Abstract
This work aimed at investigating the feasibility of surface modification of cellulose nanocrystals (CNCs) using in situ ring opening polymerization of ε-caprolactone (ε-CL) at room temperature. Residues of flax and milkweed (Asclepias syriaca) stem fibers were used as a source of cellulose to obtain and isolate CNCs. The cationic ring opening polymerization (CROP) of the monomer ε-CL was used to covalently graft polycaprolactone (PCL) chains at the CNCs surface. Silver hexafluoroantimonate (AgSbF6) was used in combination with the extracted CNCs to initiate, at room temperature, the polymerization and the grafting reactions with no other stimulus. Fourier-Transform InfraRed (FTIR), X-ray Photoelectron Spectrometry (XPS), UV/visible absorption and Gel Permeation Chromatography (GPC) analyses evidenced the presence of PCL chains covalently grafted at CNCs surface, the formation of Ag(0) particles as well as low or moderate molecular weight free PCL chains.
Highlights
Reaction mechanism: AgSbF6 and hydroxyl groups of cellulose nanocrystals (CNCs) were used as initiators and co-initiators, respectively, to simultaneously graft PCL on the surface of CNCs and formed free PCL macromolecules at room temperature
In the activation step, AgSbF6 acts as a Lewis acid and reacts with hydroxyl groups at the CNCs surface according to an alcohol reduction reaction that leads to the formation of carbonyl compounds, protons and Ag(0) particles (R.0) [23]
This study highlighted that, simultaneous PCL polymerization and grafting at CNCs surface through in situ cationic ring opening polymerization (CROP) at room temperature are possible thanks to the presence of AgSbF6 and CNCs that act as initiator and co-initiator respectively
Summary
The use of cellulose fibers has been extensively studied due to their renewability and interesting properties as compared to petro-sourced materials [2]. Natural fibers exhibit a low durability under certain circumstances such as high humidity and biodegradation, preventing their use at a larger scale for certain applications [3]. To overcome this problem, many studies focus on the use of cellulose nanocrystals (CNCs). As compared to cellulosic fibers, CNCs are the crystalline parts of cellulose that present a better resistance to biodegradation and offer interesting properties for composite applications, such as large specific surface area and high stiffness [4]
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