以木质素为炭源的膨胀炭质层品质的研究

Foamed charring layer of the IFR system is crucial for flame retardent properties, but it still has some problems. For example, the amount of the residual carbon is relatively low; the structure compactness is unsatisfactory and the thermal stability is poor. In this proposal, we use lignin, which is rich of the carbon atoms and hydroxyl and could induce the polymer into carbon to form a hard charring layer, to improve the quality of the foamed charring layer of the new type IFR system as an charring agent. The thermal stability of the lignin as carbon source is characterized by the thermal gravimetric analysis method and the mutual matches among the lignin, acid source and gas supply are explored. Methods of modern analytical tools, the macro and micro, are used to characterize the quality of the foamed charring layer of the IFR system in order to research the influence of lignin on the amount of the residual carbon, structure compactness, heat insulation, thermal stability of the foamed charring layer and flame retardant properties of the IFR system. The objective of the project is to construct the lignin-based IFR system and related theories, to uncover the synergy mechanism and the influence law of the lignin in the system, and to establish a evaluation methods based on the cone calorimeter method on the quality of the foamed charring layer of the IFR system. The significance of the project is to promote technological progress in the field of fire retardant by the technical innovation of “Green flame retardant” using biomass to replace fossil raw materials.

膨胀炭质层品质对IFR体系的阻燃效果起着决定性作用。本项目针对IFR体系膨胀炭质层存在的残碳量低、致密性和热稳定性差等品质问题，利用木质素含碳量高、苯环结构多且成炭性好等特点以及木质素可以诱导聚合物成炭，形成坚硬炭层，提高聚合物热稳定性等特性，提出以木质素替代季戊四醇等作炭源，构建基于木质素的IFR体系，以改善膨胀炭质层的品质。项目研究不同类型木质素的热稳定性，探讨其与酸源、气源间的匹配性；从宏观和微观结构、元素组成及化学特性等方面表征基于木质素的膨胀炭质层的品质，研究木质素对膨胀炭质层残碳量、致密性、隔热性、热稳定性及阻燃性的影响。本项目旨在构建基于木质素的IFR体系及相关理论，揭示木质素对膨胀炭质层品质和性能的影响机制及协同作用机理，建立基于锥形量热仪法的膨胀炭质层品质评价方法。项目通过以生物质原料替代化石原料，实现具有“绿色阻燃”特征的技术创新，以推动材料阻燃技术的进步。

膨胀炭质层品质对IFR体系的阻燃效果起着决定性作用。本项目针对IFR体系膨胀炭质层存在的残碳量低、致密性和热稳定性差等品质问题，以木质素为碳源，开展了以下内容：1）木质素为碳源对炭层品质的影响。a. 碱木质素的加入能提高炭层热稳定性。然而碱木质素与膨胀体系适配性差，对气源分解不利，导致其炭层膨胀受到抑制。b. 通过对木质素增加有效基团来提高其与膨胀体系的适配性，改性木质素由于对炭层生成有促进作用对炭层热稳定性都有一定提升。磺酸盐木质素阻燃板材则在降低释热峰值的同时，延长了释热峰时间并提高了炭层保护时间。在木质素中引入磺酸基团能的改善炭层的热稳定性和膨胀性。2）炭层结构演化过程的研究: a. 阻燃树脂在早期成炭作用下，大幅提高了炭层的热稳定性，其热重降解可分为三个主要阶段：炭层发育；炭层的快速热解阶段；缓慢热解阶段。b. 炭层演化过程中炭层体积先增大后减小。在第二阶段，由于大孔隙(D>5 mm)的坍塌，使炭层体积收缩超过50%。扫描电镜显示炭层在发育阶段气体逐步释放，炭层由多泡结构逐渐转变为片状结构。c. 初期形成的炭层石墨化程度较低导致化学稳定性较低。缓慢热解阶段主要是P-O-C键的形成以及占比增大，体现出无机炭层的形成。膨胀炭层演化过程具备明显的阶段性。3）炭层品质的调控及其影响因素: a. 酸源占主导的A3P1的热稳定最高，说明了酸源与碳源的协同作用才能生成更加稳定炭层。b. 同样酸源占主导的A3P1膨胀体积最大，其生成的炭层的形态结构为密闭的泡层结构，缺乏合适酸源或碳源的膨胀效果不理想。用红外光谱法发现P-N、P-O-C和C=O等新键在炭层发育后形成的并且与酸源与碳源的相对比例有关。c. A3P1由于碳源占比低使得生成炭层较慢，导致前期隔热能力较差。合适比例的酸源与碳源的配合才能生成密闭泡孔结构且膨胀体积大的膨胀炭层。项目通过以生物质原料替代化石原料，实现具有“绿色阻燃”特征的技术创新，以推动材料阻燃技术的进步。