A series of polycarbonate-poly(butylene terephthalate) blends has been formed via melt blending in a torque rheometer. Initially polycarbonate and poly(butylene terephthalate) were blended alone to determine the extent to which the two homopolymers were able to cross-react (transesterify), and hence, how the morphology of the blends developed as a result of transesterification. Subsequently the degree of transesterification between the two homopolymers was controlled by the incorporation of an alkyl titanium catalyst, and the effect on morphological development determined. Resultant uncatalysed and catalysed materials were characterised by DSC, DMA, FTIR, microscopy, solubility studies and X-ray scattering. No evidence for direct inter-chain transesterification was seen for the uncatalysed blends. No new thermal transitions or absorptions were noted from DSC, DMA or FTIR, nor was there any evidence for phase refinement from microscopy, or variation in solubility behaviour. However, there was evidence for some degree of phase mixing from DMA damping behaviour, indicated by convolution of the PC and PBT transition peaks. Due to the lack of transesterification relatively coarse morphologies, indicative of an immiscible two phase blend, were apparent from microscopical analysis. Thermal behaviour of the uncatalysed blends showed evidence of thermal degradation above 270°C, promoting transesterification via acidolysis. As the degree of transesterification was increased (catalysed materials) the composition of the blends became increasingly complex, comprising mixtures of the homopolymers and various AB-type block copolymers of polycarbonate and poly(butylene terephthalate), with concomitant changes in their thermal behaviour. DSC and FTIR proved useful in analysing blends containing greater than 150 ppm of added catalyst, whilst DMA highlighted the subtle differences in the blends with less than 200 ppm additional titanium transesterification catalyst. Microscopical analysis provided visual evidence for the transformation in the materials morphology through progressive transesterification: the relatively coarse structure characteristic of two phase blends developing into a more refined sub-micron iv structure exhibited by blends containing a significant volume of interphase material. This morphological change was due to the formation of increasing concentrations of random block copolymers. At increasing degrees of transesterification this change in morphology was accompanied by variations in the solubility of the blends. With increasing amounts of additional catalyst up to 150 ppm, the blends became increasingly resistant to solvent (dichloromethane). Whereas above this level the blends became increasingly soluble, as copolymers of a more random nature (with increased solubility) were formed. X-ray scattering showed the pure PBT to exhibit highly reproducible crystallisation behaviour. In contrast a 50/50 blend showed a progressive reduction in the degree of crystallinity, melting and crystallisation temperatures with increasing transesterification.

Abstract The degree of homogeneity and H-bond interaction in blends of low-molecular-mass poly(ethylene glycols) (PEG, Mw = 400, 600, 1000) and poly(vinylpyrrolidone) (PVP, Mw =9×103) prepared in supercritical CO2, ethanol and as physical mixtures were studied by differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy and dynamic mechanical analysis (DMA) techniques. Homogeneity of samples prepared in supercritical CO2 were greater than physically mixed samples, but slightly less than ethanol-cast samples. PEG–PVP H-bond interaction was higher for ethanol-cast blends when compared to blends prepared in supercritical CO2. This reduced interaction was attributed to a combination of: (1) shielding of PEG–PVP H-bond interactions when CO2 is dissolved in the blend; (2) rapidly reduced PEG and PVP chain mobility upon CO2 venting, delaying rearrangement for optimum PEG–PVP H-bond interaction.

Rheological and processing behavior of a number of linear low-density polyethylene(LLDPE)/low-density polyethylene (LDPE) blends was studied with emphasis on the effects of long chain branching. First, a linear low-density polyethylene (LL3001.32) was blended with four LDPE's having distinctly different molecular weights. At high LDPE weight fractions, DSC melting thermograms have shown three different polymer phases; two for the pure components and a third melting peak of co-crystals. Different rheological techniques were used to check the thermo rheological behavior of all blends in the melt state and the effect of long chain branching. It was found that all blends are miscible in the melt state at small LDPE concentrations. The elongational behavior of the blends was studied using a uniaxial extensional rheometer, SER. The blends exhibit strain hardening behavior at high rates of deformation even at LDPE concentrations as low as 1%, which suggests the strong effect of branching added by the LDPE component. On the other hand, shear rheology was found to be insensitive to detect addition of small levels of LDPE up to lwt%. The second set of blends prepared and studied consisted of two Ziegler-Natta LLDPE's (LL3001.32 and Dowlex2045G) and two metallocene LLDPE's(AffinityPL1840 and Exact 3128) blended with a single LDPE. In DSC melting thermograms, it was observed that blends with metallocence LLDPE's exhibit a single melting peak at all compositions; whereas the Ziegler-Natta blends exhibit three melting peaks at certain compositions. It was found also that the metallocene LLDPE's are miscible with the LDPE at all concentrations. On the other hand, the Ziegler-Natta LLDPE's were found to be miscible with LDPE only at small LDPE concentrations. The processing behavior of all blends with emphasis on the effects of long chain branches was also studied in capillary extrusion. The critical shear stresses for the onset of sharkskin and gross melt fracture are slightly delayed with the addition of LDPE into LLDPE. Furthermore, the amplitude of the oscillations in the stick-slip flow regime, known as oscillating melt fracture, were found to scale with the weight fraction of LDPE. Amounts as low as 1 wt% LDPE have a significant effect on the amplitude of pressure oscillations. These effects are clearly due to the presence of LCB. It is suggested that the magnitude of oscillations in the oscillating melt fracture flow regime can be used as a method capable to detect low levels of LCB. Finally, the sharkskin and stick-slip polymer extrusion instabilities of a linear low-density polyethylene were studied as a function of the type of die geometry. The critical wall shear stress for the onset of flow instabilities, the pressure and flow rate oscillations, and the effects of geometry and operating conditions on the instabilities are presented for a LLDPE. It was found that sharkskin and stick-slip instabilities were present in the capillary and slit extrusion. However, stick-slip and sharkskin in annular extrusion are absent at high ratios of the inside to outside diameter of the annular die. This observation also explains the absence of these instabilities in polymer processing operations such as film blowing. These phenomena are explained in terms of the surface to volume ratio of the extrudates.

Blends of Poly(ethylene Terephthalate) with Bisphenol-A-Polycarbonate The objective of the study was to determine the extent to which bisphenol-Apolycarbonate (PC) influences the rheology, processing behaviour and subsequent crystallinity and mechanical properties of poly(ethylene terephthalate) (PETP) in the 'compatible' region, when the polycarbonate is the minor blend component. Also, further characterisation of this blend system, in terms of miscibility and micro- structure development was required. After careful drying in a desiccant-type hopper drier melt-phase, blending was carried out using a twin-screw extruder with a purpose-designed screw configuration. Blends were made up at three levels (PETP/PC); 85/15,80/20 and 75/25 using three different molecular weights of PC, and virgid-materials were also included in the study. The extrudates were then dried and injection moulding was carried out under various conditions, which were chosen to modify the degree of order in the crystallisable phase. The effects of PC on the shear-flow behaviour of the blends was examined, and in general the PETP/PC 80/20 blends demonstrated lower shear viscosities than expected from additivity. Otherwise the shear flow behaviour was generally consistent with blend composition. Thermal analysis and crystallisation behaviour of the blends were investigated to determine the effects of PC on the crystallisability of the blend and the PETP T. Solid state isothermal crystallisation behaviour was studied using a modified thermal analysis technique. Crystallisation of the PETP portion of the blend was shown to be impeded by PC. A specific and rapid technique has been developed to determine depth-dependent orientation distributions Three dimensional analyses of birefringence were obtained for moulded plaques of various PETP/PC blends. The orientation distribution was in accordance with the flow pattern during processing and was noticeably planar in nature. However, the level of orientation in the mouldings investigated was very low. Thermal analysis and microscopy techniques indicate there is no evidence for miscibility in the blends. The effect of PC molecular weight and content on mechanical properties of the blend was investigated. Generally, the PETP/PC blends exhibited improved toughness, in terms of total energy absorbed, and the properties were influenced further by the degree of crystallinity. It has been shown that mechanical properties of the blend deteriorate rapidly when samples are stored for extended periods in water at 70'C. Due to the PET? portion in the blends crystallising, and hydrolysis, the samples pass into the brittle mode. The addition of PC to PETP was found to modify the thermoelastic behaviour. Addition of PC permits thermoelastic processing of PETP/PC blends over a wider temperature range than would be suitable for PETR Also, the addition of PC appears to accelerate the onset of strain-induced crystallisation in the PETP.

Rheological and processing behavior of a number of linear low-density polyethylene(LLDPE)/low-density polyethylene (LDPE) blends was studied with emphasis on the effects of long chain branching. First, a linear low-density polyethylene (LL3001.32) was blended with four LDPE's having distinctly different molecular weights. At high LDPE weight fractions, DSC melting thermograms have shown three different polymer phases; two for the pure components and a third melting peak of co-crystals. Different rheological techniques were used to check the thermo rheological behavior of all blends in the melt state and the effect of long chain branching. It was found that all blends are miscible in the melt state at small LDPE concentrations. The elongational behavior of the blends was studied using a uniaxial extensional rheometer, SER. The blends exhibit strain hardening behavior at high rates of deformation even at LDPE concentrations as low as 1%, which suggests the strong effect of branching added by the LDPE component. On the other hand, shear rheology was found to be insensitive to detect addition of small levels of LDPE up to lwt%. The second set of blends prepared and studied consisted of two Ziegler-Natta LLDPE's (LL3001.32 and Dowlex2045G) and two metallocene LLDPE's(AffinityPL1840 and Exact 3128) blended with a single LDPE. In DSC melting thermograms, it was observed that blends with metallocence LLDPE's exhibit a single melting peak at all compositions; whereas the Ziegler-Natta blends exhibit three melting peaks at certain compositions. It was found also that the metallocene LLDPE's are miscible with the LDPE at all concentrations. On the other hand, the Ziegler-Natta LLDPE's were found to be miscible with LDPE only at small LDPE concentrations. The processing behavior of all blends with emphasis on the effects of long chain branches was also studied in capillary extrusion. The critical shear stresses for the onset of sharkskin and gross melt fracture are slightly delayed with the addition of LDPE into LLDPE. Furthermore, the amplitude of the oscillations in the stick-slip flow regime, known as oscillating melt fracture, were found to scale with the weight fraction of LDPE. Amounts as low as 1 wt% LDPE have a significant effect on the amplitude of pressure oscillations. These effects are clearly due to the presence of LCB. It is suggested that the magnitude of oscillations in the oscillating melt fracture flow regime can be used as a method capable to detect low levels of LCB. Finally, the sharkskin and stick-slip polymer extrusion instabilities of a linear low-density polyethylene were studied as a function of the type of die geometry. The critical wall shear stress for the onset of flow instabilities, the pressure and flow rate oscillations, and the effects of geometry and operating conditions on the instabilities are presented for a LLDPE. It was found that sharkskin and stick-slip instabilities were present in the capillary and slit extrusion. However, stick-slip and sharkskin in annular extrusion are absent at high ratios of the inside to outside diameter of the annular die. This observation also explains the absence of these instabilities in polymer processing operations such as film blowing. These phenomena are explained in terms of the surface to volume ratio of the extrudates.

Biaxial orientation of PET for the production of high strength films for demanding applications, such as slot liners for electrical motors and sound and audio visual tapes, is a well established process. More recently biaxial orientation of PET has been utilised for the production of carbonated beverages, bottles and cans for processed food packaging to achieve high strength and impact resistance. These containers, however, are not suitable for hot filling and high temperature sterilization purposes owing to the lack of dimensional stability.

With the rapid spread in use of polymers the study of diffusion in them is becoming increasingly important. For a number of industrial processes diffusion coefficients and elemental distributions need to be quantified precisely. From a more scientific approach accurate models need to be devised to describe the various diffusion mechanisms involved as well as the concentration and temperature dependencies of the diffusion coefficients. Using ion beam analysis techniques (Rutherford Backscattering and Nuclear Reaction Analysis) three systems were studied. The first was an industrially relevant system of relatively small dye molecules diffusing into a number of different polymer matrices. For fixed diffusion settings, diffusion coefficients were measured and found to correlate with the matrix glass transition temperatures. Surface dye concentrations, on the other hand, were independent of matrix properties. The other two systems studied involved polymer interdiffusion. Based on different assumptions, two contradictory theories have been developed to describe the concentration dependence of the mutual diffusion coefficient; the 'slow' and 'fast' theories. In one system, blends of low molecular weight (unentangled) polystyrene and poly(methyl methacrylate) our data followed the 'slow' theory at low temperatures and the 'fast' theory at high temperatures. An equation describing the concentration dependence of the mutual diffusion coefficient at all intermediate annealing temperatures (hence linking the 'slow' and 'fast' theories) was developed and found to describe the data accurately. In the second system, blends of entangled poly(methyl methacrylate) of several molecular weights, the mutual diffusion coefficient was found to follow the 'fast' theory at all studied temperatures. In all three systems the temperature dependence of the tracer diffusion coefficients of the various components were accurately described by the semi-empirical equations of the Free Volume theory.

Rheological and processing behavior of a number of linear low-density polyethylene(LLDPE)/low-density polyethylene (LDPE) blends was studied with emphasis on the effects of long chain branching. First, a linear low-density polyethylene (LL3001.32) was blended with four LDPE's having distinctly different molecular weights. At high LDPE weight fractions, DSC melting thermograms have shown three different polymer phases; two for the pure components and a third melting peak of co-crystals. Different rheological techniques were used to check the thermo rheological behavior of all blends in the melt state and the effect of long chain branching. It was found that all blends are miscible in the melt state at small LDPE concentrations. The elongational behavior of the blends was studied using a uniaxial extensional rheometer, SER. The blends exhibit strain hardening behavior at high rates of deformation even at LDPE concentrations as low as 1%, which suggests the strong effect of branching added by the LDPE component. On the other hand, shear rheology was found to be insensitive to detect addition of small levels of LDPE up to lwt%. The second set of blends prepared and studied consisted of two Ziegler-Natta LLDPE's (LL3001.32 and Dowlex2045G) and two metallocene LLDPE's(AffinityPL1840 and Exact 3128) blended with a single LDPE. In DSC melting thermograms, it was observed that blends with metallocence LLDPE's exhibit a single melting peak at all compositions; whereas the Ziegler-Natta blends exhibit three melting peaks at certain compositions. It was found also that the metallocene LLDPE's are miscible with the LDPE at all concentrations. On the other hand, the Ziegler-Natta LLDPE's were found to be miscible with LDPE only at small LDPE concentrations. The processing behavior of all blends with emphasis on the effects of long chain branches was also studied in capillary extrusion. The critical shear stresses for the onset of sharkskin and gross melt fracture are slightly delayed with the addition of LDPE into LLDPE. Furthermore, the amplitude of the oscillations in the stick-slip flow regime, known as oscillating melt fracture, were found to scale with the weight fraction of LDPE. Amounts as low as 1 wt% LDPE have a significant effect on the amplitude of pressure oscillations. These effects are clearly due to the presence of LCB. It is suggested that the magnitude of oscillations in the oscillating melt fracture flow regime can be used as a method capable to detect low levels of LCB. Finally, the sharkskin and stick-slip polymer extrusion instabilities of a linear low-density polyethylene were studied as a function of the type of die geometry. The critical wall shear stress for the onset of flow instabilities, the pressure and flow rate oscillations, and the effects of geometry and operating conditions on the instabilities are presented for a LLDPE. It was found that sharkskin and stick-slip instabilities were present in the capillary and slit extrusion. However, stick-slip and sharkskin in annular extrusion are absent at high ratios of the inside to outside diameter of the annular die. This observation also explains the absence of these instabilities in polymer processing operations such as film blowing. These phenomena are explained in terms of the surface to volume ratio of the extrudates. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

No description available.

In this study we synthesized poly(tyrosine) (PTyr) through living ring-opening polymerization of £\-amino acid-N-carboxyanhydride and then blended with poly(4-vinyl pyridine) (P4VP) homopolymer in N, N-dimethylformamide (DMF) and methanol solutions to control the miscibility behavior and the secondary structures of poly(tyrosine). Infrared spectrum analysis suggests that the mixture of PTyr/P4VP possesses strong hydrogen-bonding interaction between the hydroxyl group of PTyr and the pyridine group of P4VP. DSC analyses indicate that these PTyr/P4VP complexes from methanol solution always have higher glass transition temperatures than the corresponding PTyr/P4VP miscible blends obtained from DMF solution. We proposed that the polymer chain behavior of PTyr/P4VP blend from DMF solution is the separated random coil and thus the PTyr chain possesses the random coil secondary structure after solvent evaporation. However, by increasing the hydrogen bonding for PTyr/P4VP complex from methanol solution, inter-polymer complex aggregate is proposed and the corresponding chain behavior enhances the intermolecular hydrogen bonding interaction of PTyr with P4VP that results in the £]-sheet conformation based on Fourier transforms infrared (FTIR), solid state nuclear magnetic resonance (NMR) spectroscopy, and wide-angle X-ray diffraction analyses.