IENCE SC • VTT SCIENCE • T S E Formability of paper and its improvement N C O H I N S O I Paper and paperboard are the most utilized packaging materials in V Dissertation L • O S the world. This is due to such features as: renewability, G T 94 Y H • R biodegradability, recyclability,sustainability and unmatched G I E L S H printability. However, paper packaging is inferior to plastics in 94 E G A I R H C respect to moisture sensiivity, and limited ability to be converted H into advanced 3D shapes with added The ability of paper and paperboard to be formed into 3D shapes is described as formability, and in the fixed blank forming processes formability is governed by the extensibility of paper. The primary objective of this thesis is to improve the formability of Formability of paper and its improvement paper by increasing its extensibility. An additional objective is the characterization of formability as a mechanical property of paper and the development of a testing platform for the evaluation of formability. The formability (extensibility) of paper was improved using a set of methods which included: mechanical treatment of fibres, spraying of agar and gelatine, in-plane compaction of paper and unrestrained drying. Extensibility of paper was increased from 4% points (untreated fibres) to 15–18% points (mechanical treatment and addition of polymers), and up to 30% (in one direction) after compaction. This corresponds to tray-like shapes with a depth of 2–3 cm, depending on the curvature. Such values of formability are the highest reported so far in the scientific literature. This approach allows the production of a paper-based material with unmatched formability, which can replace certain types of plastic packaging. Replacement of plastics with paper reduces the harmful environmental impact of non-degradable and non- renewable packaging. Formability of paper and ISBN 978-951-38-8304-1 (Soft back ed.) ISBN 978-951-38-8305-8 (URL: http://www.vtt.fi/publications/index.jsp) its improvement ISSN-L 2242-119X ISSN 2242-119X (Print) ISSN 2242-1203 (Online) Alexey Vishtal VTT SCIENCE 94 Formability of paper and its improvement Alexey Vishtal VTT Technical Research Centre of Finland Ltd Thesis for the degree of Doctor of Science (Technology) to be presented with due permission for public examination and criticism in Auditorium 1702, at Tampere University of Technology, on the 4th of June, 2015, at 12:00. ISBN 978-951-38-8304-1 (Soft back ed.) ISBN 978-951-38-8305-8 (URL: http://www.vtt.fi/publications/index.jsp) VTT Science 94 ISSN-L 2242-119X ISSN 2242-119X (Print) ISSN 2242-1203 (Online) Copyright © VTT 2015 JULKAISIJA – UTGIVARE – PUBLISHER Teknologian tutkimuskeskus VTT Oy PL 1000 (Tekniikantie 4 A, Espoo) 02044 VTT Puh. 020 722 111, faksi 020 722 7001 Teknologiska forskningscentralen VTT Ab PB 1000 (Teknikvägen 4 A, Esbo) FI-02044 VTT Tfn +358 20 722 111, telefax +358 20 722 7001 VTT Technical Research Centre of Finland Ltd P.O. Box 1000 (Tekniikantie 4 A, Espoo) FI-02044 VTT, Finland Tel. +358 20 722 111, fax +358 20 722 7001 Cover image: Trays prepared from moldable paper developed by VTT. Courtesy of Marja Juvonen. Juvenes Print, Tampere 2015 Abstract Paper and paperboard are the most utilized packaging materials in the world, accounting for one third of the total packaging market by volume. This position has been achieved due to several advantageous features of paper such as: renewability, biodegradability, recyclability, and unmatched printability. Paper can be produced anywhere in the world, using local resources and at relatively low cost, which also makes it the most sustainable packaging material. Despite these beneficial features, paper packaging is in tough competition with plastic materials. The competitiveness of paper is mitigated by barrier properties, sensitivity to moisture, and limited ability to be converted into advanced 3D shapes with added functionality. The ability of paper and paperboard to be formed into 3D shapes is described as formability, or sometimes, mouldability. The investigation of formability is the core of the present thesis work. Formability can be conditionally defined as the ability of paper to be formed into 3D shapes without defects in appearance and functionality. Formability as a mechanical property represents a group of parameters which vary according to the type of forming process used. The primary objective of this thesis is to improve the formability of paper by increasing its extensibility. Such paper can be used to replace certain plastics in thermoforming packaging lines. An additional objective is the characterization of formability as a mechanical property of paper and the development of a testing platform for the evaluation of formability. It was found that the formability of paper in fixed blank forming processes is governed by the extensibility and tensile strength of paper. On the other hand, in sliding blank forming processes, it is dependent on the compressive properties of paper, elastic recovery, and the paper-to-metal coefficient of friction. The criteria of good formability are also different in these two cases, as fixed blank process formability is evaluated via the maximum depth of the shape, i.e. the deeper the shape, the better the formability. In the sliding blank process, formability is evaluated via the visual appearance of the shapes, i.e. the shapes with less profound compressive wrinkles and defects reflect good formability of paper. These results were established by comprehensive investigation of different forming processes and comparison of the outcome with the mechanical properties of paper. Taking into account the hypothesis that the formability of paper is governed by the extensibility of paper, a set of methods for its improvement was suggested. These 3 methods included combined high- and low-consistency treatment of fibres, spraying of agar and gelatine, in-plane compaction of paper and unrestrained drying. High- consistency treatment of fibres under elevated temperature induces permanent deformations to fibres such as microcompressions and dislocations, which in turn may decrease the axial stiffness of fibres, promoting shrinkage of paper and fibres. The low-consistency treatment straightens the fibres and induces the fibrillation of fibres to promote bonding, while microcompressions in fibres still exist. The spraying of agar and gelatine is likely to modify the character of the fibre joints by making them more deformable, and the drying shrinkage is also increased due to polymer addition. Finally, the fibre network was subjected to in-plane compaction and drying shrinkage which lead to buckling and fibre and network compression. As a result of the mechanical modification of fibres and improvement of bonding by the addition of agar and a combination of agar and gelatine, the extensibility of unrestrained dried paper was increased from 4% points (untreated fibres) to 15–18% points (mechanical treatment and addition of polymers). The extensibility can be increased further by up to 30% points in one direction by compaction. This corresponds to tray-like shapes with a depth of 2–3 cm, depending on the curvature. Such values of formability are the highest reported so far in the scientific literature. The approach for the production of formable paper developed in this thesis work allows the production of a paper-based material with unmatched formability, which can replace certain types of plastic packaging. Replacement of plastics with paper improves the sustainability of packaging in general, and reduces the harmful environmental impact of non-degradable and non-renewable packaging. Keywords: formability, extensibility, packaging, 3D forming, paper, fibres, bonding, compaction 4 Preface The work in this thesis was carried out at the VTT Technical Research Centre of Finland Ltd. during the period of 2011–2015. As VTT has broad expertise in the field of fibre-based material, it has been a great honour and privilege to work in such an environment. This work was funded by the Finnish Bioeconomy Cluster’s (FiBiC) Future Biorefinery (FuBio and FuBio JR2) and the Advanced Cellulose materials (Acell) programmes and by the VTT Graduate School. In addition, the International Doctoral Programme in Bioproducts Technology (PaPSaT) has provided funding for participation in scientific conferences and in many interesting courses. COST Action FP1003 (Impact of renewable materials in packaging for sustainability – development of renewable fibre and bio-based materials for new packaging applications) has provided many interesting training opportunities and EFPRO (European Fibre and Paper Research Organisation) provided funding for a short- term scientific mission to Technical University of Dresden in 2012. I am grateful to all my funders for providing me with the possibility to conduct high quality research and networking. My deepest gratitude goes to Dr. Elias Retulainen, my supervisor at VTT, for providing inspiration and guidance through the whole Ph.D. process and for always being open to discussion. My thanks to Prof. Jurkka Kuusipalo from Tampere University of Technology for guiding me through the whole Ph.D. process and for being very flexible and helpful regarding all legal issues. I also wish to thank all of my collaborating colleagues at VTT, my fellow Ph.D. students in the field, and especially the technical personnel at VTT Jyväskylä for valuable discussions and relevant advices. Dr. Kristiina Poppius-Levlin and Dr. Jukka Ketoja, former and current coordinators of the VTT Graduate School, are thanked for their support in reaching the doctoral degree. I also wish to thank the pre-examiners of my thesis, Prof. Sören Östlund and Prof. Robert Pelton, for their extremely valuable comments on the thesis manuscript. Finally my thanks go to my wife, parents, relatives, friends, and cat for moral support and making my life more diverse and interesting. Jyväskylä, April 2015 Alexey Vishtal 5 Academic dissertation Supervisor Prof. Jurkka Kuusipalo, Department of Materials Science, Tampere University of Technology, P.O.