Iw In

0,55

0,24

0,44

In/Iw

. N

OH

O

ESR Study of NR/Montmorillonite Nanocomposites

M. Didović1, D. Klepac1 S. Valić1,2 A.P. Meera3 and S. Thomas3

1 University of Rijeka, School of Medicine, Braće Branchetta 20, Rijeka, 51000, Croatia2 Rudjer Bošković Institute, Bijenička 54, Zagreb,10000, Croatia

3School of Chemical Sciences, Mahatma Gandhi University, Priyadarshini Hills P.O. Kottayam -686 560, Kerala, India

Objective

investigate the influence of the filler content on the local chain dynamics and motional heterogeneitycorrelate the ESR results with those obtained by other methods

TEM images indicate intercalation of the clay by NR, which is confirmed with XRD analysis that showes an increase of interlayer distance for about 10 Å, thus proving the existence of layered clay-NR intercalates certain amount of clay in NC-5 exfoliates, as can be concluded from the TEM image and the broadening of the (001) diffraction peak SEM images show more homogeneous distribution of the clay particles in NR matrix for NC-5 compared to other two samples DSC curve of the pure clay displays an endothermic peak at ~40 °C, also observed at composite samples, where it is shifted towards slightly higher temperatures ESR spectra in low-temperature region consist only of a broad component, indicating slow local chain dynamics; the fraction of the narrow component increases from ~40 °C untill ~90 °C, above which it abruptly decreases; ESR spectra of NC-2 and NC-10 display similar temperature dependencecomparison of the ESR spectra of samples recorded at 50 °C exibits difference between In/Iw ratios for NC-5 and other two samples

Z. Veksli, M Andreis, B. Rakvin, ESR spectroscopy for the study of polymer heterogeneity, Prog Polym. Sci. 25 (2000) 949-986.

S. Joly, G. Garnaud, R. Ollitrault, L. Bokobza, Organically modified layered silicates as reinforcing fillers for natural rubber, Chem. Mater. 14 (2002) 4202-4208

SampleAmount of

Cloisite 20A / phr

NC-2 2

NC-5 5

NC-10 10

Materials

References

Conclusions

Results

electron spin resonance (ESR), spin probe methoddifferential scanning calorimertry (DSC)transmission electron microscopy (TEM)scanning electron microscopy (SEM)X-ray diffraction (XRD)

0.25 wt.% of spin probe was incorporated in NR samples by swelling the samples in the toluene probe solution at 35 °C; solvent was removed and samples were annealed at 60 °C for 72 hoursESR measurments were preformed in the temperature range from -100 ºC to 130 ºC

Figure 1. TEM images of a) pure NR, b) NC-2; c) NC-5 and d) NC-10.

a) b) c) d)

Figure 5. ESR spectra of NC-5 in thetemperature range from -10 ºC to 130 ºC.

natural rubber (NR) with different amounts of organically modified clay - montmorillonite (Cloisite 20A)

ESR spin probe

Figure 2. XRD patterns of Cloisite 20A and NR/Cloisite 20Ananocomposites.

Sample 2θ/ ° d001 / Å

Cloisite 20A 2.94 30.0

NC-2 2.14 41.2

NC-5 2.20 39.8

NC-10 2.20 40.0

Figure 3. SEM images of a) NC-2, b) NC-5 and c) NC-10.

a) b) c)

Figure 6. ESR spectra of NC-2, NC-5 and NC-10 at50 °C and intensity ratios of narrow and broad line.

Figure 4. DSC curves of Cloisite 20A and NR/Cloisite 20Ananocomposites.

the shape of the ESR spectra depends on type of dispersion (intercalation/exfoliation of clay lamellae) and homogeneity of distribution of the clay particles: intercalation of the polymer chain segments in the clay lamellae hinders the chain motions, resulting in a greater fraction of a broad component in ESR spectra compared to the pristine NR exfoliaton of the layers enhances interactions between clay and polymer; organic part of the clay causes extra entanglements that slow down chain segment motion, what leads to broader ESR spectra compared to purely intercalated nanocomposites and hence to the decrease of In/Iw ratio

the apperance of the narrow ESR component around 40 ºC could be related to the endothermic peak observed by DSC in the same temperature region unexpected disapperance of the narrow component in ESR spectra above 90 ºC might be due to stronger interaction of the clay particles and NR matrix

Methods