Blend other polyolefins

The first article may be a polymer composition with a COC as basic material. Suitable low crystallinity polymers to fabricate the second article include COCs and blends of COCs with poly(methyl pentene), other polyolefins, and styrenics. 

The decorative laminates described in the previous chapter are made with selected thermosetting resins while resins of this type can be moulded and extruded by methods similar to those outlined in the present and the next chapter the materials employed for these processes predominantly are thermoplastic. Many such plastics can be moulded and extruded under suitable conditions, the most important in terms of quantities used being those that combine properties satisfactory for the purpose with convenience in pro-cessing-especially the polyolefins (polyethylene and polypropylene), poly(vinyl chloride), and styrene polymers and blends. Other plastics with special qualities, such as better resistance to chemical attack, heat, impact, and wear, also are used—including acetals (polyformaldehyde or polyoxymethylene), polyamides, polycarbonates, thermoplastic polyesters like poly(ethylene terephtha-late) and poly(butylene terephthalate), and modified poly(phenylene oxide),... 

In addition to the polyolefin blends designed for thermoplastic elastomer applications, a great deal of interest also has centered on other kinds of blends of polyolefins as has been reviewed recently (see chapter 21 of Ref. 10 by Plochocki). In a recent paper (84), we showed that blends involving polypropylene-high density polyethylene-low density polyethylene in various proportions and combinations exhibit additivity of tensile strength however, there are serious losses in ductility in some cases such that the blends are less ductile than either pure component. It is interesting to note, however, that these losses in ductility can largely be restored by addition of rather small amounts of an amorphous ethylene-propylene rubber (84). 

There have been recent efforts to predict, or at least rationalize, the x parameters of these and other polyolefin-polyolefin blends. Bates et al. (1992) and Fredrickson et al. (1994) suggest that the x parameter is correlated to a difference in statistical segment length of the polymer molecules, on a volume-normalized basis. The volume normalization is required because the definition of the statistical segment length depends on how the monomer unit... 

Injection molding conditions of blends of polyolefin resins and other commodity resins are listed respectively in Tables 10.25 and 10.26. The conditions represent an average for each type of blend. They usually vary slightly from one grade to another. Recommended practices and specific comments are discussed below for each type of blend. 

One of the major areas for potential involves the synthesis of polyolefin block copolymers. A PP-EPR-PP or PE-EPR-PE block copolymer could have large potential as is or in blends with other polyolefins. PE-EPR-PE block copolymers have been synthesized via anionic polymerization of butadiene-isoprene-butadiene ABA block copolymers followed by hydrogenation [Mohajer et al, 1982 Rangarajanout et al., 1993]. These materials would have utility in hot melt adhesive formulations as well as general-purpose thermoplastic elastomer applications. Improvements on the synthesis procedures to offer viable approaches to polyolefin block copolymers could open up a new class of commercial polyolefins. In summary, several opportunities exist for new combinations of commercial blends from the list of commodity polymers. 

There are two classes of polyolefin blends elastomeric polyolefin blends also called polyolefin elastomers (POE) and nonelastomeric polyolefin blends. Elastomeric polyolefin blends are a subclass of thermoplastic elastomers (TPEs). In general, TPEs are rubbery materials that are processable as thermoplastics but exhibit properties similar to those of vulcanized rubbers at usage temperatures (19). In TPEs, the rubbery components may constitute the major phase. However, TPEs include many other base resins, which are not polyolefins, such as polyurethanes, copolyamides, copolyesters, styrenics, and so on. TPEs are now the third largest synthetic elastomer in total volume produced worldwide after styrene-butadiene rubber (SBR) and butadiene mbber (BR). 

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. 

It is our purpose here to summarize the characteristics of blends of polyolefins. We consider both blends of polyolefins with other polyolefins and with nonpolyolefins including polyamides and polystyrenes. In the case of interpolyolefin blends, our primary concern is with miscibility. In the case of blends of polyolefins with nonpolyolefins, the blends are all inuniscible and our concern is with phase morphology. We also consider three component blend systems where the third component is a surfactant or compatibilizing agent, which collects at the interface. 

TERNARY BLENDS OF POLYOLEFINS WITH OTHER POLYMERS AND COMPATIBILIZING AGENTS... 

The miscibility of olefin copolymers such as ethylene-a-olefin copolymers was found to be controlled by the structural composition and the primary strucmre of the copolymers. Using these copolymers, binary blends with various compatibilities were prepared and the effects of compatibihty on mechanical properties in the binary blends were investigated. The tensile properties in binary blends of iPP with rubbery olefin copolymers are considerably influenced by the miscibility between iPP and the copolymers. The miscibility of iPP with other polyolefins is described in detail based on the dynamic mechanical properties, morphology observation, and solidification process. It is found that EBR, EHR, and EOR having more than 50 mol% of a-olefin are miscible with iPP in the molten state. In the solid state, the miscible copolymers are dissolved in the amorphous region of iPP, although the copolymers are excluded from crystalhne lattice of iPP. The isotactic propylene sequence in the EP copolymers with a propylene-unit content of more than 84 mol% participates in the crystallization process of iPP, resulting that a part of the EP copolymers is included in the crystalline lattice of iPP. 

Multiple notable reviews of elastomer blends exist. The first general treatment of the subject by Hess et al. (1993) reviews the applications, analysis, and the properties of the immiscible elastomer blends. Two related treatments by Roland (1989) and Ngai and Roland (2004) exist and describe the physics of mixing immiscible polymer blends and a more recent account of the analytical methods. Mangaraj (2002) has a more detailed review of elastomer blends. Other reviews by Corish (1978) and McDonel et al. (1978) deal with specific aspects of elastomer blends. A publication by Zhang (2009) on specific EPDM blends with NR/BR for tire sidewall approaches this area from the view of a specific application. Less comprehensive accounts of this area are also described for polyolefin elastomer blends by Slusarski et al. (2003) and Feldman (2005). 

Future applications of blending include blending the polyolefin with other polymers such as polyaniline (PANI) to reduce oxidation in food packaging due to the fact that PANI has free radical scavenging properties. 

A number of other polymers have been blended with polyolefins for a number of applications. Space does not allow one to give too many details about work done on these systems. This section will therefore summarize the proposed applications for these systems, and some veiy interesting observations will be included. 

COC is often blended with other polyolefins. Manufacturers and trade names Topas Advanced Polymers Topas . 

There are some newer application areas and polymer blend products targeted to fit those new opportunities. The latter include such combinations as PVC and PS blended with PP, HOPE, and each other metallocene-polymerized nanoscale blends of polyolefins with more polar polymer partners and, for high-temperature/high-performance applications, PPS blended with PSF, PEI, and polyamides as well as blends incorporating poly(aryl ketones), polyimides, and poly(amide-imides) (Thomas et al. 2006). 

---