Phase co-continuous

Miles IS, ZurekA (1988) Preparation, structure, and properties of two-phase co-continuous polymer blends. Poly Eng Sci 28 796... 

See Figure 20.1 for a schematic illustration of the general types of behavior often observed in multiphase systems containing components differing widely in a property. This figure also highlights the qualitative nature of the effects of phase co-continuity as well as of phase inversion which occurs in some (but not all) types of multiphase systems. While the illustration in Figure 20.1 is for the shear modulus, qualitatively similar behavior is often also observed for the other elastic moduli, the coefficients of thermal expansion, and the transport properties. 

The first ABS/PA blends were announced in 1961 [Grabowski, 1964b, 1966], and much later introduced as Elemid . Triax -1000 is an alloy of PA-66 with ABS-MA, having the phase co-continuity [Lavengood et al., 1986, 1988]. PA-6 was also blended with BR grafted with styrene andMA (SBMA) [Asahi-Dow Ltd., 1981]. Later, transparent blends of copolyamide(s), PA, and ABS were developed [Fox et al., 1989]. 

PEST s are immiscible with polyphenylsulfides (PPS) or polyphenylenesulphidesulfone (PPSS). The customary three types of uncompatibUized blends are known, with 5-10 wt% of the dispersed (either PPS or PEST) phase and the phase co-continuity. The compatibilized blends (with a copolymer containing either epoxy or acid anhydride groups) show high tensile and impact... 

By contrast, the ECP must have conjugated rigid-rod macromolecules. Several such polymers show high electrical conductivity (usually after doping), viz. polyacetylene (PAc), polyaniline (PANI), polypyrrole (PPy), polyparaphenylenes (PPP), or poly-3-octyl thiophene (POT). The resins are expensive, difficult to process, brittle and affected by ambient moisture, thus blending is desirable. For uniaxially stretched fibers the percolation threshold is 1.8 vol%, hence low concentration of ECP (usually 5-6 vol%) provides sufficient phase co-continuity to ascertain conductivity similar to that of copper wires (see Table 1.79). 

Figure 7.1. For immiscible blends the onset of phase co-continuity should coincide with the percolation threshold.

Similarly, the first normal stress difference, Nj, also is predicted to be proportional to the shear stress. The phase co-continuity condition was derived from the equal shear stress principle between two phase-separating phases. The dependence is the same as empirically derived by Paul and Barlow — see Eq 7.6. 

Commodity resins. Most polymers are immiscible, some, as PS with PO, antagonistically so. Outside the ranges of high dilution and of phase co-continuity, the PO/PS blends need to... 

It is good to remember two ways for generating well-performing, immiscible blends generation of phase co-continuity [Morrow et al.,... 

Since the successful S-S thermodynamic theory assumes fee or hep packing with the coordination number z = 12, the most probable value of Pc is 0.120. However, if the cluster formation starts at Tc, from Tc/Tg=l/ 1 -pc)= 1.15 - 1.35, then pc = 0.13 to 0.26, which suggest fee hep or bcc packing. It is noteworthy that the hindered molecular dynamics at Tg occurs at the percolation threshold similar in magnitude to the values found for formation of percolative phase co-continuity in polymer blends (i.e., Pc = 0.15 to 0.21) [Lyngaae-Jprgensen and Utracki, 1991]. 

PA 6/ABS 45/55 MWCNT masterbatch PA 6 phase Co-continuous structure. Tensile modulus increases, while elongation at break and impact strength decrease with the addition of CNT. The onset of electrical conductivity was observed at 2-3 wt% CNT Meincke et al. 2004... 

PE/PA6 PA 6 20-37 wt% MWCNT PA 6 phase Co-continuous structures were obtained by blending PE with PA6-CNT masterbatch. Nanocomposites showed solvent resistance, improvement in tensile modulus, and increase in the tensile strength as the PA 6 and CNT content increase Perie et al. 2012... 

The boundary region between two phases in polymer blends, the matrix polymer and the dispersed phase, or (in case of phase co-continuity) between two polymeric phases. In compatibilized blends, the interphase contains the compatibilizer as well as low-molecular-weight additives and fractions. 

The phase co-continuity provides the best balance of properties, e.g. maximum ductility, high rigidity and large elongation. Two basic methods are used to generate this structure (1) SD by control of T, P, and solvent evaporation rate and (2) rheologically controlled phase inversion. CompatibUization is used to optimize the degree of dispersion [1, 9]. 

Almost all PP blends are immiscible the only miscible ones are those with aPP, some sPP, EPR containing la s 10% of ethylene, and atactic polybutene-1 (PB-1) [4]. However, the isotactic PB-1 was reported immiscible with PP [5]. In immiscible blends, the interfacial adhesion in both molten and solid states is usually poor, thus compatibilization is advisable. However, as for any immiscible polymer pair, there are three cases where acceptable product is obtained without compatibilization (1) at low concentration of either component, i.e., at < ) = 1 - s 0.1 (2) blends with phase co-continuity, e.g., = < >inversion/ (3) for applications not requiring high strength. 

In a sense, the styrene-butadiene block copolymers, SB or SBS, (first reported in 1956) constituted the next stage of PS modification. The triblock styrene-diene thermoplastic elastomers were patented in 1962, and soon incorporated in blends with PS, PP, LDPE, HDPE, PPE, PET, PBT, or PC, either as impact modifiers or compatibilizers [Bull and Holden, 1977]. In the 1977-78 patents (applications in 1976) it was disclosed that selective hydrogenation of these copolymers leads to new materials, with properties particularly attractive for polymer blends. For example, blending hydrogenated-SBS, or SEES, generated phase co-continuity in blends with PP, PA, PC, PBT, PES, etc. [Gergen et al., 1987]. More recent modification of these copolymers involved incorporation of acidic or acid-anhydride moieties. 

In this case, the matrix and the dispersed phase are equally deformed. Because of the mass convective processes, the phase co-continuity (similar to the interpenetrating... 

Commodity resins. Outside the range of phase co-continuity the PO/PS blends need to be compatibilized. There are several methods of compatibilization out of which the addition of styrene-elastomer block copolymers and reactive radical co-grafting are most conunon. For example, PCW comprising 55-75 wt% PO, 5-25 wt% PS, 5-15 wt% PVC, and 0-10 wt% of other thermoplastics, was compatibilized with 3-20 wt% SB, and stabilized by adding 0.1 -0.5 wt% of pentaerythritol ester and tris(2,4-di-tert-butyl phenyl) phosphite at a ratio of 5 1 to 1 5. The recycled mixtures showed good long-term performance [8]. 

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