Biomedical Engineering Reference
In-Depth Information
Funami et al.(
2005
) reported that the addition of small amounts of konjac glucomannan
(KGM;,
Section 10.6.1.1
) increased the peak viscosity for the starch system (13%) during
the process of gelatinization. During short-term retrogradation, adding KGM (0.5%)
increased tan
for the starch system (5%) after storage at 4°C for 24 h. During long-term
retrogradation (4°C for 14 days), addition of KGM (0.5%) decreased the rate constant
expressing the relationship between storage time and creep compliance for the starch
system (15%). They hypothesized that there are structural compatibility and molecular
interactions between KGM and the starch components, amylose and amylopectin.
δ
10.5
Filled gels
A range of systems closely related to mixed gels are those formed by adding an inert
(filler)
to a gelling system, in a manner quite analogous to the reinforcing of synthetic polymer
resins by, for example, glass or carbon
fibres. Clearly the results obtained, for example in
mechanical measurements, depend on the size, shape and volume fraction of
(filler)
particles, just as they do for the resin.
One early publication is that by Richardson and co-workers (Richardson et al.,
1981
). In
this work, small-deformation measurements were performed on the model system of glass-
filled gelatin gels. By using well-characterized samples of glass spheres, rods and irregular
pieces of intermediate shape, e.g. plates at varying phase volume of
filler, the effect of size,
shape and phase volume on the shear storage and loss moduli could be investigated. The
main effect was obviously to increase the small-deformation modulus, and in a predictable
manner. The relative
filled particles was
plotted against volume fraction relative to the maximum packing (volume) fraction
'
reinforcement factor
'
G
f
/G
u
for
filled and un
ϕ
m
.
This was measured independently and found to be c.0.64 for the spheres and ~0.27 for the
rods (length typically ~150
m). These values produced quite satisfactory superposition, so
that the reinforcement factor depended only on the ratio
μ
ϕ
m
.
Measurements were then carried out in the large-deformation regime using precast
dumbbell-shaped replicates and extending the samples until they failed (Ross-Murphy
and Todd,
1983
). The effect of reinforcement could again be rationalized in relatively
simple terms using Smith
ϕ
/
s failure envelope approach (Smith,
1963
). In his review,
Kasapis (
2008
) described his own data on gelatin
'
filled with microcrystalline cellulose
(MCC)
fibrils. The corresponding value of
ϕ
m
is 0.52, which, in one model, corresponds
to random orientation of
fibres, although this seems high compared to the results for glass
rods reported above.
A number of papers have subsequently been published in which alternative
'
soft
lled systems. Such systems
have applications in the food and pharmaceutical sectors. Dickinson and his
co-workers (Dickinson,
2012
) have extended the work on
fillers'
'
have been used, including microemulsion and gas-
filled gels by characterizing
so-calledemulsiongels.Here,anemulsionis
first prepared by conventional routes but
using a protein as emulsi
er. By then heating or acidifying the system, the protein
component can be induced to gel (
Chapter 9
), producing a material in which the
included (
(filler) phase consists of oil droplets. Matsumura et al.(
1993
) examined the
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