The challenges of alternative polymer materials—namely, those that are “biobased” and lay claim to being compostable and degradable—loom large. None have captured any significant market share even for single-use items such as cutlery, serviceware and food containers, primarily because of these challenges.
Last month, Colorado State University (CSU; Fort Collins) chemists announced in the journal Science a major step toward waste-free, sustainable materials that one day could compete with conventional plastics. Led by Eugene Chen, a professor in the department of chemistry, they have discovered a polymer with many of the same characteristics as conventional plastics: Light weight, heat resistance, strength and durability. Unlike typical plastics, however, the new polymer can be converted back to its original small-molecule state for complete chemical recyclability. This can be accomplished without the use of toxic chemicals or intensive lab procedures.
The work builds on a previous generation of chemically recyclable polymer that Chen’s lab first demonstrated in 2015. Making the old version required extremely cold conditions that limited its industrial potential. The previous polymer also had low heat resistance and molecular weight, and while plastic-like, was relatively soft, said the report published in ScienceDaily (April 26, 2018).
That has been the problem with many attempts to make “eco-friendly” polymers using bio-based or plant-based materials. Obviously, all petroleum is plant-based—it’s called “fossil fuel” because it comes from the remains of ancient organisms such as plants and animals. It has taken millions of years to go from plants to oil but, technically, all petroleum is biobased, so we in the industry should not make a distinction such as, petroleum based = bad; plant- or biobased = good.
According to the CSU report, the new, much improved polymer resolves the issues surrounding the first-generation material. While the report doesn’t specify where the monomer comes from, it does reveal that the monomer can be conveniently polymerized under environmentally friendly, industrially realistic conditions: Polymerization is achieved solvent-free at room temperature, with just a few minutes of reaction time and only a trace amount of catalyst.
The resulting material has a high molecular weight, thermal stability and crystallinity, and mechanical properties that perform very much like a plastic. Most importantly, the report said, “the polymer can be recycled back to its original, monomeric state under mild lab conditions using a catalyst." Without need for further purification, the monomer can be re-polymerized, thus establishing what Chen calls a circular materials life cycle.
Chen and his colleagues are excited about the prospects for a “future in which new, green plastics, rather than surviving in landfills and oceans for millions of years, can be simply placed in a reactor and ‘depolymerized’ to recover their value—not possible for today’s petroleum plastics. Back at its chemical starting point, the material could be used over and over again, completely redefining what it means to ‘recycle,’” said CSU’s report.
“The polymers can be chemically recycled and reused, in principle, infinitely,” Chen said.