Browsing by Author "Mota, Manuel"
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- Cellulose-binding domains as a tool for paper recyclingPublication . Pala, Helena; Pinto, R.; Mota, Manuel; Duarte, A. P.; Gama, Francisco MiguelTreatement of secondary paper fibres with cellulose-binding domains allows for improvements of pulp durability and of paper mechanical properties. The interfacial system fibre-water-fibre, may be affected by the CBD treatement, influencing the pulp and paper technical properties. Inverse Gas Chromatography provides experimental evidence that support this hypothesis.
- Effect of cellulase adsorption on the surface and interfacial properties of cellulosePublication . Dourado, F.; Pala, Helena; Mota, Manuel; Gama, Francisco MiguelThe surface properties of several purified cellulose (Sigmacell 101, Sigmacell 20, Avicel pH 101, andWhatman CF 11) were characterised, before and after cellulase adsorption. The following techniques were used: thin-layer wicking (except for the cellulose Whatman), thermogravimetry, and differential scanning calorimetry (for all of the above celluloses). The results obtained from the calorimetric assays were consistent with those obtained from thinlayer wicking – Sigmacell 101, a more amorphous cellulose, was the least hydrophobic of the analysed celluloses, and had the highest specific heat of dehydration. The other celluloses showed less affinity for water molecules, as assessed by the two independent techniques. The adsorption of protein did not affect the amount of water adsorbed by Sigmacell 101. However, this water was more strongly adsorbed, since it had a higher specific heat of dehydration. The more crystalline celluloses adsorbed a greater amount of water, which was also more strongly bound after the treatment with cellulases. This effect was more significant for Whatman CF-11. Also, the more crystalline celluloses became slightly hydrophilic, following protein adsorption, as assessed by thin-layer wicking. However, this technique is not reliable when used with cellulase treated celluloses.
- Effects of enzymatic treatment and refining on the properties of recycled pulpPublication . Pala, Helena; Mota, Manuel; Gama, Francisco MiguelThe effect of refining and enzymatic treatment on secondary fibre properties is shown. The following treatment sequences were studied: (i) refining; (ii) refining + enzymatic treatment; (iii) enzymatic treatment + refining; (iv) enzymatic treatment. The effectiveness of the methods was evaluated by measuring physical and mechanical properties of pulp and paper (drainage rate, burst, tensile and tear indexes). The obtained data revealed that combined refining and enzymatic treatment can be considered as a valuable methodology to upgrade recycled pulps. The first is responsible for increasing burst and tensile resistance. The second, if developed under controlled conditions, alloes better drainage, with only slight variation on paper mechanical properties.
- Enzymatic depolymerisation of cellulosePublication . Pala, Helena; Mota, Manuel; Gama, Francisco MiguelCellulose degree of polymerisation (DP) was determined in paper pulps and commercial powder celluloses before and after the enzymatic treatment with a blend of cellulases and hemicellulases. Three different methods were used: (i) chemical method, based on the measurement of the cellulose reducing power; (ii) viscosimetry; and (iii) gel permeation chromatography. Although based in very different principles, the three methods find similar DP values in the case of pure cellulose with narrow molecular weight distributions. The chemical method is more sensitive to detect enzymatic depolymerisation and appears to provide a good estimation of the number-average DP. GPC data offers more detailed information about the enzymes mode of action on the fibres, showing that cellulose hydrolysis in the presence of the commercial preparation Celluclast 1.5L follows a layer-by-layer solubilisation mechanism. 2006 Elsevier Ltd. All rights reserved.
- Enzymatic modification of paper fibresPublication . Pala, Helena; Mota, Manuel; Gama, Francisco MiguelThe enzymatic mode of action in paper fibre upgrading is still uncertain. In an attempt to clarify how enzymes modify pulp and paper properties, several parameters were analysed in the present work: (i) thermal analysis of the water–solid surface interactions; (ii) fibre cake permeability; (iii) particle size analysis. The results obtained suggest that enzymes modify the interfacial properties of fibres, increasing the water affinity, which in turn change the technical properties of pulp and paper, such as drainability and strength. The modification of paper and pulps following a treatment with cellulosebinding domains further supports this hypothesis.
- Enzymatic upgrade of old paperboard containersPublication . Pala, Helena; Lemos, M. A.; Mota, Manuel; Gama, Francisco MiguelThe use of enzymes in secondary fiber (old paperboard containers) upgrading was investigated. The following aspects were analyzed: (i) the effect of several enzymes and (non-hydrolytic) cellulose-binding domains on the pulp and paper properties; (ii) factors influencing enzymatic treatment of secondary fiber: enzyme dosage and reaction time; and (iii) enzyme action on fractions with different fiber-length. In general, all the tested enzymatic preparations were able to improve the pulp drainability. In most cases this improvement was obtained at the expense of paper strength. The use of cellulose-binding domains allowed for the simultaneous increase in drainability and strength properties.
- Enzymatic versus chemical deinking of non-impact ink printed paperPublication . Pala, Helena; Mota, Manuel; Gama, Francisco MiguelEnzymatic versus chemical deinking is examined for MOW and photocopy prints. Several enzymatic preparations and two fibre/ink particle separation methods are tested. Deinking was monitored by image analysis and standard pulp and paper characterisation procedures. The effectiveness of the fibre/ink particle separation method depends on the ink particle’s size: for smaller particles a washing step is recommended whereas for larger particles, the use of flotation is necessary. The enzymatic treatment is a competitive alternative for MOWand photocopy paper deinking. However, the process requires the selection of an adequate enzymatic preparation for each paper grade.
- Factors influencing MOW deinking: laboratory scale studiesPublication . Pala, Helena; Mota, Manuel; Gama, Francisco MiguelThe deinking of MOW is examined at laboratorial scale. The effect of deinking aids, pre-washing and mixing are studied. The operating conditions during pulp treatment affect the pulp and paper properties, interfering with the mechanism of ink removal and modifying the ink particle characteristics. Pre-washing the pulp facilitates the deinking process. Cellulolytic enzymes and deinking chemicals are comparable in terms of ink removal ability.
- Induction of xylanolytic activity by Aureobasidium pullulans using xerographic paperPublication . Marques, Susana; Gírio, Francisco M.; Pala, Helena; Gama, Francisco Miguel; Mota, Manuel; Amaral-Collaço, M. T.
- Induction of xylanolytic activity in Aureobasidium pullulans using xerographic paperPublication . Marques, Susana; Gírio, Francisco M.; Amaral-Collaço, M. T.; Pala, Helena; Gama, Francisco Miguel; Mota, ManuelThe possibility of using cheaper culture media for endo-1,4-b-xylanase production by the color variant-derivative strain of Aureobasidium pullulans Y-2311-1, one of the known best producers of this activity, was investigated. Of all the studied alternative substrates, xerographic paper showed to be the best inducer of xylanolytic activity of this strain, using different carbon sources. The highest extracellular xylanase activity obtained was 15 U/mL when using lactose as the carbon source in the presence of xerographic paper.