The Synthesis And Properties Of Polyester Polyurethane/Silica Composites And Low Hardness Polyurethane

The polyurethane (PU) is a polymer formed with urethane segment, as very high resistance to tear and abrasion, good resistance to ozone, oil and petrol, is widely used. Fumed silica, also called silica aerogel, have small diameters, porous inside the structure, the advantages of a large specific surface and highly activated property, enabled to improve the performance of rubber. Polyurethane/silica (PU/SiO₂) composites have great mechanical and good heat-resistance property. The microstructure, in addition to raw material types, plays a key role to the comprehensive performance of composites. Chain extender 3, 5-dimethyl mercapro toluenediamine (DMDTA) can be used in room temperature, is easier to operation than common chain extender MOCA, but there is a little literature about PU with DMDTA. In this paper, PU and composites with different crosslink density micro-domains were synthesized with chain extender DMDTA. The properties of multi-crosslink PU/SiO₂ composites were investigated and the influence of different crosslink way on these properties was discussed further.In this paper, the PU/SiO₂ composites , multi-crosslink PU and multi-crosslink PU/SiO₂ composites were prepared with pre- polymerization method with the main raw materials of PEA, TDI-100, fumed silica and DMDTA. Properties of these materials were investigated by SEM, DSC and mechanical tests. The main factors which affect the properties were also analyzed.SEM analysis showed that SiO₂ has a good dispersion in PU. The tensile sectional morphology of PU/SiO₂ composite is rough, which leads to absorbing more energy at break and good mechanical properties.The mechanical test results showed that when the content of–NCO group in prepolymer is about 4%, the hardness, tensile strength and the tear resistance properties of PU were greatly improved by loading SiO₂ particle, but the elongation at bresk a little decreased. PU/SiO₂ composites have best over-all performance when the SiO₂ content comes to 3% (based on the mass of polyols).Multi-crosslink PU materials had much better tear-resistance property and elongation at break, similar tensile strength, compared with homogeneous PU. PU/SiO₂ composites with multi-crosslinking method had better tear-resistance property and elongation, kept good drawing behavior of homogeneous PU/SiO₂ composites.The solvent resistance property test revealed that multi-crosslink PU changed the microstructure, improved the solvent resistance property.The DSC results verified that both adding SiO₂ particles and taking multi-crosslinking way can raise the thermal decomposition temperature. The thermal properties of multi-crosslink PU were much dependent on the differences between crosslink densities of micro-domains.Conclusively, Multi-crosslink PU/SiO₂ composites have excellent tear-resistance and heat-resistance performance, great tensile strength, good elongation at break and solvent resistance properties.The second part work of this paper is that the influences of different extenders and polyols on properties of low hardness PU materials were investigated. Mechanical tests and TG analysis results showed that when the content of–NCO group in pre-polymer is about 2%, PU with extender DMDTA have higher hardness, but lower thermal decomposition temperature than PU with extender MOCA. PU made from PEA and DMTDA have the best mechnical property when the crosslink coefficient is 0.9. But the solvent resistance decreased with increasing crosslink coefficient.