Flexible Polyurethane Foams

Polyurethane Flexible Foams At the beginning of the 1900s, synthetic polymers were little known. However, in the following years, polyvinyl chloride (PVC) was invented in 1913, polyethylene (PE) in 1933, nylon (Nylon 66) in 1934, and Teflon® in 1938, and these inventions found applications in many fields and became widespread up to the present day. After nylon was discovered and well-protected by patents by Dupont in 1934, Otto Bayer worked on an alternative raw material that could compete with nylon using different feedstocks. In 1937, he discovered polyurethane that could be made into filaments and formed films, and obtained its patent. The reactions forming the urethane group had actually been known for a long time, but commercial use began thanks to Otto Bayer. In the post-war years, many organizations and scientists, particularly in Germany, the United States, and Japan, developed various types of polyurethane for flexible, rigid, film, coating, and adhesive applications, and polyurethane became one of the most widely used industrial products today. The building blocks of polyurethane are mainly polyol and isocyanate. The polyol contains catalysts, chain extenders, crosslinkers, flame-retardant additives, UV absorbers, UV stabilizers, antioxidants, and colorants. Isocyanate typically contains prepolymers of aromatic isocyanates in most applications other than paints and lacquers. Polyols can be either polyether or polyester-based depending on their final application. Polyether-based products are generally used in durable consumer goods and shoe-slipper soles in tropical regions due to their hydrolysis resistance. Polyester polyols are used in safety work shoes and widely in shoe-slipper manufacturing in non-tropical regions due to their resistance to oil-based products. Isocyanate prepolymers are generally obtained by converting MDI and TDI into larger molecules with diols and reducing volatility. In this way, workers involved in polyurethane production are not exposed to the monomers of these health-hazardous chemicals. In the automotive industry, polyurethanes are used for seats, steering wheels, side trims, armrests, headrests, noise and vibration damping purposes, NVH (noise, vibration, harshness), absorbing energy released in potential accidents and collisions, and especially in electric vehicles, increasingly for thermal and sound insulation. Up to 15 kg of polyurethane can be used in a sedan-type vehicle. Approximately two-thirds of polyurethane is produced as foam. Flexible foams produced from these foams are particularly used in the furniture industry as filler in beds, armchairs, and chairs, laminated onto fabrics used in underwear, swimwear, and upholstery to provide volume, and for thermal and sound insulation purposes. Flexible foams are also used as dishwashing sponges, toys, acoustic insulation panels, and packaging for sensitive equipment. Flexible foams are produced in different densities, firmness, and softness depending on their final application. These products are colored for two main purposes: sponges found in applications such as dishwashing sponges and toys are colored for decorative purposes, while sponges used in furniture are colored to be distinguished by their properties during manufacturing, storage, sales, and use stages. Flexible foams can be produced in different densities, firmness, and elasticity, and these sponges, which are very similar to each other in their uncolored state, are produced in colors such as black, blue, yellow, and pink to be distinguished. The produced sponges undergo quality control according to many criteria such as density, firmness, permanent deformation, volatile organic compound analysis, tensile strength, elongation at break, tear strength, and water absorption. The produced sponges are certified through organizations such as TSE, Europur, Oeko-Tex, FIRA, and SATRA for reasons including compliance with quality and flammability standards and chemical laws. Flexible foam production is conducted in three types: molding production, box-type production, and continuous production. In molding production, polyurethane components are mixed and poured into molds made of metal or composite that have been heated to a temperature determined by the manufacturing company and treated with mold release agent. Dosing machines are used to ensure that the proper mixture and the ratios of the components are exactly as desired. Dosing machines keep the components in their tanks at a temperature determined by the manufacturing company and dispense the dosing in predetermined amounts for each mold, mixing within 5 to 15 seconds. These mixtures are mixed in the head section of the dosing machine either through mechanical mixing or with high pressure between 150-250 bar. Using mold release agents, the molded polyurethane is formed within 2-5 minutes and removed from the mold. The main applications of flexible foams produced by molding include vehicle headrests, seats, pillows, medical neck supports, and seat cushions. In box-type production, 3-6 m³ boxes are used. Preferably by machine or manually, polyol, water, blowing agent, catalysts, additives, and colorants are fed sequentially into the container on top of the box and pre-mixing is provided. Isocyanate is finally added to this homogenized mixture, and after mixing for about 5 seconds more, the mixture is poured into the box and foam is obtained within approximately half an hour. In continuous production, these inputs are dosed and mixed with computer-controlled pumps and foam is produced along the line. While tons of polyurethane are produced with continuous-type production, boutique productions are made with box-type production. Recycling of flexible foams is important due to increasing awareness, global warming, and circular economy needs.

Sponges can be recycled through various methods:

• By grinding and molding mixed with adhesive, • By giving recycled pieces a different form inside a mold, • By chemically recycling using hydrolysis and pyrolysis methods, To facilitate recycling, improvements are being made starting from seat and bed design. New technologies are being developed to remove heavy metal contamination in the content of sponges produced according to old regulations. Automation techniques are being developed to recycle old mattresses. Polyols derived from vegetable oils have also been developed to reduce dependence on petroleum. Naturally occurring castor oil containing hydroxyl groups can only be refined for use in flexible foam production. Teknik Kimya produces Armacolor® PUR series, Armaliz® water-based series, and Sintaliz® solvent-based mold release agents for flexible foam polyurethanes.

Sources:

•Gama, N. V., Ferreira, A., & Barros-Timmons, A. (2018). Polyurethane foams: Past, present, and future. Materials, 11(10), 1841. •Dutta, A. S. (2018). Polyurethane foam chemistry. In Recycling of polyurethane foams (pp. 17-27). William Andrew Publishing. •www.formsunger.com.tr •https://www.laaderberg.com/laaderberg/Maxfoam%20The%20Concept/Maxfoam%20the%20Process/Maxfoam%20Basic.aspx •https://www.cannonplastec.com/products/machinery/dosing-machine/a-prima/ •Sonnenschein, M.F., 2015, Science, Technology, Markets, and Trends, John Wiley & Sons, Inc. Hoboken, New Jersey, ISBN 978-1-118-73783-5. İlker Akça Technical Director Teknik Kimya