Studies on sublimation of disperse dye out of dyed polymers. I. Rate of sublimation and amorphous transition points of poly(ethylene terephthalate)

Four samples of poly(ethylene terephthalate) film of various crystallinities and orientation were dyed with p-nitroaniline and disperse dyes. When these films were heated under a 2–3 × 10^?3 mm Hg vacuum at a specified temperature T, the dye sublimed out of the dyed specimen. The amount (M_t/M_∞) of sublimed dye is in linear proportion to the square root of the sublimation time, t^½, where M_t and M_∞ are the amounts of dye sublimed for times t and t = ∞. The diffusion coefficient D, calculated from the slope of the above plot, is independent of the dye concentration of the film. When log D is plotted against 1/T°K over the temperature range 320–520°K, the relation is composed of two to four intersecting lines with the slope decreasing with elevation of temperature and with the breaks at about 89°–98°, 122°–135°, 155° and 175°–176°C. These breaks are the amorphous transitions: the first is the glass transition temperature T_g, the second and the fourth are the amorphous transitions corresponding to the crystalline transition points, i.e., the cold crystallization temperature and the smectic–triclinic transition temperature. With some exceptions, these amorphous transitions are found also by dilatometry and electrical conductivity measurements. The apparent activation energy for diffusion decreases from about 100 kcal/mole for the glass state to 22–24 kcal/mole for the region above 180°C. The activation energy for each region changes slightly with the size of dye molecule and the crystallinity and orientation of the film.     

Isothermal rupture characteristics of a plasticized poly(vinyl chloride) in the glass–rubber transition zone

Constant strain-rate uniaxial extension tests to rupture were performed at 23°C on a plasticized poly(vinyl chloride) (PVC) in the glass-to-rubber transition zone, T_g = ?18°C, where experimental failure time t_f is equal to or greater than material relaxation time τ. Range of strain rate is from 1.8 × 10^?4 to 1.8 × 10^?1 sec^?1. The rupture characteristics in stress/strain time space are analyzed on the three coordinate planes. Time and deformation separability are examined in a nonlinear-constitutive relation. Rupture data on the coordinate planes are described by the Bueche-Halpin theory in which time effects are considered through a small-deformation viscoelastic property. Fracture surface morphology and separation processes in the crack tip are related to rupture characteristics.     

The degradation of polystyrene during extrusion

An investigation was made of the magnitude and mechanism of shear degradation of a narrow distribution, high molecular weight (M_w = 670,000) polystyrene. An Instron rheometer was used to perform the extrusion at temperatures from 164° to 250°C. The change in molecular weight distribution was studied by gel permeation chromatography. The maximum shear stress employed was 5.83 kg/cm². It was found that degradation could be induced at high stress at temperatures of 50°C lower than degradation of polystyrene would occur exclusively due to thermal forces. An activation energy for the degradation, calculated at constant shear rate, was +20.2 kcal/mole. The direction and magnitude of this value are consistent with degradation induced through a mechanical reduced activation for thermal degradation.     

Head to head polymers IX: The rheological behavior of H-H and H-T atactic polystyrenes

The rheological behavior of a sample of H-H polystyrene of M_n of 41,000 and a M_w/M_n of 2 was compared at 160 and 190°C with a sample of H-T atactic polystyrene of similar molecular weight. The melt viscosity of H-H polymer (unlike the H-T polymer) was non-Newtonian at low stresses and decreased more rapidly with stress. This observation seems to indicate a stiffer polymer chain for the H-H polystyrene. The flow activation energy (E*) of H-H polystyrene was found to be dependent on the dynamic shear stress and decreased with increasing dynamic shear stress. The dynamic shear storage modulus of the H-H polymer has a smaller increase of G′ with ω than that of the H-T polystyrene.     

Craze healing in polymer glasses

Craze healing was observed in many amorphous glassy polymers. A detailed study of the kinetics of craze healing in atactic polystyrene (M_w = 255,000) was conducted. The crazes were created in 0.08 mm films in air at room temperature, T_o, and constant stress, σ_o ? 2,300 psi, healed at temperature T_h for a time, T_h, at σ = 0, and recrazed at T_o and σ_o. Nucleation times, τ₁ and τ₂, and growth rates, L₁, and L₂, for the first and second loading, respectively, were measured as a function of t_h and T_h for individual crazes using dark field optical microscopy. Complete optical and mechanical healing was observed for T_h ? 70°C(T_g ? 100°C). At constant T_h, healing progressed in five stages with increasing th as follows; (i) no healing, τ₂ = 0, L₂ ? L₁; (ii) partial healing, τ₂ <τ₁, L₂ > L₁; (iii) similar growth, τ₂ = τ₁, L₂ = L₁; (iv) slower growth, τ₂ > τ₁, L₂ < L₁; (v) disappearance, τ₂ → ∞, L₂ → 0. A craze healing envelope of T_h vs T_h was obtained for the above stages. Craze healing occurred by line mode in which uniform healing occurred along the entire length of the craze.     

Dynamic mechanical properties of polystyrene‐block‐poly[ethylene‐co‐(ethylene‐propylene)]‐block‐polystyrene triblock copolymer/hydrocarbon oil blends

Blend systems of polystyrene‐block‐poly(ethylene‐co‐(ethylene‐propylene))‐block‐polystyrene (SEEPS) triblock copolymer with three types of hydrocarbon oil of different molecular weight were prepared. The E″ curves as a function of temperature exhibited two peaks; one peak at low temperature (? ?50°C), arising from the glass transition of the poly[ethylene‐co‐(ethylene‐propylene)] (PEEP) phase and a high temperature peak (? 100°C), arising from the glass transition of the polystyrene (PS) phase. The glass transition temperature (T_g) of the PEEP phase shifted to lower temperature with increasing oil content. The shifted T_g depended on the types of oil and was lower for the low molecular weight oil. The T_g of PS phase of the present blend system, were found to be constant and independent of the oil content, when molecular weight of the oil is high. However, for the lower molecular weight oil, the T_g of the PS phase also shifted to lower temperatures. This fact indicates that the oil of high molecular weight is merely dissolved in the PS phase. The E′ at (75°C, at which temperature both of PEEP and PS phases are in glassy state, was found to be independent of oil content. In contrast, at 25°C, at which temperature the PEEP phase is in rubbery state, the E′ decreased sharply with increasing oil content. This result indicates that the hydrocarbon oil was a selective solvent in the PEEP phase. It mainly dissolved in the PEEP phase, although slightly dissolved into the PS phase as well, when molecular weight of oil is low. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Controllable τf value of barium silicate microwave dielectric ceramics with different Ba/Si ratios

Ba_1+1/M[Si₂O_5+1/M] low‐permittivity microwave dielectric ceramics are prepared using the conventional solid‐state method. Pure phases are obtained in barium silicates with M = 1, 3, 4, 5, and ∞, except for M = 7, in which two phases, Ba₅Si₈O₂₁ and BaSi₂O₅, are observed. As the complexity of the crystal structure described by the Shannon information per reduced unit cell increases, the τ_f value tends to change from a negative to a positive value, except for M = 5, which has the highest complexity. A single Ba₅Si₈O₂₁ phase with ε_r anomaly peak at ?180°C exhibits a rare positive τ_f value (+25 ppm/°C), which is a novel temperature compensator.     

The kinetics of the α relaxation in an amorphous polymer at temperatures close to the glass transition

The kinetics of the α relaxation of a crosslinked copolymer of acrylonitrile and butadiene (T_g = ?7°C) were studied in the temperature range (T_g + 17°C) down to (T_g ? 8°C). The techniques used were shear creep analysed by time-temperature (t-T) superposition and thermal sampling (TS) with correction procedures proposed by McCrum. In this range the kinetics do not follow the compensation rule, as had been proposed in the pioneering TS experiments by Zielinski, Swiderski and Kryszewski and by Lacabanne et al.. The McCrum correction removes a discrepancy between the pioneering TS experiments and the conclusions of classical t-T superposition experiments. The methods of TS and t-T superposition are compared. At low temperatures, below (T_g + 3°C), the TS method is superior: t-T superposition is unreliable due to lack of normalization and to the physical ageing perturbation. At temperatures from (T_g + 3°C) to (T_g + 11°C) t-T superposition is highly reliable since normalization is not required and there is no ageing. At temperatures above (T_g + 11°C) the precision of t-T superposition depends on the validity of the normalization procedure. It has yet to be determined whether or not the compensation rule applies at temperatures below (T_g ? 8°C): the method most likely to settle this important question is TS, mechanical or dielectric variant, with McCrum correction for the distribution of relaxation times.     

Thermal and physical properties of allyl PPO and its composite

The thermal behavior of allyl PPO and its cured resin were investigated. In the allyl PPO curing process, the specific temperatures were T_gel = 173.6°C, T_cure = 225.4°C, and T_treat = 237.7°C, and the activation energy (E_a) was 122 kJ/mol. The average number of PPO molecular units between two crosslinking points was about 20. In the degradation process of cured allyl PPO resin, the temperature at which mass loss equaled 1% was much higher than 300°C. The E_a for degradation was calculated as 125 kJ/mol, with a degradation fraction (α) in the range of 0.15–0.65, or 117 kJ/mol with an α of 0.10–0.90. The most probable mechanism function of decomposition of the cured allyl PPO resin was f(α) = 2(1 ? α)^3/2 or g(α) = (1 ? α)^?1/2 ? 1. The thermocompressed laminate of the allyl PPO blending with an additive resin (made from BDM and DP) exhibited the desired properties. ©2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4111–4115, 2006     

Chain orientation in sheared molten poly(ethylene oxide) fractions by measurement of infrared dichroism

Rheo-infrared spectroscopy was used to study the development of orientation of molten narrow molar mass fractions of poly(ethylene oxide) [molar masses between 18,000 and 120,000 g/mol] during non-Newtonian shear flow at shear rates between 2 and 270 s^?1 and temperatures between 75 and 100°C. The steady state degree of orientation [expressed as the Hermans orientation function (f_ss)] reached a saturation level with increasing shear rate; f_ss increased with increasing molar mass (M) according to f_ss = C₁ ? C₂/M (C₁ and C₂ are coefficients; the latter depended on shear rate and temperature). The coefficient C₁ (f_ss) for a polymer with infinite molar mass took a universal value close to 0.05 for the temperatures and shear rates used. Under large shear stresses, the relationship between stress and orientation deviated markedly from linearity. The time to establish a steady state level of orientation was proportional to M^1/2. The recovery of the isotropic state after the cessation of shear could initially be described by a simple exponential relaxation law: f ∝ e, where τ_ρ is the relaxation time. The latter showed a weak molar mass dependence according to τ_r ∝ M^0.6 and an Arrhenius temperature dependence with an activation energy of ～60 kJ/mol. The relaxation of the shear stress after the cessation of shear was more rapid than the recovery of the isotropic state.     

Dielectric relaxations of shellac/amino resin blends

The dielectric constant (ε′) and loss (ε″) of shellac/melamine resin blends have been determined at temperatures between 20° and 120°C and frequencies between 0.1 and 100 kHz. ε′ decreases with increase in the percentage of melamine resin in the blend. Two relaxations have been observed, of ΔH = 4.99 kcal/mole and 11.1 kcal/mole. The glass transition is observed between 60° and 70°C. The cole-cole parameter increases with temperature and becomes constant above T_g.     

Effects of polycaprolactone molecular weights on thermal and mechanical properties of polybenzoxazine

Polymer blends of polybenzoxazine (PBA‐a) and polycaprolactone (PCL) of different molecular weights (M_n = 10,000, 45,000, and 80,000 Da) were prepared at various PBA‐a/PCL mass ratios and their properties were characterized. The results from dynamic mechanical analyzer (DMA) revealed two glass transition temperatures implying phase separation of the two polymers in the studied range of the PCL contents. Moreover, a synergistic behavior in glass transition temperature (T_g) was evidently observed in these blends with a maximum T_g value of 281°C compared with the T_g value of 169°C of the PBA‐a and about ?50°C of the PCL used. The blends with higher M_n of PCL tended to provide greater T_g value than those with lower M_n of PCL. The modulus and hardness values of PBA‐a were decreased while the elongation at break and area under the stress?strain curve were increased with an increase of the content and M_n of PCL, suggesting an enhancement of toughness of the PBA‐a. Scanning electron micrographs (SEM) of the sample fracture surface are also used to confirm the improvement in toughness of the blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41915.     

Effect of Glass Addition on the Microwave Dielectric Properties of CaMgSi2O6 Ceramics

CaMgSi₂O₆ (CMS) ceramics prepared by the solid-state ceramic route have a sintering temperature of 1300°C/2 h. The sintering temperature of CMS was reduced below the melting point of Ag using low-melting LBS and LMZBS glasses. In the case of CMS+15 wt% LMZBS sintered at 900°C/2 h, the dielectric properties obtained were ɛ_r=8.2, Q_u×f=32,000 GHz (10.15 GHz), and τ_f=–48 ppm/°C. The CMS+15 wt% LBS composite, sintered at 925°C/2 h, showed ɛ_r=8, Q_u×f=15,000 GHz (10.17 GHz), and τ_f=–49 ppm/°C. The chemical compatibility of Ag with the ceramic–glass composites was also investigated for low-temperature co-fired ceramic applications.     

Wood-dowel rotation welding – a heat-transfer model

The relationship between temperature, time of friction and thermal flux for high-speed rotational wood-dowel welding has been modelled through a heat-transfer model. It was shown that the interface temperature could be estimated as a function of the friction time by the general equation T ₀ = T _i + 2βuτ√α/h√π √t, where T ₀ – temperature at the welding interface, T _i – initial temperature of the wood, t – time, τ – the friction stress, u – the rate of rotation or vibration, β – the fraction of mechanical energy convertible into thermal energy, and h and α are, respectively, the thermal conductivity and diffusivity of the wood. For both the rotation welding and linear welding systems, the value of β is found to be 0.080±0.01. The results obtained for dowel rotation welding indicate that a temperature of 180°C is optimal for rotational dowel welding. The model was validated from experimental data on rotational dowel welding for the portion of the curve in which temperature increased as a function of time. Furthermore, it was also validated from experimental data for linear vibration welding.     

Poly(phenylene oxide) composites containing crosslinked polystyrene microspheres. II. Dark crosses observed in microscope

Extinction phenomena observed between crossed polaroids in microscope were classified into three groups: (1) Poly(2, 6-dimethyl-1, 4-phenylene oxide)/polystyrene composite with crosslinked polystyrene microspheres. Negative dark crosses were observed in the shells of the spheres, the cores of the spheres were completely extinct. The crosses disappeared at 170°C, which is 20°C above T_g of the matrix polymer. (2) Polycarbonate composite with glass beads. The dark crosses were positive and outside the glass beads. The crosses disappeared at 130°C, which is 20°C below T_g of the matrix polymer. (3) In situ polymerized composites with crosslinked polystyrene microspheres. The dark crosses were the same size of the spheres. They were negative in poly(methyl methacrylate) and poly(vinyl acetate) and positive in polystyrene. The disappearing temperatures of the crosses were 150, 110, and 285°C, respectively. The first two groups of phenomena are explained as the photoelastic effects caused by the thermally induced stresses. The last group is due to the inhomogeneous swelling or contracting of polystyrene networks in the matrices.     

Quantitative study of the annealing of poly(vinyl chloride) near the glass transition

Poly(vinyl chloride) displays a normal DSC of DTA curve for the glass transition when quenched from above its T_g. However if cooled slowly or annealed near the glass transition temperature, a peak appears on the DSC or DTA curve at the T_g. In this paper quantitative studies of the time and temperature effects on the production of this endothermal peak during the annealing of PVC homopolymer and an acetate copolymer are presented. The phenomenon conforms to the Williams, Landell, and Ferry equation for the relaxation of polymer chains, the rate of the peak formation becoming negligible at more than 50°C below T_g. The energy difference between the quenched and annealed forms is small. For a PVC homopolymer annealed 2 hr at 68°C, which is T_g ?10°C, the difference is 0.25 cal/g. For a 13% acetate copolymer of PVC similarly annealed, the difference is 0.36 cal/g. The measured rates of the process give a calculated activation energy of 13–14 kcal/mole for PVC homopolymer and copolymer. This appearance of a peak on the T_g curve for a polymer when annealed near the glass temperature appears to be a general phenomenon.     

Characterization of optical properties of acrylate based adhesives exposed to different temperature conditions

Optical adhesives combine the traditional function of structural attachment with a more advanced function of providing an optical path between optical interconnects. This article aims to characterize refractive index and birefringence of such adhesives under environmental exposure to different temperature conditions. Optical time domain reflectometery (OTDR) and prism coupling methods were employed to measure optical properties of an optical adhesive. Thermo‐optic coefficient (dn/dT) of the adhesive was observed to decrease noticeably from ?2 × 10^?4°C^?1 to ?4 × 10^?4°C^?1 around the glass transition temperature (T_g ～ 78°C). It is observed that refractive indices for both T_E and T_M modes increase with increasing annealing temperature, but the birefringence (T_E ? T_M) is decreasing. This suggests that the material has become more isotropic due to the annealing. The environmental changes in optical properties of the adhesive are discussed in the light of Lorentz–Lorenz equations. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 950–956, 2005     

Dynamic mechanical analysis of fibers. I. Effect of experimental variables and material type

Depending upon the fiber material, some of the experimental variables can have a profound effect on the dynamic tensile modulus vs. temperature data. With the use of an experimental fiber (25°C < T_g < 75°C; T_m > 220°C; hot stretched), the effect of several variables, e.g., moisture/volatiles, annealing/relaxation, frequency (strain rate), pretension, and % strain on the modulus retention term [(E_100°C/E_25°C) × 100] have been studied. Of these variables, pretension and especially % strain dramatically increase the modulus retention and this effect is attributed to the elastic orientation under force (EOF), i.e., it exists only in the presence of tensile forces and is reversible. Such an effect was insignificant for Kevlar (T_g ? 375°C) and absent for steel wire. Dynamic modulus measurements at 25°C using sonic techniques also support the EOF phenomenon in polyethylene yarns (T_g ～ ?30°C) but not in Kevlar polymide yarns (T_g ～ 375°C).     

In-chain functionalization by alternating anionic copolymerization of styrene and 1-(4-dimethylaminophenyl)-1-phenylethylene

Anionic copolymerizations of styrene (M₁) with excess 1-(4-dimethyl-aminophenyl)-1-phenylethylene (M₂) were conducted in benzene at 25°C for 24h, using sec-butyllithium as initiator. Narrow molecular weight distribution copolymers with M?;_n = 16.1 × 10³ g/mol (M?_w/M?_n = 1.04) and 38.2 × 10³g/mol (M?_w/M?_n = 1.05), and 24 and 38 moles of M₂ per macromolecule, respectively, were characterized by size exclusion chromatography, ¹H NMR spectroscopy and DSC. The monomer reactivity ratio, r₁ = 5.6, was obtained from the copolymer composition at complete consumption of M₁, assuming that the rate constant k₂₂ =0,i.e. r₂ =0. The polymers exhibited T_g values of 128 and 119°C, respectively, which correspond to an estimated T_g = 217°C for the hypothetical homopolymer of M₂.     

Glass transition phenomena in melt‐processed polystyrene/polypropylene blends

Blends of an amorphous and a semi‐crystalline polymer—polystyrene and polypropylene, respectively—were prepared by melt processing in an extruder at 220°C. These polymers are known to be immiscible and the composite morphologies were characterized by electron microscopy and thermal analysis. Fine micron‐scale morphologies, ranging from 0.5 to 20 microns were observed. Thermal analysis and dynamic mechanical analysis showed changes in both the polystyrene and polypropylene glass transition temperatures (T_g) over the composition range. The major effect was a sharp increase in polystyrene T_g with increasing polypropylene content in the blend. A T_g elevation of 5.5°C was observed at 85% polypropylene. The polypropylene T_g also increases with increasing polypropylene content, starting at a depressed value in discrete polypropylene domain environments and approaching the bulk polypropylene value after the phase inversion is crossed. Qualitative structural models are proposed based on spatial and mechanical interactions between the components. POLYM. ENG. SCI., 45:1187–1193, 2005. © 2005 Society of Plastics Engineers