EP0073872A1

EP0073872A1 - Chemical process in the manufacture of paper

Info

Publication number: EP0073872A1
Application number: EP81850146A
Authority: EP
Inventors: Björn Magnus Sivert Dillner; Inga Kristina Margareta Akerblom
Original assignee: Billerud Uddeholm AB
Current assignee: Billerud Uddeholm AB
Priority date: 1981-09-03
Filing date: 1981-09-03
Publication date: 1983-03-16

Abstract

A process for eliminating or reducing the formation of gaseous organic trace substances which may cause taste and smell on products based on paper pulp, particularly for use in packaging of food stuffs, without resorting to the use of bleaching agents characterized by adding a sequestering agent to the paper pulp.

Description

The present invention relates to a process to eliminate or reduce the formation of gaseous organic trace substances which may cause taste and smell of products based on paper pulp, particularly for use in packaging food stuffs.
When making materials for food stuff packaging it is of great importance that the material does not affect taste or smell of the contents of the package. This is of particular importance when packing liquids, particularly milk which is a highly taste-sensitive product. In milk card-board packages there have been used for a long time different types of card-board, usually provided with a surface layer of plastic on both sides. Card-hoard made from bleached chemical pulp seldom results in taste or smell problems which, however, is the case when using unbleached pulp. From milk producers the view point has been put forward that when using unbleached paper in milk packages the milk will be subjected to taste and smell changes which seem to be caused by the use of unbleached paper.
For many reasons it is desirable to be able to utilize unbleached materials in food stuff packages, i.a. thereby that an increased utilization of raw materials will be made possible, energy consumption can be reduced and it is possible to delimit the environment problems of the manufacture. The bleaching requires supply of energy and results in decreasing yield and discharges causing environmental problems. At the same time the material is hardly given any operationally better properties and only the appearance of product will be more attractive. Rather the opposite is the case in that the product will have impaired rigidity.
Thus, many reasons point to the use of unbleached pulps in the packaging material and the major obstacle of so doing are the test and smell changes that the contents of the package will be subjected to. The smell substances in question are usually present in extremely small concentrations and quite advanced analysis processes will be required in order to detect and determine the different components. A special technique has been developed for classifying by using ultra-sensitive gas chromatografy the substances of relevance in this connection, and the developed technique gives the possibility of tracing sources of smell so that the influence of smell hereby can be eliminated. A comprehensive presentation of the technique is given in "JOURNAL OF APPLIED POLYMER SCIENCE SYMPOSIUM No . 28, Part II.I Timell-Proceedings of the Eighth Cellulose Conference, 1976, by John Wiley & Sons, Inc."
In the present disclosure the term "smell relation number" is used which in the chromatografic analysis is a measure of the total contents of gaseous organic components of a smell character above a test sarple under specified conditions.
In connection with classifying the compounds involved in connection with the paper pulp and which may cause the above-mentioned changes in taste and smell of for example milk, a series of conceivable measures in connection with the paper making procedure have been tested and in this context also the influence of different additives to pulp and paper. It was then quite surprisingly found that already the addition of small quantities of a conventional complexing agent to the paper pulp gave quite a substantial reduction of the smell of the pulp.
The explanation for the fact that addition of complexing agents to the paper pulp results in a significant reduction of the smell is probably the fact that heavy metal salts of for example manganese, iron and copper, which usually are present in unbleached pulps, catalyze formation of the odorous substances, particularly in the presence of air oxygen. It is thus known that heavy metal ions easily can generate reactive so called free radicals. Although the invention is not delimited to this theory it is, however, probable that this radical-forming ability of the heavy metal ions will be strongly delimited or eliminated if the metal ions are bound in the form of strong complexes.
The invention thus provides a process for eliminating or reducing taste and/or smell of products based on paper pulp. This process is characterized thereby that the paper pulp is supplied with a complexing agent in the .presence of water. In view of the fact that the reaction between the complexing agent and heavy metal ions present in the mass shall take place easily it is suitable to supply the complexing agent at some stage of the process preceding the final drying of the product. Thus, the complexing agent can be supplied to the paper pulp before being taken up in the paper machine, but it is also conceivable to supply the complexing agent at a later stage of the process, for example in the sizing stage of the paper making machine. It is, of course, also possible to treat already manufactured paper or card board in accordance with the technique of the invention, but in this case the product prepared must be moistened or immersed in water in connection with adding the sequestering agent. This does, of course, involve an extra process step making this alternative less attractive.
As a complexing agent all conventional types of compounds may be used, such as inorganic sequestering agents, for example phosphates, such as metaphosphate, hexametaphosphate etc., or organic sequestering agents of the type aminopolycarboxylic acids or hydroxycarboxylic acids. Among preferred organic complexing agents there may be mentioned diethylenetriaminepentaacetate (DTPA) and ethylenediaminetetraacetic acid (EDTA).
The complexing agent is added in a quantity suitable in relation to the nature of the paper pulp. A suitable quantity lies within the range of about 0.2 to 5 kg per ton pulp, and often a quantity of about 1 to 2 kg per ton pulp is suitable in practice.
Depending on the place where the complexing agent is added the temperature may vary of from cold water temperature, i.e. about 5°C, up to normal environmental temperature, which in summer time can be about 20°C and further all the way up to the actual process operating temperature which may exceed the boiling point of water and reach up to about 155°C.
In the following the invention will be described by non-limiting examples, the technical effect being veryfied while using the above-mentioned smell relation number.

EXAMPLE 1

An unbleached chemical sulphate pulp having a kappa-number of about 30 was slushed in water at a concentration of 2 % and a temperature of 40°C. Diethylenetriaminepentaacetate as a sequestering agent was then added to the pulp slurry in an amount of about 1.5 kg per ton pulp dry weight, a sheet of paper being then made by hand and dried and analysed with regard to smell. As a control and for comparison the same procedure was carried through but without addition of diethylenetriaminepentaacetate.
As a result of the experiment a smell relation number for the pulp treated with sequestering agent of about 500 was obtained, whereas the untreated pulp showed a smell relation number of 1175.
It should be added that it has been found empirically that the smell treshold under the prevailing conditions corresponds to a smell relation number of about 600. Below said level thus hardly any differences could be noticed. However, the taste-sensitivity increases drastically above a smell relation number of about 700 and a value of 1200 constitutes an unacceptable level. Applying the technique of this invention thus means that a practically unacceptable sulphate pulp will be transformed by adding a sequestering agent to a level which is acceptable from a taste point of view.

EXAMPLE 2

Example 1 was repeated but using ethylenediaminetetraacetic acid instead of the diethylenetriaminepentaacetate as a sequestering agent. The treatment of the pulp by the process of the present invention brought about reduction of the smell relation number down to 475.

EXAMPLE 3

The application of the invention on some different pulps of the type unbleached chemical pulps was investigated in the same manner as according to Example 1. The sulphate pulps used and the results obtained are given in the following TABLE. The quantity DTPA used was 2 kg per ton pulp.
As is clear from the table in all cases a substantial reduction of the smell relation number was obtained, however, for sulphate pulp A the value did not reach below the taste threshold value of about 600. This may possibly be due to the fact that a too small quantity of sequestering agent was added.
Sulphate pulp C was tested also with an addition of DTPA of 1 kg per ton pulp, a smell relation number of 550 being obtained.
In all tests described above no other influence on the paper pulp than that intended could be noticed and nothing else was to be expected.
It should be observed that the invention is not delimited to the embodiments described above which merely are intended for illustrating preferred embodiments of the invention. Thus, the invention is applicable not only to unbleached chemical sulphate pulps but also on other chemical, semi-chemical or mechanical pulps suited for the purposes stated above.

Claims

1. A process for eliminating or reducing the formation of gaseous organic trace substances which may cause taste and smell in products based on paper pulp, particularly for use in packaging of food stuffs, without resorting to the use of bleaching agents, characterized by adding a sequestering agent to the paper pulp.

2. A process according to claim 1, characterized by adding the sequestering agent before the final drying of the product.

3. A process according to claim 2, characterized by adding the sequestering agent to the paper pulp before being taken up in a paper making machine.

4. A process according to any preceding claim, characterized by using as a sequestering agent an organic amino or phosphorous compound.

5. A process according to any preceding claim, characterized by adding the sequestering agent in a quantity of about 0.2-5 kg per ton pulp.

6. A process according to any preceding claim, characterised by adding the sequestering agent at a temperature of up to normal environmental temperature.

7. A process according to any preceding claim, characterized by adding the sequestering agent at an increased temperature.

8. A process according to any of claims 4-6, characterized by using as a sequestering agent DTPA.

9. A process according to any of claims 4-6, characterized by using as a sequestering agent EDTA.

10. A product prepared by the process of any preceding claim.