Synthesis Of Novel Ureido- Or Urethano-Containing Organosilicon Compound And Its Suppression Effect On The Tracking And Erosion Of Addition-cure Liquid Silicone Rubber

Silicone rubber is widely used in national defense, aerospace and high voltage outdoor insulation, because of its high dielectric strength, high thermal stability, high weather resistance and capability to maintain and recover surface hydrophobicity in wet and contaminated conditions. However, with rising voltage level and worsening air pollution seriously, the working conditions of silicone rubber become more and more severe and diverse. The security and stability of the high voltage and extra high voltage power transmission are severely threatened by the contamination flashover and tracking. In this dissertation, a large amount of reseach work has been carried out to overcome the deficiencies of the existing anti-tracking agent, such as heavy loading, poor compatibility, single function and so on. A reactive organic anti-tracking agent named ureido- or urethano-containing organosilicon compound was synthesized. Subsequently, it was incorporated into addition-cure liquid silicone rubber(ALSR) via hydrosilylation reaction during vulcanization, and the ALSR with excellent tracking and erosion resistance and good mechanical properties was prepared. Its suppression mechanism on the tracking and erosion of ALSR was intensively studied. The main research contents and results are listed as following:Firstly, three novel ureido-containing silanes, 3-(ureidopropyl) ethoxyallyloxysilane(UPAS), 3-(isopropylureidopropyl) ethoxyallyloxysilane(IPUPAS) and 3-(diisopropylureidopropyl) ethoxyallyloxysilane(DIPUPAS), were synthesized by the trans-etherification of ureido silane coupling agents with allyl acohol(AA), and the chemical structures were characterized by Fourier transform infrared spectrometry(FT-IR) and 1H nuclear magnetic resonance spectrometry(1H-NMR). The effects of the ureido-containing silanes on the curing properties, mechanical properties, tracking and erosion resistance and thermal stability of ALSR were investigated, and the possible suppression mechanism of the ureido-containing silanes on the tracking and erosion of ALSR was further explored. It was found that the ureido-containing silanes significantly improved the tracking and erosion resistance of the ALSR samples. When using 2 phr the ureido-containing silane, the ALSR samples could pass the 4.5 k V level in the IP test, and the eroded mass of the ALSR/UPAS, ALSR/IPUPAS and ALSR/DIPUPAS were respectively 0.042 g, 0.038 g and 0.034 g, which were 6.8%, 6.1% and 5.5% as that of ALSR without ureido-containing silane. Meanwhile, the incorporation of the ureido-containing silane enhanced the mechanical properties and thermal stability of the ALSR samples. Furthermore, the possible suppression mechanism of the ureido-containing silanes on the tracking and erosion of the ALSR was revealed. On one hand, during dry band arcing, the ALSR containing the ureido-containing silanes could generate nitrogen oxides and ammonia to quench electrical arcs. On the other hand, the incorporation of the ureido-containing silane could improve the thermal degradation stability and the residual weight of the ALSR, which was beneficial to form a strong ceramic barrier on the surface to protect the underlying materials from further degradation, thus remarkably suppressed the tracking and erosion of the ALSR.Secondly, six novel alkyl-disubstituted ureido silanes were synthesized by the trans-etherification of alkyl-disubstituted ureido silane coupling agents with AA, and their chemical structures were characterized by FT-IR and 1H-NMR. The effects of the alkyl-disubstituted ureido silanes on the mechanical properties, tracking and erosion resistance and thermal properties of ALSR were investigated. The eroded surfaces of the ALSR samples were analyzed by SEM and SEM-EDX, and the possible suppression mechanism of the alkyl-disubstituted ureido silanes on the tracking and erosion of ALSR was further explored. It was found that the alkyl-disubstituted ureido silanes not only significantly improved the tracking and erosion resistance but also enhanced the mechanical properties of the ALSR. When using DIPUPAS, DBUPAS or DIBUPAS, the ALSR samples could pass the 4.5 k V level in the IP test. Additionally, the incorporation of the alkyl-disubstituted ureido silanes improved the thermal stability of ALSR and the effect was more obvious as the chain length of alkyl-disubstituted group decreased. The results of SEM and SEM-EDX showed that the honycomb-like ceramic barriers formed on the eroded surfaces of ALSR/DIPUPAS, ALSR/DBUPAS and ALSR/DIBUPAS during dry band arcing were compact and less cracks, and their C content was low. Therefore, the tracking and erosion of the ALSR was suppressed and the tracking and erosion resistance of ALSR was remarkably improved.Thirdly, ureido-containing MQ silicone resin(DIPUPES-MQ) was prepared by the hydrolytic condensation of tetraethoxysilane(TEOS), (3-diisopropylureidopropyl) triethoxysilane(DIPUPES), hexamethyldisiloxane(MM) and divinyltetramethyldisiloxane(MViMVi). The chemical structure of DIPUPES-MQ was characterized by FTIR, 1H-NMR, 29 Si nuclear magnetic resonance(29Si-NMR) and gel permeation chromatography(GPC). The effects of DIPUPES-MQ on the tracking and erosion resistance, mechanical properties and thermal stability of ALSR were investigated, and the suppression mechanism of DIPUPES-MQ on the tracking and erosion was investigated by FTIR and TG-FTIR. The incorporation of DIPUPES-MQ could enhance the tracking and erosion resistance as well as the mechanical properties of ALSR. When the content of DIPUPES-MQ was 3.75 phr, the ALSR samples could pass the 4.5 k V level in the IP test, and the eroded mass of ALSR decreased to a minimum of 0.023 g, which was 2.7% as that of the ALSR without DIPUPES-MQ. The FT-IR and TG-FTIR results showed that upon heating, the ureido groups of DIPUPES-MQ were initially decomposed to isocyanic acid, which then reacted with hydroxyl groups to form carbamate groups. And at higher temperature, the carbamate groups were degraded to from the carboxylate groups. When DIPUPES-MQ was incorporated into ALSR, the decomposition of the ureido groups produced isocyanic acid, which could react with Si-OH produced by the oxidation of methyl groups during the thermal degradation of ALSR, so that the “unzipping” depolymerization initiated by Si-OH was decreased. Therefore, the thermal stability of ALSR was improved and the residual weight increased, which was beneficial to form a strong ceramic barrier on the surface to protect the underlying materials from further degradation, thus remarkably suppressed the tracking and erosion of the ALSR.Fourthly, 3-(1,2,2,6,6-pentamethyl-4-piperidinurethanopropyl) ethoxyallyloxysilane(PMPURPAS) was synthesized by using 1,2,2,6,6-pentamethyl-4-piperidinol(PMPO), (3-isocyanatopropyl) triethoxysilane(ICPES) and AA via the addition reaction and trans-etherification, and its chemical structure was characterized by FTIR and 1H-NMR. The effects of PMPURPAS on the tracking and erosion resistance, mechanical properties, thermal stability and flame retardancy of ALSR were investigated. It was found that PMPURPAS could enhance the tracking and erosion resistance and the flame retardancy of ALSR. When the content of PMPURPAS was 3.0 phr, the ALSR samples could pass the 4.5 k V level in the IP test and had a good self-extinguishing. The TG and TG-FITR results showed that, the urethane group of PMPURPAS could decompose to isocyanic acid to react with Si-OH produced by the oxidation of methyl groups during the thermal degradation of ALSR with a similar effect as the ureido group. Therefore, the thermal stability of ALSR was improved and the residual weight increased, which was beneficial to form a strong ceramic barrier on the surface.Finally, 3-(5,5-dimethylhydantoinurethanopropyl) ethoxyallyloxysilane(DMHURPAS) was synthesized by using 1-(hydroxymethyl)-5,5-dimethylhydantoin(HDMH), ICPES and AA via the addition reaction and trans-etherification, and it was incorporated into ALSR via hydrosilylation reaction during vulcanization. The surface of ALSR containing DMHURPAS was treated with sodium hypochlorite solution. The chemical structure of DMHURPAS was characterized by FT-IR and 1H-NMR. The effects of DMHURPAS on the mechanical properties, tracking and erosion resistance and thermal stability were investigated, and the antibacterial properties of ALSR containing DMHURPAS were further investigated. The results showed that the incorporation of DMHURPAS could significantly improve the tracking and erosion resistance as well as the thermal stability. When the content of DMHURPAS was 1.5 phr, the ALSR samples could pass the 4.5 k V level in the IP test, and the temperature of 10% weight loss(T10) and the temperature of 20% weight loss(T20) were respectively increased by 11 oC and 29 oC. Meanwhile, the residual weight at 800 oC increased from 47.8 wt% to 68.7 wt%. Moreover, the ALSR containing 2.0 phr DMHURPAS after chlorine bleach treatment had antibacterial effect on E. coli and Staphylococcus aureus. In particular, its antibacterial effect to E. coli was very obvious, and the antibacterial rate to E. coli was 95.7%.