## 3 Results and Discussion
### Thermal Analysis in Nitrogen  
Figures 6 and 7 show TG/DTG curves of the same eight samples but recorded in N\({}_{2}\) atmosphere. Up to 400 \({}^{\circ}\)C, both pure resins (M/H, G/H) decomposed just like in air (Figures 6a and 7a vs. Figures 3a and 4a). However, at about 400 \({}^{\circ}\)C, there was only one intensive transformation in N\({}_{2}\) (in air there were two separate transformations), including decarboxylation and decomposition of the polymeric matrix (loss in mass 71.0 wt% for M/H and 62.0 wt% for G/H). For M/H and G/H, the end temperature in N\({}_{2}\) was significantly lower than in air. The solid residue from M/H pyrolysis accounted for approximately 6.0 wt%. The solid residue from G/H pyrolysis (12.0 wt%) had an unusual form of foam/sponge, which \"tried to get out\" of the crucible (Figure 2, last column). As one can see in Figures 6b-d and 7b-d, all HIXs in N\({}_{2}\) decomposed in four stages (as in air); they decomposed much faster than the reference material (pure resin) and slightly slower (at a slightly higher temperature) than in air. The interesting issues of the pyrolysis of six HIXs are connected with the composition and amount of the solid residue (pyrolysate). The pyrolysate has a much larger mass than the ash (the post-combustion residue) since, besides a mineral phase, it contains an organic phase (carbon char). More precisely, the pyrolysate contains carbon char (a mixture of various high molecular weight organic compounds constituting a product of the decomposition of the polymer's matrix in air-free conditions) and inorganic matter (mainly deriving from the cupric deposit). Our previous study showed that during pyrolysis, the particles of copper compounds such CuO, Cu (OH)\({}_{2}\), and Cu\({}_{2}\)O contained in the HIX received from anion exchangers had undergone reduction to Cu\({}^{0}\)[40; 41]. Although, in this case, the mass of cupric deposit in the skeleton was several times greater, the result was the same. Figure 8 shows six XRD patterns revealing that the inorganic load consisted of metallic copper (peaks at 20 = 43.44 and 50.57, ICSD Card No. 43493). This is a valuable result as it means that, during pyrolysis, the whole of Cu (II) in CCE has been reduced to metallic copper (not to a mixture of copper compounds at different oxidation levels), for which a large amount of reducer (above 10.0 meq/g) was needed. In the photographs of pyrolysates (Figures 1 and 2, last column), the characteristic color of metallic copper can be seen. The pyrolysates obtained during this study stand out in terms of mass and chemical composition. For the first time, we obtained pyrolysates with mass that represented as much as 50 wt% of the initial sample. For the first time, we obtained pyrolysates in which the inorganic phase (which was metallic copper) dominated. The high content of metallic copper in pyrolysate was due to the high Cu (II) content in the material subjected to pyrolysis and the process conditions for quantitative reduction. Comparing \"solid residue\" and \"Cu content in respective starting sample\" (Tables 2 and 3), it can be estimated that HIX/M pyrolysates contained 70-80% wt% Cu and HIX/G pyrolysates 60-70% wt% Cu. As in the previous research [40; 41; 60], it turned out again that under N\({}_{2}\), more pyrolysate formed from HIXs than in the case of the same transformation of pure resins (M, G). The research presented here shows that the polymeric matter from which the carboxylic cation exchanger is made (in addition to carbon and hydrogen atoms containing oxygen atoms) during pyrolysis does not give as much carbon char as in the case of a hydrocarbonaceous (oxygen-free) polystyrene matrix of anion exchange resin. However, there is no doubt that during pyrolysis of the polyacrylic/polymethacrylic matrix, the products of its decomposition (free radicals and hydrogen) participate in creation of an additional amount of carbon char due to the consumption of a certain amount of hydrogen to reduce Cu(II) to Cu\({}^{0}\).