Thermal Degradation Characteristics And Mechanism Research Of Typical Organic Insulation Materials For Building

In recent years, as the driven of various construction technology policy and energy conserving, building insulation materials get rapid development. Among them, organic insulation materials are widely used because of its excellent integrated performance, total accounts for more than two-thirds of the market share. However, the biggest disadvantage of these materials is flammability, and will release a large amount of smoke even toxic substances during burning. With the increasing application of these materials, more and more fires were caused, resulting in great economic and life loss, even serious social impact. The investigations to these fire disasters showed that combustion caused by organic insulation materials can quickly spread from the fire origin to the entire building. It is generally accepted that the thermal degradation of materials is the initial step of solid combustion processes and the pyrolysis products that contain gaseous fuel support the combustion. Thus, it is of great importance to study the thermal degradation characteristics and volatile products of such organic insulation materials.In this paper, two typical organic building insulation materials were selected as the research object, one is rigid polyurethane (PU) foam and the other is extruded polystyrene (XPS). The formula used was typical for building insulation systems in the materials market. Thermal degradation characteristics of PU foam and XPS were studied by means of thermogravimetry and differential scanning calorimetry (TG-DSC) hyphenated techniques. In order to investigate the characteristic functional groups of the decomposition residues, in situ Fourier Transform Infrared (FTIR) is employed. And the volatile products in helium are studied using a TGA instrument coupled with FTIR spectroscopy, gas chromatography and mass spectrometer (TG-FTIR-GC-MS). And the research were proceed from these three aspect:(1) Influence of different gas environments on the material pyrolysis characteristics and kinetics parameters;(2) Rupture mode of chemical bonds in materials;(3) Gaseous products and thermal degradation mechanism of the insulation materials.In kinetics study, the two gaseous environments were non-oxidizing gas nitrogen and oxidizing gas air, respectively. Kissinger-Akahira-Sunose (KAS) method was utilized to calculate activation energy with respect to conversion rate. In N2, E values both show a rising trend at the initial and last stages of PU degradation. In air environment, the values first increase in the conversion range α=0.05～0.5and decrease when α>0.5. XPS requires less activation energy at the initial stage of thermal degradation in N2, and then maintain an approximate constant in the main reaction stage. In air, the E values can be distinguished into three stages. Furthermore, the influence of heating rate on the thermal degradation characteristics was discussed as well.In research of the thermal degradation products and mechanism, in situ FTIR was employed to investigate the rupture mode of chemical bonds in materials. In addition, reaction rate in different gaseous environments were compared. Based on the FTIR experiment analysis, the thermal degradation mechanism of insulation materials under non-oxidizing gaseous environment was evaluated. For PU thermal degradation, the blowing agent HCFC-141b and some other small molecules, such as H2O and CH3OCH3, volatilize at the initial stage. Secondly, the urethane bond groups in PU foam break up into isocyanates and polyols from200℃. Then, the polyols segments start to decompose into some kinds of aliphatic ether alcohols as temperature increases. And the products become more complex with temperature increasing, even epoxy compound is formed as a result of interactions among evolved products. In the temperature range of350-500℃, the materials decompose to primary amines, secondary amines, vinyl ethers and CO2. At temperature above500℃, the material residues continue to decompose into volatile products. Thus the aliphatic alcohol with branched chains, benzene alkyls and small molecule CO2are generated as well. Several different types of volatile products were released during XPS thermal degradation, most of them are flammable. It is demonstrated that depolymerization reaction predominate the thermal degradation of XPS in helium and styrene monomers are the dominant volatile gases. Methylbenzene, a-methyl styrene, dimer and some other oligmers of styrene are also detected.