The Quantitative analysis of carbon derived from black printing ink in waste paper or deinked pulp has been made by microscopic measurements of its numbers and dimensions in a hand sheet pulp.
However, this method has several disadvantages; the contents of carbon thus determined contain some non-carbon dirts, and this must be carried out on the pulp sheets and is usually accompanied by some observational errors.
In order to solve these disadvantages, a new determination method, what is called, wet decomposition method has been developed.
The principle of this method is as follows.
(1) Dissolve materials except carbon in waste paper or deinked pulp by wet oxidation, and filter off dissolved materials.
(2) The collected residue consisting mainly of carbon is washed, dried and measured for its blackness with an optical densitometer.
A constant ratio has been observed between the carbon contents and the blackness density for the residue.
Therefore, the carbon contents can be determined by measuring the density of blackness.
Decomposition of non-carbon materials containing wood cellulose, lignin and others is done with a boiling concentrated nitric acid and perchloric acid for about one and half hour in a Kjeldahl flask.
In this study, the carbon contents were compared on the samples before and after deinking waste news by the floatation method.
By means of employing both the new and the conventional method, carbon and other non-carbon dirts in deinking pulp can be determined separately.
This method, however, can not be applied for waste paper with the high content in ash because of their ash weight exceeding those of carbon in waste paper or deinked pulp.
Therefore, the new method is suitable for samples with the low content in ash and applicable only for printed papers with black ink such as newspaper.
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