Researchers create fully-biodegradable polymer from carrots

22 Feb 2023 --- Canadian researchers have developed a carotenoid-sourced compound to make a fully-degradable, soluble polymer that disintegrates with acid and sunlight. They note that the work lays the foundation for a new class of fully degradable conjugated polyazomethines that uses building blocks from nature.

The research team combined 10-carbon dialdehyde and p-phenylenediamine to make three polyazomethines with different side chains.

The resulting materials ranged in colors from black to bright red after drying. 

The researchers could also improve the polymer’s solubility by changing from methyl to hexyl side chains through side-chain engineering. Solubility makes the polymer easier to characterize and process. 

In initial experiments, the team determined that the polymer created with p-phenylenediamine containing two hexyl side chains was the best candidate to test further.

By using a carotenoid-sourced compound, researchers were able to create a biodegradable polymer. Creating biodegradable polymer 
The research team notes that side engineering is a promising strategy to tune properties to meet specific application needs, such as conductivity and environmental compatibility. 

The researchers assessed the side chain modification’s influence on the polymer’s solubility with nuclear magnetic resonance, gel permeation chromatography, infrared spectroscopy and ultraviolet-visible absorption spectroscopy. 

In testing the degradation of the resulting polymer, the researchers determined that it could be degraded with both acidic and artificial sunlight conditions. Acid hydrolysis accelerated the polymer degradation rate and artificial sunlight generated additional degradation products. 

The polymer completely broke down into its original components in acidic solutions. However, over an extended period, the sample broke down even further into smaller dialdehydes and other compounds in the presence of light. 

According to the researchers, follow-up research will include evaluating the polymer’s ability to conduct electricity, yield polymers with a higher molecular weight and investigate the recovery of monomers. They add that exploring enzymatic degradation that mimics nature in follow-up degradation studies would be interesting. 

The University of Toronto, Canada, research team published their results in the Journal of the American Chemical Society. 

Carrot building blocks 
The molecular structure of carotenoids, such as β-carotene, resembles polyacetylene, a well-known conductive but insoluble polymer. 

Carotenoids, derived from carrots, are interesting compounds as they are expected to transfer charges and have known degradation pathways, the researchers explain. However, these have yet to be widely tested in polymer design. 

Many polyazomethines with sufficient electron mobility do not benefit the environment, as they use non-biobased monomers or hazardous agents, according to the study.  

Carotenoids can be degraded in several ways, giving alternative options to lessen the compound when integrated into different polymer systems. Carotenoids are susceptible to UV light and enzymatic and chemical oxidation damage. 

The research team obtained 10-carbon dialdehyde from β-carotene with oxidative degradation. This commercially available compound has di-aldehyde functionality, which means it can be used directly in polycondensation reactions without further needing other synthetic modifications. 

P-Phenylenediamine derivatives were selected as these are used to synthesize other degradable conjugated polymers and their toxicity has been well documented. Demand for polymers and plastics from biodegradable ingredients is growing.

Natural compounds used as polymers 
Polymers and plastics from natural, biodegradable ingredients are increasingly demanded in consumer products and packaging. These offer a more sustainable alternative to conventional non-biodegradable plastics of fossil origin. 

The researchers note that other natural compounds have also been incorporated into electro-conducting polymers, as these are commercially available and inherently present in nature. 

Compounds such as indigo, vanillin and eumelanin have been used in biobased polymers attractive for energy storage, biomedical and sensor applications. 

Edited by Jolanda van Hal