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Microindentation and differential scanning calorimetry of ‘‘liquid wood’’
Dumitru Nedelcu
a,
⇑
, Ciprian Ciofu
a
, Nicoleta Monica Lohan
b
a
‘‘Gheorghe Asachi’’ Technical University of Iasi, Department of Machine Manufacturing Technologies, Blvd. Mangeron, No. 59A, 700050 Iasi, Romania
b
‘‘Gheorghe Asachi’’ Technical University of Iasi, Department of Materials Engineering and Industrial Security, Blvd. Mangeron, No. 59A, 700050 Iasi, Romania
article info
Article history:
Received 20 February 2013
Received in revised form 12 April 2013
Accepted 20 May 2013
Available online 1 June 2013
Keywords:
B. Mechanical properties
D. Thermal analysis
E. Injection moulding
abstract
Lignin was used only as a fuel until not so long ago, but the research done in the last few years has shown
that it is a substance that confers wood its strength and takes the form of granules that may be melted.
Thus, lignin was used to produce a material out of which almost anything can be manufactured, from fur-
niture, accessories, toys, plastic cases for electronic devices, and food containers of any shape, to car
bodies, and which is known as ‘‘liquid wood’’. Its properties recommend ‘‘liquid wood’’ as an alternative
to all plastic products in the near future, as it is biodegradable and reusable several times, and its prop-
erties remain intact. Three types of ‘‘liquid wood’’ are known: Arbofill, Arboblend and Arboform. Whereas
Arboform is 100% biodegradable, the other two materials are only partially biodegradable. The following
types of ‘‘liquid wood’’ were used: Arbofill Fitchie, Arboblend V2 Nature and Arboform L, V3 Nature. The
research described in this paper focuses on the study of microindentation and differential calorimetry.
Also, the software package we used enabled us to read both the microhardness values, and the reduced
indentation modulus and Young’s modulus.
The studied test samples showed the following mean recovery values: 45.9170
l
m for Arbofill Fitchie,
22.2783
l
m for Arboblend V2 Nature and 17.7430
l
m for Arboform L, V3 Nature. These values are in
agreement with the microhardness and modulus of elasticity values. Differential calorimetry research
has shown that Arboblend V2 Nature and Arboform L, V3 Nature suffered two transformations each,
one endothermal and the other exothermal, during which we measured the transformation onset and
completion temperatures, as well as the temperature in the middle of the transformation process. We
also measured the amount of absorbed and dissipated heat, respectively. As far as Arbofill Fitchie is con-
cerned, the DSC diagram showed no temperature-dependent heat flow variation that could suggest a
solid state transformation. We could safely state that the Arbofill Fitchie sample is thermally stable up
to a temperature of 423 K.
Ó2013 Elsevier Ltd. All rights reserved.
1. Introduction
The need to find cheaper and more reliable building materials
has been a major preoccupation for scientists in the last decades,
due to the dramatic decrease of available stock of wood and to
the massive pollution caused by the manufacture of cement, brick,
plastics or other similar products. Almost 40 years ago, American
scientists took the first steps in stopping humanity dependence
on plastic products which, as everyone knows, are made of oil.
Now, the German company Tecnaro say that they managed to
manufacture a product that looks like wood, has a woody struc-
ture, may be cast as plastics and, in addition, is biodegradable
and known as ‘‘liquid wood’’. In fact, the product is extremely
appreciated for this last quality, especially since there is so much
plastic waste that, if spread out, it would cover an area of more
than one million square kilometers! [1].
Liquid wood is a substance that comprises a mixture of cellu-
lose, hemp, fax and lignin used until not so long ago only in the pa-
per making process. Due to its properties, liquid wood may replace
all the current plastic products in the world. Being one of the new-
est green materials, it has an extremely important property: it may
be reused several times without diminishing its properties. Not-
withstanding its price, which is higher than that of polypropylene,
we may safely predict that in a very short time this will be the
most sought after material, since it is biodegradable and does not
pollute the environment. Although it is heavier than plastic, which
is contained in almost all the products that are currently sold
throughout the world, liquid wood has the advantage that it is a
100% natural product, which has no adverse reactions against hu-
man health [2].
As it was considered a mere residue resulted in the paper mak-
ing process, so far lignin has been used only as a fuel. Nevertheless,
the research work conducted these last few years has shown that it
is a substance that confers wood its strength and takes the form of
granules that may be melted. Thus, a special material was obtained
1359-8368/$ - see front matter Ó2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.compositesb.2013.05.024
⇑
Corresponding author. Tel./fax: +40 232 217290.
E-mail address: dnedelcu@tcm.tuiasi.ro (D. Nedelcu).
Composites: Part B 55 (2013) 11–15
Contents lists available at SciVerse ScienceDirect
Composites: Part B
journal homepage: www.elsevier.com/locate/compositesb
which may be used to manufacture almost anything, from furni-
ture, accessories, toys, plastic cases for electronic devices, and food
containers of any shape, to car bodies. Arboform may be destroyed
and reused up to ten times without losing its mechanical proper-
ties, like for instance resistance to fire and durability. The only dis-
advantages of liquid wood would be its weight, as it is much
heavier than regular plastic materials, and its manufacture costs,
which are almost double than those of polypropylene, the most
common plastic material. In addition to its positive effects on the
environment, unlike oil-derived plastic, which is considered car-
cinogenic, liquid wood is a product made of natural substances.
The need to find biodegradable building materials has become a
major preoccupation for specialists all over the world, since plastic
waste take between 100 and 1000 years to decompose. Specialists
say that soon Arboform will become the material of the future, as it
will be used in all the fields of activity and will be appreciated at its
true value [3].
The ‘‘liquid wood’’ material was invented by a team of research-
ers from the Fraunhofer Institute for Chemical Technology (ICT) in
Pfinztal (Germany). Three types of liquid wood are known, namely
arbofill, arboblend and arboform [4]. Arboform is 100% biodegrad-
able, whereas Arbofill and Arboblend are only partially biodegrad-
able. The results of the research conducted on microindentation
and differential calorimetry have not yet been known.
Calorimetry has played a very important role in research since
the 20th century, being used is various fields such as: physics,
chemistry, science and materials technology. Its applicability
has also extended to other fields, such as nano-thermodynamics
and bio-thermodynamics [5]. Differential scanning calorimetry
(DSC) measures the amount of heat absorbed/dissipated by a test
sample as compared to a reference value, when the test sample is
subjected to a heating and/or cooling cycle. The calorimetric ef-
fect may be revealed by the temperature- and/or time-dependent
heat flow variation, and its evaluation makes sense when partic-
ular heat flow variations, specific to the various transformations
accompanying temperature variation, occur. These may take the
form of exothermal peaks, which mark increases of the amount
of absorbed heat, or of endothermal minimums, which mark
the dissipation of an amount of heat. These may be attributed
to solid state transformations, like for instance direct and re-
versed martensitic transformation of a shape-memory material
[6]. The calorimetric effect may also refer to an endothermal
stage marking the vitreous transition of an amorphous material
[7,8].
Fig. 1. Average effects of input parameters upon indentation modulus: 1 – Arboform L, V3 Nature; 2 – Arboblend V2 Nature; 3 – Arbofill Fitchie.
12 D. Nedelcu et al. / Composites: Part B 55 (2013) 11–15
2. Experimental part
The technical issue that the project is solving is the obtaining of
‘‘liquid wood’’ benchmarks through monocomponent injection into
molds, a process by means of which products with characteristics
superior to those made of plastics are obtained. ‘‘Liquid wood’’ pel-
lets, which are mainly composed of lignin, discarded during the pa-
per-making process, in combination with cellulose, wood waste
from industrial plants, pellets also known as material under the
name of ‘‘liquid wood’’, are introduced into a bunker where they
are subjected to a hot-air drying process for two hours, after which
the pellets are pneumatically transferred by a pneumatic conveyor,
into the bunker of an injection machine, from where the material
enters an injection cylinder, electrically heated at 150–170 °C (for
Arbofill Fitchie – 170 °C, for Arboblend V2 Nature – 150 °C and
for Arboform L, V3 Nature – 160 °C), being afterwards injected into
a mold, which is cooled with water at a temperature of 15 °C, the
water being transferred into the mold through a circuit provided
with a cooler.
The advantages of this new technology are: the products ob-
tained have characteristics superior to those of plastic-injected
products, are harder, more flexible and have a better resistance
to shocks; the lack of carcinogens in the product material and their
biodegradability; the multiple recycling of the product obtained
and energy savings due the lower melting temperatures compared
with other plastics [9].
The planning of the experiments was achieved by means of the
Taguchi methodology [10].
The model proposed by Viger and Sisson is also easy to study;
this is the matrix model of the system comprising ‘‘I’’ factors: F
1
,
F
2
,...,F
i
each factor having n
i
levels. Each experiment was con-
ducted three times. The proposed matrix model takes into consid-
eration six technological parameters with two levels. The
coefficients of a type (1) model were determined within the exper-
imental research:
Z
t
¼MþT
top
þt
inj
þt
r
þS
s
þP
inj
þT
mat
þP
inj
T
top
þP
inj
t
inj
þP
inj
t
r
þP
inj
S
s
þP
inj
T
mat
ð1Þ
where M– general average; T
top
– melting temperature (°C); t
inj
–
injection time (s), t
r
– cooling time (s), S
s
– screw speed (mm), P
inj
– injection pressure (MPa), T
mat
– matrix temperature (°C) [11,12].
The most significant influence on the process is exercised by the
injection pressure followed by the melting temperature and the
matrix temperature (Fig. 1). Screw speed, injection time and cooling
time have less influence on the injection process (Fig. 1).
The DSC experiments were conducted on max. 25 mg fragments
taken from the three Arbofill Fitchie, Arboblend V2 Nature and
Arboform L, V3 Nature test samples. The experiments were carried
out on a type F3 Maia differential scanning calorimeter (DSC) sup-
plied by NETZSCH Company in argon protective environment. Here
are the characteristics of the DSC F3 Maia calorimeter we used:
temperature range: (170...+600) °C; heating rate:
(0.001...100) K/min; cooling rate: (0.001 ...100) K/min; tempera-
ture accuracy: 0.1 K; sensitivity: <1
l
W; enthalpy determination
accuracy: ±0.5%. The device was calibrated on Bi, In, Sn and Zn,
according to standards. The test samples were heated from room
temperature to 423 K, at a heating rate of 1.67 10
1
Ks
1
, then
left to cool freely down to room temperature.
The DSC thermograms recorded during the heating process
were assessed using the Proteus software. Determination of the
critical transformation points: the temperature on transformation
onset (T
s
), temperature in the middle of the transformation process
(T
50
) and temperature on transformation completion (T
f
) were cal-
culated using the tangent line method. The amount of dissipated/
absorbed heat (
D
H) was determined using a sigmoidal baseline.
3. Results and discussion
A Universal UMT-2 (CETR-Center of Tribology, INC., USA) device
was used for the Microindentation Tests. We used a 2 kg sensor
and applied a maximum force of 10 N. We also used diamond tip
Rockwell indenter with a radius of 200
l
m. The capacitive sensor
used measured the vertical indenter displacement.
Thus, Figs. 2–4 show the load diagrams dependent on the verti-
cal indenter displacement. The software package we used enabled
us to read both the microhardness values, and the reduced inden-
tation modulus and Young’s modulus. These values are shown in
Table 1. The table also includes the displacement and recovery val-
ues of the three materials. The research was conducted on three
test samples of each material. The relative density was calculated
as the ratio between the mass density and the reference density
(melt density at 170 °C). The values obtained are as follows: Arbo-
fill Fitchie, 1.08; Arboblend V2 Nature, 1.01; Arboform L, V3 Nat-
ure, 1.06.
The studied test samples showed the following mean recovery
values: 45.9170
l
m for Arbofill Fitchie, 22.2783
l
m for Arboblend
V2 Nature and 17.7430
l
m for Arboform L, V3 nature (see Table 2).
Fig. 2. Microindentation Test on Arbofill Fitchie.
Fig. 3. Microindentation Test on Arboblend V2 Nature.
Fig. 4. Microindentation Test on Arboform L, V3 Nature.
D. Nedelcu et al. / Composites: Part B 55 (2013) 11–15 13
Figs. 5–7 show the calorimetric response of the fragments taken
from the three studied test samples, which were subjected to con-
trolled heating up to a temperature of 423 K.
According to Fig. 4, the DSC Thermogram Recorded during the
Arbofill Fitchie test sample heating reveals no significant deviation
from linearity, which suggests that the test sample undergoes no
solid state transformation.
The DSC curves (heat flow variation) recorded during the heat-
ing of the Arboblend V2 Nature and Arboform L, V3 Nature test
samples are shown in Figs. 4 and 5. As one may notice, two peaks
appear on the DSC thermograms: (i) an endothermal peak occurs
during heating from room temperature to 350 K (I) and (ii) an exo-
thermal peak of greater intensity occurs during heating to temper-
atures exceeding 350 K (II). The endothermal peak occurs within
the same temperature range for both the Arboblend and Arboform
test samples (337–347 K according to the data provided by the Pro-
teus software); the greatest 1.7 K difference was recorded for the
transformation completion temperature T
f
. This deviation from lin-
earity of the heat flow suggests the presence of a solid state endo-
Table 1
Synthetic presentation of the research results.
Parameter
Material Material displacement (
l
m) Recovery (
l
m) Micro hardness (GPa) Indentation modulsus (GPa) Load (N)
Reduced Young’s
Arbofill Fitchie Sp. 1 98.374 42.907 0.079393 0.805 0.826 8.941
Sp. 2 94.205 35.604 0.0811 1.011 0.983 8.942
Sp. 3 110.195 59.24 0.07364 0.591 0.575 8.934
Arboblend V2 Nature Sp. 1 60.051 18.057 0.140298 2.617 2.547 8.965
Sp. 2 63.996 21.793 0.128738 2.429 2.363 8.975
Sp. 3 75.957 26.985 0.110428 1.419 1.38 8.954
Arboform L, V3 Nature Sp. 1 42.575 12.673 0.231877 3.078 2.997 8.970
Sp. 2 46.121 16.005 0.197364 3.541 3.449 8.978
Sp. 3 61.361 24.551 0.150256 1.844 1.794 8.972
Table 2
Summary of data evaluation with proteus software using the tangent method for
critical temperatures determination (T
s
,T
50
and T
f
) and sigmoidal baseline for specific
absorbed/dissipated heat
D
hdetermination.
Sample T
sI
(K)
T
50I
(K)
T
fI
(K)
D
hI
(kJ/kg)
T
sII
(K)
T
50II
(K)
T
fII
(K)
D
hII
(kJ/kg)
Arbofill Fitchie –––– ––––
Arboblend V2
Nature
337.4 341.2 345.4 5.654 359.6 366.3 374.5 19.38
Arboform L, V3
Nature
337.6 341.0 347.1 11.94 363.1 367.6 374.2 28.08
Fig. 5. DSC Thermogram Recorded during Arbofill Fitchie Test Sample Heating.
Fig. 6. DSC Thermogram Recorded during Arboblend V2 Nature Test Sample
Heating.
Fig. 7. DSC Thermogram Recorded during Arboform L, V3 Nature Test Sample
Heating.
14 D. Nedelcu et al. / Composites: Part B 55 (2013) 11–15
thermal transformation occurring upon heating in both test sam-
ples analyzed.
The second solid state transformation (II) is exothermal and, ex-
cept for the transformation onset temperature – T
sII
, the other crit-
ical transformation points occur at about the same temperatures.
This heat flow variation may be attributed to a solid state transfor-
mation occurring with heat generation.
The analysis of the amounts of heat absorbed and dissipated,
respectively, during the two solid state transformations, recorded
for the Arboblend V2 Nature and Arboform L, V3 Nature samples
heated up to a temperature of 423 K, reveals the following
tendencies:
If we compare the amount of heat absorbed by the two analyzed
samples during the first endothermal transformation, recorded
during the heating process, we may easily notice that, in order
for the transformation to take place, the Arboform L, V3 Nature
sample needs twice as much heat as the Arboblend V2 Nature
sample; this assumption is supported by the data included in
Table 1.
The amount of heat dissipated by the Arboblend V2 Nature
sample during exothermal transformation is 1.5 times lower
than the amount of heat absorbed by the Arboform L, V3 Nature
sample during the same transformation.
If we compare the amount of absorbed and dissipated heat by
the same heated material, one may notice that the exothermal
transformation suffered by the Arboblend V2 Nature sample is
greater
D
hI=5.654 whereas
D
hI = 19.38 kJ/kg). The same
ascending tendency is noted for the Arboform L, V3 Nature
sample.
4. Conclusions
Liquid wood is a substance that comprises a mixture of cellu-
lose, hemp, fax and lignin used until not so long ago only in the pa-
per making process. Due to its properties, liquid wood may replace
all the current plastic products in the world.
Notwithstanding its price, which is higher than that of polypro-
pylene, we may safely predict that in a very short time this will be
the most sought after material, since it is biodegradable and does
not pollute the environment. Three types of liquid wood are
known: Arbofill, Arboblend and Arboform. Arboform is 100% biode-
gradable, whereas Arbofill and Arboblend are only partially biode-
gradable. The research was conducted on Arbofill Fitchie,
Arboblend V2 Nature and Arboform L, V3 Nature. The microinden-
tation research revealed following mean recovery values for the
studied materials: 45.9170
l
m for Arbofill Fitchie, 22.2783
l
m
for Arboblend V2 Nature and 17.7430
l
m for Arboform L, V3 Nat-
ure. These recovery values are in agreement with the microhard-
ness and modulus of elasticity values.
During the Arbofill Fitchie sample heating, the DSC diagram
showed no temperature-dependent heat flow variation that could
suggest a solid state transformation. Therefore, we could safely
state that the Arbofill Fitchie sample is thermally stable up to a
temperature of 423 K.
The DSC thermograms recorded during the heating of the Arbo-
blend V2 Nature and Arboform L, V3 Nature samples show two
peaks, one endothermal and the other exothermal, which are
attributed to a series of transformations occurring in the solid
state; the two transformations occur within the same temperature
range for both analyzed samples.
The amount of absorbed/dissipated heat is at least 1.5 times
higher in the Arboform L, V3 Nature than in the Arboblend V2 Nat-
ure sample.
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