Melt, generally blending

When both phases are fluid, such as melt polymer blends, no general predictions of macrorheological behavior can be established. Generally, two distinct morphologies are observed, with the dispersed phase distributed either as ribbons or droplets. Droplets appear to be less deformable than an equivalent viscous Newtonian droplet. The resistance to breakdown in shear often makes most intensive shear mixers ineffective and leads to the need of employing other flow fields different from shear to achieve a good dispersion. 

Bitinis et developed for the first time a novel and industrially scalable PLA-NR blend prepared by melt mixing blends at 5,10 and 20 wt% of natural rubber to analyze the effect of the NR concentration on the blend morphology. Figure 7.5 shows SEM micrographs of the blends fracture surfaces where it is observed that the size of the rubber particles is similar for 5 and 10 wt% but increases for the blend at 20 wt% from 1.15 to 2.00 pm. In general, in an immiscible binary polymer blend, the size of the dispersed phase increases as a function of the concentration of the minor phase in the blend, due to coalescence phenomena. ... 

PBS has properties similar to PET. It has a crystallinity of 35 5%, a glass transition temperature of —32 °C and a melt temperature of 114-115 °C. PBS is generally blended with other compounds, such as starch and adipate copolymers (to form PBSA). PBSA has a crystallinity of 20-35%, a Tg of —45 °C and a Tm of 93-95 °C. Its properties are close to those of LDPE (linear low density polyethylene). 

Block (Star) Arrangement. The known star polymers, like their linear counterparts, exhibit microphase separation. In general, they exhibit higher viscosities in the melt than their analogous linear materials. Their rheological behavior is reminiscent of network materials rather than linear block copolymers (58). Although they have been used as compatibiUzers in polymer blends, they are not as effective at property enhancements as linear diblocks... 

Blends with styrenic block copolymers improve the flexibiUty of bitumens and asphalts. The block copolymer content of these blends is usually less than 20% even as Httie as 3% can make significant differences to the properties of asphalt (qv). The block copolymers make the products more flexible, especially at low temperatures, and increase their softening point. They generally decrease the penetration and reduce the tendency to flow at high service temperatures and they also increase the stiffness, tensile strength, ductility, and elastic recovery of the final products. Melt viscosities at processing temperatures remain relatively low so the materials are still easy to apply. As the polymer concentration is increased to about 5%, an interconnected polymer network is formed. At this point the nature of the mixture changes from an asphalt modified by a polymer to a polymer extended with an asphalt. 

Appendix B General Properties and Data on Elastomers and Plastics 175 Table B.IO True Stress at Break of Selected Melt-Mixed Rubber-Plastic Blends ... 

Many confections are coated in a thin layer of chocolate. The latter is a mixture of chocolate, cocoa butter and other fats, blended to form a suitable coating material. This layer melts at a temperature generally in the range 27-34°C. The manufacturer wishes to coat the confection in a thin, continuous layer, and then harden this layer so that the product can be wrapped and packed with the least delay on the production line. 

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,... 

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