Materials Sciences and Applications, 2013, 4, 730-738
Published Online November 2013 (http://www.scirp.org/journal/msa)
http://dx.doi.org/10.4236/msa.2013.411092
Open Access MSA
Morphology, Thermal Behavior and Dynamic Rheological
Properties of Wood Polypropylene Composites*
Diène Ndiaye1#, Vincent Verney2,3, Haroutioun Askanian2,4, Sophie Commereuc2,4, Adams Tidjani5
1Section Physique Appliquée, Université Gaston Berger, Saint-Louis, Sénégal; 2Institut de Chimie de Clermont-Ferrand, Université
Blaise Pascal, Clermont-Ferrand, France; 3CNRS, UMR 6296, ICCF, Université Blaise Pascal, Aubière, France; 4Ecole Nationale
Supérieure de Chimie de Clermont-Ferrand, Université Blaise Pascal, Clermont-Ferrand, France; 5Département de Physique, Université
Cheikh Anta Diop, Dakar, Sénégal.
Received September 2nd, 2013; revised October 18th, 2013; accepted November 7th, 2013
Copyright © 2013 Diène Ndiaye et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Wood polymer composites (WPCs) were made with pine and polypropylene matrix (PP). The composites were pro-
duced by melt blending in a Brabender at 180˚C. Characterization of the samples, with the aid of scanning electron mi-
croscopy supplemented by microscope photography, showed an improved dispersion of wood in the polymeric material
in presence of polypropylene grafted with maleic anhydride (MAPP) or nanoclay. The use of the MAPP instead of clay
seems to have enhanced the level of crystallinity in the composites for the same levels of wood loading and also accel-
erates the crystallization. Melt rheological measurements of neat PP and PP-wood composites were carried out at 180˚C
with an ARES Rheometer scientific mechanical spectrometer in oscillatory frequency. All the composites materials
exhibit viscoelastic values greater than those for neat PP. The samples containing MAPP as comptabilizer show the
higher Newtonian viscosity, however, the addition of a small concentration of nanoparticles like nanoclays does not
improve the resulting melt viscoelastic behavior of the composite.
Keywords: Morphology; Thermal Behavior; Dynamic Rheological Properties; Wood Polypropylene Composites
1. Introduction
In recent years, thermoplastic composites reinforced with
a natural component such as wood, sisal, jute, rice husk,
and flax fiber have been found to show a lot of important
applications. They are found mainly in the buildings ma-
terials (ramps, fences, doors, windows, patios, phonic
isolations…), in automotive sector (dashboards, rear
lockers, panels, doors and other internal accessories of
vehicles...) where they not only reduce the mass of the
component but also lower the energy needed for produc-
tion by 80% [1], in consumer industries (furniture/cabi-
netry, floors, pallets, packaging or decorative moldings…)
and in various applications (equipment of amusement
parks, tables of picnics, game’s modules, etc...). This
craze to WPC is mainly due to their technical perform-
ances. Among them we can notice the enough good di-
mensional stability, good mechanical properties and
acoustic performance, reduction of cost production and
weight of items and their renewability. There is a con-
siderable commercial interest in thermoplastic compos-
ites filled with wood fibers, due to the potential opportu-
nities. The product has the aesthetic appearance of wood
and the processing capability of thermoplastics and its
performance in humid area. In spite of these attributes,
disadvantages associated to the use of natural fibers as
reinforcement in thermoplastics are the result of a lack of
a good interfacial adhesion and a poor resistance to hu-
midity absorption. The compatibility between the wood
fibers and polymeric matrix constitutes one important
factor in the production of WPCs with improved me-
chanical properties. Wood is hydrophilic in nature (with
a high surface tension), which lowers its compatibility
with hydrophobic polymeric materials (with a low sur-
face tension) during composite preparation. The first key
point for the production of acceptable WPC is the com-
patibility between fibers and the polymer. Properties of
WPCs depend on the characteristics of matrix and fillers,
chemical interaction between wood fibers and polymer,
*Conflict of interest: None declared.
#Corresponding author.

Morphology, Thermal Behavior and Dynamic Rheological Properties of Wood Polypropylene Composites
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humidity absorption and processing conditions. The high
level of moisture absorption of the wood beers and the
poor adhesion with hydrophobic polymeric matrices
(such as PP) can lead to deboning with age and to lower-
ing mechanical properties. The three most important
constituents of wood (cellulose, hemicellulose and lignin)
are subject to low degradation temperature which can
occur during processing. All these disadvantages can
lead to debonding with age and produce a detrimental
effect on the mechanical properties of the composites,
both by changing the structure of the fiber and by pro-
ducing volatile compounds that create micro voids across
the interfaces. The need for coupling agents to improve
fiber-matrix adhesion in such composites is well docu-
mented. The most commonly used coupling agent is
maleic anhydride polypropylene (MAPP). The mechani-
cal properties of wood fiber-polypropylene composites
showed the best performance with the addition of 5% (by
wt.) of MAPP [2,3]. MAPP is also able to compensate
for insufficient breakup forces during processing, such as
low shear stress, by reducing the interfacial tension be-
tween PP and the cellulose, which leads to finer disper-
sion of the fiber throughout the system [4]. There are
some studies on using other coupling agents such as si-
lane [5,6] and isocyanates [7]. Recently, investigations
have shown that the mechanical properties of WPCs can
also be significantly improved by the addition of nano-
clay to the composites [8,9]. The use of clay instead of
MAPP is interesting in terms of the fire retardancy of the
WPCs, which tend to burn quite easily; this is a heavy
drawback. This is what justifies the use of clay and
MAPP as coupling agent in our samples. Therefore, in
this study, we examined the effects of MAPP and nano-
clay, as coupling agent on the morphology and thermal
behaviors of the WPCs. The dispersion of the function-
alized filler into polypropylene matrix was performed.
Another goal of this work is to characterize the thermo
viscoelastic properties of this kind of WPC over a wide
range of temperatures, which corresponds to the classical
variations observed in the used domain of these materials.
The rheological phenomena resulting from the high filler
contents (e.g. high viscosity and complex stress-strain
rate dependence) must be understood for proper formula-
tion design and process control. Filler wetting, dispersion
and wood-matrix polymer interactions are also important
factors for WPC, because they strongly contribute to
properties [10-14]. The rheological properties are studied
as a function of the temperature and discussed in com-
parison to the behavior of neat PP. The performing mate-
rials of the future are based on the deep knowledge of the
relationship: morphological structure—composition—pro-
perties. It is well established that the properties of these
composites depend mainly on the characteristics of the
polymer-filler interface.
2. Experimental
2.1. Materials
The basic materials used in this study are listed below.
Polypropylene (PP) in the form of pellets from the East-
man Chemical Co. (Kingsport, TN) was used as the ma-
trix. It had a melt flow index of 5.2 g/10 min (at 190˚C
and a 2.16 kg load) and a density of 0.910 g/cm3. The
wood flour particles of 425 microns (40-mesh) in size
were kindly donated by American Wood fibers (Scho-
field, WI) and are constituted predominantly with pon-
derosa pine, maple, oak, spruce, southern yellow pine,
cedar. The wood was oven dried at100˚C for 24 h before
processing to remove moisture. The isotactic polypro-
pylene matrix (PP) in the form of pellets was provided by
Solvay Co from the Eastman Chemical Co. (Kingsport,
TN). It had a melt flow index of 5.2 g/10 min (at 190˚C
and a 2.16 kg load) with a density of 0.910 g/cm3.
Polypropylene grafted with maleic anhydride (PPgMA)
with an approximate maleic anhydride (MA) content of 3
wt.% was purchased from Aldrich Chemical Company,
Inc. (Milwaukee, WI). All ingredients were used as re-
ceived.
2.2. Compounding and Processing
Before compounding, the wood flour was dried in an
oven for at least 48 h at 105˚C to a moisture content of
less than 1% and then they were stored in a sealed plastic
container to prevent the absorption of water vapor. First,
the PP was put in the high-intensity mixer (Papenmeier,
TGAHK20, Germany), and the reinforcement was added
after the PP had reached its melting temperature. The
mixing process took 10 min on average. After blending,
the compounded materials were stored in a sealed plastic
container. Several formulations were produced with vari-
ous contents of PP, Wood flour, MAPP or clay. For the
extraction of volatile and harmful gases, the hood was
open. The different samples and their code are summa-
rized in the following Table 1.
2.3. Evaluation of the Composite Properties
2.3.1. Morphology Properties
The state of dispersion of the wood inside the polymeric
Table 1. Composition and code of the samples (percentage
is in weight).
Sample PP (%) Wood (%) MAPP (%) Clay (%)
PP 100 0 0 0
WPPC3 75 25 0 0
WPPC4 50 50 0 0
WPPCC 45 50 0 5
WPPCG 45 50 5 0

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matrix was analyzed using optical microscopy on sam-
ples of 100 - 200 μm thick. Scanning Electron Micros-
copy (SEM) was used to obtain microphotographs of the
fracture surfaces of the wood composites. These fractures
have been performed in liquid nitrogen to avoid any de-
formation. SEM has been performed using a FEI Quanta
400 microscope working at 30 kV etched polymer sur-
face was examined with LEICA optical microscope
working in a transmission mode. Samples were thin
enough that no special preparation of the samples was
needed for their observations with the optical micro-
scope.
2.3.2. Thermal Analysis
DSC is widely used to characterize the thermal properties
of WPCs. DSC can measure important thermoplastic
properties, including the melting temperature (Tm), heat
of melting, degree of crystallinity χ (%), crystallization,
and presence of recyclates/regrinds, nucleating agents,
plasticizers, and polymer blends (the presence, composi-
tion, and compatibility). Thermal analysis of the WPC
samples was carried out on a differential scanning calo-
rimeter (Perkin Elmer Instruments, Pyris Diamond DSC,
and Shelton, Connecticut) with the temperature cali-
brated with indium. All DSC measurements were per-
formed with powdered samples of about 15 ± 0.2 mg
under a nitrogen atmosphere with a flow rate of 20
mL/min. All samples were subjected to the same thermal
experiment with the following thermal protocol, which
was slightly modified from the one reported by Valentini
et al. [15]:
1. First, the samples were heated from 40 to 200˚C at a
heating rate of 10˚C/min to eliminate any thermal history
effect;
2. Second, the samples were cooled from 200 to
40.00˚C at a cooling rate of 10˚C/min to detect the crys-
tallization temperature (Tc);
3. Finally, the samples were heated from 40˚C to 180˚C
at a heating rate of 10˚C/min to determine Tm. Tm and the
heat of fusion

Δm
H
were obtained from the thermo-
grams during the second heating. The values of Δm
H
were used to estimate χ (%), which was adjusted for each
sample in χcor (%) based on the percentage of polypro-
pylene in the composite. The degree of crystallinity (χcor)
of the PP component was determined from the following
equation [16,17]:
 
 
0
Δ
%1Δ
m
cor
HJg
χ
M
FHJg
 (1)
where Δm
H
and 0 Δ
H
are the heat of fusion of the
composites and 100% crystalline polypropylene respec-
tively. In this calculation, 0
Δ
H
is taken to be 190(J/g)
[18].
2.3.3. Melt Rheological Measurements
Background
The viscoelastic behavior of molten polymers can be
determined using oscillatory rheological experiments such
as dynamic mechanical testing, which offers a conve-
nient way to assess frequency dependence of mecha-
nical properties of polymers.
An oscillatory strain is applied and the resulting stress
is measured. By the deconvolution of the stress-strain
rate in-phase and the out-of-phase components, both real
part and imaginary one of the complex shear viscosity η*
can be determined.
 
j






  (2)
where
η* is the complex viscosity,
η′ is the loss viscosity,
η″ is the storage viscosity,
ω is the pulsation of the frequency:
ω = 2πN (3)
Then, the real component of the complex viscosity (η′)
describes the viscous dissipation in the sample, while the
imaginary component (η″) represents the stored elastic
energy. Furthermore, the tangent of the phase angle (tanδ)
describes the balance between the viscous and elastic
behaviors in a polymer melt:
tan





(4)
Another useful representation is to plot the experi-
mental frequency sweep data points in the complex plane.
That means that imaginary part (of the complex viscosity)
η′ values are reported along the abscissa (X axis) and the
imaginary ones (η″) in ordinate (Y axis). Usually, the ex-
perimental points are located on arc of circle charac-
teristic for a Cole-Cole distribution. The extrapolation of
this arc of circle to the zero ordinate value gives the
Newtonian viscosity which is related to the average
molecular weight Mw of the considered polymer through
a power law: (η0 = K. (Mw)3.4) [19].
Melt rheological measurements of neat PP and PP-
wood composites were carried out at 180˚C with an
ARES Rheometer Scientific mechanical spectrometer in
oscillatory frequency sweep mode with a parallel-plates
measuring cell. The diameter of the plates was 8 mm and
the gap was 1.5 mm. The rheological properties of the
wood polymer composite melts were measured at 200˚C;
the frequency was ranged from 0.1 rad/s to 100 rad/s.
The imposed oscillatory shear strain amplitude was tested
for each temperature to valid all the measurements inside
the linear viscoelastic domain.
3. Results and Discussions
3.1. SEM Results
The morphologies of the fracture surface of different

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composites were presented in Figure 1. Examination of
all composites under SEM magnification reveals the oc-
currence of a heterogeneous matrix composed of areas of
predominately PP and areas of wood particles embedded
in the PP. It is possible to observe deep cavities and dis-
tinct gaps at higher magnifications of the 1st specimen
indicating poor adhesion. It has also some gaps and pull-
outs between the reinforcement fibers and the polymer
matrix in the overview micrographs of the two last ones.
Micrographs taken from the fractured surface of all the
specimens showed different organization of the fibers in
the composites, depending on the content of wood flour
and the presence or not of coupling agent (MAPP or
clay). When comparing WPPC3 to all other samples, we
see that the surface of WPPC3 is much smoother and
there’s less aggregates. Most of the wood fiber was en-
veloped by the polymer matrix (i.e. the weight ratio of
the polymer (75%) is higher than that of wood (25%)).
There is less wood in WPPC3 and the molten polymer
can quite well encapsulate the particles of wood flour. In
the other ones, when the rate of wood increases, it ap-
pears a poor interfacial adhesion between the filler and
the matrix. This shows that the morphology is depending
on the rate of wood incorporated. The incorporation of
filler into the polymer matrix disrupted the homogeneity
of the matrix. Particles did not adhere very well to the
surface of polymeric matrix that cracks and voids can be
observed around the particles clearly (Figure 1(b)). The
composites exhibited interfacial debonding with the ap-
pearance of voids and fiber pullout with further increases
in the wood-flour content (Figures 1(b)-(d)). This phe-
nomenon is more accented in Figure 1(b) having only
wood and PP. The non-coupled composite (Figure 1(b))
displayed a rough morphology with the presence of many
voids and cavities resulting from fiber pullout. This indi-
cates poor interfacial adhesion, thus revealing the low
affinity between the polymer matrix and the wood-flour
filler. Water can be easily absorbed by the voids and
Figure 1. SEM micrograph of composites: (a) WPPC3; (b) WPPC4; (c) WPPCC; (d) WPPCG.

Morphology, Thermal Behavior and Dynamic Rheological Properties of Wood Polypropylene Composites
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cavities, thus explaining the high level of moisture ab-
sorption found for the non-coupled composite in our past
studies [3]. The addition of clay in the formulation led to
the improvement of the fiber dispersion, as shown in
Figure 1(c). This dispersion was even better when
MAPP replaced the clay (comparison of Figure 1(c) with
Figure 1(d)). Comparing Figure 1(d) and the others
ones, one can see that the presence of MAPP greatly im-
proved the homogeneity of the blends. Strong interfacial
shear strength between the filler and the matrix was ob-
served; this indicated that the presence of MAPP helped
to bind the two phases together. Some of the OH groups
of wood flour reacted with maleic anhydride to form lin-
kages and, thereby, improved the dispersion of wood in
the composites. In our previous studies, it has been
shown that the addition of MAPP in the composite
showed improved fiber matrix adhesion [20]. It was also
observed that the layers of the matrix material were
pulled out together with the fibers during fracture. This
indicated better interfacial adhesion, and further sup-
ported the higher mechanical properties of WPC with
MAPP. Studies have shown that the presence of wood
flour favors the separation of clay platelets [9]. Addition-
ally, the clay platelets could be separated with the forced
orientation of the extruder, which accounted for the good
dispersion obtained when clay was added. Nevertheless,
the possibility of replacing MAPP with clay appears to
be interesting because the combination of wood flour
with the polymeric matrix made the composite more sen-
sitive to flame. So far, halogenated flame retardants, such
as organic brominated compounds, are generally used to
improve the flammability of composites, but they usually
increase both smoke and carbon monoxide yield rates,
which is catastrophic for the environment. Clay, when
used instead of MAPP, may play the role of flame retar-
dant and also improve the mechanical properties. The
rule of clay is not negligible; the chemical structure of
this additive allows combining the function of dispersing
and coupling agents, so it is capable of bonding the filler
and PP matrix by chemical bonds. Hence, mechanical
properties are improved. Meanwhile flame retardancy
could also be improved [21-24].
3.2. DSC Results
The thermal properties and crystallization behavior of PP
and composites were analyzed by DSC. The results of
crystallization temperature (Tc), heat of crystallization
(Δc
H
), melt temperature (Tm) and the degree of crystal-
linity cor
χ
(%) from DSC were summarized in the fol-
lowing Table 2.
Figure 2 shows the DSC thermograms of cooling
(Figure 2(a)) and melting (Figure 2(b)) curves of PP
and composites. The presence of MAPP or wood flour
showed significant effects on the cooling behavior of the
Table 2. Thermal properties of PP and its composites.
Sample Tm (˚C) Tc (˚C) χcor (%)
PP 165.2 119.5 37.9
WPPC3 170.0 124.4 41.1
WPPC4 169.7 123.7 38.8
WPPCC 170.5 123.8 38.5
WPPCG 165.5 126.5 42.3
Figure 2. DSC curves of neat PP and its composites: (a)
Cooling; (b) Melting.
composites. Only one exothermic peak was registered for
all the samples. For neat PP processed the crystallization
peak was observed at around Tc = 120.5˚C while for the
composites these exothermic peaks shifted to higher tem-
peratures in all cases. The determined Tc values are
shown in Table 2. The higher Tc values of the compos-
ites indicate that the crystallization is favored in the
presence of MAPP or wood particles. The results imply
that MAPP and wood acted as precursor and increased
crystallization; it is due to the nucleation effect of MAPP
or wood: fibers act as sites for heterogeneous nucleation

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thus inducing the crystallization of the matrix [25,26].
The results also indicate that the addition of fiber in-
creased crystallinity of the test materials. This is attrib-
uted to the nucleation effect of the fibers which provide
nucleation sites and facilitate crystallization of the poly-
mer as well as transcrystallinity [27].
The same observation was reported in flax fiber/PP
[28,29]. It was reported that clay, especially the exfoli-
ated clay, increased the crystallization temperature and
acted as a nucleating agent [30,31].
The use of the MAPP instead clay seems to have en-
hanced the level of crystallinity in the composites for the
same levels of wood loading and also accelerates the
crystallization.
Figure 2(b) shows the heating thermograms of PP and
its composites obtained from the second heating range.
For all the samples only one single endothermic peak
was observed at similar temperatures (near 165˚C), cor-
responding to the melting of the α-crystalline phase of
the PP sequences. The peak area of neat PP was larger
than that of composites. The area of melting peak dimin-
ished in all the composites. However after normalizing
the melting enthalpy with respect to the fraction of PP in
the composites (Table 2) it was possible to verify that
the melting peak showed a significant increase. The pos-
sible reason is that wood fibers may restrict the flow
ability of PP molecules during the melting process. Cal-
culations based on the extrapolated melting enthalpy for
a 100% crystalline sample lead to the degree of crystal-
linity, cor
χ
(%) reported in Table 2. These results con-
firmed the behavior observed during heating that the fil-
ler favors the crystallization of the polymer matrix prob-
ably due to the creation of nuclei on the filler surface that
induce the formation of a transcrystalline layer [25].
Nevertheless, the possibility of replacing MAPP with
clay appears to be interesting because the combination of
wood flour with the polymeric matrix made the compos-
ite more sensitive to flame [32]. So far, halogenated
flame retardants, such as organic brominated compounds,
are generally used to improve the flammability of com-
posites, but they usually increase both smoke and carbon
monoxide yield rates, which is catastrophic for the envi-
ronment. Clay, when used instead of MAPP, may play
the role of flame retardant and also improve the thermal
stability of the composite which is in accordance with
our study. In Figure 2(b), WPPCC (sample with clay)
has the highest melting temperature, which demonstrates
its greater thermal stability. Another feature of these re-
sults is the decrease of the peaks accompanied by a re-
duction of its width in all the composites. It was reported
that clay, especially the exfoliated clay, increased the
crystallization temperature and acted as a nucleating
agent. Compared to the neat PP, the wood/PP composites
displayed a better thermal stability. The use of these
composites shows a potential for promising applications
in cost-effective composites with enhanced mechanical
and thermal properties.
3.3. Rheological Results
Figure 3 shows the variations of the real and the imagi-
nary parts of the complex viscosity for neat polypropyl-
ene. Moreover the complex plane diagram is also plotted
onto this figure. The extrapolation of the best fit of the
arc of circle through the experimental set of points (η′, η″)
lead to a value of 3500 Pa.s for the Newtonian viscosity
η0 of the virgin PP at T = 180˚C. This value will serve us
as a reference to exemplify the changes observed with
wood PP composites.
On Figure 4 are drawn the frequency variations of
both the loss and the storage viscosities (Real and im-
aginary parts of the complex viscosity) measured at T =
180˚C for all samples. Obviously, all the composites ma-
terials exhibit viscoelastic values greater than those for
neat PP. Moreover one can notice several orders of mag-
nitude for the changes in these values (about two dec-
ades). The closer to the unfilled PP is the sample with the
lower concentration of wood filler (WPPC3).
Figure 3. Frequency variations of the loss (η′) and the
storage (η″) viscosities (upper figure) and complex plane
representation (bottom figure) at T = 180˚C for neat PP
(η″ versus η′).

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Figure 4. Frequency variations of the loss (η′) and the stor-
age (η″) viscosities for neat PP and its composites at T =
180˚C.
Figure 5 represents the complex plane variations for
the neat PP and the wood polypropylene composites.
Again, great changes are observed for WPP regarding the
reference PP. However, for samples WPPC3, WPPCG
and WPPCC the circular variation seems still quite valid.
Sample WPPC4 exhibits a deviation to the circular be-
havior and shows a linear variation of the storage viscos-
ity versus the loss viscosity. This is characteristic for a
gel behavior indicating then a high level of interaction
between the matrix and the filler however no compatibi-
lizer is used; Table 3 reports the Newtonian values de-
termined for all the samples:
WPPC4 exhibits the higher viscoelastic behavior but it
contains 50% wood filler and 50% PP matrix while sam-
ples WPPCC and WPPCG contain only 45% PP matrix
and 50% Wood filler. Thus in the second case the ratio
matrix/filler is less than 1 (0.9) while it is 1 in the first
case. If we compare samples with the same ratio
(WPPCC and WPPCG) we can notice that the higher
Newtonian viscosity is obtained with the sample con-
taining MAPP as comptabilizer. Then the addition of a
small concentration of nanoparticles like nanoclays does
not improve the resulting melt viscoelastic behavior of
the wood polymer composite.
Figure 5. Complex plane diagrams for all the WPC (upper
right curve: complex plane diagram for neat PP) at T =
180˚C.
Table 3. Newtonian values for WPC composites.
SamplePP (%)Wood (%)MAPP (%) Clay (%)η0 (Pa.s)
PP 100 0 0 0 3500
WPPC375 25 0 0 22,500
WPPC450 50 0 0 ∞
WPPCC45 50 0 5 210,000
WPPCG45 50 5 0 260,000
4. Conclusions
The polymer matrix in none coupled composites was not
continuously distributed and most of the wood fibers
directly contacted one another, thus resulting in poor
adhesion at the interface. The presence of the coupling
agents changed the morphology of the materials. The
addition of MAPP or clay to the composites produced a
more homogeneous surface with less voids and cavities.
This indicated that these coupling agents have a positive
effect on the interfacial adhesion between the filler and
the matrix. Melt rheology confirms this behavior. The
comptabilizer induces a better interface between the fill-
ers and the matrix. However, the effect of the compatibi-
lizer is more efficient than this of the nanoclay. But it is
difficult to discriminate one effect from another. It
should be interesting to study wood filler polypropylene
composites containing both the comptaibilizer (Maleic
anhydride) and the nanoclay in different proportions.
This will be a further development of this study. The
sample with the higher amount of wood filler (50%) ex-
hibits the higher viscoelastic behavior; however, it does
contain neither compatibilizer nor nanoclay. In such a
case, we can observe a change in the flow regime from a
linear entangled melt flow to a gel flow. The conse-
quence is the very high magnitude of change in the vis-

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cosity values that can lead to difficulties in the further
processing operations. The thermal degradation trends of
both kinds of composites were similar and increased the
thermal stability of PP in comparison to the neat PP. The
cooling process shows an increase in the crystallization
temperature of PP with the addition of fillers. This phe-
nomenon may be attributed to the fillers being dispersed
in PP matrix, promoting the heterogeneous nucleation.
Finally, the success of WPP composites lies in the
compromise between the high level of interaction be-
tween the filler and the matrix to improve the solid state
mechanical properties on the condition that the melt vis-
cosity range of the blends will render them still proc-
essable. Then a development of this work would be to
process high fluidity WPP with a high content of wood
filler and a high level of interaction.
5. Funding
This research received no specific grant from any fund-
ing agency in the public, commercial or not for profit
sectors.
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