Commercial Polyolefin Blends

Blends of ethylene copolymers (such as ethylene-vinyl acetate, ethylene-ethyl acrylate, ethylene-acrylic acid copolymers) have been typically added to LDPE, HDPE and LLDPE to improve filler and additive acceptance, balance film properties, improve environmental stress crack resistance, tear resistance, toughness and surface properties. These blends are particularly prevalent in film formulations and as such are rarely disclosed by the manufacturer. Equistar has introduced functionalized polyolefins (Integrate ) to improve dispersion and adhesion in wood fiber filled and mineral filled polyolefin composites. Arkema Group offers Lotryl ethylene-acrylate (methyl, butyl and 2-ethyl hexyl) copolymers and notes the wide range of compatibility with other polyolefins as well as polyamides and polyesters. 

Metallocene based polyolefins and polyolefin elastomeric compositions (POE) are often noted in supplier product literature to exhibit useful (and commercially viable) properties in blends with other polyolefins. Metallocene based polyethylene has also been noted to have the potential to replace the LLDPE/LDPE blends that are employed in a myriad of film applications [32 ]. PP/metaUocene ethylene-a-olefin copolymer blends for car interior applications have been noted [33 ]. MetaUocene-LLDPE blends with HDPE have been proposed for heavy-duty industrial grade bags as well as food packaging films [34]. Exxon-Mobil product literature notes the utility and ease of blending the metallocene LLDPE Exceed with other polyolefins. PP/POE blends showed similar mechanical properties and lower viscosity than the more conventional PP/EPDM blends [35]. Polyolefin plastomers (POP) imder the tradename Affinity GA were introduced by Dow as a polymer blend additive to improve the flow without loss of 

Polyisobutylene has been added to HDPE and LDPE to improve toughness, tear resistance and environmental stress rupture resistance. Commercial systems include Allied Chemical s ET polymers and BASF s Lupolen . Polypropylene/poly(butene-l) blends have been shown to exhibit miscibility and utility in films has been noted with some commercial activity [43, 44].Increased crystallization rate of poly( 1 -butene) with PP addition offers a blend approach as a nucleation additive [45]. Poly(l-butene)/LDPE blends have been employed as peelable films in packaging applications [46]. 

Ticona s COC (cyclic olefin copolymer) (Topas ) has been noted to significantly reduce the part warpage of fiberglass filled polypropylene. Commercial utility in automotive apphcations has been noted. 

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In this chapter, an overview of the commercially important blends is presented with a particular emphasis on the rationale for their commercial development, the compatibilization principles, their key mechanical properties and their current applications and markets. To facilitate the discussion, the commercial polymer blends have been classified into twelve major groups depending on the type of the resin family they are based on, viz. (i) polyolefin, (ii) styrenic, (iii) vinyl, (iv) acrylic, (v) elastomeric,... 

Several approaches to compatibilizing PPE blends with commercial polyolefins (polypropylene, etc.) have been reported in the literature [Lee, 1990 Kirkpatrick, 1989]. However, no commercial blends of PPE/polyolefins have been offered to date. CompatibUization and impact modification of PPE/polypropylene can be achieved by choosing a selected type of styrene-ethylene/butylene-styrene block copolymer and PPE of low molecular weight [Akkapeddi and VanBuskirk, 1992]. 

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... 

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. 

Polyolefin blends of commercial importance are normally made via two methods blending in the melt either during polymerization or mechanically after the polymerization process. The first method, called in-reactor blending, involves the blending of different polyolefins (homopolymers, random, and block copolymers) in a polymerization reactor. This is enabled by the presence of multiple catalyst species... 

Table 1.3 shows a summary of specific polyolefin blends that have been studied in the literature extracted from references (25-310). These blends involve the following polyolefins PP, PE (LLDPE, LDPE, HDPE, and UHMWPE), EPR, EPDM, and PB. Some of the blends listed in Table 1.3 are of commercial... 

Numerous nylon blends prepared by compatibilization or reactive blending are commercially successful. The modifiers fiequenfly utilized in commercial nylon blends include polyolefin, thermoplastic polyolefin, thermoplastic polyunethane, ionomer, elastomer, ethylene-propylene rubber, nitrile mbber, polyftetrafluoroethylene), poly (phenylene ether), poly(ether amide), silicone, glass fiber, and carbon fiber. The nonpolar modifiers such as polyolefin, maleic anhydride or a polar vinyl monomer such as acrylic acid, methaciylic acid and fimiaric acid is fiequently incorporated to introduce reactive sites in nylon. 

Blending within the family of polyolefins has, however, been more common (Plochocki 1978). Although they are usually immiscible with each other, there exists some degree of mutual compatibility between them. The similarity of their hydrocarbon backbones and the closeness of their solubility parameters, although not adequate for miscibility, account for a relatively low degree of interfacial tension. For example, the solubility parameters of polyethylene, polyisobutylene, ethylene-propylene rubber, and polypropylene are estimated to be 16.0,16.4,16.5, and 17.0 cm respectively, all very close to each other (VanKrevelen 1990). Similarly, the interfacial tension coefficients between PE or PP and EP-elastomers are quite small (typically ca. 0.1 MN/m) (Shih 1990 Wu 1989). Hence, polyolefin blends have been made since the early days of polyolefin commercialization via a simple melt mixing, without a compatibUizer. 

Thermoplastic polyolefin (TPO) is a generic name that refers to polyolefin blends usually consisting of some fraction of polypropylene (PP), polyethylene (PE) or polypropylene block copolymer (PP-b-EP or BCPP ), and a thermoplastic olefinic rubber, with or without a mineral reinforcing filler such as talc or wollastonite. Common rubbers include ethylene propylene rubber (EPR), EPDM rubber, ethylene-octene (EO) copolymer mbber, ethylene-butadiene (EB), and styrene-ethylene-butadiene-styrene (SEBS) block copolymer rubbers. Currently, there are a great variety of commercial polypropylene homopolymers, PP block copolymers, and olefinic rubbers available to make a wide range of TPO blends with densities ranging from 0.92 to 1.1. 

Several approaches to compatibilizing PPE blends with commercial polyolefins (polypropylene, etc.) have been reported in the literature (Lee 1990 Kirkpatrick et al. 1989). Simultaneous compatibilization and impact modification of PPE/polypropylene blends was achieved by choosing selected types of styrene-ethylene/butylene-styrene block copolymers and PPE resin of low molecular weight (Akkapeddi and VanBuskirk 1992). A family of PPE/polypropylene alloys were commercially launched by G.E. in 2001, under the Noryl PPX trade name, and these are now sold by Sabic. Typical properties of a commercial PPE/PP blend are shown in Table 19.32. These PPE/PP blends are claimed to offer a balance of cost and performance between the TPOs and other higher-cost engineering thermoplastics such as nylons, modified PET, and PBT resins. Basically, the PPE/PP blends offer a balance of key properties stiffness, toughness, chemical, and heat resistance. 

Polyolefin blends are of critical importance to the success of the material. Ethylene propylene diene rubber (EPDM) immiscibly blends with PP as an impact modifier. It is the most common and most commercially utilised blend of polyolefins. High-density polyethylene (HOPE) can be added to this blend to achieve maximum toughness [11-13]. Applications include wire and cable insulation, automotive... 

Only two classes of polypropylene (PP) blends have achieved commercial success blends wiA polyolefins and with polyamides (PA). With PP/polyolefin blends, the goal is either to improve the impact resistance of the base resin (impact-modified PPs) or to produce thermoplastic elastomers (d)mamically vulcanized blends). PA/PP blends aim at bridging the property gap between the two pol5oners. Therefore, sigitificant information on processing is available only for these two families of blends. 

Melt blending of polymers is a widely used technique for tailor-making polymeric materials to generate the desired properties. Blending polypropylene block copolymer (PPBC) with elastomeric ethylene-propylene-diene terpolymer (EPDM) produces a range of useful materials commercialized in early 1970 s that found significant uses in the automotive industry. Polyolefin-based bumpers dominate the automobile market in Europe and Japan and have made in-roads in the North American market. In India, the polyolefin blend for car bumpers was commercialized in 1992. 

Plastic automobile bumpers entered Indian market along with the Maruti car production in India. Initially, the bumpers were molded in India with an imported blend from Japan. The development and commercialization of the high impact polyolefin blend came as a break-through in achieving self-reliance in polymer blend technology in Indian industry as the import of this blend from Japan was halted. 

The demand for the polyolefin blend from M/s. Maruti Udyog Ltd., for their Maruti-800 CC car bumpers alone was around 250 tons in the first year of its commercialization. In the succeeding year its consumption for the bumper application is expected to rise up to 800 tons. Diversification of this blend for different applications is going to boost up the demand. 

Other elastomer blends of commercial utility have been cited in the literature [96-98]. Polyolefin blends have been utilized in many forms to achieve modifications yielding environmental stress rupture resistance and to improve impact strength, flexibility, and filler acceptance [99,100]. The addition of ethylene-propylene rubber (EPR) or blends of EPR and high-density PE to PP has been specifically utilized for improving the low-temperature impact strength [101]. Low-modulus materials can be produced from EPR-PP blends containing more than 50% of EPR. These products include those under the trade names TPR, Somel, and Telcar [102-105]. Addition of rubber inclusion has been shown to yield definite improvements in the environmental stress rupture resistance [106]. Other examples of commercial rubber-based blends are impact-PS, ABS and bisphenol A polycarbonate blends and polysulfone blends made of a block copolymer of polysulfone and nylon 6 [107]. 

Generally fair to good mechanical compatibiUty exists with various combinations of the noted polyolefins, as may be expected due to the similarity of structure. This has resulted in a large number of combinations achieving commercial status (as wih be discussed in Chapter 7). The blends are often prepared via extrusion melt mixing however, the utiUzation of multiple catalysts or variations in monomer feed compositions can produce polyolefin blends during... 

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