Researchers develop “seasoning” technique for bioplastic conversion

06 Feb 2023 --- Researchers have developed a novel synthesis method branded “seasoning” that enhances the mechanical performance of commercially inactive poly(butylene succinate) (PBS) with a minimal amount of biomass-derived tartaric acid (TA) and citric acid (CA).

Biodegradable and bio-based plastics are carbon-neutral and do not generate microplastics that can enter food systems. The cooking-inspired method transforms a weak bioplastic into a strong one through “seasoning” with a minimal dose of a sustainable additive, CA or TA, that pinch the chain ends at the molecular level in the amorphous region. 

The scientists assert the method is economical and feasible because it maintains the original processes. In addition, it facilitates and solves the trade-off relationship between mechanical strength, shelf life and the biodegradation rate of a bioplastic. 

The developed “seasoning” brings the properties of PBS, one of the most underwhelming biodegradable and biorenewable polymers, to a new level. By adopting their novel approach, the scientists expect to transform traditional PBS into a biodegradable plastic that overcomes current limitations and transcends the boundaries of non-degradable products, such as active food packaging and fishing nets, while strategically minimizing changes to existing production facilities and processes. 

Study findings 
The new “seasoning” method brings the properties of PBS, one of the most “underwhelming” biodegradable and biorenewable polymers, “to a new level,” assert the researchers. 

“By adopting our novel approach, we expect to transform traditional PBS into a biodegradable plastic that overcomes the current limitations and transcends the boundaries of non-degradable products, such as active food packaging and fishing nets, while strategically minimizing changes to existing production facilities and processes.”

Biodegradable and bio-based plastics are carbon-neutral and do not generate microplastics that can return through food systems.In a similar manner to cooking, the scientists carefully selected TA and CA, derived from grapes and lemons, respectively, as biomass-based seasonings that function as bio-derived crosslinking agents. 

The addition of these monomers in very low amounts were found to maintain most of the merits of PBS without sacrificing its biodegradability or eco-friendliness, explain the researchers. 

TA and CA can function as molecular pinchers that connect chain ends in the amorphous region. “Pinching” on the nanoscale was found to have a tremendous impact on the mechanical characteristics of the polymer, with the resulting PBS illustrating enhancements in tensile strength, elongation and toughness of 200, 300 and 400%, respectively. 

The trace amounts of seasoning ingredients were tracked by electrospray ionization mass spectrometry (ESI-MS) during hydrolytic degradation, revealing their involvement in the amorphous region. 

The pinching mechanism of the synthesized samples was investigated by measuring oxygen transmission rates and tear strengths, which also highlighted the potential for expanding the applications of the polymer. Furthermore, the modified structure showed altered rheological and deformation behavior that enabled PBS to exceed its current limits. 

Commercializing biodegradables 
Plastics have recently been fabricated using natural ingredients. Consequently, small categories of these plastics may decay or degrade naturally by the action of microorganisms in a similar manner to food waste. 

Foods have expiration dates and commercially available biodegradable plastics have shelf lives that relate to their time-dependent mechanical strengths. Therefore, the commercialization of biodegradable polymers requires ensuring performance and guaranteed shelf life.

The researchers furthermore warn that both foods and plastics seem to end up on the dinner plate these days. Reportedly, an average person consumes 39,000–52,000 microplastic particles per year, which is roughly the size of a credit card per week. These particles are potentially toxic and have already been shown to damage the ecosystem and impact human health. Moreover, the current COVID-19 pandemic has forced the use of large amounts of sterile disposable plastics. 

The ongoing problems associated with non-degradable plastics have persisted for 65 years without any process changes, resulting in the global accumulation of billions of metric tons of these plastics. 

Hence, the need to adapt biodegradation technology, especially for short-term plastic products contaminated by organic waste to reduce accumulation, is stronger than ever. Research into biodegradable plastics has attempted to solve the pollution problem through recognizable inventions, such as poly(lactic acid) (PLA), poly(butylene adipate-co-terephthalate) (PBAT) and PBS. However, most biodegradable plastics do not meet shelf life requirements. The “seasoning” method transforms a weak bioplastic into a strong one. 

In addition, the thermomechanical performance requirements of consumer products are required to match the non-degradable plastics. Consequently, the development of commercially available biodegradable products has reached its current non-evolving state. 

Finally, seasoning is a hidden aspect of apparent glamor in food. With precision, a relatively small amount of salt or pepper facilitates preservation, brings out the natural flavor of the ingredients, and highlights their true potential. 

Embedding additives 
Likewise, small amounts of additives in plastics can function as reinforcing fillers, plasticizers, antioxidants, and colorants, among others. An end-capping agent is often used to resolve the trade-off between commercial acceptability and the degradation rate of biodegradable plastic.

The agent functions as a bridge between the two end groups of a polymer chain, reducing acidity and preventing the permeation of moisture and enzymes, thereby slowing down the degradation process. However, many petrochemical additives have some toxicity which is why biocompatible and bio-based ingredients are needed to prevent harmful exposure.

Small amounts of additives are embedded in the product in the same manner as seasoning is included in food, which is an additional benefit. Full conversion in the synthetic setup is mandatory when formulating a new material. 

In addition, using a new ingredient is challenging owing to the lack of facilities for the mass production of monomers and associated technological boundaries. Therefore, new methods that use existing industrial production methods while resolving the above mentioned problems are required, stress the researchers. 

The study was published in ACS Sustainable Chemistry & Engineering. 

Recently, PackagingInsights explored toxic additives and possible alternatives for food packaging with the Institute for the Advancement of Food and Nutrition Sciences and SP Group. 

Edited by Natalie Schwertheim