Epoxy resins have a relatively low thermal stability, light stability and high flammability. Decomposed at a temperature in excess of 150 ° C and ignited at 400 ° C; the linear velocity and the weight velocity of combustion are 3.4-4 mm / min and 7-8 g / cm², respectively. The corresponding surface temperature in the combustion -500-530 ℃, the flame temperature -950-970 ℃.
Epoxy polymer flammability like other polymer compounds, and their chemical composition. In particular, the flame retardancy of these polymers is primarily affected by the ratio of oxygen to carbon in the oligomer molecule (oxygen index equal to 0.198-0.238). In general, combustibility increases as the oxygen content in the molecule increases. Because the cycloaliphatic epoxy resin has the largest proportion of O and C, it burns at the maximum rate. The combustibility of epoxies is affected by the presence of the curing agent. Epoxy oligomers cured with dicarboxylic anhydrides are more combustible than homogeneous oligomers that are cured with amines.
In the preparation of epoxy-based compounds containing curing agents, fillers and other components, the resulting cured product can be flame retarded by the use of flame retardant grades of epoxy resin; Retardant curing agent; special flame retardant additives; flame-retardant filler.
The substituents imparting flame retardancy to the epoxy oligomer are additives containing halogen, phosphorus, nitrogen and sulfur atoms. Additives - Inorganics or organic matter, can be used alone or in combination with each other. As flame retardant additives for halogen, chlorine and bromine are mainly used. In evaluating the effectiveness of the flame retardant, the dissociation energy of the carbon-chlorine bond should be 280.7 kJ / mol and the dissociation energy of the carbon-bromine bond should be 226.5 kJ / mol. Thus, the bromine-containing mixture is easier to form groups upon separation, increasing the efficiency of the flame-retardant effect. The effectiveness of the halogen-containing flame retardant additives is arranged as follows: halogen-containing aliphatic compounds, halogen-containing alicyclic compounds, halogen-containing aromatic compounds. The main problem is that when these flame retardant additives are added to the polymer, their thermal stability order is just the opposite. As a result, the categories and selection methods for epoxy-based, higher flame-retardant materials must take into account the range of applications, material processing conditions, cost, performance and other factors. As a result of the use of mixtures of various flame retardants, the efficiency and the improvement of their performance are successfully improved. In general, it is necessary to introduce a large amount of a halogen-containing compound in order to impart flame retardancy to a polymer in some cases, since it has good properties, characteristics and high flame retardancy.
The most widely used method of imparting flame retardancy to epoxy polymers is the introduction of halogen-containing compounds. As additives used in polymeric materials, and has been industrial-scale production, according to the information has been about more than 2,300 kinds of chemical compounds and mixtures. It must be noted that there is a certain amount of antimony trioxide associated with flame retardants in almost all applications where halogen-containing organic derivative compounds are used. And antimony trioxide does not affect the flame retardancy of the polymer in the absence of chlorinated derivatives. The flame retardant effect of antimony oxide on polymer combustion is dependent on the flame retardant mechanism of the flame retardant.
The formation of free H and OH groups to form branches, prompting the flame spread in the gas phase. R from the H, OH into water, and the formation of R., oxidized after the re-formation of OH, and continue to burn. As the H and OH groups decrease, the combustion slows and the flame extinguishes. In the presence of chlorinated hydrocarbons, pre-heating decomposition range, antimony trioxide, such as (1), such as the case of chemical reactions. The antimony oxide layer on the surface of the material at a temperature of 600 ° C or higher was subjected to the reaction shown in the example (2) in the flame region. It can be seen from the reaction formula (2) that Sb2O3 reacts with all HCl to form SbOCl, and further reacts to precipitate antimony trioxide in the gas phase and undergoes metathesis. As a result, antimony trioxide acts as a reaction with hydrogen chloride and prevents premature volatilization thereof, thereby reducing the gradient of hydrogen halide decomposition. Premature volatilization of hydrogen chloride can lead to loss of polymer halogens, accelerated combustion, because even in the case of low halogen-containing intense combustion. While antimony trioxide acts with it to keep it in the polymer. For this reason it is necessary to determine the optimum proportion of the components in the polymer, some beyond the optimum range, to increase the combustibility of the polymer.
In this way, the introduction of flame retardants into the polymer results in suppression of combustion and reduction of heat in the combustion zone. In addition, the antimony halide compound forms a protective film on the surface of the polymeric material to prevent oxygen from entering the combustion zone and, consequently, to extinguish the flame.
