Defence of doctoral thesis: Maria Wennman – Biobased and biodegradable binders for paper and nonwoven

Abstract:

Nonwovens are textile-like materials with similarities close to paper. One significant sector where nonwovens are used is for single-use products such as wet wipes and hygiene products. With an increasing global population, the manufacturing and use of nonwovens have grown significantly. With a higher standard of living worldwide, the demand for nonwoven products is expected to continue its growth in the foreseeable future. Several nonwoven materials are composed of cellulosic fibers and binder.This can be referred to as chemically bonded nonwovens. The binders are typically fossil-based and non-degradable. In this thesis, it is demonstrated that a binder composed of two polyelectrolytes (carboxymethyl cellulose and chitosan) along with citric acid, can serve as an excellent replacement for synthetic binders. Since the polyelectrolytes have opposite charges, they combine to form a polyelectrolyte complex (PEC).The PEC binder can be used both in the wet-end of a papermaking process and for treating already formed webs. Mechanical tests showed that the dry tensile strength increased significantly compared to untreated materials, as did the important wet tensile strength. It was found from Fourier-Transform Infrared Spectroscopy and Dynamic Nuclear Polarization enhanced NMR that newly established ester bonds and amide bonds, along with electrostatic interactions, were the key factors for the enhanced mechanical properties. PEC combined with sunflower oil resulted in fine emulsions that provided higher dry and wet tensile strength. Hydrophobicity in terms of high contact angles (>125°) for treated materials were also attained. Furthermore, combining PEC with two vegetable protein sources, pea protein and wheat gluten, demonstrated how the scope for PEC binders can be broadened. Together with the proteins, cellulosic materials acquired properties such as hydrophobicity and high tensile strength.