The effect of modified Cu(II) kaolinite on interactions with rubberizing components

Abstract The interactions of modified Cu(II) kaolinite with rubberizing components, such as stearic acid (SA), zinc oxide (ZnO), sulphur (S) and benzothiazole (Btz) after heating to 150 °C cure temperature were investigated. More over the given prepared modified kaolinite was used for investigation of its effect in model rubber composites. Commercially calcined kaolinite (Kaol) was chemically treated using 0.5 M copper acetate solution in presence of NaOH solution. The modified resulting sample was designated as K Cu sample. Different techniques such as Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction patterns analysis (XRD), thermogravimetry/differential thermal analysis (TG/DTA) and scanning electron microscopy (SEM) were used to characterize kaolinite and K Cu samples. The different techniques (mainly FTIR an XRD) demonstrated that the copper acetate treatment of kaolinite resulted in formation of monohydrate copper hydroxy acetate complex, which influenced the clay surface. XRD pattern and FTIR spectrum of the modified K Cu proved that copper acetate treatment did not affect the clay structure significantly. High-temperature X-ray diffraction patterns analysis (HTXRD) was also used for investigate the interactions of modified K Cu with rubberizing components. Heating process of K Cu and SA without or with ZnO caused the formation of copper stearate and zinc stearate respectively and it let to the occurrence of the stretching vibrations of the carboxyl group (νCOO−). K-Cu2(OH)3Ac·H2O complex on the clay surface influenced the mutual interaction with benzothiazole and it can be seen in IR spectra involving stretching vibrations (νCH) of aromatic ring and the stretching vibrations of functional groups ν(N=C S) and ν(C=N). Finally, for the supplementation of the results, the model rubber composites, filled with kaolinite and K Cu and ranged 5, 10 and 20 phr, were prepared. The effect of modified kaolinite on the curing characteristics (minimum torque – ML, maximum torque – MH, optimal vulcanization time – t90, coefficient of vulcanization rate – Rv) and mechanical properties (tensile strength at break – TSb, elongation at break – Eb and hardness) in sulphur-cured natural rubber (NR) composites was investigated. A low viscosity of the NR compounds was achieved throughout the kaolinite and K Cu fillers used. The cure time increased by K Cu dosing in amount of 10 and 20 phr. The decrease of the maximum torque (MH) value indicates a lower stiffness as well as the viscosity of the mixture at the end of vulcanization. However, the mechanical properties of the vulcanizates with K Cu showed significant improvement of TSb and Eb, compared with standard and mixtures with non-modified kaolinite. The modified Cu(II) form of kaolinite had positive effect on the properties of rubber compounds in amount of 5 and 10 phr.