Joint formation and paper strength

14.12.2021

Within FibreNet I am involved in a project related to fundamental understanding of paper strength linked to light weight boards for packaging materials. The interest in light weight packaging materials is due to environmental aspect where a goal is to reduce the amount of fibres used in packaging material while keeping the paper strength. With a reduced fibre consumption in packages material one saves energy for transportations of the gods that are shipped in the packages and also there will be a saving in the raw material used.

My research within FibreNet involves my PhD student Mengxiao (a joint PhD student between Kemira and KTH Royal institute of Technology), employed by Kemira, is working with dry strength additives. In her project we evaluate how various type of additives affect the final paper strength by combining strength measurements on hand-made paper sheets with model studies using model cellulose surfaces for a better fundamental understanding of the dry paper strength that are strongly dependent on the joint formation between individual fibres.

I have a strong background in using advanced AFM techniques to understand surface interactions and various adhesion mechanisms between different materials. Additionally, I have also developed AFM technics for measurements of elasticity of never dried pulp fibres and model cellulose beads. One of my long-time vision is to find out the molecular mechanisms that occurs during joint formation during the production of fibre-based materials, such as paper. To evaluate this, I am using high resolution measuring techniques, such as AFM and x-ray based scattering techniques (SAXS, GI-SAXS and WAXS) at large scale international synchrotron facilities. 

When producing paper out of fibres, pulp fibres are dispersed in water aiming to minimize the fibres to bundle together and enable the dispersion to be pumped into a formation unit where the paper are formed. In the formation step the water are filtered away and forcing the fibres to get close contacts and form a network were the fibres are locking them self in position. The dewatering process continues by pressing and drying with heat to remove almost all water. In water the fibres are highly swollen (in the radial direction, that makes the radius of the larger compared to the dried fibre) and during the drying the radius of the fibre is shrinking. During the dewatering step, the fibres are forced into contact and joints between the fibres can be formed. The fundamental mechanisms of what is happening on molecular level during this joint formation are far from fully understood but we are working on increasing the knowledge. However, by including chemical additives in the pulp dispersion, the paper forming process is affected and the properties of the final paper can be fine-tuned.


Figure 1: Schematic illustration of GISAX measurements performed to evaluate the internal molecular structure and its changes during cellulose drying while forming a joint.  Reprinted with permission from [1]. Copyright 2021 American Chemical Society.

 

 

 

During the recent 4 years I have initiated collaboration with scientists at the research facilities in NSLS II at BNL (Brookhaven National Laboratories), Petra III at DESY (Deutsches Elektronen-Synchrotron), and Forschungszentrum Jülich. These collaborations have resulted in multiple scientific publications where we have evaluated the drying of cellulose. Among theses our newest publication in ACS Biomacromolecules [1] where we are combining AFM and GI-SAXS to follow the drying process of cellulose while forming a joint between cellulose and cellulose. By our development of the GI-SAXS measuring principles and combining multiple analysis techniques.  We have shown that the joint strength between cellulose and cellulose is due to interpenetration of cellulose from surface to the other in combination with molecular rearrangement that occurs during the drying process, illustrated in Figure 1. We believe that this is an important step into further understanding of joint formation of cellulose. This will help us to understand how to to keep paper strength when reducing the amount of fibres used to form environmental friendlier light weight packaging materials within the continuation of the research within our FiberNet project.

 

[1] Biomacromolecules 2021, 22, 10, 4274-4283, https://doi.org/10.1021/acs.biomac.1c00845.

 

Writer:

Torbjörn Pettersson, Ph D.

KTH Royal Institute of Technology