Polyurethane-Based Rubber and Foam Binder Systems

Polyurethane-Based Rubber and Sponge Binder Systems in Recycling Recycling, which can be viewed as an investment in the future, has played a significant role in environmental protection by preserving our limited natural resources, reducing waste volumes and achieving energy savings. Recycling can be fundamentally divided into three groups: mechanical, chemical and energy conversion. Of these, mechanical methods have come to the fore in addressing synthetic polymer waste, which is one of the main causes of environmental pollution today. In rubbers, a type of polymer, the recycling process performed through mechanical means causes shortening of polymer chains and is therefore not suitable for repetition, but it is in a more advantageous position than chemical and energy conversion methods due to the excessive time and energy required. Polyurethane binders hold an important place in making environmentally friendly products available to use, with the possibilities they provide for rubber recycling alongside various materials. Rubber materials that can be ground through mechanical methods and separated into particles of different sizes and then reunited with polyurethane binders to be produced in desired structures and dimensions have a wide range of applications. Examples of these include children's playgrounds, walking paths, sports fields, garden grounds and bicycle paths. The binder used must provide certain flexibility and hardness to the final product. If these two parameters deviate from optimum levels, movement on the surface will become difficult. Moving on a surface with excessive flexibility and insufficient hardness will turn into a tiring experience, whereas in the opposite case, a hard and non-resilient surface will restrict movement with an uncomfortable feeling. However, products properly manufactured and applied provide comfortable and easy use in various physical activities such as walking, running or sports activities. Although different methods are used in the production of recycled rubber materials found in many fields, there is fundamentally similar logic. In production systems, rubber materials must first be cleaned and stripped of oils and moisture. Through this process, high-level efficiency can be obtained from the binder and better adhesion will be provided. As a result, a product with high tear strength will be obtained and the product's service life will be longer. Rubber granules mixed with polyurethane binder can be applied by pressing or casting methods depending on desired properties and application areas. The products obtained are mostly called binders in the industry. In the pressing process, the binder and rubber mixture is placed in molds in appropriate amounts and pressed under high temperature and pressure. Color can be added to the mixture as needed. Products obtained through this process in different dimensions with the help of different molds show dimensional stability as they are joined together and cover the ground, which is important. If they shrink due to temperature differences, gaps will form on the ground, resulting in insufficient results both visually and in terms of performance. [caption id="attachment_144825" align="aligncenter"] Figure 1. Rubber products manufactured with the pressing method[/caption] Kobe Poliüretan serves customers with three different products through Kobenat I-801, Kobenat I-810 and Kobenat I-811, which have high binder properties for hot press applications. These products are solvent-free and aromatic in nature and are suitable for use with SBR (styrene butadiene rubber) and EPDM (ethylene propylene diene monomer) particles. The binder usage rate in production processes, along with conditions such as ambient and mold temperature, allows us to provide solutions to our customers with optimum mixture and mold opening times. Our Kobenat I-811, which demonstrates water resistance, high strength and dimensional stability, stands out with its bio-based structure in addition to its contribution to recycling. [caption id="attachment_144826" align="aligncenter"] Table 1. Products and properties used in the pressing method[/caption] In casting applications, processing is performed by using a higher proportion of binder without benefiting from the accelerating effect of high pressure and temperature. Rubber granules, after being homogeneously mixed with the binder in appropriate proportions, are evenly spread on a previously primed ground and pressure is applied for good adhesion. The product must be left for 24 hours to fully cure and be ready for use. After that, painting can be done as desired. Since there are no additional parts in the casting method, a very suitable surface is provided for decorative work. In the casting method, it is important that during the mixing period, the binder and rubber mixture does not cure and remains in fluid form for the process to be completed flawlessly. Kobenat I-803 and Kobenat I-814 are compatible with SBR and EPDM rubber particles, solvent-free and aromatic in nature, and are products that provide successful results in casting applications. In addition to providing appropriate curing times, water-resistant structures and ease of application, Kobenat I-814, one of these two products with excellent binder properties, provides an advantage in reducing carbon footprint with its bio-based structure. [caption id="attachment_144828" align="aligncenter"] Figure 2. Rubber flooring applied with the casting method[/caption] [caption id="attachment_144829" align="aligncenter"] Table 2. Products and properties used in the casting method[/caption] Polyurethane binders are frequently used in recycling applications of materials such as EVA, integral, sponge, cork, wood and stone in addition to rubber. From these materials, sponge finds the opportunity to be used again in various fields thanks to the recycling of waste and scraps generated during its production stage. These products are called sponge panels and are created as a result of small pieces of sponge being homogeneously mixed with binders and molded according to desired density at high temperature. Sponge panels can be easily cut into requested shapes and thicknesses. In the industry they are also known as bondex and rebonded sponge. Kobe Poliüretan is present in the market with four different products meeting customer demands in sponge recycling. Kobenat I-804, Kobenat I-806, Kobenat I-816 and Kobenat I-817 impart high tear resistance and strength to products through their strong adhesive properties, while their different reaction profiles enable adaptation to various application conditions. The sponge panels in which our products are used provide heat and sound insulation, as well as impact-absorbing properties. This makes them frequently used in sports halls, beds, furniture production, construction and automotive sectors. [caption id="attachment_144831" align="aligncenter"] Table 3. Products and properties used in sponge panel production[/caption]     References Jeswani, Harish, et al. (2021). Life cycle environmental impacts of chemical recycling via pyrolysis of mixed plastic waste in comparison with mechanical recycling and energy recovery. Science of the Total Environment, 769, 144483. Vollmer, Ina, et al. (2020). Beyond mechanical recycling: Giving new life to plastic waste. Angewandte Chemie International Edition, 59(36), 15402-15423.   Sibel Özyılmaz Research and Development Engineer Kobe Poliüretan