Cellulose acetate

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Cellulose acetate
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Introduction

Cullulose acetate is a material that is easily made from the most abundant organic polymer in the world - cellulose - and is already widely produced.

Cellulose acetate is a modified form of refined cellulose that can be isolated from biomass and has applications for bioplastics, glazing, semipermeable membranes, water absorption, and lacquers. Cellulose is a polymer of B-1,4 linked glucose, and cellulose acetate is formed by replacing the glucoses' hydroxyl (OH) groups. Glucose has three hydroxyl groups (C2, C3, C6) that can be modified and the degree of substitution affects the characteristics of the polymer. For a high strength bioplastic polymer all three hydroxyl groups are replaced with acetate resulting in cellulose triacetate. Cellulose acetate with a lower degree of substitution can absorb water and has other applications. Cellulose acetate can be made by reacting cellulose biomass with acetic anhydride and an acid catalyst. Cellulose acetate has good optical and packaging characteristics but is not as durable as other bioplastics. Depending upon the degree of substitution cellulose acetate can be biodegradable. Cellulose acetate can also be composited with other materials improve product characteristics.

OSE context

Cellulose acetate is one of the oldest and easiest to manufacture forms of bioplastics. Unfortunately it is relatively unstable and not durable. Cellulose acetate or cellulose reacted with other anhydrides are useful for a number of applications but its use is more limited in existing OSE product ecologies. Lacquers, adhesives and applications that don't need robust or durable materials are a few possible OSE uses. Cellulose acetate is also flammable. A cellulose acetate lacquered Moldable mycelium could be an innovative, easily, and locally produced product. Cellulose acetate depending on its level of substitution and residual catalytic acid content can be biodegradable. Biodegradable cellulose acetate mixed with other biodegradable bioplastic products, such as starch and glycerol, can create a biodegradable product with favorable characteristics. Whether it is useful for OSE to pursue a biodegradable bioplastic is open for debate.

Production

  • Cellulose acetate would be the most easily produced bioplastic and can be produced with very simply from acetatic acid and cotton cellulose.
  • This industrial ecology paper discusses how cellulose acetate is actually made in China - S83 right hand side of [1]

Proposed Applications

  • Membranes/filters: reverse osmosis, dialysis membranes for continuous run fermentors and bioreactors, filters for chemical engineering processes
  • Thermomolded composite: a biodegradable composite of starch and plasticizer may be thermomolded by a 3D printer or plastic entruder
  • Lacquer: a fire resistant lacquer could be used to seal wooden materials or moldable mycelium parts for longterm use (OSE car interior?)
  • Light-weight packaging: cellulose acetate films for clear biodegradable packaging, the degree of durability and biodegradability can be controlled by the degree of substitution, type of anhydride substitution, and inclusion of other materials.
  • Glazing for greenhouses. See patent - [2]. Study of cellulose acetate windows for airplanes concludes they could work, but weathering and shrinkage must be addressed. [3] Plasticizers should be used, such as glycerol. This says glazing is an application - [4]. Window panes patent - [5]
  • 3D printing. Sure. [6] Also, check out hype piece from MIT - [7]
  • Protective gear - visor face shelds, impact-resistant glasses - [8]

Thermomolded composite

Thermomolded composites based on plant derived polyesters are currently in large scale industrial production. Current industrially produced bioplastic are often based on starch composited with a lignocellulosic component. Possible lignocellulosic components can have undergone various degrees of refinement and substitution and include low refined lignocellulosic filler to highly refined regenerated cellulose acetate butyrate. Appropriate technology must be selected to fulfill OSE product ecologies with minimal processing, energy, and resource imports. Starch based bioplastics made of kitchen starch and a plasticizer, such as glycerol or vegetable oil, are easily made in a kitchen and demonstrations are on youtube. The resulting product most likely would not be suitable for OSE product ecologies but could serve as a based for further development using a compatible composite component and further processing. A preliminary proposal:

  1. Produce a simple starch bioplastic with glycerol plasticizer, dry the product and break the product into pellets for compositing and extrusion.
  2. Refine lignocellulosic filler material from bagasse waste from on-site agricultural operations. Bagasse with low oil and high lignocellulosic content should be chosen, and possibilities include pressed sorghum, trees or shrubs, cotton, or corn stalks. Refinement involves an oil and hemicellulose removing step(s), such as a basic wash. The refined material should be powdered and filtered to a small uniform size.
  3. The starch plastic pellets, lignocellulosic filler, and further plasticizer are then combined and co-extruded, and more likely thermo injection molded. The products properties will be studied and further adjustments made.

Membranes

Membranes are often used in filtration processes and cellulose acetate plays an important role. Cellulose acetate can be combined with copolymers and/or treated to produce different pore sizes and charge selectivity.

Lacquer

Film

Links

  • Acetic Acid
  • Patent for producing Cellulose Acetate - 1935 - [9]
  • The Michigan Technic article discussing production and properties, 1941 - [10]
  • Cellulose Acetate Butyrate - [11]