Correlation of regenerated fibres morphology and surface ... - Lenzing

Lenzinger Berichte, 82 (2003) 83-95
( a − b ⋅1,
33)
⋅ F ⋅ 2,
538
ISV = (5)
ma
where a is volume [ml] of Na2S2O3 solution (c
= 0.01 mol/l) for aliquot of blank KI solution, b
is volume [ml] of Na2S2O3 solution (c = 0.01
mol/l) for aliquot of sample solution, c is
constant (for cellulose: 1.33), F is aliquot factor
of Na2S2O3 solution, determined by KMnO4
(0.02 mol/l) and ma is weight of absolutely dry
fibre sample [g].
Mechanical properties
Stress-strain curves were measured using a
Vibrodyn 400 dynamometer (Lenzing Technik
Instruments) with a length between the clamps
of 20 mm according to ISO 2062, linear density
was determined using a Vibroskop 400
(Lenzing Technik Instruments). Testing
conditions were T = 20ºC, Rh = 65%, the
presented data are averages from 10
experiments.
Sorption measurements
Sorption measurements were carried out with
fibres (raw and treated) placed in a cylindrical
cell coming in contact with fluids of different
polarity. The mass increase as a function of
time (capillary velocity in a fibre plug) was
monitored as described in earlier publications
[4]. The results presented are statistically
processed average values of 10 parallel
measurements. The liquids (water, ethylene
glycol, formamide, ethanol, and n-heptane)
used in the sorption experiments (tensiometry)
were chosen because of their specific polarities
[12] which are appropriate to calculate contact
angles and solid’s surface energies from
measured capillary velocities. A Krüss
Tensiometer K12 GmbH Hamburg was used for
these gravimetric measurements.
Calculation of contact angle and surface free
energy. The modified Washburn Equation 1
[26,28,38] allows to calculate the contact angle
θ from measured sorption velocities:
2
mass η
cos θ = ⋅
. (6)
2 t ρ ⋅γ
⋅c
87
1
c ⋅
2
2 2 2
= ⋅π
⋅ r nk
. (7)
where mass 2 /t represents the sorption velocity
(g 2 /s), η is liquid ’ s viscosity (mPa.s), ρ is
liquid’s density (g/cm 3 ), γ is the liquid’s surface
tension (mN/m), θ is contact angle between
solid and liquid phase ( o ), c is material constant
or c factor, r is the capillary radius (m), and nk
is number of capillaries.
The fibre’s surface energy (γs) was determined
indirectly - from the contact angle data.
According to Young’s Equation (3), the surface
energy of a solid is given as [13]:
γ s −γ SL = γ L ⋅cosθ
(8)
where γ represents surface tension of the solid
(s) (mNm -1 ), SL the solid-liquid interface, L the
liquid and θ ( o ) is the contact angle between the
solid and liquid phase.
Fowkes [7] proposed that the surface energy of
a liquid or a solid could be separated into a
disperse and a polar component:
γ = γ + γ
s
d
s
p
s
γ = γ + γ (9, 10)
l
where γ represents the surface energies (mJm -2 )
of the solid (s), and liquid (l) with the disperse
part (d) and the polar part (p). The interfacial
energy of liquids and solids with both disperse
and polar components are described as [13]:
SL
S
L
d
l
p
l
γ = γ + γ − 2 γ γ − 2
d
s
d
L
p p
γ s γ L
(11)
Introduction of the work of adhesion [36] and
conversion leads to an equation of the type:
y = mx + b
1 + cos θ
2
γ L
d
γ L
=
p
γ s ∗
p
γ L
+ d
γ L
d
γ s
(12)
d
p
The valuesγ l , γ l and γ l are known material
constants and the values of x and y can be
determined. From the linear fit of the plot y
versus x one gets the polar (Equation 13) and
disperse (Equation 14) component of surface
free energy [14,30]: