Plastic pollution is one of most daunting sustainability challenges. Multi-functional and biodegradable plastics are critical for both desirable end-of-life outcomes and petrochemical plastics replacement.
Current bioplastics are either: short of mechanical properties, like polyhydroxybutyrate (PHB); lack room temperature biodegradability, like polylactic acid (PLA); or lack the functionality to create additional values. Here, we present the bioinspired Layered, Ecological, Advanced, and multi-Functional Film (LEAFF), for sustainable plastic packaging. This biomimetic composite, based on the structure of the natural plant leaf, synergistically improves mechanical strength while empowering PLA for rapid ambient soil biodegradability, achieving complete degradation in 5 weeks.
The film is also highly transparent and water stable, and achieves high gas barrier properties to improve food shelf life and reduce waste. The biomimetic design showcases the synergistic advantage leveraged by the LEAFF’s multilayer structure to enhance mechanical performance while simultaneously retaining biodegradability and achieving multifunctionality for broad applications.
Plastics are indispensable to the everyday functioning of the modern world. However, their ubiquitous use presents significant sustainability challenges due to their high carbon emissions and persistent environmental pollution. Since their industrial adoption in 1950, plastic production has exponentially increased from 2Mt. in 1951 to over 459Mt. in 2019. Globally, nearly half of all of the plastic waste generated annually is due to single-use plastic (SUP) packaging, the vast majority of which are not biodegradable. Today, 91% of plastic waste is landfilled or incinerated, with only 9% being recycled. This landfilled or incinerated waste fragments into microplastics that find their way into humans through our water, food, and air.
Consumption or inhalation of microplastics has been associated with increased risk for numerous pathologies such as cardiovascular and respiratory disease and lung cancer. Additionally, non-degradable plastic waste finds its way into the world’s waterways and oceans, severely negatively impacting marine life. Even though recent policies advocate for interdictions on single-use plastic manufacturing, or seek to implement recycling programs for repurposing plastic packaging materials, these efforts are not effective due to low recovery rates. Furthermore, it has been estimated that an SUP ban alone will not be enough to solve the plastic waste problem. Thus, sustainable material alternatives are necessary to replace petroleum plastic use cases.
Today’s $23.5 billion plastic packaging market is dominated by polyethylene and polypropylene, accounting for more than half of non-fiber plastic production. These polymers are utilized for their high tensile strength (polyethylene: 20-45 MPa; polypropylene: 35 MPa) and water resistance. In recent years, numerous designs for biomaterial alternatives have been realized. These material syntheses often utilize blending approaches to create biopolymeric composites comprised of polylactic acid (PLA), polyhydroxyalkanoate (PHA) such as polyhydroxybutyrate (PHB), starch, or cellulose However, these materials are limited in their mechanical performance or water resistance and thus have challenges in industrial adoption. Additionally, the bioplastics that have the best mechanical properties, are the hardest to biodegrade. For example, PLA has a high tensile strength around 65 MPa but is recalcitrant to biodegradation in soil and marine environments, often requiring industrial composting conditions.
For this reason, PLA is considered compostable, instead of biodegradable. Designing biodegradable PLA has been a well-sought goal for bioplastics advancement. As compared to PLA, PHB films are more readily biodegradable, though PHB is much less mechanically robust than PLA. Alternative synthetic strategies have emerged to enhance biodegradability, such as electrospinning. However, these materials demonstrate a significant decrease in mechanical performance, and increased gas and liquid permeability. Aside from mechanical strength and biodegradability, other highly sought-after features of plastic materials include: water stability, air impermeability, transparency, and printability. It is highly challenging to achieve broad multi-functionality in a single material to address all these needs.
The LEAFF composite addresses these challenges through its layered film structure, which combines the individual advantages of CNF and PLA materials, while minimizing their disadvantages by leveraging the synergistic effects that emerge through the interfacial crosslinking of the two polymers. The LEAFF overcomes the previous paradigm of biomaterials engineering where a material can either be strong or biodegradable, achieving both robust mechanical performance and high biodegradability in ambient condition soil. To create a biodegradable and mechanically robust plastic alternative, with the aforementioned important features, we turned to nature to look for a biomimetic material design. For centuries, cultures around the world have used plant leaves as a material for food in cooking, packaging, and storage. The plant leaf is a complex composite material composed of an intricate network of water (xylem) and sugar (phloem) transport vasculature, photosynthetic cells, and a strong internal structure from cellulose-rich cell walls, all covered by a thin wax-like coating called cutin.
News Courtesy : Nature.