RHEOLOGICAL BEHAVIOR OF NANOCELLULOSE SUSPENSIONS AND NANOCELLULOSE REINFORCED COMPOSITES

VERONICA MUCCI; NORMA E. MARCOVICH; MIRTA I. ARANGUREN

Elastomeric Nanocellulose Composites

Woodhead Publishing

Lugar: Sawston; Año: 2024; p. 349 - 363

Elastomeric materials with covalent, physical and/or associative “crosslinking” linkagesshow viscoelastic responses that can be linear or nonlinear depending on therange of deformation considered in the assay. The addition of the nanocellulose (NC)usually results in the improvement of the viscoelastic response, generally increasingthe elastic contribution. Several of the responses linked to specific tests (such as DMAor creep) are presented in other chapters of the book. In this chapter, the focus ofthe rheological approach is the analysis of the results obtained from other less usualtests (steady shear and frequency oscillatory scan tests as well as start-up of the steadyshear response) and the response of the uncured mixtures that eventually lead to thefinal elastomer. Moreover, a brief presentation of the rheological behavior of NC suspensionsis also initially included as a basis to understand the effect of these nanoparticles(NPs) in a continuous media.NCs are a family of NPs with different characteristics. Microfibrillated cellulose(MFC) is usually obtained by mechanical methods and/or homogenization; simultaneousapplication of chemical or enzymatic treatments can be used in combinationwith the above to obtain nanofibrillated cellulose (NFC) leading to the desired reductionof diameter that is accompanied by the reduction of the length [1–6]. Furtheracid (and occasionally 2,2,6,6-tetramethylpiperidine-1-oxyl, TEMPO treatment)and sonication is used to obtain shorter, more rigid and thinner cellulose nanocrystals(CNCs) [7]. Marginal and ill-defined differences separate MFC from NFC andare based on the size of the NPs. Usually, diameters of approximately 100 nm andlengths on the order of 1 to several microns are reported for MFC, while diametersof approximately 20–100 nm are common in NFC and sometimes their mixtureis also used. Both NC structures comprise amorphous-flexible and crystalline-rigidsegments, overall showing flexibility as one of their distinctive characteristics. Onthe other hand, CNCs are essentially rigid nanorods, mostly formed by the crystallinesegments in cellulose and showing no flexibility; with lengths between 100and 300 nm and smaller diameters, between 5 and 20 nm. Bacterial cellulose (BC),a frequently used NC excreted by some bacteria, consists of very pure ribbon-like nanofibers that can be used as such (long flexible fibers) or defibrillated to obtain thinnernanofibers, and also in the form of CNC when acid hydrolysis is applied. This lastform has not been used as much as the long flexible BC fibrils.Any of these forms can be selected and have been used in the reinforcement ofdifferent polymers, including elastomeric nanocomposites.The original NP suspensions, as well as the elastomeric composites, can presentviscoelastic behavior. In this chapter, the liquid-like response of the materials will becovered with particular focus on the results of the steady shear tests, start-up of thesteady shear response, complex viscosity and frequency oscillatory scan tests appliedto the NC suspensions and in mixtures of these NPs already incorporated in reactivemonomers (in a prevulcanization stage), rubber latexes and in molten thermoplasticelastomers.