1. The effect of the percentage of isocyanate group (NCO) in the prepolymer: as the NCO increases, the hardness, tear resistance, elongation strength, and tensile strength increase, and the viscosity of the polymer decreases, which is easy to defoam and mix, and the elongation. If the NCO is too high, the curing speed of the rubber material will be too fast, and the life in the kettle will be shortened, which is extremely unfavorable to the pouring process. Therefore, the NCO% is generally 2.4-6.5%.
2. The influence of chain extension coefficient:
The equivalent ratio (NH2/NCO) of amine curing agent (MOCA) to NCO in the prepolymer (NH2/NCO) has obvious influence on the physical properties of the rubber compound. Generally, 0.85-0.95% is appropriate. Polyurethane should generally maintain a slight excess of NCO for the MOCA cross-linking system, so that the elastomer product has a suitable degree of cross-linking. When the chain extension coefficient is 0.88, the chemical cross-linking and physical cross-linking reach a good balance, and the overall performance of the elastomer When it reaches 1 or more, due to the plasticizing effect of MOCA, and the weakening of chemical crosslinking and hydrogen chains, the strength is obviously reduced, and the permanent deformation is large. (So it is practical for insurance, and the chain extension system usually takes 0.85).
3. Effect of mixing temperature: Due to the different types of prepolymers and chain extensions, the process conditions (mixing temperature) are also different. The mixing temperature increases the life in the tank and shortens the gel time, and the low mixing temperature is not allowed by the solid chain extender. Although it is beneficial to prolong the life in the kettle and improve the physical properties, it is not easy to degas and mix uniformly (because of the increase in viscosity). It is better not to precipitate the chain extender in the prepolymer. For example, MOCA is better at 110-120 °C .
4. The main factor of polyol molecular weight to performance: the size of molecular weight determines the density of characteristic groups in polyurethane elastomers. As the molecular weight of the polyester type increases, its physical properties can be improved; while the polyether type increases its flexibility with the increase of the molecular weight, and the tensile strength and modulus will decrease. Generally, the molecular weight of polyol should be controlled between 1100-2200.
The above is the professional explanation brought to you by Xinruituo about the main reasons affecting the performance of polyurethane. If you are interested in our products, please feel free to contact us. Looking forward to your cooperation.
