| The mechanical properties of polyurethane(PU) can be adjusted over a wide range. Its products are widely used in the fields of sealants. PU sealant has good water-resi stance and high temperature-resistance besides a simple preparation process. However, t he moisture-curing process will produce a lot of bubbles leading to insufficient strengt h. There is no byproducts when silicone sealant is curing. While the preparation of P U sealant modified by silicone is studied, the impact on the physical and chemical pr operties of the components has important theoretical and practical significance.According to the formulation(diphenylmethane diisocyanate MDI:polyether diols PP G2000:polyether triol330N=13.5wt%:19.5wt%:46.5wt%) PU sealant was synthesized to end of that R-NCO%to3wt%by the method of bulkpolymerization. By using NXS-11A rotational viscometer, it showed that the apparent viscosity of the system changed with temperature increasing. Di-n-butylamine was diluted by xylene solution, which m easure the concentration of R-NCO to provide the relationship between the concentrati on and the reaction time. The results showed that:in the reaction of R-NCO and R-O H at70℃during the time of0-230min, the viscosity increased from0.1pa.s to2.1pa. s; in the reaction at85℃during the time of0-200min, the viscosity increased from0. lpa.s to2.0pa.s; its activation energy is58.01kJ/mol in the polymerization reaction.The paper studied the plasticizer-effect and mechanical properties by the rotational viscometer and the universal testing machine. It shows that, if PU systems is added by dimethoxy ethyl phthalate(DMEP), with the contents increased from6.67%to30%, the value of colloidal viscosity of PU produced at70℃decreased from17.4pa.s to7.8pa.s, while that is done at85℃that value decreased from18.5pa.s to8.6pa.s. Na mely, DMEP increased the mobility of the systems; when adding DBP and DMEP fro m20wt%to30wt%, fracture strength of DBP/PU decreased by22.2%and16.7%, whil e break elongation increased from8.9%to8.7%and shaw hardness decreased from13.0%to7.9%. If the content of PPG2000increased from0%to49%, the breaking st rength of the sealant decresed from the2.3MPa to0.9MPa while the break elongation increased from43%to71%and the shore hardness decrease from22to13. These r eflected their plasticizing effect on sealant. Moreover, the paper studied the surface cur ing time influenced by the content of stannous octoate, dibutyltin dilaurate and silane coupling agent KH550、KH580. The effect of anti-oxidants1010and fillers to sealant have been studied in silane-modified polyurethane (SPU).The results indicate that:the dry rate ratio of SPU added by stannous octoate and dibutyltin dilaurate was1.3:1at temperature of25℃and35℃; the dry rate was1.25:1:0.5while KH550、KH580and no silane coupling agent added to PU respectively.The curing time at35℃shorten by20%than that of at25℃; the KH550/SPU and KH580/SPU with the addition of0.2%antioxidant1010make the retention rate of break strength increased by8%and7%while that of the elongation retention increased by15%and13%; the breaking stre ngth of five kinds of packing was:calcium sulfate whisker> graphite>talc> glass beads> attapulgite. Meanwhile identified by IR, target products were PU and SPU; thermal gravimetric analysis shows that DMEP/SPU sealants starting decomposition temperatur e T1%was369.14℃, SEM photos showed their good dispersibility of the filler partic les in SPU.Further studies using single factor were on the rate of retention of SPU in the as pects of mechanical parameters in the acid、alkali and the xylene solution. It showed t hat:at60℃with5%HC1for7days, breaking strength retention rate was only15%, while the elongation long retention rate was10%, shore hardness retention rate of w as39%at60℃with5%NaOH/xylene soak for7days, retention rate of the breaking strength, break elongation and shore hardness of SPU were greater than87%. So the performance of acid-resistant of SPU sealant is not acceptable, which needed in-depth study in the future. |
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