Polypropylene chain scissions and molecular weight changes in multiple extrusion

Review on the thermo-oxidative degradation of polymers during processing and in service

“…Degradation of PP during processing leads to chain scission, resulting in a decrease of the molecular weight and a reduction of the polydispersity [69,104]. It was shown that during multiple extrusion of PP its molecular weight decreases and the polydispersity was reduced with increasing cycle number or temperature [105]. This phenomenon used to make controlled rheology PP.…”

“…Peroxide concentrations as calculated according to the above-mentioned equations (lines) and determined by an iodometric method (points) during a peroxide decomposition experiment at 70 °C with polypropylene pre-oxidized for several times at 70°C [108] Reprinted from Polymer Degradation and Stability, Vol 51, P. Gijsman, J. Hennekens and J. Vincent, The mechanism of the low-temperature oxidation of polypropylene, [95][96][97][98][99][100][101][102][103][104][105]1993, , with permission from Elsevier This decay could not be described with first or second order decomposition kinetics. Assuming that the titrated concentration of peroxides consists of two fractions (both decomposing according to first order kinetics), the calculated data could be fitted with the experimental values (see Fig.…”

“…Also shown are the measured peroxide concentration (∆) and the calculated concentration of rapidly decomposing peroxides (+) after the above mentioned decomposition times. Reprinted from Polymer Degradation and Stability, Vol 51, P. Gijsman, J. Hennekens and J. Vincent, The mechanism of the low-temperature oxidation of polypropylene, [95][96][97][98][99][100][101][102][103][104][105]1993, with permission from Elsevier.…”

The Effect of Multiple Extrusions on the Properties of Montmorillonite Filled Polypropylene

“…The recycling of different polypropylene (PP)-based conventional composite systems has been an important topic of research [1][2][3][4][5][6][7][8]. Multiple extrusion of these materials under intensive shearing at elevated temperature can lead to thermal (temperature), thermal-oxidative (temperature and oxygen) and thermal-mechanical (temperature and shear level) degradation of the matrix and to modification of the filler morphology.…”

Effect of screw element type in degradation of polypropylene upon multiple extrusions

“…Kim and White 10 and Ebner and White 4 analyzed the effect of the screw profile through the peroxide-induced degradation in the PP. Hinsken et al 11 and González-González et al 12 studied the degradation of PP upon multiple extrusions, confirming that it happens mainly via chain scission, altering the molecular weight distribution profile and reducing its average value. Carbonyl groups in the chain were detected via IR spectroscopy.…”