Week 13 Cellulose and its Derivatives Flashcards
CEllulose- material properties and bonding
- long chain polymers with a lot of _OH groups, which attract water through hydrogen bonding
the chains also bond to eachother through h bonding
this makes a rigid 70% crystalline structure, these features make it a useful polymer in nature
Cellulose nitrate; process and history of production
what happens when cellulose is nitrated, and what properties occur from this
the hydrogen is replaced with an NO2 group
How? this uses nitric acid, h2so4, giving hydrogen and oxygen to the hydrogen, producing water and no2 which joins onto the cellulose chain
the water produced needs to be removed with acid , maintaining the reaction process
what is hydrolysis, and its reverse reaction
why is the degree of substitution, or nitration, important in the production
- there is a maximum possible nitration, which would produce an explosive, trinitrate, or gun cotton
- a lower substitution level produces plastics, a slightly higher one, produces a stiffer polymer, and transparent lacquer used in nail polish
- higher again substitution produces films
brittleness is a problem, how do we solve this in the production of plastics, and how does it work
source of decay in future, due to migration
migration leaves gaps for oxygen and moisture to get in
in the presence of acidity, better dissolution to form acid solution, or a higher level of oxidation because of increased oxygen (this is initiated by heat and light).
past and current uses of cellulose nitrate. what technical properties make it an excellent adhesive
- waterproof aircraft wings- very stiff
- painted on textiles used for early biplane wings
-imitation tortoise shell - st cuthberts coffin
examples of coatings containing cellulose nitrate
- lacquer for metal and paint
- produces very think high gloss finish
stability of cellulose
- manufacturing; built in acidity, bad washing
- cellulose nitrate hydrolyses or becomes acid
- brittle and micro-cracking (paving effect)
how does cellulose nitrate decay
heavily plasticiser, migration causes shrinkage and cracking
thinking about a cinematic collection at a museum; what are the major concerns fro cellulose nitrate decay
- originally used for film, very unstable
- ferrous and ferric ions produces an acidic environment through hydrolysis
- produces a catalytic effect, speeding up decay of cellulose nitrate
- storage in or with metal is a big no no
- film copied/ moved to cellulose acetate
how is cellulose acetate produced and what are its uses
both nitrate and acetate use sulphuric acid as a dehydrating agent (problematic if the manufacturing is bad)
acetic acid is very volatile, but less aggresive then nitric acid, an organic acid
uses and decay of cellulose acetate
takes dyes differently, different finish
produces a thin film
what is important to consider in the environment and display of cellulose nitrate
what is regenerated cellulose
breaks down in burial after 2 months
What are cellulose ethers, traditional uses
Family of polymers, can be modified to be water soluble.
Traditionally used in paper conservation or as sizes/ adhesives, or to bulk out paper.
CEllulose ethers: structure
cellulose, wood derived, beta glucose units joined together between condensation reactions between two alcohols, three OH groups in ring structure. Compatible with water, absorbs moisture.
Is modified by producing these groups. Adding an aliphatic group C,H, produces ethyl cellulose, adding a carbon produces methyl cellulose. modifying the side group by adding alcohol produces hydroxyethyl cellulose
The length of the side chain can be variable.
What do the modifications to cellulose to produce these new molecules cause, in terms of changes to properties
Ethyl cellulose: more hydrophobic, side chain not compatible with water. the longer you make it, the more hydrophobic
hyroxyethylcellulose: maintaining compatibility with water, added branching of chains, increasing viscosity and changing flow
process of modifying cellulose into hydroxy cellulose ether
with the structure of hydroxy cellulose ethers, what do you get by keeping the -OH groups
compatibility with water
Good properties of cellulose ether
what does using a combination of added side groups produce in terms of cellulose ether properties
match cellulose ethers to their solubility in water, using groups that ensure solubility and that decrease it.
what is sodium carboxy methylcellulose (NaCMC)
Used before Cellulose ethers were introduced as consolidants, 30 yrs ago.
a carboxylic acid and sodium substitution,
can get disassociation of sodium in water, but its polarity makes it have good adhesive properties
what does this nomenclature mean (cellulose ethers)
DS, MS, high DS, high MS
These influence properties like solubility and viscosity