Early commercial operation

In its early pilot mill days APM found that the standard chipper knives supplied from overseas blunted very quickly when used on eucalypts and, with the co-operation of a local steel manufacturer, developed a new steel and a new grinding procedure to remedy this.[84] APM's problems were greatly increased while the Maryvale mill was being built as the 1939 bushfires destroyed most of the extensive mountain ash forests from which it had planned to draw pulpwood. This meant not only the complication of using fire-killed timber for many years but also an increasing use of older and denser foothill species (known as 'mixed species'). Because of differences between these and the low density ash many operating problems had to be overcome, mainly due to the higher alkali requirement and lower pulp strengths of the mixed species and the more troublesome behaviour of their black liquor, particularly from older trees, during evaporation and combustion in the chemical recovery process.[85] APPM found similar black liquor problems, as well as increased corrosion when old eucalypts were used. Research by the companies and CSIRO related these problems to the high content of polyphenolic extractives in some species.[86]

The production of an acceptable groundwood at ANM also proved to depend on wood age but unlike what was found for the chemical pulping processes, the best results were obtained from older trees, as their fibres could be separated mechanically in the grinding process without the excessive damage that was caused when young woods were used. Polyphenols were also a problem for ANM, necessitating the use of much stainless steel and other resistant materials not only to prevent corrosion itself but also to minimize the strong colour that developed when they reacted with iron and some other cations. ANM's early newsprint was of a poor colour compared with overseas products made from softwoods, even though some bleaching with zinc hydrosulphite was applied. A product of better appearance resulted after ANM developed and introduced a special treatment to remove polyphenols based on acidifying and then extracting the groundwood with sodium hydroxide.[87]

A major area of concern for the new industry proved to be the refining of the eucalypt soda and kraft pulps, that is, the mechanical treatment which must be applied to make fibres 'felt' together well enough when the fibre suspension is being drained on the moving wire mesh of the paper machine and subsequently form strong inter-fibre bonds during pressing and drying. Eucalypt pulp fibres are relatively short and stiff compared with the softwood pulp fibres for which the refining equipment of the time was designed and this meant that both APM and APPM had to develop suitable methods to meet their special needs as, although hardwood soda pulps had been used overseas in printing papers, they were generally a minor component, whereas in APPM's case they were to form 80 or even 100 per cent of the furnish. While APM used generally lower eucalypt percentages (40-80 per cent) their strength requirements were very high; moreover, no other company in the world was known at that time to be successfully using hardwood kraft pulps as a major component in strong papers.

Australian Academy of Technological Sciences and Engineering