Rising concerns about the environmental impact of petrochemical-derived plastics have driven the search for substitutes. Biopolymers offer one solution to this challenge.
Biopolymers – polymers produced by living organisms – consist of long chains made of repeating, covalently bonded units, such as nucleotides, amino acids or monosaccharides. Typically originating from plant materials (non-food crops) or microorganisms, biopolymers are biodegradable, renewable and sustainable.
Some biopolymers can be used as plastics (Table 1). Currently, bioplastics represent about 1% of the 320 million tonnes of plastic produced annually, but the market for bioplastics is growing with the emergence of more sophisticated biopolymers, applications and products. According to the latest data compiled by European Bioplastics in cooperation with nova–Institute, global bioplastics production capacity is set to increase from around 2.05 million tonnes in 2017 to approximately 2.44 million tonnes by 2022.
Braskem is currently the world’s largest biopolymer producer, most memorably hitting the news last year when they signed a deal with the LEGO Group to supply I’m greenT polyethylene, a globally certified plastic made from sugarcane, for the iconic toys. Today, Braskem’s green plastic is present in more than 150 brands across the world, being used in anything from food packaging to personal care products, as well as more durable goods such as chairs and vases. Since the CO2 released at their degradation can be readsorbed by the organisms grown to replace them, biopolymers are generally accepted as being close to carbon neutral – going further than this, in 2018, the Carbon Trust endorsed Braskem’s carbon-negative claims for its bio-based polyethylene.
As well as environmental benefits commonly associated with these materials, it is useful to note that there is little variation between biopolymers of a given type. As their synthesis is controlled by a template-directed process (replication within a living cell), biopolymers are associated with the natural phenomenon of monodispersity, in contrast to the polydispersity that is typically encountered in synthetic polymers. This is relevant because the number and length of branches in a polymer affect its rheological properties and crystallization behaviour. As well as offering greater control and predictability over these properties, monodispersity offers advantages, for example, in the generation of homogenous particles for the delivery of drugs.
Table 1. Some biopolymers can be used as plastics.
|
Biopolymer
|
Type
|
Source
|
Example uses
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Polylactic acid
(PLA)
|
Thermoplastic polyester
|
Corn, cassava, sugarcane
|
- Loose-fill packaging, compost bags, food packaging, disposable tableware
- In the form of fibres: upholstery, clothing fabric, feminine hygiene products and diapers
- Thanks to its biocompatibility and biodegradability: medical implants and drug delivery
|
|
Polyhydroxybutyrate (PHB)
|
Thermoplastic polyester
|
Microorganisms (e.g. Cupriavidus necator, Methylobacterium rhodesianum, Bacillus megaterium)
|
- Rubbish bags, food packaging (PHB possesses better physical properties than polypropylene [PP] for food packaging and is non-toxic), disposable tableware, disposable razors etc
- Medical applications (e.g. biocompatible stiches that dissolve)
|
|
Zein
|
Prolamine protein
|
Corn
|
- Coatings for paper cups, bottle cap linings, clothing fabric, buttons, adhesives, coatings and binders
- Can be further processed into resins and other bioplastic polymers
- Coatings for encapsulated foods and drugs
|
The main challenge of biopolymers has always been the high expense of manufacturing them. Indeed, ICI developed PHB to pilot plant stage in the 1980s, but interest faded when it became clear that the cost was too high, and its properties could not match those of polypropylene (PP) in terms of physical, chemical and mechanical resistance. However, in June 2005, US company Metabolix received the Presidential Green Chemistry Challenge Award for developing a cost-effective method for manufacturing polyhydroxyalkanoates (PHAs), including PHB. Further innovation is also solving challenges with physical properties. For example. WACKER Chemie‘s VINNEX, a polyvinyl acetate based binder system, enhances the physical properties of both PLA and PHB, making them easier to process. Similarly, the poor low-impact strength of PHB can be fairly simply solved by the incorporation of hydroxyvalerate monomers to produce polyhydroxybutyrate-co-valerate (PHBV).
With these advances removing barriers to profitability and utility, more companies are moving into biopolymers. For example, Mango Materials produces a naturally occurring biopolymer from waste biogas (methane), Xylophane offers a unique renewable barrier material for packaging, and dozens of other companies are active specifically in this space – many (if not most) founded since 2010.
Established big players are also maximizing on natural opportunities. In 2013, BASF launched Ecovio, a biodegradable polymer that contains 45% PLA blended with a biodegradable polyester that is derived from petrochemicals. Earlier this year, Evonik launched a line of thermoplastic semi-crystalline polyamides, derived from castor bean plants, that can be used for fibres and filaments, including high-performance materials for sportswear. Also in 2018, DuPont Industrial Biosciences received the Americas Coating Award for engineering a family of polysaccharides for use in coating applications. Even more recently, Stora Enso acquired Sweden-based Cellutech, which specializes in the development of new materials and applications based on cellulose, micro-fibrillated cellulose (MFC) and other wood-based components. Cellulosic foams can, for example, be used in packaging to replace polystyrenes which are the most widely used plastics.
A future without plastics is unthinkable. The hope, clearly, is that these innovations will permit society’s continued dependence on plastics, but in a sustainable manner with minimal impact on the environment.
Join us at the European Biopolymer Summit in Ghent, Belgium on 13–14 February 2019– don’t forget to pick up your copy of Chemicals Knowledge!
