Polypropylene resins morphology

Heterophasic copolymer resins (so called because their morphology typically shows two or more phases) have lower stiffness and improved toughness at low temperature, down to -40°C (depending on the dispersed phase type and amount). These resins often demonstrate more complex thermal behavior (e.g., two or more melting points and reduced stiffness at elevated temperature). You can find examples of typical grades of polypropylene resins in Table 1.7. Chapter 2 describes propylene structure-property relationships that suit a variety of end-use applications. 

The molecular structure and morphology of individual polypropylene resins can be readily modified at the reactor stage via new catalyst systems. Postblends of available resins with various additives promote impact resistance, controlled rheology, thermal stability, and other desirable characteristics of the polymer matrix. The incorporation of chemical coupling agents and mineral-filler or glass-... 

Since the last edition several new materials have been aimounced. Many of these are based on metallocene catalyst technology. Besides the more obvious materials such as metallocene-catalysed polyethylene and polypropylene these also include syndiotactic polystyrenes, ethylene-styrene copolymers and cycloolefin polymers. Developments also continue with condensation polymers with several new polyester-type materials of interest for bottle-blowing and/or degradable plastics. New phenolic-type resins have also been announced. As with previous editions I have tried to explain the properties of these new materials in terms of their structure and morphology involving the principles laid down in the earlier chapters. 

The solidification of the polymer melt in rotational molding is relatively slow, in comparison to other processes, and is estimated to be in the range of 10-30°C/min. Moreover, the melt solidification is gradual and nonuniform across the molded part thickness, leading to important variations in the morphological features, as illustrated in Fig. 9, and dictating the properties and overall performance of the final product. The effects are more dramatic for resins with slower crystallization rates, such as polypropylene, compared to that observed with polyethylene. 

Composition (type of polymeric components). The base polymer (which is to be modified) may be an amorphous polymer [e.g., polystyrene (PS), styrene-acrylonitrile copolymer, polycarbonate, or poly(vinyl chloride)], a semicrystalline polymer [e.g., polyamide (PA) or polypropylene (PP)], or a thermoset resin (e.g., epoxy resin). The modifier may be a rubber-like elastomer (e.g., polybutadiene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, or ethylene-propylene-diene copolymer), a core-shell modifier, or another polymer. Even smaller amounts of a compatibilizer, such as a copolymer, are sometimes added as a third component to control the morphology. 

Ultraviolet and fluorescent microscopy has been applied to a variety of polymer systems to investigate changes of morphology and composition on the scale of 0.25 ym upwards. Studies are briefly described on the behaviour of stabilisers in polypropylene, diffusion of additives in polymers, spherulite morphology, polyolefin oxidation, inhomogeneities in epoxy resins and polymer blends. 

S. Cimmino, D. Duraccio, C. Silvestre, M. Pezzuto, Isotactic polypropylene modified with clay and hydrocarbon resin compatibility, structure and morphology in dependence on crystallization conditions. Applied Surface Science 256 (3 Suppl.) (2009) S40-S45. 

Quantitative and qualitative methods were developed to measure the surface mechanical properties of polymers by atomic force microscopies. They were used to study the effects of molding processes and of viscosity on the surface morphology of polypropylene / (ethylene-propylene) copolymer blends (PP/EP). On compression-molded "physical blends", EP nodules are present at the outermost surface while, on injection-molded "reactor blends", they are covered by a PP layer. Resins with high viscosity ratio between EP and PP present heterogeneous surface elastic properties corresponding to the dispersion of spherical EP nodules below the surface. The low viscosity ratio resins have homogeneous surface elastic properties comparable to those measured above EP nodules on high viscosity ratio resins. This is compatible with a fine dispersion of plate-like shaped EP nodules below the surface... 

The surface content and the distribution of (ethylene-propylene) copolymer (EP) in toughened polypropylene (PP) resins (PP/EP) have important impact on a lot of properties such as gloss, paint adhesion, hardness,. .. These surface properties are more and more important in the multiple applications of these resins, for instance for paint adhesion in the automotive industry. It has already been shown that the introduction of EP in PP provides better paint adhesion but its role remains speculative (1-4), A major drawback to the understanding of the EP influence on PP/EP surface properties is the lack of knowledge concerning the blends surface morphology (EP content, EP lateral distribution,. ..). This is essentially due to the similar chemical composition of both polymers that prevents surface analysis by classical chemical surface spectroscopies. 

SEM has been used extensively in morphological studies on polymers. Polymers studied include epoxy resin-polyaniline composites [3], polyoxyethylene [15], polypropylene-polycaprolactone blends [16], polydimethylsiloxane-co-ethylene oxide [17], PET fibres [18], polyurethane/polybutylmethacrylate polymer networks [19], methylacrylate-co-cellulose [20], styrene-butadiene copoylmer [21], Nylon 6-ethylene vinyl alcohol [22] and propylene-calcium carbonate or talc composites [23]. 

Lai et al. [29] discussed this issue for a polypropylene nanocomposite using as compatibilizers polypropylene grafted maleic anhydride (PP-g-MA) and poly-ethylene-octene elastomer grafted maleic anhydride (POE-g-MA). Another aspect is related to system crystallinity and its morphology. The optical transmittance for nanocomposite without compatibilizers was generally higher than that of the translucent PP resin. 

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