Bioplastics offer improved material properties and potentially lower environmental impacts than conventional plastic materials made from petrochemicals. &#;Drop-in&#; bio-based plastics are compatible with current recycling processes, and some of these products are designed for biodegradation.
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However, the growing industry must overcome challenges common to many immature technologies if it is going to thrive: lack of standardization and unclear classification; ambiguous and conflicting results from life cycle assessments; and relatively high production costs.
The IUPAC (International Union of Pure and Applied Chemistry) characterizes bioplastics as biobased polymers that can be shaped by flow when they are processed, and that are made out of either biomass directly or monomers which themselves were derived from a biomass source.
In general, bioplastic can be understood simply as plastic that is not derived from fossil resources like oil and gas.
The IUPAC actually discourages the use of the term &#;bioplastic,&#; instead recommending scientists use the expression &#;biobased polymer&#;. This is because, per the IUPAC definition notes, &#;bioplastic&#; implies that all plastics made out of biomass are environmentally friendly. This is not always the case, as recent studies (see below) make clear.
Bioplastic or biobased polymer production is growing, but it still represents only a fraction of the total plastic produced worldwide. In , global production of biobased polymers was 3.8 million tonnes. This represented 1% of the total plastic production for that year, with the remaining 99% being made up of petrochemical-based polymer materials.
There are numerous types of biobased polymer being produced currently with different production techniques.
Drop-in bioplastics, for example, utilize existing plastic manufacturing infrastructure to make materials that are chemically identical to petrochemical-based counterparts. Popular polymer materials PE, PET, propylene, PP, and nylon can all be replicated with biobased polymers (bio-PE, bio-PET, bio-propylene, bio-PP, and biobased nylons).
Some bioplastics are manufactured with biobased production processes that are newly designed from the ground up, including materials manufactured using microbial reactions and nanotechnology synthesis processes like epitaxial growth.
Chemical engineers have developed biobased polymers made using numerous biomass sources. The choice of biomass source is crucial not only to achieve desired material properties in the final plastic but also to ensure environmental and financial viability in scaled-up, market-ready products.
The most common source for biobased polymers is starch. Thermoplastic starch makes up about half of the entire bioplastics market, with applications ranging from packing &#;peanuts&#; to food and pharmaceutical packaging.
Cutting-edge starch-based nanocomposites have also been relatively widely researched in recent years. These nanomaterials display superior mechanical, thermal, hydrophobic, and gas-blocking properties in tests.
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Cellulose is another common biomass source for biobased polymers. Cellulose-based polymers include celluloid (the key component for analog film) and the household product cellophane.
Bioplastics can also be made from polysaccharides like chitosan and alginate. Chitosan can be dissolved in light acidic environments, which makes it suitable for processing into films through the solution casting method. Recent research has blended chitosan with plasticizers, nanoparticles, and other biobased polymers to create composites with improved properties.
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Recent research by Yale, University of Wisconsin, and University of Maryland engineers introduced a &#;lignocellulosic&#; biobased polymer made out of wood powder. Wood powder is a cheap and readily available byproduct from wood processing, and it forms the basis of the new material.
The researchers employed a deep eutectic solvent (DES) made out of choline chlorine and oxalic acid to deconstruct the wood powder. The DES itself was selected due to its biodegradability and recyclable properties, and it broke the wood powder made out of cellulose, hemicellulose, and lignin down before polymerization.
Biobased polymers have been engineered to feature a range of properties, just like their petrochemical-based counterparts. In fact, there is little mechanical or chemical difference between the two groups of products, as polymers made from petrochemicals are simply made out of fossilized biomass.
Biobased polymers can be hard, pliable, durable, degradable, heavy, light, and anything in between. They can be nanostructured, doped with additives, and designed for recycling. The properties of biobased and conventional polymers depend primarily on their molecular structures, not the source of their raw material.
The main advantage of biobased polymers is the fact that they can be made without using petrochemicals like oil and gas, provided the energy required to manufacture them is also produced without using oil or gas.
In some life cycle analyses, bioplastics have been found to perform better than petrochemical alternatives in terms of their total carbon footprint. This is generally the case if biomass is used as the energy source as well as the raw material for the production process. But less efficient production has resulted in biobased polymers with a greater carbon cost than comparable petrochemical polymers.
The IUPAC reminds scientists that biobased polymers cannot be assumed to be more environmentally friendly than petrochemical-based alternatives unless detailed life cycle assessments prove them to be so.
Researchers at the University of Sheffield (UK) recently published a meta-analysis of life cycle assessments for different types of plastic products. They found significant variations between the studies available to their research and were unable to conclusively declare any polymer type as being less environmentally harmful than others.
This kind of ambiguity over the environmental credentials of biobased polymers may simply be a feature of a nascent industry.
In a study published in Nature Reviews Materials in , MIT and Harvard researchers argued for more identification standards and better guidelines for life cycle assessments for bioplastics. The scientists argued that clearer regulations and financial incentives could help grow the industry and scale niche products to market-ready applications ready to deliver significant environmental impact.
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Panner, S., (). Yale study introduces breakthrough bio-based plastic. [Online] Yale News. Available at: https://yaledailynews.com/blog//04/05/yale-study-introduces-breakthrough-bio-based-plastic/
Rosenboom, J-G., R. Langer, and G. Traverso (). Bioplastics for a circular economy. Nature Reviews Materials. doi.org/10./s-021--8.
Walker, S., and R. Rothman (). Life cycle assessment of bio-based and fossil-based plastic: A review. Journal of Cleaner Production. doi.org/10./j.jclepro...
Vert, M., et al (). Terminology for biorelated polymers and applications (IUPAC Recommendations ). Pure and Applied Chemistry. doi.org/10./PAC-REC-10-12-04.
The manufacturing process for biodegradable plastics varies depending on the type of plastic being produced. However, there are some common steps involved in the manufacturing of all biodegradable plastics.
Certain raw materials are used in combination to create biodegradable plastics through the process of handling, mixing, extrusion, and cooling. Pneumatic conveying systems and other bulk material handling systems are used as a starting point in the manufacturing of biodegradable plastics.
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