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4. Methods of conservation

4.1 The diethylzinc (DEZ) method
4.2. The Wei T'o method
4.3. The deacicification system of the Bibliothèque Nationale
4.4. The methods of the British Library in London
4.6. Further developments

 

The lifespan of library material may De prolonged many times over by an effective policy of conservation on the basis of suitable techniques and methods of conservation. The necessity of restoration is thus delayed or prevented.

A considerable amount of effort in conservation is spent on looking for ways to cheaply renovate large collections which are suffering from paper deterioration due to acidity.

Behind this problem is the fact that from about 1850 onwards pacer with acid content was used for printing with apart from some exceptions is still the case. At the moment, information is growing worldwide on the worrying state of library contents. The Library of Congress believes a quarter of its stock to be so badly endangered that it may soon be unusable. The British Library in London fears the damage to be of a similarly high degree in the library. The French Notational Library in Paris reported of 800,000 books with were detrimentally affected. The academic libraries of this country have also been aware of this problem for a long time. he amount of money necessary to renovate the library contents on this scale cannot be estimated at present because the development of specialized knowledge is not able to give a clear picture on effective methods. At the moment, various systems of deacidification on library stocks are being developed or are already in use.

By the term "deacidification" we mean the removal or neutralization of acid substances with have a damaging effect on the paper. The impregnation of an alkaline buffer is necessary to maintain the effect of deacidification for as long as possible. This buffer or reserve should act as protection against the secondary build-up of acidic substances or their penetration from outside.

The work of William James Barrow is of central importance a researching the lifespan of paper The most important findings for us from his, in parts, contraversial research results may be thus summarized: The lifespan of paper is determined by the presence or absence of alkaline earths. If there are enough alkalines in the paper damage done by acid can be prevented. If there are too few alkaline earths in relation to the amount of acids or if there are more acids then can be combined then the pH value will fall.

From the many types of alkaline substances, there are few which are suitable for the deacidification of paper. Particularly strong alkalines are unsuitable because a vigorous reaction to the cellulose causes a similar tendency towards ageing The most valuable deacidifying agents are the alkaline earth salts

calcium carbonate (CaCO3),
magnesium carbonate (MgCO3) and
Barium hydroxide (Ba(0H)2).

In mass-deacidification the paper should be neutralized to a pH level of 7-8 by the treatment. Technically, this means that books or bundles of paper have to be rapidly impregnated pH a neutralizing agent, with is deposited in a sufficient concentration in the paper-web, at the same time building up the alkaline reserve. The chemicals used must not damage the books. They must be non-toxic and must not leave any kind of odour. The techniques of mass-preservation with have been developed up to now are gas or fluid processes. Some of the latest use both aqueous and non-aqueous systems.

Deacidification is purely a preventive measure. It does not return any of the paper's strength with is also essential so that the book can be used and the pages can be turned, and the strength with is lost as a result of the chemical pro ceases, making as a whole a difference to its ageing. The deacidification simply has the effect that these processes are in future slowed down as much as possible.

4.1 The diethylzinc (DEZ) method

After an exhaustive research programme lasting five years, the library of Congress decided for the gas phase method, where a substance called diethylzinc (or DEZ for short) is used. This method has been demonstrated on a laboratory basis on test models.

DEZ cannot be directly exposed to an excess of water or oxygen because of its reactive characteristics. Therefore the process has to be carried out in an enclosed chamber, so that the books and the DEZ gas can react in one enclosed space with is free from excess water and oxygen. Diethylzinc is a compound with characteristics which raise its deacidification mechanism above others.

Firstly, the DEZ vapours in the form of gas can flow between the pages of the book unhindered, disperses itself in the paper fibres, coming into close molecular contact with the cellulose chains and reacting with and neutralizing all weak and strong acids.

Secondly, it simultaneously reacts with the water on the fibres and forms the alkaline reserve compound zinc oxide. This reaction between the DEZ molecules and the water leads to an even distribution of small alkaline reserve particles in the paper fibres which means a completely reproducible increase in the lifespan of each book treated.

Thirdly, the zinc oxide buffer gives the paper fungistatic activity which prevents any later biological growths.

The DEZ process consists of 3 stages with altogether 17 single steps. The schematic sequence consists of the following:-

The treatment chamber is filled with books. All the air is pumped out to ensure the total absence of air, producing a pure nitrogen atmosphere. A vacuum of approximately O.2 torr is then created in the chamber at a temperature of 45°C to draw out the greater part of the water content in the books. Approximately 0.5% water must remain in the paper The water content of the pacer is checked by measuring the weight loss of the vacumm chamber then full of books. This preliminary stage of treatment takes 20 hours.

The DEZ is condensed out of its transport medium (mineral oil) from a closed system linked with the vacumm chamber, and in the from of a gas, is dispersed slowly amongst the books. in the vacumm chamber. The pressure inside the chamber a thus increases to 20 torr, The DEZ gas reacts with the 0.5% water which produces zinc oxide and ethane This process is intensively exothermic. The ethane with is produced is constantly drawn off. At the same time the vacuum chamber is cooled so that a temperature of 80°C can be maintained. The conversion of DEZ into zinc salts and zinc oxide takes about 4 hours and the weight check of the vacuum chamber may then be carried out.

The safe removal of the unused DEZ gas is achieved by re creating the conditions of the pre-treatment stage in the vacuum chamber 0.2 torr a nitrogen atmosphere, 40°C.
Under these conditions water is let into the chamber to increase the water content of the books again Afterwards carbon dioxide is pumped into the chamber raising the inner pressure to 550 torn It is assumed after 24 hours that most of the zinc oxide has been converted into carbonate and that the books have absorbed so much water that they are again flexible enough to handle.

The advantages of the DEZ process are as follows:

- The use of a substance in gas from generally means that many of the acutely damaging side-effects on parts of the boot; can be avoided.
- The alkaline reserve which is created reacts almost neutrally.
- The selection of library materials is not necessary prior to treatment.

From the present point of view the disadvantages are as follows:

- The construction and maintenance costs of a DEZ deacidification plant is very expensive.
- There are some elements of uncertainty because of the unstable reactive nature of the DEZ gas.
- Specialists are required to run this kind of plant.
- The whole chemistry of the process is, at present, being questioned by experts.
- The present stage of development of the process does not permit its use by potential customers.

4.2. The Wei T'o method

The Wei T'o 0.5% non-aqueous book deacidification system, or simply the Wei T'o system, invented by Richard D. Smith in Canada, and developed by the National Archive in Canada. Work on the test plant started in 1974 and ended in 1978. After completion, meticulous tests on books from the Canadian Book E: change Centre of the NLC began. By December 1981, the system was ready for practical use. It works as follows: The books to be deacidified are soaked in a mixture of freezing substances (frigen, FCKW's) as a transport medium and a deacidification agent met methoxy magnesium methyl carbonate dissolved in 5% methanol.

As a result, the acids in the paper are neutralized through the formation of magnesium sulphate and the depositing of magnesium carbonate as a buffer with a pH value of between 7 and 8. The Wei T'o 0.5% spray Nr. 10 consists more or less of this combination, its use being widespread in the deacidification of single sheets.

The rooks which have been sorted out for the mass deacidification are dried in wire baskets for 36 hours in a vacuum dryer In this way, the paper is natural water content is removed. Two caskets with contain between 20 and 30 books are then placed in the reaction chamber. The deacidification solution is then pumped in and the pressure increased so that the books are fully saturated with the solution. The solvent is then removed (to be used again later) through a second drying process. At the end of the treatment warm air is pumped in, normal air pressure is restored and the books are then taken out.

The deacidification cycle requires approximately one hour. The baskets are placed in simple containers with corrugated bottoms where the books can cool off to room temperature and regain their normal water content through the air. They are then checked and taken back to their respective departments. The plant in the cellar of the Canadian National library is actually only a test plant. It has been in constant use since 1982. The output of the plant depends on the amount of capital and personnel available.

At the moment around 800 books can be treated by the two employees during their 37 1/2 hour working week - that is about 40,000 books every year. The output is to be doubled: 80,000 books is the amount of books coming into the Canadian library and it GDR planned to deacidify them as a completely preventative measure. The maximum output in a 12-hour shift system shared between 7 employees would amount to around a pillion books a year. A further development to the plant, such as a multiple single-chamber system would cut out the re-loading from the vacuum-dryer chamber to the intermediate chamber and finally to the treatment charmer, which is at present the case, and would therefore reduce the amount of employees at this level of output.

The technical advantages of the Wei T'o system lie in its chemical agents:

- The metallo-organic compound magnesium methylate is soluble in methyl alcohol.

- If this solution is introduced to paper it decomposes, simultaneously forming magnesium hydroxide and magnesium carbonate as well as methyl alcohol with evaporates very quickly.

- Magnesium hydroxide and magnesium carbonate remain in the paper, form an alkaline reserve and delay the process of oxidation.

- There are no reservations as for as the chemicals are concerned.

The disadvantages lie, at present, in the following problems:

- Due to the fairly good experience in its use, further developments to optimize the process would be possible. Improvements in the procedure were announced already some time ago by the inventor, although not yet put in concrete terms.

- The solvents used or produced in the process are not ecologically feasible (cooling substances) and are toxic (methyl alcohol).

- A great disadvantage of the present plane is the full recovery of the solvent.

- The library materials to be deacidified must be preselected.

- The amount of methanol in the deacidification solution can lead to unwanted changes in specific materials.

- A serious drawback is the potential customer's dependence on the manufacturing monopoly of the deacidification solution.

4.3. The deacicification system of the Bibliothèque Nationale

Out of all European countries, efforts to find a preventive mass deacidification system are the furthest advanced in France. The Notional library installed a conservation centre in the Chateau de sable, 250 km south-west of Paris, with as pat into use in mid 1987.

The procedure is similar to that of the Canadian Wei T'o 0.5% system. The books are neutralized with methyl magnesium carbonate in a solution of methanol and cooling agents.

As opposed to the Canadian system, the system in Sable is geared towards the distillatory processing of the used solution so it may The employed again. The way of working is roughly the same as in Ottawa The money invested in the plant amounted to 2 million French francs. The books are dried in a vacumm at 50°C for 24 hours, then taken to a cooling chamber and intermediate chamber for 48 hours and then with 1% humidity for 10 minutes in an evacuated pressure chamber which is saturated with the deacidification solution. Afterwards the surplus deacidification solution is pumped out of the pressure chamber and the saturated books are heated to remove the methanol, The pressure chamber can be filled three times a day with 200 books. Exact figures on the output of the plant are expected.

The advantages to the French system are exactly the same as those of the Wei T'o process in its chemical activity of neutralization and impregnation of alkaline reserve. Another advantage is the effort made to win back the expensive solvent.

The disadvantages of the French system are currently as follows:

- The whole plant can only be seen as an experimental plant.

- A number of technical changes aimed at replacing the present manual control with partly automatic operation must be achieved.

- There are problems with ink running in books which could be solved by reducing the amount of methanol

- Efforts to find a supplier of the deacidification solution in the surrounding area of the plant have proved unsuccessful.

4.4. The methods of the British Library in London

The library, commissioned the research of possible alternative processes to treat paper with would delay decomposition and strengthen the paper for further future use. This could be achieved by the absorption of polymers into the substratum, thus strengthening and protecting each individual paper fibre. Present laboratory results show that the treatment must include the following steps:

- The books to be treated have to be stacked in a suitable container.

- Nitrogen is pumped into the container in order to remove air and free oxygen.

- a quantity of monomer compound with corresponds to the weight of the books is introduced into the container.

- The set-up has to rest some hours so that the monomer compound can diffuse and distribute itself evenly throughout the paper.

- The monomers and the books are passed through a weak gamma ray source until the correct amount of radiation is achieved. The monomers are thus converted into polymers and are simultaneously chemically attached to the paper or substratum forming a polymer compound.

- The monomer residue as removed with air from the container to avoid endangering the employees involved.

- The books re then taken out of the container and stored for a few days in a well-aired environment to make sure that all traces of monomers have disappeared before the books are returned for sorting and shelving.

Furthermore, it was found that it is possible to also use a basic co-monomer (an amine-substituted acrylic methacrylate as for example dimethylaminoethy methacrylate to neutralize any acids in the paper and so that resistance is increased to later acid attack, thus combining neutralization and strengthening GDR one step The basic co-monomer is simple to polymerize and only small amounts are needed for the neutralization to function.

Test pieces which have been treated with the usual polymer compound and with the small amounts of polymerized amine show noticeable differences in paper strength and in its neutrality over a certain period of time. Recently it was discovered that multiple unsaturated co-monomers with the monomer compound added to them could cause an even greater improvement in the fold endurance, 3 5 times more than that of the original polymer compound, increasing life expectancy.

The expected results of this process is the combination of deacidification and at the same time, stabilization. The present stage of development does not permit the use of the process by any potential customers.

The "Viennese methods"

The procedure for preservation of newsprint developed at the Austrian National Library is based on an aqueous immersion treatment The treatment involves the simultaneous neutralization and re-strengthening of the paper. The method allows the renovation of embrittled paper in the sense of prolonging its further library use, but also the preventive treatment of undamaged stock. As with the DEZ process and the methyl magnesium carbonate process, a vacumm chamber is required for the immersion of the paper in neutralizing and strengthening solution. The simultaneous neutralization and re-strengthening has the advantage that, besides causing considerable deacidification and the formation of an alkaline reserve in the paper, an additional strengthening solution is introduced, retarding further decomposition of the paper, due to the influence of oxidising agents. On the basis of previous test experiments, calcium hydroxide was selected as a deacidification solution and a methyl cellulose of low viscosity was chosen as a strengthening agent. After impregnation, the items are shock frozen at a temperature of -40°C and then freeze-dried. The freeze-drying prevents the individual sheets from sticking together during the drying process. The process is basically designed for the treatment of complete book-blocks after the removal of the book's cover. The ability of the immersive solution to penetrate through the book-block is decisive for the success of the treatment A closed book acts like a selectively absorbing filter towards the immersive solution, comparable to the absorbing layers of a thin-layer chromatography plate. This means in practice that the solvent - in this case water - penetrates through the material more easily than the dissolved chemicals with should bring about a neutralization and strengthening of the paper. This problem can be overcome technically by limiting the thickness of the spine to a maximum of 4cm. Thicker books can be treated by splitting the bindings and dividing the boo; blocks so that the resulting spine thickness of the individual blocks does not exceed 4cm. The oversewing of the book-block remains to prevent the individual pages from moving during treatment.

A further improvement of the solution is ability to penetrate can be achieved by using a re-strengthening agent of very low viscosity - with the solution of MC 40. Although the strengthening effect of MC 40 is weaker than products of higher viscosity, as for example MC 400, the paper fibres are evenly coated and according to present experience and tests, sufficient strengthening of the treated paper is achieved.

The advantage of the Viennese process is the combination of deacidification and strengthening of the bound sheets. The idea of the process and its implementation is the result of many years of experience in restoration. The Viennese method can be adopted by those who are interested.

The disadvantage of the method lies, at present, in the restricted output, which depends on the size of the plant.

4.6. Further developments

Besides the deacidification systems described above, which require considerable investment due to their dimensions and comprehensive technical plants, deacidification and strengthening processes which involve little effort are becoming more known.

A recent development is that an English firm "Archival Aids" in Spondon, Derby, has been Sable to offer a "paper treatment spray" and the "Archival Aids HCMC solution" to deacidify and strengthen paper. The deacidification solution is based on methyl magnesium carbonate. HCMC is a non-aqueous, colorless, alkaline cellulose solution which can be applied either by spraying, dipping or painting or with the help of "Archival Aids" spraying equipment.

At present solutions contain, apart from methyl alcohol also trichlor-triflour-ethane. The spraying equipment offered by fine firm permits the treatment of individual sheets and bowed cooks in a manual way.

The Interleaf VPD process of W.H. Langwell consists of a gaseous phase deacidification process. Cyclohexylamine carbonate chrystals are impregnated into the paper or sealed in porous packets. The impreganted sheet is interleaved in books or the sealed chrystals bags are placed inside boxes containing the documents. In the successive days the chrystals volatize, producing cyclohexylamine gas which deacidifies. The treatment is not permanent. Cycloherylamine is a toxic substance.

The book-keeper process of J. Kozak and Richard E. Spatz is based on the application of a non-aqueous suspension, impregnating the books With magnesium oxide and freon. The impregnation process is optimized by agitating the books in the suspension. The Pothole process takes 3 hours. The freon is evaporated and recovered in a vacuum during the renovation phase. At the moment, tests are being carried out With the help of a pilot container in a pilot project.

The parylene gas phase consolidation, a joint project between the American Institute and the library of the Science Academy in Leningrad aims to strengthen paper using polymers in the form of a gas (diparaxylylene). At the present stage of development, paper can be strengthened through the mechanical combination of parylene and cellulose. The process is irreversible.


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