Polycarbonate Phase Research Articles

Reactive dual‐component compatibilizers for polycarbonate/high‐density polyethylene blends

AbstractEnhanced compatibility for blends of polycarbonate with high‐density polyethylene has been achieved with the addition of 5 wt% compatibilizers composed of 1 : 1 mixtures of phenoxy and the sodium ionomer of an ethylene methacrylic acid copolymer at two different levels of neutralization. Both components of the compatibilizer have been found to be capable of reacting with the polycarbonate phase to produce branched polymer chains. These impart a degree of compatibilization in polycarbonate/high‐density polyethylene blends, however at higher levels of sodium in the compatibilizer the polycarbonate phase undergoes crosslinking reactions, causing severe embrittlement. Compatibilization effects are confirmed by morphological examinations, dynamic rheological data, and dielectric loss spectra. © 1995 John Wiley & Sons, Inc.

Dielectric properties of blends of polycarbonate and acrylonitrile‐butadiene‐styrene copolymer

AbstractThe low frequency dielectric properties of polymeric blends of polycarbonate (PC) and acrylonitrile‐butadiene‐styrene (ABS) were studied in the temperature interval of 100 to 170°C. Attention was focused on a 60/40 (m/m) PC/ABS blend. The results were compared with dynamic mechanical measurements in torsion and with the results of a morphological investigation using scanning electron microscopy (SEM). Besides the relaxations at the glass transition temperatures of the components an additional strong low frequency dielectric dispersion was observed, which was not found in mechanical measurements. This low frequency polarization process is due to interfacial polarization at the boundaries between conductive ABS and non‐conductive or slightly‐conductive PC. It is shown how this process can be described by the dielectric models for two‐phase heterogeneous materials. The Looyenga model offers the best description of the detected effects, while the Hanai model is less suitable. The shape factor of the ABS phase as used for modeling the dielectric properties agrees well with the observed morphology using SEM. It is shown for the dielectric measurements on the 75/25, 60/40, and 45/55 (m/m) PC/ABS blends how the connectivity of the ABS phase can be sensitively derived from the eletrical conductivity of the blend, whereas mechanical measurements are highly senstive to the connectivity of the PC phase.

Dynamic nuclear polarization enhanced nuclear magnetic resonance of polymer-blend interfaces

Heterogeneous blends of [3,3′- 13C 2]polycarbonate and [uniform-ring- 12C 6]polystyrene were formed by serial film casting. The polystyrene phase of each blend was homogeneously doped with 2% by weight of a bis (diphenylene) phenylalyl free-radical complex with benzene. Proton polarization enhanced by dynamic nuclear polarization was generated in the polycarbonate phase by dipolar coupling to electrons in the polystyrene phase under 39 GHz microwave irradiation at the difference of the electron and proton Larmor frequencies. Proton magnetization was then transferred to carbons under matched spin-lock conditions for detection with chemical-shift selectivity by magic-angle spinning 13C nuclear magnetic resonance. The 13C signal from polycarbonate arises exclusively from chains which are at the polycarbonate-polystyrene interface. Signals from bulk polycarbonate were suppressed by differencing techniques. The dominant mechanism of polarization transfer from the electrons in the polystyrene phase to the protons in the polycarbonate phase is by direct polarization transfer. The interface signal arises from a 60 Å region which is 2% of the film thickness. As monitored by dynamic nuclear polarization selected dipolar rotational spin-echo 13C nuclear magnetic resonance, polycarbonate chains have less motion at the interface than in the bulk.

Herringbone fracture of a polycarbonate/ABS blend

Tensile fracture mechanisms in single edge notched injection-moulded specimens of a polycarbonate/ABS 30/70 wt% blend have been studied by fractography. When the tensile force was applied parallel to the injection direction, a herringbone pattern could be observed on the fracture surface, while for the perpendicular case, a reverse herringbone pattern was seen. At the same testing condition, the former was tougher than the latter. Fracture images and two-dimensional temperature profiles in the thickness direction were used to locate the crack initiation sites. Herringbone fracture occurred when the main crack repeatedly interacted with secondary cracks initiated along the centreline. Reverse herringbone fracture was formed in a similar mechanism but secondary cracks initiated near the edge. Anisotropy of the fracture modes was attributed to the processing-induced orientation of the polycarbonate phase near the edge.

Thermal degradation of blends of PVC with bisphenol A polycarbonate

The thermal degradation of blends of PVC with bisphenol A polycarbonate has been studied by thermogravimetry and thermal volatilisation analysis. In the TG experiments, both programmed heating and isothermal heating (at 280°C) were used and the full composition range from PVC to polycarbonate was examined. In the TVA experiments, blends of equal weights of the polymers were employed and the volatile and tar wax fractions of products were both studied. As initial separation of the volatile product fraction by subambient TVA was used to assist product identification, which was based on IR and MS methods. In the degradation of the blends, the PVC is slightly stabilised, but there is a considerable destabilisation of the polycarbonate. The latter phenomenon has been explained in terms of a reduction in molecular weight in the temperature region in which dehydrochlorination is occurring due to migration of chlorine radicals from the PVC phase to the polycarbonate phase, where hydrogen abstraction from methyl groups in the polycarbonate is believed to occur.

Selective observation of the interface of heterogeneous polycarbonate/polystyrene blends by dynamic nuclear polarization carbon-13 NMR spectroscopy

Heterogeneous blends of [3,3' -13 C 2 ] polycarbonate and [ul-ring- 12 C 6 ] polystyrene were formed by serial film casting. The polystyrene phase of each blend was homogeneously doped with 2% by weight of a bis (diphenylene) phenylallyl free-radical complex with benzene. Proton polarization enhanced by dynamic nuclear polarization was generated in the polycarbonate phase by dipolar coupling to electrons in the polystyrene phase under 39-GHz microwave irradiation at the difference of the electron and proton Larmor frequencies

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

AbstractThe 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.

Preparation of composite dispersed phase morphologies in incompatible and compatible blends during melt processing

Most processing/morphology studies of multi-phase polymer blends have been concerned with controlling the size and shape of the dispersed phase. The dispersed phase is generally a pure homo- or copolymer (apart from low levels of interfacial modifier). This paper describes the preparation during melt processing of a complex polymer blend morphology known as a composite dispersed phase system. Microscopically this structure can be seen to be composed of three parts: two distinct phases with sub-inclusions within one of the phases. This system is a type of blend within a blend. Various microscopic techniques are used to show that a composite multi-phase morphology can be prepared in an incompatible polypropylene/ polycarbonate (PP/PC) blend as well as in a compatible polyethylene copolymer/polyamide blend. This structure has been generated at two compositions for polypropylene/ polycarbonate through melt blending. At 50% volume fraction (near the region of dual-phase continuity), simultaneous addition of components results in co-continuous polypropylene and polycarbonate phases with the latter containing small PP spherical sub-inclusions. At 25% PC (volume fraction) the generation of a composite dispersed phase in a polypropylene matrix is obtained by imposing phase inversion followed by controlling the mixing time. The morphology in this case consists of a polypropylene matrix, a polycarbonate dispersed phase and spherical polypropylene sub-inclusions within the dispersed polycarbonate. Partial stabilization of the composite morphology in incompatible blends with mixing time can be obtained through control of the viscosity of the dispersed phase. Polyethylene copolymer/polyamide blends have also been prepared by the phase inversion process and show that strong interfacial interactions between the polyamide sub-inclusions and polyethylene copolymer dispersed phase material results in complete stabilization of the composite dispersed phase morphology with very high retention of sub-inclusions persisting even after long mixing times.

Phase morphology of injection-moulded polycarbonate/acrylonitrile-butadiene-styrene blends

The morphology of injection-moulded blends of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) has been examined across the entire composition range. Brittle fracture surfaces were etched to remove selectively the PC phase and viewed in the scanning electron microscope. Morphological features observed through the thickness of injection-moulded plaques were the basis for the identification of three composition ranges. In PC-rich blends, the ABS phase formed a bead-and-string structure oriented in the injection direction near the edge, while in the centre the ABS was dispersed as rubber domains and spherical particles of free styrene-acrylonitrile (SAN). A transition occurred between PC/ABS 70 30 and 60 40 wt% compositions from the bead-and-string structure with some interconnections to a coalesced, stratified morphology near the edge; while in the centre, the morphology changed from a dispersion of rubber particles and free SAN particles to thick coalesced ABS domains that created regions where ABS was co-continuous with PC. The ABS-rich blends had a conventional blend morphology with PC domains dispersed in ABS. Qualitatively, the solid-state morphology could be explained in terms of the melt morphology created by the melt flow pattern during mould filling, and subsequent relaxation during cooling prior to solidification.

Polystyrene/Polycarbonate/Polystyrene‐block‐Polycaprolactone blends. Emulsification and mechanical performance

AbstractTwo polystyrene–polycaprolactone diblock copolymers, of differing molecular weights, have been extrusion‐blended with polystyrene and polycarbonate. The morphologies of the resultant blends were studied using differential scanning calorimetry and scanning electron microscopy. In all compositions studied, the polystyrene and polycarbonate phases exhibited discrete glass transitions indicative of the immiscibility of these components. However, addition of the copolymer increased the extent of dispersion of the homopolymer components within one another quite effectively. Blend specimens were tested with respect to tensile, flexural, impact, thermal, and flow characteristics to probe the effects of morphology and composition on these factors. In general, the blends were rigid, brittle materials with thermal characteristics in the range between those of the polystyrene and polycarbonate components. Addition of polystyrene‐block‐polycaprolactone polymer to the blends resulted in increased brittleness, reduced thermal performance, maintenance of rigidity, and improved flow.

Blends of polycarbonate and polyacetal

Immiscible blends of polycarbonate (PC) and polyacetal (polyoxymethylene, POM) were investigated through rheological measurements, tensile, impact, TEM, SEM, FTi.r. and thermal analysis. The large difference in melt viscosities between these two matrix polymers makes this blending system extremely difficult to process and results in partial thermal degradation of POM. The formation of a strong interpenetrating interface in PC/POM blends significantly raises tensile yield strength, modulus and heat distortion temperature above the average values for the individual polymers. Thermoplastic polyurethane elastomer is not very efficient in toughening PC/POM blends because the elastomer distributes selectively in the PC phase. The rheological morphologies of the blends are interpreted through TEM and SEM photomicrographs.

Mechanical behavior related to the phase morphology of PC/SAN polymer blends

AbstractThe phase morphology of intensively melt mixed and injection moulded bisphenol‐A polycarbonate (PC)/styrene‐acrylonitrile copolymer (SAN) blends changes on annealing above the glass‐transition temperature (Tg) of both components. For the selected PC and SAN resins, the phase morphology of the 60/40 PC/SAN blend changes from a fine dispersion of the PC phase in a SAN matrix to a coarse co‐continuous phase network, whereas a co‐continuous 70/30 PC/SAN blend changes to a dispersion of SAN domains in a PC matrix. The effect of the blend morphology on dynamic mechanical properties and ambient tensile stress‐strain properties have been studied thoroughly. An increase of the storage modulus between Tg(SAN) and Tg(PC) is observed with increasing coarsening of the phase structure until a continuous PC matrix is formed. The coarsening of the phase structure of the blends gives rise to a transition from ductile to brittle fracture. The loss in ductility is related to a decrease in relative amount of interface and a transition in the type of dispersion.

Blends of polyamide 6 with bisphenol‐A polycarbonate. I. Thermal properties and compatibility aspects

AbstractBlends of polyamide 6 (PA6) and polycarbonate (PC) have been investigated, over a full range of composition, to check interactions between them. SEM observations show that the mixtures are characterized by domains of clearly segregated homophases and voids between the two polymers. DSC and DMTA data indicate the presence of two Tg' s, corresponding to two separate phases, with the Tg of the PC phase decreasing on increasing the PA6 amount. Moreover, the crystallization kinetics of PA6 is slightly showed down by the PC. Chemical reactions between the two polymers are supposed to give rise to low molar mass compounds, as shown by GPC; these species plasticize the PC and partially dissolve into the molten polyamide, causing decrease of PC Tg and reduction of overall crystallization rate of PA6. Apparent influence of PC on melting temperature and enthalpy of PA6 is also discussed.

Thermal behavior, morphology, and the determination of the Flory–Huggins interaction parameter of polycarbonate–polystyrene blends

AbstractBlends of bisphenol‐A polycarbonate (PC) and polystyrene (PS) prepared by screw extrusion and solution casting have been investigated with weight fractions of PC in the blends varying from 0.95 to 0.05. From the measured glass transition temperatures (Tg) and specific heat increments (ΔCp) at the Tg, the polystyrene appears to dissolve more in the PC phase than does the PC in the PS phase. The blend appears to be near eqilibrium under extrusion conditions so that the polymer–polymer interaction parameter of PC/PS blends was calculated and found to be 0.038±0.004 for extruded blends at 250°C. Scanning electron microscopy supports the conclusion that the compatibility increases more in the region of PS‐rich compositions than in the regions of PC‐rich compositions of the PC/PS blends.

The morphology and deformation behavior of poly(butylene terephthalate)/BPA polycarbonate blends

In this communication the results of a series of recent studies of the morphology and deformation behavior of toughened poly(butylene terephthalate) (PBT)/BPA polycarbonate (PC) blends are briefly summarized. Several papers containing a more detailed account are currently in press (1–3). Among the unique morphological features of these blends are the consistent isolation of the core/shell impact modifier (IM) in the PC phase and the crystallization and phase separation of the PBT from the partially miscible PBT/PC melt on slow cooling. DSC studies provide corroborating evidence for melt miscibility of the two resins. The blends deform through a combination of cavitation and shear processes. In all cases cavitation occurs exclusively within the IM particles and is suppressed at higher PC concentrations and elevated temperatures.

Microscopy techniques used in polymer research

AbstractMicrostructural analyses with optical and scanning electron microscopy can identify processing variables that lead to less than optimum mechanical properties of molded and friction welded polymer components. Delineation of the major phase arrangements in blends of polycarbonate (PC) and poly(butylene terephthalate) (PBT) was key to identifying stress concentrations and internal defects. Phase separations, crystalline arrangement, structure refinements, and shear stresses introduced during molding or friction welding were evident and help to explain the unpredictable impact fracture mode and strength. The techniques help identify when the brittle ribbonlike PC phase extends to the surface without being encapsulated or surrounded by the PBT phase.

Viscoelastic and thermal behaviour of partially compatible polymer blends polycarbonate/tetramethylpolycarbonate

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) measurements show that, in the case of polycarbonate (PC) with tetramethylpolycarbonate (MPC), the homopolymers are miscible up to 70% PC weight fraction; at higher PC content, an additional PC phase appears. The partial miscibility of PC and MPC has been confirmed by ultrasonic attenuation measurements and scanning electron microscopy. The viscoelastic behaviour of these blends has been correlated with the blend composition and compatibility. The free volume contraction, found to explain the variations of glass transition temperature and viscosity with concentration, suggests strong intermolecular interaction in the compatible range.

Damping modulus studies of poly(dimethylsiloxane)‐bisphenol‐a‐polycarbonate block copolymers

AbstractRandom multiblock copolymers of bisphenol‐A‐polycarbonate and poly(dimethylsiloxane) were hot‐pressed or solvent cast into films which were studied by dynamic mechanical methods over the range 11 to 110 hertz (Hz) and 100 to more than 2200 Hz, respectively. The samples were studied also by differential‐scanning calorimetry. The two phases are separated well in spite of the low‐molecular weights of the blocks. This separation is altered by thermal history and by the solvent medium when solvent casting is used to prepare the films. The damping properties do not vary greatly with frequency. Damping is greatest near the glass‐transition temperatures of the two components. The expansion of the block copolymer with heat appears to be retarded by the polycarbonate phase until the glass transition of that phase is approached.

Phase structure and properties of polymethyl methacrylate-polycarbonate mixtures

Abstract Special features of the phase structure in PMMA-polycarbonate mixtures were studied according to composition and molar mass of PMMA. It was shown by electron-microscopy that the mixture is two-phase in the range of 0·5–99·5 wt.% polycarbonate, phase inversion taking place with 50–70 wt.% polycarbonate. When the mixture contained over 30 wt.% polycarbonate, transition occurred from the droplet dispersion to band, or layer structure, which resulted in the appearance of pearly lustre. Properties of the mixture are determined both by phase structure and structural disintegration of the polycarbonate phase in the mixture.

Phase equilibrium and glass‐transition temperatures in plasticized amorphous bisphenol‐A polycarbonate

AbstractGlass‐transition temperatures and phase separation have been studied in amorphous bisphenol‐A polycarbonate plasticized with pentaerythritol tetranonanoate (PETN), trimellitic acid, tridecyloctyl ester (TMDO), and tritolyl phosphate. (TTP). Phase separations occur with partially compatible plasticizers like PETN or TMDO. With PETN, for compositions situated in the miscibility gap, the system is composed of a pure plasticizer phase and of a plasticized polymeric phase characterized by a transition temperature of 110°C. In the case of TMDO and additional phase separation occurs below 55°C and two plasticized polycarbonate phases are observed. In compositions falling in the region where the could point curve crosses the glass‐transition diagram the phase separation may be delayed by quick cooling. TTP is completely compatible with polycarbonate and the variation of the glass‐transition temperature follows a Gordon and Taylor equation.