Stanley Young Hobbs

Effect of interfacial forces on polymer blend morphologies

Abstract In this study, the way in which the components of complex polymer blends (those consisting of more than two resins) are segregated after melt processing is described. Depending on the composition of the blend, the dispersed phases are found to remain separated or form more complicated encapsulated structures. The various morphologies which are formed are shown to be consistent with those predicted from an analysis of spreading coefficients.

Toughened blends of poly(butylene terephthalate) and BPA polycarbonate: Part 1Morphology

The morphologies of melt blends of poly(butylene terephthalate) (PBT) and bisphenol A polycarbonate (PC) toughened with a core/shell impact modifier have been characterized by transmission and scanning electron microscopy. Selective staining with ruthenium and osmium tetroxide and etching with diethylene triamine have been used to assess the distribution of the various blend components and investigate the effects of thermal history on morphology. Strong evidence for partial melt miscibility of PC and PBT and rate-dependent segregation during cooling is presented.

Toughened blends of poly(butylene terephthalate) and BPA polycarbonate

The toughening mechanisms of blends of poly(butylene terephthalate) (PBT) and bisphenol-A polycarbonate (PC) toughened with core/shell impact modifier have been studied by transmission electron microscopy, notched impact testing and uniaxial tensile dilatometry. It was found that in both toughened PBT and toughened PBT/PC blends, shear deformation is the major toughening mechanism. Brittleness at low temperatures is caused by a reduction in the ability of the matrix to undergo shear deformation. In tensile dilatometry this effect is indicated by an increase in the extent of internal cavitation of the impact modifier particles. The low-temperature impact toughness of toughened PBT/PC blends is significantly greater than that of toughened PBT. Modification of PBT with partially miscible PC appears to have a beneficial effect on the ability of PBT to undergo shear deformation. This effect has been attributed to the PC residing in the amorphous interlamellar regions of the PBT spherulites, thus facilitating interlamellar slip.

Deformation mechanisms in toughened poly(phenylene oxide)-polyamide blends

The deformation behaviour of several toughened poly(phenylene oxide)-Nylon 6,6 blends made with different coupling agent levels and having different copolymer concentrations has been studied by tensile dilatometry and scanning electron microscopy. Volume strains were measured at rates from 10−3 to 10−1 sec−1. At high copolymer concentrations, shearing was the primary deformation mode with dilation accounting for only 25% of the total strain. At lower copolymer levels, fracture occurred abruptly with no measurable increase in the level of cavitation prior to failure. Samples without rubber exhibited lower levels of dilation than their toughened counterparts. The observed differences in behaviour are discussed in terms of microscopic failure processes in the materials. Rate-dependent values for selected engineering parameters are presented.

Partial miscibility of poly(butylene terephthalate)/BPA polycarbonate melt blends

SummaryDifferential scanning calorimetry (DSC) measurements have been carried out on a number of poly(butylene terephthalate) (PBT)/BPA polycarbonate (PC) blends prepared by melt compounding and solution casting from hexafluoroisopropanol (HFIP). The results clearly indicate that appreciable mixing of the two polymers takes place in the melt phase whereas complete separation is observed in cast films. The failure of the casting procedure to mimic the melt blending results is related in part to liquid-liquid phase separation and to crystallization of both polymers from the casting solvent.

Morphology and properties of toughened poly(phenylene oxide)-polyamide blends

High impact strength poly(phenylene oxide)-polyamide blends can be prepared by chemically coupling the two components and incorporating a rubbery impact modifier in the resin. The resulting materials exhibit a distinctive morphology in which the rubber is selectively incorporated in the dispersed poly(phenylene oxide) phase. In this paper both the structure and toughening mechanisms in these blends are examined. An analysis of their deformation behaviour is presented in a companion paper.

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

SummaryIn 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.

Morphology and deformation behaviour of toughened blends of poly(butylene terephthalate), polycarbonate and poly(phenylene ether)

Abstract The morphology and properties of blends of poly(butylene terephthalate) (PBT), bisphenol A polycarbonate (PC), poly(2,6-dimethyl-1,4-phenylene ether) (PPE), toughened with styrene-ethylene/butylene-styrene (SEBS) rubber have been found to be strongly affected by spontaneous phase segregation which occurs during melt compounding. In the composition range of interest, such segregation leads to the formation of a unique microstructure in which dispersed particles of rubber-modified PPE are encapsulated by thin envelopes of PC and embedded in a PBT matrix. Electron microscopy and tensile dilatometry studies of partially and fully formulated PBT/PC/PPE/SEBS blends have been used to relate the morphology of these materials to their deformation behaviour.

Diffusion bonding between BPA polycarbonate and poly(butylene terephthalate)

Abstract The diffusion bonding of poly(butylene terephthalate) (PBT) to BPA polycarbonate (BPAPC) has been studied over the temperature range 100–230°C. The studies were carried out on laminates of the two polymers prepared by a novel spray application procedure. Variations in adhesive bond strength with temperature at fixed times and with time at fixed temperatures were determined by means of peel tests. Concurrently, TEM studies of interfacial cross sections were used to monitor the extent of diffusion. The results suggest that adhesion is strongly coupled to the level of solubility between the two resins and is independent of the rate or extent of diffusion once an equilibrium number of interfacial chains has been established. A phenomenological model is presented.

Determination of interfacial tensions between BPA polycarbonate and styrene-acrylonitrile copolymers from capillary thread instability measurements

Abstract The interfacial tensions between BPA polycarbonate (PC) and a series of styrene-acrylonitrile (SAN) blends having S/AN ratios varying between 100 0 and 60 40 (wt%) have been determined by measuring capillary thread breakup rates at 200°C. A distinct minimum in the interfacial tension is observed close to the SAN composition reported to show maximum miscibility with PC. For the case of PC/PS, the measured values are compared with those calculated from published studies on PS/poly methyl methacrylate (PMMA) and PC/PMMA.