Fundamentals of Pulp Fiber Quality and Paper Properties, 1999 Pulping Conference Proceedings

Göran Annergren

JAG Consulting

Fundamental aspects of pulp fiber quality and paper properties are discussed on the basis of different levels in a hierarchical structure of paper, the molecular level, the fiber-wall level, the fiber level, and the fiber-network level. Different paper and board grades have different priorities regarding properties of the pulps in the furnish. Strength is only one of several different quality criteria, but a very important one.

The chemical composition of the pulps has a strong influence on the fiber properties. Cellulose is the main strength-giving component, hemicelluloses are softeners in the wet state, and lignin gives wet stiffness and resistance to strength development through refining. The amount of lipophilic extractives in pulp is always rather small but they may still be quite disturbing. Fiber morphology is a dominating factor for pulp quality (both the structure of the fiber wall and the fiber dimensions). Fiber length and coarseness are important quality criteria as is the heterogeneity of the fibrous material. In these respects there is a fundamental difference between softwood and hardwood pulps which determines how they are used.

The determination of mechanical properties of standard paper after mild beating in the laboratory is discussed as is the interpretation of the results. As an indication of potential papermaking properties, they are important for the pulp producer in the control of fiber characteristics, but the results should not be used directly to predict the behavior of the pulp in the paper mill or its impact on final paper properties. For such predictions, data are needed from applied tests in the laboratory, and on a pilot and/or commercial scale.

The lack of simple translations of current test results and often also of a common technical language for communication between pulp producer and papermaker shows that there is a need for better and more relevant test methods. Zero-span and short-span tensile testing, optical measurements and image analyses on individual fibers, and NIR spectral measurements on-line are developments which may meet the need for new methods.