| 1. |
- Bjurhager, Ingela, et al.
(författare)
-
State of degradation in archeological oak from the 17th century vasa ship : Substantial strength loss correlates with reduction in (holo)cellulose molecular weight
- 2012
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; :8, s. 2521-2527
-
Tidskriftsartikel (refereegranskat)abstract
- In 1628, the Swedish warship Vasa capsized on her maiden voyage and sank in the Stockholm harbor. The ship was recovered in 1961 and, after polyethylene glycol (PEG) impregnation, it was displayed in the Vasa museum. Chemical investigations of the Vasa were undertaken in 2000, and extensive holocellulose degradation was reported at numerous locations in the hull. We have now studied the longitudinal tensile strength of Vasa oak as a function of distance from the surface. The PEG-content, wood density, and cellulose microfibril angle were determined. The molar mass distribution of holocellulose was determined as well as the acid and iron content. A good correlation was found between the tensile strength of the Vasa oak and the average molecular weight of the holocellulose, where the load-bearing cellulose microfibril is the critical constituent. The mean tensile strength is reduced by approximately 40%, and the most affected areas show a reduction of up to 80%. A methodology is developed where variations in density, cellulose microfibril angle, and PEG content are taken into account, so that cell wall effects can be evaluated in wood samples with different rate of impregnation and morphologies.
|
|
| 2. |
- Nilsson, Helena, et al.
(författare)
-
Compression molded wood pulp biocomposites : A study of hemicellulose influence on cellulose supramolecular structure and material properties
- 2012
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 19:3, s. 751-760
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the importance of hemicellulose content and structure in chemical pulps on the property relationships in compression molded wood pulp biocomposites is examined. Three different softwood pulps are compared; an acid sulfite dissolving grade pulp with high cellulose purity, an acid sulfite paper grade pulp and a paper grade kraft pulp, the latter two both containing higher amounts of hemicelluloses. Biocomposites based the acid sulfite pulps exhibit twice as high Young's modulus as the composite based on paper grade kraft pulp, 11-12 and 6 GPa, respectively, and the explanation is most likely the difference in beating response of the pulps. Also the water retention value (WRV) is similarly low for the two molded sulfite pulps (0.5 g/g) as compared to the molded kraft pulp (0.9 g/g). The carbohydrate composition is determined by neutral sugar analysis and average molar masses by SEC. The cellulose supramolecular structure (cellulose fibril aggregation) is studied by solid state CP/MAS 13C-NMR and two forms of hemicellulose are assigned. During compression molding, cellulose fibril aggregation occurs to higher extent in the acid sulfite pulps as compared to the kraft pulp. In conclusion, the most important observation from this study is that the difference in hemicellulose content and structure seems to affect the aggregation behaviour and WRV of the investigated biocomposites.
|
|
