Eucalyptus bleached kraft pulps are rich in fibers, but fibers are not the sole anatomical elements in their contents. Fibers, fiber debris, fines and vessel elements are combined in a rich blend, in a very low pulp consistency. This complex blend is usually referred to as eucalyptus pulp. On the other hand, there is a relative trend among papermakers to consider eucalyptus pulps as a commodity product; one product that independently from the origin, the performance would be required to be similar. This is an enormous technological mistake. The purpose of this manual is to show the potential differences we may find in distinct eucalyptus pulp furnishes for papermaking. Eucalyptus bleached kraft pulps may have very distinct papermaking properties, depending on the wood raw material and on the conditions applied in the manufacture of the pulp (chipping, digesting, washing, screening, bleaching, drying, etc).
The papermaking behavior of the pulp depends very much on the anatomical and chemical properties of this mixture, but also in the different pulping and papermaking processes applied to these elements. Fiber morphology and chemical constituents are both very important to allow predictions about pulp behavior in papermaking operations. Fibers consist in the most abundant pulp component. Although their dimensions in lengths and widths are rather similar for different eucalyptus pulps, the cell wall thickness plays important difference. Based on the variations of the fiber morphology and dimensions, there are important characteristics being affected in the paper-machine operation and runnability. Fiber population and coarseness may, up to certain extent, reflect this potential behavior. However, there are other issues to be considered. Fines and
fiber deformations are some of them.
Fines are important for bonding. A pulp with no fines has poor bonding ability and low strengths. However, excess of fines brings problems in drainage in the wet end section, in dewatering in the press section, and higher density in the paper sheet. Fiber deformations are not natural on fibers, the pulp and paper manufacturing processes create them. Fiber deformations may reduce individual fiber strengths, but they are important to promote bulk and absorbency properties in paper dry sheet. Cell wall integrity and microfibril organization is another issue frequently forgotten.
The pulp maker is used to change the pulping and bleaching conditions and he has no indications about the disastrous effects he may eventually be bringing to the fiber wall. The only figure he has is the measurement of the pulp viscosity, very little to really show the damages being happening in the fiber wall. Chemical characteristics of the pulps have also been proved to be important.
The hemicellulose content plays important role. In addition to hemicelluloses, fines, fiber population, fiber coarseness and bonding, there are some other important pulp characteristics, such as water retention value, fiber collapsibility, wet fiber flexibility and wet web strength. Moreover, the ability of the fiber to hold water is becoming a critical issue. Fiber charges and hysteresis-associated properties are now being part of a pulp evaluation, due to their potential influence in the paper-machine performance (drainage and dewatering) and final product quality. Pulp quality is, for all these reasons, a group of attributes that 5 may vary according to the eucalyptus wood, the pulping process and with the particular papermaking operations the pulp user has on his hands to utilize this pulp. Pulp quality is so far very dependent on the production chain: it is built along this complete chain.
Eucalyptus pulps are recommended for papermaking due to specific properties they impart to paper: bulk, opacity, formation, softness, porosity, smoothness, absorbency, dimensional stability. Faster and more sophisticated machines are being developed to run with these pulps, but the aim is not to lose these paper properties. All the considerations about pulp quality for papermaking presented in this book chapter are solely related and valid for eucalyptus bleached kraft pulps. We are not making comparisons about different fibrous raw materials or different pulping processes. When comparisons are presented, they are comparing one type of bleached kraft eucalyptus fibers to another one. When high coarseness fibers are suggested for a specific utilization (tissue and filter papers), we are referring to high coarseness eucalyptus fibers (around 9 - 11 mg/100m). Low coarseness eucalyptus fibers are in the range 4.5 - 6 mg/100m.
The same to other properties, It has to be understood that other pulp grades, as the high yield eucalyptus pulps have also their distinct advantages and own destination for paper manufacture.