Polyblends compatibilization

Where the two phases are completely compatible, a homogeneous polyblend results which behaves like a plasticized resin (one phase). If two polymers are compatible, the mixture is transparent rather than opaque. If the two phases are incompatible, the product is usually opaque and rather friable. When the two phases are partially compatibilized at their interfaces, the polyblend system may then assume a hard, impact-resistant character. However, incompatible or partially compatible mixtures may be transparent if the individual components are transparent and if both components have nearly the same refractive indices. Furthermore, if the particle size of the dispersed phase is much less than the wavelength of visible light (requiring a particle size of 0.1/a or less), the blends may be transparent. 

By combining the concepts of copolymer homogeneity, matching refractive indices, and partial compatibilization via grafting, impact resistant polyblend systems can be produced from numerous monomer combinations that approach optical clarity. 

Khandpur AK et al. (1995) Compatibilizers for A/B blends A-C-B triblock versus A-B diblock copolymers. Polyblends 95, SPE Regional Technical Conference on Polymer Alloys and Blends. Boucherville, Quebec, Oct 19-20, pp 88-96... 

Enhanced interphase interactions, deduced from thermal and dynamic mechanical properties and morphology observed by SEM, demonstrate the efficient compatibilizing effect of iPS-fo-iPP copolymer on iPS-iPP blends. Each sequence of the iPS-fc-iPP diblock copolymer can probably penetrate or easily anchor its homopolymer phase and provide important entanglements, improving the miscibility and interaction between the iPS and iPP phases. This is in good agreement with what is inferred from the mechanical properties of the iPS-fo-iPP-iPS-iPP polyblends. 

For useful polyblends, the term compatibilization refers to the absence of separation or stratification of the components of the polymeric alloy during the expected useful lifetime of the product. Optical clarity of a polyblend is related to the particle size of the dispersed phase and/or the difference in the... 

The mix of different colors may also become a drawback.) Improvement of performance can be achieved at extra cost by special additives such as impact modifiers, thermal and light stabilizers, but mainly coupling agents (so-called compatibilizers) for polyblends. 

Equation-5, X and Phi denote the molar and volume fiaetion of the components, respectively. Eor two polymers to be miscible, the free energy of mixing must be negative. If the solubility parameters of the polymer pairs are too far apart, the free energy of mixing becomes positive, and compatibilizers are often needed to reduce the interfacial tension between incompatible components in a blend. In industry, both miscible and immiscible polyblends are important materials because they fill (filFerent market needs. 

Ternary blends containing LCPs also show an attractive approach to the development of reinforced systems. The differences between ternary polyblends and polyblends with a third component (a compatibilizer) added are that in the latter, usually the third components is a pre-made compound (or polymer) and its fraction in compatibilized blends is less than 10 wt%. The third polymer used in ternary blends is an as-received commercial product, and its content in ternary blends can be changed for tailoring the properties of blends. 

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. 

Radical functionalization of iPP with acrylic acid (AA) gives iPP-AA, which acts as a compatibilizer for PP/liquid crystal polyblend fibers and increases fiber crystallinity and interfacial adhesion. " The reaction of PP with maleic anhydride in xylene at elevated temperatures (120 °C) in the presence of benzoyl peroxide gives maleated iPP. Co-melting of this material with poly(e-caprolactone) (PCL) for 6 h at 120 °C gave a PP-g-PCL graft copolymer. Similar methods have been employed for the grafting of A-phenylmaleimide and maleimido benzoic acid onto iPP oligomers in order to... 

Palabiyik M and Bahadur S (2000) Mechanical and tribological properties of polyamide 6 and high density polyethylene polyblends with and without compatibilizer, Wear 246 149-158. 

Thus physical processes alone can contribute toward practical compatibilization of polyblend systems. It should be remembered, however, that while sueh solely physical processes may affect the degree of compatibility, they do not generally make a qualitative differenee between incompatible and compatible polyblends. For such qualitative improvement in compatibility, additives and/or reactions are generally required. 

A variety of other third polymers may be added to incompatible polyblends to improve compatibility. Most of them are random eopolymer structures with flexible or rubbery properties. Their compatibilizing action may be visualized in three ways ... 

Addition of a physical compatibilizer is obviously the simplest and most straightforward technique for the average plastics processor. However, the compatibilizer must be matched to the polymers in the blend, with segments either identical to the base polymers, or else similar, miscible, or at least compatible with them. Such tailor-made compatibilizers are rarely available commercially, and when they are, they are usually speciality materials, made in small volume and quite expensive. For many polyblend systems, they do not exist at all, and require considerable research and custom synthesis, which are very expensive. 

In addition to the three major families of compati-biUzation reactions outlined above, organic polymer chemists have applied their ingenuity to a great variety of other reactions which can be used to compatibilize polyolefin polyblends. These may be classified as reactions of certain functional groups epoxy, carboxylic acid, hydroxyl, amine, oxazoline, and miscellaneous others. 

Future development will see two competing trends. On the one hand, major polymer producers will develop and sell standard grades of compatibilizers for major polyblend markets. On the other hand, with growing understanding and experience in compatibilization, increasing numbers of polyblend processors will develop their own proprietary ingredients and techniques for compatibilizing the polyblends they sell. 

Another area that must see serious development progress is increased understanding of the effects of compatibilizers and processes on morphology and final properties of polyblends. Only in this way can the field become more mature and productive. 

Polymer blending is a very convenient technique to produce materials of improved property/cost performances. Since most polymers are immiscible, polyblends usually have to be compatibilized in order to improve the poor mechanical performances associated with gross phase separation and low interfacial adhesion. Excellent reviews have been published on the compatibilization of multiphase polyblends [1-11]. 

These compatibilizers can be either pre-made or formed in situ in reactive blending processes. Fayt and co-workers [17-19] have compared the efficiency of pre-made compatibilizers in improving the ultimate mechanical properties of polyblends. The main conclusions were that... 

Recently, compatibilized polyblends have been prepared by mixing immiscible polymers able to interact mutually by hydrogen bonding, ionic bonding and acid-base complexation [23-25]. A macrophase separation, however, occurs commonly at temperature exceeding the dissociation temperature of the intermolecular interactions, the key issue being then the thermal stability of the released functional groups [26]. 

It may, however, be anticipated that the final phase morphology and mechanical properties strongly depend on the kinetics and completeness of the interfacial reaction with respect to the blending time and the phase morphology development. This chapter aims at emphasizing the experimental parameters, which are expected to control the reactive compatibilization with a special attention to the kinetic control of the interfacial reaction and its consequence on the performances of the polyblends. 

The use of reactive precursors of the compatibilizer offers a series of advantages. Indeed, the reactive polymers can be formed by easily implemented techniques, such as free radical copolymerization and melt grafting of reactive groups onto existing polymers. The compatibilizer is formed where it has to be localized, i.e. at the interface of the polyblend. Moreover, when the interface is saturated, the compatibilizer is no longer formed, so that the chance that the critical micelle concentration is exceeded is low compared to the use of pre-made compatibilizer, even though the in situ formed copolymer can be repelled from the interface after formation. Finally, the melt viscosity of the reactive precursors is lower than that of the parent pre-made compatibilizer, which is beneficial to the blend processing. 

The mechanical properties of the polyblends also depend on the architecture of the compatibilizer. A Monsanto patent reported on the influence of the MA content of... 

---