Environmental Engineering Reference
In-Depth Information
Table 6.4 Main changes observed in cellulosic fibres after esterification of the hydroxyl
groups with organic acids.
Cellulose fibres
Esterified cellulose fibres
Reference
Thermoplasticity
Do not melt, thermal
degradation above 200°C
Show apparent melting
point
[23]
Hydrophobicity
Hydrophilic; swell in water
Water resistance;
dimensional stability
[24]
Biological
resistance
Easily attacked by insects
and fungi
Resistance to termites
and fungi
[25]
Biodegradability
Readily biodegradable
Retarded biodegradation
[26]
Solubility
Insoluble in ordinary
organic solvents
Soluble in various
organic solvents
Inflammability
Burn easily
Do not burn readily
[25]
Weathering
resistance
Fast degradation due to
water absorption (rotting
and biological attack)
Increased UV and water
resistance
[25]
limiting point for the commercialisation of long-chain esters of cellulose in the
plastic industry.
Nevertheless, cellulose fatty esters with low DS values show other qualities
such as a high hydrophobicity. The development of water-repellent cellulosic
materials (i.e. cotton, wood), has led to interesting applications in the textile and
wood industries. For instance, the direct esterification of timber with fatty acids
(and their derivatives) has resulted in materials with extraordinary outdoor dura-
bility and resistance to biological attack (e.g. rotting, termites). Industrial exploi-
tation of this technology has recently started in France (WoodProtect [7]). In this
case, the water-repellent properties conferred to wood and the lack of recognition
from predators' enzymes account for these properties.
In general terms, esterification with organic acids lead to significant changes in
the properties of cellulosic fibres, as described in Table 6.4.
6.3.2.3
Cellulose Ethers
Cellulose ethers are the most widely produced cellulose derivatives. Depending
on the nature of the substituent that replaces the hydroxyl function, the cellulose
ether can be soluble in water or in organic solvents, yielding viscous solutions.
When added to water at concentrations of around 1-2%, viscosity can rise up to
50 Pa s (50,000 times the viscosity of pure water). They are therefore used as rheo-
logical modifiers in numerous formulations and are good substitutes for xanthan
gum. The raw material can either be wood pulp or cotton linters. The latter, which
have a higher degree of polymerisation, are used for the production of cellulose
ethers with high viscosity.
Carboxymethyl cellulose (CMC) is a white solid, without odour and harmless.
Its sodium salt is more common, obtained by reaction of alkali cellulose with
 
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