## 2 Materials and Methods  
An acrylonitrile-butadiene-styrene copolymer (ABS), with the commercial name of Rocadur RABS 52, was provided by S.C. Romcarbon S.A. (Buzau, Romania) in granule form with a density of 1.03 kg/m\({}^{3}\). Two phosphorus fire retardant (FR) additives were considered: an ammonium polyphosphate (APP), Exolit\({}^{\circledR}\) AP422, and an aluminum diethylphosphinate (AlPi), Exolit\({}^{\circledR}\) OP1230, both supplied, in the form of white powder, by Clariant (Germany) with the properties shown in Table 1, as per given by the manufacturer. The two FRs were used in manufacturing the samples in a 1:1 proportion, as was recommended by the manufacturer. In addition, nanoparticles of organic montmorillonite (OMT) with the name Shelsite 30B Montmorillonite Nanoparticles (Nanoshell) was used as clay for preparing the samples. The OMT properties are as follows: particle dimension--less than 80 nm; purity--99%, pH--8-9; humidity--less than 2% and density--2.8 g/cm\({}^{3}\). Several formulations were prepared (see Table 2) and all the materials were first dried at 100 C for 24 h than were mixed at a blending temperature of 205 \({}^{\circ}\)C in a Brabender mixing chamber (Brabender, Germany), with a rotating rate of 60 rpm applied for 10 min. The materials final composition was chosen according to the open literature [1; 2; 3; 4; 5] and with the scope to determine the most favorable minimum addition of OMT and fire retardants in order to get the best fire properties. The specific specimens used for further tests were obtained at 205 \({}^{\circ}\)C in a Carver press over three minutes at a pressure of 50 atm and two minutes at 150 atm. For better accuracy of results, 2-3 specimens were manufactured for each composition and tests were performed on 2-3 samples, while the average values were used for the results discussion. Limiting Oxygen Index (LOI) of ABS and its nanocomposites were measured using an Oxindex type equipment manufactured by the Hungarian Polymer Research Institute in compliance with \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Exolit OP 1230** & **Exolit AP 422** \\ \hline Chemical formula & [(C\({}_{2}\)H\({}_{5}\))\({}_{2}\)PO\({}_{2}\)]\({}_{3}\)Al & (NH\({}_{4}\)PO\({}_{3}\))\({}_{n}\) \\ Phosphor content, \% & 23.3\%–24\% & 31\%–32\% \\ Humidity, \% & max 0.2\% & max 0.25\% \\ Density, g/cm\({}^{3}\) & 1.35 & 1.9 \\ Decomposing temperature, \({}^{\circ}\)C & \textgreater{}300 & \textgreater{}275 \\ Particle dimension & 20–40 \(\upmu\)m & 17 \(\upmu\)m \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Properties of fire retardant materials. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Recycled Acrylonitrile-**} & \multicolumn{2}{c}{**Organic**} & \\
**Specimen** & **Butadiene-Styrene,** & **Montmorillonite,** & **Exolit OP 1230** & **Exolit AP 422** \\  & **reABS** & **OMT** & **(wt\%)** & **(wt\%)** \\  & **(wt\%)** & **(wt\%)** & **(wt\%)** & **(wt\%)** \\ \hline reABS & 100.0 & - & - & - \\ reABS 1\% OMT & 99.0 & 1.0 & - & - \\ reABS 15\% FR & 85.0 & - & 7.5 & 7.5 \\ reABS 1\% OMT 15\% FR & 84.0 & 1.0 & 7.5 & 7.5 \\ reABS 1\% OMT 18\% FR & 81.0 & 1.0 & 9.0 & 9.0 \\ reABS 15\% OMT 20\% FR & 79.0 & 1.0 & 10.0 & 10.0 \\ reABS 2\% OMT & 98.0 & 2.0 & - & - \\ reABS 2\% OMT 15\% FR & 83.0 & 2.0 & 7.5 & 7.5 \\ reABS 2\% OMT 18\% FR & 80.0 & 2.0 & 9.0 & 9.0 \\ reABS 2\% OMT 20\% FR & 78.0 & 2.0 & 10.0 & 10.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Prepared samples. standards ASTM D2863 (i.e., Standard Test Method for Measuring the Minimum Oxygen Concentration to Support Candle-Like Combustion of Plastics (Oxygen Index)) and ISO 4589 (i.e., standard for Determination of burning behaviour by oxygen index). Tests were performed on sheets with a size of \(120\times 10\times 4\) mm\({}^{3}\) and were based on the lowest oxygen gas concentration that still sustains combustion of the sample.