Cellulose fibre modified, mechanism

Dall Acqua et al.45 reported the development of conductive fibres made by cellulose-based fibres embedded with polypyrrole. Several efforts with cotton, viscose, cupro and lyonell have followed. The conductivity is directly related to the amount of polypyrrole, oxidant ratio and fibre structure with significant differences between viscose and lyonell. Polymerisation occurs uniformly inside the fibre bulk, by producing a coherent composite polypyrrole/cellulose. The mechanical and physical properties of cellulose fibres were not significantly modified as they are the best available45. 

Figure 13.22 Possible mechanism of NR containing the modified cellulose fibre with silane (modified from ref. 11).

The effect of corma treatment on the peifonnance of cellulose lyolefin composites has been investigated in great detail [64,65] Corona exposure of PE and/or of the cellulose fibres improved the composites mechanical properties. Figure 12 shows that yield strengths and strains, and elongations at break, were stron y affected by corona treatment, particularly in the case when the fibre surfaces were modified. Similar results have been obtained for cellulose/PP composites [66]. 

Table 6.6 The mechanical properties of natural fibres modified with bacterial cellulose nanofibrils...

Cellulosic fibres used for reinforcement in nonpolar thermoplastics, such as PP, have to be modified because effective wetting of fibres and strong interfacial adhesion are required to obtain composites with optimised mechanical properties [31, 32]. Several methods for improvement in the adhesion between polymer and cellulosic fibres have been developed. 

Chemical compounds which contain reactive groups such as the methanol group (-CH2OH) as in methanolamine compounds are able to form stable, covalent bonds with cellulose fibres. This treatment decreases the moisture pick-up and increases the wet strength of reinforced plastics. Isocyanates are also suitable to modify the chemical structure via its reaction with the OH groups of cellulose. The mechanical properties of composites reinforced with wood-fibre and PVC or PS can be improved by an isocyanate treatment of those cellulose fibres or the polymer matrix. The improvement of the properties of the composites can be explained by the reduction in the number of OH groups responsible for moisture uptake and consequently the increase in the hydrophobicity of the fibre s surface... 

Most fibres made from regenerated cellulose such as viscose, lyocell, and Celsol are characterised by stiffness as well as a fuzzy and uneven surface that makes fabrics susceptible to pilling, even over a short period of use. In order to modify the surface properties of cellulosic fibres and fabrics and to improve their quality biotechnological approaches based on specialised enzymes are widely used. Finishing processes, employing cellulases and xylanases, can replace a number of mechanical and chemical operations, which have been applied until now to improve comfort and quality of fibres and textiles. The principle of enzyme action in the finishing process is controlled hydrolysis of cellulose, in which impurities and fuzz are removed from the surface of fibres, without decreasing their mechanical tenacity or the elasticity of the fabric. 

With this work we intend to contribute to the study of the mechanism by which modified cellulose fibres are able to trap dissolved organic pollutants from water. Indeed, as we have shown previously [15, 16], grafting of linear alkylchains on the fibre s surface boosts its capacity to uptake organic solutes from aqueous solution. By ensuring grafted alkyl chains, one gives rise to hydrophobic domains... 

Bacterial cellulose-modified sisal and hemp fibres have also been used to produce unidirectional natural fibre reinforced CAB and polylactide (PLLA) model composites [9]. The mechanical properties of bacterial cellulose-coated sisal fibre reinforced polymers showed significant improvements over neat polymers (Table 6.8). The tensile strength and modulus for sisal/PLLA composites improved by as much as 68 and 49%, respectively. However, improvements were... 

Table 6.8 Mechanical properties of bacterial cellulose modified hemp and sisal fibres reinforced CAB and PLLA composites ...

Microbial synthesis of ceUulosic fibres affords the opportunity of obtaining products with unique properties suitable for practical application in medicine and the electronics industry. For synthesis of modified bacterial cellulose, the Acetobacter subsp. strains have been applied. The selection of suitable polyaminosaccharide modifiers allows the production of bacterial cellulose characterised by valuable mechanical, electro-acoustic and biological properties. Practical applications of this ceUulosic composite material for manufacture of novel wound-heaUng dressings as well as diaphragms for loudspeakers have been tested. ... 

C5 ras VP, Manfredi LB, Ton-That M-T, Vazquez A (2008) Physical and mechanical properties of thermoplastic starch/montmorillonite nanocomposite films. Carbohydr Polym 73 55-63 de Morals Teixeira E, Correa A, Manzoli A, de Lima Leite F, de Oliveira C, Mattoso L (2010) Cellulose nanofibers from white and naturally colored cotton fibers. Cellulose 17 595-606 de Moura MR, Aouada FA, Avena-Bustillos RJ, McHugh TH, Krochta JM, Mattoso LHC (2009) Improved barrier and mechanical properties of novel hydrox5q)ropyl methylcellulose edible films with chitosan/tripolyphosphate nanoparticles. J Food Eng 92 448—453 Dean K, Yu L, Wu DY (2007) Preparation and characterization of melt-extruded thermoplastic starch/clay nanocomposites. Compos Sci Technol 67 413 21 Duanmu J, Gamstedt EK, Rosling A (2007) Hygromechanical properties of composites of crosslinked allylglycidyl-ether modified starch reinforced by wood fibres. Compos Sci Technol 67 3090-3097... 

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