If polyurethane is to be more sustainable, then more sustainable feedstocks will be required. Several key papers at the Automotive and Sustainability Congress held in Amsterdam late last year addressed this important topic.
The ideal sustainable polyol will be odour-free, easy to process on existing equipment with minimum adjustments, and will give additional advantages in the finished product, according to many of the speakers in the sustainability session of the UTECH Congress. They all also agreed that polyols must not contribute to fogging, VOC or staining.
Peter Groome of Chinaâs Jiahua Chemical used the congress to outline his companyâs capacity and range of sustainable polyurethane additives, and to explain their use in automotive applications.
Jiahua developed its own natural oil polyols at its R&D labs in Shanghai. âWe looked to see where the new polyols would fit in to replace existing polyether polyols,â he explained. âWe have commercialised two processes from this work, and these are running on our plants. Our polyols have found use in slabstock polyurethane foam, moulded foam, insulation, glass mat reinforcement and truck bed liners.â
The aim was to use high-volume raw materials, and produce the polyols on a plant with a positive eco-balance. âAdditionally, it should not affect the food chain,â Groome said.
No odours, pleaseâWe have a capacity of 700kT/year of polyols and five manufacturing sites in Fushan, near the Korean border, Guangzhou, Shandong, Shanghai, and Maoming, China,â he told delegates. Conventional polyurethane polyols are dominated by polyether polyols because of their flexibility and compatibility. âThese can be used with a range of initiators to give, for example, autocatalytic polyol, and to modify their functionality, which ranges from 2 to 8,â Groome said. Polyester polyols account for around 25% of the total used and, again, have great flexibility in the acids and alcohols that can be used to produce them. Natural oil polyol properties vary widely because of the chemical composition of natural oils. A typical chemical composition for natural oils is shown in Table 1. âWe looked at soya, sunflower and palm oil,â Groome explained. InÂ this Table, the first number in brackets gives the number of carbons in the backbone, and the second gives the amount of unsaturation within the fatty acid. The differences in unsaturation give the different levels of functionality. Castor oil contains an unsaturated fatty acid bearing a hydroxyl group. âThis makes it one of natureâs natural polyols,â Groome said.
|Table 1:Compostion of Natural Oils|
|Natural Oil||Oleic||Linoleic||Linoleic||Ricinoleic (b)||Stearic||Palmitic||Other|
|Notes:||(a) first number = No Carbon bonds; Second No=unsaturation sites; (b) Ricinoleic acid residue contains hydroxyl|
Addition ReactionDirect addition to a double bond made it possible to produce polyols with a functionality of 2 to 2.2 and a hydroxyl value between 47 mgKOH/g and 320 mgKOH/g. âWith the co-initiation process, we achieved functionalities between 2 and 5 and hydroxyl values between 200 and 400 mgKOH/g,â he explained. Groome also spoke about work in automotive applications that has been done in Jiahuaâs Shanghai labs, and also some carried out in the field. This concentrated on seating, glass-mat reinforced PU, truck bed liners and thermal insulation. In slabstock formulations, they used a natural polyol with hydroxyl number of 52mg KOH/g, with a 10% SAN solids slabstock polymer polyol. The NOP was used at between 0 and 30%. The SAN polyol on its own had good stability, and the product with between 12 and 25% NOP in the polyol had the same properties as the standard. âAt much higher levels of NOP, we ran into significant problems with the product,â he said. In moulded foam applications, they concentrated on automotive seating using MDI. A 20% NOP loading was compared with conventional polyol at a density of 35 kg/m3 and compression set, indentation, tear, tensile strength, elongation and resilience were all found to be similar for both conventional and NOP polyols in the laboratory. The product was used in truck-body insulation using various production processes. âWe looked at producing discontinuous PU panels, continuous PU/PIR panels, PIR discontinuous blocks and spray foam,â Groome said. âAt 30% NOP from the co-initiation process, we found the results for compression strength, lambda value, specific density and dimensional stability after ageing were identical to formulations made with the 100% conventional polyol.â
Using yeastReverdiaâs sustainable approach is slightly different. Instead of modifying polyols directly, it uses succinic acid produced by GM yeast to produce the feedstock for polyols, according to Lawrence Theunissen, the companyâs global director for application development. âReverdia is a joint venture between DSM and Roquette Freres,â he said. âWe produce Biosuccinium, a bio-based succinic acid that is made via fermentation. In addition to supplying our direct customers, we also try to collaborate with people further along the chain.â The companyâs Italian factory has 10 kt/year capacity. âSuccinic acid is converted into polyester polyols and then into polyurethanes,â he said. It is chemically related to adipic acid â it is a four-carbon dicarboxylic acid, whereas adipic acid has a six-carbon chain â and thus can often be used in a similar way. âWe sometimes also offer our product as an alternative to phthalic anhydride or isophthalic acid.â Moving to a biotechnological production route leads to significant savings in carbon dioxide, Theunissen explained. âAccording to work at the Copernicus Institute of Utrecht University, the Netherlands, there is a 53% reduction in carbon dioxide emitted in producing succinic acid using Reverdiaâs biological product compared to the traditional petrochemical solution,â he claimed. âThe petrochemical option leads to emissions of 1.9 kg CO2/kg succinic acid produced, whereas Reverdiaâs process leads to 0.9 kg/CO2/kg. There could be scope to capture more carbon dioxide in the process than is generated by it.â The carbon dioxide savings are even more notable when compared to petrochemically derived adipic acid. âTypically, Reverdiaâs approach produces a 90% saving in CO2 emissions, compared with the petrochemical adipic acid process,â he said. âIf the Reverdia material is used in a pair of running shoes, for example, then it is possible to reduce carbon emissions from 15kg/pair to 12.5kg/pair. That could be a significant saving for a brand owner.â
Cut back on CO2Theunissen explained that, most of the time, the decision to use a bio-based material comes from the other end of the value chain â the brand owners. âThis group is driven by its own targets and goals, and that is where we find traction,â he said. âWe work with people along the chain to help all the stakeholders understand what can be done. The furthest, brand owners, typically talk up the chain to the polyurethane and polyol suppliers, their direct suppliers. Brand owners indicate it is quite uncommon to be visited by monomer suppliers to discuss brand ownerâs needs and the opportunities for biobased raw materials.â In the polyurethane sector, shoe soles are a key market, while in the automotive sector, textiles in flame lamination applications are important, he said. âTPU elastomers, PU dispersions and adhesives are also interesting.â Polyols built from fossil-based succinic acid are specified in applications because they perform better in the application than alternatives. âIt has nothing to do with being bio-based, it is about functionality,â Theunissen said. âLooking at bio-based succinic acid, the starting point is often different: our customers want to replace oil-based products, for example adipic acid, and they try our material. However, once theyâve started to experiment, they see new properties, some of which are better than the one they are used to.â He cited the use of bio-based succinic acid in Vaudeâs 2018 summer collection of Skarvan trekking shoes. âHere, bio-based TPU is used in the toe-cap because the brand wanted to use sustainable, bio-based resources,â he said. âIn a separate footwear-related project in Asia, Reverdiaâs material is used in a high-density (500-600 kg/m3) micro-cellular foam slipper sole. Here again, the main drive is to replace fossil-based raw materials with bio-based materials.â Theunissen gave the example of an industrial squeegee used in the printing industry. Here, PU strips are used to spread the ink in the screen printing process, and the strips are exposed to solvents and other types of chemicals during use. TPU based on succinic acid is a well-established product, but he said that companies have switched from fossil to bio-based materials because of production economics. âAlong with flame lamination products, bio-succinic acid can be used in the automotive sector for acoustic foam,â said Theunissen. He outlined the work done at the Institute of Polymers, Composites and Bio Materials in Italy, a research institute working with local company Adler Plastics. This looked at Dowâs SpecFlex system, where part of the fossil-based polyether polyol is replaced with a polyester polyol made by COIM using Reverdiaâs bio-succinic acid.
Flame laminationThe formulations are shown in Table 2Â and the cell structure of a typical polyurethane foam produced is shown in Figure 1.
|Table 2: PU formulations|
|Sample||%SP||%BP||%H2O a||% TEP a||% CB a|
There were differences in sound absorption at frequencies > 1 kHz. The foam made with biopolyol and carbon black had the greatest improvement in absorption. Similarly, using the biopolyol resulted in foams with greater transmission loss than standard foams.