The stabilization of ethylene-propylene diene rubber (EPDM) with naringenin and caffeic acid is studied. The selected concentrations were 0.25, 0.50 and 1phr. The degradation was performed by ...γ–irradiation. The protective effect of these antioxidants was investigated by isothermal chemiluminescence at 170°C and FTIR spectroscopy. The synergetic action of these compounds and metallic selenium was also revealed. The exceptional contribution provided by these phenolic stabilizers is characterized by three kinetic parameters: initial CL intensity, oxidation induction time and maximum period of degradation. The radiation stability of stabilized EPDM is efficiently depicted by induction periods which are the minimum 6times longer for unirradiated samples and 2–50 times longer for 50kGy-irradiated specimens than pristineEPDM.
A chemiluminescence study on thermal degradation of some polyethylenes (LDPE, LLDPE, HDPE, UHMWPE) on seven metal trays in the presence of triazines as stabilisers was carried out. The kinetic ...effects of metals (Al, Zn, Ti, Mo, Mn, Fe and Cu) were assessed at 200 °C by the calculation of oxidation induction period, half-oxidation time, maximum oxidation time and rate in the propagation stage. Different sequences of catalytic effect provided by the studied metals in LDPE and HDPE are reported. A characteristic copper index for each metal was also calculated. Some considerations on the thermal stability of polyethylenes in intimate contact with metal surfaces are presented.
PA 6 and PA6,6 sheets irradiated with electron beam were investigated in relation to their thermal stability in various environments (air, distilled water and NaCl 5% solution) at 70
°C. The ...preexposure doses were 100, 200, 400 and 600
kGy at a dose rate of 22.4
kGy/s. The FTIR spectra allowed the evaluation of the progress of sample oxidation by elucidating the contributions of each environment to the ageing of polyamides. The increases in the absorbance at 1652
cm
−1 placed the surrounding aggressive attack in the following sequence: air<water<NaCl solution. A scheme of degradation mechanism is proposed for the explanation on the involvement of amidic units.
Polyacrylonitrile (PAN) and some copolymers of acrylonitrile with divinylbenzene (AN-DVB) were investigated by the characterization of their thermal and radiation stabilities. The contribution of DVB ...to the thermal stability of PAN by the modification in the amount of unsaturated hydrocarbon between 6 and 20% was revealed by the evaluation of oxidation induction periods and required activation energies. The exposure of these materials to the action of γ-radiation points out the higher stability of copolymers (AN-DVB) in comparison to the relative stability of PAN.
The effect of capsaicin on the radiation stability of low density polyethylene was accomplished by applying the chemiluminescence procedure. The neat and modified polymer with 0.25% and 0.50% (w/w) ...capsaicin were exposed to γ-irradiation in air receiving 10, 20 and 30
kGy. The synergistic effect due to the presence of metallic selenium was demonstrated. The significant improvement in oxidation induction time was obtained demonstrating the efficient antioxidant activity of capsaicin in LDPE. The simultaneous protection action of metallic selenium in LDPE/capsaicin systems brought about a supplementary enhancement in the oxidation resistance of irradiated samples.
The oxidative degradation of
γ-irradiated ethylene–propylene elastomers (EPR and EPDM) in the presence of some phenolic antioxidants (Topanol OC, Cyanox 2246, Santonox R, Irganox 1010 and Irganox ...1076) was studied. The stabilization activity of these antioxidants was related to the gel content of polymer matrix and the G values for radiochemically formed ketones, aldehydes, acids, esters and alcohols. The oxidation rates, obtained by IR measurements of CO concentrations, provide an order of antirad efficiency. Some considerations concerning the influence of the chemical structure of antioxidants on the stabilization of elastomers and a radiochemical oxidation mechanism are presented.
RTL study of structural modifications in irradiated PTFE Jipa, S.; Zaharescu, T.; Setnescu, R. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
12/2007, Letnik:
265, Številka:
1
Journal Article
Recenzirano
The exposure of polytetrafluorethylene to the action of high energy radiation is examined by radiation thermoluminescence. The radiolysis causes the formation of various traps, which correspond to ...four maxima in the glow curve of PTFE. The activation energy of molecular motion is discussed. The modification of emission intensity at a large dose range is evaluated for three glow maxima that appear at 139, 173 and 205
K. The RTL emission is correlated with different types of oxygenated products that are formed during the radiolysis of PTFE. Changes in other properties like molecular mass, density, crystallinity are investigated for emphasizing the radiodegradation in this matrix. The mechanism of RTL emission is explained by the recombination of thermalized electrons with positive intermediates.
