Conventional plastics – what are the problems?
Conventional plastics are heavily relied on for modern living; their durability, versatility, and low weight and cost, means they are used in everything from food packaging to circuit boards. However, these same beneficial properties provide significant challenges to both disposal of waste and the search for replacement materials. The chemical structure of the most common plastics, such as polyethylene (PE), polypropylene (PP) and polystyrene, comprise strong C-C bond links, requiring thousands of years to fully degrade. When disposed of improperly, plastics persist in the natural environment, creating vast amounts of plastic pollution. A notable example being the Great Pacific Garbage Patch, floating at the ocean’s surface between Hawaii and California and comprising more than 80,000 tonnes of plastic, it spans an area three times the size of France – a number which has been increasing exponentially from the 1970s.
Exacerbating this problem is the fact that current plastic consumption is mostly single use, for example, in 2016, 480 billion plastic bottles were bought, equating to a million bottles a minute. The problems associated with improper plastic disposal include toxicity to sea surface feeders, entanglement of wildlife, bioaccumulation of plastic chemicals and micro plastic particles in the food chain, and the economic costs of environmental damage to marine and land ecosystems. However, disposal of plastics is not the only problem. Conventional plastics are petroleum derived, and therefore associated with a high carbon footprint, contributing to global warming.
The need for viable alternatives to conventional plastics is clear. However, creating alternatives with comparable material properties which can be both produced and disposed of in a sustainable way, sets a high bar for research.
Bioplastics – a solution?
The term bioplastic defines any polymeric material that is derived from a renewable biomass source, such as starch, food waste, and vegetable oils. Bioplastics may not necessarily biodegrade faster than petrochemically-derived analogues but the by-products they produce are non-toxic and environmentally benign. While bioplastics have the potential to tackle many of the problems associated with petrochemically-derived plastics, they may still persist in the environment for considerable periods of time and can be equally pervasive if disposed of improperly.
While the environmental issues associated with plastic have been widely covered in recent news, research into bioplastics has in fact been ongoing for decades. Potential replacement materials are known already, including synthetic bioplastics where monomers are derived from biomass and subsequently polymerised to form polymers, for example polyhydroxyalkanoates and the PET replacement, polyethylene furandicarboxylate (PEF), in addition to polymers derived from the valorisation of biomass where lignocellulosic material is processed to produce thermoplastics. The growing interest in bioplastics is reflected in a steady increase in the number of patent applications; from 500 applications in 1999 to around 7000 applications in 2016, including from companies such as Natureworks and Corbion. However, the high cost associated with producing these materials, in addition to insufficient material properties, has inhibited the wide spread penetration of these materials into the commodity plastics market.
One bioplastic that has received significant attention is polylactic acid (PLA), an aliphatic polyester produced from lactic acid monomers. The monomers are derived from the fermentation of carbohydrates, in a method similar to that which occurs in the body, and conversely can be enzymatically broken down, firstly into soluble oligomers and then CO2 and H2O. PLA’s position as one of the leading bioplastics is evident in the increasing number of patent applications directed towards this material, from 350 in 1999 to 3300 in 2016.
The production of high molecular weight PLA was first patented by DuPont in 1954, utilising ring-opening polymerisation of the cyclic dimer (lactide). The resulting polymers were found to have good mechanical properties and have fast rates of biodegradation. As a result, PLA has found utility in medical applications, such as bioabsorbable sutures, orthopaedic devices, and drug-delivery applications. However, the high costs associated with the production of PLA, which requires temperatures in excess of 200 °C and volatilisation steps, has restricted its use to high-end applications. Furthermore, additives are often required to provide the required properties for certain common applications such as barrier properties suitable for food packaging applications. Consequently, PLA production is still relatively small (ca. 200,000 tonnes in 2014 compared to 350 million tonnes of plastic in total produced globally in 2017), a number which reflects the relative penetration of all bioplastics into the commodity plastics market.
What comes next?
An example of a more recent advance in sustainable polymer technology is poly(diketonenamine) (PDK). Whilst not a biopolymer, per se, PDK is a new material capable of reversible polymerization, giving it the potential to provide a plastic with minimal environmental impact. Researchers at Berkeley Lab in the USA discovered that PDK can be depolymerised to their monomers with the simple addition of an acid and then easily separated from the other chemical additives (for example, those added to improve material properties, such as flexibility).
The discovery allows for the recovery of the monomers from PDK, which can then be re-manufactured into the same, or other, polymer compositions without loss of performance. This represents a significant advance from traditional plastics recycling, where the materials are normally “downcycled” i.e. made into products of inferior quality. The material, termed a “circular plastic”, therefore has the potential to improve the efficiency of plastic recycling and ultimately provide “closed loop” plastic recycling, where the same material can theoretically be remade an infinite number of times. More research into how to tweak the properties of PDKs to make them suitable in consumables such as textiles and foams is now on the cards.
There are still some significant challenges for PDK however. The material requires processing to be depolymerised, and so requires energy, to divert the material from landfills and oceans. Furthermore, it will be challenging to scale up the depolymerisation process to the size required should PDK become a commodity material. It is desirable that the PDK monomers are bio-derived, to ensure that PDK is not another petrochemically-derived plastic material.
What about IP?
From an IP perspective, whilst new bioplastic materials may be readily patentable, it may prove more challenging to obtain protection for improvements to existing materials and processes. Whilst such improvements are essential for obtaining materials with the improved properties and reduced cost required to facilitate effective market penetration, the fact that many of the most promising replacement bioplastics have been known for decades means that the prior art landscape may be quite congested.
Therefore, innovators will need to consider the new features of their material or process and what improvements they provide. For example, if two known bioplastics are blended together, does the blend have properties that are unexpectedly improved relative to the properties of the individual materials? For bioplastics, these features/improvements will often involve its material properties, in which case the invention may need to be defined using a parameter, such as molecular weight, viscosity, modulus, or particle size.
When claiming a material using a parameter, it is important that the parameter is clearly defined in the patent application, especially when the particular value of the parameter distinguishes the invention. Typically, this is achieved through the inclusion of the specific method of measurement in the description. Defining this method is particularly important when there is more than one method of measuring the parameter, as different methods could lead to different values and therefore result in ambiguity in what is actually claimed.
For example, a bioplastic may be defined in terms of its molecular weight. However, the molecular weight parameter has multiple variants, for example number average or weight average, and can be determined using different methods such as gel permeation chromatography, dynamic light scattering, or viscosity.
In order for such a parameter to be clearly defined, all of this relevant information needs to be included in the application at the time of filing. In the absence of such a definition, a patent examiner during examination may raise a clarity objection to a claim including an ill-defined parameter. Depending on whether the invention can be defined in alternative ways, such an objection may prevent the application proceeding to grant. Furthermore, opponents can attack parameters in opposition proceedings at the EPO arguing that, in absence of a defined measurement method, the application does not sufficiently disclose the invention and cannot be worked. Whilst there may be options for responding to such clarity and sufficiency objections, the best option is to avoid any potential objections by defining any parameters with a specific measurement method.
In summary, there is no one single solution to the plastics problem. While replacement materials may be more environmentally benign both to produce and at their end of life, the success of such replacements may rely on significant investment in both infrastructure and education. Innovators looking to patent bioplastics will need to consider carefully the new features of their inventions and what improvements these features provide, in addition to being sure that any parameters included in their claims are clearly defined.
Grossman, A., Vermerris, W., Curr. Op. in Biotech., 2019, 56, 112-120
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 Tokiwa, Y., Calabia, B. P., Appl. Microbiol. Biotechnol., 2006, 72, 244-251
 From an Orbit search of “polylactic acid”
 For PLA reviews, see: Hamad, K., et al., Express Polym. Lett. 2015, 9, 435-455; Dechy-Cabarat, O., et al. Chem. Rev., 2004, 104, 6147-6176; S. Mecking, Angewandte Chemie-International Edition, 2004, 43, 1078-108; 7. R. E. Drumright, P. R. Gruber and D. E. Henton, Advanced Materials, 2000, 12, 1841-1846.
 Prieto, A., Microbial. Biotech. 2016, 9, 652-657