ORI GIN AL PA PER

Effect of cloisite 30B on the thermal and tensilebehavior of poly(butylene adipate-co-terephthalate)/poly(vinyl chloride) nanoblends

Assia Siham Hadj-Hamou • Sabiha Matassi •

Habi Abderrahmane • Farida Yahiaoui

Received: 11 December 2013 / Revised: 17 March 2014 / Accepted: 23 March 2014 /

Published online: 3 April 2014

� Springer-Verlag Berlin Heidelberg 2014

Abstract Ternary PBAT/PVC/C30B nanoblends were successfully prepared via

melt blending process at 130 �C and characterized by different techniques. The

properties of the elaborated PBAT/PVC/C30B nanoblends were compared with

those of the nonfilled PBAT/PVC blends to examine the C30B effects on the

structure and properties of PBAT/PVC/C30B nanoblends. FTIR spectra revealed the

presence of specific interactions between C=O of PBAT and acidic hydrogen of

PVC, supporting the formation of miscible nanoblends. The PBAT/PVC/C30B

morphology was investigated by both X-ray diffraction and transmission electron

microscopy analyses. It was suggested the formation of mixed intercalated/partially

exfoliated structures. Differential scanning calorimetry thermograms of PBAT/

PVC/C30B nanoblends exhibited a single Tg and a full disappearance of the PBAT

melting endotherm, confirming the complete compatibilization between PVC and

PBAT. It was found that the Tg of the nanoblends were higher than those of the

pristine blends due to their mixed intercalated/partially exfoliated structures. PBAT

and PVC chains would be confined in a same C30B gallery causing a reduction of

the chain mobility. Nanoblends showed a reduction of their thermal stability

compared to their pristine blends, as a result of the catalytic effect of the C30B in

the thermal degradation process. Tensile measurements displayed an improvement

of mechanical properties for the ternary PBAT/PVC/C30B nanoblends relative to

their virgin blends due to the insertion of clay particles into composite matrix.

A. S. Hadj-Hamou (&) � S. Matassi � F. Yahiaoui

Laboratoire des Materiaux Polymeres, Faculte de Chimie, Universite Houari Boumediene,

B.P. 32 ElAlia, Bab Ezzouar, Alger, Algeria

e-mail: hadjhamouassia@yahoo.fr

H. Abderrahmane

Algerie Laboratoire des Materiaux Organiques (LMO), Faculte de Technologie,

Universite A. MIRA, Route de Targa Ouzemour, 06000 Bejaıa, Algeria

123

Polym. Bull. (2014) 71:1483–1503

DOI 10.1007/s00289-014-1137-y

Keywords Poly(butylene adipate-co-terephthalate) � Poly(vinyl chloride) �Cloisite 30B � Nanoblends � Thermal stability � Mechanical properties

Introduction

Polymeric materials, especially those obtained from renewable resources [1–4],

have attracted an increasing interest during the past few years due to environmental

protection issues. Hence, great attention has been directed toward their use owing to

their exceptional properties (such as biocompatibility, biodegradability, non-

toxicity,…). In this context, the aliphatic polyesters have been the subject of

increasing research of new applications in various sectors for instance in medicine,

pharmacy, food, and eco-packaging [5–7]. Among them, the poly(butylene adipate-

co-terephthalate) PBAT, fully biodegradable crystalline polymer is an aliphatic/

aromatic copolyester based on the monomers 1,4-butanediol, adipic acid, and

terephthalic acid. PBAT has excellent physical properties and can be blended with

other biodegradable resins to impart high flexibility. It degrades naturally within a

few weeks, and its typical applications are in packaging, agricultural films and

compose bags [8]. Moreover, the high cost of PBAT in comparison with other

plastics has led to the limitation of its applications [9]. So combining PBAT with

other stiff polymer is taken into consideration to encounter its weaknesses.

On the other hand, poly(vinyl chloride) (PVC) has a high mechanical strength

and wear-resistance [10]. It is a common plastic and widely used in construction

sector, food package, and toy factory. However, under processing and end-use

conditions, PVC undergoes a severe degradation, accompanied by a characteristic

color; the more this latter is pronounced the more the PVC properties decrease and

the PVC becomes increasingly cracked and brittle to disintegrate completely. The

thermal degradation of PVC during processing is well known to be caused by the

liberation of hydrogen chloride at the labile sites of the PVC molecular chain [11–

13]. Therefore, it is necessary to mix PVC with a number of additives before

processing to prevent and delay its degradation [14]. The addition of plasticizers to a

PVC formulation decreases many mechanical properties such as hardness, tensile

strength, and modulus of the PVC, although the low temperature flexibility,

elongation, and the ease of processing are all improved. PVC is known for its

efficiency to form miscible systems with several other low- and high-molecular-

weight substances acting as plasticizers. Many studies on PVC blends [15–19] have

reported that the specific interactions via hydrogen bonding between the blend

components are suggested to be the basis of their miscibility [15–17, 20–23].

Since the occurrence of liquid–solid interface can offer an effective route to

produce a wide variety of morphological patterns [15, 16, 20–26], the blending of an

amorphous polymer with a crystalline polymer can be a convenient way to improve

the impact of strength, toughness, ductility, and other physical properties.

In recent years it has been found that composites reinforced with nano-sized

fillers often exhibit remarkable improvement of mechanical, thermal, and physi-

cochemical properties compared with pure polymer and their conventional

composites. Many of these polymer–clay nanocomposites show significant

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improvements mainly in their mechanical, barrier, and thermal properties compared

to micro and macro composites [27–32]. It is reported that the effective dispersion

of the clay within the polymer matrix is primarily responsible for the improvement

of such properties. Tough extensive research has been recently carried out on

polymer–clay nanocomposites; only a limited number of articles have been reported

on nanoblends based on polymer blends and clay [33–35].

In this study, a series of miscible crystalline/amorphous polymer blends based on

poly(adipate-co-butylene terephthalate) (PBAT), poly(vinyl chloride) (PVC), and

cloisite 30B are prepared by melt-blending process. The effects of cloisite 30B on

the morphology, thermal, and mechanical properties of miscible PBAT/PVC blends

were investigated by FTIR, XRD, TEM, DSC, TGA, and Tensile tests.

Experimental part

Materials

Commercial grade poly(butylene adipate-co-terephtalate) (PBAT), trade name

ECOFLEX-BASF and poly(vinylchloride) (PVC) (SHINTECH) with 1.21 and

1.38 g cm-3 densities, respectively, were used as received without any preliminary

purification. Calcium/Zinc (Ca/Zn) stearate (0.37 g cm-3) used as the heat stabilizer

for PVC was supplied by REAPAK B-CV/3037.

Blending

Binary PBAT/C30B and PVC/C30B and ternary PBAT/PVC/Cloisite 30B materials

were prepared by adding a small amount of cloisite 30B to their virgin matrixes.

Before processing, PBAT, PVC, and C30B were dried overnight at 40 �C under

reduced pressure. The clay concentration was fixed at 3 wt% to potentially

minimize the effect of the viscosity ratio on the particle size reduction [36].

The PBAT/PVC/C30B composites were manufactured using a twin-screw

microextruder (5&15 Micro Compounder DSM Xplore) and mixing process

parameters (60 rpm screw speed, 10 min mixing time, and temperature profile:

120–125–130 �C) were modulated to optimize material final properties. The

addition of 5 % stabilizer by weight to PVC was needed during the preparation of

the mixtures by melt-blending process. The mass ratios of PBAT to PVC were fixed

at 69/28, 48.5/48.5 and 28/69.

To obtain the desired specimens for characterization, the molten composite

samples were transferred, after extrusion, through a preheated cylinder to a mini-

injection mold (Tmold = 30 �C, Pinjection = 0.5 MPa).

Unfilled PBAT/PVC blends were processed in the same way as the composites

and were used as controls.

All these materials were characterized by FTIR, XRD, TEM, DSC, TGA, and

tensile tests.

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Characterizations

FTIR spectra of PBAT, PBAT/C30B, PVC, PVC/C30B and their virgin binary

PBAT/PVC and filled ternary PBAT/PVC/C30B blends were recorded at 2 cm-1

resolution and 60 scans in the range 4,000–400 cm-1 on a Thermo Nicolet, Nexus

670 spectrometer. Samples were prepared by mixing a small amount of pure

polymer (PBAT, PVC), PBAT/PVC blend, or PBAT/PVC/C30B composite with

spectroscopic KBr and pressed in disks.

X-ray diffractograms of pure polymers (PBAT, PVC), binary (PBAT/C30, PVC/

C30B), and ternary (PBAT/PVC/C30B) composites were recorded on a Philips

PW3710 diffractometer in the range of 2h (1�–10�). The Monochromatic radiation

applied was Cu Ka (1.5406 A) operating at 35 kV and 25 mA.

Differential scanning calorimetry (DSC) measurements were performed on

8–12 mg samples under nitrogen atmosphere using a 204 F1 Phoenix (Netzsch

Company). Samples were heated from -60 to 140 �C at 10 �C min-1 (1st heating),

cooled to -60 �C at the same scan rate, then heated again to 140 �C at 10 �C min-1

(2nd heating). From these scans, melting temperature (Tm), and glass transition

temperature (Tg) of the samples were measured.

TGA thermograms were recorded on a TGA Q500 from TA instruments, at a

heating rate of 10 �C min-1 under nitrogen atmosphere from room temperature to

600 �C.

Tests specimens for tensile measurements were prepared from 1 mm thick plates.

The Tensile modulus, strength, and elongation at break were measured in a Tensile

Instron Zwick/Roell Z 100.Tester, at a strain rate of 200 mm min-1. The films were

conditioned in desiccator under 50 % RH, at 25 �C, for 48 h before being characterized.

Results and discussion

FTIR analysis

PBAT/PVC blends

As can be seen from Fig. 1, PBAT spectrum displays characteristic absorption

bands of both ester and aromatic functions. Bands located between 1,050 and

1,300 cm-1 corresponded to the deformation vibration dC–O: the one that appeared

at 1,732 cm-1 is related to the stretching vibration (mC=O), while the one which is

located at 1,270 cm-1 reflects the deformation vibration dC–O–C. Deformation

(dCH2) of the methylene groups appear at 728 cm-1. The stretching vibrations of

aromatic unit are, respectively, between 1,500 and 1,600 cm-1 (mC=C stretching) and

3,020 cm-1 (mC–H stretching).

In FTIR spectrum of PVC, the absorption bands at 2,970 and 2,912 cm-1 are

assigned to the stretching vibration m (–CH–), those located around 1,333 and

1,267 cm-1 are ascribed to the vibration deformation of d (C–H). The bands

appearing at 830 cm-1 are assigned to the stretching vibration m (C–C) and those

located around 688 and 609 cm-1 correspond to stretching vibrations in C–Cl.

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After blending PBAT with PVC, the carbonyl stretching modes of PBAT at

1,732 cm-1 gradually shifted to lower wavenumbers with increasing PVC content

in the blend. Thus, a new band appeared at 1,725 cm-1 revealing a new specific

interaction between the acidic hydrogen of PVC and PBAT carbonyl group

(Scheme 1), which leads to the miscibility of the blends [16, 19]. The most

important interactions that may occur upon blending PBAT with PVC are shown in

Scheme 1:

It should be also noticed the asymmetry of the PBAT free carbonyl band to the

lower wavenumbers (around 1,652 cm-1) for pure PBAT (or for 70/30 blend). This

is mainly due to the presence of the residual water molecules associated with the

carbonyl group. However, the addition of PVC polymer to PBAT tends to remove

this shoulder in favor of the appearance of the new band at 1,725 cm-1. This

confirms the presence of specific interactions between the polymer chains of

different nature. Indeed, the PBAT carbonyl groups, responsible for the retention of

moisture, are involved in hydrogen bonding with the acidic Hydrogen of PVC [37].

PBAT/PVC/C30B nanoblends

The C30B is dispersed differently within the individual polymer matrices due to the

attractive interactions of different strength that occurred between the clay surface

and the polymer chains of different nature. For instance, we illustrate in Fig. 2 the

Fig. 1 FTIR spectra of PBAT/PVC blends at different ratios

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comparative FTIR spectra between pristine PBAT and its PBAT/C30B hybrid. The

shifting of the absorption band at 1,732–1,729 cm-1 due to mC=O of the carbonyl

groups indicates that this band develops interactions with the hydroxyl group of

C30B.

In PBAT/PVC/3 % C30B spectra, in addition the absorption bands of PBAT

(stretching vibration mC=O and deformation vibration dC–O) and PVC (stretching

Scheme 1 Hydrogen bonding between PVC and PBAT polymers

Fig. 2 FTIR spectra of virgin PBAT and its PBAT/C30B composite

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vibrations mC–Cl), other bands attributed to C30B are also observed (Fig. 3). Indeed,

the bands located at 1,044 and 473 cm-1 are assigned to the vibrations of Si–O

group, and those appearing at 920 and 880 cm-1 correspond to the octahedral and

tetrahedral layers of Cloisite C30B.

The miscibility of the virgin PBAT/PVC blends is mainly due to the sufficient

acidic hydrogen-carbonyl hydrogen bonding interactions that occurred between the

polymers, as evidenced qualitatively by FTIR spectroscopy from the appearance of

a new band at 1,725 cm-1 for PBAT/PVC/C30B 70/30 (and at 1,723 cm-1 for

PBAT/PVC/C30B 50/50 and 30/70), attributed to associated carbonyl groups.

The presence of C30B within the blends will affect these interactions. Several

kinds of interactions of various strengths may occur between the clay and the

individual polymer chains or polymer blend. The FTIR analysis still revealed the

presence of hydroge-bonded acidic hydrogen–carbonyl interactions occurring

between PVC and PBAT within the studied nanoblends as illustrated in Fig. 4.

The intensity of the band at 1,725 cm-1 attributed to associated carbonyl groups and

characterizing these PVC acidic hydrogen-PBAT carbonyl group interactions

decreased as C30B is added to the blend. This shows that the number of interacting

sites between the two polymers within the nanoblends is less than that within the

virgin blends. This is presumably due to the presence of competitive hydrogen

bonding interactions that occurred between the C30B and polymer blend matrix

[38].

Fig. 3 PBAT/PVC/C30B nanoblends at different ratios

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X-ray diffraction analysis (XRD)

The Cloisite 30B exhibited a broad peak at 2h = 4.6� corresponding to a d-spacing

of d = 1.90 nm. The characteristic peak of C30B was shifted to the lower angles of

2h = 2.84� and 2.77�, corresponding to d-spacing of 3.10 and 3.18 nm in PBAT/

C30B and PVC/C30B binary composite, respectively (Fig. 5). These results suggest

the formation of intercalated binary nanocomposites. Indeed, Cloisite 30B

organoclay contained methyl tallow bis(2-hydroxyethyl) quaternary ammonium

ions which were being relatively polar, formed thermodynamically favorable

Fig. 4 Normalized FTIRspectra of pristine PBAT/PVC70/30 blend and PBAT/PVC/C30B 70/30 nanoblend

Fig. 5 XRD patterns of C30B, PBAT/C30B, PVC/C30B and their PBAT/PVC/C30B mixtures atdifferent ratios

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interactions with both PBAT and PVC chains, resulting in polymer intercalation. It

is worth mentioning here that no significant change induced by the nanoclay

incorporation had been observed by XRD on the PBAT crystal structure. Its original

crystalline form remains unaltered after nanocomposites preparation. However, the

XRD patterns of PBAT/C30B nanocomposite exhibits a slight decrease of the

intensity of the crystalline peaks compared to those of pristine PBAT, revealing that

the crystallinity in PBAT-based nanocomposite decreases. This behavior is

essentially attributed to the hydrogen bonding interactions between C30B and

PBAT causing a restriction on the stretched chains which impedes the

crystallization.

The XRD patterns of ternary PBAT/PVC/C30B composites at different ratios

were shown in Fig. 5. As can be seen, all composites exhibited weak diffraction

peak at lower angle compared to C30B. The movement of the basal reflection of

C30B to lower angle indicates the formation of an intercalated nanostructure, while

its broadening and the decrease in its intensity are most likely due to the presence of

disordered intercalated or intercalated/partially exfoliated mixed structure.

The increase of interlayer distances in ternary PBAT/PVC/C30B composites

compared to their PBAT/C30B or PVC/C30B binary blends (Table 1) suggested

that both PBAT and PVC polymers were commonly intercalated at the interphase.

Therefore, a higher initial gallery height will provide a higher number of polymer

chains for the more common intercalation at the interphase. Furthermore, in our

case, the nanocomposite formation may be mainly controlled by hydrogen bonding

interactions between PBAT (carbonyl), PVC (acidic hydrogen), and clay

(hydroxyl), in accordance with FTIR study.

Transmission electron microscopy

X-ray diffraction studies indicated an increase in d-spacing of the Cloisite 30B in

the binary and ternary nanocomposites revealing the formation of intercalated

morphology.

Transmission electron microscopy (TEM) provides complementary information

on PBAT/C30B, PVC/C30B, and PBAT/PVC/C30B nano-morphology and struc-

ture. TEM micrographs of PBAT/C30B and PVC/C30B, illustrated in Fig. 6a, b,

respectively, confirm the formation of intercalated nanocomposite structures

evidenced at high magnification by the presence of tactoids randomly dispersed

Table 1 Diffraction peaks and d-spacing of PBAT/PVC/C30B composites

PBAT/PVC/C30B 2h (�) Basal spacing d (nm)

0/0/100 4.61 1.91

97/0/3 2.80 3.10

68/29/3 2.68 3.30

48.5/48.5/3 2.44 3.61

29/68/3 2.39 3.70

0/97/3 2.77 3.18

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in the polymer matrix of relatively small dimensions [31, 39, 40]. On the other hand,

TEM images of PBAT/PVC/C30B nanoblends show the formation of mixed

intercalated/exfoliated nanocomposite structures, as evidenced by the presence of

some intercalated layered stacks of relatively small thickness, randomly dispersed

within PBAT/PVC matrix coexisting with of disorderly exfoliated platelets

(Fig. 6c). It also appears that the PBAT/PVC/C30B nanoblends have more

homogeneous structures and well dispersed when compared to the binary

nanocomposites.

DSC analysis

PBAT/PVC blends

The glass transition temperatures (Tg) of PBAT and PVC are -30 and 85 �C,

respectively. The PBAT shows an endothermic peak located at 125 �C, which is

ascribed to melting temperature (Tm) owing to its semi-crystalline structure. The

melting enthalpy of PBAT evaluated from the integrated area of melting peak

corresponds to 12.3 J g-1. The degree of crystallinity vc is 10.8 % (calculated under

the assumption that the heat of fusion was proportional to the crystalline content, as

Fig. 6 TEM micrographs of typical a PBAT/C30B, b PVC/C30B and c PBAT/PVC/C30B nanoblends

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v ¼ DHm=DH�m, where DH�m is the melting enthalpy of completely crystalline sample

and taken in this work as 114 J g-1) [41] and Eric Pollet [42].

Figure 7 shows DSC curves of PBAT and PBAT/PVC blends of different ratios

(70/30, 50/50 and 30/70). As can be seen, when PBAT is diluted in the amorphous

matrix of PVC, the melting endotherm greatly reduces and tends to disappear when

the composition of the mixture exceeds 50 % by weight of PVC. This behavior is

may be due to the presence of strong interactions between the two polymers which

prevent the PBAT crystallization.

The single glass transition temperature observed with PBAT/PVC blends is an

evidence of their miscibility (Table 2). The addition of PVC to PBAT matrix

reduces the flexibility of PBAT and increases the glass transition temperature of

PBAT. The shifting in Tg confirms the presence of significant attractive interactions

that occurred between PBAT carbonyl group and PVC acidic Hydrogen as already

evidenced by FTIR analysis [43].

Fig. 7 DSC curves of PBAT, PVC and their blends at different ratios

Table 2 DSC results of PBAT/PVC and PBAT/PVC/C30B mixtures

PBAT/PVC 100/0 70/30 50/50 30/70 0/100

Tg (�C) -30 -17 13 33 85

Tm (�C) 125 121 – – –

v (%) 11 6 – – –

PBAT/PVC/C30B 97/0/3 68/29/3 48.5/48.5/3 29/68/3 0/97/3

Tg (�C) -28 -3 22 42 88

Tm (�C) 127 122 – – –

v (%) 8 5 – – –

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PBAT/PVC/C30B nanoblends

A similar study was carried out to investigate the effect of nanoclay on the thermal

properties (Tg, Tm and v) for PBAT/C30B, PVC/C30B nanocomposites, and PBAT/

PVC/C30B nanoblends of different ratios as illustrated in Fig. 8.

Table 2 summarizes the results obtained by DSC measurements. According to

these letters, it seems that C30B has no effect on the melting behavior of PBAT/

C30B nanocomposite and PBAT/PVC/C30B 70/30 nanoblend. The Tm values of

PBAT and PBAT/PVC/C30B 70/30 were not appreciably influenced by C30B

(Fig. 9). These results confirm that C30B does not change PBAT crysal organization

in pristine PBAT or in PBAT/PVC 70/30 blend. However, the melting enthalpy

(DHm) and, therefore, the crystallinity degree vc were affected by clay addition. For

instance, when 3 % of C30B was added to PBAT matrix, the crystallization degree

vc decreased from 11 to 8 %. This result reveals that C30B hinders the PBAT

crystallite growth. Indeed, the specific interactions which occurred between C30B

and PBAT could prevent the polymer chains’ movement and the restricted chains

might not crystallize. Hence, the crystallinity decreases in the presence of C30B.

These results are in good agreement with those obtained by FTIR and XRD

techniques. Similar findings are found by Chivrac et al. [41].

As also shown in Table 2, Tg of both PBAT/C30B and PVC/C30B nanocom-

posites increased by 2–3 �C compared to their pristine polymers, respectively.

Moreover, the single compositionally dependent glass transition temperature

observed with PBAT/PVC/C30B nanoblends is an evidence of their miscibility.

The Tg of the nanoblends increased by 9–19 �C compared with their corresponding

virgin blends. This is possibly due to the presence of C30B which would promote

the formation of strong attractive interactions between the chains of PBAT and

PVC, causing a reduction of their mobility [44–46]. These results are in agreement

Fig. 8 DSC curves of PBAT/C30B, PVC/C30B and their PBAT/PVC/C30B nanoblends at differentratios

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with XRD observation showing larger interlayer distances in the ternary PBAT/

PVC/C30B nanoblends compared to the binary PBAT/C30B or PVC/C30

nanocomposites.

Subsequently, the XRD technique has allowed us to examine the structure of the

obtained composites. Figure 10 displays typical XRD patterns of PBAT/C30B and

its mixtures with PVC. In [10�–30�] 2h angle range, five diffraction peaks of the

PBAT/C30B crystal structure were observed at 2h angle 16�, 17.4�, 20.3�, 22.8�,

and 24.8� [40], while the PVC/C30B was really amorphous. As it can be observed

from this figure, when the PVC composition is[48.5 % by weight in the composite,

no characteristic diffraction peaks of PBAT crystallinity appeared. These observa-

tions are in good agreement with those obtained by DSC and confirm once more the

presence of strong specific interactions between PVC and PBAT which would

inhibit the PBAT crystallization phenomenon and the crystallinity is significantly

reduced in mixtures containing an excess of the amorphous polymer.

Thermal stability

The thermal stability was assessed by thermogravimetric analysis (TGA). Figure 11

displayed typical TGA thermograms obtained for PBAT, PVC, and their different

blends.

PVC and PBAT underwent two degradation steps, respectively, while their

blends with different ratios showed three degradation steps. The thermal

Fig. 9 Comparative DSCcurves of PBAT, PBAT/C30B,PBAT/PVC 70/30 blend andPBAT/PVC/C30B 70/30nanoblend

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degradation of virgin PBAT starts at 270 �C and its maximum weight loss is

397 �C. At 458 �C, 95 % of PBAT have been degraded. Similar observations were

reported by Luc Averous et al. [8]. The TG and DTG curves for the thermal

degradation of PVC show an initial peak in the temperature range of 220–350 �C,

corresponding to the dehydrochlorination of the PVC matrix, followed by the

formation of the conjugated polyene sequences [11, 13, 47, 48]. The temperature at

the maximum weight loss (Td) corresponding to this stage is 279 �C. The second

decomposition peak is observed at 453 �C. This was attributed to the thermal

decomposition of the dehydrochlorinated PVC, which consisted mainly of

conjugated double bonds [11, 13, 49]. At the end of this step, a residue of 22 %

is obtained.

As shown in Fig. 11a, the onset of degradation of PVC is detected from 230 �C.

In the case of their mixtures with PBAT, the onset of degradation shifts to higher

temperatures, suggesting a delay in the degradation compared to the pristine PVC.

The first degradation step of PBAT/PVC blends in the temperature range from

240 and 330 �C was attributed to the volatilization of hydrogen chloride molecules

with the formation of conjugated polyenes in the PVC chains. It is interesting to

note that the dehydrochlorination of PVC was delayed with the introduction of

PBAT. This could be interpreted by the fact that acidic Hydrogen of PVC, likely to

be liberated as HCl, was engaged in hydrogen bonding with the carbonyl group of

PBAT. This confirms once again the presence of specific attractive interactions

between PBAT and PVC, supporting the miscibility of their blends.

The second degradation step was between 330 and 430 �C and it reflects the main

degradation of PBAT caused by the scission of the polymer chains. The decreased

decomposition temperature of PBAT Td2 was attributed to the catalyzing action of

chlorine radical liberated from the PVC chain. The chlorine radicals liberated from

Fig. 10 XRD patterns of PBAT/PVC/C30B nanoblends in [10�–30�] 2h angle range

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the PVC chain influence the degradation of PBAT. The degradation behavior of

polymer molecules is known to be influenced by the presence of the second polymer

due to the interaction which occurs between the polymers.

The last step between 430 and 500 �C, including both the two last steps of

degradation of PVC and PBAT, corresponds to the total decomposition of the two

components in the form of fragments by the liberation of CO2, H2O and CH4.

Table 3 summarizes the degradation temperatures of all the samples and their

residues yields.

Fig. 11 TGA (a) and DTG (b) curves of PBAT/PVC blends at different ratios under nitrogen at10 �C min-1

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It is well known that layered silicates improve the thermal stability of the

polymer matrix because they act as a heat barrier, and this enhances the overall

thermal stability of the system, as well as assists in the formation of char during

thermal decomposition [32, 50–53].

The effect of C30B on the thermal stability of the PVC/PBAT/C30B composites

is shown in Fig. 12. Temperatures Tonset, Td corresponding to the onset of

degradation and maximum weight loss of degradation, respectively, are shown in

Table 3.

Incorporation of C30B substantially increased the thermal stability of PBAT

copolyester. Indeed, PBAT/C30B nanocomposite has its initial degradation

temperature, maximum degradation temperature and final degradation temperature

higher than those of virgin matrix.

This improvement in thermal stability is primarily due to the fact that the

nanoclays act as heat barrier, thereby increasing the thermal stability of the system

as well as assisting in char formation during thermal decomposition [28]. However,

in the case of PVC a reverse phenomenon was observed. The C30B accelerates the

PVC degradation and catalyzes its dehydrochlorination [54]. The organic ammo-

nium cations act as Lewis acid and accelerated chlorine ion separation from the

PVC matrix, and then absorb it to form the hydrochloric salt of organic amine. The

salt easily releases hydrochloric gas at a high temperature and induces the PVC to

self-catalyze degradation [54].

After the incorporation of 3 % by weight of cloisite 30B into PBAT/PVC

mixtures, a similar degradation process to that of PBAT/PVC blends was obtained

for PBAT/PVC/C30B nanoblends. The degradation was performed at three stages

process indicating that there was no significant change in decomposition courses of

PBAT/PVC blends when clay particles were introduced into different mixtures. The

first stage corresponds to the dehydrochlorination of the PVC, the second is

attributed to the degradation of PBAT, which consists of decomposition of the

aliphatic copolyester (adipic acid and 1,4-butanediol) and the last one reflects both

thermal decomposition of the dehydrochlorinated PVC and the decomposition of

aromatic copolyester (terephtalic acid). From the TGA and dTG curves, the onset

Table 3 Thermogravimetric parameters of PBAT/PVC blends and PBAT/PVC/C30B nanoblends

Sample Tonset (�C) Td1 (�C) Td2 (�C) Td3 (�C) Wres (%)

100/0 272 – 397 458 5

97/0/3 278 403 461 10

70/30 240 303 393 445 9

69/28/3 227 291 390 450 16

50/50 235 300 391 444 17

48.5/48.5/3 225 285 384 454 19

30/70 234 297 385 448 20

29/68/3 223 282 381 450 24

0/100 230 279 – 453 22

0/97/3 220 275 – 452 25

1498 Polym. Bull. (2014) 71:1483–1503

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degradation temperature Tonset, Td1, Td2, and Td3, the residue yield (Wres) were

determined and collected in Table 3.

From Table 3, it can be noticed that Tonset, Td1, Td2, and Td3 were shifted towards

lower values for PBAT/PVC/C30B nanoblends compared to the pristine PBAT/

PVC blends. The addition of C30B to PBAT/PVC matrixes reduced their thermal

stability. Although the Cloisite C30B played a catalytic role in the degradation of

PVC and accelerated the formation of hydrogen chloride, the addition of PBAT to

Fig. 12 TGA (a) and DTG (b) curves of PBAT/PVC/C30B nanoblends at different ratios under nitrogenat 10 �C min-1

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PVC tends to delay the dehydrochlorination step. This latter was even more shifted

to higher temperatures that the composition of PBAT in the composite was high.

This behavior confirms the presence of specific interactions between the a-hydrogen

of PVC and the carbonyl group of PBAT. Thus, the two polymers of different kinds

would be confined within the same interlayer space.

Mechanical properties of binary PBAT/PVC blends and ternary PBAT/PVC/

C30B composites

In the last part of this contribution, Tensile measurements on the pristine PBAT/

PVC blends and PBAT/PVC/C30B nanoblends were carried out in traction mode to

investigate the C30B effect on the mechanical properties. The Young modulus (E),

Tensile strength (r), and elongation at break (e) values of different specimens are

presented in Table 4.

As shown in Table 4, the Young modulus (E) of the PBAT/PVC blends

decreased with the increase of PBAT content indicating that PBAT reduced the

stiffness of PVC. The Tensile strength (r) of the PVC/PBAT also decreased with

increasing PBAT composition in the blend. The PBAT weakens the blend by

reducing polymer–polymer chain secondary bonding and provided more mobility

for the macromolecules, resulting in a softer material. The elongation at break (e)increased with the increased of PBAT, indicating that PBAT managed to improve

the elasticity of PVC [8]. The improvement in the mechanical properties is

presumably from the compatibility between PBAT matrix and PVC chains.

From the Table 4, it is clear that the majority of the mechanical properties have

been enhanced with the addition of 3 % C30B to the virgin PBAT and PVC as well

as to PBAT/PVC blends.

For PBAT/PVC/3 % C30B nanoblends, we can note that the evolution of the

Tensile modulus was not very important in the whole composition range. The

introduction of Cloisite 30B in PBAT/PVC mixtures led to a moderate increase in

Young’s modulus, which was due to their mainly intercalated structures as has

already been shown by XRD and TEM techniques.

The Tensile strength of the PVC/PBAT/C30B nanoblends followed the same

trend as the Young’s modulus. It decreased with increasing PBAT content in the

composite. Recent studies have reported [55] that the introduction of clay in a

Table 4 Tensile tests results of PBAT/PVC blends and PBAT/PVC/C30B nanoblends

PBAT/PVC

r (MPa) e (%) E (MPa) PBAT/PVC/C30B

r (MPa) e (%) E (MPa)

100/0 18.9 (±0.6) 436.0 (±38) 62.0 (±2.6) 97/0/3 26.8 (±0.4) 612.6 (±34) 82.7 (±1.2)

70/30 19.2 (±0.7) 383.0 (±25) 103.0 (±3.8) 68/29/3 36.4 (±1.2) 474.7 (±26) 408.0 (±3.2)

50/50 20.6 (±1.2) 215.5 (±15) 560.0 (±10.4) 48.5/48.5/3

39.2 (±1.6) 353.2 (±18) 1,345.0 (±15)

30/70 29.1 (±1.7) 14.2 (±0.8) 1,493.0 (±47) 29/68/3 48.3 (±2.7) 25.3 (±3.4) 2,745.0 (±46)

0/100 42.0 (±3.1) 3.6 (±0.6) 2,400.0 (±123) 0/97/3 49.5 (±3.0) 5.75 (±0.8) 3,087.0 (±87)

1500 Polym. Bull. (2014) 71:1483–1503

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polymer matrix affected significantly the Tensile strength. It was found that this

latter varied considerably with the clay–matrix interactions. For polyamide

nanocomposites [55–57], the Tensile strength increased due to strong polyamide-

clay interactions, while in the non-polar polymers such as polypropylene, the

Tensile strength varied slightly due to the lack of interfacial interactions between

the clay layers and polypropylene [58]. In our case, we observed an increase in the

Tensile strength of the nanocomoposites and nanoblends compared to those

obtained for the virgin polymers or their blends (Table 4). This variation reflects the

presence of strong interactions developed between the polymer matrix and Cloisite

30B. The values of the elongation at break of the different mixtures were higher

than those of pristine PBAT/PVC blends. Thus, it could be said that C30B led to a

good interfacial adhesive strength, which facilitated good mechanical properties of

the PVC/PBAT blend.

Conclusion

Ternary PBAT/PVC/C30B nanoblends were successfully prepared through melt-

blending and their properties have been studied and compared with those of their

pristine blends. Based on TEM and XRD observations, mixed exfoliated/interca-

lated PBAT/PVC/C30B nanoblends were obtained. The miscibility of these

nanoblends is evidenced by the observation of single Tgs higher than the ones of

their corresponding virgin blends due to attractive interactions that may occur

between the clay surface and the polymer chains. Nanoblends showed a reduction of

their thermal stability compared to their pristine blends, as a result of the catalytic

effect of the C30B in the thermal degradation process. The insertion of clay particles

into composite matrix leads to the improvement of the mechanical properties for the

ternary PBAT/PVC/C30B nanoblends relative to their virgin blends.

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