Enhanced crystallization of bisphenol-A polycarbonate by nano-scale clays in the presence of supercritical carbon dioxide

The crystallization behavior of bisphenol-A polycarbonate (PC) and PC/clay nanocomposites were studied in the presence of supercritical carbon dioxide (SCCO₂) using DSC, WAXD and AFM. In the absence of SCCO₂, nano-scale clay itself does not change the crystallization behavior of PC under our experimental conditions. In the presence of SCCO₂, clay appears to be an efficient nucleating agent and enhances the crystallization of PC. The addition of clay reduces the induction time of crystallization and increases the crystallization rate. The increase in crystallinity with clay depends on the crystallization time. When the crystallization time is sufficient, PC and PC/clay composites tend to have similar crystallinity in the range of 26%. Two melting temperatures are observed during the DSC heating scan, and are mainly associated with the melting of both secondary and primary crystals. Results show that the clay influences the primary crystallization process more than the secondary crystallization process.     

Effect of physical ageing on enthalpy relaxation and isothermal contraction in bisphenol-A polycarbonate

The intention of this paper is to correlate the decrease of free volume and the enthalpy relaxation which occur in high polymers during annealing. We used a simple correlation relation, with one chief parameter (the ‘equilibrium temperature’ ?), which can be deduced from different models. Data on polycarbonate (PC) show no correlation between enthalpy relaxation and isothermal contraction using that relation: the assumption that the decrease of free volume in PC in the glassy state obeys a Williams-Landel-Ferry (WLF) type equation could not be confirmed. Moreover, it seems that the changes of configuration occurring during annealing cannot be described with only one parameter.     

Influence of deformation on physical aging of polycarbonate

Summary Volume recovery of polycarbonate samples has been investigated by dilatometric and density measurements near ambient temperature. The volume changes with time have been measured either after heating above T_g and quenching, or after cold drawing at ambient temperature. Cold drawing drastically increases the volume recovery rate of polycarbonate, as compared with the rate observed after quenching. This is quite similar to the behavior previously reported on physical aging measured by dynamic mechanical tests (1). The observed decrease of specific volume after cold drawing can be explained by a densification effect due to molecular orientation.     

Liquid-induced crystallization of a bisphenol-A polycarbonate

The liquid-induced crystallization of bisphenol-A polycarbonate films in the presence of CCl₄ and acetone as swelling agents has been investigated by means of differential microcalorimetry and differential scanning calorimetry (d.s.c.). Results of microcalorimetric measurements were used to obtain thermokinetic curves and to determine heat effects in the liquid-induced crystallization process. Results of calorimetric measurements were subjected to Avrami analysis. The d.s.c. experiments revealed a maximum crystallinity of about 17% in the case of samples swollen in CCl₄ and 20% for those swollen in acetone.     

Thermal aging of bisphenol-A polycarbonate/acrylonitrile–butadiene–styrene blends

Thermal aging of immiscible bisphenol-A polycarbonate/acrylonitrile–butadiene–styrene (PC/ABS) blends containing 25, 60, and 75% PC and the PC and ABS blend components have been studied. Changes in Izod impact properties and dynamic mechanical spectra are reported following aging at 90, 110, and 130°C for times up to 1500 h. PC/ABS blends containing 60 and 75% PC were found to retain high impact performance following aging at elevated temperatures, compared to the PC blend component. Dynamic mechanical spectroscopy is an effective probe for investigating the structure–property changes occurring and the mechanisms of aging. For PC and ABS, the changes were mainly due to physical aging of the amorphous polymers when aged below the glass-transition temperature. For the PC/ABS blends, oxidative degradation additionally contributes to loss of toughness. Although structure–property changes are related to the behavior of the blend components, additional factors of potential importance for multiphase polymer–polymer systems have been identified, including a redistribution of stabilizers during the blend manufacture. © 1995 John Wiley & Sons, Inc.     

The optical properties of bisphenol-A polycarbonate

The optical properties of bisphenol-A polycarbonate resin as described by the complex index of refraction, N = n – ik, are derived by Kramers-Kronig analysis of experimental absorption and reflectance data obtained in the range 40μm ≥ λ ≥ 105 nm. Electronic absorption processes in polycarbonate are characterized by two broad absorption peaks centered at ～200 and ～100 nm.     

Pyrolysis of γ-irradiated bisphenol-A polycarbonate

Summary A new approach to study the mechanism of radiation-induced degradation of polymeric materials based on the combined analysis of radiolytic gases and pyrolytic products from preirradiated polymers is proposed. Bisphenol-A polycarbonate (PC) was γ-irradiated under vacuum in the dose range from 0.125 to 1.0 MGy followed by its flash pyrolysis under an inert atmosphere coupled to GC-FTIR-MS. Pyrolyzed PC at 750°C released mainly carbon dioxide, methane, benzene, toluene, phenol and 4-methylphenol. The yields of some of these products linearly decrease or increase with absorbed dose. On the basis of this behavior and combining our previous data on gas evolution, we infer two main pathways of PC radiation-induced scission with equal probabilities: (a) carbonate bond and (b) aliphatic-aromatic bond ruptures. Received: 14 September 2001/ Revised version:16 January 2002/ Accepted: 18 January 2002     

Transport of oxygen and carbon dioxide through polycarbonate membrane

Sorption equilibria and permeation rates for oxygen and carbon dioxide in polycarbonate membrane were measured at different temperature between 30 and 60°C and at pressures up to 2.5 MPa. The pressure dependence of mean permeability coefficient to oxygen obeyed the conventional dual-mode mobility model, whereas that to carbon dioxide followed a modified dual-mode mobility model with concentration-dependent diffusivities, as that of polystyrene to the same gas did.     

CO2吸收材料的研究进展

全球变暖已成为当前困扰人类生存和发展的重大障碍,因此,CO2吸收材料的研究成为了当前科学研究的热点。本文介绍了CO2捕获和富集的几种方法,主要包括溶剂吸收法、吸附法,并按照基质的不同将吸附法分为金属氧化物类、纤维类、活性炭类、分子筛类、碳纳米管类、聚合物类。同时介绍了其研究进展,并简述了各自的优缺点。指出氨基修饰的碳纳米管是一种很有潜力的CO2吸收材料。     

On the molecular weight determination of bisphenol-A polycarbonate

In order to assess the reliability of absolute molecular weights of bisphenol-A polycarbonate samples measured by size exclusion chromatography, the results obtained from two experimental systems and two calibration methods are compared with each other as well as with data provided by light scattering determinations. The interest of coupling a light scattering detector to the chromatographic system is discussed.     

双酚A聚碳酸酯合成新方法的研究进展

介绍了双酚A聚碳酸酯不同于工业生产中常用的光气法和熔融酯交换法的3种新的合成方法,即固相缩聚法、开环聚合法、完全非光气法的实施方法、主要特点及其新进展,探讨了各种方法存在的主要问题以及对生成的聚合物结构和性能的影响。固相缩聚是由预聚物结晶后在固相缩聚,可以获得结晶型双酚A聚碳酸酯并提高聚合物质量;开环聚合法首先合成环状碳酸酯低聚物再开环聚合得到聚合物,可以获得很高分子质量聚合物;完全非光气法在合成过程中完全避免了光气的使用,环境友好,聚合物质量高,很有发展前景。     

Effect of cocatalyst and carbon dioxide pressure on the synthesis of polycarbonate from phenyl glycidyl ether and carbon dioxide

The copolymerization of phenyl glycidyl ether (PGE) and carbon dioxide was performed in the presence of ionic liquid catalyst. 1-Butyl-3-methyl imidazolium chloride, tetrabutylamouim chloride and 1-n-butylpyridinium chloride were used as catalyst for this reaction carried out in a batch reactor. All the ionic liquid catalysts showed good catalytic activity for the synthesis of polycarbonates with very low polydispersity, close to 1. The carbonate content, turnover number (TON), and average molecular weight of the copolymer were affected by the structure of the ionic liquid. High carbon dioxide pressure enhanced TON and carbonate content because of the increase of carbon dioxide absorption in PGE solution. ZnBr₂ and a Zn-Co cyanide complex were also tested as a catalyst and/or cocatalyst for this reaction to compare their catalytic performance with the imidazolium salt ionic liquids.     

Anisotropic loss of toughness with physical aging of work toughened polycarbonate

We have studied the response of mechanically toughened and physically aged polycarbonate primarily using Charpy impact and ultrasonic wave speed measurements. The toughening was conducted through plastic compression on as‐received PC. The Charpy impact tests showed anisotropic toughening, both in the absorbed energy and in the mode of fracture. The amount of toughening with plastic compression, even though anisotropic, is centered around the response of annealed and quenched samples, which represent the response of an unaged PC. There was an anisotropic drop in the toughness of some samples with aging. The time of this drop was uncorrelated in the different directions and disappeared for the highly toughened samples. This transition was bimodal and statistically distributed between either a fully ductile or a fully brittle failure. As the samples were prepared in a manner to remove induced residual stresses, this drop in toughening may be associated with an intrinsic anisotropic thermal aging of the deformed material. POLYM. ENG. SCI., 54:794–804, 2014. © 2013 Society of Plastics Engineers     

Multiple dielectric relaxation processes in an unequilibrated bisphenol-A polycarbonate

Complex relative permittivity data within the ranges 0·1 Hz–3 MHz and −175°C to +200°C are presented for an unequilibrated compressionmoulded bisphenol-A polycarbonate of commercial origin (LEXAN 141). Comparisons are drawn with the nitrogen-equilibrated material in which eight distinct absorption regions have been identified. One low-frequency region common to both materials at low temperature is shown to be caused directly by a processing stabiliser. A second at high temperature is though to originate in part from an interfacial polarisation associated with a second phase of polycarbonate. An absorption observed only in the unequilibrated polycarbonate is attributed to bound water. Two intermediate-temperature losses are differentiated and delineated for the first time. Their origins and reason for diminution by annealing are examined. The multiplicity of overlapping absorptions, including a low-temperature loss region which is almost continuous at higher frequencies, is consistent with the high impact strength of polycarbonate over an extended temperature range.     

Some new aspects of the crystallization of bisphenol-A polycarbonate

This paper concerns the action of plasticizers and nucleating agents on the crystallization of bisphenol-A polycarbonate. The influence of plasticizers is to increase the rate of crystallization to a great extent using 10 percent of a plasticizer such as trimellitic acid, tridecyloctyl ester. The influence of nucleating substances on plasticized and undiluted polycarbonate is investigated. A large number of substances have been found capable of nucleating polycarbonate crystallization. The un-plasticized semi-crystalline polycarbonate is characterized by a much higher melting point (300°C) than the plasticized semi-crystalline systems (210–245°C). The stability of bisphenol-A polycarbonate in the presence of nucleating salts is also examined. We observe a substantial decrease in the molecular weight in the presence of a great number of nucleating substances. The modulus-temperature curves of two semi-crystalline polymers are reported in the last series of experiments.     

Miscibility behaviour of bisphenol-A polycarbonate and poly(para-chlorostyrene)

The miscibility behaviour of bisphenol-A polycarbonate (PC) and poly(para-chlorostyrene) (PpCIS) has been investigated. Special attention has been paid to the influence of the molar mass of PpCIS. Molar masses varying from 10 to > 1,000 kg/mol were used. The blends were studied by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and scanning and transmission electron microscopy (SEM and TEM). It was concluded that the blends of all three PpCIS grades and PC phase separate. In the low concentration region, some intermixing was found, especially for the blend with the low molar mass PpCIS. The most important effect of lowering the molar mass of PpCIS was an acceleration of the phase separation. The combination of SEM with electron probe X-ray microanalysis (EPMA) gave qualitative information on the miscibility behaviour and was found to be a useful extension of routine microscopy techniques used in blend studies.     

Multistage melt polymerization of bisphenol-A and diphenyl carbonate to polycarbonate

A multistage melt polycondensation of bisphenol-A and carbonate has been studied experimentally using LiOH·H₂O catalyst. The reaction process consists of batch and semi-batch periods with different temperature and pressure conditions. It was observed that a small amount of diphenyl carbonate lost from the reaction mixture by vaporization had little effect on the molecular weight in the batch reaction period but the efficiency of subsequent low-pressure semibatch polycondensation was affected by the change in the mol ratio of the phenyl carbonate group to the hydroxyl end group. A molecular species model developed for the multistage process was used to analyze the kinetics of the polycondensation process. The composition of the reaction mixture was analyzed of HPLC and compared with model simulations. In particular, the effect of evaporative loss of diphenyl carbonate on the progress of reaction is discussed in detail. © 1993 John Wiley & Sons, Inc.     

Influence of matrix molecular weight and processing conditions on the interfacial adhesion in bisphenol-A polycarbonate/carbon fiber composites

The adhesion of bisphenol-A polycarbonate, an amorphous thermoplastic, to carbon fiber was studied by varying both the intrinsic and the extrinsic properties such as the molecular weight, processing conditions, and test temperature. It was seen that processing methods and conditions had a significant effect on adhesion as measured by the interfacial shear strength. Commercial grade Lexan 141 solvent deposited onto carbon fibers showed poor adhesion when processed below the glass transition temperature and reached a limiting value at a higher temperature. Melt consolidated pure polycarbonate specimens showed increases in adhesion both with increasing processing temperature and with time. Pure polycarbonate having a molecular weight above the critical molecular weight exhibited a higher adhesion at different processing conditions, while for polycarbonate below the critical molecular weight adhesion was poor and unaffected by the processing temperature. Increases in temperature lowered the adhesion as a result of the dependence of adhesion on the matrix modulus, which decreases with increasing temperature.     

Solubilities of carbon dioxide,hydrogen sulfide and sulfur dioxide in physical solvents

Solubilities expressed by Henry's law constants for carbon dioxide, hydrogen sulfide and sulfur dioxide in four physical solvents (propylene carbonate, N-formyl morpholine, Selexol, and methyl cyanoacetate) have been measured at several temperatures ranging from 25°C to 70°C, using gas-liquid chromatography. Thermodynamic properties including enthalpies and entropies of solution have been derived from the solubility data.     

Blends of polyamide 6 and bisphenol-A polycarbonate. Effects of interchange reactions on morphology and mechanical properties

Blends of polyamide 6 (PA6) and polycarbonate (PC) were prepared in a Brabender mixer, at 240°C, applying long mixing time, for 45 min. It was observed that the morphology and the mechanical properties tend to resemble those of a homogeneous material as the mixing time and PA6 concentration increase. This is attributed to chemical reactions taking place between the two homopolymers. Acidolysis, amidolysis, and aminolysis, catalyzed by the terminals and the amide groups of the polyamide, should in principle be possible. Our results indicate that the aminolysis is the main process, inducing simultaneously scission of PC chains and formation of PC-PA6 copolymer chains. The latter act as interfacial agents between incompatible PA6 and PC, improving the mechanical properties of PA6-rich blends, in agreement with the predictions of some theoretical models assuming good phase interpenetration. © 1992 John Wiley & Sons, Inc.