Study On The Structures And Properties Of Constructive Polyurethane Sealant

Characteristics, advantages, current conditions and developments of different kinds of polyurethane (PU) sealants were summarized. The relationship between structures and properties of PU was discussed, and the effects of formulation, preparation process on the properties of PU sealant were studied. The kinetic parameters of different PU pre-polymer reaction systems were measured through rheological test and differential scanning calorimetry (DSC) measurement. Moreover, the rheological behaviors of PU sealant filled with calcium carbonate (CaCO3) were investigated through dynamic rheological measurements. Strain (y), frequency (ω) and temperature (T) dependent rheologies of different samples were investigated.The PU pre-polymers were synthesized using toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), liquified MDI (L-MDI), polymethylene polyphenlene isocyanate (PAPI), polyoxytertramethylene glycol (PTMG), polyoxypropylene glycol (PPG), and the pre-polymers were mixed with different kinds of additives to obtain constructive PU sealant with desired properties. The mechanical properties, adhesive properties, tack-free time of different samples were analyzed systematically. Effects of isocyanate, molecular weight and functionality of polyols,-NCO content and the type and amount of additives were investigated. The relationship between structures and properties was discussed.The reaction between L-MDI and polyols were chosen as examples to probe kinetic parameters through rheological and DSC measurements. Activation energy (E), pre-exponential factor (A) and reaction order (n) were obtained. Moreover, influences of filler volume fraction (φ) on the rheological behaviors including the strain (γ) frequency (co) and temperature (T) dependences of PU filled with CaCO3 were investigated through dynamic rheological measurements. The results reveal that the span of the linear viscoelastic region narrows and the "Payne" effect multiples with increasing filler volume fraction (0). It is noted that a high filler volume fraction (φ) can lead to a "pseudo solid-like" behavior of dynamic storage modulus (G') at low frequency (ω) region, which can be attributed to the formation of percolated filler network structure. Furthermore, it is suggested that the rheological behavior of this filled system follows the "Cox-Merz" rule on the basis of steady and dynamic rheological curves.