Carbon tetrachloride-induced crack healing in polycarbonate

Crack healing induced by carbon tetrachloride in polycarbonate has been studied at temperatures in the range of 40–60°C. The carbon tetrachloride treatment reduces the glass transition temperature of polycarbonate. Crack healing is observed because the effective glass transition temperature in polycarbonate is reduced to below the test temperature by the carbon tetrachloride treatment. Two distinctive stages of crack healing are divided based on the recovery of mechanical strength and fractograph. The first stage corresponds to the progressive healing due to the convolution of wetting and self-diffusion, which has a constant crack closure rate. Immediately following the first stage, the second stage, corresponding to the self-diffusion of polymer chain, enhances the quality of healing behavior. The transport of carbon tetrachloride in polycarbonate consists of case I (concentration gradient controlled) and case II (relaxation controlled) behaviors. The direction of case II is opposite to that of case I. The solubility decreases with increasing temperature, but diffusivity and velocity for mass transfer, crack closure rate, and diffusion coefficient for the diffusion front have the opposite trend. The first stage of crack healing is controlled by case II transport. The transport of carbon tetrachloride changes the fracture behavior of polycarbonate from ductile to brittle. A comparison of crack healing in polycarbonate and poly (methyl methacrylate) is made. © 1994 John Wiley & Sons, Inc.     

Molecular orientation induced by cooling stresses. Birefringence in polycarbonate: III. Constrained quench and injection molding

Residual stress and birefringence distributions are determined in polycarbonate samples obtained by quenching in a specially designed apparatus and by injection molding. The molecular orientation is distinguished from the thermally and pressure-induced residual stresses. The birefringence in the quenched samples is found to be positive and almost constant, independent of the quench temperature, but varying strongly with initial quench temperature between 150 and 180°C. The residual stress level, as determined by layer removal and sectioning, is very low. The birefringence distribution is mainly due to a tensile equibiaxial orientation induced by transient cooling stresses built up above T_g. The samples which are injection-molded with a high injection speed and without packing pressure display the same birefringence distribution as the quenched samples, apart from a local maximum beneath the surface due to the shear flow during filling. Apart from the flow during filling and packing, the frozen-in molecular orientation in injection-molded samples is also induced by transient thermal stresses present during vitrification. The birefringence from thermally induced orientation was found to be of comparable magnitude to that from flow-induced orientation. For a correct prediction of molecular orientation the thermal strains above T_g must therefore be included in simulation programs. Because of the low level of thermal stresses, the application of a packing pressure will lead to tensile stresses at the surface in general. © 1994 John Wiley & Sons, Inc.     

Miscibility of tetramethyl-hexafluoro copolycarbonates with styrene-methyl methacrylate copolymers

The compositions for which blends of copolycarbonates of tetramethyl bisphenol-A and hexafluoro bisphenol-A (TMPC-HFPC) with styrene-methyl methacrylate copolymers (SMMA) are miscible were determined experimentally. These copolymer compsition boundaries were compared to predictions based on the Flory-Huggins theory combined with the binary interaction model. The theoretical predictions employed interaction energies from the literature for the TMPC/PS, PS/PMMA, and TMPC/PMMA pairs, and values for the TMPC/HFPC, HFPC/PS, and HFPC/PMMA pairs were established or verified using independent experiments. The recommended set of interaction energies predicts that miscibility occurs in two separate regions of copolymer compositions. These predictions agree well with the experimental observations. The theoretical requirements for a single, continuous miscible region versus two disjointed miscible regions when the two limiting homopolymer pairs exhibit miscibility, that is, TMPC-PS and HFPC-PMMA in this example, are described. © 1994 John Wiley & Sons, Inc.     

Application of proton multiple-quantum NMR to the study of dynamics in bulk chloral polycarbonate

Proton multiple quantum (MQ) nuclear magnetic resonance (NMR) is applied for the first time to probe chain dynamics in the polycarbonate of 1,1-dichloro-2,2-bis(4-hydroxyphenyl)ethylene (chloral) over a temperature range of 195–280 K. Since chloral polycarbonate contains only one essentially indistinguishable proton, any dynamical information is associated with the phenylene group motion, the dominant sub-T_g motion. First, the fractional multiple quantum (f_MQ) signal which can be refocused at a fixed MQ preparation time decreases with increase in temperature from 195 to 200 K, associated with the onset of the phenylene π flips. Since π flips do not modulate dipolar couplings between phenylene protons at positions 2 and 3 on the same ring, this decrease in f_MQ can be attributed to modulation of the remaining couplings on the time scale of the MQ experiment. Next, over the range 200–240 K, the f_MQ maintains a reduced, nonfluctuating value. This suggests a broad distribution of correlation times exists for the π flips, since at any one temperature in this intermediate range, only a small portion of the phenylene groups undergo motion at the precise kHz frequency required to refocus the MQ signal. The increase in the signal strength as the temperature rises above 240 K is due to the majority of π flips occurring in the fast motional limit. These observations are in agreement with previous single quantum proton NMR studies on phenylene group rotation in choral polycarbonate. Furthermore these f_MQ measurements show several similarities to those for PTFE (poly(tetrafluoroethylene)), measured by ¹⁹F MQ-NMR. One notable difference is that in as-polymerized PTFE at intermediate temperatures (200–220 K) rapid oscillations of f_MQ were noted as the temperature was changed by a few degrees. Such behavior is not observed in the chloral polycarbonate. © 1994 John Wiley & Sons, Inc.     

Dynamic mechanical and gas transport properties of blends and random copolymers of bisphenol-A polycarbonate and tetramethyl bisphenol-A polycarbonate

Dynamic mechanical and gas transport properties for homogeneous homopolymer blends and random copolymers of bisphenol-A and tetramethyl bisphenol-A polycarbonates (PC-TMPC) were determined. The gas transport measurements were performed at 35°C for the gases He, H₂, O₂, Ar, N₂, CH₄, and CO₂. The results show that the copolymers have lower permeability, apparent diffusion, and solubility coefficients than the blends. Permeability coefficients for blends follow a semilogarithmic ideal mixing rule while copolymers exhibit negative deviations from this. Specific volume measurements show that the free volume available for gas transport is slightly larger in copolymers than in blends of the same composition. These apparently contradictory results may relate to the differences in local mode chain motions observed for the copolymer and blend series. The γ relaxation processes in PC and TMPC seem to operate independently in the blends (no intermolecular coupling) while there is clear evidence for intramolecular coupling in the copolymers. © 1992 John Wiley & Sons, Inc.     

Sulfone-Containing polymers as high barrier materials

Three types of sulfone-containing polymers, poly(carbonate-sulfone)s, poly(ester-sulfone)s, and poly(urethane-sulfone)s, were characterized as high barrier materials. They were made by condensing sulfone-containing diol, 1,3-bis(3-hydroxypropylsulfonyl)propane (Diol-333), or 1,4-bis(3-hydroxypropylsulfonyl)butane (Diol-343), with diphenyl carbonate, diphenyl esters, and diisocyanates, respectively. The incorporation of polar sulfone groups into polymer backbones increases the glass transition temperature of polymers in all cases; however, the increment is different with different functional linkages. The increments in polycarbonates and polyesters are higher than that in polyurethanes. This is because the interactions between carbonate or ester groups are much weaker than the interactions between sulfone groups, whereas the hydrogen bonding between urethane groups is comparable with the polar interaction between sulfone groups. The polymers were coated on 50-μm-thick Kapton films by solution casting and their permeabilities toward carbon dioxide were measured at 25°C using the ASTM D1434 volumetric method. The sulfone-containing polymers have carbon dioxide permeability coefficients at least 50 times smaller than the corresponding polymers without sulfone groups. The carbon dioxide barrier properties of sulfone-containing polymers are comparable with ethylene/vinyl alcohol copolymers (EVAL), which are commercial high barrier polymers. An isomer effect on polymer permeability was observed in the aromatic-aliphatic poly(ester-sulfone) series. The permeability coefficients of the aromatic-aliphatic poly(ester-sulfone)s decrease from terephthalate to isophthalate to phthalate, corresponding to the increase of chain flexibility above the T_g. These results support the hypothesis that high chain flexibility in the rubbery state and a glass transition temperature above room temperature are two key factors that promote low permeability. © 1994 John Wiley & Sons, Inc.     

Miscibility and cure kinetics studies on blends of bisphenol-A polycarbonate and tetraglycidyl-4,4′-diaminodiphenylmethane epoxy cured with an amine

Differential scanning calorimetry (DSC) has been applied to characterize the glass transition behavior of the blends formed by bisphenol-A polycarbonate (PC) with a tetrafunctional epoxy (tetraglycidyl-4,4′-diaminodiphenyl methane, TGDDM) cured with 4,4′-diaminodiphenylsulphone (DDS). A rare miscibility in the complete composition range has been demonstrated in these blends. Additionally, the blend morphology was examined using scanning electron microscopy (SEM) and a homogeneous single-phase PC/epoxy network has been observed in the blends of all compositions. Moreover, polycarbonate incorporation has been found to exert a distinct effect on the cure behavior of the epoxy blends. The cure reaction rates for the epoxy-PC blends were significantly higher due to the presence of PC. In addition, the cure mechanism of the epoxy blends was no longer autocatalytic. An n-th order reaction mechanism with n = 1.2 to 1.5 has been observed for the blends of DDS-cured epoxy with PC of various compositions studied using DSC. The proposed n-th order kinetic model has been found to describe well the cure behavior of the epoxy/PC blends up to the vitrification point. © 1995 John Wiley & Sons, Inc.     

Anticipation on the Development of Polycarbonate Production Technology by Using Ester-interchange Method in China

Polycarbonate (hereinafter referred to as "PC ") is the sole product having good transparency among the 5 major engineering plastics. In 2000, the worldwide PC production capacity was reached up to 2,800,000 tons of several hundreds of brands of various grades. It is estimated that the global PC production capacity will exceed 3,500,000 tons in 2005. The global demand for PC was 1,900,000 tons in 2000, which will reach to 2,600,000 tons and more than 3,000,000 tons in 2003 and 2005 respectively according to relevant estimations. The total production capacity of PC of the whole country reached to 3000-4000 tons in 2003. PC imported to China in 2003 was up to 534,000 tons and the apparent amount of consumption of that year was 447,000 tons.The scientific and technical personnel of Chenguang Chemical Research Institute engaged in the research and development of PC production technologies have been advancing wave upon wave with a combatant spirit and the spirit of "Storming the gate" for more than 40 years, having made important breakthroughs in a continuous PC manufacturing process by using ester-interchange method and in project amplification techniques. We consider that favorable conditions are now already available in China for building up PC production plants (each has an annual production capacity of 10,000 tons or above) by using ester- interchange method.In the recent 2 years, the growth rate of domestic annual PC consumption was up to more than 30 %, almost all of which relied on imports from foreign countries. Consequently, the development of domestically made PC has become a task, which brooks no delay. At present, conditions for building up domestic large-scale PC production plants are already available. It should be noted that PC production technologies are matured, PC products have a huge market potential and the returns on investment are optimistic. Therefore, building PC production plants, each with an annual production capacity of 10,000 tons ( approx. ) making use of domestic scientific research achievements and engineering technologies are fully in conformity with the industry policies issued by the State, which will have very important practical significance and far-reaching strategic significance for alleviating a sharp contradiction between PC supply and demand existed in China nowadays, breaking down the blockage against PC production technologies in China and the monopolization over the supply of PC products and product prices of foreign companies and developing our national industries having our own autonomous intellectual properties by means of our own intellectual properties.     

内窥镜的红外激光传输用柔性空芯光纤的研制

通过理论计算确立了多功能介质-金属结构空芯光纤的结构参量,优化了液相镀膜法的有关条件,明确了具体制作参量。制作了以聚碳酸酯毛细管为基管的,高柔韧性的,可同时低损耗传输红外目标波长激光和可见导航光红外的空芯光纤。对光纤传输性能进行了测试。在2.94μm波长的Er∶YAG和0.63μm波长的红色半导体激光器的直线损耗分别为0.4 dB/m和3 dB/m。组装在医疗内窥镜中的柔性空芯光纤,在先端以0.9 cm半径135°角弯曲时,对Er∶YAG激光仍有近70%的传输效率;绿色导航光在内窥镜中的的损耗值为11 dB,绿色指示点在内窥镜的视窗中清晰可见。结果表明此种光纤在内窥镜的激光传输方面有重要的应用价值。     

Study of effects of γ-irradiation on Tuffak polycarbonate track detector by TG

Effects induced by r-irradiation in the dose range of 0–10 Mrad on Tuffak polycarbonate track detector films have been studied by thermogravimetry (TG). The samples were irradiated with ⁶⁰Co r-rays for doses of 3, 5 and 10 Mrad. The TG studies indicate that unirradiated and the r-irradiated samples degrade in two steps. The kinetics of the two steps of degradation was also evaluated from the TG curves. Irradiation enhances the degradation rate and the effect increases further with increasing radiation dose. The activation energy values calculated for all the steps decrease on irradiation. A linear relationship observed between the decrease in activation energy and the dose received by the sample suggests the possibility of the use of Tuffak polycarbonate detector as r dosimeter.The authors are thankful to Dr. V. K. Manchanda, Head, Radiochemistry Division, BARC for his encouragement and support during this work.