In this study, ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) and L-lactide (L-LA) has been performed from cellulose fibers. The hydroxyl groups on cellulose act as initiators in the polymerization, and the polymers are covalently bonded to the cellulose fiber. As an attempt to introduce more available hydroxyl groups on the surface, and thereby obtain higher grafting efficiency in the ROP of epsilon-CL and L-LA, unmodified paper was modified with xyloglucan-bis(methylol)-2-methylpropanamide (XG-bis-MPA) and 2,2-bis(methylol)propionic acid (bis-MPA), respectively. The grafted substrates were characterized via Fourier transform infrared spectroscopy (FTIR), contact angle measurement, atomic force microscopy, and enzymatic degradation. The results showed a successful grafting of poly(epsilon-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) from the cellulose fiber surfaces. Furthermore, the results showed an improved grafting efficiency after activation of the cellulose surface with bis-MPA, and showed that the amount of grafted polymer could be controlled by the ratio of added free initiator to monomer.

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In the present work, microfibrillated cellulose (MFC) made from bleached sulfite softwood dissolving pulp was utilized to reinforce a poly(ε-caprolactone) (PCL) biopolymer matrix. To improve the dispersibility of the hydrophilic MFC in the nonpolar matrix and the interfacial adhesion in the composite material, we covalently grafted the MFC with PCL via ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). To be able to investigate the effect of the PCL graft length on the mechanical properties of the composite material, we performed ROP to different molecular weights of the grafts. Bionanocomposites containing 0, 3, and 10 wt % MFC were prepared via hot pressing using both unmodified and PCL grafted MFC (MFC-g-PCL) as reinforcement. PCL grafting resulted in improved dispersion of the MFC in a nonpolar solvent and in the PCL matrix. The mechanical testing of the biocomposites showed an improvement in the mechanical properties for the PCL grafted MFC in comparison to ungrafted MFC. It was also shown that there was an impact on the mechanical properties with respect to the PCL graft lengths, and the strongest biocomposites were obtained after reinforcement with MFC grafted with the longest PCL graft length.

The efficiency of poly(ε-caprolactone) (PCL) as a matrix polymer for cellulose nanocomposites has been investigated at the macromolecular contact level using atomic force microscopy in a colloidal probe configuration. Model cellulose microspheres grafted with PCL were prepared via ring-opening polymerization. Force measurements between the functionalized particles revealed the adhesion to be highly dependent on the contact time because of a diffusion-controlled mechanism. Moreover, an increase of the temperature to 60 degrees C (close to T(m) for the PCL graft) greatly enhanced the adhesion at the polymer-polymer interface, demonstrating the importance of entanglements in the annealing of composite materials.