Thermoplastic urethanes

The thermoplastic polyurethane (TPU) adhesives must, of necessity, contain low gel content because they must be processable in an extruder. Most adhesives are relatively linear, with a functionality of 2.0, although small amounts of branching may be introduced, usually at the expense of a lower melt flow. Good physical properties of TPU s are obtained when the thermoplastic urethanes have molecular weights of 100,000 or higher (see p. 56 in [63]). Most TPU adhesives are based on symmetrical polyesters with a fast crystallizing backbone or a backbone slightly modified to increase the open time. 

Thermoplastic urethane adhesives may be processed into an adhesive film. I,amination of two substrates can, in theory, be done immediately, but the film is often extruded onto one substrate, covered by a release liner, and allowed to cool. Crystallization follows to create a non-tacky film that may be cut into specific shapes. The release liner is then removed, and the shaped adhesive can be heat-activated on one substrate, using infrared lamps. The second substrate is then nipped under pressure, followed by a cooling press to speed crystallization. Once the backbone has crystallized, the bond should be strong. 

Styrene acrylonitrile Styrene butadiene Styrene maleic anhydride Styrene methyl methacrylate Thermoplastic urethane, rigid... 

The elasticity of thermoplastic polyurethane rubbers (which are also known as thermoplastic urethanes or TPUs) is a function of their morphology which comprises hard and soft phases. The hard phases consist of hydrogen bonded clusters of chain segments, which are linked by flexible chain segments that make up the soft phase. The hard blocks, which are the minor phase, exist as separate domains within a continuous matrix of the majority soft phase, as shown schematically in Fig. 25.9. 

We take advantage of the shock absorbing characteristics of thermoplastic urethane rubbers in automotive, motorcycle, and bicycle suspensions and power transmission systems. Industrial shock absorbing applications include buffers for elevators and cranes. 

How does the elasticity of thermoplastic urethanes arise from the structure of the polyurethane ... 

Expandable PS Thermoplastic urethane Abietic acid derivatives Polyester fiber Chlorinated polyether resins Butadiene-acrylonitrile copolymers Melamine resin Polyurethane filament Cast epoxy Nylon-6... 

Includes thermoplastic urethanes and synthetic leather. Includes paints. 

Because the components must initially form miscible solutions or swollen networks a degree of affinity between the reacting components is needed. Therefore, most of the investigations into epoxy IPNs have involved the use of partially miscible components such as thermoplastic urethanes (TPU) with polystyrenes [57], acrylates [58-61] or esters which form loose hydrogen-bound mixtures during fabrication [62-71 ]. Epoxy has also been modified with polyetherketones [72],polyether sulfones [5] and even polyetherimides [66] to help improve fracture behavior. These systems, due to immiscibility, tend to be polymer blends with distinct macromolecular phase morphologies and not molecularly mixed compounds. 

It would seem that such broadened use of flexible plastics and rubbers in exterior-body structural members will compel the conclusion that high performance materials are needed. They must not only be relatively light, flexible, serviceable at temperature extremes, and easily fabricated and finished, but they must be as strong and as tough as possible. The public will demand this. One type of flexible synthetic polymer which meets these requirements very well indeed is the thermoplastic urethane elastomers which have already proved themselves in flexible front ends, sight shields, and fascia in production model automobiles. 

A silicone semi-IPN modified thermoplastic urethane illustrates this technology. The following composition is mixed in the melt state by pumping a preblend of the silicones into a counter-rotating twin-screw extruder with... 

The mixture is pelletized, and 1 g of a platinum-tetramethyl-tetravinylcyclotetrasiloxane complex (2.5% Pt) is tumbled onto the pellets and then deactivated by the addition of 0.05 g of 3-methylisobutynyl alcohol. The apparently homogeneous material contains two unreacted silicones in a thermoplastic urethane matrix. 

Figure 1. Thermoplastic urethane elastomer chain organization.

Published information on urethane polymerization detail largely concerns thermoset urethane elastomers systems.4 13 In particular, the work of Macosko et. al. is called to attention. The present paper supplements this literature with information on the full course of linear thermoplastic urethane elastomer formation conducted under random melt polymerization conditions in a slightly modified Brabender PlastiCorder reactor. Viscosity and temperature variations with time were continuously recorded and the effects of several relevant polymerization variables - temperature, composition, catalyst, stabilizer, macroglycol acid number, shortstop - are reported. The paper will also be seen to provide additional insight into the nature and behavior of thermoplastic polyurethane elastomers. 

Figure 2. Thermoplastic urethane melt polymerization. Key X, Polymer 1 O, Polymer 2 A, Polymer 3.

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