Blend immiscible, rubber

Immiscible blends of polyolefins have been compatibilized by copolymer formation brought about by radical coupling across a melt phase boundary, as shown in the examples listed in Table 5.44. The work of Kim et al. involved simultaneous copolymer formation between immiscible rubber and plastic phases with the dynamic vulcanization of the elastomeric phase. 

Blending PLA with immiscible rubber-like polymers represents a more interesting way to reduce PLA brittleness, while keeping stiffness acceptable and preventing any undesirable aging. This yields a new type of polymeric materials with different properties, in which each polymeric partner provides its own feature in terms of impact-absorbing ability from impact modifiers and stiffness from PLA [49-51]. Recently, NatureWorks has defined the key parameters of impact modifiers useful for toughening PLA as follows [52] ... 

Over the past decade extensive work has been done to develop a novel extrusion process with the aid of high power ultrasound [18-22], A number of studies on the effect of ultrasound on polymers have been published and reported in various review articles and books. It was shown that ultrasonic oscillations can breakdown the 3-D network in vulcanized rubber within seconds. Ultrasound was found to improve the compatibilization of immiscible plastic blends, plastics/rubber and rubber/rubber blends during extrusion process [23]. In recent years, use of ultrasound to disperse nanofdler in a polymer matrix is gaining attention. Ultrasound helps in rapid exfoliation and intercalation of nano-clay in a polymer matrix [24]. 

Park et al. [20] reported on the synthesis of poly-(chloroprene-co-isobutyl methacrylate) and its compati-bilizing effect in immiscible polychloroprene-poly(iso-butyl methacrylate) blends. A copolymer of chloroprene rubber (CR) and isobutyl methacrylate (iBMA) poly[CP-Co-(BMA)] and a graft copolymer of iBMA and poly-chloroprene [poly(CR-g-iBMA)] were prepared for comparison. Blends of CR and PiBMA are prepared by the solution casting technique using THF as the solvent. The morphology and glass-transition temperature behavior indicated that the blend is an immiscible one. It was found that both the copolymers can improve the miscibility, but the efficiency is higher in poly(CR-Co-iBMA) than in poly(CR-g-iBMA),... 

The important factors that affect the rubber toughening are (1) interfacial adhesion, (2) nature of the matrix, (3) concentration of the rubber phase, and (4) shape and size of the rubber particles. In the PS-XNBR blend containing OPS, due to the reaction between oxazoline groups of OPS and carboxylic groups of XNBR, the interfacial adhesion increases and as a result, the minor rubber phase becomes more dispersed. The immiscible blend needs an optimum interfacial adhesion and particle size for maximum impact property. In PS-XNBR, a very small concentration of OPS provides this optimum interfacial adhesion and particle size. The interfacial adhesion beyond this point does not necessarily result in further toughening. 

Pandey et al. have used ultrasonic velocity measurement to study compatibility of EPDM and acrylonitrile-butadiene rubber (NBR) blends at various blend ratios and in the presence of compa-tibilizers, namely chloro-sulfonated polyethylene (CSM) and chlorinated polyethylene (CM) [22]. They used an ultrasonic interferometer to measure sound velocity in solutions of the mbbers and then-blends. A plot of ultrasonic velocity versus composition of the blends is given in Eigure 11.1. Whereas the solution of the neat blends exhibits a wavy curve (with rise and fall), the curves for blends with compatibihzers (CSM and CM) are hnear. They resemble the curves for free energy change versus composition, where sinusoidal curves in the middle represent immiscibility and upper and lower curves stand for miscibihty. Similar curves are obtained for solutions containing 2 and 5 wt% of the blends. These results were confirmed by measurements with atomic force microscopy (AEM) and dynamic mechanical analysis as shown in Eigures 11.2 and 11.3. Substantial earher work on binary and ternary blends, particularly using EPDM and nitrile mbber, has been reported. 

Recently, a new concept in the preparation of TPVs has been introduced, based on the reaction-induced phase separation (RIPS) of miscible blends of a semicrystalline thermoplastic in combination with an elastomer, with the potential for obtaining submicrometer rubber dispersions. This RIPS can be applied to a variety of miscible blends, in which the elastomer precursor phase was selectively crosslinked to induce phase separation. Plausible schematic representation of the morphological evolution of dynamic vulcanization of immiscible and miscible blends is shown in Fig. 9. For immiscible blends, dynamic vulcanization leads to a decrease in the size... 

Immiscible Blends. Rubber. Elastomer/elastomer blends are used extensively for commercial applications, particularly in the construction of automobile tires. There is an extensive patent and technological literature on this subject. A recent review (see chapter 19 of Ref. 19 by McDonel, Baranwal, and Andries) summarizes a great deal of this... 

Abis et al. [32] also obtained evidence on compression molded blends of sPS/ SEBS of the occurrence of a phase compatibility between the components arising from the solubility of the polystyrene end-block of SEBS with the amorphous phase of sPS. In fact, although immiscible, a very fine dispersion and adhesion of the rubber particles is observed on SEM. However, contrary to the previous case, no improvement in the mechanical properties of sPS measured by tensile tests is observed, probably owing to the poorer performances of thermo-compressed samples than injection molded samples [38,39]. 

PP-PA6 Blends Containing Dispersed Core-Shell Microparticles. In the third type of PP-PA6 blend system, the PP-g-MA blend com-patibilizer and rubber was completely substituted by maleic anhydride-grafted rubbers such as EPR-g-MA and SEBS-g-MA. As reported previously (22, 23) and schematically represented in Figure 4, imide-coupling at the PP-PA6 interface, and surface-tension gradient and immiscibility between PP, PA6, and rubber are responsible for the accumulation of the rubber at the PA6 microparticle surface, which results in microparticles with a PA6 core and a rubber shell. Like PP-g-MA blend compatibilizers, maleic anhydride-grafted rub-... 

Blending within the family of PO has, however, been more common [Plochocki, 1978]. Although they are usually immiscible with each other, there exists some degree of mutual compatibihty between them. The similarity of their hydrocarbon backbones and the closeness of their solubility parameters, although not adequate for miscibility, accounts for a relatively low degree of interfacial tension. Eor example, the solubility parameters of polyethylene, polyisobutylene, ethylene-propylene rubber and polypropylene are estimated to be 16.0, 15.4,... 

---