Interfacial behavior of lignin containing cellulose nanofibrils (LCNFs) and their impact on composite materials
Type of DegreePhD Dissertation
Forestry and Wildlife Science
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Over the last decade, the utilization of nanocellulose for novel applications has positioned this renewable source as a promising alternative substitution for petroleum-based materials. In an attempt to utilize and incorporate lignocellulosic materials from different raw materials and varying chemical compositions into composite materials, it is crucial to understand the interfacial interactions between the different chemical components of such composites. These interactions will dictate the behavior of the nanocellulosic suspensions, and they will directly impact the intrinsic properties of the resulting materials. Thus, understanding the fundamental physico-chemistry of the raw material and how they influence properties such as morphology, chemical composition, thermal degradation, and surface charge will offer a better understanding of the performance of the products. Through this dissertation, specific emphasis was made on the rheological behavior of the nanocellulosic suspensions. Rheology provides insight into interfacial interactions and knowing the flow characteristic of the materials might help during the handling and processing. Chapter 1 of the dissertation is a literature review focused on the interfacial interactions between different chemical components in lignocellulosic materials. Chapter 2 states the objectives and hypotheses consider in each chapter. The nature of the raw material and the processes used to produce the nanofibers and how those affect the viscoelastic behavior of the samples is presented in Chapter 3. Furthermore, focusing on a single raw material, Chapter 4 is centered on the rheological study of four different softwood LCNFs samples with lignin contents from <1.0 to 16.8%. Particularly in Chapter 5, the analysis of the interfacial interactions between wood adhesives and LCNF suspensions was emphasized. After investigating the fundamental properties of those nanocellulosic suspensions, their incorporation into a composite material to improve properties such as adhesion, wettability, and mechanical performance was studied. Along this dissertation, the interfacial interactions using a quartz crystal microbalance with dissipation monitoring (QCM-D) and surface free energy analyzed by contact angle (CA) measurements were studied. These techniques were supported with the fundamental study of the samples in terms of morphology, using atomic force microscopy (AFM) and scanning electron microscopy (SEM); viscoelastic behavior; chemical composition, using Fourier transform infrared spectroscopy (FT-IR); thermal behavior by thermal gravimetric analysis (TGA), crystallinity by X-ray powder diffraction (XRD), surface charge density, and zeta potential by dynamic light scattering (DLS). Together these results highlight the importance of understanding the atomic and molecular interactions in the nanocellulosic systems to take full advantage of the biomass. The use of the explained phenomena within this dissertation opens a wide range of possible materials and applications that can be targeted with these renewable and sustainable materials. As a result, the use of forest and agricultural by-products can be enhanced, increasing its potential value, and providing a more environmentally friendly alternative to displace fossil-based polymers.