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Limited fossil resources, their growing cost, public concern about climate change, and important breakthroughs in white biotechnology and related polymer technologies are all significant drivers to move from fossil-based polymers to bio-based polymers in all polymer categories and markets. Major global investments make it happen.
JAN RAVENSTIJN, FORMER GLOBAL R&D DIRECTOR VISITING PROFESSOR BIOPOLYMERS
The use of synthetic polymers is forecast to grow from 250,000 kt/ year in 2000 to more than 1,000,000 kt/ year by the year 2100 due to prosperity and world population growth. In such a case, we would need 25% of the current oil production to make plastics alone by the end of this century.
Economic (oil cost), ecologic (climate change) and technology (white biotechnology and bio-based polymers) developments are driving the change from fossil-based to bio-based polymers. The bio-route is reportedly cheaper than the fossil-route at oil prices above $50/ barrel. As the new technology develops, this cut-off point will further decrease while the performance spectrum expands rapidly. The cost-to-performance balance of many of these materials is already quite competitive. In order to achieve economic sustainability for other materials, efforts are focusing on economies of scale and on white biotechnology (Wave II feedstock moving away from competition with the food chain, process technology, metabolic engineering).
It is a misunderstanding to think that biobased polymers are biodegradable since this is true for only a select few (Table 1).
Most polymers known on the market today, like:
Most bio-based polymers are durable and the global volume of bio-based thermosets is currently larger than that of bio-based thermoplastics.
The initial market interest in bio-based plastics came from producers of onetime- use applications or of applications that generate a lot of plastic waste.
Biodegradability was considered to be the important property here seeing that we waste 3.7 billion plastic cups, 350 billion plastic bottles and 3,750 billion plastic bags every year. Still, focus is shifting slowly but surely from biodegradable to bio-based materials in an attempt to counter climate change. Biodegradation is a useful property in some applications, but uncontrolled biodegradation is a wasteful end-of-life option.
Although the bio-based polymer business only represents 1,000 kt/ year or 0.4% of the total polymer business early 2010, current annual growth rates are 30%. New technology developments and related product introductions could further boost these numbers during this decade. Moreover, the number of new polymer introductions wholly or partly based on renewable feedstock is very comparable to that of the middle of the previous century (Figure 1), even though the volume remains modest.
Renewable raw materials are developed and used for bio-versions of existing polymers and for new polymers. The development stages for several bio-based polymers are shown in Figure 2. A stepwise approach is taken for many polymers by first making a partly bio-based material, before eventually making a material based entirely on renewable resources.
Based on state-of-the-art technologies, PLA, polyurethane, starch and PE are expected to be the dominant contributors to biopolymer growth (thermoplastics & thermosets) over the next 5 years. However, tremendous R&D budgets and capital investments are being made around the world to advance product and application technologies for several polymer groups like bio-PP, PLA (stereo complex, block polymers, functionalization), PHA, PBS, polyamides (PA-4,4, PA-11, PA-6,10, PA-4,10, and others), unsaturated polyesters (composites & resins), natural fibres (bamboo, kenaf, etc.), and polymers based on building blocks that are new to the polymer industry and have become cost competitive (like isosorbide, itaconic acid, succinic acid, furanics).
In a number of countries, the local authorities encourage these developments and capital investments through large subsidies, i.e. Brazil, China, Japan and the USA.
Although much is said about bio-based thermoplastics, bio-based thermoset products and the corresponding market are developing faster. Base polymers can often be produced with existing equipment, which means that capital investments are not so high in many cases.
Four major chemical companies and one agricultural company developed and commercialized bio-based polyols for polyurethane production. In 2007, natural oil polyol (NOP)-based polyurethanes already represented more than 75% of the global bio-based polymer market, although only the polyol part of PU was (partly) bio-based. Based on the biopolymer technologies known today, bio-based PU should still account for more than 35% of the total bio-based plastic market by 2020. Several companies have major programmes going on to make NOPs a success and to significantly increase the renewable Fig. 2: Commercialization of bio-based polymers content of their polyols. The application possibilities of these bio-based polyols are rapidly growing due to improved functionalization technologies.
The main fatty acid from castor oil is ricinoleic acid (12-hydroxy-9-cisoctadecenoic acid), with a hydroxyl group on C12 and a C=C double bond in the middle of the chain. Soybean oil has C=C double bonds but no hydroxyl groups. Esters or alcohols can be produced through oxidation of this double bond. These materials clearly have limited hydroxyl functionalities, so chemistry is required to modify them so that a larger portion of these raw materials can be used for the desired polyols.
In the meantime, castor oil is reacted with diisocyanates to produce polyurethanes for coating and foam applications, while castor oil derivatives are used to produce PU foam for mattresses. The use of plant-based polyols for PU products attracted considerable market attention and demand in 2004, although early developments date back to the previous century. Several companies were forerunners in using these products for seats, body panels, armrests, etc.
In addition to polyurethanes, there is also a high potential for using NOPs in unsaturated polyester resins, alkyds (done for some time now) and thermoplastic elastomers like copolyester elastomers and polyurethane elastomers.
Today, NOPs are used in rigid insulating foams for building and appliance insulation with renewable contents up to 70%, thus resulting in rigid PU foams with renewable contents of ≥ 15%. Other polyol-based products with up to 20% renewable content are used in the production of flexible slabstock foam. These are suitable substitutes for the current commercial petroleum-based polyols. Of course, the challenge remains to further increase the renewable feedstock content without losing physical, mechanical and durability properties of the end products.
A polyol derived from castor oil by up to 31% was introduced in 2008. It can be used to manufacture slabstock foams for mattress production, which would then contain up to 25% renewable material. While odour, emission and processing problems used to keep NOPs out of flexible slabstock, these deficiencies have now been resolved. This drop-in is claimed to have no effect on processing or foam properties.
Another series of products are currently used in flexible polyurethane cushioning for a growing number of applications, including furniture, bedding, automotive and carpeting. The BiOH® polyols are used to replace a growing portion of petrochemical-based polyols in downstream PU products. These products should be further developed to increase the renewable content of the resulting polyurethanes and to make them suitable for other applications (in addition to flexible foam).
A distinct multistep process is used to break down and functionalize vegetable oil molecules to make products with high renewable content (10-30%) without the odour often associated with bio-based polyols in PU foams. This process also makes them suitable for many automotive, furniture & bedding, metal & plastic coatings, carpets, footwear, adhesives and sealants applications.
By the end of this decade, we expect to see a significant further increase in the use of bio-polyol in PU foam products.
An ever larger number of renewable monomers for thermoplastics and thermosets are being investigated for cost-attractive manufacturing through white biotechnology routes, with several of them on the market already.
A distinction can be made between monomers that used to be produced from fossil resources and monomers that are based on renewable resources and bring differentiation options to the polymer industry. There are several examples of bio-based monomers that are relevant for thermosets, but are still produced in small quantities or are in the development stage.
Itaconic acid, isosorbide, isoidide, long chain diols, diacids, diamines and 2,5- furandicarboxylic acid (FDCA) are examples of renewable monomers that are being developed and investigated for use in thermosets, thermoplastics and composite materials.
Recently, isosorbide has been investigated to replace bisphenol-A in polycarbonates (PC) and in epoxy resins. Its cycloaliphatic structure should provide better UV properties and extra rigidity to the polymer chain but the question is: to what extent will this suffice to replace some of the existing resins. Its moisture sensitivity appears to be lower than that of the original PC. A 300 MT/ year demonstration plant is under construction for bio-PC based on isosorbide.
The material is claimed to have better optical properties than traditional PC and comparable properties to PMMA. Its mechanical properties are comparable to traditional PC and it has a Tg of about 130°C. This combination of properties makes the material suitable for functional optical films in flat panel displays.
The newly developed bio-based FDCA (Figure 5) is currently being investigated for use in thermosets and thermoplastics (polyesters, polyamides and polyesteramides). This new monomer is expected to cost the polymer industry about $600-800/ MT when produced on an industrial scale.
Natural fibres are already used to some extent to reinforce thermosets and thermoplastics but the industry’s focus has broadened over the last couple of years. Wood fibres and long agricultural fibres like kenaf, bamboo, jute, hemp, sisal and flax are all relevant materials. Kline & Company forecast this demand to grow by 15- 20% per year for automotive applications, and even by 50% or more in selected products for building and construction applications.
There are several reasons for replacing glass fibres with natural fibres: cost, weight reduction – natural fibres weigh about 55% of the weight of glass fibre (Table 2) – and the desire to lower the environmental impact by using natural products to reduce CO2 emissions and energy consumption over the product’s life cycle.
But properties like acoustics, aesthetics and processing are also positively influenced by the use of natural fibres. New composite formulations are and will be used in automotive, electronics, electrical, furniture, building & construction, and railroad applications.
To promote the widespread use of sustainable composites, we need to develop and use fibres, resins and reactive diluents based on renewable resources.
Several optimizations and developments have been identified for the foreseeable future:
The polyester resins on the market also need further development. A few resins with 25-100% bio-based content are available but they all need to go to 100% and offer the required properties.
The growing demand for plastics cannot be satisfied cost-competitively with oil in the longer term. There is also an urgent need to generate no more CO2 than we consume.
It will take decades to convert the polymer industry from fossil resources to renewable resources, but this also offers new business opportunities.
In the meantime, the renewable resource-based plastic business is growing by 30% every year, but still remains small. Major global efforts and investments are boosting this development significantly.