Polypropylene Carbonate Decomposition

Li and co-workers [3] have studied the thermal dynamic decomposition of polypropylene carbonate (PPG) occnrring at varions pyrolysis temperatures up to 250 C and examined the pyrolysis products by a combination of Py-GC-MS and thermogravimetry - infrared (TG-IR) spectroscopy. 

High molecular weight PPC decomposes through scission and unzipping while low molecular weight PPC decomposes only by unzipping. 

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Propylene oxide represents a very attractive epoxide monomer for copolymerization with C02, as polypropylene carbonate) is industrially valuable. The low glass transition temperature (Tg) of 313 K, the sharp and clean decomposition above 473 K, and biodegradability of this copolymer are the reasons for its attracting interest in several applications. On a similar basis, H NMR spectroscopy is useful for assessing the coupling products resulting from the reaction of PO and C02 (Figure 8.21). 

Li and co-workers [50] used Py-GC-MS and TGA-IR spectroscopy to study the thermal decomposition of polypropylene carbonate (PPC). 

The majority of packaging plastic materials consists of polyolefins and vinyl polymers, namely polyethylene (PE), polypropylene (PP), polystyrene (PS) and poly(vinyl chloride) (PVC). Obviously, these polymers have many other applications not only as packaging materials. Chemically they are all composed of saturated hydrocarbon chains of macro-molecular size their typical thermal decomposition pathway is free radical one initiated by the homolytic scission of a backbone carbon-carbon bond. In spite of the basic similarity of the initial cleavage, the decomposition of the hydrocarbon macroradicals is strongly influenced by fhe nafure of the side groups of the main chain. 

Tsuchlya and Suml (6) have thermally degraded polypropylene in the temperature range ShO-AOO C and have made a detailed analysis of all products with 1-12 carbon atoms. On this basis, a decomposition mechanism has been proposed. Initiation occurs by random scission of the main chain. The radicals thus formed undergo transfer reactions most readily at tertiary carbon atoms but the distribution of products indicates that intramolecular transfer to both third and fourth carbon atoms is particularly important. 

More detailed product information was provided by Uemichi et al. who used a fixed bed flow reactor to examine the decomposition of polypropylene in the presence of silica-alumina.Detailed product analysis was carried out for compounds with 16 or fewer carbon atoms, resolving the products into normal alkanes, isoalkanes, alkenes and aromatics. For a reaction temperature of 750 K, a catalyst weight of 3.0 g and a polypropylene feed rate of 0.150 g min , the polymer was converted over 95% to low molecular weight products, forming C4 and C5 isoalkanes and alkenes in the highest yields. The overall carbon number distribution for reaction over SA is summarized in Figure 4, in which thermal degradation results for even more severe conditions of 799 K and a feed rate of 0.116 g min are included for comparison. The increased rate of conversion and the shift of the product distribution to lower carbon numbers are apparent from this plot. 

Thermoplastics such as polypropylene, polycarbonate, nylon, and thermo set such as epoxy, as well as thermoplastic elastomers such as butadiene-styrene di block copolymer, have been reinforced with carbon nanofibers for example. Carbon nanofibers with 0.5 wt% loading were dry-mixed with polypropylene powder by mechanical means, and extruded into filaments by using a single screw extruder. Decomposition temperature and tensile modulus and tensile strength have increased because of dispersion of CNF [121] (Fig. 8.19). 

Figure 2.13 The effect of the prescence of a polypropylene matrix on the decomposition of a huntite - basic magnesium carbonate filler...

In the case of polymer/clay nanocomposites, alkylammonium exchange species influence the affinity between the polymer and the clay surface. For example, it was reported that clays treated with dialkyl dimethylammonium halides, in particular with two chains of about 18 carbon atoms, have a surface energy similar to poly(olefins) such as polypropylene (PP) and polyethylene (PE) [27]. Polar polymers as polyamides (PA) have been recommended to get better interactions as reported by Toyota [8]. The alkyl chain length is related with increase in interlayer space required for the intercalation of polymer chains. Because of the nonpolar nature of their chains, they reduce the electrostatic interactions between the silicate layers and lower the surface energy of the layered silicates. As a consequence, an optimal diffusion of the polymer to dissociate the stacked clay layers, that is, an exfoliation process, can be obtained. Despite the compatibility of MMT modified by long alkyl chain quaternary ammonium with hydrophobic polymers (PE and PP), conventional alkylammonium ions show low thermal stability, that is, an onset decomposition temperature is close to 180°C.This poor thermal stability could limit their use in the preparation of PLS with matrices processed at high temperatures such as PA, poly(ethylene terephthalate) (PET), and poly(ether ether ketone) (PEEK) [30]. 

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