## 3 Results and Discussion
### Flame Retardancy Tests  
All polypropylene, low density polyethylene and polystyrene formulations containing various sulfenamides as flame retardant additives successfully pass the DIN 4102-1 B2 classification. According to the DIN 4102-1 standard, a 20 mm flame is applied for 15 s, and the average burning time when the flame is removed is recorded. However, in many cases, the sample self-extinguished already before the flame was removed, and only melting was detected after that. Therefore, in Tables 1-3, burning time is given from the application of flame, not from the flame removal. In addition, a 40 mm flame was used in order to better differentiate between the flame retardant efficacies of different sulfenamide derivatives. DIN 4102-1 B2 classification is comparable with class E in the EN 13501-1 \"Fire classification of construction products and building elements\". Figure 3: Collected thermogravimetric analysis (TGA) graphs of sulfenamides denoted Ic, IIc, IIIa, Vb, VIa and VIb. The optimal temperature range for flame retardant (FR) decomposition between polypropylene (PP) processing (230 \({}^{\circ}\)C) and ignition temperatures (250–360 \({}^{\circ}\)C) is marked with a grey border. The first group of synthesized sulfenamides based on 2,2,6,6-tetramethylpiperidinone, i.e., Ic-Id, with different thioaryl groups exhibited all very similar and short burning times in thin polypropylene films of 200 \(\upmu\)m (Table 1). Additional fire tests were performed using Ic in thick polypropylene plaques of 1 mm in accordance with DIN 4102-1 standard and films of 300 \(\upmu\)m based on a UL94 VTM test standard. The results revealed that even polypropylene plaques and films containing 0.5 wt % of Ic passed the criteria's set forth for DIN 4102-1 B2 (see Table 2) and UL94 VTM-2 classifications, respectively. The prepared LDPE samples flame retarded with Ia and IIa passed the DIN 4102-1 B2 test. Both burning time and damage length were, however, somewhat longer than for the corresponding PP thin samples (Table 3). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Flame retardant**} & \multirow{2}{*}{**TGA weight**} & \multicolumn{3}{c}{**DIN 4102-1 B2 1**} \\ \cline{3-5}  & & **FR amount (wt \%)** & **Average damage length (mm)** & **Average burning time (s) 1** & **Pass/Fail** \\ \hline Reference LPPE & 0 & 190 & 37 & Fail \\ Ia & 0.5 & 108 & 36 & Pass \\ Ia & 0.5 & 133 & 36 & Pass \\ Ia & 1.0 & 122 & 28 & Pass \\ \hline \hline \end{tabular}  
* Burning time is calculated from the application of flame. Flame application time 15 s, edge ignition, flame height 40 mm. LDPE film thickness 200 \(\upmu\)m.  
\end{table} 
Table 3: Flammability results for low density polyethylene (LDPE) with a given amount of added FR. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Flame retardant**} & \multicolumn{3}{c}{**DIN 4102-1 B2**} \\ \cline{2-5}  & **FR amount (wt \%)** & **Average damage length (mm)** & **Average burning time (s) 1** & **Pass/Fail** \\ \hline Ic & 1.0 & 43 & 20 & Pass \\ IIb & 1.0 & 43 & 21 & Pass \\ Ilc & 1.0 & 52 & 30 & Pass \\ \hline \hline \end{tabular}  
* Burning time is calculated from the application of flame. Flame application time 15 s, edge ignition, flame height 40 mm. LDPE film thickness 200 \(\upmu\)m.  
\end{table} 
Table 2: Flammability results for 1 mm thick PP plaques with a given amount of added FR. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Flame retardant**} & \multicolumn{3}{c}{**DIN 4102-1 B2**} \\ \cline{2-5}  & **FR amount (wt \%)** & **Average damage length (mm)** & **Average burning time (s) 1** & **Pass/Fail** \\ \hline Reference LPPE & 0 & 190 & 37 & Fail \\ Ia & 0.5 & 108 & 30 & Pass \\ IIa & 0.5 & 133 & 36 & Pass \\ Ia & 1.0 & 122 & 28 & Pass \\ \hline \hline \end{tabular}  
* Burning time is calculated from the application of flame. Flame application time 15 s, edge ignition, flame height 40 mm. LDPE film thickness 200 \(\upmu\)m.  
\end{table}