In Situ Silanization of Ligno-Cellulosic Microfibers Derived from Industrial Waste to Enhance Mechanical Properties of Natural Rubber Compounds

Nowadays, the use of materials from renewable resources, such as agricultural waste and forest residues, has increased. In this work, industrial waste recovered from a recycled paper/cardboard company was mechanically refined to obtain ligno-cellulosic microfibers (LCMFs). The obtained LCMFs were well characterized and chemically modified in situ together with natural rubber through silanization. The effect of in situ silanizated LCMFs, by using (3-triethoxysilylpropyl) tetrasulfide (Si69) as a silane coupling agent, on natural rubber (NR) compound properties was studied. The NR compound with silanizated LCMFs at 2.5 phr of Si69 (NR MF Si2) increased NR stiffness significantly. For example, the 300% modulus of NR MF Si2 was around 9 units higher than that of NR. The physical–mechanical properties, crosslink density, curing behavior, infrared spectroscopy, and microscopy of the compounds were studied to confirm the in situ silanization of the microfibers and its reinforcement effect on the NR matrix. The storage modulus (E′) obtained from Dynamic Mechanical Analysis suggested that the silanizated samples presented an uneven crosslinking, but it was enough to stiffen the NR chains.