Surface Modification of Cellulose by Covalent Grafting and Physical Adsorption

Abstract: The interest in new environmentally friendly cellulose?based productshas increased tremendously over the last years. At the same time theSwedish forest industry faces new challenges in its strive to increase the utilization of cellulose fibers in high?value end?products. The aim of this study was to expand the toolbox for surface modification of cellulose byemploying covalent surface?initiated (SI) polymerizations or by physicaladsorption of polymers. SI?ring?opening polymerization (ROP) of ??caprolactone (??CL) was performed from filter paper (FP) and high surface area nanopaper (NP).Larger amounts of polycaprolactone (PCL) were grafted from NP, compared to FP, owing to the higher amount of available initiating hydroxyl groups. Furthermore, the mechanical properties of PCL were improved by the grafting of FP and NP, as compared to pure PCL.It is challenging to characterize a polymer grafted from a surface. Hence, quartz crystal microbalance with dissipation (QCM?D) was employed to investigate SI?ROP in real time from a cellulose model surface. Furthermore, it was shown by colloidal probe AFM that increased lengthof grafted PCL, from cellulose microspheres, improved the interfacialadhesion to a pure PCL surface, suggesting that chain entanglements havea significant impact on the interfacial properties. Increased temperatureand time in contact also improved the adhesion.In order to investigate the degree of substitution (DS) and the degree of polymerization (DP), PCL?grafted hydrolyzed cellulose cotton linters (HCCL) were studied by solid state NMR. It was found that despite a DS of only a few percent, the surface character changed considerably; furthermore, the DS was virtually independent of the DP. To increase theamount of grafted polymer, ring?opening metathesis polymerization (ROMP) of norbornene was performed from FP. Short polymerizationtimes and low temperatures resulted in highly grafted surfaces. Alternatively, physical adsorption by electrostatic interactions was employed to modify a cellulose model surface in the QCM?D. Cationic latex nanoparticles of poly(dimetylaminoethyl methacrylate?co?methacrylicacid)?block?poly(methyl methacrylate) were produced by reversible addition?fragmentation chain?transfer (RAFT)?mediated surfactant?freeemulsion polymerization by polymerization?induced self?assembly (PISA).This strategy does not require any organic solvents and could potentiallybe introduced in industrial processes.