Preparation and characterization of water-redispersible nanofibrillated cellulose in powder form |
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Authors: | Ch Eyholzer N Bordeanu F Lopez-Suevos D Rentsch T Zimmermann K Oksman |
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Institution: | 1.Swiss Federal Laboratories for Materials Testing and Research (EMPA),Dübendorf,Switzerland;2.Division of Manufacturing and Design of Wood and Bionanocomposites,Lule? University of Technology (LTU),Lule?,Sweden |
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Abstract: | Water-redispersible, nanofibrillated cellulose (NFC) in powder form was prepared from refined, bleached beech pulp (RBP) by
carboxymethylation (c) and mechanical disintegration (m). Two routes were examined by altering the sequence of the chemical
and mechanical treatment, leading to four different products: RBP-m and RBP-mc (route 1), and RBP-c and RBP-cm (route 2).
The occurrence of the carboxymethylation reaction was confirmed by FT-IR spectrometry and 13C solid state NMR (13C CP-MAS) spectroscopy with the appearance of characteristic signals for the carboxylate group at 1,595 cm−1 and 180 ppm, respectively. The chemical modification reduced the crystallinity of the products, especially for those of route
2, as shown by XRD experiments. Also, TGA showed a decrease in the thermal stability of the carboxymethylated products. However,
sedimentation tests revealed that carboxymethylation was critical to obtain water-redispersible powders: the products of route
2 were easier to redisperse in water and their aqueous suspensions were more stable and transparent than those from route
1. SEM images of freeze-dried suspensions from redispersed RBP powders confirmed that carboxymethylation prevented irreversible
agglomeration of cellulose fibrils during drying. These results suggest that carboxymethylated and mechanically disintegrated
RBP in dry form is a very attractive alternative to conventional NFC aqueous suspensions as starting material for derivatization
and compounding with (bio)polymers. |
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