Tissue World Magazine
Alexandra Stuthridge, Technical Business Manager, BioProducts Institute (BPI)

The Northern softwood pulp supplied by Metsä Fibre in its Botnia-branded products are used as raw material for a range of fibre-based paper and board products, and products based on refined wood-based biochemical. For tissue producers, their requirements for raw material generally include excellent softness and high tensile strength. Depending on the end product, functional properties such as absorption
capacity may also play an important role. Botnia softwood in tissue provides high strength to the base sheet throughout the process. The ideal softwood fibre for tissue requires a minimum amount of refining
energy to reach the desired strength level in order to minimise generation of fines and maximise dewatering properties and bulk.

Gaining deeper knowledge
Metsä Fibre has recently been studying the effect of the fibre number of its tissue-grade pulps. When producing low-basis-weight paper such as tissue, the fibre number becomes more important than in the case of printing paper or board, with thicker paper and more fibres. The company has observed that the fibre number can be used in conjunction with the yield figures expressed in its Botnia FOX quality index to guarantee performance in both paper machines and converting lines beyond that of competitors’ pulps. With the aim of improving customer satisfaction and helping tissue producers more thoroughly, the company has been undertaking an ambitious development project to increase its competences  in the field of tissue-grade pulps. By working together with chemical and machinery suppliers, Metsä Fibre has gained valuable feedback, also with regards to the converting stage.

Critical converting stage
One of the main findings reached  during the study is the specific role of high-quality NBSK (Northern bleached softwood kraft) in the production of toilet tissue. Although the type of furnish and pulp grade may not have much effect when making the base paper in tissue mills, critical differences can become visible at the converting stage. The quality of the raw material base becomes particularly evident if embossing is done to the end product.

Another finding during the programme was the realisation how the terminology of paper making can be interpreted differently by different operators along the value chain. For converting
operations, for example, “strength” refers to runnability – meaning that there are no breaks in paper production.  While for paper machine operators, strength is defined as a different kind oftensile strength.

Based on the results, Metsä Fibre can assert that softwood pulp is one of thekey contributors for guaranteeing the runnability of converting lines. For tissue makers, securing the efficiency of the complete production process is crucially important.

Answering to Asian demand
Metsä Fibre’s bioproduct mill in Äänekoski, central Finland, started up in August 2017 and is the largest wood-processing plant in the Northern Hemisphere, with a yearly pulp production capacity of 1.3m tonnes. As a completely fossil-fuel free mill, boasting an electricity self-sufficiency level of 240% and a broad range of bio-products made from production side streams, the plant offers additional advantages for tissue producers looking to sustain the ecological image of their products.

The bioproduct mill was predominately created to address the continuing demand in the Asian markets. In these developing areas, a growing group of middle-class, urban consumers with rising incomes are increasing the demand also for tissue and hygienic products.

A particular observation is the growing demand in certain Chinese cities for embossed toilet tissue. This means that embossing will most certainly be a future technical challenge for China’s papermakers, and one with which Metsä Fibre is well positioned to assist with. In Europe, over 90% of the comparable local products are embossed, enabled by the softwood component of the pulp.

Making the most of pulp
The team at Metsä Fibre’s Technical Customer Service unit aims to ensure that customers are able to get the most out of the company’s high-quality pulp, providing services that are designed to tune production processes and equipment to allow for the reliable and even production of the desired quality and grade of the end product.

For example, Botnia FIT (Fibre Improvement Tool) is a tool for benchmarking commercial pulp grade properties and for simulating applications. The software makes it possible to investigate the impact of changes in the end product furnish or refining on quality and costs.

Another tool offered by the Technical Customer Service team is Botnia FORE (Fibre Optimisation and Refining Evaluation), which helps to overcome challenges related to refining. The software makes it possible to examine all of the various available refining methods and fillings to find the optimal combination for each specific case.

Since softwood pulp is the most expensive component in the furnish, the tools aim to exploit the strength potential  of pulp to its greatest extent and reduce the proportion used. This offers tissue producers the attractive advantage of making savings while improving strength.

This article was written for TWM by Metsä Fibre.