Oriented nanofiber templates for resin impregnation of cellulose nanocomposites

FOR THESIS University of Oulu Faculty of Technology Degree Programme (Bachelor's Thesis, Master’s Thesis) Major Subject (Licentiate Thesis) Environmental engineering Author Thesis Supervisor Tuukka Nissilä Prof. Kristiina Oksman Title of Thesis Oriented nanofiber templates for resin impregnation of cellulose nanocomposites Major Subject Type of Thesis Submission Date Number of Pages Industrial energy and environmental engineering Master’s thesis December 2016 107 Abstract The increasing environmental awareness and tightening legislative regulations concerning the ecological sustainability of the materials used in everyday applications has led to a significant research effort being targeted on finding new alternatives to previously used materials. Especially the replacement of petroleum-based products with novel bio-based ones has been of great interest. More specifically, in the field of materials science, a significant amount of attention is being paid on finding ecologically sustainable substitutes to the traditional petroleum-derived plastics. However, the bio-based polymeric materials suffer from inferior thermomechanical properties compared to the petroleum-based ones. To improve the properties, the use of natural fibers from various plants as reinforcement has been widely studied. More recently, the interest has been in combining various nanometer scale fibers with polymer matrices to obtain materials with more favorable characteristics. A particularly potential reinforcement material is nanocellulose that can be derived from plants mechanically, chemically or enzymatically and is also synthesized by some bacterial species.The increasing environmental awareness and tightening legislative regulations concerning the ecological sustainability of the materials used in everyday applications has led to a significant research effort being targeted on finding new alternatives to previously used materials. Especially the replacement of petroleum-based products with novel bio-based ones has been of great interest. More specifically, in the field of materials science, a significant amount of attention is being paid on finding ecologically sustainable substitutes to the traditional petroleum-derived plastics. However, the bio-based polymeric materials suffer from inferior thermomechanical properties compared to the petroleum-based ones. To improve the properties, the use of natural fibers from various plants as reinforcement has been widely studied. More recently, the interest has been in combining various nanometer scale fibers with polymer matrices to obtain materials with more favorable characteristics. A particularly potential reinforcement material is nanocellulose that can be derived from plants mechanically, chemically or enzymatically and is also synthesized by some bacterial species. The most significant problem in using nanocellulose as a reinforcement in composites is achieving a sufficient fiber dispersion. The fibers are strongly hydrophilic and have a poor compatibility with hydrophobic polymers. They also have a strong tendency to form aggregates through interactions between the fibers. This leads to a less than ideal level of reinforcement and poor properties in the final composite materials. The main objective of this master’s thesis was to find an efficient way of preparing a strong composite material from pulp-based cellulose nanofibers and a polymer matrix. A literature survey was first conducted on nanocellulosic materials and their composites. The main focus was on the various ways of producing cellulose nanofiber networks with varying porosity and impregnating them with a polymeric resin. Based on the literature survey, a suitable method to prepare porous low-density cellulose nanofiber networks was then developed and the properties of the resulting samples were studied with field emission scanning electron microscopy, micro-computed tomography, image analysis and permeability measurements. Based on these characterizations the suitability of different types of samples for resin impregnation was evaluated and the most promising structures were filled with a polymer and pressed to form composite sheets. The porous nanocellulose networks, also called aerogels, were prepared via a freeze casting method. With this method, aerogels with unidirectionally aligned channel structures could be obtained. The resulting porous networks were filled with an epoxy resin using a vacuum infusion process. The final composite materials were studied with field emission scanning electron microscopy. The cellulose nanofiber network preparation process led to surprisingly strong porous structures. The pore channels were mostly unidirectionally aligned and the networks formed templates suitable for subsequent resin impregnation. However, the impregnation could not be easily accomplished and the filling of the templates was incomplete. This was due to incompatibility of the samples with the vacuum infusion method. In future, the use of different sample dimensions should be studied in addition to improving the aerogel preparation process and modifying the impregnation method. Additional Information