Thermoplastic Polyurethane (TPU)
Although most of the commercial production of isocyanate is consumed by the manufacture of the foams, RIM, cellular materials, the remaining part is used to make very wide range of polymers like elastomers. There are different types of polyurethane elastomers such as TPU, CPU (cast polyurethane elastomer), 1K&2K coatings, spandex.
Unlike liquid polyurethanes, thermoplastic polyurethanes are supplied as granules or pellets in order to be processed by conventional plastic processing techniques such as injection molding and extrusion. TPUs are generally classified by their degree of hardness and available in a range from 60 Shore A to 70 Shore D. The physical properties, range of working temperature, processibility allow TPU to fill the gap between conventional rubber
materials and engineering plastics like nylon, polycarbonate.
Chemistry
TPUs are block copolymers based on alternating hard and soft segments (AB)n. The usefulness of its physical properties is due to 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 usually made from pure MDI which is reacted with a linear polyether or polyester diol and with a low molecular weight short-chain extending diol. Covalently bonded hard segments are formed from the reaction of MDI and short-chain diols. Covalently bonded soft segments are formed from the reaction of MDI and longchain diols. Strong molecular interactions (hydrogen bonding) of high polarity hard segments create crystal structures and these structures are surrounded by a matrix formed by soft segments. That phase separation constructs a physical crosslinking and leads to the elastic properties and easy processability of TPU. Unlike chemical crosslinking in other liquid thermoset polyurethan types, TPUs can be processed by injection and extrusion processes because physical crosslinks break with heat.
Packaging – Pre-Treatment – Coloring
Thermoplastic polyurethanes are usually supplied ready for use in 25kg moisture-proof bags. TPUs are hygroscopic materials, they absorb moisture if left exposed to the air. Humidity is one of the important factors that reduce the quality of the final product. To ensure satisfactory end products free from bubbles and streaks and to avoid the risk of hydrolysis of TPU products should be dried to reach a moisture level below 0.1% before
use. Drying should be done with a specific time and temperature in a desiccant dryer according to the grades.
Processing wastes and scraps can be re-granulated and reused due to its thermoplastic nature. The recycling ratio should not be high because it affects the quality of the material and its dimensional stability. TPUs can be coloured with masterbatches. TPU based masterbatches are recommended.
Processing
Standard injection end extrusion machines with general purpose screws between 40mm and 60mm and with L/D ratio between 20:1 and 30:1 is recommended to ensure a uniform melt. Blisters, splay marks, burn marks, uneven color distribution, short shots, sinks, voids, sticking parts are some injection molding problems; Scratches, uneven thickness, cross section variety, yellowing and odor, black spots, rough surface inside or outside, die
lines, lack of gloss, surface defects are some of the important problems in extrusion. Extrusion and injection operating temperatures, screw types, speed and pressure values, cooling line settings are important parameters to obtain satisfactory products.. Problems can be solved by correct diagnosis, correct raw material usage and using appropriate parameters.
The appropriate TPU type must be selected for different applications.
1. According to the type of polyol:
a. Polyester based TPUs – high resistance to oil and chemicals, high abrasion resistance.
b. Polyether-based TPUs – high flexibility at low temperatures, high hydrolysis (water) and microbial resistance.
c. Polycaprolactone based TPUs – low compression set, low temperature performance.
2. According to the type of isocyanate:
a. Aromatic – flexibility, strength and stiffness, physical performance.
b. Aliphatic – light and yellowing resistance, improved
optical properties.
Physical and Chemical Properties
Properties such as high abrasion resistance, tear and tensile strength, high resistance to chemicals, oils, grease, solvents, transparency, flexibility at low temperatures, high elongation at break, low compression set, perfect adhesion to PU substrate, compatibility with PVC, FDA compliance in some grades make TPU a relevant polymer for wide range of application.
Fields of Use – Applications
Shoe soles and heels, industrial wheels, sieves, automotive parts, cable sheathing, spiral hoses, layflat, hydraulic and pneumatic hoses, sealings, belts, profiles, 3D filaments, film and sheet, elastic tapes, animal ear tags, phone cases, dhesives, artificial leather.
Unigrup, based on its customer satisfaction priority and solution-oriented sales strategy, is offering reliable, fast and high quality products and services to its customers since 1995 with its 4 companies. As the first company of our group, Unipol Kimya has been providing chemical raw materials, alternative solutions and technical support to the Polyurethane industry with its wide product range and experienced staff since 1995.
In the field of TPU, we are official distributor of Italian company Epaflex Polyurethanes S.P.A . Epaflex is one of the major player in the market since 1991. Due to its substantial
investments, the company has 15,000 tons TPU per year production capacity along with 50,000 tons for polyurethane systems and 95,000 tons capacity for saturated polyesters.
TPU Products
The main grades in our portfolio are:
• Epamould; polyester and Polyether based TPU designed for injection moulding processes.
• Epaline; polyester and polyether based TPU designed for extrusion processes.
• Epacol; polyester based TPU designed for solventbased adhesive production.
• Pakoflex; polyester and hybrid (polyester/polyether) based TPU designed for coating and coagulation processes.
• Epamet; bio-based TPU made from renewable resources.
Ege Çağatay
TPU Sales Representative
Unipol Kimya San. ve Tic. A.Ş.
