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Deacidification Activity

I.  Purpose:
To deacidify paper using precipitated calcium carbonate technology which is based on a type of chemical reaction known as double displacement.

II. Background:
Until 1864 paper was made with rags and the process was an alkaline one. Due to the shortage of rags during the Industrial Revolution, wood pulp was introduced as a way to make large quantities of paper. The acid paper produced from the wood pulp survives only 30 to 40 years due to the treatment of the pulp. The pulping, bleaching, and sizing processes generate hydrochloric and sulfuric acids and the atmospheric pollutant, sulfur dioxide, produces sulfuric acid, too. The result is brittleness and deterioration of the paper products. The paper produced from wood pulp and used in books prior to 1976 was acidic. The remedy to conservation and restoration for valuable papers is to deacidify the paper and to initiate manufacturing processes that will generate alkaline paper for future use.

Conservators deacidify valuable books by treating the paper with a mildly alkaline solution (pH<10) that deposits a carbonate salt into the fiber of the paper. By adding 3% by weight of calcium carbonate the deacidification process may extend the life of a document or valuable book as much as 500 years.

The calcium carbonate fillers were introduced in the 1980's and developed into today's precipitated calcium carbonate technology. As much as 30% carbonate filler is now possible which not only neutralizes present and future acidic reactions but adds to the paper's opacity and brightness. For a paper to be considered permanent it should have a pH of 8 - 8.5 with a 3% by weight alkaline reserve (carbonate). These alkaline papers must be specially marked to prevent unnecessary preservation efforts.

III. Materials:
Calcium chloride (CaCl2) solution (saturated)
Sodium carbonate (Na2CO3) solution (saturated)
3 shallow trays or pans
acidic paper (several numbered samples)
pH pens

IV. Procedure:
A. Test paper samples with pH pen. Record the pH as well as the number of each sample.
B. Choose one of the samples that tests acidic and mass on centigram balance. Record sample number and mass.
C. Submerge the paper sample in the shallow pan filled with calcium chloride solution until it is completely soaked through. Carefully remove and dry. You may use a hair dryer or blower but NO HEAT!
D. Place the dried paper sample into a shallow pan filled with sodium carbonate solution and allow to react completely (5-10 minutes). Remove carefully and dry. Again you may mechanically dry with NO HEAT.
E. Thoroughly wash the paper with water. This will require several washings!
F. Dry paper and mass on centigram balance.
G. Test paper with pH pen. Record.
H. Determine the % calcium carbonate in the deacidified sample.

V. Data
Sample # 1 2 3 4 5
pH __ __ __ __ __
Acid sample # ___
pH before treatment ___
pH after treatment ___
mass before treatment _______g
mass after treatment _______g
mass of calcium carbonate filler added ______g

V.  Observations:

VI. Calculations
% CaCO3 filler = mass of CaCO3 x100
mass of deacidified paper

VII. Questions
1. Write and balance the equation for the double displacement reaction.
2. Why is it necessary to wash the paper after the process?
3. How could thin fragile paper be treated without handling?
4. Would the deacidified paper be classified as permanent? Explain.

VIII. Hazards
The sodium carbonate solution may dry hands so gloves should be worn. Eye protection is ALWAYS required!

IX. References
Visit these web sites for background information and sources for ordering pH pens.

This activity was developed for Charleston County Public Library by Norma L. Ashburn, retired chemistry teacher (Hanahan High School, Berkeley County, South Carolina). It is intended for use in high school chemistry classes and is especially relevant to "Chemistry and Art", the theme of National Chemistry Week, 2001.