Reactively processed polymer blends

It is usually difficult to isolate and characterize a copolymer from a melt-processed polymer blend. Model studies of copolymer formation between immiscible polymers have been performed either in solution (where there is unlimited interfacial volume for reaction) or using hot-pressed films of the polymers (where the interfacial volume for reaction is strictly controlled at a fixed phase interface). Model smdies using low molecular weight analogs of the reactive polymers are useful but their applicability to high molecular weight reacting systems is limited. 

Xanthos, M. and Dagli, S. S. 1991. CompatibiUzation of pol5nner blends by reactive processing. Polymer Engineering Science 31 929-935. 

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. 

Xanthos M, Dagli SS. Compatibilitation of polymer blends by reactive processing. Polym Eng Sci... 

Inoue, T. and Marechal, P. (1997) Reactive processing of polymer blends polymer-polymer interface aspects, in Processing of Polymers, ed. Meijer, H.F..H. Materials. Science and Technology, A Comprehensive Treatment, eds. Cahn, R.W., Haasen, P. and Kramer, E.J. (VCH, Weinheim) p. 429. 

Bhowmick A.K., Chiba T., and Inoue T., Reactive processing of rubber-plastic blend Role of a chemical compatibilizer, J. Appl. Polym. Sci., 50, 2055, 1993. 

Stewart, M. E., Cox, A. J., and Naylor, D. M Reactive processing of poly(ethylene 2,5-naphthalene dicarboxylate)/poly(ethylene terephthalate) blends, Polymer, 34, 4060-4067 (1993). 

Figures 20.13 and 20.14 describe the effect of dibutyltin dilaurate (DBTDL) on the tensile strength and tensile modulus for the 25/75 LCP/PEN blend fibers at draw ratios of 10 and 20 [13]. As expected, the addition of DBTDL slightly enhances the mechanical properties of the blends up to ca. 500 ppm of DBTDL. The optimum quantity of DBTDL seems to be about 500 ppm at a draw ratio of 20. However, the mechanical properties deteriorate when the concentration of catalyst exceeds this optimum level. From the previous relationships between the rheological properties and the mechanical properties, it can be discerned that the interfacial adhesion and the compatibility between the two phases, PEN and LCP, were enhanced. Hence, DBTDL can be used as a catalyst to achieve reactive compatibility in this blend system. This suggests the possibility of improving the interfacial adhesion between the immiscible polymer blends containing the LCP by reactive extrusion processing with a very short residence time.

Keywords Dynamic vulcanization Polymer blends and alloys Reactive processing Thermoplastic elastomers Thermoplastic vulcanizates... 

The conceptual breakdown in Fig. 1.9 (27) simply indicates the fact that in compounding, blending, and reactive processing, the base polymer(s) undergo two thermomechanical elementary-step experiences, and that the product of the first are value-added and microstructured pellets, while the second is used primarily for fabricating finished products. The important elementary steps for each experience, and the physical mechanisms that affect them, are different, because of the different objectives in each. 

---