I have a lab experiment in which I have a slurry of wood pulp at a pH of 4.0; I'm asked to use sodium carbonate to raise the pH of the slurry to pH 5.5. I then press the wood slurry to de-water and place it in an oven until it is bone dry. I then take the wood sample out of the oven and place it in a bath of water to determine how much water the wood absorbs.
Why would the addition of sodium carbonate potentially cause more water to be absorbed into the wood specimen?
And, if I wanted to continue to use a carbonate chemistry for pH adjustment (because it has other beneficial properties), is calcium carbonate less hydrophylic than sodium carbonate? Is there another carbonate chemistry compound such as aluminum carbonate or zinc carbonate that would cause less water to absorb into the wood specimen.
This is a lab in wood pulping technology and therefore prescribes the use of carbonate chemistry ---- it is up to us however to find a carbonate chemistry that would cause less water to be absorbed into the wood?
Please see the attached file.
Hmmm...lets first note WHY we need residual carbonate in the paper end product, and that is to de-acidify the product to aid in its long-term preservation. Thus we probably don't want to use compounds that are toxic (heavy metal carbonates) or too alkaline (lye, ammonium compounds, etc)
As to why does the mass absorb more water with carbonate present - I can think of two things. First, the carbonate itself might be absorbing some water, second in the preparation of wood fiber, base is used to de-lignify the wood fibers. De-lignification will allow more adsorption onto fibers as the fibers become released from the natural polymer matrix. Carbonates are bases and would therefore have the tendency to de-lignify.
Regarding carbonates proper,
Solubility of the carbonates
The carbonates tend to become less soluble as you go down the chemical Group columns.
Few of ...
Problem addresses the hydrophilic nature of carbonate based wood pulp processing and potential carbonate reactions in this scenario. Includes live HTML reference links