Better formability for materials through increased extensibility

Paper-based materials constitute a significant share of the world packaging market, successfully competing with plastic packaging. Paper is renewable, recyclable, sustainable and biodegredable material. However, it is lacking certain barrier properties and it is not very flexible in terms of package design; i.e. paper packaging appears in rather simple geometrical forms while plastics can be formed to the multiple shapes. Overcoming the problems of poor barrier properties and insufficient formability of paper is the key to novel packaging applications, and eventually to the strengthning the role of paper on the world packaging market. Extensibility is considered to be of high importance for the formability of paper, when advanced 3D-shapes are formed. Moreover, it affects the runnability of paper web in paper machine, finishing operations and, in printing houses. Additionally, extensibility plays a major role in converting operations such as creasing, embossing, folding, and especially 3D-forming. The primary objective of this work was to find a feasible method to increase extensibility of paper to a clearly higher lever, than for existing commercial papers. Additional objective was to evaluate applicability of such paper to be used in 3D-forming. These objectives were fulfilled by utilization of several methods, including: mechanical modification of fibres, addition of polysaccharides, and in-plane compaction of the fibreweb. Improvements in extensibility of paper obtained with these methods were further assessed for their practical relevance in the production of advanced 3D-shapes, using 2D-formability tester. Based on the obtained results, several principal observations on components of extensibility of paper-based products were made. Extensibility of paper relies on three principal factors: properties of single fibres, character of inter-fibre bonds, and the structure of the fibre network formed in the papermaking process. Extensible fibres do not necessarily form paper with high extensibility, which is emphasizing the role of the fibre network structure. A combination of mechanical treatment of fibres, addition of polysaccharides, and in-plane compaction treatment of the fibre web were found to have a positive synergy effect on the extensibility, providing values of up to 30%. The elongation of paper can be improced from 4% to 17% by the combination of tailored refining, spray addition of certain polysaccharides, and unrestrained drying of paper. Mechanical in-plane compaction of the web can further improve extensibility of unrestrained dried paper up to 25-30%. Formability of the obtained laboratory paper samples was evaluated using 2D-formability tester, and was found to be superior to currently existing formable papers. Significant improvements in the extensibility of paper allow producing novel paper-based packaging products, increasing their competitiveness compared with plastic-based packaging.