A study of spinnability in the wet-spinning of acrylic fibers

An extensive study of spinnability is presented for the formation of acrylic fibers by wet-spinning. The system consisted of an acrylonitrile–vinyl acetate copolymer with dimethylacetamide as the solvent and water in most instances as the nonsolvent. The term spinnability is used here to denote the type of filament breakage that occurs in the spin bath near the spinnerette face as the withdrawal speed V₁ is increased to some critical value. This maximum speed V_{1, m} depends on essentially every spinning variable. Data are presented for a wide range of spinnerette hole diameters, flow rates per hole, coagulation rates, temperatures, and polymer concentration in the spinning solution. The freely extruded velocity of the filaments, V_f, is also given over the same range of variables. The free velocity is much less than the average velocity because of the Barus effect. Some similarities are noted in the response of V_{1, m} and V_f to certain variables. In fact, V_{1, m} seems to be determined by V_f. Through this observation the influence of the Barus effect on spinnability is easily seen. Spinnability is discussed also in terms of coagulation rates. It is concluded that both rheological and coagulation phenomena are important in the breakage mechanism. These observations are probably applicable in part to other wet-spinning systems.     

Extrudate swell during the melt spinning of fibers—influence of rheological properties and take-up force

A theoretical and experimental study has been carried out on extrudate swell B, especially the influence of rheological properties and applied take-up force on the emerging melt. The problem is analyzed in terms of (1) dimensional analysis, (2) force–momentum balances, (3) partially constrained elastic recovery. Analyses in terms of force–momentum balances are only able to give extrudate swell B in the asymptote of high Reynolds numbers. For low Reynolds numbers, they simply relate the take-up force to the pressure field in the spinneret. Increasing the take-up force predicts a decrease in the exit pressure. The partially constrained elastic recovery theory yields an expression for B as a decreasing function of applied take-up force. Specifically, this is where B(0) is the extrudate swell in the absence of applied forces, λ_eff is the effective relaxation time, μ is viscosity (both evaluated at the capillary wall), and D is the spinneret capillary diameter. An experimental study of extrudate swell of several rheologically characterized melts (high density polyethylene, low-density polyethylene, polypropylene, polystyrene) has been carried out at 180°C by four different methods (frozen, annealed in hot silicone oil, photographed emerging into air, photographed emerging through 180°C silicone oil) in the absence of applied take-up forces. Extrudate swell for a melt emerging from dies with differing diameters correlates with capillary-wall shear rate. A comparison of extrudate swell with normal stress–shear stress ratio shows the best agreement for frozen extrudates and photographs of melts emerging into air. The data is compared to the Tanner theory of extrudate swell. B has been determined during melt spinning and shown to be a function of take-up force for both a high-density polyethylene and polypropylene melt. B decreases rapidly with applied take-up stresses. The results are compared to the predictions of the partially constrained elastic recovery theory.     

Rubber elasticity on chemical relaxation

The applicability of the formula f(t) = n(t)RT(α ? α^?2) suggested by Tobolsky as the basis of chemorheology has been discussed. In this expression, f(t) is the stress after t hours, n(t) is the crosslinking density (mole/cc) after t hours, R is the gas constant, T is the absolute temperature, and α is the extension ratio. We have discussed the applicability of this formula, in another words, whether the degraded stress f(t) calculated from this formula would be consistent with the initial stress f_t(0) of other polymer if the degraded crosslinking density values n(t) are equal to those of n_t(0), the initial density values n(0) of other polymer. Natural rubber vulcanizates and SBR vulcanizates were used as samples in these experiments. Assuming n(t) = σ(t) n(0), α(t′) = 1, the applicability of the above formula was recognized from our experimental results.     

Thermooxidative decomposition and its kinetics on chlorinated natural rubber from latex

Thermooxidative decomposition and its kinetics on chlorinated natural rubber (CNR) from latex are studied by thermal gravimetry (TG) analysis and TG coupled with FTIR spectroscopy. The thermooxidative decomposition of CNR is a two‐step reaction. The first step is the reaction of dehydrochlorination of which the reaction order (n) is 1.1; the reaction activation energy (E) increases linearly with the increment of the heating rate (B), and the apparent activation energy (E₀) is 101.7 kJ/mol. The initial temperature of weight loss (T₀) is 1.29B + 248.7, the final temperature of weight loss (T_f) is 0.86B + 312.4, and the temperature at the maximum weight loss ratio (T_p) is 1.05B + 286.2. The decomposition ratio at T_p (C_p) is not affected by B, and its average value is 38%. The decomposition ratio at T_f (C_f) is also not affected by B, and its average value is 60%. The second step is an oxidative decomposition reaction of the molecular main chain. The value of n is 1.1, E increases linearly with the increment of B, E₀ is 125.0 kJ/mol, the relation between B and T is similar to that of the first step, and C_f approaches 100%. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1305–1309, 2001     

Synthesis and Properties of Polyimides Based on an Ether Ketone Diamine, 4,4'-Bis(4-aminophenoxy)benzophenone

A diamime monomer with ether-ketone group, 4,4'-Bis(4-aminophenoxy)benzophenone (II) was prepared through the nucleophilic substitution reaction of 1-chloro-4-nitrobenzene with 4,4'-Dihydroxybenzophenone in the presence of potassium carbonate in N,N-dimethylformamide, followed by catalytic reduction with hydrazine and Pd/C. Polyimides (PI) V _a–f (H), V _a–f (C) and copolyimides (co-PI) V _{b–d/m(e–f)} were synthesized from II and six kinds of commercial aromatic dianhydrides (III _a–f )via thermal or chemical imidization method. Poly(amic acid) (IV _a–f )had inherent viscosities range from 0.81 to 0.98 dL/g. PI of thermal imidization method was showed poor solubility even sulfuric acid. But PI of chemical imidization method V _e,f (C) and (co-PI(C)) could be dissolved. The reason is that the ketone group of poly(amic acid) segments linked with the terminal amino group of polymer chains during thermal imidization. PI films V _a–f (H) had tensile strengths of 101–118 MPa, elongations to break of 11–32%, and initial moduli of 2.1–2.8 GPa. The glass transition temperatures of V series were in the range of 252–278°C, and the temperatures of 10% weight loss (T ₁₀) were above 529°C and their residues more than 50% at 800°C in nitrogen. V series also measured the color, dielectric constants and moisture absorptions. Their films had cutoff wavelengths between 378–421 nm, b ^* values ranging from 16.4 to 77.1, dielectric constants of 3.47–3.85 (1 MHz), and moisture absorptions in the range of 0.31–0.46 wt%.     

Theoretical validation of the physical scale modelling of the electrical potential characteristics of marine impressed current cathodic protection

The criteria for the electromagnetic scaling of electrolytic (seawater) systems are reviewed and are shown to be satisfied in the DACS (dimension and conductivity scaling) physical scale modelling of the potential characteristics of the surface of cathodically protected surfaces and the surrounding seawater.Nomenclature r(x, y, z) position vector - t time - t physical scaling factor - E(r, t electric field - E _f electric field under flow conditions - H(r, t) magnetic field - static dielectric constant - magnetic permeability - J(r, t) electrical current density - J _f electrical current density under flow conditions - J _lim (diffusion) limited electrical current density - electrical conductivity - V electric potential (voltage) - V _a anode potential - V _i interface potential - V _ia anode/electrolyte interface potential - V_s potential in electrolytic solution - V _ic cathode/electrolyte interface potential - V _c cathode potential - V ₀ cathodic overpotential constant - V _h hull potential - V _ic(J) current-voltage characteristic of cathode/electrolyte interface - electrical charge density - ₊ electrical charge density of positive ions - _– electrical charge density of negative ions - v(r, t) velocity of ion - v ₊ velocity of positive ion - v _p flow velocity of electrolyte - R _p polarization resistance at electrode/electrolyte interface - a Tafel a-constant - b Tafel b-constant - T absolute temperature - P pressure - n unit normal - n _i number of ions with charge z _i     

Studies on melt spinning. II. Steady-state and transient solutions of fundamental equations compared with experimental results

In the part installment of the present paper, the authors formulated the dynamics of melt spinning by introducing a set of fundamental equations that consist of the equations of heat, force, and material balances. Some steady-state solutions were also given. Additional steady-state solutions corresponding to many different spinning conditions for polyester and polypropylene filament yarns consistently show good agreement with experimental results. These steady-state solutions that give filament cross-section A (x) and filament temperature t(x) as functions of position x are correlated with yarn qualities: yarn density and birefringence, crystallinity and molecular orientation, are correlated respectively with the speed of Polymer cooling at 100°C. and the maximum tensile stress (F/A)_w acting on the filament. A transient solution of the fundamental equations computed on an IBM 1401 machine shows that the filament cross-section A at the take-up roll forms a large transient peak after a stepwise increase in the speed v_y of cooling air. This agrees with experiments fairly well. The fundamental equations, therefore, clarify the dynamic relations between cooling air speed and yarn weight variations.     

Micromechanics for fiber volume percent with a photocure vinyl ester composite

Micromechanics for fiber volume percent (V_f) from 0.0V_f to 54.0 V_f were conducted using (3 mm long × 9 μm diameter) high‐purity quartz fibers in a visible‐light vinyl ester particulate‐filled photocure resin. MTS fully articulated four‐point bend fixtures were used with a 40 mm test span and 50 × 2 × 2 mm³ sample dimensions. Specimens were tested following the combined modified ASTM standards for advanced ceramics ASTM‐C‐1161–94 and polymers ASTM‐D‐6272–00 for modulus, flexural strength, and yield strength. Experimental data provided reliable statistical support for the dominant fiber contribution expressed through the rule‐of‐mixtures theory as a valid representation of micromechanical physics. The rule‐of‐mixtures micromechanics described by V_f could explain 92, 85, and 78% of the variability related to modulus, flexural strength, and yield strength respectively. Statistically significant improvements with fiber addition began at 10.3V_f for modulus, 5.4V_f for flexural strength, and 10.3V_f for yield strength, p < 0.05. In addition, correlation matrix analysis was performed for all mechanical test data. An increase in V_f correlated significantly with increases in modulus, flexural strength, and yield strength as measured by the four‐point bending test, p < 10⁻¹⁰. All mechanical properties in turn correlated highly significantly with one another, p < 10⁻⁹. POLYM. COMPOS., 28:294–310, 2007. © 2007 Society of Plastics Engineers     

Kinetic study of the free‐radical polymerization of vinyl acetate in the presence of deuterated chloroform by 1H‐NMR spectroscopy

The free‐radical polymerization of vinyl acetate was performed in the presence of deuterated chloroform (CDCl₃) as a chain‐transfer agent (telogen) and 2,2′‐azobisisobutyronitrile as an initiator. The effects of the initiator and solvent concentrations (or equivalent monomer concentration) and the reaction temperature on the reaction kinetics were studied by real‐time ¹H‐NMR spectroscopy. Data obtained from analysis of the ¹H‐NMR spectra were used to calculate some kinetic parameters, such as the initiator decomposition rate constant (k_d), k_p(f/k_t)^1/2 ratio (where k_p is the average rate constant for propagation, f is the initiator efficiency, and k_t is the average rate constant for termination), and transfer constant to CDCl₃ (C). The results show that k_d and k_p(f/k_t)^1/2 changed significantly with the solvent concentration and reaction temperature, whereas they remained almost constant with the initiator concentration. C changed only with the reaction temperature. Attempts were made to explain the dependence of k_p(f/k_t)^1/2 on the solvent concentration. We concluded from the solvent‐independent C values that the solvent did not have any significant effect on the k_p values. As a result, changes in the k_p(f/k_t)^1/2 values with solvent concentration were attributed to the solvent effect on the f and/or k_t values. Individual values of f and k_t were estimated, and we observed that both the f and k_t values were dependent on the solvent (or equivalent monomer) concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Structure characterization of cold drawn high density polyethylene thin film

This work throws light to study the changes of optical birefringence for cold drawn high density polyethylene (HDPE) thin film at different stresses. A stress–strain device connected to a scattering optical system was used to investigate the dynamical behavior of opto‐mechanical properties at room temperature (27°C ± 1°C). Some structural parameters, optical and mechanical orientation factors, f(θ), f₂(θ), f₄(θ), f₆(θ), F_av, P₂(θ), P₄(θ), f_c, and f_m, were calculated. Also, the distribution segments at an angle (θ), the number of random links per chain (N₁), the number of chains per unit volume (N_c), and the average work per chain W′ were calculated. The average value of the maximum birefringence was evaluated. The obtained studies demonstrate changes to the molecular orientation functions and evaluated micro structural parameters as a result of the applied cold‐drawing process on (HDPE) thin film. Relationships between the calculated parameters and draw ratios were presented for illustration. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Rheological interpretation of heat generation associated with fatigue of polycarbonate

Temperature change was measured of polycarbonate under monotonically increasing tensile and pulsating tensile loads. In the former case, the specimen temperature began to rise when an appreciable amount of viscoelastic strain was noticed on the stress—strain diagram. The rise, θ_v, could be formulated as a function of the viscoelastic strain, εv: In fatigue tests, the average temperature began to rise immediately after the decrease due to the thermoelastic effect. The amount of the heat generation, σ, was nearly constant for each cycle throughout the fatigue process and has a relation to the fatigue life, N_f, (α? a)·N_f = constant, where a is another adjustable constant. From a rheological aspect of dissipation energy, the equation is transformed to a relation between the viscoelastic strain and the fatigue life as εV^1/2 · N_f = constant, which is similar to the one for metals given by Manson and Coffin.⁶ The temperature rise in the fatigue was also related to the viscoelastic strain. The relation is of the same form as for static tension but less by a factor of one order.     

Ultralow-k hollow glass microsphere filled perfluoroalkoxy composites

Perfluoroalkoxy (PFA) composites filled with different volume fractions of hollow glass microsphere (HGM) and HGM/PFA–HGM/HBO₃–HGM/PFA sandwich layered composites were prepared by simple dry mixing and hot-pressing process. The dielectric frequency and temperature response characteristics, thermal expansion coefficient, and mechanical strength were investigated as a function of the loading fraction of HGM fillers. The obtained .6V_fHGM/.4V_fPFA composite demonstrates ultralow-k (ε_r ∼ 1,63@1 MHz; 1.57@10 GHz) with low-dielectric loss (∼7.2 × 10⁻⁴@1 MHz; ∼1.73 × 10⁻³@10 GHz), water absorption of ∼1.21%, in-plane thermal expansion coefficient of 42 ppm/°C, and temperature coefficient of dielectric permittivity (τ_εr) of ∼−92 ppm/°C. The temperature stabilities of dimension and dielectric permittivity for the .6V_fHGB/.4V_fPFA composite could be substantially improved by forming .6V_fHGM/.4V_fPFA–.6V_fHGM/.4V_fHBO₃–.6V_fHGM/.4V_fPFA sandwich–layered composite, which still maintained reasonable dielectric properties and mechanical rigidity with flexural strength of ∼8.1 MPa.     

Cooling and attenuation of threadline in melt spinning of poly(ethylene terephthalate)

Melt spinning of poly(ethylene terephthalate) was studied by measuring the filament tension at the take-up roll and by measuring filament diameter D(X) at various distances X below the spinnerette. A new method is developed to calculate temperature distribution both along and perpendicular to the fiber axis. Results of these calculations are compared with experimental values. The attenuation of filament diameter depends primarily on the take-up speed and the output rate. Spinning temperature and molecular weight have relatively small effects. Mass flow rate and take-up speed are the major factors controlling the cooling rate, while other spinning parameters such as polymer molecular weight and spinnerette orifice size have a small effect. The Trouton viscosity β is both temperature and molecular weight dependent. Values of β derived from these experiments can be expressed mathematically as follows:      

The development of the velocity field in polymer melts in a reservoir approaching a capillary die

Color motion pictures have been made of the flow of low-density polyethylene, polystyrene, and isotactic polypropylene at 180°C in the reservoir approach to a capillary extrusion rheometer. Detailed observations of the variation of flow patterns with extrusion rate were made. At low flow rates, essentially radial flow into the capillary entrance was observed in all polymers. With increasing flow rate, the included entrance angle α for the polyethylene and polystyrene decreased from 180°C and a “wine glass” structured velocity field was observed with stagnant circulating regions in the corners and the melt channeling in through the wine glass to the capillary entrance. The angle α was related to entrance pressure drop Δp_e and capillary wall shear stress σ_w data through the semilogarithmic equation where α is in degrees; Δp_e/σ_w is interpreted as a Weissenberg number. The breakdown of stable laminar flow of the melts in the reservoir and the distortion of extrudates was observed. These phenomena seemed to be initiated by the formation of a spiralling motion in the reservoir.     

First normal stress difference in capillary extrusion flow of nanometer calcium carbonate‐filled PLLA biocomposites

The nanometer calcium carbonate (nano‐CaCO₃)‐filled poly‐L ‐lactide (PLLA) biocomposites were prepared using a twin‐screw extruder. The first normal stress difference of the composites were measured by means of a capillary rheometer under experimental conditions with temperatures ranging from 170 to 200°C and shear rates varying from 50 to 10³ s^?1. The first normal stress difference (N₁) increased roughly linearly with increasing shear stress (τ_w). The sensitivity of the N₁ to τ_w increased with an increase of the die length–‐diameter ratio, and the N₁ value varied slightly with the filler weight fraction (?_f) as test temperature was constant. When the shear stress was fixed, the N₁ reached a minimum value for ?_f = 1%. The values of the N₁ of the composite melts decreased roughly linearly with a rise of temperature when the shear rate was constant. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Estimates of the Properties of Liquids

An equation which relates the volume term (V=M/_(ρL-ρg)) of unassociated liquids to pressure P and temperature T has been obtained by the combination of (a) 03V(?I/?V)_P→0=T_x-T for the effect of temperature on V at low (atmospheric) pressure and (b) - V(?P/?V)_T = P_x V_x/⁶/V⁶ _p→0+9(P-p) for the effect of pressure on volume at constant temperature. In the equations, p is the vapour pressure; pL the density of the liquid and pg the vapour density. Often pg can be neglected compared with pL and p is small compared with the large pressures required to affect the densities of liquids appreciably. There are three constants: Tx, Px, which equals 4.455 × 10⁹ N m², and Vx which can be calculated by the addition of atomic values for all the atoms in the molecule and subtraction of a value (6.56 × 10⁶ m³ mol¹) for each bond. When V approximates to M/ρL, the molar volume, the equation can be integrated to give the work and heat of isothermal compression. The viscosity of a liquid is related to the work of compression and solubilities in a liquid to the work required to bring the solute to the compressibility of the liquid. Many relationships can be derived and can be used to estimate properties of unassociated liquids.     

The influence of molecular weight of acid dyes on the yield stress of dyed nylon monofilament

The yield stress of nylon filament dyed with several acid dyes has been determined as a function of dye content and the molecular weight of acid dyes. The nylon filament dyes with acid dye has greater yield stress than undyed one. The relation between the increment of the yield stress (f) due to the adsorption of acid dye and the dye content (C) in the filament can be expressed by parameters A and B as log f = A log(C ? _C) + B, where C₀ is the dye content under which no contribution to the yield stress is observed and C₀ depends on the number of sulfonic groups in acid dye. It is found that these parameters A and B are expressed by M (the difference between the molecular weight of acid dye and the weight of SO₃Na groups in it) as A = 1 ? 100/M, B = k₁ M^k2, where k¹ and k² are the constants which depend on the parent chemical structure of dyes. The parameters A and B are expected to give available informations as to the physical state of adsorbed dye on nylon filament.     

Contribution of interferometry and mechanical parameters in evaluating molecular orientation for drawn polyester

Mechanical and structural parameters related to the optical properties of polyester (PET) (woollen type) fibres drawn at room temperature have been investigated. The changes in the strain were evaluated to obtain the molecular orientation factors 〈P₂(cos θ)〉 and 〈P₄(cos θ)〉. From the optical orientation, the values of f₂(θ), f₄(θ) and f₆(θ) orientation parameters were calculated. The structure and properties of oriented PET have been studied in the light of the rubber elasticity theory. The dielectric constant, magnetic susceptibility, number N′ of chains between crosslinks per unit volume, optical configuration parameter and the segment anisotropy, were among the calculated parameters. The results of the extension were used to calculate the shrinkage factor. Relationships between the calculated parameters and the draw ratios, together with micro-interferograms, are given for illustration. The present study throws light on how the applied stress changes the molecular orientation factors and the structural parameters. © 1999 Society of Chemical Industry     

Preparation and electrochemical performance studies on Cr-doped Li3V2(PO4)3 as cathode materials for lithium-ion batteries

Cr-doped Li₃V_2−xCr_x(PO₄)₃/C (x = 0, 0.05, 0.1, 0.2, 0.5, 1) compounds have been prepared using sol–gel method. The Rietveld refinement results indicate that single-phase Li₃V_2−xCr_x(PO₄)₃/C with monoclinic structure can be obtained. Although the initial specific capacity decreased with Cr content at a lower current rate, both cycle performance and rate capability have excited improvement with moderate Cr-doping content in Li₃V_2−xCr_x(PO₄)₃/C. Li₃V_1.9Cr_0.1(PO₄)₃/C compound presents an initial capacity of 171.4 mAh g⁻¹ and 78.6% capacity retention after 100 cycles at 0.2C rate. At 4C rate, the Li₃V_1.9Cr_0.1(PO₄)₃/C can give an initial capacity of 130.2 mAh g⁻¹ and 10.8% capacity loss after 100 cycles where the Li₃V₂(PO₄)₃/C presents the initial capacity of 127.4 mAh g⁻¹ and capacity loss of 14.9%. Enhanced rate and cyclic capability may be attributed to the optimizing particle size, carbon coating quality, and structural stability during the proper amount of Cr-doping (x = 0.1) in V sites.     

Calculation of the Detonation Velocities and Detonation Pressures of Dinitrobiuret (DNB) and Diaminotetrazolium Nitrate (HDAT‐NO3)

The enthalpies of combustion (Δ_combH) of dinitrobiuret (DNB) and diaminotetrazolium nitrate (HDAT‐NO₃) were determined experimentally using oxygen bomb calorimetry: Δ_combH(DNB)=5195±200 kJ kg⁻¹, Δ_combH(HDAT‐NO₃)=7900±300 kJ kg⁻¹. The standard enthalpies of formation (Δ_fH°) of DNB and HDAT‐NO₃ were obtained on the basis of quantum chemical computations at the electron‐correlated ab initio MP2 (second order Møller‐Plesset perturbation theory) level of theory using a correlation consistent double‐zeta basis set (cc‐pVTZ): Δ_fH°(DNB)=−353 kJ mol⁻¹, −1 829 kJ kg⁻¹; Δ_fH°(HDAT‐NO₃)=+254 kJ mol⁻¹, +1 558 kJ kg⁻¹. The detonation velocities (D) and detonation pressures (P) of DNB and HDAT‐NO₃ were calculated using the empirical equations by Kamlet and Jacobs: D(DNB)=8.66 mm μs⁻¹, P(DNB)=33.9 GPa, D(HDAT‐NO₃)=8.77 mm μs⁻¹, P(HDAT‐NO₃)=33.3 GPa.