(655e) Reverse Dialysis to Concentrate Cellulose and Chitin Nanomaterials and Their Polymer Composite Gels

Cellulose nanomaterial is a biopolymer material from abundant cellulose sources, such as wood and plant. Two types of nanocellulose are mostly studied: cellulose nanocrystals (CNC), which consist of rod-like colloidal particles; and TEMPO oxidized cellulose nanofibrils (TEMPO-CNF), which are flexible fibers. Both CNC and TEMPO-CNF have negative surface charges. Chitin nanofiber, another biopolymer material, which is extracted from crustacean shells, are also flexible fibers, but with positive surface charge. All of these nanomaterials have high surface area-to-volume ratio, making them attractive to be used in gels or as reinforcing agents in a polymer matrix for applications like coatings, hydrogels, and composites. These applications require that the nanomaterial is fully dispersed to take advantage of its nanoscale morphology, which is difficult to achieve and is often only successful at low concentrations. In contrast, a high concentration of nanomaterial is often desired to improve the mechanical properties of gels and composites. Unfortunately, increasing the concentration by conventional methods like drying often results in aggregation. A processing method is needed to concentrate these nanomaterials and retain the benefit of large surface area.

In this work, we will show the potential of reverse dialysis as an effective and controllable method to concentrate cellulose and chitin nanomaterials and their PVA composite gels. Water is removed by dialyzing suspensions of the nanomaterials against a concentrated polymer solution. Although this method has been proposed before to concentrate nanocellulose, prior studies did not provide much detail. We first investigated the water removal kinetics at different PEG concentrations to understand the dialysis process and were able to concentrate CNC and TEMPO-CNF to at least twice the concentration of the existing commercially available slurry products. Rheological characterization of the samples dialyzed to various concentrations will be shown. Secondly, in addition to concentrating pure cellulose and chitin nanomaterials, we also use reverse dialysis to obtain high loadings of well-dispersed nanomaterials in polymer composite gels. The TEMPO-CNF/PVA composite gels were prepared in suspension at low concentration to ensure full dispersion, followed by water removal via reverse dialysis to form the gel. We will show that the composite gels prepared by this method are homogeneously dispersed at high loadings of polymers and nanomaterials, which cannot be easily achieved by directly mixing concentrated solutions of pure components. We used the new procedures to make PVA composite gels that contain TEMPO-CNF of different fibril sizes in order to study the effect of nanomaterials morphology. The reverse dialysis method enables quick processing of the materials, and samples can be retrieved with little loss. The method also increases the processing range of the cellulose and chitin nanomaterials, which can help to expand applications of these sustainable nanomaterials.