Biopolymers - Wood-based Flashcards
(24 cards)
What does wood consist of and give a short description
50% Cellulose (load-bearing compound), 25% Lignin (the glue), 20% Hemicellulose (the linkers) and extractives
What main processes are there for wood?
Wood material technology, pulping and papermaking and biorefinery.
What are the most common wood products?
Construction material, paper, fibers, energy, chemicals, polymers and nanomaterials.
Whats makes lignin a potential compound for uses in biopolymer chemistry?
It’s aromatic, abundant and have reactive functional groups.
Name some challenges for processing wood and utilize products.
extraction does not give 100% purity, structure dependent on extraction method, complex molecules,
Whats the hierarchical structure of wood?
Cellulose polymer - elementary fibril (amorphous and crystalline regions) - microfibril - secondary wall structure (cellulose, lignin, hemicellulose) - cell wall layer - fibers - wood
Whats the basic structure of cellulose?
glucose molecules creates a cellobiose based unit. The polymer have non-reducing and reducing end groups.
What different region does cellulose have and what are their properties?
Amorphous domain - reactive and accessible for water (can swell)
Crystalline domain - not accessible for water, can only be modified on the surface, have polymorphs, differ by hydrogen bonding
What are cellulose polymorphs?
The crystalline domain can have different structure. Natural cellulose I have the structure I alpha and beta. Cellulose produced by bacteria/algae is enriched in I alpha while plants mainly consists of I beta. With chemical modification cellulose I can be turned into cellulose II, III, IV.
How can crystalline cellulose I be detected and whats the hypothesized structure?
Can be detected by x-ray. The structure is that the molecules lies in sheets. Within the sheets there is hydrogen bonds and between the sheets van der waals interaction.
What nanocellulose grades are there from wood?
Microfibrillated cellulose MFC, Cellulose nanofibrils CNF, Cellulose nanocrystals CNC
Whats the difference between the nanocellulose grades
MFC - fibers that have fibrillar surface due to mechanial or chemical treatment, CNF - individual fibrils liberated from the cell wall, CNC - crystalline parts of the cell wall fibrils.
How do you produce MFC or CNF?
The raw material is pulp or biomass, this is pretreated with alkaline, acidic, enzymatic or oxidative solutions. Then it is disintegrated either by mechanical or enzymatic treatment. Then oxidative post-treatment and concentration or drying up to 15 w%
Name some properties of nanofibrils
It’s a water-rich viscous gel or paste. This property can be modified to create different types of gels with different appearance and hardness. They are generally strong. films can also be created. good oxygen barrier.
Why can cellulose be used for biosensing
It’s biocompatible, nontoxic, biodegradable, resistant to many solvents. Nanocellulose have high surface area and high mechanical strength.
How is cellulose nanocrystals CNC produced?
pulp, biomass or cotton is pretreated by bleaching, disintegrated by acid or enzymatic hydrolysis and then post-treated by oxidation or removal of charges. Then it is concentrated or dried.
Name some properties of CNC
Rod-like rigid particles. Can be a water-rich viscous gel or paste and its property can be modified. The modification can affect how light is reflected => appearance.
How is nanocrystalline created from cellulose
By acidic hydrolysis
Name some uses of CNC
It has hydrophilic and hydrophobic regions and can be used as emulsifier for pickering solutions. Can also be used to create films when it’s charged. The chiral property can give the film different colors.
What is hemicellulose?
It’s a polysaccharide that is a little branched. Side product from the pulp industry.
How is the hemicellulose different in soft- and hardwood.
In softwood the hemicellulose is mostly galactoglucomannans (mannose, glucose in the backbone with galactose branch) with some xylan, some acetyl groups. In hardwood it’s mosty xylans and some glucomannan. Backbone mainly xylose, have glucuronic acid and acetyl groups.
What can hemicelluloses be used for?
To produce films and film additives that are renewable, oxygen, grease and aroma barrier. Can also be used as a surface active hydrotrope (emulsifier without a long tail). Because it is branched (soft wood galactoglucomannan)
What is Lignin?
It’s a matrix material usually binding fibers together/the structural part of wood, it’s not a polysaccharide - more like a phenolic molecule/macromolecule. The structure is a bit unkown. The brown stuff left from pulping. Not so moist-sensitive as polysaccharides usually are.
What uses are there for lignin?
Currently it’s main use is for energy but material uses are on the making. The particles can be used for pickering emulsions and encapsulate substances.
