Journal
INDUSTRIAL CROPS AND PRODUCTS
Volume 92, Issue -, Pages 227-235Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.indcrop.2016.08.006
Keywords
TEMPO; Cellulose nanofibers; Poly(N-isopropylacrylamide); Morphology; Swelling behaviors; Compression properties
Categories
Funding
- National Natural Science Foundation of China [31370568]
- Public Welfare Projects of Zhejiang Province [2016C33029]
- Scientific Research Foundation of Zhejiang Agriculture and Forestry University [2013FR088]
- New-shoot Talents Program of Zhejiang province [2015R412046]
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Owing to the higher aspect ratio and presence of negatively-charged carboxylate groups that would favorably interact with hydrophilic amide groups in poly(N-isopropylacrylamide) (PNIPAM) molecules, TEMPO-oxidized cellulose nanofibers (TO-CNF) is a kind of promising candidates to improve both swelling and mechanical properties of PNIPAM hydrogels. In this work, a series of TO-CNFs were isolated from inexpensive and abundant bamboo pulp to clarify effects of carboxylate contents (0.5-1.8 mmol/g) on the surfaces of TO-CNF on microstructure as well as compression and swelling properties of PNIPAM/TO-CNF composite hydrogels. An increase in the carboxylate content on the surfaces of TO-CNFs resulted in a higher degree of nanofibrillation. With increasing carboxylate content in the added TO-CNFs, the pore size of the composite hydrogels progressively became larger. It was found that the lower critical solution temperature (LCST) of PNIPAM hydrogels was independent of presence of TO-CNF and its carboxylate contents, while the equilibrium swelling ratio of PNIPAM/TO-CNF composite hydrogels below LCST were largely influenced by carboxylate contents of added TO-CNFs. The incorporation of rigid TO-CNF markedly strengthened the three-dimensional network structure of PNIPAM hydrogels, and compressive properties of the composite hydrogels were found to continuously increase with the carboxylate content in the TO-CNF. When carboxylate content of TO-CNF was 1.8 mmol/g, both compressive strength and modulus of the composite hydrogel reached 79.60 kPa and 0.97 MPa, respectively, which were 300% and 900% higher than those of pure PNIPAM one. Thus, TO-CNF appeared to be a green nanofiller that can simultaneously improve swelling and mechanical properties of PNIPAM hydrogels. (C) 2016 Elsevier B.V. All rights reserved.
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