Caracteritzacio microestructural i mecanica de l'envelliment de nanocomposits de matriu poli(acrilonitrilbutadie) amb sio2 i contenint diferents agents protectors
- Autores: Francesc Andreu Mateu
- Directores de la Tesis: Xavier Colom Fajula (dir. tes.), Fernando Carrillo Navarrete (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2010
- Idioma: español
- Tribunal Calificador de la Tesis: Santiago Esplugas Vidal (presid.), Francisco Javier Cañavate (secret.), Montserrat López Mesas (voc.), Fernando González Lagunas (voc.), Juan José Suñol Martínez (voc.)
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- Resumen
An elastomer matrix based on acrylonitrilebutadiene, with a 20% of acrylonitrile and a content of 32 pphr of fine silica, besides other vulcanisation additives and different antioxidant and antiozoning agents has been degraded in different media: hot forced air at 140ºC, outstanding weathering and dry ultraviolet radiation.
Times of ageing have been : in hot forced air oven 12, 24, 48, 84, 120 and 240 hours; in outstanding weathering 25, 50, 100, 200 day; in dry UV radiation time have been 15, 25, 50, 72, 100, 200 hours. Other intermediate times have been used when it seemed appropriate.
The anti-ageing agents in study, IPPD, TMQ and Wingstay-L have been compared to samples without antioxidant in the same conditions and ageing times.
NBR elastomeric samples were prepared in two steps: mixing and vulcanisation. So, grinding and homogenisation of all ingredients followed by a vulcanisation; once the plaques became cool were shaped in samples according to ISO 37:1994.
The ageing study has been followed by means different ways: Infrared Spectroscopy by Transformed Fourier or FTIR and Attenuated Total Reflectance or FTIR-ATR, Strength-Strain tests, Hardness Shore, Degree of Cross-linking and Scanning Electronic Microscopy or SEM. To corroborate some data DSC or Differential Scanning Calorimetry and TGA or Thermal Gravimetric Analysis have been used.
All them have allowed knowing and in its case confirm, what are the structural and content changes that modify the mechanic characteristics of the composite. IPPD has showed best performance in UV exposures. IPPD extends the period of exposure during which the good mechanical properties of the nanocomposites were maintained. By the contrary, TMQ and above all Wingstay-L shows the best performance when moderate temperature is present, for instance, thermo- oxidation at 140ºC. With regard to structure, the presence of antioxidizers decreases the NBR's capacity for cross-linking. By means of ATR-FTIR spectroscopy it has been observed that the degradation process increases the volatility of the plasticizer in all the nanocomposites studied and at the same time, generates new unsaturated sites, which later become cross-lining nuclei. The extended exposure time generates various oxygen-bearing species, as has been observed by ATR-FTIR, and also allows the transition of the different configurations (cis, trans and vinyl) of polybutadiene (PBD). The antioxidant behaviour of IPPD is better than that of the other antioxidants whether moderate or high temperature are not present. IPPD improves mechanical properties in NBR submitted to UV. Wingstay-L shows the best performance in this NBR material submitted to temperature. Overall, elastomeric nanocomposites, with or without antioxidants, lost most of their mechanical properties after enough time of ageing. They degrade completely when they are subjected to these type of treatment over a long period. Thermal oxidation is faster than the dry UV radiation, and this one, faster than outdoor ageing.
Some chemical mechanisms of degrading have been proposed in each case.
