| 1. |
- Bordeanu, Nico, et al.
(författare)
-
Chemical routes for functional redispersible cellulose nanofibrils
- 2008
-
Ingår i: Abstracts of Papers of the American Chemical Society. - 0065-7727. ; 235:24
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)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).
|
|
| 2. |
|
|
| 3. |
- Eyholzer, Christian, et al.
(författare)
-
Preparation and characterization of water-redispersible nanofibrillated cellulose in powder form
- 2010
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 17:1, s. 19-30
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 4. |
|
|
| 5. |
- López-Suevos, Francisco, et al.
(författare)
-
DMA analysis and wood bonding of PVAc latex reinforced with cellulose nanofibrils
- 2010
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 17:2, s. 387-398
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 6. |
|
|
| 7. |
|
|
