A biodegradable composite material based on polyhydroxybutyrate (PHB) and carnauba fibers
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7/25/2019 A biodegradable composite material based on polyhydroxybutyrate (PHB) and carnauba fibers
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A biodegradable composite material based on polyhydroxybutyrate (PHB)
and carnauba fibers
J.D.D. Melo, L.F.M. Carvalho, A.M. Medeiros, C.R.O. Souto, C.A. Paskocimas
Department of Materials Engineering, Federal University of Rio Grande do Norte, Natal, RN 59078-970, Brazil
a r t i c l e i n f o
Article history:Received 21 August 2011
Received in revised form 13 January 2012
Accepted 16 January 2012
Available online 11 May 2012
Keywords:
A. Polymermatrix composites (PMCs)
B. Mechanical properties
B. Thermal properties
E. Surface treatments
a b s t r a c t
In this investigation, carnauba fibers obtained from the leaves of the carnauba palm tree were chemicallymodified and their potential for the development of a biodegradable composite was evaluated. Fiber
treatments to improve interfacial bonding were carried out by alkali, peroxide, potassium permanganate
and acetylation. Biodegradable composites were prepared using carnauba fibers and polyhydroxybuty-
rate (PHB) as matrix. Mechanical properties of the composites prepared with 10 wt.% of short carnauba
fibers were investigated and related to fiber treatment. According to the results, the tensile strength of
the composites made from peroxide treated fibers was superior to those using untreated fibers or any
other fiber treatment. SEM observations on the fracture surface of the composites suggest improved
fibermatrix adhesion after peroxide treatment. This surface modification of the fibers was found to con-
tribute to the enhancement of the mechanical properties of the composites, even though the tensile
strength of the fibers was slightly reduced. Dynamic mechanical thermal analyses suggested improve-
ment in storage modulus of the composites reinforced with carnauba fibers at higher temperatures as
compared to the neat polymer.
2012 Elsevier Ltd. All rights reserved.
1. Introduction
The growing environmental awareness and new environmental
regulations observed in recent decades have led to increasing
interest in biodegradable materials. Studies focusing on the use
of natural fibers as a replacement to man-made fibers in fiber-
reinforced composites have gained ever-increasing importance.
Besides biodegradability, natural fibers offer cost savings and
reduction in density when compared to some man-made fibers
such as glass. Thus, even though the strength of these fibers is low-
er than fiberglass, natural fiber composites have potential use in
many applications[13].
A major market for the application of plant-derived fibers as
replacement of fiberglass is the automotive industry. Currentapplications for these fibers in vehicles include door trim panels,
rear parcel shelf, damping and insulation parts, center console trim
and seat cushion parts[4]. However, the large scale production of
cellulosic fiber composites is still limited by two important issues:
compatibility with the polymer matrix and water absorption. As a
result of the incompatibility between the hydrophilic fibers and
the hydrophobic polymer matrix, the wettability of the fibers is
poor and strength of natural fiber composites is low compared to
glass fiber reinforced composites. Water absorption is also a
limiting factor since it produces swelling and reduces strength, in
addition to an increase in mass.
Natural cellulosic fibers consist primarily of cellulose, hemicel-
lulose, pectin, lignin, waxes and water soluble substances[5]. Cel-
lulose is a semicrystalline polysaccharide with large amount of
hydroxyl groups which is responsible for the hydrophilic nature
of the natural fibers. Hemicellulose is an amorphous polysaccha-
ride of lower molecular weight when compared to cellulose. Hemi-
cellulose is partly soluble in water and hygroscopic because of the
many hydroxyl and acetyl groups in its structure[6]. Pectin is also
a polysaccharide and its main function is to hold the fiber together.
Lignin is an amorphous mainly aromatic polymer and has the least
water absorption of all natural fiber components[6].
There are many chemical treatments that havebeen successfullyapplied to natural cellulosic fibers aimed at improving fiber proper-
ties and also their adhesion to polymer matrices. These include
alkaline, acetylation, permanganate and peroxide treatments,
among others [5]. Alkaline treatment with sodium hydroxide
(NaOH) also known as mercerization is oneof the most common
chemical treatments of cellulosic fibers intended to be used as rein-
forcement to polymers. This treatment has been reported as having
two main effects on the fiber: (1) it increases the surface roughness
that results in a better mechanical interlocking; and (2) it incre-
ments the amount of cellulose exposed on the fiber surface, thus
increasing the number of possible reaction sites[7,8]. Acetylation
is a well-known treatment that can reduce the hygroscopic nature
1359-8368/$ - see front matter 2012 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.compositesb.2012.04.046
Corresponding author. Tel./fax: +55 84 3342 2406.
E-mail address:[email protected](J.D.D. Melo).
Composites: Part B 43 (2012) 28272835
Contents lists available atSciVerse ScienceDirect
Composites: Part B
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o m p o s i t e s b
http://dx.doi.org/10.1016/j.compositesb.2012.04.046mailto:[email protected]://dx.doi.org/10.1016/j.compositesb.2012.04.046http://www.sciencedirect.com/science/journal/13598368http://www.elsevier.com/locate/compositesbhttp://www.elsevier.com/locate/compositesbhttp://www.sciencedirect.com/science/journal/13598368http://dx.doi.org/10.1016/j.compositesb.2012.04.046mailto:[email protected]://dx.doi.org/10.1016/j.compositesb.2012.04.046 -
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of natural cellulosic fibers [9] and increase the dimensional stability
of composites. In a previous study, acetylation treatment of sisal
fibers was reported to increase surface roughness and improve
the fibermatrix adhesion[10]. Fiber treatments using potassium
permanganate (KMnO4) reduce the hydrophilic nature of the fibers
[9]. In an investigation involving sisal-LDPE composites, it was
shown that the tensile properties of composites made from per-
manganate treated fibers can be significantly improved as com-pared to composites made from untreated fibers [8]. Peroxide
treatments can also decrease hydrophilicity of the cellulosic fibers
[9]and increase the tensile properties[8].
Even though natural cellulosic fibers have been successfully
used with petroleum-derived polymers, the environmental bene-
fits of natural fiber composites can be enhanced considerably if
biodegradable polymers are used. Polyhydroxybutyrate (PHB) is a
biodegradable polymer produced by bacteria from renewable raw
materials such as sugarcane[11]. PHB has been studied for many
applications ranging from construction applications[12]to nano-
particles used as drug carrier [13]. PHB and its co-polymers have
been combined with natural cellulosic fibers such as hemp
[14,15], jute[16],flax [14,1719], and bamboo[20].
In this investigation a novel biodegradable composite material
based on polyhydroxybutyrate (PHB) and carnauba fibers is pro-
posed and evaluated. Carnauba (Copernicia prunifera (Miller) H. E.
Moore) is a palm tree native to Brazil. Its main product is the car-
nauba wax which has many applications in the pharmaceutical
industry, food industry, cosmetics, electronics components, grease
and lubricants and as mold release. Alkali, peroxide, potassium
permanganate and acetylation treatments were carried out on
the carnauba fibers to improve fibermatrix compatibility.
Mechanical and thermal properties of the carnauba fibers and com-
posites prepared with PHB and 10 wt.% of fibers were investigated
and related to fiber treatment.
2. Experimental
2.1. Materials
PHB was obtained from PHB Industrial S/A BRAZIL. This poly-
mer is produced from sugarcane by microorganisms of the alcalig-
enes s.p. species [11]. Typical properties of the PHB used are:
density: 1.3 g/cm3; tensile strength: 2536 MPa; and melting
point: 165170 C.
The carnauba fibers used in this investigation (Fig. 1) were col-
lected from the State of Piau in the northeastern region of Brazil.
The typical cross-section of the fibers observed using an optical
microscope (Olympus BX60m) is shown in Fig. 2. As shown in
Fig. 2, the cross-section is irregular in shape and can be approxi-
mated to an ellipse. The chemical composition of the carnauba fi-
bers is shown inTable 1.
2.2. Fiber treatments
The following fiber treatments were conducted: alkaline at con-
centrations of 1%, 3% and 5% (FT1%, FT3%, FT5%), acetylation (FTAc),
permanganate (FTP) and peroxide (FTPH). The fiber treatments are
summarized inFig. 3.
For the alkaline treatments, fibers were immersed in a NaOH
solution with the specified concentration (1%, 3% or 5%), at room
temperature (approx. 25C), for 3 h, 2 h, and 1 h, respectively.
The fibers were then washed thoroughly with distilled water to re-
move the excess of NaOH. After that, the fibers were oven dried at
60C for 24 h.
The acetylation and permanganate treatments were conducted
in fibers previously treated with NaOH at 1%. For the acetylation,
the dewaxed fibers were first immersed in glacial acetic acid for1 h, at a temperature of approximately 25 C. The fibers were then
washed with distilled water and air dried. The acetylation reaction
was performed with fibers soaked in acetic anhydride containing
sulfuric acid as reaction catalyst. The solution containing the fibers
was stirred for 5 min. The fibers were then washed thoroughly
with distilled water and dried at 60 C for 24 h. For the permanga-
nate treatment, the alkali treated fibers were soaked with a 0.25%
solution of KMnO4 in acetone for 3 min. This solution was then
decanted and the fibers were washed thoroughly with distilled
water and dried at 60 C for 24 h.
The peroxide treatment started with fiber purification by reflux-
ing with toluene and ethanol (2:1 v/v) for 6 h in a Soxhlet extractor,
followed by washing with distilled water. The fibers were then
dried at 30 C for 24 h. The dried fibers were then immersed for2 h in a NaOH solution at 1%, at a temperature of 55 C. After that,
the fibers were washed repeatedly with distilled water and then
dried at 30 C for 24 h. The dry fibers were soaked for 6 h in a
hydrogen peroxide 1% solution at 45 C. After that, the fibers were
oven dried at 60C for 24 h.
Fig. 1. Carnauba fibers (untreated).
Fig. 2. Typical cross-section of the carnauba fibers.
Table 1
Chemical composition of the carnauba fibers [21].
Component (%)
Cellulose 58.04 4.49
Hemicellulose 14.02 0.64
Lignin 19.03 1.02
Humidity 7.53 0.63
Ash 1.80 0.47
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2.3. Fiber characterization
The morphologies of the fibers, before and after the chemical
treatments, were examined by means of a Philips XL30 ESM. Fiber
density was measured with a gas pycnometer using helium dis-
placement method (Model AccuPyc 1340; Micromeritics Co.).Tensile properties of the fibers tensile strength and Youngs
modulus were measured using a dynamic mechanical analyzer
(DMA Q 800 TA) in a tensile test mode and following recommen-
dations of ASTM C1557-03 (2008). All tests were conducted under
displacement-control with rate of straining set to 1%/min. The
length of the gage section was 20 mm. A piece paper was
epoxy-bonded at the gripping area of thefiberspecimens to prevent
gripping damage which could cause premature failure. The cross-
sectional areas of the fibers were calculated assuming an elliptical
cross-section. Cross-sectional dimensions major and minor axes
were measured using a profile projector (Mitutoyo PHA-14) at se-
ven locations along the fiber length. Twenty-five specimens were
tested for each fiber treatment.
Thermogravimetric analyses (TGA) were carried out in a TA
Instruments, model TGA 2050, to measure the thermal stability
of the fibers and of the PHB. The samples were scanned over tem-
perature ranges of 30600 C (fibers) and 30350 C (PHB), using a
heating rate of 10C/min, in a nitrogen-gas atmosphere (150 cm3/
min).
2.4. Prepreg preparation
The first step in the fabrication of the composites was the prep-
aration of a prepreg. PHB-carnauba fibers prepreg was prepared by
a solution mixing technique. First PHB was dissolved in chloroform
under reflux (Fig. 4) to form a solution, which was thoroughly
mixed for 15 min at 90 C. Carnauba fibers cut to 30 mm length
were then added to the solution (10 wt.%), which was mixed foradditional 15 min at 90 C. After that, the material was poured into
a mold and covered with a polyamide fabric to reduce the solvent
evaporation rate and thus minimize cracking. The material was
then removed from the mold and oven dried at 50 C for 24 h to
evaporate the solvent. Similar procedure has been described in
the literature for processing PHB-flax composites[19]. The prepreg
obtained is shown inFig. 5.
2.5. Composite processing and specimen preparation
Composite plates (250 200 2 mm) with randomly distrib-
uted fibers were prepared in a hot-press from a stack of four pre-
preg films for the total thickness of 2 mm. The prepreg stack washot-pressed at 190 C, for 2 min. Then, the composite plates were
CARNAUBA FIBERS
NaOHsolution1%, 3h
Distilled water
Drying60 C, 24h
Acetic Acid1h
Distilled water
Acetic anhydride+ H2SO4 5 min
Drying60 C, 24h
Drying60 C, 24h
KMnO4 solution0,25 %, 3 min
NaOH solution3%, 2h
Distilled water
Drying60 C, 24h
NaOH solution5%, 1h
Distilled water
Drying60 C, 24h
SoxhletExtractortoluene + ethanol
6h
Distilled water
Drying30 C, 24h
Drying60 C, 24h
NaOH solution1%, 55 C, 2h
Hydrogen peroxide1%, 45 C, 6h
Distilled water
FT1% FT3% FT5% FTPH
FTPFTAc
Fig. 3. Chemical treatments of carnauba fibers: FT1% alkaline treatment at 1%; FT3% alkaline treatment at 3%; FT5% alkaline treatment at 5%; FTAc acetylation; FTP
permanganate treatment; and FTPH peroxide treatment.
Fig. 4. Schematic of the apparatus for PHB/carnauba fiber prepreg preparation.
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water cooled to room temperature. Tensile and flexural specimens
were cut using a laser cutter (Versa Laser).
2.6. Composite characterization
Tensile tests of the composites were carried out in a Shimadzu
(Autograph) universal testing machine, which has a load capacity
of 100 kN. All measurements were conducted at a temperature of
approximately 25C and following recommendations of ASTM D
638-99. A constant cross-head displacement rate of 5.0 mm/min
was used in all tests. Seven specimens were tested for each fiber
treatment. The surfaces of the tensile fractured specimens were
examined using a Philips XL30 ESM model scanning electron
microscope (SEM).
Fig. 5. PHB/carnauba fiber prepreg.
Fig. 6. SEM micrographs of carnauba fibers: (a) untreated; (b) alkaline (1%) treated; (c) alkaline (3%) treated; (d) alkaline (5%) treated; (e) acetylation treated; (f)permanganate treated; (g) peroxide treated.
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Flexural tests were conducted using a dynamic mechanical ana-
lyzer (DMA Q 800 TA) in quasi-static and also oscillatory modes.Quasi-static tests were carried out in a 3-point bending mode, with
a 20.0 mm span between the supports, using a crosshead speed of
0.5 mm/min. These tests were conducted at 25 C for the determi-
nation of the composite flexural modulus. The test procedure fol-
lowed general recommendations of ASTM D 7264-07. Oscillatory
flexural tests were carried out under sinusoidal strain-control for
the determination of the glass transition temperature and the tem-
perature dependence of storage modulus. These tests were con-
ducted following recommendations of ASTM D 5418-07.
Specimens were tested in double-cantilever mode, using strain
amplitude of 0.1%. Temperature scan measurements were per-
formed over the temperature range of 120C to +40C, with a
heating rate of 2.0C/min, and under a constant frequency of
1.0 Hz. Storage modulus (E0) and tan d were determined as a func-
tion of temperature. Five specimens were tested in each of the flex-
ural test condition.
3. Results and discussion
3.1. Fiber characterization
SEM photomicrographs of the surface of untreated and treated
carnauba fibers are presented in Fig. 6. The untreated fibers
Fig. 6a have deposits of wax on the surface which was removed
by all treatments. Alkaline treatment was proven effective to re-
move waxes from the fiber surfaces (Fig. 6bd). However, theSEM micrographs suggest that part of the surface topography of
FNT FT1% FT3% FT5% FTAc FTPH FTP
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
Fig. 7. Density of carnauba fibers: untreated (FNT); alkaline (1%) treated (FT1%);
alkaline (3%) treated (FT3%); alkaline (5%) treated (FT5%); acetylation treated
(FTAc); peroxide treated (FTPH); permanganate treated (FTP).
0 100 200 300 400 500 600
0 50 100 150 200 250 300
0
20
40
60
80
100
0
20
40
60
80
100
FNT
FT1%
FT3%
FT5%
FTAc
FTPH
FTP
236 - 393 C
383 ~ 500 C
30 -132 C
350
(a)
(b)
Fig. 8. Thermogravimetric curves of: (a) neat PHB; and (b) carnauba fibers under
various treatments.
FNT FT(1%) FT(3%) FT(5%) FTAC FTPH FTP
0
50
100
150
200
250
0
2
4
6
8
10
12
FNT FT(1%) FT(3%) FT(5%) FTAC FTPH FTP
(a)
(b)
Fig. 9. Mechanical properties of carnauba fibers: untreated (FNT); alkaline (1%)
treated (FT1%); alkaline (3%) treated (FT3%); alkaline (5%) treated (FT5%); acetyla-tion treated (FTAc); peroxide treated (FTPH); permanganate treated (FTP).
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the fibers can be destroyed as the NaOH concentration increases.
Acetylation treatment resulted in a more preserved surface topog-
raphy (Fig. 6e), while the SEM micrographs of permanganate trea-
ted fibers shows residue attached to the fiber surface (Fig. 6f).
Among all treatments studied, peroxide treated fibers have a clea-
ner surface with rougher surface topography (Fig. 6g). This devel-
opment of a rough surface topography improves fibermatrix
interface adhesion and therefore increases mechanical properties.
This will be corroborated by the subsequent results presented.
Fiber densities ranged from 1.34 to 1.47 g/cm3 which are similar
to many other lignocellulosic fibers[3,5]. Even though fiber densitywas not significantly affected by fiber treatment, fibers treated
with NaOH (FT1%, FT3%, FT5%), permanganate (FTP) and peroxide
(FTPH) presented a small increase in density (Fig. 7). A previous
work have indicated that fiber treatments such as alkali may result
in a more compacted cellular structure, with reduced void content
and hence increased density[22].
Thermogravimetric curves (TGA) of neat PHB and carnauba fi-
bers are presented inFig. 8. The TGA curve for PHB shows a gradual
weight loss with the increasing temperature, which started at
about 220 C and entirely degrading at around 315 C, leaving a
weight residue of 2.32%. The thermal instability of PHB above
250C has been reported in previous works [20,23]. It has been
suggested that the degradation process involves chain scission
and hydrolysis which leads to a reduction in molecular weight.
The processing temperature of 190 C for the composite used in
this work is about 30 C below the initial degradation temperature
of the polymer. PHB is known to thermally degrade at tempera-
tures just above the melting temperature [19]. Thus, processing
time was reduced to a minimum, which in this case was 2 min at
190C.
The TGA curves for the carnauba fibers show a weight loss be-
tween 30 and 130 C corresponding loss of humidity and other res-
idue solvent vaporized (Fig. 8). Above this temperature, thermal
stability gradually decreases with increasing temperature andthermal decomposition takes place in two main stages. The first
stage of thermal degradation occurred over the range 240380 C
and is due to thermal depolymerization of hemicelluloses [24]
and destruction of crystalline regions [25]. The weight loss over
this temperature range was about 50%. The final stage occurs above
380C and up to 530 C and represents the final decomposition.
The mechanical properties of all fibers tested treated and un-
treated are presented inFig. 9. Stressstrain behavior of all fibers
was rather linear up to failure. Strength and Youngs modulus of
carnauba fibers are found to be similar to the same properties of
cotton fibers, and therefore lower than other cellulosic fibers such
as jute, flax, hemp, ramie and sisal [5].
Tensile strength of treated carnauba fibers was in general lower
than that of the untreated fibers. For peroxide treated fibers, thestrength was similar to that of the untreated fibers if the standard
deviation is considered. Acetylation and permanganate treated fi-
bers presented the lowest strengths. In this case, the treatment
may have affected the cellulose which is the main responsible for
the fiber strength. Strain to failure of fibers was typically around
2% for all fiber treatments.
The Youngs modulus of chemically treated fibers was improved
by alkali and peroxide treatments. As in the case of strength, acet-
ylation and permanganate treated fibers presented the lowest
properties.
A summary of the properties of carnauba fibers is presented in
Table 2, where the same properties of other common cellulosic fi-
bers are also presented for comparison. The properties presented
for the carnauba fibers correspond to untreated and peroxide trea-ted fibers.
Table 2
Properties of carnauba fibers as compared to other natural cellulosic fibers.
Fiber Density (g/cm3) Elongation (%) Tensile strength (MPa) Youngs modulus (GPa)
Carnauba (FNT) 1.34 1.72.6 205264 8.29.2
Carnauba (FTPH) 1.44 1.72.6 148242 6.314.0
Cottona 1.51.6 3.010.0 287597 5.512.6
Jutea 1.31.46 1.51.8 393800 1030
Flaxa 1.41.5 1.23.2 3451500 27.680
Hempa 1.48 1.6 550900 70Ramiea 1.5 2.03.8 220938 44128
Sisala 1.331.5 2.014 400700 9.038.0
a Published data5.
PHB FNT FT(1%) FT(3%) FT(5%) FTAC FTPH FTP
0
5
10
15
20
25
30
PHB FNT FT1% FT3% FT5% FTAc FTPH FTP
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
(a)
(b)
Fig. 10. Mechanical properties of neat PHB and PHB/carnauba fiber composites
with the following fiber treatments: untreated (FNT); alkaline (1%) treated (FT1%);
alkaline (3%) treated (FT3%); alkaline (5%) treated (FT5%); acetylation treated(FTAc); peroxide treated (FTPH); permanganate treated (FTP).
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3.2. Composite characterization
The mechanical properties of the composites (tensile strength
and flexural modulus) are presented inFig. 10. The properties of
plain PHB are also presented in the same figure for comparison
purposes. According to the data presented, an increment of up to
45% was obtained when peroxide treated fibers were used as com-
pared to composites with untreated fibers. Composites with alka-
line treated fibers showed improvement in tensile strength only
when fibers were treated with NaOH 5%. In this case, the tensilestrength was improved by 24% in comparison to composites with
untreated fibers, due to an increase in the amount of cellulose ex-
posed on the fiber surface which improves fibermatrix interface
adhesion.
Considering that the tensile strength of treated carnauba fibers
was in general lower than that of the untreated fibers, the
improvement strength of the composites is due to better interface
properties. Improved fibermatrix interface adhesion was also
responsible for the enhancement of the flexural modulus of the
composites with untreated fibers (Fig. 10). As in the case
of strength, the composites with peroxide treated fibers pre-sented the highest modulus, which was similar to neat PHB. The
Fig. 11. SEM fractographs of PHB/carnauba fibers using fibers in the following conditions: (a) untreated; (b) alkaline (1%) treated; (c) alkaline (3%) treated; (d) alkaline (5%)
treated; (e) acetylation treated; (f) permanganate treated; (g) peroxide treated.
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improvement in modulus of composites with peroxide treated fi-
bers when compared to composites with untreated fibers was
about 14%. However, the lower strength of the composites when
compared to the plain PHB indicates that fibermatrix interface
adhesion still needs improvement. Further development in fiber
treatment needs to be studied.
The SEM micrographs of the fractured surfaces of the specimens
after the tensile tests are shown inFig. 11. Poor fibermatrix adhe-
sion was observed in the fracture surface of composites with un-
treated fibers (Fig. 11a). Among all specimens evaluated, the best
adhesion was verified for composites with alkaline (5%) treated
(Fig. 11d) and peroxide treated (Fig. 11g) fibers. These are also the
composites with highest tensile strength (Fig. 10). Superior interfa-
cialinteractions obtained with peroxide treatmentwas alsoreportedin a previous work published in the literature for sisal fiber-rein-
forced LDPE (low density polyethylene) composites[8]. In this case,
dicumyl peroxide and benzoyl peroxide treatments were used.
Fig. 12shows the temperature dependence of storage modulus
and tan delta of neat PHB and PHB/carnauba fiber composites with
various fiber treatments. According to the data presented, the E0
values of neat PHB and all composites decrease considerably with
increasing temperature, over the temperature range studied (120
to 40C). This is due to increased mobility of the polymer chain at
higher temperatures.
Up to the glass transition region, the storage modulus of the
neat polymer was larger than that of the composites. However,
over the glass transition region the storage modulus of neat PHB
falls sharply resulting in lower storage modulus at higher temper-atures, when compared to the fiber reinforced composites. Thus,
the addition of fibers will provide higher storage modulus at higher
temperatures, where the matrix modulus is lower. Below the Tg,
the matrix material is in the glassy state and the storage moduli
of the composites are matrix dominated. In this case, the presence
of fibers results in lower modulus.
Based on the peak of tan d, the glass transition temperature of
the neat polymer was higher than that of the composites. All fiber
reinforced composites presented a glass transition temperature ofabout 20 C, while for the neat polymer the glass transition occurs
at a temperature of about 30 C. The lower Tg of the composites
may be attributed to the presence of residual solvent entrapped
during the preparation of the prepreg. Similar behavior was de-
scribed in a previous work for polystyrene based composites rein-
forced with short sisal fibers[10].
4. Conclusions
In this research, carnauba fibers were modified by alkali, perox-
ide, potassium permanganate and acetylation treatments and used
for the development of a biodegradable composite. PHB based
composites containing 10% by weight of carnauba fibers were pre-
pared using randomly distributed fibers of 30 mm length.The mechanical properties of carnauba fibers were found to be
comparable to many other natural fibers. The fiber treatment using
hydrogen peroxide resulted in better mechanical properties than
any other treatment considered and was also found to improve
wettability. The thermal decomposition of the carnauba fibers
was found to start at about 240 C what makes them suitable for
combination with many thermoplastics.
Strength and elastic modulus of composites made from perox-
ide treated carnauba fibers randomly dispersed was superior to
those using untreated fibers or any other fiber treatment and sim-
ilar to neat PHB. Storage modulus measured by dynamic mechan-
ical analysis was lower than that of the neat PHB at temperatures
below the glass transition, but higher above the Tg.
In summary, carnauba fiber reinforced PHB biodegradable com-posite may prove as an alternative to plain PHB with cost reduction
and similar mechanical properties. The addition of these fibers to
PHB may provide a smaller reduction in modulus at higher temper-
atures, where the matrix modulus is lower. However, the lower
strength of the composites when compared to the plain PHB indi-
cates that fibermatrix interface adhesion still needs improve-
ment, which should be the subject of future work.
Acknowledgements
The authors are grateful to Eduardo Brondi of PHB Industrial S/A
BRAZIL for donating the polyhydroxybutyrate (PHB) used in this
investigation.
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