degradation is actually happening afterwards. Attempts at replicating the results have failed, which
then led to claims of false advertising.
9
The State of California even fined Walmart $1 million USD for
selling products that claimed to be biodegradable under laws targeting specifically plastic bag
labels.
10
The companies explained the failed replication studies as the result of the researchers not
following the proper degradation conditions, which then raises more concerns about whether those
conditions are actually applicable in real world situations such as in landfills. If those conditions
cannot be met, then the additive cannot do its job. Another concern relates to the degradation by-
products. CO
2
and methane gas can be generated during the process, which are greenhouse gases
that pose an environmental concern. As well, degradation of polymers can result in generation of
more toxic by-products than the initial plastic, posing a risk to public health and to the environment if
the leachate escapes confinement.
11
As well, the transition metal salts in the additive itself could
pose an environmental risk.
12
Lastly, this solution does not solve the problem of non-renewable
feedstock, as fossil fuel is still used to make biodegradable plastics. Despite its downsides and some
government backlash, other governments have actually supported this solution. Saudi Arabia and
the United Arab Emirates have mandated that all plastic bags need to contain a biodegradable
additive, which provided a huge boost to a struggling industry.
13,14
The science on biodegradable
additives is not concrete by any means and is shaped equally by economic and political factors as it
is by scientific ones. However, biodegradable additives could be the band-aid on this major problem
of plastic waste accumulation until a longer-term solution is fully developed, such as improving
bioplastics to reach or exceed the properties of current fossil fuel-based plastics.
The best bet for a long-term and sustainable solution, at the moment, seems to be the use of
biobased polymers, more commonly known as bioplastics. The word “biobased” does not
automatically imply biodegradability, but only refers to the fact that these polymers are derived from
biomass, such as plant material and microbiota. In fact, the majority of bioplastics are not
biodegradable due to the fact that they either simply replicate the structure of existing bioplastics in
the case of biobased polyethylene (PE), which is derived from bioethanol
15
, or are only partially
biobased in the case of the new Dasani water bottle, which only contains 30% biomass
16
.
Clearly, not all bioplastics are part of the solution. So, let’s identify three characteristics that
an ideal bioplastic would have. These would be renewability, energy efficiency, and environmentally-
friendliness in terms of biodegradability and greenhouse-gas emissions. The big advantage the
bioplastics have over conventional plastics is, by definition, that they are derived from biomass,
which is a renewable source so the first criteria is easily fulfilled. The second criteria of energy
efficiency is also rather easily fulfilled because bioplastics contain reactive groups containing
oxygen, which can be easily targeted by enzymes, thus lowering the temperature and pressure
necessary for the polymerization reaction to occur
17
. Let's look at a specific example to further
explore this criterion.
The front-runner that fits this criteria at the moment is polylactic acid (PLA), the most
common form of which is under the trade name “Ingeo” by Greenworks. The PLA monomer is lactic
acid, which is produced by milling corn starch to produce dextrose, and then using microbes to
ferment the dextrose into lactic acid
18
. The lactic acid molecules undergo a dehydration reaction to
produce lactic acid oligomers, which are then converted to lactide via a process known as thermal
cracking. The final step is the ring opening polymerization (ROP) of lactide into PLA (Figure 1)
16
.
There are several areas in this process that can be optimized using green chemistry principles such
as the reusing of solvents and biocatalysts, and the use of more efficient biocatalysts (19). The most
resource-intensive and inefficient step in the process is the production of lactide via thermal cracking
and is an area where green chemistry principles can be applied to make it more cost-effective
(Figure 2). One of the reasons for the inefficiency is the production of water molecules after the
addition of each lactic acid molecule, which makes the reaction increasingly unfavourable. This can
be mitigated by the use of a class of enzymes known as zeolite, which allow for the production of
