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- Fernández, A., et al.
(author)
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Effects of ionizing radiation in ethylene-vinyl alcohol copolymers and in composites containing microfibrillated cellulose
- 2008
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In: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 109:1, s. 126-134
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Journal article (peer-reviewed)abstract
- This study reports on the effect of gamma radiation on morphological, thermal, and water barrier properties of pure ethylene vinyl alcohol copolymers (EVOH29 and EVOH44) and its biocomposites with the nanofiller microfibrillated cellulose (2 wt%). Added microfibrillated cellulose (MFC) preserved the transparency of EVOH films but led to a decrease in water barrier properties. Gamma irradiation at low (30 kGy) and high doses (60 kGy) caused some irreversible changes in the phase morphology of EVOH29 and EVOH44 copolymers that could be associated to crosslinking and other chemical alterations. Additionally, the EVOH copolymers and the EVOH composites reduced the number of hygroscopic hydroxyl functionalities during the irradiation processing and novel carbonyl based chemistry was, in turn, detected. As a result of the above alterations, the water barrier properties of both neat materials and composites irradiated at low doses were notably enhanced, counteracting the detrimental effect on water barrier of adding MFC to the EVOH matrix. © 2008 Wiley Periodicals, Inc.
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| 4. |
- Pääkkö, M., et al.
(author)
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Long and entangled native cellulose i nanofibers allow flexible aerogels and hierarchically porous templates for functionalities
- 2008
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In: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 4:12, s. 2492-2499
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Journal article (peer-reviewed)abstract
- Recently it was shown that enzymatic and mechanical processing of macroscopic cellulose fibers lead to disintegration of long and entangled native cellulose I nanofibers in order to form mechanically strong aqueous gels (Pääkkö¶ et al., Biomacromolecules, 2007, 8, 1934). Here we demonstrate that (1) such aqueous nanofibrillar gels are unexpectedly robust to allow formation of highly porous aerogels by direct water removal by freeze-drying, (2) they are flexible, unlike most aerogels that suffer from brittleness, and (3) they allow flexible hierarchically porous templates for functionalities, e.g. for electrical conductivity. No crosslinking, solvent exchange nor supercritical drying are required to suppress the collapse during the aerogel preparation, unlike in typical aerogel preparations. The aerogels show a high porosity of ˜98% and a very low density of ca. 0.02 g cm -3. The flexibility of the aerogels manifests as a particularly high compressive strain of ca. 70%. In addition, the structure of the aerogels can be tuned from nanofibrillar to sheet-like skeletons with hierarchical micro- and nanoscale morphology and porosity by modifying the freeze-drying conditions. The porous flexible aerogel scaffold opens new possibilities for templating organic and inorganic matter for various functionalities. This is demonstrated here by dipping the aerogels in an electrically conducting polyaniline-surfactant solution which after rinsing off the unbound conducting polymer and drying leads to electrically conducting flexible aerogels with relatively high conductivity of around 1 ×— 10-2 S cm-1. More generally, we foresee a wide variety of functional applications for highly porous flexible biomatter aerogels, such as for selective delivery/separation, tissue-engineering, nanocomposites upon impregnation by polymers, and other medical and pharmaceutical applications.
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