Addition-cure Liquid Silicone Rubber Research Articles

Suppression Effect and Mechanism of Amine-Containing MQ Silicone Resin on the Tracking and Erosion Resistance of Silicone Rubber.

How to effectively enhance the antitracking performance of silicone rubber is a huge challenge in the field of high-voltage insulation. In this contribution, amine-containing MQ silicone resin (A-MQ) was prepared to enhance the tracking and erosion resistance of addition-cure liquid silicone rubber (ALSR). The results showed that A-MQ imparted ALSR with excellent tracking and erosion resistance. When A-MQ content was 4 phr, all test samples passed the inclined plane test at 4.5 kV, and the erosion mass decreased by 67.8%. In addition, the tensile strength and tear strength increased by 13.2 and 13.6%, respectively, compared with that of ALSR without A-MQ. The suppression mechanism was further investigated in the aspects of heat attack and plasma bombardment by laser Raman spectroscopy, thermogravimetry, thermogravimetry-Fourier transform infrared spectrometry, scanning electron microscopy, attenuated total reflection-Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy. This revealed that at the elevated temperature caused by arc discharge, A-MQ promoted crosslinking of the polysiloxane molecules and suppressed the generation of cyclic oligomers, which reduced the intensity of the electrical arc. Moreover, when suffering from plasma bombardment, which was also produced by arc discharge, A-MQ protected the silicone chains from degradation and eliminated the carbon deposited on the surface.

Effect of the platinum catalyst content on the tracking and erosion resistance of addition-cure liquid silicone rubber

An addition-cure liquid silicone rubber (ALSR) with ureido-containing MQ silicone resin (U-MTQ) was prepared by hydrosilylation with platinum catalyst (Pt). ALSR samples were characterized by thermogravimetric analysis (TGA) and thermogravimetry coupled with infrared spectroscopy (TG-FTIR), and the char layers of ALSR samples after inclined plate tracking and erosion test (IPT) were characterized by X-ray photoelectron spectroscopy (XPS). The effects of Pt content (5–100 ppm) on the curing characteristics, mechanical properties and tracking and erosion resistance of ALSR were investigated. It was found that the cure rate increased with increase of Pt content. When the Pt content was 10 ppm or 15 ppm, the ALSR had excellent tracking and erosion resistance, all specimens could pass the 4.5 kV level in IPT, and the erosion rate was only 0.13% and 0.15%, respectively. ALSR samples possessed optimum mechanical properties and thermal stability when the Pt content was 15 ppm. TG-FTIR results showed that ALSR generated less carbonyl compounds (CH2O) and cyclic oligomers but more methane (CH4) when the Pt content was 15 ppm. This demonstrated that there were lower levels of the oxidation of methyl groups and the main chain unzipping degradation of ALSR, and more homolysis of Si-CH3 during the degradation. The XPS results also showed that the macromolecular radicals would further cross-link to form a firm Si-C ceramic barrier to protect ALSR samples under Pt catalysis and high temperature, thus the tracking and erosion resistance of ALSR could be improved.

An efficient strategy for simultaneously improving tracking resistance and flame retardancy of addition-cure liquid silicone rubber

How to effectively improve tracking resistance and flame retardancy of silicone rubber is one of the key problems needed to be resolved in the development of high performance silicone rubber insulating materials. In this work, a novel functional silane containing hindered amine and urethane groups, named PPAS, was synthesized by using 1,2,2,6,6-pentamethyl-4-piperidinol, (3-isocyanatopropyl) triethoxysilane and allyl acohol via the nucleophilic substitution and trans-etherification. The effects of PPAS on the tracking resistance, flame retardancy and thermal stability of addition-cure liquid silicone rubber (ALSR) were investigated. It was found that PPAS could effectively enhance the tracking resistance and flame retardancy of ALSR simultaneously. When the content of PPAS was only 3.0 phr, ALSR/PPAS could pass the 1A4.5 kV level in the inclined plane (IP) test and had outstanding electrical erosion resistance, which showed great potential in exterior insulator. In particular, the limiting oxygen index (LOI) of the ALSR/PPAS was 30.0%, and it had a good self-extinguishing capability. Meanwhile, the risk of fire measured by cone calorimeter was also significantly reduced. The mechanism for these phenomena were further studied and revealed: PPAS could effectively quench the peroxyl radicals and suppress the oxidation degradation of Si-CH3 groups, eliminate the Si-OH groups and promote the cross-linked reaction during the thermal degradation of ALSR.

Effect of alkyl-disubstituted ureido silanes with different alkyl chain structures on tracking resistance property of addition-cure liquid silicone rubber

Ureido silane is considered to be a novel tracking resistance additive for effectively improving the tracking resistance property of addition-cure liquid silicone rubber (ALSR). In this work, a series of alkyl-disubstituted ureido silanes (ADUSs) with different alkyl chain structures were synthesized by the transetherification of allyl alcohol (AA) and alkyl-disubstituted ureido siloxanes from the nucleophilic addition between alkyl-disubstituted amides and 3-isocyanatopropyltriethoxysilane (ICPES). The effect of ADUSs with different alkyl chain structures on the tracking resistance property of ALSR was investigated by inclined plane test (IPT), thermogravimetry analysis (TGA), thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR) and energy dispersive spectroscopy (EDS). The results showed that ADUSs could effectively improve the tracking resistance property of ALSR, especially for (γ-diisopropylureidopropyl) allyloxyethoxysilane (DIPUPAS), (γ-dibutylureidopropyl) allyloxyethoxysilane (DBUPAS) and (γ-diisobutylureidopropyl) allyloxyethoxysilane (DIBUPAS). ALSR incorporated with DIPUPAS, DBUPAS and DIBUPAS passed the inclined plane test (IPT) at the alternating voltage of 4.5 kV and the average erosion mass was only 3.8%, 3.4% and 4.4% of the virgin ALSR, respectively. TGA and TG-FTIR results revealed that DIPUPAS, DBUPAS and DIBUPAS could also effectively improve the thermal stability of ALSR. Accompanying with the weakened oxidation reactions of methyl groups in molecular chains, the formed cyclic oligomers decreased. Meanwhile, the release of methane and cross-linking reaction of the silicone rubber chains were enhanced, leading to the increase of residue under high temperature and the formation of a ceramic barrier layer to protect the silicone rubber matrix. EDS results showed that the carbon content in ceramic barrier layer decreased, which was beneficial to prohibit the development of tracking.

Synthesis of a novel hydantoin-containing silane and its effect on the tracking and bacteria resistance of addition-cure liquid silicone rubber

A novel hydantoin-containing silane, [3-(5,5-dimethylhydantoinurethano) propyl] ethoxyallyloxysilane (DMHURPAS), was synthesized and the structure was characterized by FTIR and 1H NMR. The effect of DMHURPAS was investigated on the anti-tracking and antibacterial properties of addition-cure liquid silicone rubber (ALSR) after surface chlorination. It was found that ALSR containing only 1.5phr of DMHURPAS passed 1A 4.5kV level and erosion mass decreased from 0.843g to 0.037g. The thermal stability of ALSR was significantly improved and the mechanical properties were also enhanced. From thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR), ALSR/DMHURPAS showed significant decrease of carbonyl compounds and cyclic oligomers but increase of CH4 and CO2 during thermal degradation, indicating that DMHURPAS could inhibit oxidation of methyl groups and unzipping reaction, and promote the cleavage of methyl groups in ALSR. The antibacterial rates of ALSR containing 2.0 phr of DMHURPAS against Escherichia coli and Staphylococcus aureus were 95.7% and 83.4%, respectively.

The preparation of fluorine-containing polysiloxane low-melting glass and its effect on the tracking resistance and thermostability of addition-cure liquid silicone rubber

Enhancement of tracking resistance of ALSR by FPLMG with different FAS content.

Investigation of the tracking and erosion resistance of cured liquid silicone rubber containing ureido-modified MQ silicone resin

Ureido-modified MQ silicone resin (DIPUPES-MQ) was prepared by the hydrolytic condensation of tetraethoxysilane (TEOS), (γ-diisopropylureidopropyl) triethoxysilane (DIPUPES), hexamethyldisiloxane and divinyltetramethyldisiloxane. Subsequently, DIPUPES-MQ was employed to improve the resistance to tracking and erosion of addition-cure liquid silicone rubber (ALSR), and it showed that DIPUPES-MQ could significantly enhance the tracking and erosion resistance as well as the mechanical properties of the ALSR. When the content of DIPUPES-MQ was 3.75 phr, all the test samples passed the inclined plane tracking and erosion (IP) test at 4.5 kV. The thermogravimetry (TG), thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR) and FTIR results showed that the striking enhancement in the tracking and erosion resistance of the ALSR was probably ascribed to the decomposition of the ureido groups. In the pyrolysis process, the ureido groups of DIPUPES-MQ could generate isocyanic acid to hinder the “unzipping” depolymerization through reacting with Si-OH groups, so that the amount of cyclic dimethylsiloxanes inducing intense and continuous dry-band arcs was decreased.

Zirconium phosphate functionalized by hindered amine: A new strategy for effectively enhancing the flame retardancy of addition-cure liquid silicone rubber

Functionalized zirconium phosphate (F-ZrP) was prepared by intercalating 1,2,2,6,6-pentamethyl-4-(vinyldiethoxysiloxy) piperidine (PMVP) into α-zirconium phosphate (α-ZrP), and was used to flame-retard addition-cure liquid silicone rubber (ALSR). X-ray diffraction (XRD) and transmission electron microcopy (TEM) were used to characterize the structural morphology of F-ZrP and ALSR/F-ZrP. The results indicated that PMVP was successfully intercalated into α-ZrP, and F-ZrP existed with a structure of the intercalated and exfoliated components in the ALSR matrix. F-ZrP could significantly improve the flame retardancy of ALSR. When only 4 phr of F-ZrP was added, the flame-retardant ALSR could pass the UL-94 V-0 rating with the LOI value of 31.0%. Such an efficient flame retardancy of F-ZrP was attributed to the synergism of the catalyzing carbonization and free-radical quenching mechanism.

Thermal degradation mechanism of addition-cure liquid silicone rubber with urea-containing silane

The reactive urea-containing silane, (γ-diethylureidopropyl) allyloxyethoxysilane (DEUPAS), was synthesized by the trans-etherification reaction. The chemical structure was characterized by Fourier transform infrared spectrometry (FTIR) and 1H nuclear magnetic resonance spectrometry (1H NMR). Subsequently, DEUPAS was incorporated into addition-cure liquid silicone rubber (ALSR) via hydrosilylation reaction. The thermal stability of the ALSR samples was investigated by thermogravimetry (TG) and thermogravimetry–Fourier transform infrared spectrometry (TG–FTIR). When DEUPAS was incorporated, the temperature of 10% weight loss and 20% weight loss under air atmosphere were respectively increased by 31°C and 60°C compared with those of the ALSR without DEUPAS. Meanwhile, the residual weight at 800°C increased from 33.5% to 58.7%. It was found that the striking enhancement in thermal stability of the ALSR samples was likely attributed to the decomposition of the urea groups to isocyanic acid, which reacted with hydroxyl groups to inhibit the unzipping depolymerization.

Effect of urea-containing anti-tracking additive on the tracking and erosion resistance of addition-cure liquid silicone rubber

Three novel urea-containing anti-tracking additives were prepared and used to enhance the tracking and erosion resistance of addition-cure liquid silicone rubber (ALSR). The suppression effect and mechanism of the additives on tracking and erosion were investigated by the inclined plane (IP) test, thermogravimetry (TG) and thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR). It was found that the anti-tracking additives not only significantly improved the tracking and erosion resistance but also enhanced the mechanical properties of the ALSR. When using 2 phr of the anti-tracking additive, all the ALSR samples could pass the 4.5 kV level in the IP test. This might be mainly attributed to the arc-quenching capability of the urea group and the formation of a ceramic barrier to protect the underlying materials from further degradation during the dry band arcing. The TG and TG-FTIR results revealed that the urea-containing anti-tracking additives could prevent the radical decomposition of the ALSR below 400 °C. Hence, it considerably improved the initial thermal degradation stability of the ALSR and prolonged the time to track.