Main alternatives to PET:
- BIO-PET: PET monomers from renewable sources
- PEF and PTF: other non-biodegradable polymers from renewable sources
- PLA and PHA: natural biodegradable polymers
Over the last few years, we have been witnessing a never before seen global campaign against the production and use of plastic. The attention of the international community is pointed in particular on so-called ‘single-use plastics’. Amongst these, the most stigmatised are certainly PET bottles because of the huge numbers of them gathered on the world’s beaches and in our oceans.
Stirring pictures of plastic waste have affected public opinion and, as a consequence of this new susceptibility of consumers, international legislators are passing restrictive laws on the use of disposable plastics.
Standard plastic materials are currently produced using monomers derived from oil, which is a non-renewable resource and hence doomed to run out within a number of decades. On the other hand, the use of plastic bottles and other disposable items is cheap, convenient and practical for the user.
The break-even point, at which all of these needs can be balanced is probably the development of new processes and polymers able to replace the current oil-based PET production.
So, what are the alternatives already on the market? Also, what are those currently under development? Let’s take a look at the foreseeable future of single-use PET.
A few words on PET and the main alternatives
PET is the common term for polyethylene terephthalate, a thermoplastic resin synthesized mainly by the reaction between terephthalic acid (TPA) and ethylene glycol (MEG) with water as a byproduct.
Traditionally the starting monomers are obtained by refining oil. The material formed in this way is what is commonly known as standard PET. Generally speaking, it is possible to classify the alternatives to standard PET into three main categories:
- BIO-PET, a particular kind of PET partially derived from renewable sources,
- Other non-biodegradable polymers derived from renewable sources,
- Natural and biodegradable polymers.
In the next sections, I will explain the state of the art within these categories together with the pros and cons of each.
Alternative 1: PET monomers from renewable sources (BIO-PET)
The basic idea of this approach is to use non-petroleum-based raw materials to extract at least one of the two PET base components. Some solutions are already available on the market, for instance, some BIO-PET resins in which MEG monomers are produced from agricultural products including molasses, corn and bagasse (the dry remainder of sugarcane after its juice is removed).
On the contrary, to this day there is still no affordable industrial process to extract bottle-grade BIO-TPA from renewable resources, however, much research is in progress on the topic. Most of this targets p-xylene (pX), the petrochemical precursor for terephthalic acid.
A partial success on this path has been achieved by Toray Industries Inc., which launched the production of a full BIO-PET with bio-based TPA in 2012 (even if the produced polymer is suitable only for textile applications) .
Another approach is represented by the work carried out by the Division of Molecular Science of Gumma University in Japan, which developed a brand new process to obtain bio-based TPA from furfural, an organic compound produced from inedible cellulosic biomass .
Coming back to the market state of the art, the only commercially available solution for food-grade BIO-PET is that using BIO-MEG to replace traditional oil-based MEG. Some examples of bottles already available on the market are those of the Japanese ‘Suntory Tennensui’ mineral water, the Italian ‘Levissima’ water and Coca-Cola’s premium water brand ‘Valpré’.
PROS: The main advantage of this approach is that these bottles, jars or trays have the same optical and physical properties as traditional virgin PET while reducing the use of non-renewable resources by about 30 %. In addition, the containers remain fully recyclable in the standard PET stream.
CONS: Issues related to BIO-PET are the same as for standard PET, namely the high environmental impact when containers are not properly recycled since Bio-PET does not biodegrade. Moreover, this solution will only really be a green alternative once bio-based TPA is widely available in the market as well.
Alternative 2: Other non-biodegradable polymers from renewable sources (PEF and PTF)
PET has a lot of very useful properties: it is light, transparent, cheap and easily recyclable. Nonetheless, it also suffers some disadvantages for the food packaging industry, mainly poor barrier properties to gas permeation. In practice, this means a shorter shelf life for the edible product due to the penetration of oxygen and the loss of carbon dioxide through the container’s wall.
Oxygen penetration speeds up the oxidative reactions of various foodstuffs like beer, milk, juices and almost all solid foods. A loss of carbon dioxide can impact the quality of carbonated soft drinks, a huge market sector for the PET industry.
For this reason, some chemical companies have been looking for an alternative to standard PET which, in addition to being more environmentally friendly, can also assure better performance in particular for gas barrier properties.
Currently, there are two of such polymers in development: polyethylene furanoate (PEF) and polytrimethylene furandicarboxylate (PTF). Beyond the tricky chemical names, the point is that they are both furan polymers potentially attainable from 100 % renewable sources.
PEF is a macromolecule similar to PET in which the terephthalic acid is replaced by another monomer named FDCA, a sugar derived molecule. PEF can improve packaging sustainability since this polymer is 100 % bio-based when BIO-MEG is used in the reaction. Moreover, FDCA is sufficiently similar to TPA to be used in existing PET polymerization plants, making this technology easily transferable to an industrial scale.
Even though PEF is for sure an interesting material, some problems related to the production and manipulation of FDCA (for instance, its poor solubility in common organic solvents or its tendency to decompose at temperatures greater than 180°C) have caused some chemical companies to seek alternatives.
The most important one, developed by the chemical giant DuPont, is PTF. This polymer is obtained by the reaction between the Furan Dicarboxylic Methyl Ester (FDME), fructose derived compound, and the 1,3-Propanediol (Bio-PDO), another bio-based molecule patented by DuPont and currently used by the brand Sorona to produce outdoor jackets.
Along with the sustainability of these two polymers, due to the fact they are obtained from renewable sources, the key point for the market is that both PEF and PTF promise outstanding performance with regard to barrier properties.
Referring to standard PET, PEF exhibited an eleven-fold reduction in oxygen permeability  and a nineteen-fold reduction in carbon dioxide permeability . Also, DuPont declares PTF is 8 to 15 times more efficient than PET as an O2 and CO2 barrier . These results are summarized in the table below.
According to available data, both PEF and PTF should be good candidates to replace PET in the food packaging industry. To see them in our shopping cart, however, we will have to wait a few years more.
In fact, the production of FDCA is currently stuck in the feasibility phase and the first industrial-scale production is expected no earlier than 2024. As regards to PTF, DuPont is a step ahead as it has already opened the world’s first bio-based FDME pilot production facility in Decatur, Illinois (USA) in April 2018 .
PROS: Both PEF and PTF can be produced using 100% renewable sources. They are recyclable and visually similar to standard PET but with far better mechanical and gas barrier performance. PEF production should be integrated into existing PET polymerisation lines, while PTF is already a step ahead in the path towards industrial production.
CONS: These materials are not yet available on the market and the timing for their industrialisation is uncertain. Furthermore, most probably they will not be recyclable in the standard PET stream and this could be a big obstacle for their adoption. Finally, some concerns are emerging in the scientific community related to the migration of some compounds from the container walls into the foodstuff .
Alternative 3: Natural biodegradable polymers (PLA and PHA)
The discussion about this third alternative to PET can open a whole world indeed. Around the globe, there’s an incredible amount of activity related to the development of biodegradable polymers for all kinds of applications traditionally associated with plastic.
In the field of food packaging, a bloom of trials and press releases on this topic is being seen. For this reason, we’ll focus the discussion only in the solutions already or almost available on the market in the food sector.
The most common biodegradable polymer currently used in food packaging is polylactic acid (PLA), a thermoplastic polyester derived from renewable resources such as corn starch, tapioca or sugar cane.
Since PLA is currently used for many applications (rigid containers, bags, jars, films…) there are many available suppliers all across the globe.
Also regarding bottles, some products are already on the market. To mention a few, the ‘Bio Bottle’ from the Italian water brand Sant’Anna has been on the market for the last 10 years, while the ‘Veganbottle’ was recently launched by the French company LysPackaging.
It may appear that PLA could be the solution to all the environmental challenges related to plastic markets but that’s not true. In fact, PLA is biodegradable only in specific temperature and humidity conditions (about 45-60 days at 50-60 °C and high humidity). This means you can’t simply throw the bottle into the sea or leave it in the woods and let it decompose: abandoned in a natural environment it will take many years to fully biodegrade.
The second piece of bad news is that PLA can heavily contaminate the recycling process of PET when inserted in the common plastic harvest stream. The solution would be to set up a brand new harvesting or sorting process fully dedicated to PLA, with all the relevant management and operating costs. Unfortunately, the PLA market is not yet large enough to justify such an investment.
The most interesting alternatives to PLA now arising in the market are the polyhydroxyalkanoates (PHA). This acronym refers to a family of natural and biodegradable polymers which can decompose not just in industrial composting equipment, but also in soil, freshwater and seawater. PHA is produced using completely new technology, as they are, in practice, the digestion byproduct of cellulosic material by some select bacteria.
In a few words: you simply feed bacteria with agricultural waste and they eject PHA polymers. Intriguing, isn’t it?
Figure 2. Electron microscopic image of microorganisms containing PHA 
Bottles and jars made with PHA look quite opaque and the mechanical properties will be probably rather poor. In any case, this material remains intact as long as it is not discarded, however, in that case, will then disintegrate within 2 months in soil or water. One of the largest PHA producers is the USA-based company Danimer Scientific, who recently signed a global partnership with Nestlè to develop biodegradable PHA bottles .
PROS: Both PLA and PHA are derived from natural and renewable feedstock. They can decompose in industrial biodegradation plants (PLA) or even in soil or water (PHA). PLA is already available on the market for packaging use.
CONS: PLA is not easily biodegradable in ambient conditions. PHA bottles are not fully transparent and are still in development. The mechanical and gas barrier properties of the containers must still be examined.
Conclusion: food packaging is about to change forever
For sure, PET has provided a revolution for the packaging industry in the last decades. However, overcoming the modern environmental issues of dwindling fossil resources and the growing challenges related to plastic waste require new solutions.
Chemical companies and packaging producers are in a joint effort to develop greener materials and several alternatives to standard PET are now on their way with strengths and weaknesses. One thing is for certain: in the next few months or years, we will witness a new revolution in the food packaging market.
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