Creep and stress relaxation behavior of functionalized microcrystalline cellulose/epoxy composites

The study of silane-functionalized microcrystalline cellulose as reinforcement in polymeric composite materials have been increasing. Since polymer composites are constantly subjected to stress and deformation over time an in-depth understanding of the creep and stress relaxation behavior and mechanisms can be determinative to its final application. This work aims to show a comprehensive study regarding the influence of MCC silane-functionalized (MCC-Si) on the creep and stress relaxation behavior of MCC-epoxy composites. Two distinct composites with 5% of microcrystalline cellulose with and without functionalization (MCC 5% and MCC 5%-Si) were compared with the neat epoxy resin. The dispersion of the microcrystalline cellulose through the matrix was observed by X-ray microtomography. Creep behavior was investigated and discussed using Findley and Weibull models while stress relaxation by the Eyring model. In addition to the classic analytic methods, the artificial neural network approach was applied (ANN) to the curves. The MCC-Si had shown only a small trend to agglomerate due to good chemical compatibility due to the functionalization. The microcrystalline cellulose prevented the rapid creep strain as observed in the neat epoxy resin while the MCC-Si demonstrated small deformation among the samples in the vitreous region. However, in the elastomeric region the same behavior for all samples was observed. A better fit was obtained using the ANN approach than the classic analytical methods due to the higher capacity to model non-linear and complex behavior. In summary, MCC-Si enhanced the creep and stress relaxation resistance at glassy region by effectively improving the interfacial adhesion. At higher temperatures, this effect was not observed.