Les objectifs principaux des travaux de recherche réalisés sont de caractériser, quantifier et corréler les changements induits lors du recyclage sur les fibres, la pâte et le papier. Pour ce faire, des techniques de caractérisation spécifique ont été utilisées telles que la chromatographie inverse d'exclusion stérique (ISEC), l'analyse mécanique dynamique (DMA), la microscopie électronique à balayage environnementale (ESEM), la microscopie à force atomique (AFM) et la tomographie à rayons X. Le racornissement des fibres à elle seule ne peut pas expliquer totalement la perte de résistance des fibres. Lors du recyclage la largeur des fibres, l'épaisseur des parois fibreuses, la courbure, le nombre de coudes et d'irrégularité diminuent. Les points faibles à l'intérieur de la paroi augmentent dans les premiers et les derniers cycles de recyclage. Les fibres deviennent plus dures et cassantes à l'état sec. Les forces capillaires et la friction de surface augmentent à l'état humide. La surface de liaison entre fibres dans le réseau fibreux diminue initialement à cause de la perte de la flexibilité des fibres à l'état humide et des éléments fins alors que l'augmentation qui suit peut être reliée au collapse du lumen. Comme la solidité des fibres de diminue pas, la baisse des caractéristiques mécaniques du papier pourrait être attribuée à la dégradation de la qualité des liaisons et plus particulièrement à une délamination partielle de la couche P/S1. / Incorporation of recycled fibres in high value paper products can reduce costand environmental loads. Papermaking potential of cellulosic fibres decreaseswith recycling. The phenomenon of fibre hornification during pressing anddrying is normally held responsible for the loss in strength. To study the impactsof recycling on pulp, fibre and paper properties some non conventionalcharacterisation techniques like fibre saturation point, X-rays microtomography,environmental scanning electron microscopic observations, atomic forcemicroscope (PeakForce QNM mode) and inverse size exclusion chromatography(ISEC) were used. In order to achieve good reproducibility of ISEC measurements,a semi-automatic column fabrication pilot system was built. Thetechniques were first validated on refining process before being applied to therecycling process. In this study, it was found that fibre hornification alone cannot fully explain loss in strength during recycling. The loss in strength is muchmore complex and it is required to understand the morphological and ultrastructural changes associated with recycling. Fibre width, cell wall thickness,curl, kink, irregularities decreased during recycling. Fibre became hard andbrittle in dry state. Number of weak points in the fibre wall were increasedinitially and in the later recyclings. The increase in wet breaking length indicatesincreased surface friction and capillary forces with recycling. Decreasein bonded area during first recycle may be caused by the loss of fines and fibreflexibility whereas the increase afterwards may be linked to the lumen collapse.The strength of fibres did not decrease with recycling as shown by zero-spanbreaking lengths therefore the quality of bond may be deteriorated. It wasthought that the partially delaminated P/S1 layers may be responsible for theloss of paper strength. It is suggested since the significant change is associatedwith the pressing and drying of never dried pulp therefore the drying processneeds to be revisited. The delaminated layer should be restored so as to increasethe recyclability of the recovered fibres for high value paper. Influenceof recycled pulp blends on physical properties of paper was also studied. It wasrevealed that small quantity of recycled pulp can be used without significantlyaffecting the mechanical strength properties.
| Identifer | oai:union.ndltd.org:theses.fr/2012GRENI075 |
| Date | 28 September 2012 |
| Creators | Ali, Imtiaz |
| Contributors | Grenoble, Bloch, Jean Francis, Passas, Raphaël |
| Source Sets | Dépôt national des thèses électroniques françaises |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation, Text |
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