Plastics are integral to our everyday life — an understatement, really, seeing as a predicted 8 million tons of plastic enters our oceans every year. Why, then, do we continue to use them? Plastic pollution isn’t news to us. Plastics do have exceptional properties, like malleability, mouldability, strength, durability, weight, and, perhaps most importantly, low price. Plastic is cheap and that makes it easy and suitable for many different products. Bioplastics have emerged as an alternative, but in some cases are just as fatal as conventional plastics.
Common Bioplastics, and Their Problem
Bioplastics can either be categorized as biobased or biodegradable. Biodegradable plastics are petroleum-based plastics combined with an additive to make them break down in a short amount of time, whereas biobased plastics are plastics derived from biological sources like food waste and corn. These both sound great in theory, but what people don’t realize is these bioplastics must be taken to a composting facility so they can be broken down in a controlled environment by microbes, and if this doesn’t happen, they end up just…not biodegrading.
Two specific conditions are required to break down these plastics: very high temperatures and exposure to sunlight. Bioplastics, however, are not buoyant so tend to sink in the ocean, therefore not only do bioplastics typically not biodegrade in the ocean but also will not decay buried in a landfill. When examining biobased plastics, eg those made from agricultural crops, this is ultimately not a scaleable and long-term solution. The process of compound extraction is difficult and also occupies an enormous portion out of our food supply which is becoming increasingly harder with climate change’s influence. The competition between land and water resources for human consumption would deprive our resources.
This is where algae’s potential to be utilized for plastics comes in.
What Is Algal Bioplastic?
Algae is a term that envelopes a group of seaweeds, kelps and photosynthetic eukaryotes. Having high yields, short cultivation times, and the potential to sequester CO2 in the process all provide great reasons for why algae could be used to displace fossil fuels as an energy source. Algae are fast-growing organisms powered by sunlight. When algae are used to clean the environment, the outcome is biomass that can be converted into bioplastic material.
Algae synthesize toxin systems and enzymes and use plastic polymers as carbon sources, which enables the degradation of plastic materials. Algal bioplastics have more or less the same properties as petroleum-based plastics while also being biodegradable. Algae have been emerging as a biomass source to manufacture bioplastics because they can be grown on non-arable lands.
Making bioplastics from algae, in many cases, refers to making bioplastics from red algae, also known as red seaweed. When companies talk about algae bioplastics made from seaweed, they mean they are using chemical agar — a jelly-like polysaccharide substance — extracted from seaweed, because agar is abundant in red algae. Polymers are what give plastic strength, and agar is a bio polymer.
Agar Extraction Through Synaeresis
To extract agar from seaweed, the seaweed must be washed to remove matter, and then heated in water for a few hours so that the agar dissolves and the mixture can be filtered to move residual seaweed. One increasingly common method for agar extraction is synaeresis.
Synaeresis works by using pressure to force the separation of the liquid and agar gel. This requires some equipment which means higher capital costs. Two grooved metal plates covered in porous cloth are taken where 1% agar gel is sandwiched into the middle of the cloth. Pressure is applied to the plates, increased over the period of a day, and the liquid is forced out of the gel, through the cloth, and down the grooves of the plate to ultimately end up in a drain. The pressure is lifted, the plates are separated, and the gel is peeled off the cloth, now containing 20% agar. This is shredded and dried in a hot-air oven which allows relatively lower energy consumption than other methods, and purer agar due to less soluble matter.
Algae as Feedstock for Bioplastic
While most algal bioplastics use red algae, algae feedstock can also make up various types of bioplastic, like hybrid, cellulose-based, poly-lactic acid, and bio-polyethylene.
Hybrid plastics are made by combining denatured algae biomass (generally filamentous green algae) with petroleum-based plastics as fillers. Although petroleum is still used and is therefore not perfect, the petroleum per unit of plastic decreases while increasing properties like biodegradability.
Cellulose-based plastics are cheap and low quality plastics derived from a biopolymer of glucose called cellulose. Certain strains of algae contain cellulose from the biomass produced post-extraction. This means that these can be feedstocks for cellulose-based plastics.
In terms of PLA, the lactic acid is produced through fermenting feedstocks which are polymerized to ultimately produce polylactic acid. The lactic adic and polymer poly-lactic acid are used as sustainable and economically incentivized alternatives to conventional plastics as mentioned earlier, but they still take a very long time to decompose. The bacterial fermentation of algal biomass converts this waste into lactic acid, which could spread the expenses of algae production and make the biofuel more cost-competitive seeing as the raw materials used to manufacture lactic acid are currently quite expensive. Learn more about this fermentation process here.
Lastly (although there are certainly other plastics that are being experimented with), algae can be used for bio-polyethylene plastics. The monomer used in polyethylene production is ethylene, produced from ethanol, which is derived from fossil fuels like petroleum, but can also be derived from — you guessed it — algae. Algae-derived ethanol is quite expensive, though, much more than petroleum-derived ethanol, so its feasibility is limited.
Unlike other bioplastics which use common crops, algae do not compete with food production for humans, and are tolerant to a variety of environmental conditions meaning they can grow in a range of different areas. They compensate wastewater and use CO2 as biomass production nutrients without emitting it back into the atmosphere. Overall, algae-based plastics would be non-toxic, plastic quality enhancing, and good for the environment.
Agar also appears to play a role in imparting unique properties to plastic sheets. It improves clarity in sorbitol formulations and resistance to microwave radiation. Furthermore, in plastics containing agar and a plasticizer called glycerol, the glycerol ends up having a longer life span because the agar slows down the increase in brittleness.
The huge downside with algal bioplastics is, unfortunately, the cost. The production cost is through the roof because of the necessary consumption for labour and water. There’s also the energy needed to circulate gases in photobioreactors where algae can grow as well as dry out the biomass. Producing fuel from algae grown in ponds at scale would cost between $240 to $332 per barrel, which isn’t plausible compared to the inexpensive plastics we use today.
Algal bioplastics could have unreal impacts in the future, but right now the economic viability is still in the infancy stage and is not ready to be commercially available. Once we get past a few barriers, the possibilities are endless!
Here’s an overview of what we learned:
- Current bioplastics only biodegrade in specific conditions so are not optimal
- Algae have many benefits because they can grow in a variety of climates, and can be turned into biomass to be turned into a bioplastic
- This requires the extraction of agar from algae, and one extraction method is synaeresis which uses pressure to force the separation of the liquid and agar gel
- Algae can also be used as feedstock for bioplastics, notably hybrid, cellulose-based, poly-lactic acid, and bio-polyethylene plastics
- Algal bioplastics boost certain qualities of bioplastics, while also sequestering carbon dioxide and hence playing a role in decreasing the greenhouse effect
- The main downside to algal bioplastic is the cost as right now it is too expensive to be widespread
Check out some of these cool companies working with algal bioplastics!
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Thank you so much for reading this! I’m a 15-year-old passionate about sustainability, and am the author of “Chronicles of Illusions: The Blue Wild”. If you want to see more of my work, connect with me on LinkedIn, Twitter, or subscribe to my monthly newsletter!