PU/silica Organic-inorganic Hybrid Materials And Their Interpenetrating Networks With Rubber

Organic/inorganic hybrid materials are multiphase materials evenly dispersed at thenanometer level. It possesses the advantage of both organic polymer and inorganic materials.It can be organic polymers modified by inorganic materials, or inorganic materials modifiedby organic polymers. The function of the materials can be tailored and assembled throughadjusting the compositions and proportions of the organic and inorganic phases.Novel polyurethane (PU)/silica organic/inorganic hybrid materials were prepared bymechanical blending in situ reactive method. The PU/silica hybrid materials were formed bythe reaction of NCO groups in the PU prepolymer and OH groups of silica in the case of nochain extenders and crosslinking agents. Silica acted as the crosslinking agent and chainextender of the PU. The method is significantly innovative in theory, and has the advantagesof simple technology, low cost, little environment pollution and significantly improving thecomprehensive performance of the materials.The mixture of PU prepolymer and silica ishigh-viscosity, which can be easily evenly mixed with rubber and synchronized crosslinked.As a result, the PU/silica hybrid materials were used to modify polar nitrile rubber (NBR) andnonpolar styrene-butadiene rubber (SBR) through interpenetrating network (IPN) technology.NBR/(PU-silica)-IPN and SBR/(PU-silica)-IPN with good compatibility and excellentcomprehensive performance were prepared by mechanical blending method. A further andcomprehensive discussion is also made on the modification mechanism of PU/silica on rubberand the relationship between structure and performance of IPN.The PU/silica organic-inorganic hybrid materials were prepared by mechanical blendingin situ reactive method. Under certain temperature and pressure, the organic-inorganic hybridmaterials were formed through the reaction of NCO groups of PU prepolymer and OH groupsof silica, which was characterized by Fourier-transform infrared (FTIR) spectroscopy, X-rayphotoelectron spectroscopy (XPS), solid-state NMR (29Si-HMR) and differential scanningcalorimetry (DSC). Curing kinetics analysis results show that the best curing temperature is120oC, the curing reaction follows first order kinetics, and the apparent activation energy is76.16kJ/mol. The PU prepolymer prepared with the molar ratio of NCO and OH of2.3:1, arecrosslinked by silica according to the equivalent ratio of OH in silica and NCO in PUprepolymer of1.06:1.00, and the resulting hybrid materials possess the most perfectcrosslinked network and have the best comprehensive performance. Compared withisophorone diisocyanate (IPDI), the appearance of soft segment crystalline melting peak andincreased hard segment crystalline melting enthalpy of PU/silica hybrid materials prepared from toluene diisocyanate (TDI) indicating the good crystalline properties and greatermicro-phase separation. They have increased curing rate and better comprehensivemechanical properties as well. Compared with polytetrahydrofuran glycol (PTMG1000),polyoxypropylene glycol (PPG1000) and polycaprolactone glycol (PCL1000), thecomprehensive mechanical properties of PU/silica hybrid materials prepared frompoly(diethylene glycol adipate)(PEA1000) are the best, the tensile strength, tear strength andelongation at break of which are48.31MPa,128kN/m and557%respectively.NBR and SBR were modified by PU/silica hybrid materials through interpenetratingnetwork (IPN) technology by mechanical blending method, and the resultingNBR/(PU-silica)-IPN and SBR/(PU-silica)-IPN were prepared. The curing kinetics studiesshow that the rubber system (NBR or SBR) and PU/silica system in the IPN crosslinkedrespectively in accordance with the radical polymerization and addition reaction. Thecrosslinking rates of the two systems matched; as a result, simultaneous interpenetratingpolymer networks were formed. NBR system and PU/silica system have an accelerating effecton the cure. The activation energy of the IPN was decreased by the addition of PU/silica. Thenetworks interpenetrate in the interface of NBR and PU/silica, which is characterized bytransmission electronic microscopy (TEM) and energy spectrum scan. The NBR matrixfracture from180oT-peel experiments of NBR and PU/silica indicated good interfacecombination. Dynamic Mechanical Analysis (DMA) results show that the Tg of NBR systemin IPN moved closer to the direction of the Tg of PU/silica system, which further evidence theimproved compatibility. The increased compatibility between the two components of the IPNis mostly due to the interpenetrating polymer networks structures in the interface of rubberand PU/silica.With increasing PU/silica content, the mechanical properties of IPN improved, and thecontinuity of the PU/silica domains in the IPN increased. When the PU/silica content is about50wt%, the NBR and PU show co-continuous morphology, however the two-phase continuityof SBR and PU/silica is a little poor. The abrasion resistance and anti-flex cracking propertiesof rubber (NBR and SBR) are significantly improved by the incorporation of PU/silica. Whenthe PU/silica content is50wt%, the flex-fatigue life of NBR/(PU-silica)-IPN andSBR/(PU-silica)-IPN are620and560thousand cycles; and the Akron abrasion loss are0.71and0.94cm3/1.61km, which are73.8%and79.0%decreases compared with neat NBR andSBR respectively. The significantly improvement of anti-flex cracking properties is mostlydue to the coordinating role of the flexible rubber networks and the rigid PU/silica networksand the hydrogen bond in the hard segment which can relax stress to prevent crack propagation. Among the IPNs prepared by the different types of diols, theNBR/(PU-silica)-IPN and SBR/(PU-silica)-IPN prepared by PEA1000have the bestmechanical properties, the tensile strength, elongation at break and tear strength of them are34.3MPa,620%,59kN/m and27.2MPa,595%,50.4kN/m respectively.