Archive Storage – Paperboard or Polypropylene
Progress has been made in Australia in the quality, variety and availability of archive storage boxes and enclosures. Australian Archives (in the 1990's) used considerable initiative to introduce improved availability of better quality paperboard, made in Australia. Albox Australia Pty Ltd has since developed a range of box designs and archival storage systems in polypropylene.
It was natural that some overlap occurred during these development processes. Archivists are being offered boxes and enclosures for particular applications in either paper or polypropylene but there is little published information to help them choose which is best for the job. The relative merits of these materials are necessarily dependent on budget factors as well as chemical, physical and mechanical properties. The best answers may test budget limits but in some climatic conditions and for some situations polypropylene provides the best solutions. The purpose of this paper is to provide a brief overview of the paperboard and polypropylene options.
Many Archivists have been trained in paper practices not in plastics. Plastics is a relatively new science which involves quite different questions. To some Archivists choosing a plastic has meant taking risks and Archivists have to be careful. In many cases this has however resulted in decisions being made in favour of the known bad characteristics of paperboard because it is cheap rather than using the unproven virtues of the more costly polypropylene.
This quandary has now been resolved by Albox Australia arranging for tests on Australian polypropylene by the Image Permanence Institute in Rochester, New York. Megara (Australia) Pty Ltd, who produce the "Promeg" polypropylene used by Albox, submitted their archive grade sheet to the Institute for testing. The Institute reported that the samples met all of the requirements of the internationally recognised "Photographic Activity Test".
No paperboard box, acid free or otherwise, could be expected to perform so well. Paperboard has had its problems. The Australian quality was not acid free.
Australian Archives' co-operation with Australian manufacturers, and the fortuitous changes in papermaking practices that have been occurring in Australia for environmental reasons, have resulted in there now being considerable quality improvements. At this stage the improved quality is restricted to large buyers but it may eventually become more generally available. It is understood that it is alkaline buffered. Polypropylene is an inert and stable product which requires no buffering.
The physical and mechanical properties of paperboard and polypropylene are quite different. It is not usually possible or desirable to simply make a paperboard box design out of polypropylene. As will be discussed later paperboard has the advantage of being often, but not always, a cheaper unit cost.
Polypropylene is however a superior material. It will not rot, support mould growth or absorb moisture. Polypropylene box designs feature outfitting lids, built-in closure clasps and greater strength, particularly along creases and folds, without any increase in weight.
Independent tests performed on both paperboard and polypropylene boxes have shown that after repeated flexing and rugged handling no reduction at all in the strength of the creases and the folds was evident in the polypropylene boxes but the cardboard boxes showed considerable wear and breakage. Warehouse space requirements are normally 50% less for unassembled polypropylene boxes. Both paperboard and polypropylene boxes can be delivered flat and assembled at time of use. Ease of assembly is about the same.
Paperboard is of course flammable and so is polypropylene but polypropylene requires a temperature of some 600 degrees C to ignite. The softening point lies between 140 - 150 degrees and the melting point is approx.165 degrees C. The low thermal conductivity of polypropylene (about one hundredth that of brass) gives some protection against external temperature changes.
The most common real life fire risk situation in archives is not fire itself but when the sprinklers are activated or the fire brigade arrives. The fire is quenched but the paperboard boxes get soaked. Polypropylene boxes with outfitting lids will protect their enclosures, unless submerged, and the boxes themselves are not damaged by the water. Weight increase on exposure to water at room temperature is less than 0.2%. Furthermore solid polypropylene can be completely immersed in water without loss of mechanical strength or function.
In The Tropics
In areas of high relative humidity, paperboard boxes will absorb moisture resulting in a marked decrease in the performance of the box. Polypropylene as a material has an extremely low, virtually zero, rate of water absorption and will not become "soggy" as a result of use in humid climates.
The fact that polypropylene will not rot, mildew or support growth is significant, particularly in pre-use storage and handling where conditions are often not ideal. Polypropylene is not eaten by rats or vermin as it has no food value or attraction.
Paperboard is usually cheaper than polypropylene to produce. The price difference has however closed in recent years. Large contract buyers can get very competitive paperboard prices. However, polypropylene can be produced economically in smaller quantities and as a result can offer better prices for small and medium volume orders. If boxes of different colours are needed for archive coding, the shorter production quantities can usually be handled by polypropylene without penalty.
Australian polypropylene competes very, very favourably with imported acid free paperboard. In large items, such as textile storage boxes, the savings can be large. Albox has a policy of stocking its more popular polypropylene lines to assist the smaller archivists needing smaller quantities. The ability to buy a few at a time can save a lot of funds being tied up in warehouse stocks.
If whole of life value is more important than initial cost then polypropylene must be considered. Conservators responsible for relocating very old paperboard boxes know the high labour costs involved and the time taken in re-boxing.
Box Designs That Favour Either Paperboard or Polypropylene
Because of the price factor there are some paperboard designs, eg: the standard or No.1 Archive Box, which are produced in very large runs and at very low prices. They are therefore the favoured solution for major archives now that acid free products are available. What is available to Australian Archivists is however not always available to others with less purchasing power.
Because of its mechanical properties polypropylene is considered to be a superior product limited only by its initial price. It could be argued that very precious records justify the price difference. In some situations, such as photographic storage systems, polypropylene is virtually the only solution. Other examples include Large Textile Boxes, Glass Negative Boxes and Audio Tape Boxes. If durability is a factor (much rehandling) then polypropylene can be a preferred option for Microfilm Boxes, Satchels, Folders and Binders.
Albox has also developed archival quality ring binders with nylon ring fittings that are much more durable than paperboard or P.V.C. equivalents. As offices switch to using these archival binders - which cost no more - the tedious and costly transfer of files into storage can be greatly reduced.
For photographic materials the Albox polypropylene systems - including a variety of storage pages and enclosures - are the preferred option as they contain no adhesives or metals. They also cost much less than "mylar" and acid free paper systems.
Because of the need to strictly control the production chemistry it is unlikely that quality acid free archive boxes will ever be made from recycled materials. Both paperboard and polypropylene are however recyclable. Polypropylene can be reused indefinitely thus reducing the "trash factor" and no trees are cut down to produce it.
Because of the innovative design and distribution activities of Albox Australia Pty Ltd, Archivists and Conservators in Australia are getting a much wider choice of options when seeking storage materials.
Many paperboard boxes will of course continue to be used for short term storage because of the initial cost factor. Polypropylene boxes are however finding a widening acceptance for long term storage. For records requiring maximum preservation standards they are now an available, affordable and approved quality option.
Thanks largely to these initiatives Australia is becoming, or has become, a world leader in archival practice and innovation. Australia is not the first to use polypropylene - it is in use by the Library of Congress in the U.S.A. - but the Australian range of design options is believed now to be well in advance of anything overseas.
Quality Control Tests
Tests by E.T.R.S. Pty Ltd, an internationally recognised independent testing authority, were undertaken in the 1990's. They compared the acid response and chemical stability of the Albox polypropylene boxes and the Australian acid free paperboard boxes. The results were:
Stability of Materials:
During the acetone digestion, no significant degradation was observed of any of the polypropylene or cardboard samples.
During the boiling water leach process, the polypropylene samples maintained their integrity. During the same process, the cardboard corrugations separated and sufficient fibres were released to slow subsequent filtration. An intense blue dye was also released.
None of the samples gave a detectable acid response when titrated. The detection limit corresponds to 0.1% by weight sulphuric acid in the original sample. No detectable metals were released from the polypropylene which gave the same results as a control blank. Sodium and calcium were leached from the cardboard together with some potassium, magnesium and sulphur (probably as sulphate) and a small quantity of copper and aluminium.
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