Polymer immiscible

The film is fibrillated mechanically by mbbing or bmshing. Immiscible polymers, such as polyethylene or polystyrene (PS), may be added to polypropylene to promote fibrillation. Many common fiber-texturing techniques such as stuffer-box, false-twist, or knife-edge treatments improve the textile characteristics of slit-film fibers. 

Fig. 7. Types of dispersion of a polymer (dark regions) in the matrix of an immiscible polymer. The spherical droplets (a) are progressively extended into...

Alloys exhibit physical properties, the values of which are typically the weighted average of those of its constituents. In particular, the blend exhibits a single glass-transition temperature, often closely obeying semitheoretically derived equations. Blends of two compatibiLized immiscible polymers exhibit physical properties which depend on the physical arrangement of the constituents and thus maybe much closer to those of one of the parent resins. They will also typically exhibit the two glass-transition temperatures of their constituent resins. 

Fig. 9. The upper panel shows the predietions of Brown s [15] model for the eoupling of an immiscible polymer interface. Clearly the predietions do not agree with his experimental results on PMMA joined to PS-r-PMMA shown in the lower panel.

The interdiffusion of polymer chains occurs by two basic processes. When the joint is first made chain loops between entanglements cross the interface but this motion is restricted by the entanglements and independent of molecular weight. Whole chains also start to cross the interface by reptation, but this is a rather slower process and requires that the diffusion of the chain across the interface is led by a chain end. The initial rate of this process is thus strongly influenced by the distribution of the chain ends close to the interface. Although these diffusion processes are fairly well understood, it is clear from the discussion above on immiscible polymers that the relationships between the failure stress of the interface and the interface structure are less understood. The most common assumptions used have been that the interface can bear a stress that is either proportional to the length of chain that has reptated across the interface or proportional to some measure of the density of cross interface entanglements or loops. Each of these criteria can be used with the micro-mechanical models but it is unclear which, if either, assumption is correct. 

Char, K., Brown, H.R. and Deline, V.R., Effects of a diblock copolymer on adhesion between immiscible polymers, 2. PS-PMMA copolymer between PPO and PMMA. Macromolecules, 26(16), 4164-4171 (1993). 

Janarthanan et al. [67] have employed roughness on a micron scale to enhance the adhesion between two immiscible polymers, polycarbonate and styrene-acrylonitrile copolymer, SAN. Grooves of depths between 5 and 35 p,m were scribed in the polycarbonate surface before laminating the two polymers. The... 

The effect of viscosity ratio on the morphology of immiscible polymer blends has been studied by several researchers. Studies with blends of LCPs and thermoplastics have shown indications that for good fibrillation to be achieved the viscosity of the dispersed LCP phase should be lower than that of the matrix [22,38-44]. 

Since the processing conditions and mixing equipment have a crucial effect on the morphology of immiscible polymer blends [45], experiments were carried out in four different types of extruders to find optimal conditions for blend preparation and fibrillation. Nevertheless, the morphologies of PP-LCP blends produced by... 

Leibler [17] and Noolandi et al. [18,19] developed thermodynamic theories concerning the emulsification of copolymers (A-b-B) in immiscible polymer blends (A-B). 

Immiscible Polymer Blends A subclass of polymer blends referring to those blends that exhibit two or more phases at all compositions and temperatures,... 

Block and graft copolymers have many similar characteristics. Thus, both graft and block copolymers behave in various respects as two immiscible polymers... 

For general aspects on sonochemistry the reader is referred to references [174,180], and for cavitation to references [175,186]. Cordemans [187] has briefly reviewed the use of (ultra)sound in the chemical industry. Typical applications include thermally induced polymer cross-linking, dispersion of Ti02 pigments in paints, and stabilisation of emulsions. High power ultrasonic waves allow rapid in situ copolymerisation and compatibilisation of immiscible polymer melt blends. Roberts [170] has reviewed high-intensity ultrasonics, cavitation and relevant parameters (frequency, intensity,... 

Sundaraj, U., Dori, Y., and Macosko, C. W., Sheet formation in immiscible polymer blends model experiments on an initial blend morphology. Polymer 36,1957-1968 (1995). Swanson, P. D., and Ottino, J. M., A comparative computational and experimental study of chaotic mixing of viscous fluids, J. Fluid Mech. 213, 227-249 (1990). 

A stoichiometric forerunner of this approach was the wolf and lamb reaction, reported by Patchornik and co-workers in 1981 [17]. Two reagents that in solution react with each other quickly to give an undesired product (hence wolf and lamb ) were immobilized on solid polymeric supports (two insoluble and mutually immiscible polymers, Scheme 5.1), rendering them unreactive towards each other. This allowed the formation of the desired product through the use of a messenger reagent. 

Another important class of copolymers synthesized by chain polymerisation are block (or sequenced) copolymers diblock and triblock copolymers being the most important ones. They are very useful as compatibilisers (emulsifiers) in immiscible polymer blends. Another major use is as thermoplastic elastomers. Both uses are best explained through the example of butadiene-styrene block copolymers. 

In the coacervation process, the core substance is first added to a homogeneous solution of the selected solvent and polymer. Mechanical agitation is used to disperse the immiscible core to create tiny droplets suspended in solution (i.e., an emulsion). The coacervation or phase separation phenomenon is then induced by several means, such as changing the temperature and/or acidity of the polymer solution or adding salts, nonsolvents, or incompatible (immiscible) polymers to... 

Immiscible liquids, static mixing of, 16 715 Immiscible polymer blends, 20 318-319 barrier polymers, 3 396-398 heterogeneous, 20 357-358 Immiscible polymers, compatibilization of, 20 324-325... 

Additionally, some properties unique to both systems may result. The majority of homopolymer blends are immiscible with one another and often experience poor interfacial adhesion between the separate phases. Since block copolymers are covalently linked together, macroscopic incompatibility at the interface is minimized. The macroscopic incompatibility of a two-polymer blend may be eliminated by the addition of a block copolymer derived from the two systems. Hence, copolymers can be used to strengthen blends of immiscible polymers by serving as emulsifiers (7-9). 

The preparation of immiscible polymer blends is another way to disperse a bulk polymer into fine droplets. It has been reported for several polymers that when they are dispersed in immiscible matrices into droplets with average sizes of around 1 pm, they usually exhibit multiple crystallization exotherms in a differential scanning calorimetry (DSC) cooling scan from the melt (at a specific rate, e.g., 10 Cmin ). Frensch et al. [67] coined the term fractionated crystallization to indicate the difference exhibited by the bulk polymer, which crystallizes into a single exotherm, in comparison with one dispersed in a large number of droplets, whose crystallization is fractionated temperature-wise during cooling from the melt. 

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.

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