Does This Patent Signal a Turning Point in Sustainable Plastics?

There are really only a handful of things that motivate humanity to act. Greed and fear are certainly close to the top of that list. Neither of those are inherently bad or evil motivations. In general we have a fiduciary obligation to maximize profits while minimizing costs — what Buckminster Fuller termed ephemeralization. Likewise fear is the perfectly legitimate desire not to perish, nor kill one’s descendants. Those motivators create cultural and societal pressures that as often as not are the reasons for innovation.

Overcoming hurdles of bioplastics production

In the last few decades, one of those cultural pressures to innovate has come in the form of demand for biodegradable plastics, fueled by widespread concerns about the effects, both long and short term, of microplastics. Yet despite increasing societal pressure on the plastics industry to make plastics biodegradable, only about one-half of one percent (0.5%) of the 400 million tons of plastics produced globally each year are bioplastics, according to a report published by European Bioplastics, "Bioplastics Market Development Update 2023." The reasons for that miniscule fraction are largely the cost of producing bioplastics, and the structural and mechanical properties of the currently available bioplastics. Now, however, those classic hurdles may be coming to an end.

US patent awarded to Helsinki-based researchers

On Jan. 25, 2024, researchers at UPM-Kymmene Corp. in Helsinki were awarded US Patent #20240026157 for a “lignin-based bioplastic material.” The patent document specifies a compound consisting of a lignin fraction and at least one or more other biodegradable biopolymers. The wording, like most patents, is a little awkward, since lignin is itself a naturally occurring organic polymer, but let’s not quibble over semantics. Lignin is the second-most abundant organic substance on Earth after cellulose, and together with cellulose is one of the major constituents of wood, and most other plants for that matter. It gives cells their structure by filling the gaps between cellulose fibers. In a very real sense you could think of it as the glue that holds together a plant’s cells. In fact, if you are familiar with pelletized wood used for heating stoves, the wood fibers are forced through the openings in a pellet mill under high pressure and temperature, and the lignin melts and forms the adhesive that holds the wood fibers together into the shiny pellets.

Representation of a lignin molecule taken from the patent document. Image courtesy of UPM-Kymmene Corp.

The fact that lignin is ubiquitous should translate to a relatively inexpensive raw material in that portion of the new biopolymer compound. The patent lists a relatively lengthy number of the other biodegradable biopolymers as candidates to form the remainder of the compound: “. . . selected from polylactic acid (PLA), polyglycolic acid (PGA), poly(lactic-co-glycolic acid) (PLGA), poly(ε-caprolactone) (PCL), poly(butylenesuccinate) (PBS), poly(γ-glutamic acid) (PGA), polyhydroxyalkanoate (PHA), polyhydroxybutyrate(PHB), poly-3-hydroxyvalerate (PHV), thermoplastic starch (TPS), polybutylene adipate terephthalate(PBAT), starch blend, copolymers and mixtures thereof.” All of which are commercially available products. The number of permutations of possible compounds makes this a seemingly far-reaching patent.

Microplastics-free biodegradable ground-cover cloth

Now the patent is careful to make the point that no specific end-product is the focus of this technology, including the rather specific reference to an item having a 2D or 3D shape. It does, however, seem to be somewhat self-restricting in specifying applications relating to agriculture, and in particular, mulching ground-cover cloth. This is not to say that the new lignin-based bioplastic material couldn’t be used for other disposables, such as straws or containers, nor that such applications would fall outside of the protections of the patent. It briefly states: “The desired shape can be imparted by techniques, such as extrusion, injection molding, casting, compression molding, blow molding, rotation molding, thermoforming.” Specifying ground-cover cloth does give the inventors an advantage to list, which would not necessarily fall under these other uses. 

Ground-cover cloth is intended to be left to degrade into the soil, and having it do so without adding microplastics into the soil would be one such advantage, but the patent goes on to say that the materials when decomposed actually enhance the soil. “Once in soil, part of the lignin fraction is converted into humic acids, which are known to be growth enhancers and soil conditioners conventionally made from fossil deposits found as brown coal or turf.” It is claimed that these nutrient enhancements additionally act to protect against plant parasites (phytopathogens). That could, in theory, reduce the need for the application of other less desirable pest control measures.

Environmentally sound and cost effective

The patent refers to lignin fairly consistently as though it were just one thing. It is not. There are a variety of chemical forms of lignin depending on where it is extracted from, such as softwoods, hardwoods, or non-woody plants or biomass. Seemingly in the patent the molecular weight of the form of lignin appears to play a more important role than the actual type. This of course increases still further the number of possible permutations in the compound, but given the almost entirely innocuous environmental impact of lignin in general, the end result will likely be both beneficial and cost effective.