Boosting the drying shrinkage, extensibility and strength of paper with fibrillated cellulose

Plastics with their multiform properties are common materials used in packaging. However, these oil-based materials have drawn lots of negative attention in recent years due to the non-renewable raw material, continuously increasing amounts of plastic waste in the environment and difficulties in waste handling and recycling. The urgent need for more environmentally friendly bio-based materials is evident. Paper-based packaging is a relevant alternative with a huge market potential but the material properties of paper must be improved. In order to actively compete with plastics, a paper material that can be formed into smooth and deep 3D shapes is needed. The aim of this project is to create a highly extensible and strong bio-based material from wood fibers that could substitute plastics in packaging applications to some extend. The extensibility of cellulose fibers can be affected, for example, by modification of the fiber properties through mechanical refining, the use of an alternative drying technique or addition of papermaking additives to modify the fiber-fiber bonds. Free shrinkage of paper during drying is known to increase the extensibility of the fiber network's. Addition of fines and fibrillated fiber material have previously been shown to increase shrinkage, density, tensile strength and extensibility of paper.The effects of micro- (CMF) and nanofibrillated (CNF) cellulose on paper shrinkage, extensibility and tensile strength of paper made from a low consistency refined bleached softwood kraft pulp were investigated after unrestrained drying. Two different addition techniques were compared; wet-end addition and spray addition. Papers with high extensibility were obtained by combining additions of fibrillated material with unrestrained drying of the sheets.Paper shrinkage, tensile strength and extensibility were all affected by additions of CMF and CNF. It was seen that the increases in extensibility of the paper was directly proportional to its shrinkage during drying. Generally, addition of CNF was found to be a more effective than addition of CMF; very small quantities of CNF produced clear changes in paper properties whereas rather larger quantities of CMF were needed in order to obtain significant effects. Wet-end addition of CNF resulted in increased tensile strength and stiffness of the paper, while spray addition of CNF boosted the extensibility of the paper to a high extent. With wet-end additions of CNF, retention of the fibrillated material was quite challenging. Spray addition of CNF circumvented the problems with retention and is therefore the preferred addition technique. However, wet-end addition of CMF was more efficient than spray addition. Wet-end addition of CMF resulted in increased tensile strength and extensibility of the paper. It could be concluded that addition of micro- or nanofibrillated cellulose in combination with unrestrained drying of the paper is a promising pathway to boost extensibility of paper.