Thermoplastic Polyurethane (TPU)

Thermoplastic Polyurethane (TPU) Although the vast majority of commercial isocyanate production is used in flexible and rigid foam, RIM, and cellular products, the remainder is used in the production of various elastomers. Polyurethane elastomers have varieties such as TPU, CPU (cast polyurethane elastomer), 1K&2K coatings, and spandex. Unlike liquid polyurethanes, TPU is supplied in granule form for processing in conventional plastic processes such as injection and extrusion. TPUs are generally classified according to their hardness grade. TPUs with different properties ranging from 60 Shore A to 70 Shore D are possible. Their physical properties, working temperatures, and ease of processing allow TPU to fill the gap between conventional rubber materials and engineering plastics such as nylon and polycarbonate.

Chemistry

TPU is a block copolymer (AB) consisting of alternating hard and soft segment sequences, like other elastomers. The utility of its physical properties stems from the presence of both hard and soft segments in its chemical structure. The ratio of hard and soft segments and additives can be manipulated to produce TPUs with different properties. TPUs are typically produced from pure MDI with linear polyether or polyester diol and a low molecular weight chain extender such as 1,4 butanediol in a one or two-step reaction. The reaction of MDI and short-chain diols results in covalently bonded hard segments, while the reaction of MDI and long-chain diols results in covalently bonded soft segments. The strong molecular interactions of highly polar hard segments with each other create crystalline structures, which are surrounded by a matrix formed by soft segments. This phase separation acts as physical cross-linking and brings elastic properties to TPUs. Unlike the chemical cross-linking present in other liquid polyurethane varieties, physical cross-linking is lost with heat, allowing TPUs to be processed by injection and extrusion.

Packaging - Pre-Treatment - Coloring

Thermoplastic polyurethanes are typically supplied ready for use in 25 kg moisture-proof bags. TPUs are hygroscopic materials that absorb moisture upon contact with air. Moisture is an important factor that reduces final product quality. Bubbles and marks form on the outer surface. Therefore, products must be dried to a moisture level below 0.1% before use. Information from suppliers regarding drying temperatures and times is important. TPUs can be colored using TPU-based masterbatch. Due to their thermoplastic nature, the final product or scrap-like pieces from production can be recycled. The recycling ratio should not be so high as to affect the material's quality and dimensional stability.

Processing

Standard injection and extrusion machines with screw diameters from 40 mm to 60 mm and L/D ratios of 20:1 and 30:1 are recommended. In injection molding, flash, burn marks, uneven color distribution, incomplete fill, flow marks, voids, and sticking; in extrusion, scratches, uneven thickness, dimensional variation, yellowing and odor, black specks, internal or external hard surface, streaks, and lack of gloss are among some common issues. Extrusion and injection working temperatures, screw values, speed and pressure values, and cooling line settings are important parameters for processing TPU without degradation. Correct diagnosis of problems, use of appropriate raw materials, and proper parameter adjustments will yield the desired final product. The correct TPU type should be selected for different applications. 1) By polyol type: a. Polyester-based TPU – high resistance to oils and chemicals, high wear resistance. b. Polyether-based TPU – flexibility at low temperatures, high hydrolysis and microbial resistance. c. Polycaprolactone-based TPU – low compression set, low temperature. 2) By isocyanate type: a. Aromatic – flexibility, strength and hardness, physical performance. b. Aliphatic – light and yellowing resistance, optical properties.

Physical and Chemical Properties

TPUs are preferred in many industries due to their high wear resistance, tear and tensile strength, high resistance to environmental chemicals, oils, solvents, flexibility at low temperatures, transparency, high elongation, low compression set, PU-PVC adhesion, PVC compatibility, and FDA compliance.

Applications

Shoe soles and heels, industrial wheels, screens, automotive parts, cable sheaths, spiral hoses, layflat, hydraulic and pneumatic hoses, sealing elements, belts and bands, profiles, 3D filaments, films and sheets, medical, elastic straps, delineators, animal ear tags, phone cases, adhesives, synthetic leather. Unigrup, with 4 companies under its roof, has been providing reliable, fast, and quality products and services to its customers since 1995. Under the Unigrup umbrella, Unipol Kimya has been providing chemical raw materials, alternative solutions, and technical support to the polyurethane sector since 1995 with its wide product range and experienced staff. In the TPU field, it acts as the Turkey distributor for Italian Epaflex Polyurethanes S.P.A. Epaflex, with its major investments in the polyurethane sector, has been a global manufacturer since 1991 with production capacities of 15,000 tons of TPU per year, 50,000 tons of polyurethane systems, and 95,000 tons of saturated polyester. Products TPUs in our product portfolio: • Epamould; polyester and polyether-based TPU designed for injection. • Epaline; polyester and polyether-based TPU designed for extrusion. • Epacol; TPU designed for solvent-based adhesive manufacturing. • Pakoflex; polyester and hybrid (polyester/polyether)-based TPU designed for coating and coagulation. • Epamet; bio-based TPU produced from renewable sources.

Ege Çağatay TPU Sales Representative Unipol Kimya San. ve Tic. A.Ş.