Introduction
1.1 Plastics
Plastics play a crucial role in modern society, exhibiting a wide array of properties such as flexibility, rigidity, resilience, and transparency. From vinyl siding on houses to disposable drinking bottles, plastics are ubiquitous in various applications. The introduction of synthetic plastics in 1907, with the creation of Bakelite, marked a significant milestone, transitioning from naturally derived plastic materials like rubber.
1.2 Why Bioplastics?
In recent times, the world is grappling with an escalating waste crisis, with the United States alone producing over 300 million tons of municipal solid waste annually, nearly half of the global total (Figure 1). Plastics constitute a substantial and growing portion of this waste stream. Three key environmental issues associated with conventional plastics are their dependence on fossil fuels, limited biodegradability, and the generation of hazardous chemicals during production and disposal processes. Once a plastic product reaches the end of its life cycle, it may undergo recycling or end up in landfills. However, plastics can only be recycled a finite number of times before their quality deteriorates significantly. Consequently, even recycled plastics eventually end up in landfills, where they persist for thousands of years.
1.3 Bioplastics
Bioplastics are derived from biopolymers, a subgroup of polymers whose monomers are sourced from living organisms. While some bioplastics, such as bio-polyethylene, closely resemble their petroleum-derived counterparts, others possess unique properties with no direct petro-polymer equivalents. Bioplastics can be sourced from plants, animals, or bacteria, with some being biodegradable and others not. This diversity is advantageous as it allows for the production of resilient products that do not degrade in the environment. Although still in its early stages, the field of bioplastics is rapidly evolving, driven by the pursuit of sustainable production and consumption.
1.4 Classification
Bioplastics encompass a diverse range of materials with varying properties and applications. According to European Bioplastics, a plastic material is considered bioplastic if it is either bio-based, biodegradable, or possesses both characteristics.
The term “bio-based” indicates that the material or product is wholly or partially derived from biomass (i.e., plants). Biodegradation is a chemical process wherein microorganisms in the environment convert materials into natural substances like water, carbon dioxide, and compost. The rate of biodegradation depends on environmental factors and the material composition. In contrast to conventional fossil-based plastics, bioplastics are either partially or entirely bio-based, biodegradable, or both.
Bioplastics can be categorized into three main groups:
1.4.1 Bio-based – non-biodegradable
This group includes bioplastics like bio-PE, bio-PP, and bio-PVC, produced from renewable resources such as bioethanol. Bio-PE is already manufactured on a large scale, with companies like Braskem producing 200,000 tons annually in Brazil. Additionally, partially bio-based polyester PET finds applications in both technical and packaging domains, including beverage bottles. This category also encompasses specific polymers like bio-based polyamides, polyesters, polyurethanes, and polyepoxides, utilized in various applications such as textile fibers, automotive components, and durable goods.
1.4.2 Bio-based – biodegradable
This group comprises starch blends and polyesters like polylactic acid (PLA) and polyhydroxyalkanoate (PHA), commonly used in short-lived products like packaging. Continued innovation in this area has led to the introduction of new bio-based monomers, expanding the potential applications of bioplastics beyond biodegradability to solutions such as recycling.
1.4.3 Biodegradable fossil-based
This smaller group is primarily used in combination with starch or other bioplastics to enhance their performance and biodegradability. Although currently produced through petrochemical processes, there is a growing trend towards developing partially bio-based versions of these materials soon.
1.5 Applications of Bioplastics:
Bioplastics offer several advantages, including hydrophilic characteristics, renewability, biodegradability, controlled release of active agents, and unique thermo-mechanical properties. They find applications in agriculture, industrial packaging, pharmaceuticals, and more.
Protein-Based Bioplastics:
Utilizing proteins like gluten from corn, wheat, or soy, bioplastics can be manufactured. Gluten-based blends are particularly promising due to their abundance, low cost, biodegradability, and suitable material properties.
Egg White-Based Bioplastics:
Egg white proteins, particularly ovalbumin, offer functional properties like gelling, foaming, and binding adhesion. Egg white proteins can be used in bioplastics for various applications, including food packaging.
Biomass:
Using renewable biomass in bioplastic production helps reduce dependence on petrochemical feedstock and environmental pollution. Proteins, polysaccharides (such as starch), and lipids can all be sources for biopolymers.
Wood Fiber-Reinforced Bacterial Bioplastics Composites:
Wood fiber-reinforced plastics, particularly those made with renewable polymers like polyhydroxyalkanoates (PHA), offer eco-friendly alternatives to conventional plastics. PHA-based bioplastics, such as polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV), can be reinforced with wood fibers to improve mechanical properties and reduce costs.
Nanotechnology for Bioplastics:
Nanotechnology offers opportunities for enhancing the properties of bioplastics, especially in food packaging applications. Nano-reinforcement of bio-based polymers can improve their economic and technical viability while maintaining their renewable and eco-friendly nature.
Overall, bioplastics derived from proteins, polysaccharides, and other renewable sources offer promising alternatives to conventional plastics, especially when considering environmental sustainability and diverse applications.
