The UMaine Process Development Center supplies cellulose nanocrystals (CNC) and cellulose nanofibrils (CNF) to academic, public and private research groups interested in evaluating and developing applications for these materials. The CNC we distribute is manufactured at the US Forest Service’s Cellulose Nanomaterials Pilot Plant at the Forest Products Laboratory (FPL), located in Madison, Wisconsin. Our CNF is manufactured here at the UMaine PDC.
Cellulose nanocrystals are tiny, rod-like particles sourced from natural materials. Cellulose nanocrystals that are derived from wood pulp and have dimensions of approximately 5 nanometers (nm) in diameter and 150-200 nanometers in length. Larger crystals can be produced using cotton (10 nm by 500 nm) or algae (20 nm by 1000nm).
Cellulose nanofibrils are noticeably longer and often branched or forked, with dimensions of 20-50 nm in width and lengths of up to several hundred microns. All of the cellulose nanomaterials produced by the UMaine PDC and by our partners at the Forest Products Laboratory are made from wood pulp.
Production of CNC
The production of cellulose nanocrystals begins by using sulfuric acid to hydrolyze the amorphous regions of the cellulose polymer, leaving the acid resistant crystals as a product (the other main by-product is glucose). The crystals are purified by diluting and neutralizing the acid and then separating the soluble chemicals from the insoluble CNC. This can be accomplished by several methods: dilution and settling, filtration on a vacuum filter, or filtration in a membrane unit. FPL uses two stages of dilution and settling to remove about 90% of the salt and sugar.
Once the ionic strength is low enough, the sulfate half ester groups on the CNC provide a stable suspension. With continuous dilution and filtration, the membrane filtration system can then be used to remove the remaining salt.
The final stage is to remove water using the membrane filtration system. This process dewaters the cellulose to a viscous, 11.8% aqueous slurry. The resultant slurry is stable enough for extended storage. While in the suspension, bacterial and fungal growth is limited by the CNC’s low water content and relatively high ionic strength.
As the suspension cannot be allowed to freeze, it must be stored in a cool, temperature-controlled environment. Freezing will cause ice crystals to form in the suspension, which in turn causes the CNC to form aggregates that cannot be easily separated after thawing. For applications that require a dry powder material, the FPL freeze-dries the CNC and produces a dry powder.
A typical batch of CNC is about 20 kg (dry weight) and requires about a week of total process time. Batch production can be staggered, allowing up to three batches to be produced every two weeks.
Precautions when Handling – Exercise caution when handling CNC or CNF samples, as the material can get dispersed in air fairly easily. We recommend using a good cartridge type respirator.
Sample Requests – To order samples, visit our Order Nanocellulose page, where you can fill in our Nanocellulose Request Form. To learn more about the properties of the nanocellulose sold by the PDC, review our Nanocellulose Spec Sheets and Safety Data Sheets.