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Researchers of the LGP2
(May 2011)
Grenoble INP-Pagora, International school of paper, print media and biomaterials
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Laboratory of Pulp and Paper Science and Graphic Arts

IV - Printing Processes

IV - 4 - Functionalization of cellulose-based materials by adsorption of active nanoparticles

The elaboration of paper sheets bearing new functional properties is becoming a technological promising way to broaden the use of cellulosebased materials.

The modification of individual cellulose fibres, before the paper sheet formation, with active substances represents an opportunity to develop these new attractive materials with advanced bulky functionalities. To avoid cellulose alteration, physicochemical treatments based on the adsorption of an active substance on the fibres surface by electrostatic interactions seem to be a suitable route. Most of these treatments can be workable because native cellulosic fibres carry negative charges when suspended in water. In this context, our studies were focused on the adsorption of functional cationic nanoparticles which bear in the mean time specific property and positive charges promoting their adsorption on fibres by electrostatic attractive forces. To reach a broader range of fibre/paper functionalization possibilities, semiconducting organic polymers were emerging as outstanding candidates because they have an excellent solution processability due to their solubility in common organic solvents (e.g. chloroform) which allows their miniemulsification in water to give charged stable emulsions with controllednano-sized droplets.

Towards this meaning, a synthesised photoluminescent copolyfluorene (PFFO) and a commercial electrical conducting polythiophene (P3OT) were efficiently miniemulsified with the cationic surfactant tetradecyltrimethylammonium bromide (TTAB) to reach stable nano-sized positive charged particles. Studies of the role of tetradecyltrimethylammonium bromide and its partition between water, chloroform and the chloroform/water interface during the miniemulsification of PFFO showed the segregation of a sizeable amount of TTAB in the final polymer nanoparticles. Furthermore, TEMPO oxidation of cellulose fibres allowed improving the PFFO nanoparticles adsorption capacity and photoluminescence properties of fibres by the increase of the density of negative charges (carboxylic moieties) on oxidized fibres.

Homogeneous bulky photoluminescent paper sheets were obtained by adsorption of the cationic photoluminescent nanoparticles on softwood cellulose fibres before sheet formation. The adsorption was optimized (amount and homogeneity) either by a mechanical (beating) or by a physico-chemical treatment (stabilisation) of fibres and particles, respectively. On the other hand, the dilution of the charged P3OT nanoparticles suspension led to a progressive particle aggregation on the fibre surface. By controlling the dilution factor, the softwood fibre saturation by P3OT nanoparticles was reached and even enhanced by increasing anionic charges of fibres surface using carboxylmethyl cellulose (CMC). Thus, efficient electrical conductive fibres based pellets were obtained under pressure after iodine doping but the progressively polymer dedoping led to a decrease of this property.

P3OT nanoparticles adsorbed on fibres
Figure 1 - P3OT nanoparticles adsorbed on fibres
PFFO nanoparticles adsorbed on fibres   Photoluminescent paper sheet
Figure 2 - PFFO nanoparticles adsorbed on fibres   Figure 3 - Photoluminescent paper sheet
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