Melt-mixing process

Migration of Impurities During the Melt-Mixing Process... 

Several factors determine the possibility for the impurities to migrate from one phase to the other phase during the melt-mixing process. 

Galeski et al. [1984] and Teh et al. [1983] have investigated PP/LDPE blends. No shift of the melting peak for LDPE has been observed. Both authors showed migration of the impurities during the melt-mixing process from the PP towards the LDPE phase. No further details on the crystallization behavior of the LDPE droplets themselves were reported. 

The crystallization of a continuous matrix in which the dispersed phase is in the molten state can be influenced by several phenomena. One of the most important factors that play a role here is the possibility that impurities and nuclei migrate during the melt-mixing process. 

Two important types of elastomeric polyolefin blends are reactor-made iPP/ EPR blends and postreactor blend iPP/EPDM. The latter is called thermoplastic vulcanizates (TPVs), produced by dynamic vulcanization of blends containing a thermoplastic and an elastomer. To make iPP/EPDM TPV, the two polymers PP and EPDM are mixed with curatives, such as peroxides, phenolic resins, or sulfur with accelerators, and dynamically cured in an extmder resulting in a blend consisting of micrometer-sized elastomer particles dispersed in the PP matrix (20-24). Paraffinic oils are added in the melt mixing process for viscosity control and cost. In iPP/ EPDM TPV, the crystalline iPP resin is normally the minor phase. Recently, polyolefin plastomers have been added to the class of elastomeric polyolefin blends. Polyolefin plastomers are ultralow molecular weight linear low density polyethylenes (ULMW-LLDPE). Nonelastomeric polyolefin blends are blends of polyolefins with mostly nonpolyolefin (other thermoplastic) matrices as mentioned earlier. 

The morphology of the uncured material prior to cure, but after incorporation of the curing agent was determined by TEM. The morphology was altered by the melt mix process much smaller particles were observed with average diameters of O.ll/ m, with no evidence of core-shell structures. 

A novel technology combining high-energy electron-induced chemical reactions and melt-mixing process was used to prepare blends of PP random copolymer with GRT particles without and with the presence of polyfunctional monomers (Sritragool et al., 2010). It was shown that to compatibilize PP/GRT blends, specific monomer is required to obtain improved properties. 

Montaudo, G., Montaudo, M.S., Scamporrino, E., and Vitalini, D., Mechanism of Exchange in Polyesters. Composition and Microstructure of Copolymers Formed in the Melt-Mixing Process of Poly(ethylene terephthalate) and Poly(ethylene adipate). Macromolecules, 25, 5099 (1992). 

PEN/phthalonitrile prepolymer blends were prepared by a melt mixing process [35]. The melt-mixed PEN/phthalonitrile blends exhibit excellent melt flow... 

Figure 35-10. Notched bar impact strengths, as a function of the mass fraction of the poly(butadiene) component in blends from cis-BR and PS made by the latex process, L, melt-mixing process, M, and the in situ polymerization process, P. (After J. A. Manson and L. H. Sperling.)...

Recently, Moad et al. [288,289] designed and prepared novel copolymer intercalant/dis-persant/exfoliant systems that are effective with unmodified clays at low levels (<20% with respect to clay), can be combined with commercial PP and clay in a conventional melt-mixing process, and do not require the use of additional compatibilizers. PP-clay nanocomposites prepared by direct melt mixing using unmodified MMX clays and a copolymer additive added at a level of only 1 wt.% with respect to PP for 5wt.% clay Authors investigated the following two classes of dispersants (1) polyethylene oxide-based nonionic surfactants... 

When polymers are grossly incompatible, mixing of these polymers generates blends that have very poor mechanical properties and produce a rough surface [5]. Both drawbacks of such blends can be minimized by appropriate use of an additive known as a compatibilizer [5-9]. The compatibilizer can also be produced in situ during melt mixing process. This process will be considered later in this chapter. Examples of common technologically compatible plastic/mbber blends are ... 

The goal here is to start with one or more plastics and rubbers and combine them together by a melt mixing process (irrespective of the type of mixing equipment) in such a way that the blend components are distributed evenly and well dispersed on a micro level, as shown by a conceptual drawing in Figure 3.1 [llj. In blends that are... 

The compatibilizer is a block or a graft copolymer. One segment of this block/graft copolymer is miscible with one component of the blend, while the other segment is miscible with the other component of the blend. During the melt mixing process, the compatibilizer becomes located at the interface of these immiscible polymers and improves the adhesion between the two phases. 

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