MATERIALS | COMPATIBILISERS
The researchers believe these massive improve- Reactor
Titanocene Polymerisation – Ethylene Monomer
Extruder
Titanate Copolymerisation – Ethylene Polymers
ments are based on molecular entanglements and co-crystallisation for tetrablocks and diblocks, respectively. “These results demonstrate exciting opportunities to recycle the world’s top two polymers through simple melt blending, obviating the need to separate these plastics in mixed waste streams,” they say. Addition of the compatibiliser does not require
More than 5% of PP in PE typically creates delamination. Kenrich Petrochemicals’s Salvatore Monte says phosphato titanate can be used to regenerate mixes with much higher PP contents (in this case, in a ratio of 80:20 LDPE:PP).
to reduce costs and boost sustainability efforts while integrating previously incompatible materials into their alloys.” Used at very low addition rates, it permits the inclusion of polyamide and polyester materials, including post-consumer recycled PET, in the alloy production process. “ZeMac Link NP is well suited for use in a breadth
of alloy applications including office furniture, fasteners, hand tools, outdoor equipment, textile bobbins and automotive accessories such as hubcaps,” says Prasad Taranekar, marketing man- ager at Vertellus. Glass fibre, minerals and impact modifiers may also be used with ZeMac Link NP. A team of researchers from Cornell University
and the University of Minnesota led by Geoffrey W. Coates are continuing their work on compatibilising polyethylene and polypropylene – which, despite their similar chemical make-up, are incompatible. They have developed ethylene-propylene multi- block copolymers (BCPs) with tunable molecular weights that create a new and mechanically tough product out of PE/PP blends. Their latest work, related to compatibilising isotactic PP and HDPE, is described in the American Chemical Society’s journal Macromolecules, 2018 51 (21), 8585-8596. “Tensile tests revealed a dramatic enhancement in toughness based on the strain at break, which increased from 10% for the unmodified blend to more than 300% with just 0.2 wt % BCP and over 500% with the addition of 0.5 wt % BCP or greater,” the resarchers say. “Incorporation of BCPs in blends also improved the impact toughness, doubling the Izod impact strength to a level comparable to the neat HDPE with just 1 wt % additive.”
52 PLASTICS RECYCLING WORLD | March/April 2019
any reactive compounding. The Cornel team note that reactive compatibilisation has many drawbacks. Reactions must be completed faster than the residence time in blending, greatly limiting the set of viable chemical reactions, for example; the formed chemical bonds need to be stable under processing conditions involving relatively high temperature and high shear; hazardous catalysts with heavy metal components are often needed to promote the reactions; and cross-linking often complicates control over morphology during processing. Non-reactive compatibilisation, on the other
hand, involves simple addition of premade compatibilisers along with PP and PE during the blending procedure. “Ideally, the compatibilisers migrate to and remain at the interfaces defining the separate phases, ‘emulsifying’ the blend and facilitating the formation of finer dispersions of the minor phase,” say the researchers. Asked about the commercial prospects for the development, Coates told Plastics Recycling World: “We have a partner and are gaining momentum. With that said, resin prices being so low are making it a tough business case.” He said he hoped to have more information to share by the end of the year. Salvatore Monte, President of Kenrich Petro- chemicals, would probably take issue with some of the comments from Cornell about reactive com- pounding. He is an advocate for the use of titanium and zirconium catalysts to regenerate various filled and unfilled plastics through repolymerisation. At the Society of Plastics Engineers’ PO2019 conference in Houston, US, in February, his presentation was full of slides showing how they work with mixes of polyeth- ylene and polypropylenes, as well as combinations of addition and condensation polymers. “For example, where delamination occurs in the injection moulding of HDPE parts containing more than 5% PP, blends of PE/PP-50/50 are made compatible with titanate catalyst,” he said. “Since Ti and Zr are used as catalysts in the formation of addition (polyolefins) and condensation (polyes- ters) polymers, the catalytic compatibilisation effect will be shown to occur in a mixture of macromol- ecules such as HDPE/PP/PET. “Multi-polymer compatibility obviates the need
www.plasticsrecyclingworld.com
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