Plastic made from plant sugars that you can break down with light and reuse over and over again? That’s the subject of new research from presented at this year’s Green Chemistry Conference.
Researchers from North Dakota State University (US) have made a new kind of plastic using renewable feedstock (biomass). By introducing an appropriate phototrigger molecule into the polymer, the scientists were able to photodegrade the polymer – once again obtaining the base starting material.
In this way, the same feedstock can be used several times, reducing the impact on the environment.
Polymers: Useful but Cause of Concern
Polymers are materials in which a basic unit (monomer) is repeated many times to form a much bigger molecule. All plastics we use in everyday life (i.e. bottles, utensiles, parts of vehicles) are examples of polymers; they are indeed essential materials for our society.
There is, however, increasing concern regarding their use for two main reasons:
- The majority of polymers are almost completely non-degradable; they constitute, therefore, a threat for the environment.
- Almost all monomers are derived from non-renewable sources, i.e. fossil fuels such as oil.
Use of Renewable Sources
Because of this, scientists have been studying alternative polymers with improved degradability and which are made using renewable source-derived materials; the use of biomass, for instance, has been considered as one of the most promising routes.
To manufacture polymers from renewable sources, one of the key molecules is 2,5-furandicarboxylic acid (FDCA) – see the chemical formula here to visualize FDCA.
FDCA could, for instance, replace terephtalic acid in the synthesis of polyethylene terephthalate (PET), a very common polymer used for example to make plastic bottles. Moreover, a polymer made of FDCA and glycol has performance comparable to PET.
Sustainability – Reusing the Monomers
For the polymer synthesis to be more sustainable, one of the key points is the possibility of reusing the monomer once the polymeric materials are disposed of. In traditional polymers this is very difficult, as it is hard to control the degradation of the polymeric chains and obtain the monomeric unit.
Researchers from North Dakota State University (US) developed a FDCA polymer derived from renewables, whose monomers could be reused. They presented their results at the 19th Annual Green Chemistry and Engineering Conference, on the 14th of July 2015 in Maryland (US).
Decoded Science spoke to professor Jayaraman Sivaguru, PhD, one of the lead scientists in the study and a speaker at the conference. Dr. Sivaguru is also an expert in designing photodegradable polymeric systems from biomass.
“We wanted to make a polymer from renewable sources, but we also wanted to be able to reuse the monomers again. To do this, we thought we could insert into the polymer block an additional molecule which could promote the polymer degradation under irradiation with an appropriate light source (a phototrigger).
In this way, by irradiating the polymer under controlled conditions, the polymer could be “decomposed” back into the monomers and into the phototrigger molecules.
This is an innovative approach that nobody has ever tried before.”
The Polymer and Its Degradation
Dr. Sivaguru and his coworkers made their polymer using FDCA from fructose, a sugar molecule found in many plants and fruit. As a phototrigger, they used 2-nitro1,3-benzenedimethanol 6, which was chemically bonded to the FDCA. This is a molecule whose phototrigger behavior is well studied and documented.
To test the controlled degradation, they suspended the polymer in a 4:1 mixture of tetrahydrofurane and water, and irradiated the suspension using a lamp with a light wavelength of 350 nm.
According to Dr. Sivaguru:
“At the beginning of the experiment, our suspension was whitish and turbid; after just three hours, it was completely transparent and yellow in color. This was the first sign that a degradation was really taking place.
To identify the product, we performed Nuclear Magnetic Spectroscopy (NMR); these tests showed that the product of the photoinduced irradiation actually was FDCA, so we were able to obtain again the monomeric starting material.”
“These first findings are very important as a proof of principle,” Dr. Sivaguru said.
“In fact, we showed that the use of phototriggers could lead to a controlled degradation of the polymers to obtain again the starting material. As the material would be used again, this lessens the impact on the environment. We want to continue this research, applying the same principle to different polymers, and see how we can optimize it. The research is highly collaborative with my colleagues Prof. Dean Webster and Prof. Mukund Sibi; their expertise of all their groups was essential to perform such a transformative study”
More Sustainable Polymers
The work done by Professor Sivaguru and his coworkers showed that it is possible to make polymers following some green chemistry principles.
The use of renewable feedstock, the minimization of the waste and of the impact on the environment are indeed all elements which should be considered for future sustainable polymer manufacture.
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