What Softwood Pulp is Best?
This is a question that we are often asked, and our answer is that “it depends.”
Different papermaking applications place different demands on their fibre components. The properties of the component pulps, especially their length, coarseness and collapsibility, strongly influence their papermaking potential and the quality of the final paper. Some papers require very high tensile strength properties while others require a very bulky porous structure. Other paper grades need folding endurance, while still others must be strong while light in weight. The skill of the papermaker produces papers in a very diverse range of grades and types and does so on a wide variety of machines. No one fibre type could possibly be ideal for all of these circumstances.
So let us start by considering the properties that contribute to Tensile strength. As before we will concentrate here on softwood fibres. Tensile strength has often been described as the most fundamental property of paper. In simple terms, tensile strength is controlled by the intrinsic strength of the fibres and the strength and area of the hydrogen bonds formed between the fibres. For a given fibre strength, increasing the sheet consolidation by wet-pressing, or increasing the strength of the bonds through hemicellulose retention, are common ways to achieve higher tensile strengths. But the most commonly used way of achieving high tensile strength in paper is through using fine, low coarseness, collapsed fibres in the paper furnish. Paper made from flat, ribbon like fibres will exhibit far higher tensile breaking length properties than paper made from cylindrical fibres (for a more detailed description, view our Morphology presentation). The graph shown here of data from pulp testing at Canfor Pulp Innovation, demonstrates the effect of coarseness on the potential to develop tensile strength. Fine fibres have a low coarseness, while coarse fibres have a high coarseness.