Blends of polyolefins

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). 

J. Gonzalez, C. Albano, M. Ichazo, M. Hernandez and R. Sciamanna, Analysis of thermogravimetric data of blends of polyolefins with calcium carbonate treated with Lica 12, Polymer Degradation and Stability, 73, 211-224 (2001). 

In addition to the studies on blends of polyolefins described above, in which the two components are crystallizable, investigations have also been carried out on blends of non-crystallizable components. 

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. 

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. 

Blends of polyolefins (e.g., HPDE/LDPE, LDPE/ ethylene copolymers, PP/EPDM, PP/HDPE/EPDM, HDPE/butyl rubber) have been commercial since the late 1960 s and early 1970 s. Specific film formulations were commonly based on polyolefin blends to achieve the proper balance of processing, environmental stress crack resistance, modulus, toughness, cling, transparency, filler acceptance, printability, tear resistance, shrinkage characteristics, and permeability. Ethylene-propylene mbber (EPR, EPDM) was commonly incorporated into polypropylene as an impact modifier at moderate levels and as a flexibilizer at high levels. One of... 

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. 

There is a history of investigations of blends of polyolefins. Many of these blends were not produced on purpose but were the results of incompletely understood polymerization processes. Examples of these are the various smdies of elastomeric polypropylenes, which are mixtures of polypropylenes of varying tacticity levels (67-71). These materials often have interesting technological properties. It is of more concern to consider the results of specially prepared blends of known characterized polymers. 

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

Mechanical properties in the blends of polyolefin materials and elastomers are of considerable importance for engineering applications (40,41). Various elastomers... 

Polyolefins, one of the largest commodity polymeric plastics in the market place, have been widely studied over six decades covering synthesis, structural, physical, as well as mechanical properties point of views. However, the study on blends of polyolefins is rather scarce relative to their neat forms. One of the polyolefin blends that gained considerable attention is thermoplastic polyolefins (TPO) due to the enhanced impact strength and toughness of polyolefins. A typical example is a blend of polypropylene (PP) and ethylene-propylene mbber (EPR). EPR has been incorporated into PP through reaction in batch reactors or physical blending. The PP/EPR... 

Compatibilization and Crystallization of Blends of Polyolefins with a Semifiexible Liquid Crystalline Polymer... 

BLENDS OF POLYOLEFINS (HIGH DENSITY POLYETHYLENE AND ISOTACTIC POLYPROPYLENE) WITH A SEMIFLEXIBLE LIQUID CRYSTALLINE POLYMER... 

Isothermal Crystallization Kinetics of Compatibilized Blends of Polyolefins with a Semiflexible LCP... 

The investigation of the compatibilization and crystallization of blends of polyolefins with a semiflexible LCP leads to the following conclusions the compatibilization of polyolefin/LCP blends has been realized successfully by the addition of ad hoc synthesized polyolefin-g-LCP copolymers. The compatibilization results into materials, characterized by a stabilized morphology, improved crystallization kinetics under nonisothermal and isothermal conditions, and enhanced mechanical properties. Moreover, polyolefin processability has been enhanced by the addition of LCP, even in the presence of compatibilizers. New high quality materials with improved processability have been produced by technologies, which are economic, friendly to the environment, and socially acceptable. 

Olefinic thermoplastic elastomers are block copolymers or blends of polyolefins — commonly, polypropylene, which forms the hard crystalline block, and another olefin block, most commonly ethylene or EPDM. Some less common soft segments include natural rubber, nitrile rubber, and EVA. Olefinic thermoplastic elastomers exhibit better processability than neoprene and have excellent resistance to oils. Therefore, they offer attractive replacements for neoprene in oil-resistant wire and cable insulation. 

When testing for polyolefins with mercury(ll) oxide (see Section 6.2.1), in most cases, a yellow color develops more or less quickly. With blends of polyolefins, no significant color differentiation sufficient for identification occurs. However, if the polyethylene content of the blend is very high, no coloration, or only a slight coloration is seen because polyethylene does not react with mercury(ll) oxide. 

In order to obtain a cost-effective biodegradable plastic, the blends of polyolefin with starch are stiU one of the best alternatives due to their low price, better properties, broad suppliers, and mature processing facilities and techniques etc. However, starch and polyolefin blends are incompatible at the molecular level, which often leads to poor performance. In order to overcome this drawback, either polyolefins or starch can be modified by introducing a compatibilising agent into the blend. 

Blending of polyolefins is increasingly used to produce usable materials from polymer waste, to improve the processing and to retain the good thermal and mechanical properties. Blend prepared from virgin and/or recycled components is a well-established strategy to handle post-consumer and post-industrial polymeric wastes. HOPE and PP constitute a significant portion of post-consumer waste [29]. 

The use of blends of polyolefin elastomers, such as HR and EPDM, as substantial components in blends of unsaturated elastomers is a rapidly developing area. Mouri et al. [51] have compared the properties of EPDM-NR and... 

Ciardelli, R, Coiai, S., Passaglia, E., Pucci, A., and Ruggeri, G. 2008. Reactive blending of polyolefins to nanostructured functional thermoplastic materials. Polymer International R57 805 36. 

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). 

Pebar Blends of polyolefins (HOPE, PP) with high nitrile resin, Barcx BP Chemicals... 

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