Ijmet 06 10_016

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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 6, Issue 10, Oct 2015, pp. 145-153, Article ID: IJMET_06_10_016
Available online at
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=6&IType=10
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
BIOCOMPOSITE WITH POLYPROPYLENE
AND ALFA FIBERS: STRUCTURE/
PROPERTIES RELATIONSHIP
F. Rhrich and F. Bourzgui
FMD- University Hassan II- Casablanca
M. Benhadou and A. Haddout
Team rheology and plastics processing-ENSEM- University Hassan II- Casablanca
ABSTRACT
We present a study on the development of thermoplastic bio-composites
reinforced by Alfa fibers (stepa tenassicma). We applied different surface
treatments on obtained fibers, to promote their adherence to the
polypropylene matrix. The mixture of the fibers and the matrix was extruded
and pelletized according to a defined operating mode.
We conducted a detailed study for the definition and optimization of
injection molding process's industrial conditions of the composites. The tests
carried out on the specimens showed that the mechanical and viscoelastic
properties of these composites display a marked improvement depending on
surface treatments and the rate of Alfa fibers and injection parameters. Other
microscopic features were used to analyze the flowing behavior of Alfa fibers
along a injected part, for fiber lengths greater than 4.5 mm, we highlighted the
phenomena of deformation and coalescence and aggregation of the fibers
according to the injection process parameters.
Key words: Bio Composite, Polypropylene/Alfa short fibers, alkali treatment,
injection molding, morphology and mechanical behavior.
Cite this Article: Rhrich, F., Benhadou, M., Bourzgui, F. and Haddout, A.
Biocomposite with Polypropylene and Alfa Fibers: Structure/Properties
Relationship. International Journal of Mechanical Engineering and
Technology, 6(10), 2015, pp. 145-153.
http://www.iaeme.com/IJMET/issues.asp?JTypeIJMET&VType=6&IType=7
_____________________________________________________________________
1. INTRODUCTION
The use of bio composites based on plant fibers is growing rapidly with many industrial
applications. Vegetable fibers are sought for the many environmental and economic and
technological and health advantages whose industries could benefit of: renewable

F. Rhrich, M. Benhadou, F. Bourzgui and A. Haddout
material - biodegradable - neutral carbon balance - low density and energy saving -
flexibility - low cost and less or no health problem of operators on production lines [1-5].
Bio-composite based on Alfa fibers may find their application in the health field
such as dentistry or auto industry for applications such as interior door trim and the
coffers of roofs and bumper.
However, technical brakes exist when processing these fibers included a specific
technical developments.. Today, the main lines of technical development of
associated fibers and bio materials lie in improving fiber properties by the selection in
optimizing industrial shaping processes [4-8].
The Alfa fibers are biological structures primarily composed of cellulose and
hemicellulose and lignin. [9] Unlike the other components of fibers having an
amorphous structure, the cellulose has a large crystalline structure portion. Inside the
fiber, the cellulose chains are joined as microfibrils that agglomerate form fibrils, the
angle between these highly structured elements and the axis of the fiber determines
the stiffness of the fiber [10].
The properties of the fibers (flexibility, smoothness, cellulose fiber content) make
this plant a valuable source of raw material for the paper industry. "A clump of Alfa
can withstand successive operations for 25 to 30 years, under the condition of a
resting 2 to 3 years after a number of holdings [11-12].
The Alfa fibers have the following composition: 45% cellulose, 25%
hemicellulose, 23% lignin, 5% of wax and 2% ash [13-16]. In terms of structure,
observation by scanning electron microscopy shows that a Alfa rod consists of fiber
bundles with lignin. Their form is a kind of tube whose section is not circular. The
largest dimension of the tube section is approximately 200µm.
The treatment of the fibers with acetic anhydride is an effective method to reduce the
hydrophilic nature of cellulose fibers, [17] and improve the dispersion of fibers in a
thermoplastic composite. Acetic anhydride reduces the fiber surface energy to make it
non-polar and more similar to the thermoplastic matrix [18-19]. Acetate bonds are formed
by reaction of acetic anhydride. The OH groups of the fiber surface are therefore no
longer available to react with other groups, such as hydroxyl groups of water.
The objective of this work is to develop a method of extracting Alfa fiber and make
thermoplastic composite's formulations of polypropylene (PP) reinforced with short Alfa
fibers with particular attention to the influence of fiber processing conditions and the
conditions of implementation. The various observations will allow us to link the
microstructure and behavior to the mechanical strength of our composites.
2. MATERIALS AND TECHNIQUES
2.1. Preparation of composite PP / Alfa short fibers
We carried on Alfa plants operations of drying and retting in a moist environment in
the presence of salt. Thereafter, the fibers were combed and untangled and subjected a
crushing operation, to prepare the mechanical carding, then grinding for optimal
average length allowing the fiber to fully play its role of reinforcement without
causing phenomena agglomeration.
Dispersing the fibers in a composite material is an important factor for achieving
good mechanical properties. Bad distribution results in the presence of fiber
agglomerations. Thus, areas rich in fiber or matrix appear randomly distributed and
have bad properties. To ensure good dispersion of the fibers in the composite, it is
essential to eliminate or limit the aggregation. Good wetting is achieved when each
fiber is totally wrapped by the matrix.

Bio-composite with polypropylene and Alfa fibers: Structure/ properties relationship
The main problem with the use of Alfa fibers as a reinforcing material is cohesion
and bonding with the matrix. Alfa fibers are hydrophilic, however the polymers used
as matrices such as polypropylene, are often hydrophobic. Therefore, the functional
groups do not bind easily. Thus, the composite loses its mechanical properties and is
more easily broken at the connection.
Pretreatment can decrease the hydrophilicity of Alfa fibers and increase that of
polymers for a better bonding is possible.
We have applied various surface treatments to the fibers obtained, for sodium
hydroxide and maleic anhydride in order to promote their adhesion to the
thermoplastic matrix.
The thermoplastic used in our composite is a polypropylene market density 0.905
g/cm3
, and melt flow index of 12g /10min at 230°C and 2.16kg (according to ISO
1133 standard).
Polypropylene modified with maleic anhydride (MA) is a coupling agent
composed of long polymer chains with a functional group MA grafted on one
extremity. MAPP acts as a bridge between the non-polar polypropylene and polar
cellulose fibers. MA group binds to the surface of the cellulose to form covalent or
hydrogen bonds with the reactive OH groups on the surface of the cellulose and
lignin. The rest of the chain remains free and forms tangles with the chains of the
polymer PP.
The mixture of fibers/thermoplastic polymer and coupling agent and additives
were extruded and granulated, in our laboratory by using an extruder whose screw
profile is adapted to the composite compounding using a defined operating mode.
Using an experimental design, we conducted an extensive study for the definition and
optimization of injection molding conditions of the manufactured composites.
-A- -B- -C- -D-
Figure 1 The main stages of development of bio composite material with polypropylene/
short Alfa fibers.
A: Harvesting Alfa plants B: Retting and treatment
C: Grinding and final treatment of fibers, D: Mixing and granulation and injection
molding of the composite
2.2. Morphological and mechanical characterization of bio-composites with
PP/Alfa Fibers
We determined the optimum processing parameters of our materials and we injected
rectangular plates (dimensions 180 x 3.5 x 98 mm), equipped with variable angle of
injection threshold over which we cut out the specimens used for morphological and
mechanical tests.

Figure 2 Geometry of molded parts with the composite PP/ short Alfa fibers
The main injection parameters used for this study are summarized in the Table 1:
Table 1 The injection molding parameters
Injection parameters Value
Injection temperature 200° C
Mold temperature 25°C - 80°C
Injection pressure 45 MPa
Clamping pressure 40 MPa
Clamping time 08 s
Screw speed rotation 142 tours/min
Injection speed 20 , 35, 58 mm/s
3. RESULTS AND DISCUSSION
3.1 Morphological analysis
Morphological observations have allowed us to assess the phenomenon of fiber
orientations in the polypropylene matrix, observe porosity defects on injected
composite and evaluate the influence of fiber lengths on their agglomeration and on
molding skin thickness.
We observed the flowing behavior of Alfa fiber along the injected part. For short
fibers whose average length is less than or equal to 2.3 mm, the distribution is
homogeneous on surface. The fibers orientation is controllable to a 15% rate of
reinforcement, beyond this level, the orientation tends to be random in the vicinity of
the mold walls, with better orientation heart.
When the composite flow in the mold cavity, each fiber moves and orients
depending on the constraints imposed by its environment: the matrix and the other
fibers and the walls of the cavity. After solidification, we observe a complex
distribution of orientation which varies from one location to another of the part.
Then the overall observation of a sample cut in the plate's thickness at a distance
of 90 mm from the injection gate, leads us to the following interpretation.
 Skin: the fibers are randomly oriented in the plane of the plate
 Under the skin: the fibers are mainly oriented in the flow direction
 Core: the fibers are oriented perpendicular to the direction of flow.
when we exceed a critical fiber length, it becomes very difficult to control their
orientation by acting on the molding parameters [20]. When we used fiber lengths
greater than 4, 5 mm, We observed phenomena of deformation and coalescence and
aggregation of the fibers according to the processing parameters, Figure 4.

Figure 3 Distribution and global fibers orientation in the thickness of the molded part
Figure 4 Observation by reflection microscopy of PP+ 20% Alfa fibers: Injection temperature
200°C and mold temperature 25°C
3.2. Influence of injection speed
The injection speed is a critical parameter. It is able to varying the fibers orientation in
the mold because it occurs during the dynamic phase of filling of the mold cavity.
Accordingly, the fibers conformation after cooling in a specific state will be strongly
governed by the applied injection speed.
We tried to highlight the variation of the heart layer in molded parts, depending on
the injection speed (Table 2).
Table 2 Evolution of the core thickness depending on injection speed
Test N° Speed (mm/s) Thickness (%)
1 20 15,4
2 35 17,8
3 58 23,5

We note that the thickness of core layer increases depending on injection speed.
This difference is explained at first by the variation of the solidified layer and the
speed profiles shape during the materials flow in the mold (fountain effect). The fluid
is highly viscous at high injection speed and the type of flow is "plug" kind, and the
shear at core is almost zero, which allows the fibers to maintain the initial orientation
to the mold inlet.
3.3. Mechanical characterization
Tensile tests were done on samples cut from molded plaques according to the
conditions identified in Table 1. Figure 5 shows the evolution of the tensile strength
of polypropylene composite reinforced with different rate of treated short Alfa fibers.
We observe a change in the tensile behavior of the composite depending on rate of
fiber and particularly a clear decrease of the nonlinear distortion depending on the
Alfa fiber content, with improved tensile strength.
Figure 5 Evolution of tensile behavior of polypropylene reinforced with different rates of
short Alfa fibers
Table 3 summarizes the results representing the average value performed on seven
specimens tested in each formulation case and highlighting the influence of fibers
chemical treatment on the mechanical properties of polypropylene bio-composite
reinforced with 20% short Alfa fibers.
Table 3 Influence of Alfa fibers treatment on tensile properties of the composite
0
5
10
15
20
25
30
35
40
0 0.02 0.04 0.06
Stress(MPa)
Strain (%)
10%
20%
30%
Specimens
σ Break
(MPa)
A%
Standard
deviation
A%
Module
(MPa)
Standard
deviation
Module (MPa)
PP+ 20% treated
Alfa fibers
48.3 4.69 0.21 2585 43
PP+20% untreated
Alfa fibers
41.5 5.56 0.26 2267 41

3.4. Analysis of viscoelastic behavior
The thermomechanical tests were performed with a dynamic mechanical measuring
device (DMTA). This measure gives the variation of the torsional shear modulus G
'and the bending elasticity modulus E' as a function of temperature at a given
frequency and mechanical damping coefficient tg.
Figure 6 shows the influence of the mold temperature on the mechanical damping
of composite PP/short Alfa fibers. A mold temperature of 25°C markedly improves
the damping of the materials thus its impact resistance.
Figure 6 Composites viscous modulus (70/30), PP / short Alfa fibers at Tm = 80°C
Similarly, Figure 7 shows the evolution of the elasticity modulus depending on the
temperature at different mold temperatures. We note that the mold temperature has a
positive effect on the elastic modulus.
Figure 7 Composite's e elastic modulus of the PP / short fiber Alfa (70/30), at different mold
temperature
0
0.05
0.1
0.15
0.2
0.25
-40 -20 0 20 40 60 80
E''(Gpa)
T(°C)
Tm=25°C
Tm= 80°C
0
1
2
3
4
5
6
-40 -20 0 20 40 60 80
E'(Gpa)
T(°C)
Tm=25°C
Tm=80°C

Figure 8 shows the evolution of the tangent of the mechanical loss angle versus
temperature for different rate of short Alfa fibers. The transition peak decreases when
the fiber content increases. This results in a decrease of the material damping and
therefore its impact resistance.
Figure 8 Evolution of the tangent of the mechanical loss angle of the composite PP/Alfa as a
function of the temperature at different rates of short fibers Alfa
The study of the evolution of the thermomechanical properties of thermoplastic
composites based on organic injection parameters, classifies the relative importance
of these parameters.
The mold temperature is the parameter whose variation induced the greatest
changes in the mechanical properties. When the mold temperature increases, the
values of stress at break and the elasticity modulus increases significantly. However,
the impact resistance and the tangent of the mechanical loss angle decreases. The
variation of the filling speed also influences the mechanical properties
4. CONCLUSION
After controlling the process of extracting Alfa fibers from the plant , we have
developed several formulations of bio thermoplastic composites reinforced with Alfa
fibers. We then conducted an extensive study for the definition and optimization of
injection molding process's industrial conditions of the composites. We determined
the optimal injection process parameters of our materials and manufactured
rectangular plates.
Morphological observations were used to analyze the flowing behavior of Alfa
fibers along an injected part. We have highlighted the distribution phenomena and
fiber's orientation based on injection molding process parameters. This partly explains
the variation of mechanical properties with the loading direction on the one hand and
on the other hand we have highlighted the influence of fiber's chemical treatment and
mold temperature on the mechanical properties of injected parts .
This study represent a very important step towards understanding the benefits of
Alfa fiber forms and qualities and opportunities to be one of fibrous plants used in the
composite industry.
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
-40 -20 0 20 40 60 80
tg
T(°C)
30%
25%
10%
0%

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