Basic principles of thermal degradation and thermal stabilization of poly(vinyl chloride). Mathematical model of the action of PVC thermal stabilizers (original) (raw)
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Kinetics of thermal degradation of poly(vinyl chloride)
Journal of Thermal Analysis and Calorimetry, 2011
Extensively studied thermal degradation of polyvinyl chloride (PVC) occurs with formation of free hydrogen chloride and conjugated double bonds absorbing light in visible region. Thermogravimetric monitoring of PVC blends degradation kinetics by the loss of HCl is often complicated by evaporation and degradation of plasticizers and additives. Spectroscopic PVC degradation kinetics monitoring by absorbance of forming conjugated polyenes is specific and should not be affected by plasticizers loss. The kinetics of isothermal degradation monitored by thermal gravimetric analysis in real time was compared with batch data obtained by UV/Visible absorption spectroscopy. Effects of plasticizer on kinetics of polyene formation were examined. Thermal degradation of PVC films plasticized with di-(2-ethylhexyl) phthalate (DEHP) and 1,2,4-benzenedicarboxylic acid, tri-(3-ethylhexyl) ester (TOTM) was monitored by conjugated double bonds light absorption at 350 nm at 160, 180, and 200°C. Plasticizerfree PVC powder degradation kinetics and that of plasticized films were also obtained thermogravimetrically at temperatures ranging from 160 to 220°C. Plasticizer-free PVC powder degradation and spectroscopically monitored degradation of plasticized PVC films occurred with the same apparent activation energy of &150 kJ mol-1. No difference in degradation kinetics of films plasticized with DEHP and TOTM was detected.
Degradation of poly(vinyl chloride) with increased thermal stability
Macromolecules, 1992
Poly(viny1 chloride) (PVC) was treatedwith ethanol, trimethylaluminum, and dibutyltiu maleate in order to substitute labile chlorine. The degradation behavior of the modified samples was compared with that of an ordinary suspension PVC and a PVC obtained by anionic polymerization. All modified samples and the anionic PVC showed the same behavior when degraded in pure nitrogen. Besides a decreased rate of dehydrochlorination, the polyenes became shorter. Degradation in atmosphere containing €IC1 resulted in a higher dehydrochlorination rate and longer polyenes for all samples with improved heat stability, except for the sample treated with trimethylaluminum which exhibited excellent thermal stability. The results showed that the polyene sequence distribution depends on the preeence of HC1 in the sample during dagradation. The content of incorporated methyl ~~O U P S in the alkylated sample was determined to about 1 per 10oO monomer units. Furthermore, the content of tertiary chlorine was reduced to less than 10% of that of unreacted PVC. It is concluded that the enhanced thermal stability is caused by removal of labile chlorine.
Journal of Applied Polymer Science, 2008
The thermal degradation behavior of poly (vinyl chloride), PVC, in presence of poly(N-acryloyl-N 0cyanoacetohydrazide), PACAH, has been studied using continuous potentiometric determination of the evolved HCl gas from the degradation process from one hand and by measuring the extent of discoloration of the degraded samples from the other. The efficiency of blending PACAH with dibasic lead carbonate, DBLC, conventional thermal stabilizer has also been investigated. A probable radical mechanism for the effect of PACAH on the thermal stabilization of PVC has been proposed.
Effect of stearate preheating on the thermal stability of plasticized PVC compounds
Polymer Degradation and Stability, 2006
Effect of preheating of stearates on the processing and post-processing thermal stability of poly(vinyl chloride) compounds, plasticized with di(2-ethylhexyl) phthalate (DEHP) and epoxidized soybean oil (ESO), using several ratios of calcium/zinc stearates and DEHP/ESO is reported. The compounds were prepared as follows: (1) dry-blending the compound components, (2) pelletizing the dry-blend and (3) extruding the pellets to obtain a ribbon geometry. Processing stability was determined by: (a) mechanical characterization and (b) visual color comparison of extruded samples. Post-processing thermal stability was followed by: (a) measurement of HCl release from heated pellets and (b) color changes in heated ribbon samples. From a practical point of view, the preheating has a negligible effect on the initial color of formulations; except for the case of formulations without both ESO and CaSt 2 . However, the effect of the preheating on the post-processing thermal stability is strongly determined by the composition formulation.
Structure and degradation of commercial poly(vinyl chloride) obtained at different temperatures
Macromolecules, 1993
The influence of microstructure on thermal degradation behavior was studied for four commercial poly(viny1 chloride) (PVC) resins with different polymerization temperatures and for two low molecular weight fractions. The samples were characterized by determining tacticity and the content of labile chlorine, i.e., internal allylic and tertiary chlorine. The degradation rates were measured both in nitrogen and in an atmosphere containing HCl, and the polyene sequence distributions were monitored by W-visible spectroscopy. It was found that there is a strong relation between the content of labile chlorine and the dehydrochlorination rate in nitrogen. For tacticity, on the other hand, the relation is much weaker. When degradation was performed in an atmosphere containing HC1, the dehydrochlorination rate was increased and the polyene sequence distribution was shifted toward longer polyenes. It is concluded that labile chlorine contributes most to the initial degradation rate and that tacticity is of minor importance. Furthermore, the presence of HCl in the sample, which depends on the dehydrochlorination rate, is an important factor determining the degradation behavior.
Thermal stabilisation of poly(vinyl chloride) by organotin compounds
Polymer Degradation and Stability, 2005
The effect of LSN 117 (dioctyl tin bis isooctyl thioglycollate, an organotin compound) on the heat stability of plasticised PVC was investigated in this study. The organotin stabiliser had carbonyl and carboxylate groups and PVC contained traces of Fe, Zn, Ca, Cu and Sn. The heat stability of the films were tested at 140 C and 160 C or 180 C by heating in an air circulation oven up to 2 h and by measuring HCl evolved using a Metrohm 763 PVC thermomat and by thermogravimetric analysis. The onset of HCl evolution was at 14.3 and 2.5 h at 140 C and 160 C, respectively, for PVC film without LSN117. On the other hand, the film with LSN117 did not evolve HCl in 30.3 h at 140 C. HCl started to evolve from the films with LSN 117 in 14.3 h at 160 C. The TGA curve also indicated PVC film with LSN 117 degraded at higher temperatures than control films. LSN 117 was found to be a good heat stabiliser for plasticised PVC and it did not have any detrimental effect on mechanical properties.
Thermal Degradation of Polyvinyl Chloride
Journal of Thermal Analysis and Calorimetry, 1999
The thermal degradation of a sort of polyvinyl chloride was investigated. Complex processes for polyvinyl chloride degradation were evidenced. The kinetic analysis of dehydrochlorination and of subsequent processes was carried out. A change of mechanism was detected when dehydrochlorination goes to completion. The values of non-isothermal kinetic parameters determined by various methods are in a satisfactory agreement. The obtained results allowed some clarifications concerning the thermal degradation steps.
Thermal Behaviour Prediction of Rigid Polyvinyl Chloride
2007
This work presents the results obtained from experiments of rigid PVC stabilization both lead stabilizer and earth alkaline carbonates as co stabilizer. Efficiency of stabilizers was tested by dynamic tests (roll mill processing or Brabender plastograph) and static test (thermogravimetric analysis). Both types of test were in concordance from point of view of stabilization efficiency and from thermal analysis can be predicted the thermal lifetime of PVC products. This is an important fact for durable usage or for recycling products made from PVC.