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A Low Cost Route to Thermoplastic Olefins with Excellent Low-Temperature Impact/Stiffness/Processability Balance

IP.com Disclosure Number: IPCOM000244378D
Publication Date: 2015-Dec-07
Document File: 12 page(s) / 44K

Publishing Venue

The IP.com Prior Art Database

Related People

Tonson Abraham: AUTHOR [+5]

Abstract

It is known that plastomers (for example ethylene/butene or ethylene/octene copolymer rubber produced by metallocene catalysis) are superior to ethylene/propylene rubber (EPR, produced by Ziegler-Natta or metallocene catalysts) for the impact modification of polypropylene (PP). However, thermoplastic olefins (TPOs) for automotive applications are produced using plastomer and EPR blends as PP impact modifier, in order to reduce compound cost. EPR is introduced via a polypropylene impact copolymer (ICP, reactor produced PP/EPR blend), as this is the lowest cost route to introducing EPR into a TPO. A judicious amount of EPR is chosen in order to minimize the negative effects of this rubber on TPO impact/stiffness balance.

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A Low Cost Route to Thermoplastic Olefins with Excellent Low-Temperature
Impact/Stiffness/Processability Balance

ABSTRACT: It is known that plastomers (for example ethylene/butene or ethylene/octene copolymer rubber produced by metallocene catalysis) are superior to ethylene/propylene rubber (EPR, produced by Ziegler-Natta or metallocene catalysts) for the impact modification of polypropylene (PP).  However, thermoplastic olefins (TPOs) for automotive applications are produced using plastomer and EPR blends as PP impact modifier, in order to reduce compound cost.  EPR is introduced via a polypropylene impact copolymer (ICP, reactor produced PP/EPR blend), as this is the lowest cost route to introducing EPR into a TPO.  A judicious amount of EPR is chosen in order to minimize the negative effects of this rubber on TPO impact/stiffness balance.

It has been unexpectedly found in this work that replacement of a small part of either the butene or octene plastomer in a TPO formulation containing plastomer as the only PP impact modifier, with a small amount of high molecular weight EPR, allows improvement in TPO impact/stiffness balance.

Furthermore, unexpectedly, once again, the use of higher Tg (glass transition temperature) butene plastomer, allowed better low-temperature ductility than the use of lower Tg octene plastomer in TPOs.

 TPOs can be reinforced with fillers such as talc, nano-talc, precipitated calcium carbonate, Wollastonite, Halloysite, and magnesium oxysulfate whiskers.

Isotactic polypropylene (PP) would be ideal for use in automobile interior and exterior applications due to low cost, low density, and high stiffness, except for the poor low temperature impact resistance of this material.  The low temperature impact resistance of PP is improved by melt compounding with polyolefinic elastomers, at the expense of reduced compound stiffness.  Reinforcing fillers are included in the melt compounding process in order to increase compound stiffness, and thus achieve the desired thermoplastic olefin (TPO) low-temperature impact/stiffness balance.

A low glass transition temperature (Tg, -50 to -65°C) is one of the key elastomer properties required to allow good low temperature (-30 to -40°C) TPO impact resistance.  Other key elastomer properties in this connection include appropriate molecular weight and appropriate compatibility with PP.  Although very high molecular weight rubber is expected to deliver excellent TPO impact properties, it would also be difficult to disperse said rubber into the PP matrix, during melt compounding, into particles with diameter of about 1-2 µm, which is required for excellent TPO impact properties.  In reinforced TPOs, particulate rubber that is much smaller or much larger than the desired size results in reduced TPO impact resistance.  The presence of very small rubber particles in a TPO would also reduce compound processability.  Rubber/plastic compatibility in the melt, and processing conditi...