Effect of Cross-linked Sodium Carboxymethyl Cellulose Water-Swelling Agent on Elastomer Properties
The intensification of oil production and the development of new well facilities highlight the need to create rubber compound formulations capable of controlled swelling and long-term retention of operational characteristics in aggressive environments. One of the most common water-swelling reagents (WSR), due to its cost and effectiveness in swelling capacity in water and aqueous salt solutions, is sodium carboxymethyl cellulose (Na-CMC). However, a problem exists with the leaching of WSR from the elastomer matrix, leading to a reduction in product volume, which may result in a loss of interlayer flow isolation integrity. One potential solution to this problem is the use of cross-linked WSRs. Their three-dimensional network structure should effectively retain the absorbed fluid, ensuring long-term stability of the material's properties without significant loss in swelling capacity. Thus, the aim of this work is to study the influence of cross-linked Na-CMC on the properties of the resulting elastomers. The subject of the study was rubber compounds based on BNKS-28AH nitrile rubber. A commercially produced cross-linked form of sodium carboxymethyl cellulose was introduced as the water-swelling agent in an amount of 100 phr. Two vulcanization systems were applied: a conventional system (sulfur with the accelerator sulfenamide C (CBS)) and an efficient system (CBS, thiuram D (TMTD) and 4,4'-dithiodimorpholine). Processing and interpretation of the obtained results established that, as expected, the use of the cross-linked form based on Na-CMC as a WSR slightly reduces (by 50-70%) the maximum degree of swelling. However, no noticeable effect of WSR leaching was observed. This is likely due to the structural features of the cross-linked Na-CMC, where the number of sodium ions is reduced. It should be noted that in samples obtained using the efficient vulcanization system, increased gel formation is observed upon exposure at elevated temperature. An assessment of the physico-mechanical characteristics of standard rubber samples in the swollen state after a 14-day exposure in water and sodium chloride solution was also conducted. The test results showed that the tensile strength after swelling in water is 7-8 MPa, and in the salt solution 8-10 MPa, indicating the retention of satisfactory strength characteristics for swelling elastomers.