Civil Engineering Reference
In-Depth Information
Borges
et al.
[78] studied the tensile properties of crosslinked (with 1,4-butyl-diiso-
cyanate) and uncrosslinked composite i lms prepared from isotropic solution of HPC
with incorporation of microcrystalline cellulose i bers. h e concentration of i bers
in the composites ranged from 0 to 30 wt%. h e mechanical parameters of isotropic
composites were invariant regardless the direction of measurement. It has been shown
that the inclusion of such i bers in the HPC matrix produce composites with supe-
rior mechanical properties, which can be improved by crosslinking. For uncrosslinked
i lms it was observed that all mechanical parameters increase when the i ber content
increases up to a maximum of 20 wt% (E = 314 ± 50 MPa,
σ
y
= 8.5 ± 1.2 MPa e
σ
u
=
11.1 ± 0.8 MPa vs. E = 109 ± 11 MPa,
σ
y
= 3.5 ± 0.4 MPa e
σ
u
= 5.2 ± 0.5 MPa for neat
u
are yield and tensile
stress, respectively. Similar results were obtained by Zimmermann
et al.
from isotropic
aqueous solutions of low viscosity hydroxypropylcellulose (HPC, 5 wt%) with microfri-
brilated cellulose (1, 5, 10 and 20 wt%) [55].
A slight improvement in the mechanical properties of the crosslinked i lms when
compared with the ones obtained for uncrosslinked i lms was observed. h e elastic and
plastic deformations appear to be inl uenced dif erently by the crosslinking agent and
the amount of i bers. Young's modulus increases with i ber content, up to a maximum
at 20% wt of i bers, and for the crosslinked i lms the authors see a slight increase of this
parameter, E
uncross
(20 wt%) = 314 ± 50 MPa, E
cross
(20 wt%) = 390 ± 97 MPa. h ese results
suggest that the elastic deformation is mainly determined by the AVICEL i ber content.
HPC isotropic i lm, where E is the Young's modulus,
σ
y
and
σ
800
60
Nano
50
700
Nano
40
600
30
500
20
400
Micro
Micro
10
Neat
HPC
300
Neat HPC
0
0
4
Content of Cellulose Filler (wt. %)
2
6
8
10
12
14
0
2 4
Content of Cellulose Filler (wt. %)
6
8
10
12
14
(
a
)
(
b
)
35
30
25
Neat
HPC
Nano
20
15
Micro
10
0.0 0.1 2 4
Content of Cellulosic Filler (wr. %)
6
8
10 12 14
(
c
)
Figure 8.6
Young's modulus (a), tensile stress (b) and tensile strain (c) variation as a function of the
content of cellulosic i ller in the HPC anisotropic all-cellulose composite i lms. Measures were taken
parallel to shear casting direction. h ese values were obtained from references [79] for NCC (nano) and
from [77] for micro-cellulosic i llers (Micro). Error bars represent standard error of n = 6 and 15 values,
respectively.
