Scientists from Germany’s University of Bayreuth said they have developed an alternative polymer modelled on the chemical structure of commercial LDPE. The new material can be produced in a more energy-efficient way and is easier to recycle, they said.

Known as LDPE-mimic, the polymer is chemically recyclable and consists mainly of ethylene. Its material properties are partially comparable to LDPE, according to Rhett Kempe, chair of Inorganic Chemistry II-Catalyst Design at the university’s Sustainable Chemistry Centre, and research team leader. LDPE-mimic has potential as a sustainable alternative in the plastics industry.

LDPE-mimic has what Kempe describes as incorporated “recycling points”. It can be chemically broken down into smaller fragments that are soluble in organic solvents at moderate temperatures and can therefore be recycled. The components can then be recombined, allowing them to be reused in a closed cycle, Kempe noted.

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The research work, published in the journal Advanced Science, focused on production of the polymer under very mild or sustainable conditions, targeted replication or imitation of the chemical structure of LDPE, and chemical recyclability. The reason for this focus is the fact that LDPE is “one of the most widely used plastics in the world” and virtually non-degradable, the scientists said.

LDPE-mimic consists of two different macromonomers, which are compounds that have the structure of a monomer, allowing them to combine to form a larger molecule that is still able to crosslink or polymerise further.

The polymer mimic is made using a new catalyst developed through research conducted at the university, which produces defined building blocks of a certain size under mild reaction conditions, of around 70°C and 2 bar pressure. 

Commercial LDPE is produced in an energy-intensive, high-pressure process, with reaction conditions of 250°C and 2,000 - 4,000 bar pressure, through a free radical polymerisation of ethylene, Kempe said. The extreme reaction conditions are crucial to achieve the highly branched and complex chemical structure and associated material properties of commercial LDPE.

Its unique structure is why LDPE previously had been difficult to imitate, according to Kempe.