Polyolefins, commodity, properties

Titanium-based solid-state catalysts for the industrial production of polyolefin materials were discovered in the early 1950 s and have been continually improved since then (see Section 7.3). Due to the high degree to which they have been perfected for the production of large-volume polyolefin commodities, they continue to dominate the processes presently used for polyolefin production. Despite (or because of) this product-oriented perfection, only limited degrees of variability with regard to some relevant polymer properties appear to be inherent in these solid-state catalysts. 

More expensive than commodities such as polyolefins, PVC and polystyrene brittle when dry, sensitive to water (swelling up to 10%, decrease in mechanical and electrical properties) opaque or translucent require UV and weathering protection significant shrinkage after moulding inherent flammability (but FR grades are marketed). 

Table 1 Typical physical and (room temperature) mechanical properties (melting point Tm, glass transition temperature Tg) Young s modulus E, Izod toughness, tensile yield stress av elongation at break b) and applications of commodity polyolefins...

Abstract Polyolefins such as polyethylene, polypropylene and their copolymers have excellent bulk physical/chemical properties, are inexpensive and easy to process. Yet they have not gained considerable importance as speciality materials due to their inert surface. Polyethylene in particular holds a unique status due to its excellent manufacturer- and user-friendly properties. Thus, special surface properties, which polyethylene does not possess, such as printability, hydrophilicity, roughness, lubricity, selective permeability and adhesion of micro-organisms, underscore the need for tailoring the surface of this valuable commodity polymer. The present article reviews some of the existing and emerging techniques of surface modification and characterisation of polyethylene. 

CEOs of a number of long-standing players appear to have decided the answers are negative, on the evidence of some major divestments of commodity chemical properties in recent years. These include BASF s and Shell s decision to divest polyolefins maker Basell, BP s spinning off its Innovene petrochemicals unit, DSM s sale of its petrochemicals to Sabic, and DuPont s divestment of its Invista fibers business, which includes leading petrochemical stakes, specifically in nylon and polyester intermediates. 

The living character of organolithium polymerizations makes such processes ideally suited for the preparation of pure as well as tapered-block copolymers. Diene-olefin pure-block copolymers have become important commodities because of their unique structure-property relationships. When such copolymers have an ABA or (AB) X [A = polyolefin, e.g., polystyrene or poly(a-methylstyrene) B = polydiene, e.g., polybutadiene or polyisoprene and X = coupling-agent residue] arrangement of the blocks, the copolymers have found use as thermoplastic elastomers (i.e., elastomers that can be processed as thermoplastics). 

Essentially, then, no new, large-volume, highly profitable fibers have been developed since the mid-1950s. Instead, the existing ones have become commodities with all the economic impact thereby implied. No major chemical engineering processes have been added, although the previously described ones have been modified to allow for spinning of liquid crystalline polymers or the formation of gel spun fibers. Research activity has been reduced and centered essentially on modifications of fiber size, shape, and properties, and many variants now are successfully marketed. Production volumes have increased enormously for nylon, polyester, and polyolefin. 

Polystyrene is one of the most widely used thermoplastic materials ranking behind polyolefins and PVC. Owing to their special property profile, styrene polymers are placed between commodity and speciality polymers. Since its commercial introduction in the 1930s until the present day, polystyrene has been subjected to numerous improvements. The main development directions were aimed at copolymerization of styrene with polar comonomers such as acrylonitrile, (meth)acrylates or maleic anhydride, at impact modification with different rubbers or styrene-butadiene block copolymers and at blending with other polymers such as polyphenylene ether (PPE) or polyolefins. 

Polystyrene was commercialized by I. G. Farben in 1931 and it has long been used as a commodity plastic. Although polystyrene is endowed with excellent properties not found in other commodity plastics such as polyolefins, its amorphous nature (relatively low heat and solvent resistance) limits its use in some application areas. 

The goal of combining two or more polymers such as pairs from those categories described above e.g., an engineering thermoplastic plus a commodity polyolefin) is to achieve in the blend a combination of favorable properties from each polymer. Figure 5.1 shows idealized expected property combinations from blending two polymers that are either miscible (solid center line), immiscible and uncompatibilized (bottom line), or immiscible and compatibilized (top line). In the case of polymers that are miscible in all propor-... 

Polyolefins are synthetic polymers of olefinic monomers. They are the largest polymer family by volume of production and consumption. Several million metric tons of polyolefins are produced and consumed worldwide each year, and as such they are regarded as commodity polymers. Polyolefins have enjoyed great success due to many application opportunities, relatively low cost, and wide range of properties. Polyolefins are recyclable and significant improvement in properties is available via blending and composite technologies. 

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... 

Copolymers exhibit properties much closer to those of LDPE, but their availability and price still represent a hindrance for these materials to be considered as serious competitors against commodity polyolefins. 

---