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Keywords: Polymer blend vs. copolymer

With this blog post, we want to establish a series within the blog that takes up technical terms and/or keywords from plastics technology. The focus here is on keywords that are often incorrectly used synonymously or in a technically incorrect context.

The technical terms polymer blend and copolymer are often used incorrectly. A polymer blend is a physical mixture of two polymer components. If, for example, polyethylene and polypropylene are only physically mixed using a compounder or extruder, the result is a polyethylene/polypropylene blend. In this particular case, polyethylene pellets and polypropylene pellets are premixed in a defined mixing ratio and melted in a compounder or extruder, homogenized and regranulated or processed further directly. In the polyethylene/polypropylene blend just mentioned, the polyethylene phase in the blend would ensure an increase in toughness on the one hand and a lowering of the glass transition point on the other.

A copolymer is a chemical mixture of two monomers. If, for example, ethylene and propylene are copolymerized using reactive processes, the result is an ethylene-propylene copolymer. In ethylene-propylene copolymers, polyethylene (specifically the monomer ethylene) and polypropylene (specifically the monomer propylene) are chemically combined (mixed). This chemical mixture just mentioned, for example, ensures no or only very little crystallization in practice, as the chain folding process of the macromolecules as a prerequisite for crystallization is severely restricted by the now rather bulky structure of the macromolecules. In practice, the ethylene-propylene copolymer is therefore rather amorphous and has a slightly sticky surface.

To summarize, the user can remember that a polymer blend is a simple physical mixture of two polymers, while a copolymer is a chemical mixture of different monomers with very far-reaching structural and property-changing effects.

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