Reactive compatibilization of polypropylene

Heterogeneous blends of technological importance are termed compatible and they constitute the majority of the commercial blends introduced in the past 20 years. In such blends, satisfactory physical and mechanical properties are related to the presence of a finely dispersed phase and resistance to gross phase segregation. Blend composition. 

Modification reactions of PP aiming at producing suitably functionalized resins with enhanced affinity towards polar polymers are summarized in [1-3]. Important functionalization reactions involve the incorporation of reactive groups through, for example, halogenation, chlorosulfonation or peroxidation, reaction with azidosulfonyl benzoic acid and monomer grafting (e.g. maleic anhydride, acrylic add) through the action of peroxides. Such modified materials are used to provide blends with enhanced properties. 

In addition to copol)oners, compatibility may also be enhanced through the addition of spedfic low molecular weight (MW) compounds which promote copolymer formation and/or crosslinking. The following is a summary of our present knowledge on the types and function of compatibilizers used in melt blended polymer mixtures with emphasis on PP blends. 

Interfacially active graft or block copolymers of the t5 pe A-B or A-C may compatibilize the immiscible polymers A and B provided that C is also miscible or capable of strong interactions with B. Poly(ethylene-co-propylene) elastomer (EPR) or poly(ethylene-co-propylene-co-diene) (EPDM) is an example of such nonreactive compatibilizer for polyethylene/polypropylene (PE/PP) blends. 

The addition of low MW compounds in a polymer blend may promote compatibility through the formation of copolymers (random, block. 

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Datta R J, Polk M B and Kumar S (1995) Reactive compatibilization of polypropylene and nylon, Polym Plast Technol Eng 34 551-560. 

Helmert, A., Champagne, M.F., Dumoulin, M.M. and Fritz, H.G. (1995) Compatibilization of polypropylene/polyamide-bb blends via reactive blending with maleated polypropylene, in Proceedings of the Conference on Polyblends 95, October 19-20, Boucher e, Canada, National Research Council Canada, BouchervUle, Canada. 

Polymer alloys are commercial polymer blends with improvanent in property balance with the use of compatibilizers. Texas A M University [1] has patented a com-patibilizer that can result in a product with high impact resistance as well as scratch resistance. The blend is composed of HIPS or polypropylene (PP) and a compati-bilizer made of a triblock copolymer of styrene-ethylene-propylene. Udipi [2] discovered that polymer blends composed of PC, a copolyester of PETG, and nitrile rubber exhibit a superior balance of properties. Reactive compatibilization of PC/ SAN blends at various AN compositions were conducted by Wildes et al. [3] using a SAN-amine compatibilizer. PC and SAN were found to be miscible over a range of AN composition by Mendelson [5]. Nylon/ABS blends can be compatibilized by use of SAN-maleic acid (Lavengood et al. [6]). Styrene-GMA copolymers can be used as compatibilizers for PS/PA, PS/PBT, PS/PET, and PPO/PBT blends. 

Chen, E. E., Wong, B., and Baker, W. E. (1996). Melt-grafting of glycidyl methacrylate onto polypropylene and reactive compatibilization of rubber toughened polypropylene. Polymer Engineering and Science 36(12), 1594-1607. 

In order to be able to modify and control the interfadal interactions in the above-described manner, it is extremely important to monitor the structure of the interfadal layer. Ellipsometry was used [15,40,50,51] to deted the procedure and influence of reactive compatibilization on polymer blends. In an early study, the reactive blending of polypropylene (PP) with amorphous polyamide (aPA) was carried out using maleic anhydride-grafted PP (MAH-gPP) as a reactive PP [50]. The emulsifying effect of the in situ-formed PP-aPA graft copolymer was indicated by finer particles and a better stability of the dispersed phase obtained in bulk. In accordance with these findings, ellipsometry showed that the interface established in the reactive system was rather thick (ca. 40 nm), indicating an improved compatibility. 

Compatibility of immiscible PP-NBR blends was improved by the reactive compatibilization technique using various modified polypropylenes. In this study. 

Els and McGill [48] reported the action of maleic anhydride on polypropylene-polyisoprene blends. A graft copolymer was found in situ through the modifier, which later enhanced the overall performance of the blend. Scott and Macosko [49] studied the reactive and nonreactive compatibilization of nylon-ethylene-propylene rubber blends. The nonreactive polyamide-ethylene propylene blends showed poor interfacial adhesion between the phases. The reactive polyamide-ethylene propylene-maleic anhydride modified blends showed excellent adhesion and much smaller dispersed phase domain size. 

Reactive compatibilization is also carried out by adding a monomer which in the presence of a catalyst can react with one or both phases providing a graft copolymer in situ that acts as a compatibilizer. Beaty and coworkers added methyl methacrylate and peroxide to waste plastics (containing polyethylene [PE], polypropylene [PP], PS, and poly(ethylene terephthalate) [PET]). The graft copolymer formed in situ homogenized the blend very effectively [19]. 

The oil resistance and chemical resistance of nitrile rubber is generally superior to that of EPDM rubbers. However, the highly polar nature of acrylonitrile comonomer is responsible for the high incompatibility between nitrile rubber and polypropylene. The dispersability and the stability of nitrile rubber dispersions in the polypropylene matrix are poor. Hence a reactive compatibilization technology was used [Coran and Patel, 1983], It consisted of blending a small amount of a low molecular weight amine-terminated butadiene-acrylonitrile copolymer (ATBN,... 

Melt blending of PA-6 (or 66) with such an anhydride functionalized polypropylene causes a fast graft copolymer reaction between the polyamide and PP at the interface, which subsequently compatibilizes the blend. Some commercial polyamide/polypropylene blends may utilize such types of reactive compatibilization techniques. Properties of commercial PA/PP blends, both unfilled and glass filled grades, are shown in Tables 15.18 and 15.19. Typically, these blends... 

Reactive compatibilizing agents of the type A-C can also compatibilize an A/B blend as long as C can chemically react with B. Such studied systems include polyethylene (PE)/nylon-6 blends compatibilized with carboxyl functional PE, polypropylene (PP)/poly(ethylene-terephthalate), with PP-g-acrylic acid, nylon-6,6/EPDM with poly(styrene-co-maleic anhydride), and nylon-6/PP with PP-g-maleic anhydride. 

Y.-Y. Cui, B.-J. Dong, B.-L. Li, S.-C. Li, Properties of polypropylene/poly(ethylene terephthalate) thermostimulative shape memory blends reactively compatibilized by maleic anhydride grafted polyethylene-octene elastomer. Int. J. Polym. Mater. Polym. Biomater. 62, 671-677 (2013)... 

Rzayev, Z. M. O., Yilmazbayhan, A., and Alper, E. 2007. Aone step preparation of polypropylene-compatibilizer-clay nanocomposites by reactive extrusion. Advance Polymer Technology 26 41-55. Ho, R. M., Su, A. C., Wu, C. H., and Chen, S. 1993. Functionalization of polypropylene via melt mixing. Polymer 34 3264—3269. 

Wu, Y, Yang, Y, Li, B., and Han, Y. 2006. Reactive blending of modified polypropylene and polyamide 12 Effect of compatibilizer content on crystallization and blend morphology. Journal... 

Zhou, H. J., Rong, M. Z., and Friedrich, K. 2006. Effects of reactive compatibilization on the performance of nano-silica filled polypropylene composites. Journal of Materials Science Letters 41 5767-5770. 

Reactive compatibilization in a specially designed twin-screw extruder was carried out during compounding maleated polypropylene, PP-MA (0-0.14 wt% MA), with PA-6. During the reaction a di-block copolymer was formed at the interface. As the copolymer content increases from zero to 20 wt%, the number average diameter of PA-6 drops decreased from the initial value do = 20 to d = 0.14 pm at 20 wt% copolymer. The concentration dependence of shear viscosity also changed with compatibilization from negative deviation from the log additivity rule, NDB, to positive deviation, PDB (Nishio et al. 1992). 

Figures 11.3 and 11.4 show that reactive compatibilization can also be used for other types of polymers. Polystyrene is a very brittle polymer and the simple addition of polypropylene already improves the maximum strain. Very significant improvements in ductileness can be achieved by reactive compatibilization. In Fig. 11.4 is indicated that the type of monomer is also important for the mechanical properties of the blend. Both volatility and the...

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