Go green, go natural! When it comes to polymers, green and natural are not the same. As their name implies, natural polymers (or biopolymers) are polymers that occur naturally or are produced by living organisms (such as cellulose, silk, chitin, protein, DNA). By a wider definition, natural polymers can be man-made out of raw materials that are found in nature.
Although natural polymers still amount to less than 1% of the 300 million tons of plastics produced per year, their production is steadily rising. In the U.S., demand for natural polymers has been predicted to expand 6.9 percent annually and rise from $3.3 billion in 2012 to $4.6 billion in 2016. The natural polymers market is driven by a growing demand for natural polymers with pharmaceutical and medical applications. Natural polymers also are used in construction and adhesives, food, the food packaging and beverage industries, and cosmetics and toiletries, as well as the paint and inks industries. The market is led by cellulose ethers and also includes starch and fermentation polymers, exudates and vegetable gums, protein-based polymers, and marine polymers.
So, What’s Green?
Green polymers, on the other hand, are those produced using green (or sustainable) chemistry, a term that appeared in the 1990s. According to the International Union of Pure and Applied Chemistry (IUPAC) definition, green chemistry relates to the “design of chemical products and processes that reduce or eliminate the use or generation of substances hazardous to humans, animals, plants, and the environment.” Thus, green chemistry seeks to reduce and prevent pollution at its source. Natural polymers are usually green.
Let’s take a closer look at what drives the green and renewable polymer industries. According to Dr. Rolf Mülhaupt from the University of Freiburg, Germany, the development of the green polymer industry is inevitable:
At the beginning of the 21st century, we are experiencing a renaissance of renewable polymers and a major thrust towards the development of bio-based macromolecular materials […] There are several reasons for this paradigm shift and for the envisioned transition from petrochemistry to bioeconomy.
From the economic point of view, […] the dwindling oil supply is likely to further boost the oil price, especially in view of the expected surge in worldwide energy demand. This could drastically impact the cost-effectiveness and competiveness of plastics. Shifting chemical raw material production to renewable resources or coal could safeguard plastics production against this expected new future oil crisis.
Hence, another even more important reason is the growing concerns of consumers regarding global warming, resulting in a surging demand for sustainable and ‘green’ products. In addition, a tsunami of environmental legislation and regulations is propelling the development of environmentally friendly products with a low carbon footprint.
In the production of polymers, green principles include:
- A high content of raw material in the product
- A clean (no-waste) production process
- No use of additional substances such as organic solvents
- High energy efficiency in manufacturing
- Use of renewable resources and renewable energy
- Absence of health and environmental hazards
- High safety standards
- Low carbon footprint
- Controlled product lifecycles with effective waste recycling
In addition, the use of renewable resources for green polymer production should not compete with food production, should not promote intensified farming or deforestation, and should not use transgenic plants or genetically modified bacteria; biodegradable polymers should not produce inhalable spores or nanoparticles.
There are three basic strategies to produce renewable plastics:
- Using biomass and/or carbon dioxide to produce ‘renewable oil’ and green monomers for highly resource- and energy-effective polymer manufacturing processes
- Through living cells, which are converted into solar-powered chemical reactors, using genetic engineering and biotechnology routes to produce biopolymers and bio-based polymers
- By activation and polymerization of carbon dioxide
To monitor the progress in green polymers and share ideas, scientists and manufacturers can attend an annual conference on sustainable production of plastics and elastomers, Green Polymer Chemistry. It’s dedicated to “the latest developments in producing conventional polymers from sustainable sources including plants and biorefineries, algae, waste and CO2.” The next one will be in March in Germany.
More Common Than You Might Think
Green polymers, renewable polymers, and bioplastics already are more common than you might think. We all know about bioethanol as an emerging biofuel, produced by fermentation of sugar obtained from sugar cane or cellulose. Bioethanol also is a versatile raw biomaterial for producing olefin and diolefin monomers, including ethylene, propylene, and butadiene. In 2010, Braskem in Brazil inaugurated a 200 kiloton/year plant producing green ethylene from sugar cane bioethanol for the production of Green Polyethylene, which is 100% recyclable.
Using processes that are even more energy-efficient, biomass can be directly converted into renewable coal and oil. Agricultural and forestry wastes already are used to produce renewable monomers. Processes have been developed to convert carbon dioxide into carbon monoxide, methanol, formic acid, and formaldehyde. Vegetable oils can be used to produce biodiesel and glycerol as a byproduct, which can be used to make a variety of monomers such as propane diol, acrylic acid, and even epichlorohydrin for the production of epoxy resins.
Carbohydrates, terpenes, proteins, and polyesters are chemically modified and used in polymer processing and applications. Natural fibers provide excellent fiber reinforcement for thermosets and thermoplastics. Microfibrillated cellulose has been used in polymer nanocomposites, including applications in medical implants. Lignin serves as renewable energy source in paper manufacturing, as a filler for cement, and in various polymers and rubbers. Thermoplastic lignin mixed with natural fibers (Arboform) combines the advantages of wood and synthetic thermoplastics. Biohybrids has been using starch as a blend component with polyolefins and compostable polyesters (Ecoflex). Chitosan and polylactic acid have numerous medical applications. Casein is used as a binder and as an adhesive.
Renewable monomers are already substituting for “oil-made” monomers. The ever-present plastic bottles are just one example. In 2011, Coca-Cola Co. announced a goal to make plastic bottles from 100% bio-based materials. Recyclable PET “PlantBottles,” which use up to 30% bio-based monomers, were introduced in 2009, and can still be recycled.
Overall, it is definitely possible for plastic production to meet meet the demands of green chemistry for lean and clean production: solvent-free processes with efficient use of resources, and no byproduct formation, waste, or exploitation of renewable resources. Will we take advantage of the possibility? As Abraham Maslow once said, “One’s only failure is failing to live up to one’s own possibilities.” Let’s not fail!
Image: “Pola Goldberg Oppenheimer: Nanoscale Fractal Branching Patterns,” by Engineering at Cambridge.
Source: “Natural Polymers to 2016 – Demand and Sales Forecasts, Market Share, Market Size, Market Leaders,” Freedonia Group, Study #2963, freedoniagroup.com, Nov. 2012
Source: “Natural Polymers Market for Medical, Food and Beverage and Oilfield Applications – U.S. Industry Analysis, Size, Share, Growth, Trends And Forecast, 2012-2018,” Transparency Market Research, researchandmarkets.com, June 2013.
Source: Green Polymer Chemistry. International conference on sustainable production of plastics and elastomers, organized by Applied Market Information, amiplastics.com.
Source: “Green Polymer Chemistry and Bio-based Plastics: Dreams and Reality,” by Rolf Mülhaupt, Macromolecular Chemistry and Physics 2013; 214: 159–174. doi: 10.1002/macp.201200439