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Development of Biodiesel-Resistant Nitrile Rubber Compositions

Fossil fuels are the most commonly used sources of energy in the world. However, many reasons have pushed the society to search for alternative fuels to meet the world’s energy demands without increasing environmental damage. Biodiesel has appeared to be an excellent replacement for petroleum diesel fuels because of its comparable physical properties in addition to its improved environmental benefits, such as low pollutant gas emissions, nontoxicity, renewability, and biodegradability. Nonetheless, biodiesel and petroleum diesel differ greatly with respect to their chemical properties. Therefore, the compatibility of the materials, which are commonly employed in contact with diesel, must also be assured for biodiesel that has been obtained from different sources. The main recommendation found in the literature is to withdraw nitrile rubber (NBR)-based articles from biodiesel applications. However, no effort has been made to better understand the interaction between nitrile rubber and biodiesel or to propose changes in and improvements to the production of nitrile rubber articles. This Thesis was devoted to evaluating the resistance of different types of NBR and different NBR formulations to biodiesel. First, nitrile rubbers with different acrylonitrile contents (33 and 45%), and carboxylated nitrile rubber (XNBR) with a 28% of acrylonitrile content were tested with soybean biodiesel. The preliminary results showed that an increase in acrylonitrile content increased the rubber resistance to biodiesel. Moreover, despite its low acrylonitrile content (28%), the carbolyxated nitrile rubber composition had almost the same performance as the NBR composition with high acrylonitrile content. This behaviour was probably due to the different types of crosslink network that XNBR was able to form during the vulcanisation process. Second, new formulations were prepared using high acrylonitrile-content NBR by employing a two-level experimental design in which the amounts of two different accelerators (tetramethylthiuram disulphide-TMTD and N-cyclohexylbenzothiazole-2-sulphenamide - CBS), and the amount of sulphur were varied to achieve different types of vulcanisation systems (conventional, semi-efficient, and efficient).

Statistically, the tensile strengths of the prepared compositions were influenced by TMTD, sulphur and the combination of TMTD and sulphur. Hardness was affected by the amount of TMTD, sulphur and the combination of CBS and sulphur, whereas elongation at break was affected by TMTD, sulphur, and the combination of both accelerators. The crosslink density was influenced only by the amounts of TMTD and sulphur. Furthermore, the choice of the accelerator played an important role on the resistance of nitrile rubber to biodiesel, and TMTD was found to be more effective than CBS with regards to the mechanical resistance to biodiesel. The crosslink density was not the only important factor with respect to the resistance. Nevertheless, dynamic mechanical thermal analyses showed that compositions prepared with an efficient vulcanisation system experienced chemical degradation of the crosslink network later than those prepared with conventional or semi-efficient vulcanisation systems. Based on these results, one could infer that nitrile rubber resistance can be still improved to meet the minimum requirements for these materials to be used in applications in which they will be in contact with biodiesel.

Lesen Sie die deutsche Zusammenfassung auf Kunststoffe.de
Author
 Felipe Nunes Linhares

Felipe Nunes Linhares
Lehrstuhl für Polymere Werkstoffe
Universität Bayreuth

Information

Free keywords: Nitrile rubber, Biodiesel, Formulation, Compatibility, Curing system
Institute / chair: Fakultät für Ingenieurwissenschaften der Universität Bayreuth / Institute of Chemistry at Rio de Janeiro State University
Language: English
Technical consultant for expert services: Prof. Dr.-Ing. Volker Altstädt (Betreuer), Prof. Dr. Cristina Russi Guimarães Furtado
Publication year: 2016
Provider: Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK) / Kunststoffe.de

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