditions, and that the entry pressure drop (ΔP_en) and the extension stress (σ_e) in entry flow increased nonlinearly, while the melt shear viscosity (η_s) and extension viscosity (η_e) decreased with increasing the wall shear stress (τ_w) at constant test temperature. The dependence of the melt shear viscosity on the test temperature was approximately consistent with the Arrhenius expression at fixed τ_w. When τ_w was constant, η_s and η_e increased while ΔP_en and σ_e decreased with the addition of the filler volume fraction. © 2002 Society of Chemical Industry