12. - 14. 10. 2010, Olomouc, Česká Republika

MORPHOLOGICAL STUDY OF PVC/MONTMORILLONITE NANOCOMPOSITES

Alena KALENDOVÁa, Lucie KOVÁŘOVÁa, Jiří MALÁČa, Michal MACHOVSKÝb, Jean Francois GERARDc

a TOMAS BATA UNIVERSITY IN ZLÍN, Faculty of Technology, Department of Polymer Engineering, Nám. TGM 275, 762 72 Zlín, Czech Republic, E-mail: kalendova@ft.utb.cz

b TOMAS BATA UNIVERSITY IN ZLÍN, Faculty of Technology, Polymer Centre, Nám. TGM 275, 762 72 Zlín, Czech Republic, E-mail: machovsky@ft.utb.cz

c INSA DE LYON, Laboratoire des Matériaux Macromoléculaires/IMP, UMR 5627, Bât Jules Verne, 20 Avenue A. Einstein, 69621 Villeurbanne Cedex, France

Abstract

Reported nanocomposites of poly(vinyl chloride) have been prepared using bentonite-based clay, Na-

montmorillonite (nature clay) and organophilic clay 30B. Na-montmorillonite is the most widely used type of

silicate clay in polymer nanocomposites. It is a reinforcing material, naturally abundant, nontoxic,

inexpensive, chemically and thermally stable. Polymer nanocomposites of differing compositions were

produced using Buss KO-kneader via melt intercalation method. The effect of different type of plasticizer

(both low molecular and high molecular) and compounding conditions on the structure of PVC/clay

nanocomposites was investigated. Different compounding conditions were tested to study their influence on

nanoparticles dispersion, orientation and exfoliation in PVC/clay nanocomposites. The structure of

PVC/MMT nanocomposites was observed using X-ray diffraction, transmission electron microscopy (TEM),

scanning elektron microscopy (SEM) and AFM (Atomic Force Microscopy). It was found that the Na-

montmorillonite offer low exfoliation level, while 30B modified by plasticizer exhibits fine dispersion of partial

to nearly full exfoliated MMT. Moreover the processing conditions play also important role in nanocomposite

production. Financial support of the Ministry of Education of the Czech Republic, project MSM 7088352101,

is gratefully acknowledged.

Keywords: Polyvinylchloride, nanocomposite, morphology, processing.

1. INTRODUCTION

Polymer-layered silicate nanocomposites have experienced an important development over the past 30

years. The serious exploitation of this technology began in the early 1990s in Toyota, when synthesis of

polyamide 6 nanocomposite via in situ polymerization had exhibited markedly improved thermal and

mechanical properties [1]. Next important step performed Vaia et. al. [2], when discover blending layered

silicate with polymers in the molten state offers a versatile and environmentally benign approach for

synthesizing nanocomposites. This two pioneering works represents the milestones for the polymer/clay

nanocomposite research. Some industrial applications have already been established by using this

technology to provide new products to various markets like automotive, packaging, coating, etc. [3].

Layered silicates such as montmorillonite, hectorite and saponite have been used for many years by industry

for preparing conventional macro or micro composites. The most famous is montmorillonite. Montmorillonite

consist of organically modified nanometer scale, layered magnesium aluminum silicate platelets. The silicate

platelets are approximately 1 nm thick and 70 – 150 nm across. [4] The platelets are modified with an

organic agents to allow complete dispersion into and provide miscibility with the thermoplastic systems.

There are some unique application areas where the nanofillers improve the physical properties of the plastic

12. - 14. 10. 2010, Olomouc, Česká Republika

products. These fillers may enhanced the properties of injection moulded pieces for the automotive industry,

of flexible and rigid packaging such as films, bottles, trays and also of electronics plastics such as wire and

cable coatings. [5]

Nanoclay benefits result from the very high surface area of montmorillonite clay (750 m2/g) and high aspect

ratio (about 70 to 150). [4] In dry form, clay exists in clusters or aggregates of montmorillonite platelets and it

exposed little surface area with low aspect ratio. Therefore it is necessary created conditions favourable for

the exposure of all this potential surface area to the polymer. Two terms are used to describe this behaviour:

exfoliation and dispersion. Both of them are necessary to realize to enhance performance of

nanocomposites.

Polyvinylchloride (PVC) is a polymer, which has a lot of characteristics suitable for industrial applications

such as good mechanical properties, fire retardancy, good processability and, in addition, it offers the

advantage of low cost. World PVC production capacity will have more than doubled over the past couple of

decades. In 1992 22 million tons of PVC were manufactured, but by 2012 this is predicted to rise to 50

million tons, according to petrochemical consultants CMAI. [6] Despite the fact that PVC is one of the major

thermoplastic polymers, PVC/clay nanocomposites are still in the introductory phase. This work is based on

the study of the influence of different processing conditions, and various plasticizers on the morphology of

PVC/clay nanocomposites.

2. EXPERIMENTAL

2.1 Materials and processing

The suspension type of PVC Neralit 652 (K = 65) from Spolana Neratovice, Czech Republic was used as

polymer matrix. The samples were stabilized with 3 % Lankromark LZB 968. As the filler was employed

bentonite-based clay, Na-montmorillonite and organophilic montmorillonite 30B from Southern Clay

Products, USA. Na-montmorillonite is a sodium type with d spacing 1,2 nm. Montmorillonite 30B is

organophilic clay with d spacing 1.8 nm. Dioctylphthalate (DOP), dioctyladipate (DOA) and polyester

Lankroflex PLA (PLA) were used as PVC plasticizer and montmorillonite modifiers.

The polymer layered silicate nanocomposites were prepared in a Buss KO-kneader MKS 30 (L/D = 18, D =

30 mm). The screw speed was at 80, 50, 35, 25 rpm. The operating temperature was at range 130–160 °C.

Selected blends were compounded two or three times. Table 1 shows overview of tested samples and

conditions.

2.2 Morphological study

The morphological study was performed via XRD and Microscopy techniques. X-ray scattering is a non-

destructive analytical technique, which reveals information about the structure, chemical composition, and

physical properties of materials. X-ray diffraction data were obtained at room temperature by an URD-6

Diffractometer, the X-ray beam was nickel-filtered CuKα (λ = 1,54 Å) radiation.

The dispersion and delamination of the clays in PVC matrix were observed through microscopic techniques,

Transmission electron microscopy (TEM) and Atomic force microscopy (AFM). TEM forms a major analysis

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method in a range of scientific fields, in both physical materials and biological sciences. An image is formed

from the interaction of the electrons transmitted through the specimen. For the transmission electron

microscopy (TEM, Phillips PM 120) the specimens were cut using an ultramicrotome equipped with a

diamond knife.

AFM is a very high-resolution type of scanning probe microscopy, with demonstrated resolution on the order

of fractions of a nanometer. For the Atomic force microscopy (AFM, ExplorerTM) were used the same

samples as for TEM. It was used non-contact AFM method and for profile determination was applied

software SPM Lab 5.01.

Dynamical thermo-mechanical analysis was used to confirm the XRD and microscopic study. It is the most

useful technique for characterizing polymer materials. The equipment DMA DX04T was employed for this

measurement. The temperature range varied from -10 °C to 100 °C with heating 2 °C/min and frequency 1

Hz. The samples with thickness 1 mm were tested.

Table 1. PVC/Clay Composition and Processing Conditions Composition Filler

(%)

Screw Speed

(rpm)

Retention time (times)

PVC/DOP 50 0 50 t PVC/DOA 50 0 50 t PVC/PLA 50 0 50 t PVC/30B/DOP 80 5 80 t PVC/30B/DOP 80 5 80 2t PVC/30B/DOP 50 5 50 t PVC/30B/DOP 50 5 50 2t PVC/30B/DOP 50 5 50 3t PVC/30B/DOA 50 5 50 t PVC/30B/PLA 50 5 50 t PVC/30B/DOP 35 5 35 t PVC/30B/DOP 35 5 35 2t PVC/30B/DOP 25 5 25 t PVC/30B/DOP 25 5 25 2t PVC/Na/DOP 80 5 80 t PVC/Na/DOP 80 5 80 2t PVC/Na/DOP 50 5 50 t PVC/Na/DOP 50 5 50 2t PVC/Na/DOP 50 5 50 3t PVC/Na/DOA 50 5 50 t PVC/Na/PLA 50 5 50 t PVC/Na/DOP 35 5 35 t PVC/Na/DOP 35 5 35 2t PVC/Na/DOP 25 5 25 t PVC/Na/DOP 25 5 25 2t vscrew.....screw speed t…..retention time

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3. RESULTS AND DISCUSSION

3.1 X-ray scattering

X-ray reflectivity is one of the most powerful techniques to study the structural aspects of intercalates and

nanostructures. Fig. 1 represents the XRD patterns PVC/30B and PVC/Na mixtures produced with Buss KO-

kneader.

The XRD measurement of PVC nanocomposites (Fig. 1a) confirms good exfoliation by samples with

montmorillonite 30B/DOP, 30B/DOA (low molecular plasticizers). It can indicate good level of filler exfoliation

to polymer matrix, and this result was confirmed by TEM (Fig. 2) and DMA. For the PVC/30B/PLA, changes

in the structure of clay 30B in presence of plasticizer PLA (high molecular plasticizer) were observed, the d

spacing increased from 1.83 to 4.3 nm. On the other hand, the compositions base on Na-montmorillonite

does not show changes in XRD patterns and low level of exfoliation was also confirmed by TEM, Fig. 1b.

The d spacing was 1.2 nm as for PVC/Na samples as for montmorillonite Na.

0

100

200

300

400

500

600

700

800

1 2 3 4 5 6 7 8 9 10

Inte

nsi

ty (c

ps)

2Θ (deg)

PVC/(30B 5% + DOP)

PVC/(30B 5% + DOA)

PVC/(30B 5% + PLA)

30B

4,83

= 2

Θ1,

83 n

m

2,1

= 2Θ

4,3

nm

0

100

200

300

400

500

600

700

800

1 2 3 4 5 6 7 8 9 10

Inte

nsity

(cps

)

2Θ (deg)

PVC/(Na 5% + DOP)

Na

7,20

= 2

Θ

1,23

nm

0

100

200

300

400

2 3 4 5 6 7 8 9 10

Inte

nsity

(cps

)

2Θ (deg)

PVC/30B/DOP 50 - t

PVC/30B/DOP 50 - 2t

PVC/30B/DOP 50 - 3t

Fig. 1. XRD a) PVC/30B 50 – t, b) PVC/Na 50 – t, c) PVC/30B/DOP 50 – t, 2t, 3t

In Fig. 1c are presented XRD patterns PVC/30B/DOP compositions prepared by different retention time t. It

was noticed, that the composition shows some ordered structures, which could be probably connected with

stacks of several layers which were not fully exfoliated. In comparison with PVC/30B the materials based on

PVC/Na have not shown dramatic changes in d spacing. The d spacing varied from 1,2 to 1,3 nm.

a) b)

c)

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3.2 Microscopy

Next very powerful technique in structural study of materials is microscopy, which is used to confirm the X-

scattering results.

In Fig. 2 and 3 are presented the TEM pictures of PVC/30B and PVC/Na samples, where the clay was

modified by different plasticizers. It can be seen that the silicate layers are dispersed evenly in the polymer

matrix in Fig. 2. The treatment with low molecular weight plasticizers gives better results compare to high

molecular plasticizer. Furthermore it was observed that the longer time of mixing in the Buss KO-kneader

caused regular dispersion and orientation of the nanoparticles in the PVC matrix. On the other hand too long

retention time leads to the destruction of exfoliated layers. For various retention time t for PVC/Na

composites, it was not noticed dramatic changes in the structure of PVC/Na/DOP. The d spacing moved very

slightly, from 1.2 to 1.3 nm.

Fig. 2. TEM Pictures of PVC/30B 50 a) PVC/30B/DOP – t, b) PVC/30B/DOA – t, c) PVC/30B/PLA – t

Fig. 3, TEM of PVC/Na 50 Composites a) PVC/Na/DOP – t, b) PVC/Na/DOA – t, c) PVC/Na/PLA – t

Further the dynamical thermo-mechanical analysis was performed. The obtained data are in Fig. 4.

Presented data confirmed good level of exfoliation for samples with 30B and low level of exfoliation for

composition PVC/Na. DMA results are in a good agreement with XRD and microscopy. At temperature 70°C

the improvement was around 300 % for PVC/30B/DOP and PVC/30B/DOA. In case of PVC/30B/PLA the

enhancement was more than 100 %. PVC/Na/DOP and PVC/Na/DOA have shown improvement only about

40 % at 70 °C.

a)

500 nm

b)

500 nm

b)

200 nm

c)

200 nm 200 nm

a)

c)

500 nm

12. - 14. 10. 2010, Olomouc, Česká Republika

0

500

1000

1500

2000

2500

-10 0 10 20 30 40 50 60 70 80 90 100

Mod

ulus

/E

*/ (

MP

a)

T (oC)

PVC/DOP 50t

PVC/30B/DOP 50t

PVC/Na/DOP 50t

0

0,1

0,2

0,3

0,4

0,5

0,6

-10 10 30 50 70 90

tan

δ

T (oC)

PVC/DOP 50t

PVC/30B/DOP 50t

PVC/Na/DOA 50t

Fig. 4. DMA: E-modulus and tan δ for materials based on PVC/DOP

4. SUMMARY

PVC/clay nanocomposites were obtained via melt compounding of PVC with clay in the presence of low and

high molecular plasticizers. The type of plasticizer play important role in the process of intercalation or co-

intercalation of montmorillonite and could be helpful during the nanocomposite processing. Better results

give low molecular plasticizers.

Next the different processing conditions were tested. It could be concluded, that the lowest screw speed had

the most positive effect on the reduction of nanofiller agglomerates and exfoliation process. On the other

hand, this process is hold only for successful intercalate agents. If the intercalation is not fruitful then

different conditions could not affect the exfoliation process and could not lead to nanocomposite systems.

Further, as was mentioned above, the dispersion and exfoliation are working together in the nanocomposite

processing.

ACKNOWLEDGEMENT

Financial support of the Ministry of Education of the Czech Republic, project MSM 7088352101, is

gratefully acknowledged.

REFERENCES

[1] Okada A. et al. Synthesis and properties of nylon-6/clay hybrids. In Materials Research Society Symposium Proceeding, 1990.

[2] Vaia R. A., Ishii H., Giannelis E. P. Synthesis and properties of twodimensional nanostructures by direct intercalation of polymer

melts in layered silicates. Chem Mater 1993, 5, p.1694–6.

[3] Ahmadi, S. J., Huang, Y. D., Li, W. 2004 Review: synthetic routes, properties and future applications of polymer-layered silicate

nanocomposites. J. Mater. Sci. 2004, 39, p. 1919–1925.

[4] www.nanoclay.com

[5] N. Yarahmadi, I. Jakubowicz, T. Hjertberg, Polymer Degradation and Stability, 2010, 95, 132-137.

[6] Brad Esckilsen, Global PVC markets: threats and opportunities, Plastics Additives & Compounding, November/December 2008,

p. 28-30.