A polymer is a large molecule (macromolecule) composed of repeating structural units typically connected by covalent chemical bonds. Examples of synthetic polymers are plastics, Bakelite and nylon, while rubber, proteins, DNA but also spider-silk are naturally occurring polymers or so-called natural bio-based polymers. Reproducing naturally occurring and/or synthetic polymers based on non renewable fossil feedstocks is common practice in the (petro-) chemical industry. When replacing the fossil feedstocks with renewable biomass in this industry, bio-based polymers can be produced.
Polymers have a very broad applicability as they can be used as adhesives, absorbents, lubricants, soil conditioner, cosmetics, medicine, textiles, high-strength structural materials, packaging materials, plastics (see the ClimateTechWiki article on bioplastics), but also computational switching devices. Using biomass feedstocks instead of fossil feedstocks for polymer production could have significant socio-economic and environmental advantages.
There are many types of bio-based polymers, which are produced in a different manner. The figure below provides an overview of some of the most important groups and types of bio-based polymers.
|Bio-based polymer (group)||Type of polymer||Structure / Production method|
|1||Starch polymers||Polysaccharides||Modified natural polymer|
|2||Polylactic acid (PLA)||Polyester||Bio-based monomer (lactic acid) by fermentation, followed by polymerisation|
Other polyesters from bio-based intermediates
a) Polytrimethyleneterephthalate (PTT)
b) Polybutylenerephthalate (PBT)
c) Polybutylene succinate (PBS)
Bio-based 1,3-propanediol by fermentation plus petrochemical terephthalic acid (or DMT)
Bio-based 1,4-butanediol by fermentation plus petrochemical terephthalic acid
Bio-based succinic acid by fermentation plus petrochemical terephthalic acid (or DMT)
|4||Polyhydroxyalkanoates (PIIAs)||Polyester||Direct production of polymer by fermentation or in a crop (usually genetic engineering in both cases)|
|5||Polyurethanes (PURs)||Polyurethanes||Bio-based polyol by fermentation or chemical purification plus petrochemical isocyanate|
a) Nylon 6
b) nylon 66
c) Nylon 69
Bio-based caprolactam by fermentation
Bio-based adipic acid by fermentation
Bio-based monomer obtained from a conventional chemical transformation from oleic acid via azelaic (di)acid
Modified natural polymer
Bacterial cellulose by fermentation
O. Wolf, et al., 2005
There are three principal ways to manufacture bio-based polymers:
- By making use of naturally occurring polymers, that either remain intact and/or are somewhat modified (e.g. starch polymers),
- By producing bio-based monomers, that can be polymerized by means of fermentation (e.g. polylactic acid),
- By producing bio-based polymers with the help of genetically modified crops and/or (in) microorganisms.
There are a great number of technologies and processes involved in producing bio-based polymers, a.o. extrusion, wet milling, drying, film blowing, thermoforming, injection moulding, foaming, hydrolysis and fermentation (all links to Wikipedia). Video 1 is a simple illustration of how bio-based polymers can be made.
The technological feasibility of bio-based polymer production is generally bound by the basic laws of physics and chemistry. Many bio-based polymers, such as polysaccharides, polyester, polyurethane or polyamide, can technically be produced based on biomass feedstocks. Development of a specific bio-polymer production-line is generally held back by the relatively high price of the raw materials and by the insufficient performance of the biotechnological conversion steps. Technology developers, subsequently try to find new ways to enhance the performance of the conversion process, so as to reduce production costs or improve the product’s characteristics and commercial applicability. However, even in cases where significant process and efficiency improvements have been made, the competition from fossil-based alternatives still remains. An example of this is provided in a report by O. Wolf et al., 2005, where “for the identified production routes to polyamides via a bio-based intermediate production [where the] costs are still prohibitively high relative to conventional petrochemical based equivalents. To illustrate: Based on a feasibility study DSM came to the conclusion that the bio-based route to nylon 6 would allow the production of competitively priced caprolactam (Nossin and Bruggink, 2002). However, the company subsequently switched to a cheaper petrochemical-derived feedstock as a precursor to nylon 6. This effectively raised the hurdle (i.e. the difference in cost price of the biobased versus the petrochemical-based monomer) for the bio-based route (DSM, 2003).” The same report notes that for production of bio-based polyactic acid “slightly modified standard industrial machinery for thermoplastics” production can be used.
Using biomass as a feedstock substitute instead of petroleum-based feedstocks is more a technological concept than a specific technology, since polymer production is based on a combined set of individual technologies and processes. For the production of polymers from petroleum feedstocks many technologies and processes already have a proven track-record. The feasibility of the large-scale bio-polymer production depends on several factors such as, process and technology advances, feedstock availability/sustainability and consumer demand and collection/distribution infrastructure.
Insofar as the bio-based feedstock characteristics are comparable to their fossil equivalent, minor changes and/or technology adaptations to the existing base manufacturing processes/installations can be expected. For instance, for the production of bio-based polylactic acid slightly modified standard industrial machinery for thermoplastics production is required. For many other (novel) bio-based polymers, dedicated production-lines and/or factories have to be set up, depending on the type and complexity of the conversion process. The availability and sustainability of the biomass is crucial to issues such as commercial feasibility, feedstock management, environmental impact, land-use impact, erosion and biodiversity impact related to the technology. In addition there needs to be a sufficiently large market for any given polymer type, in which supporting technologies for feedstock collection, storage and end-product distribution are present.
It remains to be seen whether or not the various bio-based polymers production processes will be able to reap the benefits of economies of scale as biomass feedstocks are often dispersedly available. This character of the renewable feedstock contrasts somewhat with the concentrated and centralized nature of conventional petro-chemical industry. The additional costs of feedstock logistics should therefore be as low as possible and ideally be offset by either a higher product value or price premium over the petroleum-based equivalent.
IEA’s Technology Perspectives report 2008 briefly discussed the production of biopolymers. Although biopolymers received much attention during the 1990s a lot of materials failed because of the relatively high production costs compared to petroleum based polymers. In general, biopolymer technology is now (2010) believed to be in the R&D and demonstration phase (see Figure below), although for some biopolymer production processes there already are commercially viable (global) niche markets. For instance modified starch polymers already are used for as packaging material in agriculture or horticulture or as a filler material in car tires. “A growing number of bio-based chemicals, such as the biodegradable bioplastic PLA (polylactic acid) that derives from corn, are already in commercial production (National Intelligence Council, 2008).”
|Technology stage||R&D Demonstration||Demonstration||Demonstration, Commercial|
|Investment costs (USD/t)||5.000 - 15.000||2.000 - 10.000||1.000 - 5.000|
|Life cycle CO2 reductions||50%||70%||80%|
|CO2 reduction (Gt/yr)||0 - 0,05||0,05 - 0,1||0,1 - 0,3|
IEA Technology Perspectives, 2008.
For the range of potentially available bio-based polymers, there are differing market potentials as each polymer production process can have a different cost structure and substitution potential. O. Wolf et al. 2005 have made an assessment of the technical substitution potential of petroleum based polymers by a series of bio-based polymers a few of which are briefly discussed hereafter. Starch polymers have the greatest potential to replace polyolefins, such as petroleum based low density polyethylene (LDPE), high density polyethylene (HDPE) and polypropylene (PP). Bio-based polylactic acids (PLA) have good potential for (partially) replacing PMMA, PA and PET and possibly PP, whereas bio-PTT’s substitution potential for PET and nylon is very high and moderately high for PBT, PC and PP., etc. (all links to Wikipedia).
“The (theoretical) substitution potential of bio-based for petrochemical-based PTT is 100%, since the product should be identical assuming feedstock qualities and polymerisation processes are equivalent. In practice, as for all other polymer substitutions, the price will largely determine the actual extent to which substitution takes place (O. Wolf et al. 2005)”.
The above suggests that there is significant technical substitution potential for bio-based polymers, which have wide application in medicine, textile, packaging, agriculture, transport, and several other sectors. Commercial market potentials however are difficult to determine as local market conditions are fundamental to the success or failure of bio-based polymers. Production costs obviously have an important impact on the choice of producers who determine the feedstock of choice; however for specific markets bio-based polymers could have superior characteristics over fossil alternative so as to allow for a premium market price in large niche markets. For bulk applications local circumstances (i.e. cheap, high quality availability of bio-feedstock) could enable bio-based polymers to be produced at competitive prices comparable to petroleum based polymers.
For those stakeholders that are considering implementing, bio-based polymer production in the chemicals sector, the technology could contribute to:
- A reduction of petroleum consumption,
- A relative reduction of fossil fuel import dependence,
- A reduction of greenhouse gas emissions (dependent on specific life cycle impact),
- A reduction in the discharge of polymer production associated waste streams, like effluents, toxics, air pollutants such as particulate matter, and a potential reduced ozone, eutrophication as well acidification impact (note that these and other potential environmental benefits are to a large extent case specific and in some impact categories the petroleum based alternative scores better than the bio-based polymer life cycle),
- positive health and sanitation effects can also be associated with potential positive environmental effects,
- A reduction of harmful solid waste deposition in cases where the bio-based polymer is 100% biodegradeable (note however first that bio-polymers are not necessarily biodegradeable and that when such a claim is made often industrial composting methods are assumed), and
- An increase in employment in the agriculture sector (e.g. harvesting),
- related to potential positive employment effects are regional development and positive income effects for rural areas.
The IEA (Technology Perspectives, 2010) notes that the chemical and petrochemical sector is by far the largest industrial energy user (almost 30% final industrial or about 10% global final energy demand). The industry uses fossil fuels both as an energy and feedstock resource and is responsible for about 7% of global CO2-emissions. Consequently, a (partial) switch from this industry to biomass could significantly contribute to energy conservation (e.g. due to new and more efficient conversion processes) and GHG emission reductions. To get an idea of the energy and the GHG impact (expressed in kg of CO2 saved per kg of bio-polymer produced relative to the fossil alternative) of bio-based polymers the Table below shows some data for a number of polymers.
|Energy in MJ /kg||GHG Emissions||(in kg CO2 eq./kg)|
|Pchem. polymer||Bio-based polymer||Energy savings||Pchem polymer||Bio-based polymer||Emission savings|
|TPS + 15% PVOH||76||25||52||4.8||1.7||3.1|
|TPS + 52,5% PCL||76||48||28||4.8||3.4||1.4|
|TPS + 60% PCL||76||52||24||4.8||3.6||1.2|
|Starch polymer foam grade||76||34||42||4.8||1.2||3.6|
|Starch polymer film grade||76||54||23||4.8||1.2||3.6|
O. Wolf, et al., 2005
Agricultural residues, rice husk, bagasse, palm oil solid waste, sawmill waste and black liquor (see the ClimateTechWiki article on black liquor gasifiers) are commonly used feedstocks within the CDM project pipeline, however virtually all of these projects aim at energy production by means of co-generation of heat and power, gasification or the like instead of bio-products. To date (July, 2010) there has been no submission of a bio-polymer CDM project. Subsequently, it is difficult to provide methodological examples of the expected GHG emission reductions of specific projects in any given country or region. Nonetheless, the (petro)chemical industry is familiar with life cycle analysis studies (LCA - pdf link) and in a considerable number of publications (some example PDFs: 1, 2, 3 and 4) for new bio-based polymers, GHG emission impacts are generally included.
Similar to the varying climate impact of individual bio-based polymer production lines, also the financial requirements in terms of investment (CAPEX - Wikipedia) and operational (OPEX - Wikipedia) expenditures can differ significantly, depending on factors such as feedstock costs, local investment conditions, etc. In general, bio-based polymers will have to compete with petroleum based polymers on quantity, quality and price aspects, which implies that petroleum-based polymer production processes provide a good financial benchmark.
Aside from the financial aspects of investing in and operating a bio-polymer production facility, introducing a new technology often is not solely a financial issue as many barriers to implementation remain. Non-financial barriers, such as low-awareness, insufficient market demand, legal and procedural institutional issues, lack of market relevant data, etc. are sometimes even bigger hurdles to take for individual companies. Industry association and policy makers generally try to fill this gap by starting a dialogue (EU-example - pdf).
- IEA Technology Perspectives, IEA 2008.
- IEA Technology Perspectives, IEA 2010.
- Biopolymers: Making Materials Nature's Way, US Congress, Office of Technology Assessment, September 1993, http://www.fas.org/ota/reports/9313.pdf (30 July 2010)
- Economic Aspects of Biopolymer Production, Dr. Sang Yup Lee, et al. http://www.wiley-vch.de/books/biopoly/pdf_v10/vol10_18.pdf (30 July 2010).
- O. Wolf, et al., ‘Techno-economic Feasibility of Large scale Production of Bio-based Polymers in Europe’, European Commission, 2005. http://ftp.jrc.es/EURdoc/eur22103en.pdf (30 July 2010)
- National Intelligence Council, ‘Disruptive Civil Technologies, Six Technologies with Potential Impacts on US Interests out to 2025’, Conference Report April 2008. http://www.dni.gov/nic/PDF_GIF_confreports/disruptivetech/appendix_C.pdf (30 July 2010)