Polyurethanes fabrication

In polyurethane fabrication, some special techniques are used, such as prepolymer technique, quasiprepolymer technique and one shot technique. 

All the oligo-polyols are used to build the polyurethane high MW structure in a reactive process, as a consequence of the oligo-polyols terminal hydroxyl group reaction with polyisocyanates. The reactivity of oligo-polyols in polyurethane fabrication is a very important practical characteristic. Reactivity is a measure of the reaction rate of an oligo-polyol with an isocyanate in order to make the final polyurethane polymer. One practical method is the measurement of viscosity, in time, by Brookfield Viscosity Test (BVT), especially used to determine the reactivity of ethylene oxide capped polyether polyols. Figure 3.12 shows the effect of the primary hydroxyl content upon the reactivity of ethylene-oxide capped polyether triols of MW of 5,000 daltons. 

It is very clear that only the first group of monomers, which lead to termination by recombination, can be used for synthesis of hydroxy-telechelic polymers which are useful in polyurethane fabrication and from the second group of monomers it is impossible to obtain oligo-polyols useful in PU. 

Thus, for radical polymerisation initiated by hydrogen peroxide of a monomer, which gives termination exclusively by recombination, it is possible to obtain good hydroxy-telechelic polymers, useful in polyurethane fabrication (reactions 9.3 and 9.4). 

In Chapter 3, the chemistry and technology of the most important oligo-polyols used for elastic polyurethanes fabrication, in fact high MW oligomers (2000-12000 daltons) with terminal hydroxyl groups and low functionality (2-4 hydroxyl groups/mol) were discussed. Polyalkylene oxide polyols (homopolymers of PO or copolymers PO - EO, random or block copolymers), polytetrahydrofuran polyols, filled polyols (graft poly ether polyols, poly Harnstoff dispersion - polyurea dispersions (PHD) and polyisocyanate poly addition (PIPA) polyols), polybutadiene polyols and polysiloxane polyols were all discussed. The elastic polyurethanes represent around 72% of the total polyurethanes produced worldwide. 

The remnant tertiary amines in the polyether polyols obtained in amine catalysis have a negligible effect in the reaction of -NCO groups with hydroxyl groups, in polyurethane fabrication. Generally, the formulations made with these polyols are corrected, by the decrease of the concentration of the amines used as catalysts in the foaming processes, in order to obtain similar reactivities as neutral polyols. 

Based on data from the literature, some important renewable resources used for polyols for polyurethane fabrication, without any attempt at an exhaustive presentation are presented. There are many ways of transforming natural renewable raw materials into polyols, as a consequence of the creativity and ingenuity of chemists. There are many possibilities for valorification of natural renewable materials in the area of polyols for PU. 

Matsuda T, lhara M, Inoguchi H, Kwon IK, Takamizawa K, Kidoaki S. Mechano-active scaffold design of smaU-diameter artificial graft made of electrospun segmented polyurethane fabrics. J Biomed Mater Res A 2005 73A 125-31. 

Table 17.1 Summary of common tissue engineering scaffolds for polyurethanes fabrication... 

Chain extenders are used by polyurethane fabricators to cure a liquid isocyanate-terminated prepolymer into a useful product. Typically this chain extender can be a... 

Estane thermoplastic polyurethane provides a binder that is critical to make a good finish on nylon, polyester, and polyurethane fabrics, as well as on leather materials. The Estane thermoplastic polyurethane binder can be processed into lacquers or into inks with the addition of pigments. Lacquers or inks made of Estane thermoplastic polyurethane binder can either be printed or spray-coated onto various substrates to give a perfect finish. 

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