An interesting book about pulp & paper science

After a recommendation on the Papermaking Yahoo Group a few months ago, I purchased a copy of Pulp Technology and Treatment for Paper by James d’A. Clark, published in 1978 by Miller Freeman Publications, San Fransisco, California. I purchased my copy through ABE Books, having found a copy there for a not too unreasonable price.

This book takes a scientific approach to pulp processing and paper, to try to provide a more reliable view of the process than many of the empirical methods that had been developed since wood pulp was first used in the mid 1800’s. Some of the author’s theses directly contradict lore that has been passed down in the industry for decades.

There are five major sections. The first discusses the chemistry and physics of wood fibres, pulp, and paper. Section 2 describes processing steps applied to pulp and fundamental tests that are applied to the pulp and paper. More in-depth tests of the pulp and fibres are described in section 3, and the last two sections describe process control and pulp constituents, and practical ways of managing pulp and paper testing in a mill.

The book is primarily concerned with machine-made paper produced from wood pulp. Hand-formed sheets are hardly mentioned, so the reader must infer for themselves how much various principles apply. Other fibre sources typically used in hand papermaking are mentioned to contrast their properties with those of wood fibres. In most such materials, the cellulose molecules are close to parallel to the length of the fibres, whereas the cellulose in wood fibres forms relatively steep spirals around the fibre and also reverses angle several times through the thickness of the fibre.

Some of the author’s claims that contradict conventional wisdom include:

  • Beating causes fibre shortening, external fibrillation, and internal fibrillation, but not fibre “swelling” in the proper sense of the word. A side effect of the first two is the generation of “fines” (fibres too small to be caught by the screen in the paper machine) and “chop” (fibrous material so short and stumpy that it looses its fibrous character).
  • Bonding in paper is almost entirely due to fibrils and microfibrils and the innumerable contact points they form with other fibres, and not due to the presence of hemicellulose (chemicals that are close to cellulose, but not close enough to be included in the crystalline structure that cellulose forms within the fibres). Materials such as hemicellulose do, however, have a secondary effect in that they prevent fibrils loosened by beating from bonding back to their primary fibre, so they remain available for bonding to other fibres in the paper. At several places, the descriptions of ideal fibration made me think of fractals, where the splitting of the fibres would be taken all the way down to having individual cellulose molecules swaying in the water.
  • The action of the laboratory beater (which the author often calls a “toy beater”) is not a good indicator of how the pulp will behave in a production environment. Beaters like the Valley Beater recirculate the pulp and so beat most of the fibres to the same degree. In production, the beating is done by refiners rather than Hollander beaters, and these use a single pass which produces a wider range from untouched fibres to heavily beaten ones.
  • The freeness test (Canadian Standard or Schopper-Riegler) is pretty much meaningless, as all it really measures is fines content. It is not even a good indicator of drainage speed on the paper machine because of the difference in sheet weight, and also the discrepancy between the slow steady drainage in the freeness tester as compared with the somewhat turbulent drainage on the machine. Multiple freeness test results on the same pulp are highly inconsistent, and are not a good predictor of important properties of finished paper. A better test of beating progress is to measure the density of handsheets formed in the standard sheetformer that have been lightly pressed and heat dried.

I found that the information was generally presented very clearly. Section 1 in particular gave a thorough description of the behaviour of pulp fibres starting all the way from the formation of the chemical bonds that hold the cellulose molecules together.

Due to my having only a passing familiarity with some of the various pulp, fibre, and paper tests, and also to not knowing whether a particular test result was better or worse if numerically larger, I encountered some confusion in later parts of the book. A reader might benefit from maintaining a cheat sheet of tests as they are described to avoid such problems.

All in all, this book is a valuable addition to the technical paper making section of our library.

Posted in Books, Kevin

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