Radiation crosslinking of cellulose fibers to obtain rigid lightweight paperboard
Cellulosic materials are used in a wide range of areas of application, and one of these is paperboard for packaging solutions. Paper or paperboard as a packaging material has benefits like low density, low costs, high stiffness, good printability, and paper is environmentally friendly. Compared to other packaging materials, such as plastics, paper has some weaknesses By improving some of its weaknesses, paper as a packaging material, can become more competitive on the market, and knowing how to utilize this resource in a more effective and sustainable way will become increasingly important in the future.
One way to decrease the amount of fibers needed in paper and paperboard is by improving the strength properties of cellulose fibers. Greater fiber strength can be achieved by, for example crosslinking the fibers, and crosslinking can be achieved with only a small amount of chemicals. By using electromagnetic radiation, like ultraviolet (UV) radiation, the fibers can be crosslinked with the aid of a UV curing solution. Pretreatment of the fibers through an acrylic esterification reaction may enhance UV curing since polyester and acrylate groups are prone to be more reactive for UV radiation.
In this thesis, UV curing of paper sheets with the aid of a UV curing solution is evaluated with tensile tests, microscopy and water retention measurements. Both acrylic esterified paper sheets and non-treated paper sheets are evaluated. Due to acid hydrolysis on the acrylic esterified paper sheets, the non-treated paper sheets showed the highest value in strength properties with a doubled increase in tensile index. Acrylic-acid-modified (AA-modified) sheets showed an increase in tensile index that was four times higher than non-radiated AA-modified sheets, but were weaker overall than the non-treated paper sheets due to the acrylic acid pre- treatment.