Increasing research activity on cellulose nanofibril-based materials provides great opportunities for novel, scalable manufacturing approaches. Cellulose nanofibrils (CNFs) are typically processed as aqueous suspensions because of their hydrophilic nature. One of the major manufacturing challenges is to obtain dry CNFs while maintaining their nano-scale dimensions. Four methods were examined to dry cellulose nanocrystal and nanofibrillated cellulose suspensions: (1) oven drying, (2) freeze drying (FD), (3) supercritical drying (SCD), and (4) spray-drying (SD). The particle size and morphology of the CNFs were determined via dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and morphological analysis. SCD preserved the nano-scale dimensions of the cellulose nanofibrils. FD formed ribbon-like structures of the CNFs with nano-scale thicknesses. Width and length were observed in tens to hundreds of microns. SD formed particles with a size distribution ranging from nanometer to several microns. Spray-drying is proposed as a technically suitable manufacturing process to dry CNF suspensions.

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Wood-plastic composites (WPCs) are a form of composite combining wood-based elements with polymers. The processes for manufacturing WPCs include extrusion, injection molding, and compression molding or thermoforming (pressing). Newer manufacturing processes for WPCs include additive manufacturing via fused layer modeling and laser sintering. An important constraint for polymers used in WPCs is requiring process conditions (melt temperature, pressure) that will not thermally degrade the wood filler. Wood degrades around 220°C; thus, generalpurpose polymers like polyethylene and poly vinyl chloride are typically used for manufacturing WPCs. Wood fibers are inherently hydrophilic because of the hydroxyl groups contained in the cellulose and hemicellulose molecular chains. Thus, modification of the wood fiber via chemical or physical treatments is very critical to making improved WPCs. The most abundant profiles made from wood-plastic composites are boards or lumber used in outdoor decking applications. Although early WPC products were mainly extruded for profiled sections, nowadays, many injected parts made of WPC are being introduced for various industries, including electrical casings, packaging, daily living supplies, and civil engineering applications. Mold and mildew and color fading of WPCs tend to be the durability issues of prime importance for WPCs. Most recent research on WPC durability focuses on studies to better understand the mechanisms contributing to various degradation issues as well as methods to improve durability. Most WPC products in the USA are utilized in building materials with few exceptions for residential and commercial building applications, which means that building codes are the most important national rules for the WPC manufacturers. New developments are being made especially in the area of nano additives for WPCs including nanocellulose. Recently, the trend of patent registrations for WPCs has shifted to new products or applications instead of the materials itself.

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The utilization of cellulose in reinforcing engineering thermoplastics through melt compounding processes is an argumentative topic in the natural fiber research community. Three different cellulosic materials were used to reinforce polyamide 6 (PA6) at three loading levels (2.5, 5 and 10 % by weight): (1) microcrystalline cellulose, (2) spray-dried cellulose nanofibrils (CNFs) and (3) spray-dried cellulose nanocrystals (CNCs). The particle size, morphology, and thermostability of cellulose were determined using laser diffraction, scanning electron microscopy (SEM), and thermogravimetric analysis. Compounding of cellulose with PA6 was conducted using a batch mixer at 232°C and testing samples were produced using an injection molder at 270°C. Slight mass loss of cellulose was observed at 232°C while serious thermal degradation occurred at 270°C. No serious thermal degradation of cellulose was observed in the composites because the cellulose materials were exposed to injection molding processing temperatures for a short time period. The mechanical testing results indicated that tensile modulus and strength of the composites were improved by adding cellulose while cellulose had negligible effect on the flexural properties. Impact strength decreased significantly by adding cellulose because of the poor distribution of cellulose particles throughout the matrix using the batch mixing process. Optimized mixing with improved distribution of cellulose are necessary to explore the potential reinforcing effect of cellulose, especially CNF and CNC in PA6. The SEM micrographs showed that there were no agglomerations among the cellulose particles, indicating that spray-dried cellulose materials could be suitable reinforcements in polymer-based composites.