Recently, the plastic industry has very strong influence in different aspects
in our every day life. in which most of its uses related in short life time.
The after-use valorization grabs the attention of many specialized people in
these industries. Some scientists believe that one solution of solving a problem
of plastic accumulation for the environment involves the using of biodegradable
polymers. In this area or field aliphatic polyesters play a crucial role (Franco
et al., 2004).
Essentially Polyesters are polymers by which repeating unit that are bonded
via ester linkages, there are many types of esters are present in nature and
in enzymes that degrade them. There are series of biodegradable aliphatic polyesters
are now produced on a commercial level by several companies that make this kind
of industries related directly to the biodegradable plastic. Among them poly
(lactic acid) (PLA) and poly (ε-caprolactone) (PCL) appear to be the most
attractive because of their facile availability and good biodegradability. Both
PLA and PCL can be obtained through the petro-chemical route and PLA is now
available from renewable resources as well. Therefore, PLA and PCL present a
great potential with respect to applications in agriculture and in everyday
life as biodegradable packaging material (Tsuji and Ishizaka,
2001). There are many limitations of these biodegradable polymers, because
there are the poor thermal and mechanical resistance as well as limitation of
gas barriers properties, which include the access to industrialized sectors,
for instance packaging that includes the usage of how it would be justified
when biodegradable is required (Singh et al., 2003).
These obstacles could be controlled by enhancing their thermal and mechanical
properties through copolymerization, blending and filling techniques. In fact,
the addition of nano-sized fillers would effectively confer multifunctional
enabling properties to these polymers.
In the last few decades, more over of nanofillers to polymers has drawn wide
attention for the potentiality of these fillers to influence a number of polymer
properties; for example, polymer layered silicate nanocomposites, because of
the nanometer size of the silicate sheets, exhibit, even at low filler content
(1-5 wt.%), markedly improved mechanical, thermal, barrier and flame retardance
properties, in comparison to the unfilled matrix and to the more conventional
microcomposites (Chow and Lok, 2009; Pluta
et al., 2002).
Recently, many authors have reported on the characterization and categories
of biodegradable polymer based on nanocomposite, Paul et
al. (2003) reported on the preparation of PLA/MMT nanocomposites by
melt intercalation technique using a MMT modified with bis-(2-hydroxyethyl)
methyl (hydrogenated tallow alkyl) ammonium cations (Paul
et al., 2003). The preparation of PLA based nanocomposites with three
different kinds of layered silicates via solution intercalation method in N-dimethylacetamide,
obtaining the formation of intercalated nanocomposites whatever the clay was
carried out by Chang et al. (2003). In a recent
report, Feijoo et al. (2005) prepared biodegradable
nanocomposites of amorphous poly(lactic acid) and two different types of organically
modified montmorillonite obtaining nanocomposites with stacked intercalated
and partially exfoliated layers' morphologies.
Pantoustier et al. (2002) used the in situ
intercalative polymerization method for the preparation of PCL-based nanocomposites.
They compared the properties of nanocomposites prepared with both pristine MMT
and amino dodecanoic acid modified PLA/MMT and PCL nanocomposites prepared by
adding two organically modified montmorillonites and one sepiolite were obtained
by melt blending (Fukushima et al., 2009). Di
et al. (2003) have reported the preparation of PCL layered silicate
nanocomposites using a twin-screw extruder. They used two different types of
organically modified layered silicates for the preparation of nanocomposites
and aimed at determining the dependence of clay dispersion on the processing
Lee et al. (2002) and Paula
et al. (2005) studied the biodegradability of PLA based nanocomposites
in order to study their biodegradability and compost processing. They found
an increased biodegradation rate as the nanocomposite samples were completely
mineralized in short times. This behavior was generally attributed to the high
relative hydrophilicity of the clays, allowing an easier permeability of water
into the material thus accelerating the hydrolytic degradation process. The
highest hydrophilic character of the filler, the fastest degradation of the
polymer (Wang et al., 1998).
In this study, we report the preparation and characterization PLA/PCL-MMT to produce nanocomposites using different organoclays. Octadecylamine ODA and fatty hadroxamic acids FHAs were employed to modify MMT. Characterization of nanocomposites was done by various apparatuses. Both melt blending and solution casting process were used to produce these nanocomposites.
MATERIALS AND METHODS
Materials: Sodium montmorillonite used in this study was obtained from
Kunimine Ind. Co. Japan. Hexane was from T.J. Baker, USA (2009). Octadecylamine
was from Acros Organics, USA. Polylactic acid was purchases from Japan. Polycaprolactone
was obtained from Solvay Caprolactone, Warrington, England. Hydrochloric acid
HCl was from Sigma-Aldrich, Germany.
Synthesis of (FHAs): Palm olein was dissolved in hexane with hydroxylamine hydrochloride by reflux at boiling point of hexane for 10 h using a thermostated round bottom flask equipped with water-cooled condenser and mechanical stirrer. After the reaction had finished (product changed the color to green with copper (Π) due to its ability to form complex). The product was dissolved in hot hexane and separated from bottom layer by separating funnel. The hexane phase was cooled in an ice bath for 4 h to obtain FHAs and then filtered and washed by hexane for three times and dried in a vacuum desiccators over phosphorous pentoxide.
The same procedure was used to produce the FHAs from palm stearin and corn oil.
Preparation of organoclay: Organoclay was prepared by cationic exchange process where Na+ in the montmorillonite was exchanged with alkylammonium ion in an aqueous solution. Designated amount of sodium montmorillonite (Na-MMT) was stirred vigorously in 600 mL of hot distilled water for one hour to form a clay suspension. Subsequently, desired amount of surfactant (octadecylamine) which had been dissolved in 400 mL of hot water and desired amount of concentrated acid hydrochloride (HCl) was added into the clay suspension of (octadecylamine). After stirred vigorously for 1 h at 80°C, the organoclay suspension was filtered and washed with distilled water until no chloride was detected with 1.0 M silver nitrate solution. It was then dried at 60°C for 72 h. The dried organoclay (ODA-MMT) was ground until the particle size was less than 100 μm before the preparation of nanocomposite. A similar procedure was used to prepare FHA-MMT. This organophilic clay was designated as ODA-MMT. The effect of amount of intercalation agent was studied by varying the concentration of the intercalation agent and keeping other parameters constant.
Preparation of PLA/PCL-clay nanocomposites, by solution casting: The
required amounts of PLA and PCL were dissolved in chloroform. The PCL solution
was then transferred into the PLA solution with a dropper and continuous stirring.
After all the PCL solution was transferred into the PLA solution, the resultant
mixture was then stirred for 1 h. The required modified clay (ODA-MMT) was then
added into the dissolved PLA/PCL in the small portion. The mixture was then
refluxed for 1 h and then ultrasonically stirred using the Ultra Sonic Cathode
for 5 min to make sure that the clay fully dispersed in the PLA/PCL solution.
FHA-MMT was prepared similarly to ODA-MMT to produce organoclay. The nanocomposite
was poured into a Petri dish and left to dry the amount of PLA/PCL and the modified
clay used are listed in Table 1.
Preparations of PLA/PCL-clay nanocomposites by melt blending: The designed
amount of PLA/PCL ratio were prepared by an internal mixer (Haake Polydrive),
using different conditions (temperature, speed and time) in order to obtain
the optimum conditions which were 185°C, 50 rpm and 12 min, respectively.
To prepare a sample of the composite, a specific amount of PLA was first melted
and mixed thoroughly with appropriate amount of PCL for 2 min. Various amounts
of organoclays (1, 2, 3, 4, 5, 6 and 7 php) were incorporated into the blend
in the 3 min. The mixture was compress-moulded into sheet of 1 mm thickness
sheets under a pressure of 100 kg cm-1 in a standard hot press at
150°C for 15 min and cooled pressed process for 10 min to obtain a good
blend film (Vu et al., 2001). The amount of PLA,
PCL and the organoclays used are listed in Table 2.
Characterization: The FTIR spectra were recorded on Perkin Elmer FTIR 1650 spectrophotometer at ambient temperature using a KBr disk method. The disk containing 0.0010 g of the sample and 0.3000 g of fine grade KBr was scanned at 16 scans at wavenumber range of 400-4000 cm-1.
amounts of PLA/PCL and modified clay for solution casting
amount of PLA/PCL and organoclay for melt blending
Elemental analyser (LECO CHNS-932) was used for quantitative analysis of amount
of intercalation agent present in the organoclay. A sample of approximately
2 mg of organocly burned at 1000°C under oxygen gaseous flow was used for
this test. The sulfamethazine was used as standard.
X-ray Diffraction (XRD) study was carried out using shimadzu XRD 6000 diffractometer with Cu-K α radiation (λ = 0, 15406 nm). The diffractogram was scanned in the ranges from 2-10° at a scan rate of 1° min-1.
TG analysis using Perkin Elmer model TGA 7 Thermogravimetric analyzer was used to measure the weight loss of the samples. The samples were heated from 30-800°C with the heating rate of 10°C min-1 under nitrogen atmosphere at the flow rate of 20 mL min-1.
SEM the fractured surfaces of the nanocomposites were studied using a JEOL attached with Oxford Inca Energy 300 EDXFEL scanning electron microscope operated at 20 to 30 KV. The scanning electron micro photographs were recorded at a magnification of 1000 to 3000X. SEM analysis was carried out to investigate polymer splitting, polymer pull-out, debonding, matrix cracking and polymer matrix adhesion. Samples were dehydrated for 45 min before being coated with gold particle using SEM coating unit Baltec SC030 sputter coater
Elemental analysis: The amount of surfactant being intercalated into the clay galleries was calculated based on elemental analysis of the modified clays. The amounts of atom carbon, nitrogen in the sample clay were analyzed by using elemental analyzer. Na-MMT was found to contain 0.46% carbon and 0.15% nitrogen.. The amounts of C, N in Na-MMT, ODA-MMT and FHA-MMT are given in Table 3. The maximum amount of ODA-MMT and FHA-MMT adsorbed was almost equivalent to the cation exchange capacity of the clay indicating that Na+ in clay can be easily replaced by the alkylammonium ion (Table 4).
Amounts of C, N in Na-MMT, ODA-MMT and FHA-MMT, respectively
of surfactants presence in the clay layers
Fourier transform infrared (FTIR) spectroscopy: The FTIR spectra of
PLA, PCL and PLA/PCL blends are shown in Fig. 1. The peaks
located at 2998, 2947 and 1751 cm-1 of PLA and 2942, 2867 and 1723
cm-1 of PCL were assigned to the stretching vibration of -CH2
and vibration of -C = O bonds, respectively; while in the blend materials these
peaks were found in the neutralized regions of 2995, 2944 and 1749 cm-1.
The FTIR spectra of the ODA-MMT, PLA/PCL and PLA/PCL nanocomposites are shown
in Fig. 2. The spectrum of PLA/PCL nanocomposites show the
peaks at 2997 and 2944 cm-1 are due to the C-H stretching. The peak
for C = O bending observed at 1751 cm-1. The peak for C-O bending
is at 1184 cm-1. The peak for Si-O stretching is at 460 cm-1
(Tyagi et al., 2006).
The FTIR spectra of the FHA-MMT, PLA/PCL and PLA/PCL nanocomposites are shown in Fig. 3. The spectrum of PLA/PCL nanocomposites shows the peak at 3301 cm-1 is due to the N-H amide. The peaks at 2945 and 2890 cm-1 are due to the C-H stretching. The peak for C = O bending absorbed at 1748 cm-1. The peak for C-O bending is at 1183 cm-1. The peak for Si-O stretching is at 400 cm-1.
Thermogravimetric analysis TGA: Thermogravimetric analysis (TGA) is
a quantitative measurement of mass change for a material exposed to a controlled
temperature program. It also records the temperature of the weight loss region
and the maximum temperature of decomposition. TGA detects single or multiple
loss steps from room temperature to 1000°C. This measurement was made to
determine the thermal stability of the sample. The sample mass loss due to the
volatilization of degraded by-product is monitored as a function of a temperature.
Inorganic materials are more thermally stable and resistance compared to the
organic material. Thus introduction of inorganic particles would greatly improve
the thermal stability of organic materials (Huang and Brittain,
The decomposition of PLA starts at around 265.38°C. The decomposition is
rapid above this temperature and it completes at 380.97°C. A total of 98.41%
of weight loss was observed in the decomposition of PLA. The DTG curve of PLA
in Fig. 5a shows a single peak at 337.49°C. This decomposition
corresponds to the complete dissolution of PLA (Ray and
Bousmina, 2005). While the PCL starts to decompose at around 289.94°C
and it completes at 433.96°C. The decomposition of PCL shows a higher rate
of volatile formation and higher rate of chain scission than that of PLA which
shows a single peak of DTG curve at 380.47°C (Wu et
Figure 4c and 5c shows the decomposition
of PLA/PCL starts at around 290.14°C and completes at 391.21°C the DTG
carve of PLA/PCL nanocomposites in Fig. 5c shows a single
peak at 342.15°C. After mixing PLA with PCL, the thermal decomposition of
PLA in the blend shifts to the higher temperature region.
spectra of (a) PLA, (b) PCL and (c) PLA/PCL
spectra of (a) ODA-MMT, (b) PLA/PCL and (c) PLA/PCL-ODA-MMT by melt blending
spectra of (a) FHA-MMT, (b) PLA/PCL and (c) PLA/PCL-FHA-MMT by melt blending
thermograms of (a) PLA, (b) PCL, (c) PLA/PCL, (d) PLA/PCL-ODA-MMT and
thermograms of (a) PLA, (b) PCL, (c) PLA/PCL, (d) PLA/PCLODA-MMT
and (e) PLA/PCL-FHA-MMT
Figure 4d, 5d show the TGA and DTG thermogram
of PLA/PCL-ODA-MMT nanocomposites. The degradation temperature of the nanocomposites
increase with the adding of ODA-MMT to the PLA/PCL blend, the decomposition
of PLA/PCL-ODA-MMT nanocomposites starts at around 299.51°C and completes
at 398.51°C the DTG curve of PLA/PCL-ODA-MMT nanocomposites in Fig.
5d shows a single peak t 349.24°C. Figure 4e and 5e
show the TGA and DTG thermogram of PLA/PCL-FHA-MMT nanocomposites. The degradation
temperature of the nanocomposites increase with the adding of FHA-MMT to the
PLA/PCL blend, the decomposition of PLA/PCL-FHA-MMT nanocomposites starts at
around 305.21°C and completes at 403.37°C the DTG curve of PLA/PCL-FHA-MMT
nanocomposites in Fig. 5e shows a single peak at 354.62°C.
The temperature of the main degradation is shifted towards a higher value when
OMMT is used compare to the pristine composite.
Tensile strength: The best ratio of tensile strength and modulus properties
of PLA/PCL blending in both solution casting and melt blending was 80/20 (Fig.
6). Therefore, the ratio of 80/20 was used for further experiments.
of adding PCL to PLA on tensile strength by solution casting and melt
strength of 80PLA20PCL with various contents of ODA-MMT prepared by solution
casting and melt blending
The tensile properties of polymeric materials can be improved in different
degrees if nanocomposites are formed with layered silicates. The tensile strengths
of hybrid films with different OMMT contents are shown in Fig.
7, 8. The Fig. 7 and 8
show that low contents of OMMT (2 wt% and 3% for PLA/PCL-ODA-MMT and PLA/PCL-FHA-MMT,
respectively). Further increase of the ODA-MMT and FHA-MMT content does not
significantly change the tensile strength of the blend.
X-Ray diffraction XRD: The XRD patterns of the PLA/PCL-ODA-MMT and PLA/PCL-FHA-MMT
nanocomposites with 1, 2, 3, 4 and 5 php of organoclay loading are given in
Fig. 10-13 this results is it agreement
with Yu et al. (2007). The XRD pattern of ODA-MMT
and FHA-MMT show peak 2θ of 3.04 and 2.89 which correspond to the basal
spacing 29.47 and 31.02 °A, respectively (Fig. 9).
strength of 80PLA20PCL with various contents of FHA-MMT prepared by solution
casting and melt blending
XRD patterns of (a) Na-MMT, (b) ODA-MMT and (c) FHA-MMT
In solution casting process the XRD of PLA/PCL-ODA-MMT and PLA/PCL-FHA-MMT
nanocomposites with 1, 2, 3, 4 and 5 php of ODAMMT and FHA-MMT show shift to
lower angles between 2θ of 3.0-2.89 and 2.86-2.70 correspond to the basal
spacing between 29.86 -31.02 and 31.35-33.18 °A, respectively (Fig.
10, 11). While in melt blending process the XRD of PLA/PCL-ODA-MMT
and PLA/PCL-FHA-MMT nanocomposites with 1, 2, 3, 4 and 5 php of ODAMMT and FHA-MMT
show shift to lower angles between 2θ of 2.80-2.61 and 2.82-2.48 correspond
to the basal spacing between 32.04-34.61 and 31.79-36.15 °A, respectively
(Fig. 12, 13). It is found that PLA/PCL-
ODA-MMT nanocomposites with organoclay in solution casting and melt blending
loading 2% give the highest basal spacing (31.02 and 34.61°A) while the
highest basal spacing of PLA/PCL -FHA-MMT nanocomposites with organoclay in
solution casting and melt blending loading 3% was (33.18 and 36.15 °A),
||XRD patterns of (a) ODA-MMT, (b) PLA/PCL/ 1% ODA-MMT, (c)
PLA/PCL/2% ODA-MMT, (d) PLA/PCL/3% ODA-MMT, (e) PLA/PCL/4% ODA-MMT and (f)
PLA/PCL 5% ODA-MMT (by solution casting)
||XRD patterns of (a) FHA-MMT (b) PLA/PCL/1% FHA-MMT, (c) PLA/PCL/2%
FHA-MMT, (d) PLA/PCL/3% FHA-MMT, (e) PLA/PCL/4% FHA-MMT and (f) PLA/PCL/5%
FHA-MMT (by solution casting)
||XRD patterns of (a) ODA-MMT, (b) PLA/PCL/ 1% ODA-MMT, (c)
PLA/PCL/3% ODA-MMT, (d) PLA/PCL/2% ODA-MMT, (e) PLA/PCL/4% ODA-MMT and (f)
PLA/PCL/5% ODA-MMT (by melt blending)
Scanning electron microscopy (SEM): Figure 14 shows
the SEM images of PLA/PCL blends and PLA/PCL with 2% ODA-MMT and PLA/PCL with
3% FHA-MMT in solution casting and melt blending in the same scale 10 μm.
In both of solution casting and melt blending processes, PCL was located inside
of the empty voids of the PLA continuous phase. It can be seen that the distribution
of PCL in the PLA matrix is homogenous and form single phase morphology (Fig.
Figure 14c, d show PLA/PCL-ODA-MMT and
PLA/PCL-FHA-MMT morphology. The incorporation of ODA-MMT and FHA-MMT strongly
affect the morphology and thus also the fraction behavior of PLA/PCL nanocomposites
which indicate the OMMT flow homogenous in the matrix and form smaller void
||XRD patterns of (a) FHA-MMT (b) PLA/PCL/1% FHA-MMT, (c) PLA/PCL/2%
FHA-MMT, (d) PLA/PCL/3% FHA-MMT, (e) PLA/PCL/4% FHA- MMT and (f) PLA/PCL/5%
FHA-MMT and (f) PLA/PCL/5% FHA-MMT (by melt blending)
||SEM micrographs of (a) PLA/PCL solution casting, (b) PLA/PCL
melt blending, (c) PLA/PCL 2% ODA-MMT melt blending, (d) PLA/PCL 3% FHA-MMT
melt blending, (e) PLA/PCL 2% ODA-MMT solution casting and (f) PLA/PCL 3%
FHA-MMT solution casting
The percentage of carbon and nitrogen contents in the organoclay increase after the modification. The calculation is based on either carbon atom or nitrogen atom because if the increase of their content is only due to the presence of the surfactant molecule, the calculation does not based on the hydrogen content as there are possibilities of water molecules trapped between the layers of the Na-MMT.
The FTIR spectra of PLA/PCL blend indicates that there are some molecular interactions
between PLA and PCL. The interaction between PLA and PCL may be attributized
to the possible hydrogen bonding that occurs between the C = O group in PCL
and the small amount of terminal hydroxyl groups in the PLA main chain (Yew
et al., 2005). A proposed possible site for interaction between PLA
and PCL is shown in Scheme 1. FTIR spectrum of the neat PLA supports this claim
which shows peak at 3500 cm-1 (hydroxyl group stretching). It was
observed that this characteristic peak of PLA has disappeared with the incorporation
Scheme 1:Proposed chemical interactions (intramolecular hydrogen bonding)
between PLA and PCL
The FTIR spectra of nanocomposites indicate that both ODA-MMT and FHA-MMT are
intercalated with polymers. The above results of FTIR were obtained when the
melt blending process was used. It was found that the similar results of FTIR
were obtained when solution casting process was used.
The improvement of thermal stability of PLA in the PLA/PCL blend might due
to the presence of PCL which acts as toughening filler of PCL and it needs more
energy or high temperature to degrade the blend. Chen et
al. (2003) reported that, the addition of PCL into PLA improves the
thermal stability of PLA. It has been reported that the improvement of the stability
can be achieved by adding a second polymer (Chen et al.,
The increase of thermal stability of PLA was due to the effect of PCL. With
the addition of PCL, the molecular chain of PLA was restricted due to reducing
its heat sensitivity which would increase thermal stability of PLA (Lee
et al., 2002).
It could be observed that organophilic treatment improves the thermal stability
of PLA/PCL nanocomposites due to better interaction between PLA/PCL matrix and
clay. Incorporated of the ODA-MMT, FHA-MMT in PLA/PCL improves slightly the
composites thermal stability. The increase in thermal stability of PLA/PCL0ODA-MMT
and PLA/PCL-FHA-MMT nanocomposites may result from the dispersion of the clay
and from a strong interaction between the clay platelets and the polymer matrix
(Varghese et al., 2003). The above results of
TGA and DTG were obtained when the melt blending process was used. It was found
that the similar results of TGA and DTG were obtained when solution casting
At the higher clay concentration, the organoclay is not homogeneously distributed
in the matrix. The agglomeration of the clay causes phase separation (Essawy
and El-Nashar, 2004). Both of PLA/PCL-ODA-MMT and PLA/PCL-FHA-MMT nanocomposites
prepared by melt blending have higher tensile strength compared with those of
solution casting because during polymer intercalation, a relatively large number
of solvent molecules have to be absorbed from the host to accommodate the incoming
polymer chains especially for higher clay content. Lower tensile strength is
obtained for solution casting probably due to insufficient amount of solvent
used to accommodate the incoming PLA/PCL chains. In addition, residue of solvent
in the final material prepared by solution casting may also causes reduction
in tensile strength (Ray and Okamoto, 2003).
Based above result, melt blending process gave higher basal spacing value compare
with solution casting process. The above findings indicate that there is intercalation
of PLA/PCL into the interlayers of the organoclay prepared by solution casting
and melt blending. This means that both methods can be employed to prepared
PLA/PCL clay nanocomposites Increase the organoclay content decrease the basal
spacing interlayer spacing this because increase the organoclay content will
reduce the amount of the polymer intercalated in the galleries of the silicate
layers (Vu et al., 2001). These can be also related
to the surface accessibility where the closer packing of the silicate layers
is more difficult for the polymer chains to penetrate. Based on the above results,
intercalated nanocomposites were prepared in this study.
SEM images reveal that the presence of OMMT as a filler enhanced the dispersion
and interfacial adhesion of polymer matrix. This observation is agreement with
the higher value of tensile strength during tensile test when OMMT is added
into composites. A similar morphology was observed when the samples were prepared
by solution casting process (Fig. 14e, f).
PLA/PCL-OMMT nanocomposites were prepared by both melt blending and solution casting of PLA, PCL and OMMT using ODA and FHA as modifiers of clay. X-ray diffraction (XRD) shows that both methods could be used to synthesize PLA/PCL clay nanocomposites. The silicate layers of the clay were intercalated distributed in the matrix. The addition of OMMT to the PLA/PCL blend significantly improved the tensile properties of nanocomposites. The highest values were obtained when the OMMT content was about 3% (FHA-MMT) and 2% (ODA-MMT). Further amount of organoclays could cause brittleness of nanocomposites. FTIR results indicate that both ODA-MMT and FHA-MMT are intercalated with polymer On other hand, layered silicate explicitly improved the thermal stability of PLA/PCL blend.. SEM images show the incorporation of OMMT strongly affects the morphology which indicate the OMMT flow homogenous in the matrix and form smaller void size. Both PLA/PCL-ODA-MMT and PLA/PCL-FHA-MMT prepared by melt blending gave higher tensile strength and basal spacing compare with those of solution casting. The similar results of FTIR and TGA were obtained in both methods.