Glass Transition Temperature Of Polycarbonate Research Articles

Interactions of a liquid crystalline polymer with polycarbonate and poly(ethylene terephthalate)

Thermal behaviour of blends of a liquid crystalline copoly(ester amide) (Vectra B950) with two isotropic polymers has been studied by differential scanning calorimetry. One of the isotropic polymers is an amorphous polymer – polycarbonate, the other is a semi-crystalline polymer – poly(ethylene terephthalate). It was found that the glass transition temperature of polycarbonate decreases with increasing Vectra concentration in the blend, suggesting a partial miscibility between the Vectra liquid crystalline polymer (LCP) and polycarbonate. The miscibility is enhanced through heat treatment at elevated temperatures presumably due to a transesterification reaction. Moreover, the presence of the amorphous poly- carbonate hinders the crystallization of the liquid crystalline polymer in the blends. It was also observed that heat treatment of the Vectra LCP and poly(ethylene terephthalate) blends causes a loss in crystallinity and shifts in transition temperatures of poly(ethylene terephthalate), indicating that exchange reactions occur between Vectra B950 and poly(ethylene terephthalate). Based on these results, a new strategy, in situ compatibilization, is proposed to improve the interfacial adhesion between an LCP and an isotropic polymer.

Thermal characterization and morphological study of polyphenylene sulfide–polycarbonate blends

AbstractThe thermal behavior and phase morphology of binary blends of poly(phenylene sulfide) (PPS) with polycarbonate (PC) have been investigated. Differential scanning calorimetry and dynamic mechanical thermal analysis indicate the blends are immiscible, but the glass transition temperature of PC in the blends was found to be decreased due to the degradation of the PC. The PC degradation was investigated by measuring the molecular weight of PC extracted from the blends. Rheological properties of the blends were also studied using a rheodynamic spectrometer. An inversion of the phase morphology was observed from the scanning electron microscopy and dynamic mechanical thermal analysis. The increase of crystallinity of the PPS in the blends was found from a DSC study.

Influence of reprocessing on properties of polycarbonate

The influence of reprocessing by injection moulding on properties of polycarbonate has been studied. It was found that reprocessing does not affect the tensile strength, flexural strength and flexural modulus of the polycarbonate material. Fracture parameters such as fracture toughness and the material resistance to crack propagation, also showed no variation with the number of reprocessing cycles, although both were strongly dependent on sample width. Dynamic mechanical analysis (DMA) also indicated that reprocessing has no significant effect upon dynamic mechanical properties of polycarbonate. Results further indicated that the glass transition temperature of polycarbonate is not affected by reprocessing, only the range over which it occurs seems to be broadened by reprocessing due to increase in molecular weight with number of reprocessing cycles.

Acetone Absorption in Irradiated Polycarbonate

Acetone absorption in irradiated polycarbonate was investigated. The molecular weight and glass transition temperature of polycarbonate decreased with increasing the γ-ray dose. Experimental data obtained from acetone transport in polycarbonate with various doses correlated sufficiently well with Harmon's model which was accounted for case I, case II, and anomalous transport. The diffusion coefficient for case I, velocity for case II, and diffusion coefficient for diffusion front satisfied the Arrhenius plot for all γ-ray doses. The equilibrium solubility satisfied the van't Hoff plot regardless of the γ-ray dose. Additionally, in the low-temperature range activation energies of case I, case II and the diffusion front, and the heat of mixing were found to have the same value for doses greater than 100 kGy which was different from those for unirradiated polycarbonate. This observation implied that acetone transport in irradiated polycarbonate occurs via the same mechanism for doses greater than 1000 kGy. The equilibrium solubility and diffusion coefficient for diffusion front at a given temperature were the same for all doses in the high-temperature range.

A study of creep and creep rupture of polycarbonate

AbstractThe creep characteristics of polycarbonate at elevated temperatures are investigated. The onset of glass transition temperature of polycarbonate is determined. An Arrhenius type relationship is used to describe the creep process and the concept of property retention index as applied to creep is discussed. An attempt is made to construct the master rupture curves for polycarbonate. The onset of glass transition temperature of polycarbonate was placed at around 110°C. It is concluded that the Arrhenius theory and the concept of property retention index are extremely useful in the construction of master rupture curves and that they require further investigation.

Carbon tetrachloride‐induced crack healing in polycarbonate

AbstractCrack 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.

Thermal aging of impact‐modified polycarbonate

AbstractGlassy polymers undergo relatively rapid physical aging just below their glass transition temperatures that can lead to embrittlement of normally tough materials like polycarbonate (PC). One approach for solving the embrittlement problem is to incorporate an impact modifier that can cause toughening when the matrix loses its inherent ductility due to physical aging. The effects of thermal aging below the glass transition temperature of polycarbonate on selected properties of blends of PC with various core‐shell impact modifiers have been studied. Observed changes in mechanical properties are related to rubber content, free volume, fracture morphology, discoloration, enthalpy relaxation, glass transition temperature, intrinsic viscosity, and dynamic mechanical behavior. Blend mechanical properties are affected by chemical changes in the impact modifier that occur simultaneous with the physical aging of the PC matrix. The degradation mechanisms involved reduce the effectiveness of the modifier for toughening and also lead to a loss of molecular weight of the PC matrix. Blends containing 10% methacrylated butadiene‐styrene (MBS) core‐shell impact modifiers give the maximum extension of time to embrittlement at 135°C in air. More thermally stable modifiers are required for further extending the ductile mode of failure for physically aged PC blends.

Formation and break-up of a bead-and-string structure during injection moulding of a polycarbonate/acrylonitrile-butadiene-styrene blend

The morphology gradient through the thickness of an injection-moulded blend of 10% by weight acrylonitrile-butadiene-styrene (ABS) and 90% by weight polycarbonate (PC) has been characterized. Brittle fracture surfaces were etched and examined both parallel and perpendicular to the injection direction in the scanning electron microscope. In the centre of the plaque, the morphology was isotropic with the ABS phase dispersed in the PC matrix as large composite rubber particles about 1 μm in diameter and smaller particles of free styrene-acrylonitrile (SAN) about 0.3 μm in diameter. About half the distance from the centre to the edge, the morphology of the free SAN phase changed from predominantly spherical to predominantly string-like. The SAN strings connected the rubber particles to form an oriented ABS bead-and-string structure that was essentially continuous in the injection direction. It was thought that the free SAN was highly extended under elongational or shear flow while remaining attached to the rubber particles because of miscibility with grafted SAN. The bead-and-string structure was retained near the edge where the melt solidified most rapidly. In the centre of the plaque, the low shear rate during mould filling and longer cooling time after mould filling favoured relaxation of the bead-and-string structure. The morphology gradient through the thickness was created by the competition between the relaxation rate and the cooling rate after mould filling. In this case, relaxation was thought to occur by interfacial-tension-driven break-up and end-pinching mechanisms to produce the dispersion of rubber and free SAN particles. Evidence to support the break-up mechanism was obtained when annealing above the glass transition temperature of PC for a matter of seconds, the timescale of mould cooling, caused the bead-and-string structure to convert to a dispersion of composite rubber particles and SAN particles.

Studies of the thermal and crystallization behaviour of polyphenylene sulphide/polycarbonate blends

Blends of polycarbonate (PC) and polyphenylene sulphide (PPS) of five different ratios were prepared and the thermal properties of these blends were studied using differential calorimetry (DSC) and thermogravimetry (TG). It was found that PC was partially miscible with PPS as evidenced by the decrease in the melting point of PPS and the glass transition temperature of PC. The other thermal properties such as the onset of melting temperature, the heat of fusion and the heat of crystallization were also studied. The density and melt flow index (MFI) of all the blends were studied to determine their processibility. Degradation kinetics and activation energies were computed by the Broido method.

Influence of molecular weight distribution and long chain branching on the glass transition temperature of polycarbonate

Molecular weight distribution and long chain branching were taken into account for the glass transition temperature ( Tg)-molecular weight ( M) relationships for bisphenol-A polycarbonate. A new form of the four-variable equation for Tg is proposed for polydisperse branched polymers. The extended equations were compared with the experimental results on Tg and M averages; they were also applied for characterization of branched polymer by the combined GPC/V and DSC methods.