热辐射强度对5种橡胶生胶燃烧和热解特性的影响

Influences of Thermal Radiation Intensity on Combustion Behaviors and Decomposition Kinetics of Five Raw Rubbers

为探究热辐射强度对橡胶生胶燃烧和热解特性的影响,以天然橡胶(NR)、三元乙丙橡胶(EPDM)、顺丁橡胶(BR)、丁腈橡胶(NBR)和丁苯橡胶(SBR)为研究对象,利用锥形量热仪测定生胶的燃烧行为,发现在不同强度热辐射作用下,NR和EPDM的热释放速率(HRR)曲线均为后单峰型,但BR,NBR和SBR的HRR曲线会从35 kW/m^(2)热辐射强度下的后单峰型转变为15 kW/m^(2)热辐射强度下的双峰型。该双峰型曲线的形成可以通过着火前样品的外观变化和热解特性演化进行解释。在15 k W/m^(2)热辐射作用下,BR,NBR和SBR样品的上半部分出现了多分层现象,表面形成了较多的硬质炭层,且至少有1个分层的残碳率和热解反应活化能均大于35 kW/m^(2)热辐射作用下样品表层的残碳率和热解反应活化能。该分层现象和热解特性演化可能与低强度热辐射作用下生胶较长时间处于交联反应温度区间有关,而NR和EPDM的交联作用因为返原现象而大幅削弱,故而在15 kW/m^(2)热辐射强度下没有出现双峰型HRR曲线。

To explore the combustion behavior and decomposition kinetics of raw rubber under different radiation heat fluxes,the heat release rate(HRR)of natural rubber(NR),ethylene propylene diene monomer(EPDM),butadiene rubber(BR),nitrile-butadiene rubber(NBR)and styrene-butadiene rubber(SBR)was measured via cone calorimeter.The HRR curves of NR and EPDM at both 15 kW/m^(2) and 35 kW/m^(2) radiation heat fluxes are of the single peak type.However,the HRR curves of BR,NBR and SBR change from the single peak type at 35 kW/m^(2) to the double peak type at 15 kW/m^(2).The formation of the double peak type HRR curves can be explained by the appearance variation and pyrolysis characteristics evolution of specimens before ignition.For BR,NBR and SBR at the radiation heat flux of 15 kW/m^(2),the specimen at 5 s before ignition can be divided into multiple layers,and the top surface is composed of rigid char like material.Further,at least one of the layers has a higher char yield and greater activation energy of decomposition reaction than the upper part of specimen at the radiation heat flux of 35 kW/m^(2).The formation of multiple layers and evolution of pyrolysis characteristics may be related to the fact that the raw rubber stays in the cross-linking reaction temperature range for a relatively long time at the radiation heat flux of 15 kW/m^(2).However,the cross-linking effect of NR and EPDM is greatly weakened due to the reversion phenomenon,which prevents the HRR curve at 15 kW/m^(2) from converting to the double peak type.