ABSTRACT:Rubber elements, which usually form a major part of different isolators of vibrations, are generally easily swelled by oils, greases, or fuels. This leads to meaningful changes of their mechanical characteristics and shortening of durability of rubber components in service. The influence of the semisynthetic motor oil on mechanical and, particularly, dynamic properties of swelled vulcanizates of the polar diene rubber, chloroprene (CR) and acrylonitrilebutadiene (NBR), is estimated in this article. These elastomers, as is widely known, are resistant to the mineral oils absorption. However, our investigations showed that even a small degree of swelling of the vulcanizates causes decrease of their mechanical properties and considerable changes of the dynamic characteristics of the samples. The obtained results have shown the need to take into account the environment in which isolators of vibrations and dampers have worked, while designing the suitable composition of rubber compounds.

W³aoeciwooeci mechaniczne wulkanizatów mieszanin NR/NBR spêcznionych olejem silnikowymStreszczenie -Zbadano wp³yw ilooeci sadzy i NBR w wulkanizatach NR/NBR (NBR -kauczuk butadienowo-akrylonitrylowy, NR -kauczuk naturalny) na ich w³aoeciwooeci mechaniczne i odpornooeae na dzia³anie pó³synetycznego oleju silnikowego. Zaobserwowany wp³yw sk³adu na te w³aoeciwooeci wulkanizatów zinterpretowano na podstawie badañ morfologii metod¹ SEM i oceny wzajemnych oddzia³ywañ pomiêdzy sk³adnikami uk³adu. S³owa kluczowe: wulkanizaty, mieszaniny NR/NBR, sadza, odpornooeae na dzia³anie oleju, w³aoeciwooeci mechaniczne, oddzia³ywania w uk³adach elastomer-nape³niacz. MECHANICAL PROPERTIES OF VULCANIZATES OF NR/NBR BLENDS SWELLED BY MOTOR OILSummary -The effects of carbon black amount (up to 70 phr) and NBR content in NR/NBR vulcanizates (NBR -nitrile-butadiene rubber, NR -natural rubber) on their mechanical properties and resistance to motor oil were investigated. As well the vulcanizates of individual rubbers were tested. All systems were characterized using vulcametric method (Table 1). As a result of equilibrium swelling of NR vulcanizates with oil, mechanical properties drastically deteriorated and this deterioration was directly proportional to the degree of oil absorption, lowering with carbon black content (Table 2). What concerns oil-extended NBR vulcanizates neither weight gain nor increase in volume of the samples were observed in the whole range of carbon black content. However, small changes in hardness and strength (more visible when vulcanizates contained smaller amounts of filler) show that limited oil absorption by NBR vulcanizates occurs (balanced with elution of the system components) (Table 3). Swelling degree of NR/NBR blends vulcanizates depend both on NBR and carbon black contents. Swelling degree of the systems containing 50 phr of NBR and up to 30 phr of carbon black reached still rather high values (Table 4). For vulcanizates containing 50-70 phr of carbon black it was four times lower than in case of NR samples with the same carbon black content while tensile strength decreased only 24 %. NR/NBR vulcanizates containing 75 phr of NBR and 30-70 phr of carbon black show good resistance to oil (Table 5). Mechanical properties of these vulcanizates after swelling are practically the same as before. The observed effect of vulcanizate composition on the properties tested was interpreted on the basis of morphology investigations by SEM method (Fig. 1 and 2).