Cellulose nanomaterials (CNs) are an emerging class of materials with numerous potential applications, including as additives or reinforcements for thermoplastics. Unfortunately, the preparation of CNs typically results in dilute, aqueous suspensions, and the lack of efficient water removal methods has hindered commercialization. However, water may also present opportunities for improving overall efficiencies if its potential is better understood and if it is better managed through the various stages of CN and composite production. Wet compounding represents one such possible opportunity by leveraging water’s ability to aid in CN dispersion, act as a transport medium for metering and feeding of CNs, plasticize some polymers, or potentially facilitate the preparation of CNs during compounding. However, there are also considerable challenges and much investigation remains. Here, we review various wet compounding approaches used in the preparation of cellulose nanocomposites as well as the related concepts of wet feeding and wet extrusion fibrillation of cellulose. We also discuss potential opportunities, remaining challenges, and research and development needs with the ultimate goal of developing a more integrated approach to cellulose nanocomposite preparation and a more sophisticated understanding of water’s role in the compounding process.

Cellulose nanomaterials have been demonstrated to be excellent barriers against grease, oxygen, and other vapors, but their implementation in packaging materials is challenging because of numerous technical and practical challenges. In this work, the oxygen, air, grease, and heptane barrier performance of copy papers coated with cellulose nanocrystals (CNCs), oxidized cellulose nanofibrils (TOCNs), and carboxymethyl cellulose (CMC) weas examined. The effects of different materials and processing conditions were evaluated for their impacts on the resulting barrier properties. TOCN coatings demonstrated significantly better barrier properties than CNC and CMC coatings due to the long-range networked structure of TOCN suspensions eliciting enhanced film formation at the paper surface. Neat coatings of nanocellulose did not readily result in strong oxygen barriers, but the addition of CMC and/or an additional waterborne water barrier coating was found to result in oxygen barriers suitable for packaging applications (1 cm³/m²·day transmission at low humidity with a 10 g/m² coating). Cast films and thick coatings of CMC were good barriers to oxygen, grease, and air, and its addition to cellulose nanomaterial suspensions aided the coating process and reduced coating defects. In all cases, the incorporation of additional processing aids or coatings was necessary to achieve suitable barrier properties. However, maintaining the strong barrier properties of nanocellulose coatings after creasing remains challenging.

This paper introduced a simple, efficient method to prepare mechanically strong lignin-based foams (lignofoams) with open-cell structures using a facile baking technique. The self-expansion of lignin occurred without any additional chemical blowing agents, foaming agents, plasticizers, or lubricants. During heating, kraft lignin softened, and the internal water, either initially adsorbed or generated in situ through the dehydration of hydroxyl groups, acted as a natural blowing agent for foaming a porous foam structure. Incorporating a small amount of polypropylene (PP) enhanced mechanical properties by coating the inner walls of open cells. The porous, softened composite was then cooled to room temperature and solidified into the self-expanded lignofoam. The resulting lignofoams exhibited tunable densities ranging from 0.21 to 0.49 g/cm³ and a maximum compressive strength of 3.6 MPa. The lignofoam also showed excellent thermal insulation properties with low thermal conductive coefficients (0.057–0.098 W/mK). These features highlight the great potential of lignofoam for a bio-based thermal insulation material for construction applications.