چكيده به لاتين
In the first part, devulcanizations of nitrile butadiene rubber (NBR) by mechanical, mechano-chemical, mechano-thermo-chemical and mechano-radio-chemical methods with different chemical agents including Dichlorobenzoyl peroxide (DCBP), N-cyclohexyl 2-benzothiazole sulfenamide (CBS), tetramethyl thiuram disulfide (TMTD), VitaX and without chemical agent (only mechanical devulcanization with two roll mill) were done. Where the effect of heat on devulcanization quality has been considered, electric ovens and microwaves were used to generate heat, and various properties including the time of formation on two roll mill, the crosslink density by Flory-Rehner and Sol Content were measured. Then, after adding about ten percent of virgin polymer, plasticizer and sulfur to the devulcanized product, the samples were revulcanized in the mold, and physical and mechanical properties such as hardness, tensile strength, elongation at break, Young's modulus, resilience and also rheometric MDR were measured. In this section, self-made rubber powders were used so that the quality of the products could be monitored based on the changes in the properties. It was observed that devulcanization without chemical agents had low efficiency. The results of devulcanization with Vitax were significantly better than other chemical agents. With the use of Vitax and heat, the tensile strength has improved up to 29% of the original virgin sample's tensile strength, while only 10% of the elongation percentage has decreased. The formation time on two roll mill with Vitax and heat was reduced by 90%, which increases the importance of commercial production with this method. The results showed very good result with the mechano-radio-chemical method. The low amount of devulcanization along with excellent tensile properties, indicated partial devulcanization. In the second part, by making rubber samples based on the formula used in the first stage, rubber samples with defferent molecular masses and different crosslink densities were made, and by creating hypothetical devulcanization, the changes in physical and mechanical properties were investigated and an attempt was made to monitor devulcanization quality, a faster and easier and less error method than Horix should be suggested. It was concluded that hardness and modulus 100% results have many capabilities for devulcanization monitoring. It was observed that if 187 crosslinks break for every 10 polymer molecules, one shore A of hardness decreases, and if one intramolecular bond breaks among 10 polymer molecules, 1.3 shore A of hardness decreases. Therefore, based on the hardness property, the effect of breaking an intramolecular bond is 250 times the effect of breaking a crosslink. Similar results were obtained for 100% modulus property. Based on the modulus property of 100%, the breaking effect of an intramolecular bond is 300 times the breaking effect of a crosslink.
