Effect of sub-Tg annealing on CO2 sorption in polycarbonate

High pressure CO₂ sorption data in polycarbonate (PC) are reported as a function of temperature and thermal history. The bulk physical structural changes produced by annealing at 125 and 135°C were monitored by density and thermal property changes. The sorption data are analyzed by the dual sorption model which assumes the sorption isotherm to consist of Henry's law and Langmuir sorption terms; The Langmuir capacity term C of PC can be grossly correlated with the reported volumetric parameters of the polymer. This excess volume interpretation of C has found support in the good correlation between C and the corresponding enthalpy relaxation from parallel Differential Thermal Analysis of the samples. Density measurements provide gross evidence of the free volume interpretation of C. The experimental uncertainties in the data compromise a more critical test of the relationship between C and the density of annealed samples.     

Strain-induced crystallization,Part III: Theory

A nucleation theory for strain-induced crystallization is formulated to explain and to predict the effects of molecular strain on crystallization kinetics and crystallite size. Unlike any current theories that have based their formulations on some assumed extended-chain line nuclei or folded-chain crystals, the present theory avoids all assumptions concerning the crystal morphology. It is based on experimental findings which indicate limited crystal growth in the strain direction, following a reciprocal dependence of crystal thickness on supercooling ΔT. (ΔT = T, ? T, where the equilibrium melting temperature, T, is a variable dependent on degree of molecular strain prior to strain-induced crystallization.) It is predicted that the logarithm of the nucleation rate, N^o, is dependent on (T)²/T(ΔT) or T/T(ΔT), and that the critical nucleus thickness l^*o is shown to be proportional to T/ΔT. In addition, expressions are also presented, including examples, to show the dependence of N^o, l^*o and T^o_m on degree of molecular strain, ?, or melt entropy reduction, Δs′. Our analysis predicts that, on comparing a polyethylene crystallized in the presence of strain to one crystallized in the absence of strain at 130°C, an increase in “coil” dimension of less than about 50 percent can bring about a 10⁴ fold increase in heterogeneous nucleation rate, a 30–40 percent reduction in critical nucleus thickness and a 10°C increase in equilibrium melting temperature. These results will be discussed and compared with available experimental evidence.     

Molecular weight and molecular weight distribution from dynamic measurements of polymer melts

A method for determining the molecular weight distribution (MWD) of a polymer melt has been developed using the dynamic elastic modulus (G'), plateau modulus (G), and zero shear complex viscosity (η). The cumulative MWD was found to be proportional to a plot of (G'/G)^0.5 vs. measurement frequency (ω). Frequency (ω) was found to be inversely proportional to (MW)^3.4, as expected. Results were scaled to absolute values using the empirical relationship η ∝ (M?_w)^3.4, where M?_w is the weight-average MW. M?_w, M?_n (number-average MW) and M?_w/M?_n calculated from melt measurements were found to agree with size exclusion chromatography usually well within 10 percent for broad and bimodal distribution samples. M?_w/M?_n tended to be approximately 20 percent higher for narrow distribution samples (M?_w/M?_n < 1.2) because we did not account for a finite distribution of relaxation times from a collection of monodisperse polymer chains. We also did not account for the plasticizing effect of short chains mixed with long ones which caused peak positions to be closer together for Theological vs, size exclusive chromatography (SEC) determinations of MW for bimodal distribution blends.     

Effect of microstructure on crazing onset in polyethylene under tension

The influence of microstructure on dilatation onset is analyzed in polyethylene (PE) under tension. Tests are performed by means of a video‐controlled testing system that gives access to true stress σ₃₃—true strain ε₃₃ curve and records volume strain ε_v during stretching. The results indicate that the strain ε (and the corresponding stress σ) from which viscoplastic dilatation begins depends on microstructural properties of PE. At microscopic scale, materials having a low ε are characterized by inhomogeneous deformation mechanisms leading to pronounced crazing phenomena in amorphous layers. On the contrary, materials having a high ε involve homogeneous deformation mechanisms that limit crazing. These observations are discussed on the basis of crystallinity and tie molecules density. A simple model predicting ε is developed from these microstructural aspects. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Structure development in biaxially stretched polystyrene film: Part I. Property-orientation correlation

A study of orientation development in polystyrene film by biaxial stretching is described. Stretch ratios up to 7.2 × 7.2 were used. Mechanical properties of polystyrene films were correlated with the level of molecular orientation developed by uniaxial or biaxial stretching. Sensitivity of the mechanical properties to change due to development of orientation varied as follows: Yield strength < Young's modulus < Tensile strength < Elongation to break. Brittle to ductile transition phenomena were observed at certain orientation values in the orientation triangle diagram. The transition occurs when f × f ～ 0.0025 for biaxially oriented and f ～ 0.015 in the machine direction for uniaxially oriented films. SEM photomicrographs show that the fracture surfaces of ductile failures exhibit many fibrils while brittle failures exhibit no fibrils.     

Viscoelasticity of some engineering plastics analyzed with the modified stress-optical rule

The complex Young's modulus, E*(ω), and the complex strain-optical coefficient, O*(ω), of poly(ether sulfone) (PES), polysulfone (PSF), and polyethermide (PEI), were measured over the frequency range 1 to 130 Hz. The data were analyzed with a modified stress-optical rule: The Young's modulus was decomposed into two complex functions, E(ω) and E(ω); the modified stress-optical coefficient, C_R and C_G, associated with the rubber (R) and glass (G) components, respectively, were determined. The results for six polymers, including polystyrene, poly(α-methyl styrene), and bisphenol A polycarbonate were compared with each other. One of the coefficients, C_R, equivalent to the stress-optical coefficient in melts, mainly depended on the way in which phenyl groups were connected to the chain. The other, C_G, was in the range of 20 to 40 Brewsters, and did not strongly depend on the details of polymer structure. The component function, E(ω), which was located in the glassy region and originated from the high glassy modulus, was almost the same in shape when plotted against ω with double logarithmic scales. The R component, E(ω), located at the long time end of the glass-to-rubber transition zone, was slightly sensitive to the molecular structure of polymers.     

Contribution of polyalkyl(meth)acrylates to the design of PVC melt viscosity

The shear viscosity of poly(vinylchloride) (PVC) at 200°C can be decreased by at least one order of magnitude by the addition of as little as 5 wt% poly n-alkyl-(meth)acrylates (PMA) of a much lower dynamic viscosity than PVC. For this effect to be observed, the polymeric additive must be immiscible with PVC at 200°C. The average size of the dispersed phases is observed in the range of 0.5 to 5 μm; size fluctuation in this domain has no significant effect. When these conditions are met, there is a linear increase in the shear viscosity ratio η_blend/η_PVC from 0.2 to 1.0 with increasing logarithmic values of the dynamic viscosity ratio of the additive over PVC [(log(η/η)) from −4 to −1].     

Numerical and experimental investigation of three-dimensional flow in extrusion dies

The univariant element, Q₁ P₀, and the multivariant elements, QP₀ and R P₀, are compared for the numerical simulation of the flow in extrusion dies. The pressure distribution obtained by using the Q₁ P₀ element was found to be afflicted with the checkerboard pressure mode. On the other hand, the multivariant elements, Q P₀ and R P₀, gave accurate and physically reasonable velocity and pressure distributions. The computed values of the pressure drop across extrusion dies matched well with the pressure drop determined experimentally.     

Electron sensitive negative resists of vinylaromatic polymers

Electron resist properties of three vinylaromatic polymers, polystyrene, polyvinylcarbazole and poly(3-bromo-N-vinylcarbazole) have been examined. Polystyrene and polyvinylcarbazole are high contrast resists of high dry etch resistance, but for adequate sensitivity (D ? ca. 10 μC/cm² at 25 kV) high molecular weights are needed (M _w ? 10⁶). Poly(3-brotno-N-vinylearbazole) has a much higher sensitivity (D = ca. 2 μC/cm²) than the unsubstituted polymer. The sensitivity of polystyrene and polyvinylcarbazole is increased appreciably by addition of organic bisazides as crosslinking agents, e.g. a sensitivity increase of almost an order of magnitude was found upon addition of 3% 4, 4′-diazidostilbene to polystyrene, high contrast being maintained.     

Thermal properties of poly(vinyl cyclohexane)

Isotactic poly(vinyl cyclohexane) (PVCH) was studied by thermal analysis. The deduced equilibrium melting point, T, is 405°C (678 K). The heat of fusion, Δ H was found to be 50.82 J/g (5.60 kJ/mol) and Δ C_p at T_g, is 0.273 J/(gK) [30.1 J/(molK)]. The glass transition temperature, T_g, of the amorphous PVCH is 80°C (353 K). In semicrystalline samples, T_g increases up to 165°C (438 K) for crystallinities > 40%. Beside crystalline and flexible amorphous, a rigid amorphous phase is postulated in the semicrystalline polymer.     

A quantitative description for the optical properties of crystalline polymers applied to polyethylene

A quantitative model which described the microscopic and macroscopic refractive index properties of uniaxially oriented crystalline polymers has been extended in relation to molecular bond polarizabilities in this work. Application of this extended modeling methodology in analyzing measured refractive index data for a series of unoriented and oriented samples of linear polyethylene provided Δ = 0.0585 and Δ = 0.194 as the most probable crystalline and noncrystalline intrinsic birefringences for samples exhibiting spherulitic morphology. With these intrinsic birefringences, noncrystalline orientation functions were determined from the optical measurements coupled to the model and the results compared to values obtained from infrared measurements. This comparison of noncrystalline orientation functions, as well as from low density polyethylene reported by other investigators, provided experimental justification for our modeling methodology to examine the possibility of changing intrinsic birefringences for polyethylene as a function of orientation and morphology. The results of this examination demonstrated that values for Δ = 0.0585 and Δ = 0.12 should be used for both low and high density polyethylene samples oriented above the spherulitic to fibrillar transition region.     

Melt rheology and extrudability of polyethylenes

Commercial high density polyethylene (HDPE), low density polythylene (LDPE), and linear low density polyethylene (LLDPE) resins were tested at 150, 170, and 190°C in steady state, dynamic, and extensional modes. Within the low rates of deformation \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} = ω ≤ 0.3, the steady state and dynamic functions agreed: η = η′ and N₁ = 2G′; at the higher rates, the steady state parameters were larger. The elongational viscosity, η_e, was measured under a constant rate, \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}, or stress, σ, condition. In the first case for LLDPE, the transient η reached an equilibrium plateau value, η_e. For HDPE, η increased up to the break point. For LDPE, stress hardening was recorded. Under constant stress the η_e, could always be determined; its value, within experimental error, agreed with the maximum value of η determined in a constant \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon$ \end{document} experiment. The maximum strain at break was only ε = 1.5 for HDPE and 3, to 4 for LDPE and LLDPE. The rate of deformation dependence of the η (or η′) and η_n may be discussed in terms of the Trouton ratio, R_T = η_e/3η at \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} = ω = \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon$ \end{document}: R_T ≤ 1.2 for LLDPE, R_T ≤ 2.5 for HDPE, and R_T ≤ 15 for LDPE. The PE resins were extruded at 190°C through a laboratory extruder equipped with a slit or rod die. The rotational speed of the screw varied from 0 to 90 rpm. Extrusion pressure, output, and energy were measured and correlated with the rheological parameters of the resins.     

Corona-discharge treatment of polyethylene films. I. Experimental work and physical effects

Corona treatment of films, mainly polyethylene, was studied at commercial levels in a small continuous treater. Degree of treatment was characterized by measuring polar and dispersion components of surface energy, ASTM Wipe and ASTM Adhesion Ratio (“peel adhesion”). The chief factors studied were corona current, applied frequency, web speed, dielectric thickness and air-gap thickness between electrode and film. Other factors less intensively investigated were type of film, film additives, aging time after treatment, humidity and corona atmosphere. The polar component of surface energy, γ, is the key to understanding the changes in adhesive behavior of the films during treatment. We found that, for the equipment used, γ is accurately given by the equation where D = dielectric thick ness and G = air gap, both in mils; S = web speed, ft/min; I = corona current, ma, and γ is in dyne-cm/cm². A similarly structured equation describes ASTM Wipe. Using measured surface-energy components for the pressure-sensitive tape used in the peel adhesion test, it was possible to calculate an adhesion interaction for each film on which peel adhesion was measured and to show that it closely correlates with peel strength. Humidity changes in the moderate-humidity range, number of electrodes used and corona frequency had little effect on properties. Slip additives inhibited development of adhesion until treatment levels became high; adhesion properties gradually diminished upon aging of films stored at ambient conditions.     

Intrinsic birefringence of nylon 6

Different values are reported in the literature for the intrinsic birefringence of the crystalline (Δn) and the amorphous (Δn) phases in nylon 6. Mostly, these values have either been determined by extrapolation (and then it is assumed that Δn = Δn) or calculated theoretically. In this study, intrinsic birefringence values Δn and Δn for nylon 6 were determined using the Samuels two-phase model which correlates sonic modulus with structural parameters. Three series of fiber samples were used: (1) isotropic samples of different degrees of crystallinity for estimation of E and E moduli at two temperatures. The following modulus values were obtained: 1.62 × 10⁹ and 6.66 × 10⁹ N/m² for 28.5°C, and 1.81 × 10⁹ and 6.71 × 10⁹ N/m² for ?20°C; (2) anisotropic, amorphous fiber samples for estimation of Δn = 0.076 and E = 1.63 × 10⁹ N/m² at 28.5°C; (3) semicrystalline samples of various draw ratios for estimations of Δn = 0.089 and Δn = 0.078. All measurements were carried out with carefully dried samples to avoid erroneous results caused by moisture.     

Viscoelastic response of model epoxy networks in the glass transition region

Six epoxy networks with various structures built up from a diepoxy prepolymer, DGEBA, and three different diamines or mixtures of a monoamine and a diamine were studied by dynamic mechanical analysis in the glass transition region. The systems were designed in order to investigate the dependence of glass transition T_g on both crosslink density and network chain flexibility. The time (frequency)—temperature superposition principle (WLF equation) was used to determine the viscoelastic coefficients C^g₁ and C which are related to some free volume characteristics on the molecular scale. C^g₁, related to the free volume fraction available at T_g depends mainly on crosslink density, even though the product C^g₁C, related to the free volume expansion coefficient, is dependent on both chain flexibility and crosslink density. Thus, viscoelastic properties determined over large temperature and frequency ranges are shown to yield more precise information on epoxy network structure than the simple analysis of glass transition temperature.     

Effect of varying the composition of copolymers of glycidyl methacrylate and 3-chlorostyrene (GMC) on electron lithographic performance

The polymerization kinetics, molecular parameters, and electron lithographic response of a series of copolymers of glycidyl methacrylate (GMA) and 3-chlorostyrene (CLS) have been determined. The polymerization rate, molecular weight, and polydispersity decrease with increasing mole fraction of 3-chlorostyrene (X_CLS). Similarly, the sensitivity of this system decreases as the percentage of CLS in the copolymer increases. The value of D for the copolymer containing 14.3 mole percent CLS is 0.45 μC/cm² increasing to 3.2 μC/cm² for the 54 percent CLS copolymer of equivalent molecular weight. On the contrary the wet air and O₂ plasma etch rates decrease as X_CLS increases. For example, the etch rate using wet air for PGMA is ～ 30 percent greater than GMC (X_CLS = 0.54). The post exposure polymerization rate decreases as the CLS content increases. The extent of the post cure reaction is dose dependent being a maximum at D = 0.64 μC/cm² for the copolymer containing 14.3 mole percent CLS.     

Influence of solvent and molecular weight on thickness and surface topography of spin-coated polymer films

The influence of polymer molecular weight, molecular weight distribution, and polymer-solvent interactions on the thickness and topography of spin-coated polymer films was examined. For films prepared from dilute solutions, highly volatile solvents or fair or “poor” solvents for the polymer adversely affect film surfaces causing nonuniformities (waves) to appear. However, if the concentration of these solutions is increased to approximately the concentration at which entanglements are formed, nearly uniform films are produced even if the solvent employed is highly volatile, such as dichloromethane. When toluene is employed as the solvent, which has a relatively low volatility and therefore forms nearly flat film surfaces, films prepared from dilute solution were found to have thicknesses, h, proportional to η Ω^?0.49 for polystyrene and η Ω^?0.49 for poly(methylmethacrylate) where η_o is the zero-shear rate solution viscosity and Ω is the rotational speed at which the films were prepared. These results suggest that the exponents associated with η_o and Ω may be nearly independent of the type of polymer used as long as flat films are produced. Finally, the molecular weight parameter most important in controlling final film thickness for films made from dilute solutions is M_v, the viscosity-average molecular weight.     

Characterization of crystallinity,orientation, and mechanical properties in biaxially stretched poly(p-phenylene sulfide) films

In this paper, we describe the preparation and structural characterization of biaxially oriented poly(p-phenylene sulfide) (PPS) films. These films were prepared in a biaxial stretching machine at various stretching temperatures, rates, and stretching ratios. Selected samples were constrained annealed at elevated temperatures. The state of orientation was determined by wide angle X-ray diffraction (pole figure determination) and birefringence measurements. The results are expressed in terms of the biaxial orientation functions (?,?). Mechanical properties (tensile modulus, tensile strength, and elongation to break) were obtained as a function of processing conditions and direction in the plane of the films.     

Highly oriented polyacetylene: Structures and electrical conductivity of the compounds doped with alkali metals and selected oxidants

Films of polyacetylene synthesized according to Akagi method present a high degree of crystallinity. A 6-7 times stretching of these films results in the orientation of the polymer fibers: The mosaic was ± 5 degrees. Such highly oriented polyacetylene (HOPA) films were chemically doped by heavy alkali metals in the vapor state and electrochemically with GaCl anion in nitromethane medium. The evolution of the structures and the variation of the electrical conductivity upon doping were examined in both cases. Doping with alkali metal leads to the appearance of different intercalated phases: The commensurability of these phases is discussed as a function of the nature and the concentration of the intercalated alkaline ion. The electrical maximum room temperature conductivity, which depends on the nature of the alkali metal, is maximum for K-doped materials. In the case of GaCl doping, the unique intercalated phase observed is poorly organized except in the chain direction where a GaCl ion is found every 4.5 (CH) units. The room temperature electrical conductivity measured along the chain axis is equal to 15 000 S/cm, one order of magnitude higher than the value observed in Shirakawa unoriented polyacetylene.     

The influence of inclusion geometry on the elastic properties of discontinuous fiber composites

Simplifying assumptions are used to reduce micromechanical treatments to compact expressions which directly reveal the role of the inclusion shape and aspect ratio in establishing the elastic behavior of heterogeneous materials. Attention is directed to the comparison of aligned ellipsoidal and cylindrical inclusions that exhibit transversely isotropic behavior characterized by five independent elastic constants. These comparisons show that the effective transverse in-plane moduli (E, k* and G) are essentially independent of inclusion shape for aspect ratio greater than ～ 20; ellipsoidal inclusions provide higher longitudinal reinforcement than cylindrical inclusions of equivalent aspect ratio. Comparison of predictions with measured elastic moduli shows that both the cylindrical and ellipsoidal shape models for isolated inclusions overpredict longitudinal elastic constants for systems which exhibit evidence of inclusion agglomeration. The notion of an effective aspect ratio based on clusters of filaments responding as a coherent unit appears to provide a means for reconciling a wide range of experimental observations.