Biomimetically improved materials comprising microfibrillated cellulose

Sammanfattning: Microfibrillated cellulose (MFC) is a renewable, cellulosic material mainly producedfrom wood fibers, which are found in the secondary cell walls of plant cells. With theincreased demand for renewable biopolymer films in packaging, MFC has emerged asa potential alternative to non-renewable polymer films. However, some obstacles forachieving a highly ductile material that also possesses sufficient barrier propertiesremain. Bacterial cellulose (BC) is a source of nanocellulose that has been reported tohave higher purity, higher flexibility, and better water-absorption capacity and tensilestrength than plant-derived cellulose. One source of BC is from the production ofKombucha, where BC is produced by acetic acid bacteria in a "Symbiotic Culture OfBacteria and Yeast", generally referred to as SCOBY. During SCOBY fermentation, amulti-layered biofilm will form on the air-medium interface. The film consists ofmicrofibrillated bacterial cellulose of high purity and mechanical strength. In thisstudy, the objective was to find out how mechanical properties of a film made ofmicrofibrillated cellulose can be improved by learnings obtained from investigatingthe properties and composition of a film made from SCOBY cellulose. Characterization of the intrinsic properties of washed and unwashed SCOBY wasperformed by using field emission scanning electron microscopy (FE-SEM), Fouriertransforminfra-red (FTIR) spectroscopy, and moisture uptake analysis. Gaschromatography - mass spectrometry (GC-MS) was utilized to examine the presenceof potential plasticizing compounds from the fermentation. Uniaxial tensile testingwas performed on MFC films plasticized with discovered fermentation products toanalyze their impact on the mechanical properties of MFC, such as strain-at-break andE modulus. Additionally, to evaluate how washed and unwashed BC from SCOBYpotentially could be incorporated into MFC films to improve ductility, a study on theeffect of fluidization was performed. The characterization confirmed the high purity of washed SCOBY and the high waterabsorptioncapacity of unwashed SCOBY. GC-MS of dry SCOBY revealed thepresence of hydrophilic compounds from the fermentation with potential to act as biobasedplasticizing agents in SCOBY cellulose. Glycerol and another compound foundin dry SCOBY were tested for their plasticizing properties in MFC films. Glycerolwas found to increase the strain-at-break for MFC films with 181%. The other studiedcompound also improved the ductility of the MFC material. Thereby, a newapplication of this compound was discovered. From the fluidization study, uniaxialtensile testing revealed a strain-at-break of (10.5 ± 0.4) % and E modulus of (10500 ±1140) MPa for MFC films containing 10% washed SCOBY material. Thiscorresponds to an increase in strain-at-break of 402% compared to pure MFC films(2.09 ± 0.42), successfully improving the ductility. The results from this study areplanned to be used as a basis for further studies in the area of bio-based packaging.