Abstract
To comprehend thermal melting behaviors of the thermoplastic insulation material in façade fires, a series of experiments have been conducted under various external heat fluxes. As one of the essential thermal deformation and melting parameters, glass transition temperature was explored via DSC and TMA tests. Then thermal shrinkage behavior was investigated within a range of low heat fluxes (1–15 kW/m2), and melt dripping experiments were carried out within a range of high external heat fluxes (20–40 kW/m2), with the potential influencing factors (dripping hole diameter and initial sample mass) explored. The results are divided into two parts, thermal shrinkage and melt dripping, and melt dripping has been primarily analyzed. For thermal shrinkage, the difference in thermal shrinkage behavior under various heat fluxes was characterized by the surface temperature, and a model was established to quantify the density change of the shrinkage. For melt dripping, the first dripping time and dripping frequency were analyzed to characterize the properties of melt dripping. A linear distribution was found between dripping frequency and the corresponding mass loss rate. Moreover, the effects of hole diameter and initial sample mass of large values on the dripping behaviors were investigated. The temperature stages of the dripping space were clarified to characterize the occurrence of dripping. Finally, a phenomenon of gas combustion fulfilled within very short time in the dripping space under high external heat fluxes has been observed and then analyzed using the Damköhler number (Da). The critical temperature 337 °C was obtained to reveal the formation mechanism of the instant gas combustion phenomenon when external heat flux was higher than 30 kW/m2. This research provides a deep insight into how external heat fluxes impact on properties of thermoplastic materials, with the shrinkage and melting behaviors.
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