1977 Volume 1

In general, only qualitative information is available concerning the mainly negative effect of the various processing stages of papermaking, after-processing and usage, on the recyclability and properties of wastepaper as a raw material for further paper making. However, it is quite unknown to what extent such negative influence is exerted by the various processing stages as, for instance, stock preparation, wet pressing, drying, calendering and supercalendering, printing, corrugating, and so on.

Esterification of pulp fibres have been performed in pyridine and toluene. The influence on swelling and the mechanical properties of sheets are shown to be different at the same level of esterification obtained by the two methods. This is interpreted to be due to the topological position of the acetyl group in the cell wall. Thus, esterification in toluene tends to allocate the esterification to the surface while in pyridine the interior of the cell wall is made accessible. At low degree of esterification in pyridine an increase in swelling is obtained. Thus, the hydrophobic groups may be seen as structure-breakers primarily by keeping the carbohydrate chains apart which otherwise would tend to form water-inaccessible regions, due to extensive hydrogen bonding. This maximum in swelling is maintained even in the dry state. Thus, the equilibrium moisture content is higher in a fibre moderately esterified in pyridine than a nontreated fibre. The introduction of acetyl groups is also shown to have an influence on the reswelling of the fibre after drying. The loss in swelling after drying is considerably less after drying for a moderately esterified fibre than for a nontreated fibre. Consequently the retention of the strength of the sheet has been improved. Essentially moderately esterified fibres which have been once dried yield a sheet with a strength equal to never dried virgin fibres.

The experiments with the fibres esterified in toluene did not yield the same effect indicating that the presence of hydrophoric groups inside the cell wall is necessary in order to maintain the swelling properties of the fibres. The results indicate new ways of permanenting the strength potential of recycled fibres and have illustrated the fundamental mechanism leading to the decrease of strength potential due to the drying of virgin fibres.

Thispaper is intended to summarise and follow up the papers presented at the Spring Conference of the B.P. and B.M.A. Technical Section in London in 1973 and the Eucepa Symposium in Bratislava in 1976.

In 1968 the Fibre Institute of the Netherlands Organisation for Applied
Scientific Research (TNO) initiated, in close co-operation with the Research
Association of the Netherlands Paper Industry, a programme to promote
the use of waste paper. This programme, which is still in progress, covers –

1 . An overall comparison of mills which use clean and/or mixed waste paper.
2. Pulping, deflaking, cleaning, dispersing, de-inking and bleaching.
3. Treatment of sludges.
4. An analysis of raw materials losses.

The studies are based mainly on comparisons of recycling equipments installed in Dutch paper and board mills. Special trials were made using the pilot plants of paper machine manufacturers.

The conclusions of many studies on material policy emphasise the need for materials conservation and more efficient utilisation of materials. Recycling of municipal waste is an alternative to solid waste disposal and a means for conserving our natural resources. Although the benefits from recycling are many, there are technological and economic barriers to large scale recycling in the private sector. Unless these uncertainties are removed, increased recycling will occur only when no other alternatives exist.

I believe that the most difficult and complex area in the fibre science of paper-making is precisely the theme of the present conference. This is because the subjects we have addressed owe their existence to the interaction of a trinity of complex entities: (1) water, (2) cellulose, and (3) the structure of fibres and paper.

In closing this symposium I have three things to say. The first is to thank you all for your contributions, both in public and outside this lecture theatre. The stars who were expected to shine have not disappointed us; the others of less renown have either had their say or listened and learned. Everyone has worked hard and I thank you all.

The second is the matter of the subject for the next symposium. It will take place in September 1981, probably in Cambridge. We have not yet agreed upon a form of words for the title, but we are fairly well agreed about what we mean. The idea we have is to discuss how we can use our paper science to decide what properties we require from our raw materials and exactly how they should be processed in order to obtain the specified product. Ladies and Gentlemen. Finally it only remains to wish all of you a safe journey home and to hope to meet you all again at our seventh symposium.