Desenvolvimento de nanocompósitos de borracha clorobutílica/borracha natural com montmorilonita para aplicação em revestimentos internos de pneus sem câmara de ar

Abstract

The aim of this work is combining the properties of chlorobutyl rubber (CIIR) and natural rubber (NR) in a binary blend for applications in tubeless tire inner liner, using organomodified clay - montmorillonite (OMMT) – as a filler, in order to improve barrier properties of the material. For this purpose, the blends should exhibit similar mechanical properties to the reference material, CIIR. Sixteen formulations have been prepared in an internal mixer using 5 and 10 phr (parts per hundred of rubber) of OMMT, in two binary blends: CIIR/NR 80/20 and 60/40. In all samples, the carbon black (CB) content was 50 phr. For comparison bases, CIIR and NR formulations were prepared under the same conditions. Furthermore, four nanocomposites have been prepared in absence of CB. These nanocomposites have presented the lowest results in all analyzis, likely due to the absence of carbon black in these formulations. However, in the presence of carbon black, X-ray diffraction (XRD) and scanning electron microscopy (SEM) results have indicated the intercalation of OMMT by the polymer chains and, hence, a better distribution for both blends. It was also observed a decrease in the Mooney viscosity and, therefore, an improvement in the processability, and a decrease in the curing enthalpy (ΔH), being more accentuated in the formulations containing superior amount of the NR, thus indicating the good interaction and interfacial adhesion between the nanoparticles and the polymer matrix in the presence of carbon black. With regard to the MH and ML no significant differences have been obtained as adding OMMT to the formulations with carbon black. However, the blends have showed a decrease in the maximum torque and this may be attributed to the modifier used in the clay, which acts as a lubricant, resulting in a decrease in the MH and ts2, which is interesting from a technological point of view. These nanocomposites have also presented conservation of the hardness, tensile strength and modulus values at 100 % elongation. On the other hand, the degradation of the polymer matrix in the presence of quaternary ammonium salts has had a negative effect on the thermal performance of the nanocomposites. The barrier properties of blends in the presence of OMMT e CB have not shown significant improvement. However, the good dispersion of the carbon black, the conservation of the property barrier, modulus at 100% and tensile strength before and after the aging, mainly in the system with superior amount of NR (CIIR/NR 60/40), indicate that the blends may be used to the tubeless tire inner liner, without significant change in the mechanical and barrier properties in relation to the reference material, CIIR/CB 100/50, and decreasing the cost of the final product, since the CIIR is 80% more expensive than the NR.