| Polymer materials are widespread used recent years.Its flammability has also attracted people's attention simultaneously,and many new problems accompanied with fire accident are aroused in public facilities which are easy to catch a fire.Therefore,it is of great significance to improve fireproof of polymer composites.Ceramifiable silicone rubber is widely used in some industries which are easy to catch fire,such as cable,construction,automotive and nuclear industries.The fireproof performance of ceramifiable silicone rubber mainly includes ceramic-forming property,flame retardancy,dimensional stability,and self-supporting property.We use Caster's platinum catalyst/benzotriazole?Pt/BTA?as flame retardant,methods of compounding glass powder/ammonium polyphosphate?GD/APP?flux and modified coated-APP to improve fireproof performance of ceramifiable silicone rubber and we also studied its mechanism.In this work,we added fillers,flux and other additives to the matrix using two-roll mill firstly.Effect of Pt/BTA on flame-retardancy and ceramic-forming property of ceramifiable silicone rubber and its mechanisms were investigated.When Pt/BTA content was 2.78×10-3phr,composite passed UL-94V-0 rating,and the one without Pt/BTA cannot be rated in the vertical burning test.Meanwhile,the total heat release?THR?and total smoke production?TSP?were significantly reduced when Pt/BTA was added.The reason is that Pt/BTA promoted formation of a three-dimensional network in residues and controlled dramatic depolymerization of polymer backbone,which promoted the quality of char layer,isolating heat and oxygen much more efficiently.Moreover,when Pt/BTA content was 2.78×10-3 phr,composite can support its own weight when sintered at high temperatures?600,800 and 1000°C?and three-point flexural strength of ceramics got to 29.47 MPa,which was 102.68%higher than that without the addition of Pt/BTA.Eutectic reaction mechanism showed reason for this phenomenon.Pt/BAT promoted reaction of glass dust with other inorganic fillers,which helped formation of more uniform and denser residue at a relative low temperature.In order to change poor dimensional stability of ceramifiable silicone rubber during sintering when we use GD as flux,APP was added to ceramifiable silicone rubber.Impacts on properties of ceramifiable silicone rubber were different.When GD was used as a flux,GD underwent eutectic reaction with other inorganic fillers to form a new crystal phase,which improved sintered ceramic-strength and self-supporting performance of ceramifiable silicone rubber,but the dimensional stability was greatly reduced.When APP was used as a flux,although new crystals were found,the crystals were discontinuous and ceramic-strength was reduced.And the dimensional stability was improved.When GD and APP were simultaneously used as the flux and ratio was 4:2,ceramifiable silicone rubber has more comprehensive performance.We used reaction of Al Cl3 and ammonia to generate ATH on surface of APP,and prepared ATH@APP coated filler.Studies have shown that Aluminum hydroxide?ATH?was coated on APP surface successfully,degradation rate of modified fillers decreased significantly,content of residues increased from 15.9%to 64.3%.Replacing APP and part of ATH,ATH@APP were added to ceramifiable silicone rubber.With incorporation of ATH@APP,degradational rate of composite decreased,ceramic-strength at 1000°C was significantly improved and bending angle in self-supporting property test was also significantly reduced.Eutectic reaction mechanism showed reason for this phenomenon.On the one hand,ATH and APP were more uniformly mixed,and eutectic reaction was promoted.On the other hand,it is amorphous that ATH existed in modified filler,which was more likely to lose water.This prevented APP from violent degradation and solved defect of insufficient high-temperature sintering of APP system,help the formation of Al PO4 crystals,which was reason for the improved ceramic performance. |
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