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| 2. |
- Bordeanu, Nico, et al.
(author)
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Chemical routes for functional redispersible cellulose nanofibrils
- 2008
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In: Abstracts of Papers of the American Chemical Society. - 0065-7727. ; 235:24
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Journal article (other academic/artistic)abstract
- This lecture will present chemical routes designed for the large scale production of functional, redispersible cellulose nanofibrils (CNF) with applications in the field of adhesives, packaging and textiles. Suspensions of CNF obtained by mechanical disintegration and homogenization of pulps from bleached beech, wheat straw and oat were chemically surface-treated (e.g. silane condensation, etherification, oxidation reactions) prior to drying. This facilitates redispersion of the CNF in polymer matrices, organic or non-organic solvents showing the same network formation as native CNF suspensions. Also, treated CNF are carriers of functional groups (COOH, NH2) which are amenable to further chemical modification (e.g. by cross linking with biopolymers like PLA). The chemically modified CNF were characterized by spectroscopic (NMR, FT-IR, XPS) and morphological (SEM-EDX) methods. Also, the mechanical performance of resulting nanocomposites (CNF embedded in a model polymer matrix) was evaluated by mechanical (universal tensile tests) and dynamic mechanical analysis (DMA).
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| 3. |
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| 4. |
- Borges, Ana C., et al.
(author)
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Nanofibrillated cellulose composite hydrogel for the replacement of the Nucleus Pulposus
- 2011
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In: Acta Biomaterialia. - : Elsevier BV. - 1742-7061 .- 1878-7568. ; 7:9, s. 3412-3421
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Journal article (peer-reviewed)abstract
- The swelling and compressive mechanical behavior as well as the morphology and biocompatibility of composite hydrogels based on Tween® 20 trimethacrylate (T3), N-vinyl-2-pyrrolidone (NVP) and nanofibrillated cellulose (NFC) were assessed in the present study. The chemical structure of T3 was verified by FTIR and 1H NMR and the degree of substitution (DS) was found to be around 3. Swelling ratios of neat hydrogels composed of different concentrations of T3 and NVP were found to range from 1.5 to 5.7 with decreasing concentration of T3. Various concentrations of cellulose nanofibrils (0.2 to 1.6 wt%) were then used to produce composite hydrogels that showed lower swelling ratios than neat ones for a given T3 concentration. Neat and composite hydrogels exhibited typical non-linear response under compression. All composite hydrogels showed an increase in elastic modulus compared to neat hydrogel of about 3 to 8-fold, reaching 18 kPa at 0% strain and 62 kPa at 20% strain for the hydrogel with the highest NFC content. All hydrogels presented a porous and homogeneous structure, with interconnected pore cells of around 100 nm in diameter. The hydrogels are biocompatible. The results of this study demonstrate that composite hydrogels reinforced with NFC may be viable as nucleus pulposus implant due to their adequate swelling ratio that may restore annulus fibrosus loading and their increased mechanical properties that could possibly restore the height of intervertebral discs.
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| 5. |
- Eyholzer, Christian, et al.
(author)
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Biocomposite hydrogels with carboxymethylated, nanofibrillated cellulose powder for replacement of the nucleus pulposus
- 2011
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 12:5, s. 1419-1427
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Journal article (peer-reviewed)abstract
- Biocomposite hydrogels with carboxymethylated, nanofibrillated cellulose (c-NFC) powder were prepared by UV polymerization of N-vinyl-2-pyrrolidone with Tween 20 trimethacrylate as a crosslinking agent for replacement of the native, human nucleus pulposus (NP) in intervertebral discs. The swelling ratios and the moduli of elasticity in compression of neat and biocomposite hydrogels were evaluated in dependence of c-NFC concentration (ranging from 0 to 1.6% v/v) and degree of substitution (DS, ranging from 0 to 0.23). The viscoelastic properties in shear and the material relaxation behavior in compression were measured for neat and biocomposite hydrogels containing 0.4% v/v of fibrils (DS ranging from 0 to 0.23) and their morphologies were characterized by cryo-scanning electron microscopy (cryo-SEM). The obtained results show that the biocomposite hydrogels can successfully mimic the mechanical and swelling behavior of the NP. In addition, the presence of the c-NFC show lower strain values after cyclic compression tests and consequently create improved material relaxation properties, compared to neat hydrogels. Among the tested samples, the biocomposite hydrogel containing 0.4% v/v of c-NFC with a DS of 0.17 shows the closest behavior to native NP. Further investigation should focus on evaluation and improvement of the long-term relaxation behavior.
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| 6. |
- Eyholzer, Christian, et al.
(author)
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Dispersion and reinforcing potential of carboxymethylated nanofibrillated cellulose powders modified with 1-hexanol in extruded poly(lactic acid) (PLA) composites
- 2012
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In: Journal of Polymers and the Environment. - : Springer Science and Business Media LLC. - 1566-2543 .- 1572-8919 .- 1572-8900. ; 29:4, s. 1052-1062
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Journal article (peer-reviewed)abstract
- Bionanocomposites of poly(lactic acid) (PLA) and chemically modified, nanofibrillated cellulose (NFC) powders were prepared by extrusion, followed by injection molding. The chemically modified NFC powders were prepared by carboxymethylation and mechanical disintegration of refined, bleached beech pulp (c-NFC), and subsequent esterification with 1-hexanol (c-NFC-hex). A solvent mix was then prepared by precipitating a suspension of c-NFC-hex and acetone-dissolved PLA in ice-cold isopropanol (c-NFC-hex sm), extruded with PLA into pellets at different polymer/fiber ratios, and finally injection molded. Dynamic mechanical analysis and tensile tests were performed to study the reinforcing potential of dried and chemically modified NFC powders for PLA composite applications. The results showed a faint increase in modulus of elasticity of 10 % for composites with a loading of 7.5 % w/w of fibrils, irrespective of the type of chemically modified NFC powder. The increase in stiffness was accompanied by a slight decrease in tensile strength for all samples, as compared with neat PLA. The viscoelastic properties of the composites were essentially identical to neat PLA. The absence of a clear reinforcement of the polymer matrix was attributed to poor interactions with PLA and insufficient dispersion of the chemically modified NFC powders in the composite, as observed from scanning electron microscope images. Further explanation was found in the decrease of the thermal stability and crystallinity of the cellulose upon carboxymethylation
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| 7. |
- Eyholzer, Christian
(author)
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Dried nanofibrillated cellulose and its bionanocomposites
- 2011
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Doctoral thesis (other academic/artistic)abstract
- During the past decade there has been a growing interest in the reinforcement of synthetic polymers with cellulose nanowhiskers and nanofibrillated cellulose (NFC) obtained from plants or bacteria. Their beneficial mechanical properties like high stiffness and strength, in combination with their low mass allowed successful reinforcement of water based polymer dispersions (latexes) for the production of solution cast composite films. However, the production of fully degradable or biocompatible nanocomposites containing NFC with high aspect ratio and diameters below 100 nm is still a challenging task. One of the main issues to overcome is irreversible agglomeration (hornification) of NFC. Hornification can occur during drying of aqueous NFC suspensions or during compounding of NFC with hydrophobic polymers and it can be explained with the formation of a large number of hydrogen bonds between the hydroxyl groups of adjacent nanofibrils. This process is accompanied by a considerable decrease of the NFC aspect ratio and consequently results in the complete loss of its beneficial properties. Therefore, the objective of this PhD work was to chemically functionalize NFC in order to prevent hornification during drying and to develop novel bionanocomposites with well dispersed NFC, displaying improved properties compared to the neat polymers. Successful preparation of such bio-based composites could open up ways to new applications in e.g. medicine, bio-packaging or horticulture. In this study, a method for the preparation of water-redispersible NFC in powder form was developed, comprising carboxymethylation and mechanical disintegration of refined, bleached beech pulp (RBP). The powders formed stable gels when dispersed in water and SEM images confirmed that carboxymethylation had successfully prevented hornification of NFC during drying. Dynamic mechanical analysis (DMA) of poly(vinyl acetate) latex composites showed that carboxymethylation did not negatively influence the reinforcing potential of NFC. Consistently, the reinforcing potential of c-NFC was not altered by the drying procedure, as was shown by DMA experiments and tensile tests of hydroxypropyl cellulose composites containing dried and never-dried c-NFC. In a subsequent study, bionanocomposites were developed by UV-photopolymerization of N-vinyl-2-pyrrolidone in presence of a trimethacrylate crosslinker and water-redispersed c-NFC powder to yield a biocompatible hydrogel for the replacement of degenerated human Nucleus Pulposus (NP) in intervertebral discs. The native structure and function of the NP was mimicked by the randomly oriented c-NFC fibrils in the hydrogel matrix. The biocomposite hydrogels showed similar values for swelling ratio and modulus of elasticity in compression, compared to native NP. A final study focused on the feasibility of an industrial up-scaling of poly(lactic acid) composites containing compatibilized c-NFC using extrusion.
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| 8. |
- Eyholzer, Christian, et al.
(author)
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Preparation and characterization of water-redispersible nanofibrillated cellulose in powder form
- 2010
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In: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 17:1, s. 19-30
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Journal article (peer-reviewed)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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| 9. |
- Eyholzer, Christian
(author)
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Preparation and properties of dried nanfibrillated cellulose and its nanocomposites
- 2010
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Licentiate thesis (other academic/artistic)abstract
- The production of fully degradable nanocomposites with biopolymers as matrix and cellulose nanofibrils with high aspect ratios as reinforcement is still a challenging task. Also, due to the large amount of hydroxyl groups on the surface of these nanofibrils, they tend to irreversibly agglomerate during drying. This process, known as hornification, decreases the aspect ratio of the nanofibrils. Consequently, their reinforcing potential in nanocomposites is lowered. Thus, the objective of this PhD project is to produce novel biopolymer composites that are reinforced by functionalised cellulose nanofibrils in powder form. A successful preparation of such bio-based composites could open up ways to new applications in e.g. medicine, bio-packaging or horticulture. In order to induce an optimal compounding of the fibrils with different biopolymers, good fibril/matrix embedding is required. Therefore, the cellulose nanofibrils have to be modified appropriately to match the hydrophilic or hydrophobic nature of the polymer matrix.The production of fully degradable nanocomposites with biopolymers as matrix and cellulose nanofibrils with high aspect ratios as reinforcement is still a challenging task. Also, due to the large amount of hydroxyl groups on the surface of these nanofibrils, they tend to irreversibly agglomerate during drying. This process, known as hornification, decreases the aspect ratio of the nanofibrils. Consequently, their reinforcing potential in nanocomposites is lowered. Thus, the objective of this PhD project is to produce novel biopolymer composites that are reinforced by functionalised cellulose nanofibrils in powder form. A successful preparation of such bio-based composites could open up ways to new applications in e.g. medicine, bio-packaging or horticulture. In order to induce an optimal compounding of the fibrils with different biopolymers, good fibril/matrix embedding is required. Therefore, the cellulose nanofibrils have to be modified appropriately to match the hydrophilic or hydrophobic nature of the polymer matrix. In the first study, water-redispersible, nanofibrillated cellulose (NFC) in powder form was prepared from refined, bleached beech pulp (RBP) by carboxymethylation and mechanical disintegration. The sequence of the treatments influenced the stability of the final products in water. When carboxymethylation was applied first, enhanced disintegration of RBP into its sub-structural elements was observed. The prepared powder of this route formed a stable gel in water without sedimentation after 20 h. SEM images affirmed a significant reduction of cellulose nanofibrils agglomeration compared to unmodified NFC. The results suggest that NFC in dry form could be used as an alternative to conventional NFC in aqueous suspensions used as starting material for derivatization and compounding with biopolymers.
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| 10. |
- Eyholzer, Christian, et al.
(author)
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Reinforcing effect of carboxymethylated nanofibrillated cellulose powder on hydroxypropyl cellulose
- 2010
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In: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 17:4, s. 793-802
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Journal article (peer-reviewed)abstract
- Bionanocomposites of hydroxypropyl cellulose (HPC) and nanofibrillated cellulose (NFC) were prepared by solution casting. The various NFC were in form of powders and were prepared from refined, bleached beech pulp (RBP) by mechanical disintegration, optionally combined with a pre- or post mechanical carboxymethylation. Dynamic mechanical analysis (DMA) and tensile tests were performed to compare the reinforcing effects of the NFC powders to those of their never-dried analogues. For unmodified NFC powders an inferior reinforcing potential in HPC was observed that was ascribed to severe hornification and reagglomeration of NFC. In contrast, the composites with carboxymethylated NFC showed similar behaviors, regardless of the NFC suspensions being dried or not prior to composite preparation. SEM characterization confirmed a homogeneous dispersion of dried, carboxymethylated NFC within the HPC matrix. These results clearly demonstrate that drying of carboxymethylated NFC to a powder does not decrease its reinforcing potential in (bio)nanocomposites.
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| 13. |
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| 14. |
- López-Suevos, Francisco, et al.
(author)
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DMA analysis and wood bonding of PVAc latex reinforced with cellulose nanofibrils
- 2010
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In: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 17:2, s. 387-398
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Journal article (peer-reviewed)abstract
- Suspensions of commercial refined beech pulp (RBP) were further processed through mechanical disintegration (MD-RBP), chemical modification (CM-RBP) and through chemical modification followed by mechanical disintegration (CM-MD-RBP). Nanocomposites were prepared by compounding a poly(vinyl acetate) (PVAc) latex adhesive with increasing contents of the different types of nanofibrils, and the resulting nanocomposites were analyzed by dynamic mechanical analysis (DMA). Also, the suitability of using the CM-RBP fibrils to formulate PVAc adhesives for wood bonded assemblies with improved heat resistance was studied. The presence of cellulose nanofibrils had a strong influence on the viscoelastic properties of PVAc latex films. For all nanocomposites, increasing amounts of cellulose nanofibrils (treated or untreated) led to increasing reinforcing effects in the glassy state, but especially in the PVAc and PVOH glass transitions. This reinforcement primarily resulted from interactions between the cellulose fibrils network and the hydrophilic PVOH matrix that led to the complete disappearance of the PVOH glass transition (tan δ peak) for some fibril types and contents. At any given concentration in the PVOH transition, the CM-MD-RBP nanofibrils provided the highest reinforcement, followed by the MD-RBP, CM-RBP and the untreated RBP. Finally, the use of the CM-RBP fibrils to prepare PVAc reinforced adhesives for wood bonding was promising since, even though they generally performed worse in dry and wet conditions, the boards showed superior heat resistance (EN 14257) and passed the test for durability class D1.
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| 15. |
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| 16. |
- Zimmerman, Tanja, et al.
(author)
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High potential of cellulose nanofibrils for technical applications
- 2008
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In: Abstracts of Papers of the American Chemical Society. - 0065-7727. ; 235:24
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Journal article (other academic/artistic)abstract
- Cellulose nanofibrils could be very useful for an application in waterborne coatings or adhesives to improve hardness, cohesive and adhesive strength, stiffness, exploitation or thermal creep. Application developments in electronics (LCD panels) where the transparency of cellulose nanocomposites could be used or in nanopapers for filters and membranes are also conceivable. A challenge is the combination of cellulose fibrils with natural polymers. Extensive applications in medicine, food, packaging or transportation are conceivable. Possible raw materials are polymers like poly lactic acid (PLA). To expand the use of bio-based nanocomposites for high-value applications, it is necessary to avoid the reagglomeration and internal entanglement of cellulose fibrils and to improve their homogeneous dispersion in hydrophobic polymers. Special research emphasis is therefore given to the appropriate chemical modification of cellulose nanofibrils. An overview of the high application potential of cellulose nanofibrils with respect to own product development activities will be presented.
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