Creating polymer “ladder branches” yields flexible plastics similar to LDPE, scientists find

19 Mar 2024 --- Researchers are proposing a more sustainable and “industrially viable” method to create plastics that are “comparable” to widely used low-density PE (LDPE). Speaking to Packaging Insights, the researchers highlight that LDPE’s unique properties are derived from its “tree-branch-like” molecular structure, which makes it flexible. 

The soft and lightweight material is also ductile due to its lower crystallinity. These properties set it apart from other, more linear varieties of PE.

However, LDPE’s characteristic long-chain branching polymerization is commonly achieved through an energy-intensive, high-pressure synthesis process.

In the study led by The Dow Chemical Company and the American Association for the Advancement of Science (AAAS), the authors detail a new approach to control long-chain branching in polyethylene under “milder” solution-phase conditions. 

Plastic created through “ladder-branching”
The new method uses dual-chain catalysts, which can assemble two polymer chains at once — linked to one another through a small amount of diene mixed in with the ethylene — creating a “ladder-like” molecular structure. 

According to the researchers, this novel “ladder-branching process” produces a plastic that exhibits “comparable properties” to those of LDPE or its blends with other forms of linear LDPE (LLDPE).

LDPE has a wide variety of commercial applications, including plastic films, bottles and other pliable products.“The main focus of our work has been on operability and melt properties. The ladder LLDPE process has a narrower molecular weight distribution compared to LDPE and thus would be expected to have fewer lower molecular weight extractables,” Dr. Robert Froese, research scientist at The Dow Chemical Company, tells us.

“For just the PE reactor, the LLDPE process emits 66% less CO2 equivalents and uses 64% less water than the LDPE process.”

Scalability and cost margins
Dr. Froese expects this technology to be scalable for an LLDPE process. “It does require a very small amount of diene which could incur a marginal cost increase to that of a traditional LLDPE process,” he adds.

Considering LDPE’s wide variety of commercial applications — including plastic films, bottles and other pliable products — developing a similarly performing material with a lower footprint could mean significant gains.

Dr. Froese is asked whether, beyond LDPE, this dual-chain catalyst approach be adapted to create other types of sustainable polymers with different functionalities.

“Work on the dual-chain catalyst concept is on-going, but we are focused on applications and architectures with long-chain branching,” he responds.

By Benjamin Ferrer