J. W. Barlow

A Binary Interaction Model for Miscibility of Copolymers in Blends

Abstract Miscibility windows often exist in polymer blend systems when the chemical structure of one of the components is systematically varied, e.g. a random copolymer may be miscible with another polymer when neither limiting homopolymer is. A binary interaction model is developed which explains such behaviour. From this prediction, the general notion is advanced that many cases exist where the net exothermic heat of mixing required for miscibility of high molecular weight polymer mixtures may result from appropriate considerations of both intermolecular and intramolecular interactions of component units without an exothermic interaction existing between any individual pair of units. However, it is shown that for a net exothermic mixing the individual interaction parameters for the pairs of units must differ from those predicted by solubility parameter theory. Moreover, the departures from the geometric mean assumption of the solubility parameter theory need not be large to achieve conditions for miscibility. Several examples of the use of such a model are given including one where the homologous series of aliphatic polyesters is treated as ‘copolymers’ by considering their CH x and COO constituents as the ‘monomers’.

REACTIVE COMPATIBILIZATION OF BLENDS OF NYLON 6 AND ABS MATERIALS

Abstract Blends of nylon 6 with various ABS materials including its styrene/acrylonitrile, SAN, matrix component were examined for rheological behaviour, mechanical properties, and phase morphology. These mixtures have poor mechanical properties unless properly compatibilized. This was done here by adding to the SAN phase a polymer that is miscible with it but which contains functional groups that can react with the nylon 6 to form in situ , graft copolymers at the polymer-polymer interfaces. These compatibilizer molecules contained either anhydride or oxazoline units for reactivity. Evidence of reactions in the blends was seen in the rheological behaviour of the melt and in the morphology and mechanical behaviour of the solid. Some blends exhibited outstanding toughness. A more quantitative assessment of the extent of reaction was provided by a selective solvent extraction technique. Lap shear adhesion measurements for laminates of nylon 6 with materials containing reactive polymers provided a direct way to assess the effectiveness of the interfacial reaction.

Effect of copolymer composition on the miscibility of blends of styrene-acrylonitrile copolymers with poly (methyl methacrylate)

Abstract The phase behaviour for blends of various polymethacrylates with styrene-acrylonitrile (SAN) copolymers has been examined as a function of the acrylonitrile content of the copolymer. Poly(methyl methacrylate), poly(ethyl methacrylate) and poly(n-propyl methacrylate) were found to be miscible with SANs over a limited window of acrylonitrile contents while no SANs appear to be miscible with poly(isopropyl methacrylate) or poly(n-butyl methacrylate). These conclusions were reached on the basis of lower critical solution temperature ( LCST ) and glass transition temperature behaviour. All miscible blends exhibited phase separation on heating, LCST behaviour, at temperatures which varied greatly with copolymer composition. An optimum acrylonitrile (AN) level ranging from about 10 to 14% by weight resulted in the highest temperatures for phase separation which has important implications for selection of SANs to produce homogeneous mixtures by melt processing. The basis for miscibility in these systems is evidently repulsion between styrene and acrylonitrile units in the copolymer as explained by recent models. The excess volumes for all blends are zero within experimental accuracy which suggests that the interactions for miscibility are relatively weak even for the optimum AN level. This interaction becomes smaller the larger or more bulky is the alkyl side group of the polymethacrylate.

Miscibility in PVC-polyester blends

Abstract Blends of poly(vinyl chloride), PVC, with the polyesters poly(butylene adipate), poly(hexamethylene sebacate), poly(2,2-dimethyl,1,3-propylene succinate) and poly(1,4-cyclohexanedimethanol succinate) were found to exhibit a single, composition dependent glass transition. Thus, these polyesters are miscible with PVC as others have reported for poly(ϵ-caprolactone). However, mixtures of poly(ethylene succinate), poly(ethylene adipate) and poly(ethylene ortho phthalate) with PVC were found not to be miscible. Melting point depression has been used to estimate the blend interaction parameter. These results combined with others from the literature suggest that there is an optimum density of ester groups in the polymer chain for achieving maximum interaction with PVC. Too few or too many ester groups result in immiscibility with PVC.

Effect of film thickness on the changes in gas permeability of a glassy polyarylate due to physical agingPart II. Mathematical model

Abstract Part I of this series documented a substantial loss in gas permeability over time for thin films of a glassy polyarylate made from bisphenol-A–benzophenone dicarboxylic acid. The rate of permeability loss, and, thus, aging was found to be dependent on film thickness in a way that suggested that physical aging occurs by two mechanisms. In this paper, a mathematical model was developed to quantitatively describe the physical aging process in terms of the free volume (permeability) loss observed using reasonable physical parameters. The model describes two simultaneous mechanisms of free volume loss: free volume diffusion to the film surface (thickness dependent) and lattice contraction (thickness independent). A step-wise model development is described with comparison to the data and optimization of the model parameters at each step. The final dual-mechanism model describes the experimental data presented in Part I remarkably well.

Materials for biomedical applications

Abstract This paper discusses the physical and mechanical characterization of a calcium phosphate ceramic material system developed for biomedical applications in the repair of skeletal defects. The rapid prototyping process selective laser sintering (SLS) is the preferred forming process to produce complex porous ceramic matrices suitable for biomedical applications. The effects of SLS processing conditions on the properties of fabricated objects are quantified. The effects of post-processing conditions on the properties of SLS-fabricated objects are also quantified. SLS-fabricated implants are shown to perform well in vivo exhibiting excellent biocompatibility as well as showing considerable osseous integration and remodeling of the ceramic implant material.

Thermodynamics of the phase behaviour of poly(vinyl chloride)/aliphatic polyester blends

Abstract A series of linear aliphatic polyesters having CH 2 COO ratios in their repeat units from 2 to 14 have been examined for miscibility with poly(vinyl chloride). There is a window of structures in the middle of this spectrum where miscibility is observed. At the low end there is a very sharp boundary lying between CH 2 COO = 3 and 4 dividing the polyesters which are immiscible with PVC from those which are miscible. At the high end the boundary is not so sharp but rather phase separation caused by a lower critical solution temperature occurs at progressively lower temperatures as CH 2 COO increases beyond 10. Thermodynamic interaction parameters for the miscible blends were obtained by analysis of the depression of the polyester melting point after correction for finite crystal thickness using the Hoffman-Weeks method. These results are compared with heats of mixing obtained directly using low molecular weight analogues of the polymers. The two results show very similar trends but are not quantitatively identical for reasons mentioned. A binary interaction model has been used to analyse the heat of mixing data, and it is concluded that there is a strong unfavourable intramolecular interaction between the -CH2- and -COO- units in aliphatic polyesters which is an important factor in their miscibility with PVC and other polymers.

Effect of glass fiber and maleated ethylene–propylene rubber content on the impact fracture parameters of nylon 6

Abstract The impact fracture parameters of blends of nylon 6 and maleated ethylene–propylene rubber (EPR- g -MA) reinforced with glass fibers as a function of glass fiber and EPR- g -MA content were examined. Both the linear elastic fracture mechanics (LEFM) model and a modified essential work of fracture (EWF) model were used to analyze the data. It was found that the addition of EPR- g -MA to unreinforced nylon 6 increased the EWF parameters u o and u d defined by U / A = u o + u d l, where U / A is the total fracture energy per unit area and l is the ligament length. Beyond a critical rubber content, which coincided with the ductile-to-brittle transition, there was a large increase in u d . When glass fiber reinforcement was used without rubber toughening, the EWF model was unable to model the observed fracture response. On the other hand, the LEFM model adequately described the fracture behavior, and it was found that the critical strain energy release rate, G IC , increased with increasing glass fiber content. When both glass fiber reinforcement and rubber toughening were used, the u o increased with increasing EPR- g -MA or glass fiber content; whereas, u d increased with increasing ERR- g -MA content or decreasing glass fiber content.

A completely miscible ternary blend: poly(methyl methacrylate)-poly(epichlorohydrin)-poly(ethylene oxide)

Abstract The polymer pair poly(epichlorohydrin) (PECH) and poly(ethylene oxide) (PEO) is shown to form completely miscible blends based on the observation of a single glass transition temperature (Tg) by differential scanning calorimetry and lower critical solution temperature (LCST) behaviour. Since poly(methyl methacrylate) (PMMA) is known from earlier work to form miscible binary blends with PECH and with PEO, then a ternary system (PMMA-PECH-PEO) has been identified for which all three binary pairs are miscible. Examination of ternary blends for Tg and LCST behaviour revealed that complete miscibility exists over the entire ternary composition diagram. Heats of mixing for binary mixtures of liquids whose molecular structures are analogues of the polymers are reported in order to understand better the nature of the interactions operative in each of the binary blends. It is seen that oligomeric analogues for poly(ethylene oxide) give misleading results when they have hydroxyl end groups.

Kinetics of adhesion development at PMMA-SAN interfaces

Abstract The kinetics of adhesion development at interfaces between poly(methyl methacrylate) (PMMA) and styrene/acrylonitrile (SAN) copolymers of varying AN levels have been studied at 130°C by measuring the tensile fracture strength of a butt joint configuration. For miscible pairs, SANs containing about 9.5 to 33% AN, the principal mechanism of adhesion development involves interdiffusion of PMMA and SAN chains with the joint strength growing in proportion to t 1 4 (where t = time the joint is at 130°C) as predicted by theory. The interdiffusion rate is greatest near 14.7% AN, where the interaction with PMMA is maximum as demonstrated by recent studies of phase behaviour for PMMA-SAN blends. This optimum rate of adhesion development is consistent with a stronger thermodynamic driving force for diffusion. SANs with less AN than necessary for miscibility with PMMA, including polystyrene, rapidly developed a lower but finite extent of adhesion to PMMA, resulting from physical wetting and perhaps limited segmental interpenetration. Such joints do not seem to involve a long-term kinetic process since minimal transport is needed to attain the final equilibrium state, which contrasts with the situation for miscible pairs. In general, more rapid interdiffusion or adhesion development can be expected for miscible pairs of unlike polymers relative to pairs of identical polymers having comparable mobility because of the additional driving force provided by a favourable heat of mixing beyond that of the small combinatorial entropy which is the only driving force available for self-diffusion.