Thermal degradation studies of PVC with time‐resolved pyrolysis GC and derivative TGA

Abstract

This thermal degradation study reports the application of “time‐resolved” pyrolysis gas chromatography (PGC) in addition to derivative thermogravimetric analysis (DTGA) to a series of PVC homopolymers with differing branch content and to a model copolymer series with low amounts of propylene in an otherwise vinyl chloride chain. Benzene and toluene generation and decay envelopes were determined during the controlled thermal degradation and related to the derivative TGA experiments. These data allowed interpretation as to the microstructure of the respective polymers and its effect on the degradative pathways. It was concluded that the branch content was not a dominant factor in the initiation of thermal degradation, although it was a factor in other stages of the complex mechanism. A unique fragmentation step was noted only under oxidative thermal exposures, which gave additional support for the theory of low‐level unsaturation sites as being significant triggers in the decomposition mechanism.

Effect of NaOH Concentration and the Addition of NiCl₂ on the Preparation of Ni/NiO/C Composite Nanofibers

“…3a). [1,6] It is found that all the 138 Advanced Materials and Engineering Materials III initial temperatures of weight loss stages are delayed by the addition of NiCl 2 (Fig. 3b).…”

Thermo-oxidative decomposition of polyvinyl chloride

“…Pyrolytic decomposition is generally accepted to consist of two main steps. The first one (at about 500-650 K) is dehydrochlorination, and it is believed to be initiated primarily at unsaturated sites (allylic chlorines) or at other defect sites in the polymer chain [4,6]. It takes place to form HCl and a linear polyene structure that has also been shown to produce unsubstituted aromatics (benzene, naphthalene) through intramolecular cyclization from polyene radicals formed by chain scission [5,8,11].…”

“…Some works are found concerning analysis of PVC by thermogravimetric techniques, since they provide very useful information about kinetic reaction parameters like activation energies, pre-exponential factors, reaction orders, number of processes involved, etc. Papers usually focus on mechanistic aspects and some of them have revealed the main structural changes occurring during thermal decomposition regarding initiation and propagation of both dehydrochlorination and aromatic formation [3][4][5][6][7][8][9][10][11][12][13]; several works face the great amount of reactions which appear to take place during the process [14][15], whereas others propose non-complicated mechanisms consisting of simplified reactions which gather a complex number of reactions [16][17][18][19][20]. This latter procedure has the advantage of being able to simulate rather accurately the thermal degradation behavior by using a relatively small number of equations.…”

Mechanisms and modes for ignition of low-voltage, PVC-insulated electrotechnical products

“…For pure PVC, one study [12] showed that dehydrochlorination was essentially completed by the time that 2508C was reached; another study [5] showed a peak at 2508C, while two other studies [13,14] found a peak value at about 2858C, thus, the exact temperature range is clearly test-condition dependent. But for flexible wire/cable compounds, dehydrochlorination extends into higher temperatures, with one study [10] showing the reaction is not completed until 3608C is reached.…”

“…The second-stage of the pyrolysis process takes place over about 3508-5008C and is considered to involve several parallel reactions [4]. These include [13] polyenyl macroradical production, dehydrocyclization, aromatization, and chain scission. At the end of the process, a cross-linked, charred residue remains.…”