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Wood and lignocellulosic-based material components are explored in this review as functional additives and reinforcements in composites for extrusion-based additive manufacturing (AM) or 3D printing. The motivation for using these sustainable alternatives in 3D printing includes enhancing material properties of the resulting printed parts, while providing a green alternative to carbon or glass filled polymer matrices, all at reduced material costs. Previous review articles on this topic have focused only on introducing the use of natural fillers with material extrusion AM and discussion of their subsequent material properties. This review not only discusses the present state of materials extrusion AM using natural filler-based composites but will also fill in the knowledge gap regarding state-of-the-art applications of these materials. Emphasis will also be placed on addressing the challenges associated with 3D printing using these materials, including use with large-scale manufacturing, while providing insight to overcome these issues in the future.

Cellulose nanofibrils (CNFs) have been widely used as a nanofiller for polymer composite reinforcement due to their excellent mechanical properties. However, CNF is produced in water and needs to be dried prior to use in composite materials. The presence of hydroxyl groups on the surface of CNF creates strong hydrogen bonding that makes it difficult and costly to dry. Additionally, the hydrophilicity at the fiber surface results in agglomeration of CNFs within many polymer matrices. In this study, chitosan (CS) was co-precipitated with CNF to produce a dual-bonding filler for use in poly (lactic acid) (PLA) composites. CS promotes improved interfacial interaction within the polymer matrix by forming strong hydrogen bonds with the CNF and potential covalent bonds with the PLA. The results confirmed that the addition of a small amount of CS significantly improved the mechanical properties compared to PLA + CNF composites and neat PLA. The detailed study of the PLA + CNF/CS composites reveals the synergetic effect of the hydrogen and covalent bonding mechanism for PLA reinforcement. Graphical abstract

Wind turbine blades are highly engineered structures designed to face temperature extremes and high winds. However, erosion of the blade's leading edge and subsequent repair remains a significant and costly challenge for the wind energy industry. Repair of these leading edges can lead to large amounts of downtime for the turbine and significant operational inefficiencies. In this work, the strength of adhesion and healing ability of a commercially available vitrimer (Mallinda's VITRIMAX) was compared to that of a thermoplastic resin, which has previously been demonstrated in wind energy applications (Arkema's Elium) to evaluate their efficacy as surface coatings for wind turbine blades, particularly their leading edges. Vitrimers are a class of inherently reprocessable thermosets, and it was theorized that vitrimer‐based leading edge coatings could enable more robust and efficient wind turbine blades with decreased operational downtime and safer maintenance practices. It was found that the VITRIMAX adhered better to the wind blades' surfaces than both the manufacturer's paint and Elium, with increases in pull‐off strength of adhesion ranging from 24% to 83% above that of the original paint. Furthermore, the VITRIMAX adhered strongly to the underlying composite of each blade with strength of adhesion values increasing in ranges from 42% to 97% above that of the original paint. Finally, the vitrimer coating showed an 88% decrease in surface roughness compared to end‐of‐life blade materials, and initial healing demonstrations in which coatings were manually scratched and subsequently healed exhibited an ~84.5% decrease in scratch depths.

Lignin-containing cellulose nanofibrils (LCNFs) are mainly produced commercially from treated wood pulp, which can decrease some of the carbon-negative benefits of utilizing biomass feedstock. In this work, LCNFs are prepared from non-wood feedstocks, including agricultural residues such as hemp, wheat straw, and flax. These feedstocks allowed for the preparation of LCNFs with a variety of properties, including tailored hydrophobicity. The feedstocks and their subsequent LCNFs are extensively characterized to determine the roles that feedstocks play on the morphology and properties of their resultant LCNFs. The LCNFs were then incorporated into paper handsheets to study their usefulness in papermaking applications, which indicated good potential for the use of wheat straw LCNFs as a surface additive to improve the oil resistance coating.

Commodity polymers are used in every aspect of daily life, and most of these polymeric materials are synthesized using petroleum-derived sources. There are direct environmental consequences to this petroleum dependence including greenhouse gas emissions and climate change. Biomass-based polymers show promise for the mitigation on negative environmental impact, in comparison with petroleum-derived counterparts. However, some biopolymers suffer from low chain entanglement due to bulky or long side chain structures, resulting in poor mechanical properties. In this dissertation work, macromolecular engineering is used to design biomass-derived polymers featuring a variety of structures and functionalities. Additionally, biopolymer properties (including thermomechanical enhancement) and applications such as polymer coatings and stimuli-responsive materials are discussed. The first part of this dissertation focuses on strategies to overcome poor chain entanglement. Through macromolecular engineering, resultant polymer microstructure can be controlled to produce biomass-based polymers with industrially competitive thermomechanical properties. Specifically, supramolecular interactions are introduced to facilitate chain entanglement of polymers from biomass, which exhibit impressive enhancement of mechanical properties. In Chapter 2,, hydrogen-bonding (H-bonding) is used to enhance interactions between two complementary polymers. One polymer contains pendant acid groups as H-bonding donors that interact with H-bonding acceptor polymers such as poly(4-vinylpyridine). The blending results in well-entangled polymer chains that can dissipate stress and provide enhancement in tensile strength and toughness. While in Chapter 3, metal-ligand coordination is used to promote entanglements within plant oil-derived copolymers. Metal-ligand coordination imparts unique and promising properties on these materials. The stimuli-responsive properties of both materials are also discussed. The second part of this dissertation focuses on applications of biomass-based polymeric materials. In Chapter 4, focus switches to the development of an industrially relevant free-radical emulsion polymerization approach. A series of copolymers are synthesized featuring a plant oil-derived methacrylate copolymerized with styrene, methyl methacrylate, and butyl acrylate. Finally, a simple oxidative crosslinking strategy is used to enhance mechanical properties and provide strong, tough materials for potential coating applications. In Chapter 5, epoxy resin nanocomposites are featured for their use as potential shape memory materials. Soybean-oil derived polymers are polymerized onto cellulose nanocrystals (CNCs) using a grafting-from SI-ATRP strategy with subsequent crosslinking using amine-catalyzed anhydride-epoxy curing. The strength of resulting epoxy resins provided an optimal permanent network allowing for good shape recovery, while the tunable glass transition temperature allowed for ease in shape fixity. Finally, in Chapter 6, the summary and conclusions are given. Additionally, novel strategies for future work in overcoming poor entanglement for other biomass-derived polymers are presented.