Biomedical Engineering Reference
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In contrast to the untreated composites higher tensile strength values were proved
for the lignin treated composites with a higher fiber load. Due to a better compaction of
the composites and better fiber/matrix interactions a higher reinforcement effect was
measured for 40 mass% fiber reinforced multilayer web PLA composites compared
to the 20 mass% reinforced composites. According to statistical investigations with
U- and t-tests (α = 0.05) the tensile strength values were increased significantly by the
lignin treatment (Table 1). The tensile strength of 40% lyocell 1.3-PLA was increased
from 41.9 to 51.0 N/mm², 40% lyocell 6.7-PLA from 35.6 to 52.7 N/mm² and 40%
lyocell 15.0-PLA was increased from 28.2 to 56.7 N/mm². A similar trend was ob-
served in a previous study for cotton-PLA composites reinforced with 4 mass% fibers.
In contrast to the present study, the lignin used was in the form of powder with a higher
concentration (2.5 g/100 g sample). The tensile strength of the cotton-PLA composites
was increased by adding lignin. A disadvantage of these composites was the high odor
intensity caused by the lignin (Graupner, 2008). Due to this in the present study the
lignin concentration was reduced (1 g/100 g sample) and the powder was dissolved
in ethanol. No atypical odor development was observed but similar improvements of
tensile strength values were also measured with a lower lignin concentration.
table 1.
Mechanical characteristics of PLA composites and lignin treated PLA composites produced
by compression moulding technique 1 CP-1 (mean values, standard deviations are given in brackets).
Kind of Composite
Lignin
treatment
n
Tensile
strength in
N/mm²
Young´s modu-
lus in N/mm²
Elongation at
break in %
n
Charpy impact
strength in kJ/m²
PLA reference sample
No
11
39.6 (±1.8)
2243.9 (±62.2)
2.2 (±0.2)
9
15.8 (±3.8)
PLA reference sample
Ye s
13
39.5 (± 1.8)
2299.0 (± 92.3)
2.2 (± 0.2)
7
15.6 (± 4.0)
20% Lyocell 1.3-PLA
No
7
50.9 (±3.2)
4199.4 (±260.9)
2.0 (±0.5)
8
18.1 (±4.4)
20% Lyocell 1.3-PLA
Ye s
7
60.3 (± 2.4)
4271.8 (± 149.1)
2.2 (± 0.2)
5
22.6 (± 5.7)
40% Lyocell 1.3-PLA
No
7
41.9 (±2.6)
4142.1 (±292.8)
3.3 (±0.4)
7
33.1 (±5.5)
40% Lyocell 1.3-PLA
Ye s
6
51.0 (± 3.6)
5457.3 (± 504.9)
2.6 (± 0.5)
7
31.6 (± 3.4)
20% Lyocell 6.7-PLA
No
6
35.3 (±4.3)
3648.5 (±328.5)
3.3 (±0.6)
8
23,7 (±5.2)
20% Lyocell 6.7-PLA
Ye s
6
38.5 (± 6.5)
4388.5 (± 452.3)
2.1 (± 0.5)
10
18.7 (± 4.1)
40% Lyocell 6.7-PLA
No
7
35.6 (±7.3)
5164.4 (±485.6)
3.5 (±0.4)
7
38.8 (±5.6)
40% Lyocell 6.7-PLA
Ye s
6
52.7 (± 10.8)
6221.8 (± 200.3)
3.9 (± 0.5)
9
28.0 (± 6.5)
20% Lyocell 15.0-PLA
No
7
53.9 (±3.4)
4611.8 (±248.5)
2.2 (±0.1)
7
26.9 (±7.1)
20% Lyocell 15.0-PLA
Ye s
7
54.5 (± 3.7)
4877.1 (± 268.8)
2.0 (± 0.3)
5
20.3 (± 4.4)
40% Lyocell 15.0-PLA
No
6
28.2 (±4.4)
4293.5 (±239.8)
4.6 (±0.9)
5
30.5 (±3.4)
40% Lyocell 15.0-PLA
Ye s
7
56.7 (± 3.1)
6144.9 (± 292.3)
2.7 (± 0.4)
5
23.7 (± 1.2)
In contrast to the tensile strength a clear reinforcement effect was achieved for the
Young´s modulus in comparison to the neat PLA sample. As observed for the tensile
strength, higher Young´s moduli were measured with the lignin treated composites
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