Polymer Blends Forming
The key to optimizing polymer blends performance is control of morphology. Distinct types of morphology are required to improve specific properties. The matrix/dispersed phase type is necessary to obtain the maximum impact strength, while dual phase co-co
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POLYMER BLENDS FORMING
Michel M. Dumoulin
National Research Council Canada, Industrial Materials Institute Boucherville, QC, Canada
10.1
Abstract
The key to optimizing polymer blends performance is control of morphology. Distinct types of morphology are required to improve specific properties. The matrix/dispersed phase type is necessary to obtain the maximum impact strength, while dual phase co-continuity will yield better stiffness/ductility balance and dispersion of lamellar domains allows to modify the barrier performance. Optimized properties therefore result from strict control over processing conditions and equipment, and from methods of generating and stabilizing the morphology, such as reactive compatibilization. The reviewed information shows that in addition to improving final properties, blending is increasingly carried out to improve processability. Easier processing can often be achieved through a negative deviation from the viscosity additivity rule. This route is particularly critical for high performance resins difficult, if not impossible, to process, such as PPE, PEI and aromatic polyamides. Easier processing can also be achieved indirectly, i.e., by adding a toughener to reduce a resin’s MW to lower viscosity while maintaining the system’s toughness. Other less dramatic changes include less temperature dependent rheology or increased melt elasticity. The chapter attempts to review the behavior of blends during forming. The processes are discussed first from the point of view of the general principles and the effect of material parameters. The general behavior of blends is discussed in terms of processability, flow-induced morphology and the effect of forming on blend performance. The various important forming methods are examined: extrusion, injection molding, blow molding, calendering, thermoforming, film blowing, fiber spinning, as well as solid state forming and compression molding. In each case, a description of the process and of the main process parameters is followed by a discussion on the behavior of blends of commodity, engineering and specialty resins. Processing conditions of commercially available blends are tabulated whenever possible. Forming of reinforced blends, quality and process control and finally reprocessing are also discussed.
L.A. Utracki (Ed.), Polymer Blends Handbook, 653-755. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.
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10.2
M. M. Dumoulin
Introduction to Polymer Forming
McKelvey defined polymer processing as an engineering specialty concerned with the operation carried out on polymeric materials or systems to increase their utility [McKelvey, 1962]. He further suggested to subdivide the field into three categories: (i) modification (including mixing), (ii) forming and (iii) bonding (i.e., finishing). The present chapter focuses on forming, i.e., on the processes that fix the shape of the products. Shaping is usually preceded by preparation (e.g., drying, mixing) and followed by finishing (e.g., painting, joining) steps. Some of these will be briefly
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