Polyurethane Rigid Foam-FDM Composite Materials

Special Approaches for Thermal Insulation and Energy Efficiency: Polyurethane Rigid Foam-PCM Composite Materials Work on renewable energy sources and improved energy efficiency is important for reducing carbon dioxide emissions from oil-based sources. In the European Union, approximately 40% of total energy consumption originates from residential, commercial and public buildings. For this reason, reducing energy consumption in living spaces without compromising living conditions and indoor thermal comfort limits is important for lowering carbon footprint and developing environmentally friendly green buildings. The growing population and industrialisation in our country are rapidly widening the gap between energy production and consumption. As our country is heavily dependent on imported primary energy sources, approximately 74% of energy is imported from abroad and constitutes the largest item in the current account deficit. For this reason, work on economical energy use and storage contributes significantly to more efficient use of our country's energy resources. The spread and implementation of this awareness in all sectors has gained even greater importance today. When imbalances occur in supply and demand in energy consumption, thermal energy storage becomes important. In today's environment where applications for heating, cooling and waste heat utilisation stand out, thermal energy storage systems can offer solutions to energy savings and supply-demand imbalances. The most commonly used method for thermal energy storage is sensible heat storage, which is observed due to temperature rise. In heating living spaces with hot water circulating radiators or floor heating systems, the walls surrounding the room and the floor are volumes where sensible heat is stored with temperature increase. However, a material storing heat as latent heat by undergoing phase change is a much more effective and advantageous method compared to sensible heat storage. As the material changes phase at constant temperature (or within a narrow temperature range), it absorbs or releases a large amount of thermal energy from or to the environment. Since no noticeable temperature change is observed in thermal energy storage, this is called latent heat storage. Materials used in latent heat storage are called Phase Change Materials (PCM). The oldest and most common applications are those in which cold is preserved with ice or snow. In the polymer industry, one of the fastest-growing groups in recent years is undoubtedly polyurethanes. Basically, the urethane chain is formed as a result of the reaction of isocyanate functional groups with hydroxyl functional groups. It was first synthesised by Otto Bayer and his colleagues in 1937. In commercial applications, polyester and polyether polyols are used as hydroxyl sources in polyurethane, while different types of aliphatic and aromatic isocyanates are used. Looking at application areas, polyurethanes have found a very wide range of uses from aircraft-ship construction materials, seat foams, mattress foams, packaging foams, fibres, polyurethane rigid foams (insulation materials), toys, wheels, synthetic leather, slippers/shoe soles, adhesives, medical applications and more. The main reason for the recent popularity of polyurethane rigid foams, particularly in insulation applications, is the ability to tailor them without additional measures by using different polyol groups, isocyanate types, glycols and blowing gases. By changing the types, quantities and ratios of the raw materials mentioned above used in the product application area, desired thermal conductivity values, densities and hardness values can be obtained. Moreover, during the foaming process, new-generation reactive catalysts are also used to prevent catalyst-derived emissions. Rigid polyurethane foams are intensively used in applications such as sandwich panels, refrigerators, cold storage panels, boiler and pipe insulation, and tank coatings because of their low thermal conductivity values.   The thermal insulation capabilities of rigid foam polyurethane materials, which have low thermal conductivity values due to their closed-cell structures within the foam, can be customised by developing PU-PCM composite materials for special applications. At this point, the aim is to benefit from the energy stored as latent heat as the PCM melts by absorbing heat during environmental temperature increase for thermal insulation purposes. In this way, as the PCM within the foam material melts at constant temperature (or within a narrow temperature range), it accumulates the heat from the increase in ambient temperature on itself, contributing to the material's thermal insulation properties. This property imparted by PCM to the foam material is clearly visible in the thermogram provided in Figure 1. The PCM, homogeneously distributed within the foam structure, begins to melt at around 38°C and performs latent heat storage within the foam. In the foam sample without PCM, no phase transition is observed, but a linear temperature increase occurs. When the two situations are compared, in the study conducted, during heating of the foam between 5-90°C, it was determined that depending on the amount of PCM used, it could store 21% to 34% more heat on itself in the form of sensible and latent heat. This indicates that the PUPСM foam composite material would buffer more heat for the same thickness in thermal insulation. In Figure 2, microscope images at x400 magnification show PCM materials regularly distributed within the foam structure.     The important point here is that the PU-PCM composite formulation is created in a way that minimally affects the closed-cell structure of the foam. Otherwise, the resulting increase in thermal conductivity could prevent the desired benefit from being observed. In these and similar cases, the PCM ratio can be adjusted along with the polyurethane formulation, or different additive materials that could passively contribute to thermal insulation and lower the thermal conductivity of the composite foam material can be added to the formulation. In conclusion, PU-PCM foam composite materials are a current topic open to R&D work in developing special application materials for reducing energy consumption and promoting energy savings. The content of the subject addresses a very wide range in determining the application areas and the properties of the final products needed. Assoc. Prof. Ahmet Alper Aydın Faculty Member Department of Chemical Engineering Istanbul Technical University Dr. Başar Yıldız General Manager Ideakim Global Kimya A.Ş.