Reactive processing compatibilized systems

Reactive Processing of Multicomponent Immiscible and Compatibilized Immiscible Polymer Systems, 632... 

REACTIVE PROCESSING OF MULTICOMPONENT IMMISCIBLE AND COMPATIBILIZED IMMISCIBLE POLYMER SYSTEMS... 

Poly(styrene-co-maleic anhydride) (SMA) is frequently mixed with SAN before the reactive blending with PA [Takeda and Paul, 1992]. Much attention has been paid to morphology control during the reactive processing [Serpe et al, 1990 Campbell et al., 1990 Willis and Favis, 1990]. Frequently, a third polymer is added as a com-patibilizer for binary systems, e.g., MA-grafted SEES to compatibilize (and impact-modify) blends of PE with PET [Carte and Moet, 1993]. 

As on a thermodynamic basis, the effect of compatibilization should be the same with respect to a reactively compati-bilized system, it was observed in several cases that the diffusion of the compatibilizing copolymer to the interfacial region is quite difficult for kinetic reasons. Because of the high viscosity of the molten polymer medium and the short time of blending usually adopted in industrial conditions, the premade copolymer does not quantitatively diffuse to the A/B interphase region. That is why in industrial processes the compati-bilizers are preferentially in situ formed during the compounding step of blend development. 

In Section 10.4 the properties of immiscible blends, and in particular the types of morphology, the nucle-ation processes, and crystal growth are described. The crystallization behavior of some immiscible systems (with one or two crystallizable components) is reviewed. Section 10.5 deals with compatibilized blends. The main compatibilization methods, including addition of copolymers and reactive mixing methods, are reported. The peculiar crystallization phenomena occurring in compatibilized systems (fractionated crystallization) are examined for blends of polyamides and functionalized polyolefins. 

The chemical reaction at the interface during processing influences the morphology and thus the material properties. During the reaction, block or graft copolymers are formed. These copolymers are expected to reduce the interfacial tension coefficient, and to prevent coalescence of the dispersed particles. Furthermore, the chemical reaction influences the interfacial thickness. It was shown by ellipsometry that as a result of the reactive compatibilization, the interfacial thickness in the ternary system, PA/SMA/ SAN, increased up to Al = 50 nm [Yukioka and Inoue, 1994]. 

In the last decade, considerable progress was observed in the field of PO/compatibil-izer (predominantly on the base of PO-g-MA)/organo-surface-modified clay nanocomposites. Polyethylene (PE), polypropylene (PP), and ethylene-propylene (EP) rubber are one of the most widely used POs as matrix polymers in the preparation of nanocomposites [3,4,6,30-52]. The PO silicate/silica (other clay minerals, metal oxides, carbon nanotubes, or other nanoparticles) nanocomposite and nanohybrid materials, prepared using intercalation/exfoliation of functionalized polymers in situ processing and reactive extrusion systems, have attracted the interest of many academic and industrial researchers because they frequently exhibit unexpected hybrid properties synergisti-cally derived from the two components [9,12,38-43]. One of most promising composite systems are nanocomposites based on organic polymers (thermoplastics and thermosets). 

In processing polymer blends, equipment selection, conditions, and formulation are highly important to control the final morphology. In this chapter, a review of the fundamentals in mixing (laminar, chaotic, dispersive, and distributive) is given before presenting the main limitations/problems related to interfacial properties, coalescence, and measure of mixing quality. Then, different methods and equipments are presented for lab-scale and industrial applications. A special focus is made on reactive system and phase compatibilization to improve the properties of the final blends. Also, nonmechanical techniques (solutions) are presented. 

Improved properties of commingled plastics via blend modification by reactive functionalization and compatibilization have been reported by several workers (58,65). This work is confined to a two-phase PE-PP morphology. In the two-phase immiscible PE-PP system, poor interfacial adhesion results in poor blend mechanical properties. The lack of stability in the morphology causes gross separation or stratification during later processing or use. Block and graft copolymers of the form A-B have been used as compatibilizers to improve interfacial adhesion and reduce interfacial tension between A-rich and B-rich phases to provide A-B alloys with improved and unique balances of properties. 

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