*3.1.2 Acrylonitrile-butadiene-styrene rubber (ABS)*

The sample was analyzed without any pretreatment. Two thermal ramps were adopted for the TGA analysis, the first at a rising temperature of 20°C/min in an inert atmosphere followed by an isotherm in an oxygen atmosphere. As can be seen from the thermogram (**Figure 14**), the following weight losses were recorded:


At the end of the analysis, a final residue of 7.7 wt% of the sample was present and associated with inorganic compounds that do not degrade up to this temperature.

The FTIR spectrum of the gas released by the sample during TGA analysis is reported in **Figure 15**. In the FTIR spectrum of the gas released at 330°C (black line) is present only the emission of CO2, probably due to the degradation with the temperature of inorganic compounds present in ABS. At 440°C, the FTIR spectrum shows signals associated with degradation products of a carbonate containing ABS.

**Figure 14.** *TGA analysis of ABS.*

*Microwave-Assisted Pyrolysis Process: From a Laboratory Scale to an Industrial Plant DOI: http://dx.doi.org/10.5772/intechopen.104925*

**Figure 15.** *FT-IR spectra of gases released at 330°C (black) and 440°C (red) during the TGA analysis of ABS.*

As reported in the literature, the thermal degradation of ABS polymer begins at 340°C with the formation of the butadiene monomer. The aromatic compounds begin to be noticed at 350°C, a temperature at which the degradation of polybutadiene unities is still evident. As the temperature increases, the formation of styrene becomes more important, and at 420°C, the intensities of the C-H bands of butadiene and styrene are approximately equal. At higher temperatures, the presence of aromatics decreases in intensity while that one of butadiene is very strong. The evolution of acrylonitrile begins at about 400°C and ends at 450°C [27].

According to the above description, the spectrum of gas released at 440°C (**Figure 15**, red line) shows the stretching of aromatic C-H at 3100 cm−1, and aliphatic C-H stretches at 2900 cm−1 and the stretching of the nitrile group at approx. 2200 cm−1. Another sample of ABS was crushed and subsequently subjected to DSC analysis, running three thermal ramps in the temperature range from 25 to 300°C, alternating heating–cooling–heating, in an inert atmosphere. DSC analysis shows a glass transition at T = 108.25°C (**Figure 16**, red curve) associated with the styrenic portion typical of acrylic copolymers such as acrylonitrile-butadiene-styrene (ABS), styrene–acrylonitrile (SAN), or acrylonitrile–styrene-acrylate (ASA), a glass transition at T = 124.08°C associated with polycarbonate present and a glass transition at T = 162.42°C associated with ABS.

From the DSC and TGA/FTIR analyses, the sample is a polycarbonate containing ABS (78.3%) with small quantities of polypropylene.

#### *3.1.3 Polypropylene (PP)*

Propylene experiments were carried out using single-use masks as a sample of PP. The single-use masks were cut to separate the non-woven polypropylene from the elastic bands, and the two samples were analyzed separately by DSC. For each sample, three thermal ramps were performed in the temperature range from −10 to 300°C, alternating heating–cooling–heating, in an inert atmosphere. Measurement of the glass transition temperature, (Tg), of polypropylene is generally considered difficult

**Figure 16.** *DSC analysis of ABS.*

to detect with DSC analysis because the transition is weak. The graph (**Figure 17**) instead shows a peak at 167°C corresponding to the melting temperature of polypropylene (green curve) and a peak at 221°C typical of the nylon used to realize the elastic bands of single-use masks (purple curve).
