Jeff Rowlands director, Green Urethanes, suggested that before starting on renewable polyurethane materials companies should consider which raw materials are available in the right volumes, and these should be based on plant or animal resources that have a positive eco balance story. Additionally, sources should not compete with food. They must also be processable with traditional equipment, be cost competitive with traditional raw materials and be technically competitive.
Difficult chemistry
One of the most notable aspects of the presentations is the willingness to take on difficult chemistry. Some of the more interesting papers were about using lignin – a particularly intractable group of highly cross-linked aromatic polymer mixtures which make up the structural components of trees. The other side of the intractable camp is held by carbon dioxide. They are both plentiful materials and are almost always available as waste products from industrial processes.
Lignin is an unwanted by-product of the paper industry, and carbon dioxide is plentifully available at fossil-fuel power stations. But the chemistry needed to open up lignin is not fully developed and the chemistry around carbon dioxide to polyols is complex.
Carbon dioxide was described as the basis for “dream production” of polyurethanes by Dr Chrisoph Gurtler, researcher at Bayer MaterialScience.
He explained that there are a number of reasons to use CO2, including climate protection. Earlier in the day, Professor Ramani Nayriaan of Michigan State University, had given a paper showing how the production of carbon dioxide from natural sources is largely in balance but that there is a large imbalance with man-made carbon dioxide.
At 120 giga tonne/year the amount of CO2 recycled between the atmosphere, vegetation and soils is roughly in balance worldwide. Similarly, around 90 giga tonne/year transfer in a closed system between the seas and the atmosphere. But 6.3 giga tonne/year is emitted by transport, industrial processes and energy generation which is not effectively recycled. This is carbon that has been hidden as fossil fuels and then burnt to produce energy.
While there is a great deal of zero-cost carbon to be extracted from carbon dioxide Gurtler outlined the problem with CO2: its stability.
It takes a considerable amount of energy to break the compound up sufficiently for the parts to take part in a reaction. Bayer and a group of collaborators at the University of Aachen and CDT catalysis centre with funding from the German Budnesministerum fur Bildung und Forschung. Bayer MaterialScience has been working on a range of catalysts to help reduce the amount of energy needed to make carbon dioxide and epoxides react together. Of the three catalysts that BayerMaterial Science has been examining: one produces cyclic carbonates, another will generate alternating aliphatic carbonates and finally one will generate polyether polycarbonate polyols. The processes Gurtler has been working on will enable up to 25% CO2 to be incorporated into polyols.
Gurtler outlined work that had been done using very pure CO2 captured from scrubbed stack-gas from a new build power station operated by RWE. This was converted into polyols and produced polyurethanes. The polyols produced were water-white, and of reasonable viscosity.
Also from Bayer MaterialScience, Hans-Georg Pirkl said the viscosity of polycarbonate polyols strongly depends on the functionality of the polyol and the carbon dioxide content.
Generally viscosity rises with the proportion of CO2 in the finished plyol. Pirkl said those for flexible polyurethane foams have viscosity between polyether and polyester grades.
Pirkl outlined work on the thermal stability of CO2-based polycarbonate polyols that his firm has developed. This showed that there is identical thermal stability on heating to 300˚C with foam made with conventional polyols.
So the CO2 is fully incorporated into the polyol. Bayer started pilot production in batch, semi-batch and continuous modes in the first quarter of this year. Pirkl suggested that Bayer may be able to commercialise the dream carbon dioxide polyols in 2015.
Also from Bayer MaterialScience, Gesa Behnken, head of new technologies in the coatings adhesives and specialities division, outlined how her business has developed a gas-phase route to toluene diisocyanate, cutting energy use by 40% compared to melt condensation processes. In another example she cited using a biobased drop-in replacement polyether polyol in a water-based adhesive formulation for the footwear industry reduced the size of the product’s carbon footprint by 50%.
Carbon dioxide
Peter Shephard, chief business officer, Novomer, outlined a range of high performance polycarbonate polyols also produced from CO2. These offer good strength and adhesion to many substrates; they have a competitive cost position because between 43 and 50% of the finished polyol is CO2. He also claimed that the materials can be produced using a recyclable catalyst which is 99% selective and operates under mild conditions so existing infrastructure can be used. This catalyst produces a 100% polycarbonate backbone with zero ether linkages and molecular weights between 500g/mol and 10,000+ g/mol and narrow polydispersivity index. Diols with a functionality of 2.0 can be produced with zero unsaturation. Polyols up to n6 have been demonstrated.
Lignin
Two connected papers from Canada looked at the use of lignin as a polyol feedstock. Minh Tan Ton-That, senior research officer, of the National Research Council of Canada, said lignin as a by-product from the pulp and paper industry or from biofuel production and one of the most abundant components in biomass after cellulose making up 20-40% of wood and straw. He said this makes it an attractive and cheap biomass for monomer production & polymer applications.
But there are obstacles to its use. Lignin molecules contain many hydroxyl and phenol groups but they are sterically hindered and so difficult to reach or to react with. In addition, lignin is really a series of closely related inhomogeneous macromolecular thermoplastics which are branched and are hydrophilic.
Before lignin can be processed it needs to be physically purified through a series of processes such as fractionation, changing pH and temperature to help modify particle morphology, Ton-That said.
Chemical modifications can be done on bulk material in either a solid state of aqueous process. These are highly efficient with minimised energy and water consumption and no solvents or toxic chemicals. Ton-That said they are easy to scale up too. Once the preliminary work has been done, to clean up the lignin. Armand Langlois of Enerlab explained that his firm expects to commercialise the first lignin-based polyol for polyisocyanurate insulation board. Langlois explained that there can be cost benefits in using lignin and it ticks a number of green boxes too. It’s use can reduce environmental impact and is not related to the food chain.
Enerlab has produced typical formulations using lignin that can be 10% less expensive than equivalent mixtures made using traditionally sourced polyols. The lignin accounted for about 22% of the weight of the foam, but needed more blowing agent.
Currently Langlois’ firm is fully characterising foam made with its lignin polyol looking at long-term thermal stability, mechanical properties, thermal and fungus resistance. Enerlab is working with the National Research Council of Canada and the Ecole Polytechnique de Montréal to protect the intellectual property in the polyols.
Other papers discussed using polymeric lactone-based antioxidants to reduce scorch in foam based on natural oil polyols (NOP). Polyurethane foams modified with rapeseed oil-based polyols and converting used cooking oil into polyols.
Christoph Ponce, market sector manager at Huntsman, said his firm has been working with Oleon to produce a bio-based prepolymer that meets OEM specifications, and has no problems with odour. This enabled the customer to produce a foam with 9% bio based content, using a rapeseed oil-based polyol, which is a by-product of the food chain.
Alexander Prociak, lecturer, Cracow University of Technology, Poland, also described a range of rapeseed-oil based polyols that can be used in flexible and rigid foams. These polyols, produced via epoxidation and oxirane ring opening can have variable functionality and OH value, he said. They can be used in rigid and flexible foams and offer improved tensile strength and energy absorption characteristics.
Sven de Vis, technical service and development engineer at Milliken, outlined a new stabiliser for foams that helps to protect them from degradation caused by light exposure, thermal degradation in processing and gas fading.
His firm has developed a lower toxicity polymeric lactone-based carbon-centred radical scavenger called Milliguard AOX1.
Why sustainability?
