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The mechanisms of the sulphur-only and catalytic vulcanization of polybutadiene: An EPR and DFT study
No full text
EPR AND DFT B3LYP STUDY OF FREE RADICALS FROM ELEMENTAL SULPHUR-POLYBUTADIENE MIXTURES: A CONTRIBUTE FOR THE ELUCIDATION OF THE MECHAISM OF THE RUBBER SULPHUR VULCANIZATION
No full textTHE MECHANISM OF THE RUBBER SULPHUR VULCANIZATION: IONIC, FREE RADICAL OR CONCERTED MECHANISM?
No full textRADIATION INDUCED CROSSLINKING OF SBR BASED BLENDS CONTAINING A MODIFIED SIO2 FILLER WITH ENHANCED FREE RADICAL REACTIVITY
No full textRadiation Induced Double Grafting of Polybutadiene Olygomers and Styrene onto Silica: Characterization of the Materials and Mechanistic Studies
No full textIonizing radiations from a 60-Co source have been employed for inducing radical reactions finally leading to the grafting of unsaturated olygomers and vinyl monomers onto the surface and micropores of precipitated silica Zeosil 1165 (150–170m2/g). The target was to obtain modified silica with enhanced polar compatibility with respect to polybutadiene and styrene-butadiene copolymers rubber matrices and suited to favour the formation of chemically bound rubber in a vulcanization process. The latter property was expected to follow from the characteristics of free
radical reactivity arising from the unsaturations present in the organic coating. Three classes of modified silica have been prepared: A)silica coated with polybutadiene olygomers with Mn in the range 1000–5000 and having a different relative content of
1,4-cis, 1,4-trans and vinyl double bonds [1,2]; B)Silica coated with polybutadiene olygomers further modified by subsequent grafting of styrene monomer. The type A samples were obtained by g irradiation under vacuum of silica samples preimpregnated
with the oligomers in the dose range up to 30–200 kGy. Type B samples were obtained via three different steps as outlined in the scheme below:
SiO2(PB) SiO2 PB SiO2 PB OOH SiO2 PB O-PS
Fe2+
Sty
γ
298 K
vacuum air
298 K
γ
The characterization of the modified silica was carried on by elemental and thermogravimetric analysis, FTIR (diffuse reflectance), Raman spectroscopy, inverse gas chromatography (IGC), CP/MAS 29-Si NMR, granulometry and TEM microscopy
Investigation on the radiation induced vulcanization of silica-elastomer blends: physical properties and filler-elastomer reaction mechanisms
No full textRadiation curing of silica for silica-rubber composites
No full textThe functional modification of silica samples based on the reaction of “grafting” of polybutadiene olygomers carried out by γ-irradiation in the presence of air at room temperature has been investigated. The yield of grafted PB reaches a maximum at doses of about 30 kGy, then decreases as a consequence of the oxidative degradation. The reaction is accompanied by the build up of carbonyls and peroxides up to 0.1 moles/kg and it leads to a rapid consumption of the double bonds concentration as determined by both FTIR and Raman spectroscopy. The results of the EPR analysis are diagnostic of a mechanism of immobilization of the olygomer based on cross-linking of polybutadiene which is initiated by the SiO2 radiolytic species. Depending on the nature of the SiO2 species, the mechanism of initiation leads to immobilized PB either really grafted to the silica surface or simply physically absorbed
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