10 Selected Examples of New Applications
Over 76 000 references regarding the application of polysaccharide esters are refer-
enced in Scifinder® (American Chemical Society, July 2005). The most numerous
products are cellulose esters (about 57 500 references), compared to starch- (about
9500 references), dextran- (about 7900 references), chitin- (about 430 references)
and curdlan esters(about130 references). This pronounced importance of cellulose
esters and the wide scope of “industrial applications” are illustrated in Table 10.1.
Table 10.1. Some major applications of organic cellulose esters and the amounts produced in 1985
(adapted from [94])
Cellulose ester DP DS Principal application Amount
(t/year)
Acetyl Propyl or
butyl
Triacetate 150–360 2.8–3.0 – Textile fibres
Photo film, foils,
insulating coatings
280 000
60 000
Diacetate 100–200 2.5 – Filter tow
Thermoplastic mass
370 000
2.4 – Viscose silk, foils
2.4 – Thermoplastic mass 60 000
2.3 –
Acetopropionate 150–200 0.3 2.3 Thermoplastic mass
Acetobutyrate 100–150 2.1 0.6 Raw materials for coating
and insulation, foils
5000
2.0 0.7 Foils, films
1.0 1.6 Thermoplastic mass 40 000
0.5 2.3 Melt dipping mass

Σ
815 000
Among recent developments are polysaccharide esters for modern coatings,
controlled release applications, biodegradable polymers, composites, optical film
applications, and membranes. The tailored modification of properties can be ac-
complished by multiple esterification, i.e. two or even more different ester moieties
182 10 Selected Examples of New Applications
are introduced where the one determines properties necessary for processing and
the other ester group induces a specific product feature. This approach, for a huge
variety of modified polysaccharides with focus on cellulose esters, has been excel-
lently reviewed [447]. A selection of typical cellulose esters is given in Fig. 10.1.
The trends in polysaccharide ester utilisation are discussed by Glasser in [448],
evaluating the amount of recent publications in the field of celluloseesters. The type
of journals publishing the largest numbers of work recently (Table 10.2) indicates
the increasing scientific interest in exploiting the high tendency of polysaccha-
ride esters towards the formation of superstructures, the biological activity, and
the biocompatibility resulting in the development of new separation techniques,
biomedical devices and pharmaceuticals. Some selected developments will be dis-
cussed to illustrate the potential of new polysaccharide esters.
Table 10.2. Journals currently (last 3 years) publishing most frequently in English on cellulose esters
(reproduced with permission from [448], copyright Wiley VCH)
Journal name Number of publications
(last 3 years)
Journal of Membrane Science 27
Journal of Applied Polymer Science 24
Drug Development and Industrial Pharmacy 12
Biomaterials 10
Polymer 10
Cellulose 9
Journal of Controlled Release 9

International Journal of Pharmaceutics 8
10.1 Materials for Selective Separation
Polysaccharidederivativesarewellestablishedasmembranematerialsandasselec-
tive stationary phases in chromatography. For a comprehensive overview of cellu-
losic materials forultrafiltration,reversed osmosis, and dialysis,see Refs.[447,449].
The defined superstructure of polysaccharides and polysaccharide derivatives
seems to be responsible for their high efficiency in separation processes, par-
ticularly for chiral resolution. The specific interaction of chiral molecules is ob-
served with the pure polysaccharides and their derivatives leading to similar chiral
discrimination. The reason could be a comparable superstructure of the polysac-
charide and the fully functionalised ester, as has been concluded for curdlan and
curdlan triacetate. The unit cell contains six RU related by 6/1-helical symmetry,
which is essentially the same as the backbone conformation of one of the modifi-
cations (form I) of curdlan [450]. The chiral separation applying polysaccharide
esters is not caused by hydrogen-bonding interaction with the solute, as deter-
mined for other chiral phases [451]. In contrast, the conformational regularity
10.1 Materials for Selective Separation 183
Fig. 10.1. Selection of cellulose esters for modern coatings and controlled release applications
(adapted from [447])
184 10 Selected Examples of New Applications
achieved by different solvent treatment of cellulose triacetate during solidification
on column packing materials exhibits a remarkable effect on the chiral separa-
tion properties, leading to the conclusion that the superstructure has a crucial
influence [452].
10.1.1 Stationary Phases for Chromatography
In addition to the widely used substituted phenylcarbamates of polysaccharides,
which are utilised after covalent immobilisation on the surface of silica gel [453],
the triesters of polysaccharides [447] are exploited as stationary phases for chro-
matography (Table 10.3).
Table 10.3. Examples of new cellulose esters as stationary phases in chromatography

Cellulose ester Remarks Ref.
Acetate Discrimination of
racemic thiosulphinate
[454]
Benzoate Discrimination of R(+)- and
S(–)-benzyl-3-tetrahydrofuroates
[455]
4-Methyl-phenylbenzoat Discrimination of
thiazolo benzimidazoles
[456]
Alkenoxybenzoyl/benzoate
10-Undecenoyl/benzoate
10-Undecenoate/4-methyl-benzoate
For covalent binding to a silica surface
via radical grafting with vinyl or allyl silica
[457],
[458]
Acrylates, methacrylate For covalent binding to a silica surface [459]
Interestingly, stationary phases based on regioselectively substituted cellu-
lose esters show chiral discrimination dependent on the distribution of the ester
moieties, as demonstrated for 6-O-acetyl-2,3-di-O-benzoyl cellulose and 2,3-di-O-
acetyl-6-O-benzoyl cellulose [460].
10.1.2 Selective Membranes
The most common polysaccharide membranes are based on cellulose esters, which
have found applications in all fields of separation processes [447]. In addition to
cellulose, galactomannan- and curdlan esters are potential film-forming materials.
Thus, guar gum formate can be processed into an ultrathin semipermeable mem-
brane [181], and curdlan acetate provides ultrafiltration membranes by casting
from solutions containing HCOOH and additives such as water and DMF [461].
New paths towards selective films include the defined establishment of

supramolecular structures by electrostatic interactions, and the concept of molec-
ular imprinting. Polyelectrolyte complexes are used for sulphated polysaccharides,
e.g. from sulphuric acid half esters ofcellulose and poly(diallyldimethylammonium
10.1 Materials for Selective Separation 185
chloride) [462]. These polyelectrolyte complexes can be used for the formation of
capsules with a defined cut-off value for the immobilisation of biological matter,
e.g. yeast [463, 464]. Capsules based on cellulose sulphuric acid half esters are
applied in an in situ chemotherapy strategy with genetically modified cells in an
immuno-protected environment, and may prove useful for solid tumour therapy
in man [465, 466].
Loading of a surface with ionic functions is carried out yielding compounds
with a pronounced biological selectivity. By treatment of a porous NH
+
3
-containing
polypropylene membrane with the sulphuric acid half ester of dextran, a material
for the convenient removal of the human immunodeficiency virus (HIV) and
related substances from blood, plasma or other body fluids has been developed.
Filtration of HIV-containing human plasma results in 99.2% removal of HIV [467].
Molecularly imprinted polymeric membranes are prepared from cellulose ac-
etate with benzyloxycarbonyl-l-glutamic acid and carbobenzoxy-d-glutamic acid.
The imprinted polymeric material recognises the l-glutamicacidinpreferenceto
d-glutamic acid, and vice versa, from racemic mixtures [468,469]. Polymer blends
containing cellulose acetate and sulphonated polysulphone are a matrix for the
preparation of molecularly imprinted materials via phase inversion from a cast-
ing solution containing a template. Membranes are obtained with Rhodamine B
as template. Results for rebinding of Rhodamine B during filtration through the
imprinted as well as blank membranes, prepared without Rhodamine B, provide
evidence for surface imprinting (Fig. 10.2, [470]).
Fig. 10.2. Results from membrane solid-phase extraction for molecularly imprinted (MIP) and blank

(Blk) membranes at varied cellulose acetate (CA):sulphonated polysulphone (SPS) ratio. A Bound
Rhodamine B (Rh B) after filtration of 10 ml 10
−5
M solution in water, and B Rh B eluted with 10 ml
methanol after binding and subsequent washing with water and 2 M NaCl solution (membrane area
3.5 cm
−2
, thickness ∼ 150 µm, adapted from [471], reproduced by permission of The Royal Society of
Chemistry)
The surfaces can be studied in detail with scanning force microscopy and
the gas adsorption isotherm method. Significant differences in pore structure
between imprinted and blank membranes are found, which clearly correlate with
the imprinting efficiency (Fig. 10.3, [471]).