Plastomers, additives

In addition to the two-phase TPEs, two new technologies have emerged. They are the metallocene-catalyzed polyolefin plastomers (POPs, the name given to Exxon s EXACT product line) and polyolefin elastomers (POEs, DuPont Dow Elastomer s ENGAGE), and reactor-made thermoplastic polyolefin elastomers (R-TPOs). These new types of TPEs are often called metallocene elastomers-TPEs (MEs-TPEs) [87]. The new POPs and POEs are essentially very low-molecular-weight-Unear low-density PEs (VLMW-LLDPE). These new-generation TPEs exhibit mbber-like properties and can be processed on... 

Structurally, plastomers straddle the property range between elastomers and plastics. Plastomers inherently contain some level of crystallinity due to the predominant monomer in a crystalline sequence within the polymer chains. The most common type of this residual crystallinity is ethylene (for ethylene-predominant plastomers or E-plastomers) or isotactic propylene in meso (or m) sequences (for propylene-predominant plastomers or P-plastomers). Uninterrupted sequences of these monomers crystallize into periodic strucmres, which form crystalline lamellae. Plastomers contain in addition at least one monomer, which interrupts this sequencing of crystalline mers. This may be a monomer too large to fit into the crystal lattice. An example is the incorporation of 1-octene into a polyethylene chain. The residual hexyl side chain provides a site for the dislocation of the periodic structure required for crystals to be formed. Another example would be the incorporation of a stereo error in the insertion of propylene. Thus, a propylene insertion with an r dyad leads similarly to a dislocation in the periodic structure required for the formation of an iPP crystal. In uniformly back-mixed polymerization processes, with a single discrete polymerization catalyst, the incorporation of these intermptions is statistical and controlled by the kinetics of the polymerization process. These statistics are known as reactivity ratios. 

Elastomeric composition for dynamic application of cross-linked E-plastomers has been made with filer-reinforced systems which contain a metal salt (typically zinc) of an alpha, beta unsaturated acid. These additives improve the tensile and tear strength of the elastomer and are cured with a peroxide cure system. These cross-linked articles are suitable for dynamic loading applications such as belting, including power transmission and flat belting. 

This development was technologically successful and E-plastomers are widely recognized to be very effective impact modifiers for iPP. In initial experiments, binary blends of iPP were compounded with EPDM, E-plastomers, or SEES as the elastomeric phase. In comparison to the known modifiers, such as EPDM or SEES, the binary blends with E-plastomers have properties which strongly depend on the amount and the identity of the E-plastomer. Thus, the addition of... 

In addition to the properties noted above, the formulation parameter in iPP-E-plastomer blends have a profound influence on the dynamic loading (e.g., vibration) performance. The load limits of the blend for applications in which dynamic stresses are predominant were studied by using the hysteresis measurement method. However, their technical application requires knowledge of critical load values. 

Recent advances in the application of ultrafine talc for enhanced mechanical and thermal properties have been studied [12]. A particularly important use is of finely divided filler in TPO as a flame-retardant additive. In a representative formulation, 37 parts of E-plastomer, Ml 2.0, density 0.92, 60 parts of amorphous EPR, and 4 parts of fine carbon black were dry blended, kneaded at 180°C, pelletized, and press molded into test pieces, which showed oxygen index 32 versus 31 in the absence of a filler. The oxygen index is a measure of flame retardancy. 

E-plastomers, particularly the high- and medium-density materials, have found extensive use in films [17]. They are valued for their excellent seal character which allows the formation of mechanically strong seals at relatively low temperatures compared to traditional low-density polyethylene (LDPE). In addition, these E-plastomers can be obtained in a range of crystallinities and softness. These higher-density materials are typically made in the blown-film process and are used for protective film covers and disposable bags. 

The Tg of P-plastomers changes as a function of ethylene content. The Tg decreases with increasing ethylene content, primarily due to an increase in chain flexibility and loss of pendant methyl residues due to incorporation of ethylene units in the backbone. It is well known that PP has a Tg of 0°C, and polyethylene a Tg< —65°C. The addition of ethylene to a propylene polymer would therefore be expected to decrease the Tg, as is observed here. A secondary effect would be the reduction in the level of crystallinity associated with increasing ethylene content, which is expected to reduce the constraints placed upon the amorphous regions in proximity to the crystallites. Thus, an increase in ethylene content will result in a lower T as well as an increase in magnitude and a decrease in breadth of the glass transition. 

Woods, S. S. and Pocius, A. V., The Influence of Polymer Processing Additives (PPAS) on the Surface and Optical Properties of Polyolefin Plastomer Blown Eilm, SPEANTEC Tech. Papers, 46, 191 (2000)... 

Wilkinson and Lamb 1999). The use of DEHP in domestically produced teethers and rattles has been discontinued (Consumer Product Safety Commission 1999d). DEHP is also no longer used as a plasticizer in plastic food wrap products (Mannsville Chemical Products Corporation 1999). In addition, some applications, like automobile upholstery, might switch from DEHP to linear phthalates because of their superior performance and low toxicity, which will put further downward pressure on DEHP use (Mannsville Chemical Products Corporation 1999). Finally, in the future, polyolefin metallocene plastomers might replace flexible applications for PVC altogether because they provide flexibility without the need for plasticizers. 

Impact-modifying additives designed to inaease the drop impaa resistance of rigid PP containers, for example, may also be chosen for how they affea darity. PO bottles require low-temperature drop-impact properties in particular, which can be enhanced with additions of metallocene plastomer modifiers. However, these modifiers can create haze if they have shown large enough differences in refractive index with the base resin. Specifically, in tests of HDPE bottles, plastomers with lower densities ( 0.900) were found to affea darity very little (20%-24% haze), whereas a 0.910-density plastomer produced "noticeable" haze (37%) [10-22]. 

In addition to plastomers, polymers are also used as elastomers (mbber-... 

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