In this study, the hybrid effect of nanocellulose/carbon nanotube (NCC/CNT) reinforcement on natural rubber (NR) nanocomposites was investigated. To this end, three series of NR nanocomposites were prepared: NCC/NR, CNT/NR and NCC/CNT/NR. First, the nanocomposites morphology and the filler–rubber interactions were studied using scanning electron microscopy (SEM) and the swelling behavior in toluene, respectively. The results showed that the presence of NCC improved the NCC/CNT hybrid filler dispersion forming a 3D network, while the presence of CNT increased the filler–matrix interaction. The curing results also confirmed that the degree of crosslinking increased when hybrid fillers were used, but the curing time was not modified. In addition, it was observed that using a NCC/CNT hybrid system led to superior mechanical properties, dynamic mechanical properties and thermal conductivity than each material used separately. When 10 phr hybrid filler (with a filler ratio of 1) was added to NR, the tensile strength, modulus at 300% elongation (M300), storage modulus at 10% strain and thermal conductivity were all increased by 57%, 137%, 120%, and 30%, respectively. The results also showed that the NR nanocomposites properties can be controlled by tuning the NCC/CNT filler ratio.

In recent years, cellulose fibers have attracted considerable attention as biofillers for natural rubber (NR) composites. However, neat cellulose cannot be used as a substitute for conventional fillers due to its poor compatibility with NR. Therefore, a new surface treatment via maleic anhydride grafted to polyisoprene (MAPI) in solution was developed to improve the filler–matrix interaction. Different contents of carbon black (CB) and cellulose fibers (before and after modification) were used as a hybrid filler system to investigate the possibility of CB substitution in NR composites. First, contact angle, Fourier transformed infrared spectrometry (FTIR), and scanning electron microscopy (SEM) techniques were used to confirm the successful cellulose surface treatment. Second, morphological analysis, Payne effect, and swelling behavior of the rubber compounds in toluene confirmed the effect of cellulose treatment on improving the interfacial filler–matrix adhesion. Finally, the results showed that the composite filled with 20 phr modified cellulose and 20 phr CB (50% replacement of CB) exhibited even better results than the composite filled with 40 phr of CB, since the tensile strength was only 7% lower, but the elongation at break, tensile modulus at 100%, and storage modulus at 25 °C were respectively 35%, 24%, and 22% higher.

In this study, a novel hybrid system containing lignin and cellulose nanocrystals (CNC) is developed to reinforce natural rubber (NR) and produce high-performance biocomposites. Firstly, the effect of lignin content in lignin/NR biocomposites is investigated. Despite lignin's advantages as an inexpensive biopolymer, its addition to NR results in longer cure time, reduced tensile strength and increased loss factor (tan δ); that is, lignin addition has a negligible reinforcing effect compared to conventional fillers, such as carbon black (CB). On the other hand, adding only 7.5