In situ and real-time optical investigation of nitrogen plasma treatment of polycarbonate

Polycarbonates are very attractive polymeric materials with extensive applications in optical technology as well as for replacing conventional rigid substrates, such as glass. The use of plasma treatments has been successfully employed for improving their surface properties and increasing adhesion of subsequent functional coatings. The objective of this study is to employ in situ and real-time Fourier transform infrared spectroscopic ellipsometry for a detailed investigation of the effect of nitrogen plasma treatment using a pulsed DC voltage, on the optical properties of polycarbonates. Measurements taken before, during and after plasma treatment showed the formation of a surface overlayer in which macromolecular chain scission takes place. The evolution of the overlayer thickness and its bonding has been investigated in detail. Also, the study of the surface nano-topography of polycarbonates by atomic force microscopy showed that plasma treatment increases the surface roughness.     

Compatibilization and property enhancement of poly(lactic acid)/polycarbonate blends through triacetin-mediated interchange reactions in the melt

Tetrabutylammonium tetraphenylborate (TBATPB) and triacetin were added during extrusion to melt blends of polylactic acid (PLA) and polycarbonate bisphenol A (PC) through a reactive compatibilization approach in order to enhance the materials' mechanical properties and thermal resistance. Dynamic mechanical thermal analysis revealed a new peak attributable to the glass transition temperature (T_g) of the PLA-PC copolymer at a temperature lower than the T_g typical of PC and higher than the T_g of PLA. The results of tensile tests, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy, size exclusion chromatography, and NMR analysis for the compatibilized and uncompatibilized blends were, on the whole, in agreement with the formation of the PLA-PC copolymer due to the action of the TBATPB and triacetin during the short extrusion time. The mechanical behaviour, morphology, and thermal properties of the PLA/PC compatibilized blends were investigated as a function of composition, with the intention of broadening the utility of these biobased-blends. Finally, a general scheme for the reactions that occur during extrusion was proposed based on the experimental results.     

Supercritical CO2 and polycarbonate based nanocomposites: A critical issue for foaming

Supercritical carbon dioxide readily induced foaming of various polymers. In that context, supercritical CO₂ was applied to carbon nanotubes based polycarbonate nanocomposites to ensure their foaming. Surprisingly, efficient foaming only occurs when low pressure is applied while at high pressure, no expansion of the samples was observed. This is related to the ability of supercritical carbon dioxide to induce crystallization of amorphous polycarbonate. Moreover, this behaviour is amplified by the presence of carbon nanotubes that act as nucleating agents for crystals birth. The thermal behaviour of the composites was analysed by DSC and DMA and was related to the foaming observations. The uniformity of the cellular structure was analysed by scanning electron microscopy (SEM). By saturating the polycarbonate nanocomposites reinforced with 1 wt% of MWNTs at 100 bar and 100 °C during 16 h, microcellular foams were generated, with a density of 0.62, a cell size ranging from 0.6 to 4 μm, and a cellular density of 4.1 × 10¹¹ cells cm⁻³. The high ability of these polymeric foams to absorb electromagnetic radiation was demonstrated at low MWNT content as the result of the high affinity of the polycarbonate matrix for MWNTs, and therefore to the good MWNTs dispersion.     

Flow induced orientation of multiwalled carbon nanotubes in polycarbonate nanocomposites: Rheology, conductivity and mechanical properties

We investigated the effect of flow field and deformation rate on the nanotube alignment and on the properties of PC/multiwalled carbon nanotube nanocomposites. Samples of various MWCNT loadings were prepared by diluting a commercial masterbatch containing 15 wt% nanotubes using optimized melt mixing conditions. Different processing conditions were then used to systematically change the degree of nanotube alignment, from random orientation to highly aligned. Morphological studies and Raman spectroscopy analysis revealed that the nanotubes are preferentially aligned in the flow direction, particularly at large injection or compression rates. Rheological measurements corresponding to high shear rate conditions showed drastic changes in the viscoelastic behavior. The complex viscosity significantly decreased and percolation threshold notably rose. High degrees of nanotube alignment also resulted in a significant increase in the electrical percolation threshold. The mechanical properties of the nanocomposites for different nanotube loadings were also shown to depend on the processing conditions, and somehow improved when the material was processed at higher rates. Finally, we used a power-law type equation to correlate the percolation behavior and the nanotube alignment. The estimated percolation threshold and the power index, q, significantly increase with the degree of nanotube alignment as determined by Raman analysis.     

A kinetic study of the isothermal degradation process of Lexan® using the conventional and Weibull kinetic analysis

The degradation process of commercial grade Lexan® was investigated by thermogravimetric technique under isothermal experimental conditions at four different operating temperatures: 375 °C, 387.5 °C, 400 °C and 425 °C. The kinetic triplet (E _a , A, f(α)) was determined using conventional and Weibull kinetic analysis. The applied kinetic procedure shows that the investigated degradation process can be described by two-parameter autocatalytic ?esták–Berggren (SB) reaction model. It was established that the degradation process of Lexan® can be described by the following kinetic triplet: E _a? =?158.3 kJ mol^?1, A?=?8.80?×?10⁹ min^?1 and f(α)?=?α ^0.33 (1???α)^1.62. It was established that the operating temperature has an influence on the values of SB reaction orders (m and n) (0.27?m?n??1, represent the composite value from a complex degradation reaction and can not compare with the dissociation energy of the weak bonds in bisphenol-A polycarbonate. Also, it was concluded that the Weibull shape parameter (β) shows that the considered process occurs under the same reaction mechanism, independently on operating temperature (T), i.e. the change of rate-limiting step does not occur (β?ddf) of apparent activation energies for considered degradation process. On the other hand, it was shown that the experimentally evaluated density distribution function of apparent activation energies represents the intermediate case between the calculated density distribution functions at 375 °C and 425 °C.     

Effect of detergents in the release of bisphenol A from polycarbonate baby bottles

Bisphenol A (BPA) is a monomer crucial for the production of polycarbonate (PC). Recently, it has been verified that BPA is able to migrate from PC baby bottles into food simulants and numerous studies indicate that BPA may affect human health.In this work, five different detergents and bleach were tested to verify if they were able increasing the BPA release from the PC. High performance liquid chromatography (HPLC) with fluorescence detection (FLD) and gas chromatography coupled to mass spectrometry (GC–MS) were used to quantify and identify BPA. Of all detergents tested, only with one was not detected a BPA concentration higher than the control. In the worst case, BPA levels detected were about 500 times higher than the control and the concentration kept high even after rinsing the PC samples three times. In the case of bleach, while it was in contact with the PC, the BPA released was not detected.     

Synthesis and properties of segmented copolymers containing short aramid hard segments and aliphatic polyester or polycarbonate soft segments

Segmented copolymers based on poly(ethylene adipate) or poly(hexamethylene carbonate) soft segments and short terephthalamide or 2,6-naphthalenedicarboxamide hard segments were prepared by a condensation polymerisation in solution. The polymers were characterised by NMR, IR, GPC, DSC, DMTA and tensile tests. A comparison of several soft segments revealed that the polyester soft segment led to materials with relatively poor elastic recovery, whereas the polymers possessing short aramid hard segments and polycarbonate soft segments showed high elongations at break (820-940%) and good tensile set values (38%).     

Study of the deposition parameters and Fe-dopant effect in the photocatalytic activity of TiO2 films prepared by dc reactive magnetron sputtering

The reactive magnetron sputtering method was used to prepare pure and Fe-doped titanium dioxide thin films. The films were deposited onto microscope glass slides and polycarbonate plates at different total pressure and Fe-doping concentrations. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-visible spectroscopy (UV). For glass substrates a polycrystalline TiO₂ structure was verified with X-ray diffraction, which showed typical characteristic anatase reflections. An iron phase appeared in the highly Fe-doped samples. The absorption edges of the Fe-doped TiO₂ films shifted to visible region with increasing concentration of iron. For the polycarbonate substrate an amorphous TiO₂ structure was revealed for all deposition conditions. The effects of different Fe-doping and total pressure levels on the photocatalytic activity were obtained by the degradation rates of Rhodamine-B (RoB) dye under UV light irradiation. For the deposition conditions considered in this study the highest photodegradation rates were achieved for films deposited on the polymer substrates. Of these overall highest rates was achieved for deposition at 0.4 Pa and without doping. However, for both substrates, films prepared at the particular total pressure of 0.5 Pa and a low iron concentration showed better photocatalytic activity than the pure TiO₂ films prepared under the same deposition parameters. On the contrary, the photocatalytic degradation rates of RoB on the highly Fe-doped TiO₂ films decreased strongly.     

聚碳酸酯改性环氧树脂的固化动力学与热性能研究

用动态DSC法研究了聚碳酸酯(PC)改性环氧树脂(EP)体系的固化行为,采用Flynn-Wall-Ozawa法分析了EP/PC体系固化活化能与转化率的关系,利用Kissinger和Crane方程研究了EP/PC体系固化动力学参数,并用TG和DSC研究了复合体系的热性能。结果表明:PC的加入没有改变EP的固化机理,反应级数基本不变,但是降低了EP固化物的热分解温度和玻璃化转变温度。     

Miscibility study of polycarbonate and SBS triblock copolymer blends

Polymer blends of Polycarbonate (PC) and Styrene-Butadiene-Styrene triblock (SBS) have been investigated. SBS copolymers have four different styrenic contents, three of which are linear SBS. PC and PS blends are partially miscible as revealed by dynamic mechanical analysis with two clear Tgs near 100–150°C. On the contrary, PC/SBS blends have only one Tg with a left shoulder. Based on the PS domain model of pure SBS, we suggest a micelle model based on the structure when the micelle and absorb PC in the PC/SBS blends. The micelle plays an important role in improving the miscibility. The proposed micelle model has been empolyed to interpret the testing results, such as toughness, impact strength, dynamic mechanical property and SEM morphologies. This proposed micelle model seems a worth-while method to explain the properties of partialtly miscible blends of PC and SBS.