• Wed. Jul 24th, 2024

Alternative polymers: what are they and are they any good?

The word “plastic” is increasingly being seen as a dirty word, the epitome of environmentally unfriendly, and planet Earth’s enemy #1. The industry is searching for and experimenting with sustainable alternatives. However, can these deliver according to our needs?

For the production of synthetic turf, we mainly focus on thermoplastics. Polypropylene is used to produce a backing, while the softer polyethylene is currently the material of choice to produce yarns. A recent development is the use of polyester to produce yarns.

Thermoplastics are marvellous substances as the molecular chain does not essentially change when heated and moulded. This allows for it to be heated and remoulded repeatedly, which is precisely the characteristic that makes them recyclable.

Fuel sources

The vast majority of the polyethylene we use to produce yarns comes from a fossil fuel source that produces the monomer ethylene which is polymerized to polyethylene.

Alternative polymers use an alternative source and those are a completely different animal! Commonly, these alternatives are called biopolymers. However, there are two definitions of biopolymers that need to be considered.

To be strictly accurate, you have bioplastics and biopolymers.

Bioplastics are polymer materials made from renewable biomass sources such as sugar cane, soya or corn. These are biobased-polymers, as they are derived from a natural material.

The second group, biopolymers, are natural polymers produced in the cells of living organisms. Good examples are proteins, sugars and DNA.

In this respect, the only polymers that can be regarded as both biopolymers and bio-based polymers are those that are biologically produced (by microbes) from biomass carbon sources (e.g., sugars and lipids). Examples of these include PHAs, bacterial cellulose, gellan gum, xanthan gum, and curdlan. (source: Wikipedia).

Both are significantly more expensive than fossil-based polyethylene, as the process to extract these polymers is much longer and very complicated. As a result, some biopolymers/bioplastics can cost more than 10 times per tonne.

Biomass bioplastic polyethylene is chemically identical to fossil-based polyethylene. Dependant on the grade you source and extrude they should behave the same, test the same and perform in system the same way. Because of that, products made from these source-materials still need to be recycled, while the wear and tear particles also have to be viewed as being a microplastic.

Open to “greenwashing”

In terms of environmental footprint, biomass bioplastics open the door to “green washing.” Even though they do not require fossil fuels during manufacture, thus reducing the production of greenhouse gases and they capture CO2 in the growing cycle..

The biomass source can be sugar cane, corn, soy, potatoes, rice, wood, vegetable oil and even food waste. In fact, the list is extensive.

Growing sugar cane, soy or corn requires considerable volumes of water and land. In recent years, the amount of land dedicated to growing these crops has increased significantly, often at the expense of nature. Forests (the planets lungs) are being cut down for food/”plastic” production to create monocultures. This is bad for the environment, reduces the biodiversity, and take land from native animals. Growing food to produce something different than feeding the needy is also considered as being problematic.

While plants do take in atmospheric CO2 during their lifetime, so do trees over a much longer lifespan. Unless the plastic is recycled at the end of its life, the carbon is not fixed and released back to the enviroment.

In addition, the biomass then needs to be processed to make it into the monomer ethylene in order to be polymerized. This process requires multiple steps and significant energy, which adds an additional (monetary as well as environmental) cost to the production process.

Lastly, for Europe, many of these bioplastics production sites are far away meaning they have to be imported. It is commonly known that the logistics are the biggest contributor to a product’s environmental footprint.

So, really, how much lower is the carbon footprint? Can a bioplastic really be called “green”?

There is conflicting data online regarding the environmental footprint of bioplastics and mostly this is due to the different methods utilized to measure it. This makes it difficult to get a clear picture of the full Life-Cycle-Analysis (LCA). The soon to be introduced PEFCR method by the European Union, could make it easier to answer these questions.

PLA

Polylactic acid is also a bioplastic and is derived from fermented plant starch. It is not the same as polyethylene and does not behave in the same way. It has been explored as a material for synthetic turf with limited success. The softer more suitable grades have very low melting temperatures, making extrusion very difficult, whereas grades with higher melting temperatures can be very brittle. To make it suitable for extended use, blending it with other materials is recommended.

Pure PLA can be industrially composted (it will biodegrade over time but not substantially faster or any more successfully than regular polyethylene) and there are a limited number of recycling plants that can take old PLA products and turn them back to the monomer form and produce new PLA.

Bioplastics do have a part to play, but they could and should be better in terms of production. The key point to remember is, once used, they are no different to fossil-based plastics. They will produce microplastics and will need to be recycled. It is not the end of your responsibility once installed!

Biopolymers

Biopolymers are completely different. You will not get a polyethylene grade from these materials, they will not behave like polyethylene, you can’t extrude them like polyethylene, and, interestingly, they have a very different end-of-life outcome.

Some of the most interesting biopolymers are derived from natural polyesters – polyhydroxybutyrate (PHB) and polyhydroxyalkanoate (PHA). Both are polymers belonging to the polyesters class that are of interest as bio-derived and biodegradable plastics.

These are formed from the bacterial fermentation of sugar and are biodegradable in air, soil, fresh water and sea water as well as in household and industrial composting units. Used unblended, they have a very short lifecycle before turning into biomass.

They are not easy to source and are difficult to handle. They need to be dried and the extrusion equipment needs to be modified to make fibres hence using a biopolymer requires a capital investment in the production equipment, currently they are more suited to injection moulding, but there have been some interesting work done, but mostly at pilot scale.

Regenerated cellulose from seaweed is also an interesting material. While it has not been trialled in synthetic turf, fibres that have been produced with this material have made it into textiles for clothing as well as packaging and medical applications. It is certainly something to keep an eye on!

Could bio-fibres from animal proteins such as spiders’ silk be the future?

Biopolymers tend to be weak, and durability for play is short. They also lack resilience. However, they show promise, and in time, with more work, could be part of a renewable future for turf.

In conclusion, bioplastic polyethylene can be a good option using renewable resources with very little effort required from the manufacturers. They are a step towards a renewable future, using current equipment and understanding. It will certainly be a good direction for the industry, but one that is still in its early stages. There are still many unknowns, making it very challenging for the industry to keep up with the demand for its products and live up its commitment to produce more sustainable products.

Jacki Stephen has close to 30 years experience in the production of synthetic turf yarns for sports. She is member of the Technical Committee for outdoor sports surfaces of the European Standards Committee as well as the EMEA Synthetic Turf Council. 

The views and opinions expressed in this article are those of the author and are not necessarily endorsed by the publisher.

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