Compatibility in polyblends

Kwei TK, Nishi T, Roberts RE. A study of compatible polymer mixtures. Macromolecules 1974 7 667-74. Yu AJ. Concept of compatibility in polyblends. Adv Chem 1971 99 2-14. 

Fig, VI-7 shows the electrical conductivity vs, weight fraction of the PANI-CSA complex in polyblends with PMMA [61,282,283], The results are typical in that a similar smooth onset for conductivity is observed with a number of host polymers fabricated with appropriate compatible counterions (e,g, DBSA for polythylene, etc,) [282,283], As shown in Fig, VI-7, these PANI blends are remarkable in that electrical conductivities of order 1 S/cm can be obtained in a polyblend containing only about 2% of the conductive component, with no indication of a sharp percolation threshold [284],... 

Compatible Polyblends. When the polymeric materials are compatible in all ratios, and/or all are soluble in each other, they are generally termed polyalloys. Very few pairs of polymers are completely compatible. The best known example is the polyblend of polyCphenylene oxide) (poly-2,6-dimethyl-l,4-phenylene oxide) with high-impact polystyrene (41). which is sold under the trade name of Noryl. It is believed that the two polymers have essentially identical solubility parameters. Other examples include blends of amorphous polycaprolactone with poly(vinyl chloride) (PVC) and butadiene/acrylonitrile rubber with PVC the compatibility is a result of the "acid-base" interaction between the polar substituents (1 ). These compatible blends exhibit physical properties that are intermediate to those of the components. 

A major problem in polyblend development is trying to predict polymer miscibility. The incompatibility of various pairs of polymers has been correlated with the mutual effects on intrinsic viscosities and dipole moment differences of the component polymers [67,68]. These results can give a guide for finding compatible polymer or polymer pairs or with very low incompatibility. 

Whereas incompatible partners in polyblends usually result in heterogeneous morphologies (e.g., styrene-butadiene SB), and often in highly resilient plastics, compatible partners result in plastics with moderate property profiles in accordance with the mixing percentages (e.g., PC/PBT). 

Polyester TPUs are compatible with PVC and other polar plastics. Offering value in the form of enhanced properties, they are unaffected by oils and chemicals, provide excellent abrasion resistance, offer a good balance of physical properties, and are perfect for use in polyblends. 

Evidently, the homogeneous complex phase is an equilibrium property for copolymers. Any effects resulting from the history of specimen preparation (cf., photomicrographs and dashed lines in Figures 9 and 10) are eliminated by annealing. In contrast, for polyblends the compatible phase is a metastable state. 

Appearance of Fused Product. From the fabrication point of view, if two polymers give a smooth band on a two-roll mill, the polyblend is said to be compatible. If the fused product is cheezy, it is said to be incompatible. Frequently, the fused product is pressed into a flat sheet. Transparency of the sheet signifies compatibility, whereas an opaque appearance means incompatibility. Obviously, these criteria are arbitrary and crude. They are subject to great variation owing to difference in individual judgement. In addition, they give no information on the morphological feature of the system. 

Matsuo, Nozaki, and Jyo (20) showed that heterogeneity at 100 A scale and under can be detected readily. Thus, microscopy can offer a measure of heterogeneity down to 0.01 p scale which is much smaller than the domain size of most polyblends. Results of microscopy have established convincingly that nearly all polyblends are heterogeneous two-phase systems. How does one describe the results Obviously, heterogeneity as revealed by microscopy is a relative property. If compatibility is used in a qualitative sense, a polyblend with a finer domain size will be more compatible than one with a larger size, provided equilibrium size distribution has been attained in both cases. 

In certain cases polyblends of two very compatible polymers also show just one T. The value of such a Tg can be predicted from either of the following equations ... 

It is well known that systems like polystyrene or polystyrene-acrylonitrile—generally considered brittle materials—have a remarkable increase in toughness and resistance to impact when polyblended with finely dispersed, crosslinked, but partly compatible, rubber particles. These particles are generally 0.1-10 fi in size and frequently consist of butadiene which has been grafted with monomers of similar composition to the matrix or continuous phase. 

Heat-resistant [218] soft foams were prepared from the blends of hdPE with E-P random copolymers. The azodicarbanamide acts as a thermal antioxidant and the crosslinking of the blend was increased by electron beam radiations and foamed at 225 °C with 2320% expansion. A blend of 35 wt.% PE-PP (8 92), 15 wt.% E-P block copolymers, and 50 wt.% EPDM showed accelerated weathering resitance [219] 1000 h probably due to crosslinking between constituents of the block copolymer, polyblend and EPDM. The effect of filler and thermodynamic compatibility on kaolin-filled PE-PP blend was studied by Lipatov and coworkers [220]. The thermodynamic interaction parameter (%) decreased and thermodynamic stability increased by filler addition, the degree of crystallinity decreased with increasing thermodynamic compatibility of the components due to sharp decrease in the phase separation rate during cooling. 

Polyblends are made by intimately mixing two or more polymers on mill rolls, in extruders, or in Banbury or other mixing devices. The polyblends are admixtures of either two rigid polymers or two elastomeric polymers, or combinations of the two types. Their properties, and therefore their end uses, are strongly dependent on the degree of compatibility of the components. 

Polyblends in which both phases are rigid are frequently called poly alloys. Poly (phenyl oxide) is blended with impact polystyrene to improve melt flow. Complete compatibility between the two phases is rare and was observed between poly (methyl methacrylate) and poly(vinylidene fluoride) by D. R. Paul and J. O. Altamirano. Thermoplastics are added to polyesters to reduce mold shrinkage. 

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