Journal of Metals, Materials and Minerals. Vol.18 No.2 pp.53-56, 2008
Thermal and Mechanical Properties of Wood-Plastic Composites from
Iron Wood Flour and Recycled Polypropylene Foam
Monchai TAJAN, Phasawat CHAIWUTTHINAN and Thanawadee LEEJARKPAI
National Metal and Materials Technology Center, 114 Thailand Science Park,
Paholyothin Rd., Kolng 1, Klong Luang, Pathumthani 12120'
Abstract
In this work some of the important properties of experimentally manufactured wood-plastic
composites (WPC) were determined. Specimen having 30% particle of Iron wood (Xylia Xylocarpa) was
mixed with recycled polypropylene foam (RPPF) and two different additives, glycerol as a plasticizer and
maleic anhydride grafted polypropylene homopolymer (MAPP) which is a compatibilizer. The thermal and
mechanical properties of the composites were analyzed and compared with those of non-additive
composites. Compared with RPPF, Iron wood/RPPF composites had higher melting and crystallization
temperature, but much lower crystallinity level. Their thermal stability was lower than RPPF due to the
degradation of the wood flour. The experimental results revealed that addition of the wood flour increased
the tensile modulus, but decreased the values of the tensile strength and elongation at break of the
composites. The uses of plasticizer and compatibilizer have been shown to influence on the thermal and
mechanical properties of the composites. The results indicate that both glycerol and MAPP improved the
compatibility of the Iron wood flour and RPPF in the composites, lead to the good properties determined for
these materials.
Key words :
Iron wood flour ; Recycled polypropylene foam ; Wood-plastic composites
Introduction
Wood-plastic composites have received
considerable attention from industry in recent
years. Much work has been done on wood flour
and virgin thermoplastic composites, which
succeed in wood composite industry. However,
work done on wood flour/recycled plastic systems
is still limited. Polypropylene foam is widely used
in packaging applications and transportations, and
can be collected to recycling process. Thus,
recycled PP foam is an alternative source of raw
material. Most of the physical and mechanical
properties of the wood-plastic composites depend
mainly on the interaction between the wood and
the thermoplastic material. One way to improve
this interaction is incorporating the compatibilizer.
Several studies showed that using PP modified
with maleic anhydride as a compatibilizer in the
wood-plastic composites significantly increased
interfacial bonding between the wood flours
and the plastics.(1,2) However, the wood-plastic
composites also have problems because of
characteristic of the wood flour, such as the
thermal degradation and the dispersion of the wood
flour during a compounding. On the other hand, the
use of a plasticizer may be one way to reduce
the thermal degradation and the dispersion of the
wood flour. Therefore, the main objective of this
work is to investigate the effect of plasticizer and
compatibilizer on the thermal and mechanical
properties of the wood flour and the recycled PP
foam composites.
Materials and Experimental Procedures
Materials
Recycled polypropylene foam (RPPF) was
provided as the plastic pellets by S. Pinya recycle
Co., Ltd. Its melting temperature was 109°C and
melt flow index was 9.9 g/10min at 230°C, 2.16 kg
load. Its density at room temperature was 0.889
g/cm3
. Four types of the wood flours were
analyzed by TGA to assess the thermal stability.
The results are summarized in Table 1. The
degradation temperature of the Iron wood flour
listed in Table 1 was the highest, and then used as
filler in this work at 30% by weight. The Iron
wood flour was sieved with a 500-mesh screen.
Before use, it was also oven-dried at 80°C for 24 h
and its moisture content was controlled at lower
than 2%. Mixing of the Iron wood flour and the
RPPF plastic along with a commercial glycerol
Phone 0-2564-6500 # 4457, Fax. 0-2564-6445, E-Mail: monchait@mtec.or.th
Received Nov. 13, 2008
Accepted Jan. 30, 2009 54
TAJAN, M. et al.
content of 3% by weight, play as a plasticizer.
Maleic anhydride grafted polypropylene homopolymer
(COMPOLINE CO/PP H60) was used as a
compatibilizer, in the content of 5% by weight,
supplied by Behn Meyer Chemical (Thailand) Co.,
Ltd. The melt flow index of 60g/10 min at
230°C/2.16 kg, a graft level of 0.25-0.5%, and the
melting temperature of 165°C.
Table 1. Thermal stability of the different wood flours
with thermogravimetric analyzer.
Methods
The raw materials were first dry blended
with a high speed mixer and then fed into a 20 mm
laboratory co-rotating twin screw extruder.
The barrel, screw and die temperatures were held
constant between 180-220°C, with the screw
speed of 150 rpm. Thermogravimetric analysis
was used to study the thermal stability of the wood
flours and the resultant composites with a
thermogravimetric analyzer (Mettler Toledo
TGA/SDTA 851e), under air at a scan rate of
20°C/min from 30-600°C. Experiments on the
thermal behavior of the composites were carried
out on a Mettler Toledo DSC 822e differential
scanning calorimeter. The sample size was about 5
mg with a heating rate of 10°C/min. The specimens
(specific dumbbell shape W=10 mm, L=100 mm,
D=3 mm) of the composites were prepared by
injection moulding at the melting temperature
profiles of 150-170°C and the injection speed of 20
mm/s. At least five specimens were measured for
the tensile properties, using an Universal Testing
Machine (INSTRON Model 55R4502) with a
crosshead speed of 50.0 mm/min.
Results and Discussion
Thermal Properties
When the 30% Iron wood flour was added
to RPPF, both melting temperature (Tm) and the
crystallization temperature (Tc) were significantly
increased whereas decreased the crystallinity
level (attributed to enthalpy of melting and
crystallization on DSC thermogram) as shown in
Figure 1. The wood flour particles could act as a
nucleating agent during the nucleation stage to
increased the crystallization temperature of the
composites. However, it could also act as an
interfering agent during the growth stage to
decreased in the overall crystallinity level of the
composites. Adding only the plasticizer or
compatibilizer did not obviously influence the
crystallinity level, whereas severely changed when
they were added together. The lowered crystallinity
level with introducing both plasticizer and
compatibilizer suggested that the compatibility
between the Iron wood flour and RPPF matrix was
improved.(3)
Figure 1. Thermal properties of the Iron wood/RPPF
(30/70 w/w) composites (a) melting temperature
and enthalpy of melting; and (b) crystallization
temperature and enthalpy of crystallization
(RPPF : recycled polypropylene foam, P :
plasticizer, C: compatibilizer, NP : no plasticizer,
and NC: no compatibilizer).
The TGA and DTG (is the first derivative
of the TGA) curves of RPPF and composites
under air are represented in Figure 2 and 3.
The
thermogravimetric analys is of RPPF showed a
Wood Flours Degradation Temperature
(°C)
Para rubber (general) 328
Para rubber (dark) 333
Para rubber (light) 310
Iron wood 356
108
113
118
123
128
133
138
143
148
153
RPPF NPNC PNC NPC PC
Melting Temperature (°C)
42
50
58
66
74
82
90
98
Enthalpy of Melting (J/g)
Melting Temperature
Enthalpy of Melting
95
97
99
101
103
105
107
RPPF NPNC PNC NPC PC
Crystallization Temperature (°C)
45
55
65
75
85
95
105
Enthalpy of Crystallization (J/g)
Crystallization Temperature
Enthalpy of Crystallization
(a)
(b)55
Thermal and Mechanical Properties of Wood-Plastic Composites from Iron Wood Flour
and Recycled Polypropylene Foam
single-mass loss step with maximum degradation
rate at 433°C indicated the degradation of saturated
and unsaturated carbon atoms in polypropylene.
All the composites showed multi-stepped
degradation due to the various species present. An
initial transition around 100°C due to moisture
evaporation. The first degradation peak around
380°C could derive from the degradation of
cellulosic components. The next degradation peak
around 430°C was due to the degradation of the
polymer matrix in the composites. Above 450°C
the composite showed some peaks of degradation
are probably related to further breakage of
degradation products formed during the thermal
analysis.
Figure 2. TGA curves of the Iron wood/RPPF (30/70 w/w)
composites.
Figure 3 DTG curves of the Iron wood/RPPF (30/70 w/w)
composites.
Moreover, the DTG curve of the
composites with the plasticizer addition showed the
degradation of the glycerol around 250°C.(2,3)
For the Iron wood/RPPF composites, it was
verified that the maximum degradation rate was
shifted to a lower temperature. This is indicated
that the present of the wood flour lowered the
thermal stability of the materials. However, the
degradation temperature of the wood flour
increased about 20°C in comparison to the neat
wood flour which might derive from RPPF coating
around the wood flour. The plasticizer and
compatibilizer seemed to have different influence
on the thermal degradation of the composites. The
glycerol showed better heat degrading inhibition
than that of MAPP compatibilizer. However, the
addition of both plasticizer and compatibilizer
together lowered the degradation temperature of
the materials. It was recommended that maleic
anhydride, in the presence of moisture from wood,
could convert to maleic acid which stimulated to
degradation of the composites.(4)
Mechanical Properties
Figure 4. Showed the tensile strength,
tensile modulus and elongation at break of the
composites. It can be clearly observed that
introducing the Iron wood flour increased the
tensile modulus, but decreased the values of the
tensile strength and elongation at break, when
compared to those of recycled PP foam. It is
interesting to note that the tensile modulus
progressively increased with addition of the wood
flours, probably caused by the fact that the wood
flour is more rigid than the plastic. However, the
decreases in tensile strength and elongation at
break were probably caused by a number of
reasons, as suggested by Sombatsompop et al.(5)
Figure 4. Also showed the effect of the
plasticizer and compatibilizer on the mechanical
properties of the Iron wood/RPPF composites. In
general, it was observed for all compatibilizers that
tensile strength and tensile modulus of the
composites were found to increase, accompanied
by a decrease in elongation at break, with
introducing MAPP compatibilizer. The decrease in
elongation at break was expected since the
composites with MAPP compatibilizer now were
stiffer and had higher strength. Surprisingly,
introduction of glycerol as the plasticizer resulted
in increasing tensile strength and elongation at
break. It seems act as another compatibilizer in this
wood/plastic system. The addition of both
plasticizer and compatibilizer simultaneously
showed the positive effect to enhance the tensile
0
20
40
60
80
100
0 100 200 300 400 500 600
Temperature (°C)
Weight (%)
RPPF
NPNC
PNC
NPC
PC
-0.012
-0.01
-0.008
-0.006
-0.004
-0.002
0
0 100 200 300 400 500 600
Temperature (°C)
Derivative Weight (1/°C)
RPPF
NPNC
PNC
NPC
PC56
TAJAN, M. et al.
strength, whereas showed the negative effect to
reduce tensile modulus and elongation at break of
the composites.
Figure 4. Mechanical properties of the Iron wood/RPPF
(30/70 w/w) composites (a) tensile strength;
(b) tensile modulus; and (c) elongation at break.
Conclusions
The experimental results indicated the
increase of the melting and crystallization
temperature, accompanied with the decrease of the
crystallinity level, thermal stability, the tensile
strength and elongation at break of the Iron
wood/RPPF composites with the presence of the
Iron wood flour, as it was expected. However, the
addition of the polymeric compatibilizer produced
composites with better performance, since the
tensile strength was increased. This behavior can
be attributed to the enhanced chemical compatibility
between the components. Moreover, we have
observed the positive effect of glycerol on the
maleic anhydride compatibilizer. Thus, to more
effectively improve the thermal and mechanical
properties of the composites, glycerol as plasticizer
and a MAPP compatibilizer should be selected.
Acknowledgement
The authors would like to thank National
Metal and Materials Technology Center (MTEC)
for financial support to this work.
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