Dripping behavior of burning polymers under UL94 vertical test conditions

Abstract

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.

Preparation of polystyrene/triphenyl phosphate composites by suspension polymerization and melt extrusion method — A comparative study

“…As shown in Table 2, the burning time of pure PS was only 15 s. However, with the adding of TPP, the time it took the flame to reach the holding clamp increased, and the UL-94 rating of PS/TPP-S was V-2. During the UL-94 test, we observed that the drops of PS/TPP-S nanocomposite were small, with a short initial drip time, and that the drips speed was faster than that of pure PS, which can take away flame by dripping [35] . As is known to all, TPP is not only a flame retardant but also a plasticizer; it can weaken the intermolecular force of PS, resulting in increased mobility of the polymer chain.…”

Effects of triphenyl phosphate on styrene suspension polymerization process and flame retardance properties of polystyrene/triphenyl phosphate nanocomposite

“…The droplets become small and first dripping time also decreased due to increasing TPP amount. The droplets of PS/TPP dripped fastly and took away the flame drop by drop [38]. As we know, TPP are not only flame retardants but also plasticizers and can weaken the intermolecular force of polystyrene, which results in increasing the mobility of the polymer chain increased by TPP loading.…”

Development of a pendant experiment using melt indexer for correlation with the large‐size dripping in the UL‐94 test

“…Another accepted finding is the dependence of melting/dripping behaviors on the glass transition temperature. Zhang et al, Kandola et al, and Wang et al have found that the lower the glass transition temperature is the higher tendency of melting/dripping the polymer has. The reason should be that thermoplastics easily lose their dimensional stability when their glass transition or melting temperature, respectively, is exceeded.…”

“…In our previous studies, the dripping phenomena of several polymers under the UL‐94 vertical test conditions were quantified by measuring the dripping time and the drop mass. For each specimen, the UL‐94 flame is applied for 10 seconds.…”

“…The dripping time and the drop mass of first dripping are defined as the first dripping time and the first drop mass, respectively. Based on the drop mass distribution and the dripping time, the dripping phenomena in the UL‐94 vertical test are divided into 2 types: the small‐size dripping and the large‐size dripping . Polymers such as PA6, low‐density polyethylene (LDPE), and PP with decomposition mechanism of random‐chain scission tend to generate the uniform and small‐size drops with the short first dripping time.…”