This article studied the dripping behavior of eight polymers under UL94 vertical test conditions. The results suggested two different dripping behaviors: Type I, dripping with uniform- and small-sized drops with the short first dripping time, and Type II, dripping with irregular- and large-sized drops with the long first dripping time. Polymers of Type I dripping had dominant decomposition mechanism of random-chain scission, low activation energy of viscous flow, and high ratio of effective heat of combustion to heat of gasification. Otherwise, Type II dripping dominates. The surface tension at ambient temperature and the melt flow index at processing temperatures were not as important to dripping as expected. It was found that talc could convert the dripping of low-density polyethylene from Type I to Type II at a critical talc loading level of 20 wt%, which was ascribed to the reduction in the burning rate and the formation of an integral residue. Finally, a generalized model was presented, and a derived correlation showed that the drop mass was a power law function of the dripping time.
Modeling the UL-94 vertical burning test is of practical importance in industries which, however, has not been addressed sufficiently. In this article, a 3D convective heat transfer model was developed to simulate ignition times for the UL-94 test. An experimental procedure was proposed to measure ignition times of two polymers under the UL-94 test condition. Comparisons between experimental and simulated results of ignition times showed that edge effects were significant in the ignition process of the UL-94 test and the convective heat transfer ignition model considering edge effects gave ignition times close to experimental results. Sensitivity analyses showed that the ignition time increased linearly with decreasing initial temperature and increasing density, heat capacity and emissivity, but nonlinearly with decreasing flame temperature and convective heat transfer coefficient and increasing thickness, thermal conductivity, and ignition temperature of the specimen.
We demonstrated a 512PPI mobile display with slim border (0.65mm) and high color gamut (95% NTSC). Contrast to conventional design, high aperture design (>60%), new scan drivers, and a new back-light source were integrated to realize these features.
pingwei@sjtu.edu.cn ABSTRACT: A novel solid flame retardant poly(3-aminopropyl methylsiloxane bis(3-hydroxyphenyl spirocyclic pentaerythritol bisphosphate)) (PSBPBP) consisted of phosphorus, silicon, and nitrogen was synthesized and characterized by NMR and FTIR. Then PSBPBP was added to a polycarbonate matrix. The flame retardancy and mechanical properties of the PC/PSBPBP system were tested for limiting oxygen index (LOI), UL-94 rating, tensile, and impact strengths. A significant improvement of flame retardancy of the system was observed (increase of LOI up to 31, and UL-94 V0) with an addition of 15 wt% PSBPBP to PC. Raman spectrum and SEM images have proved the formation of dense and intumescent char in the combustion, which acted as an insulator to the transfer of heat and combustible gases.
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