Multiphase polymers particle size

X-ray diffraction consists of the measurement of the coherent scattering of x-rays (phenomenon 4 above). X-ray diffraction is used to determine the identity of crystalline phases in a multiphase powder sample and the atomic and molecular stmctures of single crystals. It can also be used to determine stmctural details of polymers, fibers, thin films, and amorphous soflds and to study stress, texture, and particle size. 

As may be guessed from the names for these systems, the rubber particles are added to improve the mechanical properties of the matrix material, particularly to improve their low impact strength. The size of the rubber particles, their distribution, composition and compatability with the matrix all influence the mechanical properties of the final engineering resin. T) ical multiphase polymers which include elastomers... 

The materials that degrade into small stable particles are blends often starches are blended with non-degradable thermoplastics such as PE. The same considerations noted in this section on multiphase polymers hold true for these blends. For instance, the interfacial energy and rheology play a role in the size of the dispersed phases. These blends can often be processed by standard melt forming polymer techniques, by compounding and extrusion into films and fibers and injection or blow molded to form polymer... 

There are multiphase polymers where OM and SEM techniques cannot fully describe the microstructure due to a combination of small particle size (less than 0.5 /xm) and good adhesion between the dispersed phase and the matrix. Additionally, broad particle size distributions are often encountered, and in these cases a combination of techniques is required to describe the microstructure. TEM requires ultrathin specimens, about 50-500 nm or less in thickness, which are prepared by film casting or ultrathin sectioning. Films formed by casting or dipping methods provide a much easier specimen preparation method than ultrathin sectioning of bulk plastics. However, a major question in such studies is always whether the microstructure is the same as in bulk polymers of industrial interest. Specific stains are often required to provide contrast between the dispersed phase and the matrix pol)m[ier. 

The microscopy of rubbers generally involves the characterization of the particle size distribution of additives like carbon black. The topic of microscopy of rubbers is found in many sections of this chapter. Much of the discussion of multiphase polymers (Section 5.3.3) involves rubber domains and particles that must be characterized to imderstand the performance of... 

The structure and morphology of multiphase polymers have been discussed (Section 5.3) and the particle size and distribution have been shown to be quite important for both mechanical properties and applications. In many polymers (e.g. ABS), the particle size distribution is... 

Processing plays a major role in the nature of the dispersed phase in multiphase polymers. Changes in the shear forces and the temperature provide different structures. In the case of PS modified with polyisoprene, TEM studies showed that smaller particles, broken down in size by melt shearing, resulted in lowered impact strength and increased tensile strength [183]. Particle dimensions have also been shown to be affected by the viscosity of the molten polymer and the concentration modifier. Heikens et al. [184] investigated copolymer modified PS and... 

Fig. 5.51 SEI of a multiphase polymer (A) shows large dispersed phase particles and submicrometer sized particles and holes. BEI (B) shows that the dispersed phase particles have higher atomic number than the matrix. Elemental, mapping shows the small particles contain antimony (C) whereas the larger particles contain chlorine (D). Once the specific size/shape of the particles are identified by mapping, BEI imaging can be used to study the specimen surface.

From a theoretical point of view, fillers, introduced into the matrix, must be characterized by numerous parameters (shape, dimension, size distribution, orientation in matrix, composition, etc.) the mean particle size of disperse phase is the most convenient parameter. Here we use the word phase only to describe the reinforcing component, not the thermodynamic meaning of the notion as a structure, a uniform part of a substance. Many reinforcing fillers may be composed of heterogeneous multiphase systems. For the convenience of comparison, the mean values of particle sizes (in m), introduced into a polymer ma-... 

In the second chapter (Preparation of polymer-based nanomaterials), we summarize and discuss the literature data concerning of polymer and polymer particle preparations. This includes the description of mechanism of the radical polymerization of unsaturated monomers by which polymer (latexes) dispersions are generated. The mechanism of polymer particles (latexes) formation is both a science and an art. A science is expressed by the kinetic processes of the free radical-initiated polymerization of unsaturated monomers in the multiphase systems. It is an art in that way that the recipes containing monomer, water, emulsifier, initiator and additives give rise to the polymer particles with the different shapes, sizes and composition. The spherical shape of polymer particles and the uniformity of their size distribution are reviewed. The reaction mechanisms of polymer particle preparation in the micellar systems such as emulsion, miniemulsion and microemulsion polymerizations are described. The short section on radical polymerization mechanism is included. Furthermore, the formation of larger sized monodisperse polymer particles by the dispersion polymerization is reviewed as well as the assembling phenomena of polymer nanoparticles. 

Representative SEM images (Fig. 4.41) show a range of different multiphase polymers in notched Izod impact fractured specimens. A polymer with large, nonuniform, dispersed phase particles, not well adhered to the matrix, is shown in Fig. 4.41A. A much finer dispersed phase is shown in Fig. 4.41B with both particles and holes from particle pullouts. Smaller particles are not as obvious in Fig. 4.41 C, although the dispersed phase accounts for 15% of the specimen. Finally, the SEM image in Fig. 4.41 D does not reveal the elastomer, so the size and distribution of the dispersed phase must be provided by some other microscopy technique. 

The structure and morphology of multiphase polymers have been discussed (see Section 5.3), and the particle size and distribution have been shown to be quite important for mechanical properties and applications. In many polymers (e.g., ABS), the particle size distribution is determined during the rubber manufacturing process. The surfactant concentration during emulsion polymerization controls the size distribution of the rubber latex, and subsequent grafting increases the size further. Particle sizes can be controlled to yield a range of sizes or a monodisperse latex. Particles that are larger... 

Emulsion polymerization is usually carried out isothermally in batch or continuous stirred-tank reactors. Temperature control is much easier than for bulk or solution polymerization because the small ( 0.5 fim) polymer particles, which are the locus of the reaction, are suspended in a continuous aqueous medium. This complex, multiphase reactor also shows multiple steady states under isothermal conditions. In industrial practice, such a reactor often shows sustained oscillations. Solid-catalyzed olefin polymerization in a slurry batch reactor is a classic example of a slurry reactor where the solid particles change size and characteristics with time during the reaction process. 

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