Blends of dissolved cellulose with acrylic acid copolymers or microfibrillated cellulose

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Eve Saarikoski Name of the doctoral dissertation Blends of dissolved cellulose with acrylic acid copolymers or microfibrillated cellulose Publisher School of Chemical Technology Unit Department of Biotechnology and Chemical Technology Series Aalto University publication series DOCTORAL DISSERTATIONS 10/2015 Field of research Polymer Technology Manuscript submitted 11 September 2014 Date of the defence 30 January 2015 Permission to publish granted (date) 9 December 2014 Language English Monograph Article dissertation (summary + original articles) Abstract The aim of the thesis was to develop dissolved cellulose (dissolved in NaOH/ZnO) based blends with acrylic acid copolymers (poly(ethylene-co-acrylic acid) (PE-co-AA) or poly(acrylamide-co-acrylic acid) (PAA-co-AA)) or microfibrillated cellulose (MFC) in the way they could be used in injection molding or for film/coating applications. This thesis summarizes the research reported in five publications supported by some unpublished results. Rheological studies done in the contexts of this work demonstrate the evolution of the alkaline dissolved cellulose/acrylic acid copolymer suspensions and dissolved cellulose/MFC suspensions during mixing and in relation to blend compositions as the properties were found to be a sum of many factors, including gelation of the suspensions. Uniform quality suspension and the best possible mixing between cellulose and copolymers were obtained by using a method in which the suspension was frozen and thawed between the mixing steps. This enabled uniform morphology with no phase separation before precipitation. With this method we managed to combine the properties of cellulose and the used acrylic acid copolymers as the analyses of the co-precipitated blends indicated good mixing between polymer phases. Good mixing between the polymers also enabled cellulose/PE-co-AA blends to be used in injection molding. Co-precipitated cellulose/PAA-co-AA films showed improved mechanical strength when compared to neat cellulose films. In coating trials, cellulose/acrylic acid copolymer blends demonstrated improved barrier properties compared to neat cellulose coating. In addition, studies of dissolved cellulose/MFC suspensions proved that by blending sufficiently small amounts of microfibrillated cellulose into cellulose solution, it is possible to prepare stable suspensions without phase separation. In rheological studies of MFC suspensions, the use of transparent measuring geometry allowed direct verification of the flocculated nature of MFC suspensions. MFC suspensions were observed in various stages of the flow and it was determined that the decomposition of micro scale MFC network in a water suspension follows the same general behavior as documented for macroscopic fiber suspensions. It was also noticed that ions in the suspending medium severely influence the flocculation and as a result, to rheological behavior of MFC suspensions.The aim of the thesis was to develop dissolved cellulose (dissolved in NaOH/ZnO) based blends with acrylic acid copolymers (poly(ethylene-co-acrylic acid) (PE-co-AA) or poly(acrylamide-co-acrylic acid) (PAA-co-AA)) or microfibrillated cellulose (MFC) in the way they could be used in injection molding or for film/coating applications. This thesis summarizes the research reported in five publications supported by some unpublished results. Rheological studies done in the contexts of this work demonstrate the evolution of the alkaline dissolved cellulose/acrylic acid copolymer suspensions and dissolved cellulose/MFC suspensions during mixing and in relation to blend compositions as the properties were found to be a sum of many factors, including gelation of the suspensions. Uniform quality suspension and the best possible mixing between cellulose and copolymers were obtained by using a method in which the suspension was frozen and thawed between the mixing steps. This enabled uniform morphology with no phase separation before precipitation. With this method we managed to combine the properties of cellulose and the used acrylic acid copolymers as the analyses of the co-precipitated blends indicated good mixing between polymer phases. Good mixing between the polymers also enabled cellulose/PE-co-AA blends to be used in injection molding. Co-precipitated cellulose/PAA-co-AA films showed improved mechanical strength when compared to neat cellulose films. In coating trials, cellulose/acrylic acid copolymer blends demonstrated improved barrier properties compared to neat cellulose coating. In addition, studies of dissolved cellulose/MFC suspensions proved that by blending sufficiently small amounts of microfibrillated cellulose into cellulose solution, it is possible to prepare stable suspensions without phase separation. In rheological studies of MFC suspensions, the use of transparent measuring geometry allowed direct verification of the flocculated nature of MFC suspensions. MFC suspensions were observed in various stages of the flow and it was determined that the decomposition of micro scale MFC network in a water suspension follows the same general behavior as documented for macroscopic fiber suspensions. It was also noticed that ions in the suspending medium severely influence the flocculation and as a result, to rheological behavior of MFC suspensions.