Oak Ridge National Laboratory,
Keywords: cellulose, sustainable, composite, additive manufacturing, nanocellulose
Summary:Use of a fibrillar solid phase in thermoplastic composites can not only improve material properties, but it can also improve their processibility, such as in additive manufacturing. Additive manufacturing is a complex layer by layer process that requires control of thermal, rheological and mechanical properties of the feedstock material, as well as thermal expansion and contraction behavior. Inorganic fibers such as carbon and glass fibers are widely used to reinforce thermoplastic resins; however, there is a growing interest to replace these high carbon footprint and embodied energy fibers with more sustainable alternatives. Cellulose fibers, which are the building blocks of the plants are great renewable alternatives for reinforcing thermoplastics. With their hierarchical structures, cellulose-based fibers can be utilized from nano-scale to mm-scale. Each size scale might offer different composite properties due to their different surface-to-volume ratio and fiber-polymer interaction. High aspect ratio and strong interfacial adhesion between the reinforcing material and the polymer matrix are critical for load transfer and composite properties. As the fiber size goes down especially to nano levels, agglomeration starts to become a problem, and the final form of the cellulose fibers/agglomerates determines the final composite mechanical properties. Either larger scale pulp/cellulose fibers, or cellulose nanofibrils (CNF) prepared via different drying methods such as spray drying and freeze drying, or surface treated CNFs, all lead to wide variety of polymer matrix interactions and composite properties. Even the same form of CNFs can have dramatically different impact on mechanical properties of different polymer matrices. Therefore, establishing the understanding of the relationship between the form and scale of cellulose fibers and the composite properties is critical for the development of sustainable bio-based fiber-reinforced composites with optimized material properties for different applications. Combined with the transition of the additive manufacturing process from being a prototyping technique to becoming an advanced manufacturing technology, these sustainable bio-based composites offer new innovative application areas from a precast concrete mold to a lightweight packaging mold, from a yacht roof mold to a 3D-printed house.