Benito Díaz
The planet is facing a serious pollution problem due to the production and use of plastic materials derived from non-renewable sources. Not only the energy spent in producing them is a problem; the material itself has an impact on the environment, caused by the wrong management of waste plastic.
The estimated amount of plastic produced up to 2015 is 6.500 tons. Most, 79% has accumulated in garbage dumps, 12% was cremated (with the consequential environmental cost) and only 9% of it was recycled. “If this type of production and waste management continues, in 2050 there will be approximately 12.000 million tons of plastic garbage in dumps or in nature”, according to an article from Science magazine.
The degradation of conventional plastic products is also a great danger, given that these materials can break down into pieces of less than 5mm diameter. At that point they are called microplastics. These elements pollute water and are directly responsible for the death of marine fauna, along with toxic waste spillage and other plastics.
To face this situation, scientists are focusing on alternative and renewable solutions, like vegetal origin polymers, obtained from plants such as corn, potato or hemp. We are going to discuss this last one.
Industrial hemp
Textile and paper industries have known hemp for a long time. The use of this plant dates from thousands of years back. Its first documented use was in China to elaborate paper. It was a profitable industry in the past, cut down by the USA prohibition in the early years of the 20th Century, in favour of plastic materials such as nylon, which is not biodegradable.
Hemp bioplastics can be totally natural and easily obtained using industrial cultivation. Hemp derivates are a potential substitute for lots of petroleum plastics and they are light, enduring and biodegradable. It is not a novelty in the field of large-scale production, as the first plastics already used hemp. Another interesting factor is its high percentage of cellulose, close to 77%, compared to other natural sources like wood (40-50%) or cotton, which is 90% cellulose but comes with very high production costs.
Production
Cellulose is the key to the production of these bioplastics. The fibres can be directly extracted from the plant’s stem. The raw pulp can be hydrolysed, i.e. decomposed into parts using only water. It can also be treated with a weak acid solution, transforming it into nanocrystalline cellulose, which will be the base for manufacturing plastic products.
Soaking it in an alkaline solution and sulfuric acid will result in a cellophane film.
To obtain celluloid, one of the first plastics manufactured in history, nitric acid is added to make nitrocellulose. Adding camphor, a plasticizer is obtained, which is commonly used to produce dense thermoplastic that becomes a malleable mass when heated up, allowing it to be moulded into vehicle parts, everyday life tools, etc.
Hemp cellulose can also be combined with other vegetable forms like cotton, jute, sisal or linen, to create compostable bioplastics, ideal for compostable bin bags, packaging materials, headphones, pipes, football helmets, and others.
Other benefits
Bioplastics obtained from hemp also have a low cost, compared to other toxic petroleum plastics. Furthermore, they contribute to reduce the CO2 emissions to the atmosphere, both in the production and in the management of the waste, which is biodegradable. Miguel Gimeno explains that hemp and cannabis are “carbon sinks”, able to absorb CO2 from the atmosphere to grow, trapping it and exhaling oxygen, elaborating more and more cellulose.
According to the Department of Agriculture of the USA, “a hectare of hemp can produce four times more paper than a hectare of trees”, with the corresponding speed and sustainability.
Hemp presents great utility and experts know this. It can be used to make components for construction works, concrete, textiles. It is an ecological substitute for fiberglass, used in furniture, floors, and the list goes on. Of course, it can be used to manufacture biodegradable bags, glasses and straws for drinks.
Industrial hemp, despite having a THC content below 0,2%, is still stigmatised as much as cannabis. In Spain there are only 200 hectares used for this cultivation, compared to the French case (9000 hectares) or the Italian case (3.000).