Formulation considerations polyurethanes

Studies have been made of the elastic (time-independent) properties of single-phase polyurethane elastomers, including those prepared from a diisocyanate, a triol, and a diol, such as dihydroxy-terminated poly (propylene oxide) (1,2), and also from dihydroxy-terminated polymers and a triisocyanate (3,4,5). In this paper, equilibrium stress-strain data for three polyurethane elastomers, carefully prepared and studied some years ago (6), are presented along with their shear moduli. For two of these elastomers, primarily, consideration is given to the contributions to the modulus of elastically active chains and topological interactions between such chains. Toward this end, the concentration of active chains, vc, is calculated from the sol fraction and the initial formulation which consisted of a diisocyanate, a triol, a dihydroxy-terminated polyether, and a small amount of monohydroxy polyether. As all active junctions are trifunctional, their concentration always... 

The only other considerations are weathering, color development, and perhaps long-term oxidation. These are considered unfortunate problems to be minimized by various formulation techniques. In an extreme case, we all recognize that polyurethanes can be fire hazards, and this too must be addressed by various formulation technologies. In a sense, the slight reactivity of polyurethanes is considered a problem. We hope to show that opportunities arise from using the natural reactivity of the polymer surface and by making the polymer reactive to the environment with which it comes into contact. 

Thermoplastic elastomers are most commonly formulated from elastomeric polyurethane or block copolymers of polystyrene-elastomer, polyamide-elastomer, or polyether-elastomer bases. Thermoplastic elastomers are provided as a raw material in pelletized form for subsequent compounding. The internal domain structure that is required for thermoplastic-elastomeric performance has been established by specific considerations of blending and structural-chemical interactions. In compounding operations, specific temperature ranges are required to assure that phase separation does not occur in the TPE base polymer. 

The biochemical reaction catalyzed by epoxygenase in plants combines the common oilseed fatty acids, linoleic or linolenic acids, with O2, forming only H2O and epoxy fatty acids as products (CO2 and H2O are utilized to make linoleic or linolenic acids). A considerable market currently exists for epoxy fatty acids, particularly for resins, epoxy coatings, and plasticizers. The U.S. plasticizer market is estimated to be about 2 billion pounds per year (Hammond 1992). Presently, most of this is derived from petroleum. In addition, there is industrial interest in use of epoxy fatty acids in durable paints, resins, adhesives, insecticides and insect repellants, crop oil concentrates, and the formulation of carriers for slow-release pesticides and herbicides (Perdue 1989, Ayorinde et al. 1993). Also, epoxy fatty acids can readily and economically be converted to hydroxy and dihydroxy fatty acids and their derivatives, which are useful starting materials for the production of plastics as well as for detergents, lubricants, and lubricant additives. Such renewable derived lubricant and lubricant additives should facilitate use of plant/biomass-derived fuels. Examples of plastics that can be produced from hydroxy fatty acids are polyurethanes and polyesters (Weber et al. 1994). As commercial oilseeds are developed that accumulate epoxy fatty acids in the seed oil, it is likely that other valuable products would be developed to use this as an industrial chemical feedstock in the future. 

Polyurethanes, on the other hand, have good adhesion properties to wood and are applicable as one-component system with fast curing properties at ambient conditions. Furthermore, the mechanical properties can be readily varied with simple manipulation of the chemical formulation. Most important of all, there is considerable experience in using polyurethane to bond wood. 

SPI, soy fibre, and corn starch together with 0 0 per cent polyetho- polyol were also incorporated into a flexible polyurethane foam formulation. Stress-strain curves of the control foam and foams containing 10-20 per cent biomass material exhibited a considerable plateau stress region, but not for foams extended with 30—40 per cent of them. An increase in the hiomass content produced an increase in the foam density, whereas an increase in the initial water content produced the opposite effect. Foams extended with 30 per cent SPI, as well as those extended with 30 per cent soy fibre, displayed considerably higher resilience values than all other extended foams. The comfort factor increased by increasing the biomass content, and foams containing 10—40 per cent biomass showed significantly lower values in compression-set than the control foam [86]. 

To show the significant effect of temperature on the rate of decomposition and volatilization under vacuum, the same experiment described earlier was conducted at 107°C on the two polyurethane materials. The Adiprene L-lOO and MOCA formulation now showed a weight change of -0.75% and the PR 1535 showed a weight change of-1.45%. The 107°C temperature was considerably higher than intended for urethane formulas available at the time of testing. 

---