Studies On Preparation Of SPU Sealants And Structure- Mechanical Properties Relationship

As a kind of novel material that has both advantages of polyurethaneand organosilicone such as excellent dampheat, oil, chemical, wearresistance and shelf stability, Silylated polyurethane (SPU) is perfect resinideal to prepare high performance sealant. In the presence of catalyst,SPU can be cured by moisture on the basis of the hydrolyzation andcondensation reaction of alkoxyl in SPU and H₂O, which prevent to giveout carbon dioxide as in the process of NCO-H₂O reaction for themoisture curing of one part PU. Furthermore, SPU can adhere to nonporous material surface without using primer. Study on SPU structure,formulation and sealant strength, process and ageing property isnecessary theoretically and practically for developing high performancesealant.In present dissertation, SPU were prepared by the addition reactionof silane with NCO-terminated polyurethane prepolymer, which wassynthesized by polymerization of isocyanate and polyether. Thestructure of NCO-teminated polyurethane prepolymer and SPU was characterized by FTIR and GPC. Results showed that silane coupler wassuccessfully grafted to the end of polyurethane prepolymer. The affectionof water on synthetic process stability product was studied. Resultsshowed that water content in raw material under 300ppm slightly affectedthe viscosity of reacting system, which could be considered as themaximum water content in eligible raw material.Curing properties of SPU sealant were studied. The surface dryingtime was decreased with the increasing usage of catalyst in theformulation. Furthermore, adhesion promoter affected the surface dryingtime strongly. SPU prepolymers with different structure were designedand synthesized by varying the molecular weight of polyether and thestructure of isocyanate and silane. Mechanical properties of SPUs andtheir sealants were studied. Results showed as follows: when themolecular weight of SPU was at constant, the viscosity of SPUprepolymer and the tensile strength of vulcanized SPU and sealantdecreased with the increase of the molecular weight of polyether in theprepolymer, while the elongation at break of increased. Higher ofmolecular weight of SPU is, higher viscosity and lower tensile strengthand higher elongation at break and smaller rigidity are. SPU prepared byMDI had the best tensile strength among isocyanate-prepared SPUs. SPUprepared by silane of higher functionality owned stronger tensile strengthand lower elongation at break. The influence of other ingredients in SPU sealant on the propertywas studied as well. Results showed as follows: nano-CaCO₃ is ofexcellent reinforcement for SPU sealant. With the increase of the additioncontent, the tensile strength at break, the tensile strength at 100%elongation and elongation at break were all increased. Fumed-Silica couldreinforce the sealant to the most extent. Sealant added more Fumed-silicahad better properties. Adding ZnO to sealant, a optimum content could befound when the highest tensile strength or elongation at break or rigiditywas obtained. Plasticizer had strong effect on the mechanical propertiesof SPU sealant. The more plasticizer was added, sealant of weakermechanical properties and adhesion property was obtained. Sealant usingamine-silane as adhesion promoter had excellent adhesion property toaluminum.