Post Graduate Research Papers 2001/2002 School of Materials & Mineral Resources Engineering, USM 1

Preparation and Characterization of Natural Rubber/ Organoclay Nanocomposites

P.L. Teh, U.S. Ishiaku 1, Z.A. Mohd Ishak1, J.Karger-Kocsis2

1 School of Materials and Mineral Resources Engineering, Engineering Campus, University of Science Malaysia, 14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang. 2 Institute for Composite Materials (IVW), University of Kaiserlautern, Germany.

ABSTRACT

Reinforcement of polymer with nano-sized clay particles is a promising technique that is capable of yielding materials with enhanced performance but without involvement in expensive synthesis procedures. Polymer/clay nanocomposites are being investigated and developed worldwide by a number of public, private and corporate entities. Nano-sized filled composites can be considered as the latest development in advanced materials technology, which is yet to be applied to natural rubber. Three different gred of organoclay was added to Natural Rubber and cured by semi-efficient vulcanization system. Then the compounds were characterized in respect of their curing and mechanical properties.

INTRODUCTION

An organoclay nanocomposite is a polymer system containing inorganic clay intercalated with organic cations with one dimension in the nanometer range i.e. one billionth of a meter. Various clays are being used by exploiting the ability of the clay silicate layers to disperse into polymer to obtain nanocomposites.(1) In nanocomposites, tremendous improvement in mechanical properties such as enhanced heat stability, abrasion resistance, solvent resistance, reduced gas permeability and improved flame retardancy can be attained by optimizing molecular interactions between the reinforcing filler and matrix through reduction in size of the filler particles.(2) There are two types of polymer/organoclay nanocomposites: (a) plastic based organoclay

nanocomposite such as polypropylene, polyimide, poly(methyl methacrylate) and epoxy.

(b) elastomer based organoclay nanocomposite such as styerene butadiene rubber (SBR).

Since NR does not have polar groups in its backbone, this project will prepare NR/organoclay nanocomposites by using a functionalised natural rubber ie. epoxidized natural rubber (ENR) as a compatibilizer. The effect of organophilic nanoclays on the curing characteristics, mechanical properties, and thermoxidative ageing behaviour will be studied.

MATERIALS AND METHOD

Elastomer : Natural rubber (SMR L) Nanofiller : Organoclay (1.30TC, 1.30P, 1.28E) Filler : Carbon black (N330), Silica (vulkasil S) Compatibilizer : Epoxidized natural rubber (ENR25, ENR50) Ingredient Content (phr)a

Natural rubber 100

ENRb 5,10 Fillerc Variable

Sulfur 1.5

Zinc oxide 5.0 IPPD 2.0 Stearic acid 2.0 MBTS 1.5

ENR, Epoxidized natural rubber: IPPD, N-isopropyl-N' -phenyl-p-phenylenediamine MBTS, Mercaptobenzothiazoldisulfide a Parts Per Hundred parts of rubber b ENR 25, ENR 50

c Organoclay - 2,4,6,8, and 10 phr Carbon black - 50 phr Silica - 30 phr

Post Graduate Research Papers 2001/2002 School of Materials & Mineral Resources Engineering, USM

2

2

Compounding was done by using the Brabender Plasticorder at 80°C for 7 minutes. Compound cure characteristics were measured on Rheometer Monsanto MDR 2000, then cured by compression molding at 150°C.

RESULTS AND DISCUSSION Cure Characteristic Figure 1 shows the influence of filler content on the cure characteristics of NR/organoclay compounds that derived from MDR20000 measurements.

FIG 1: t90 of compounds with different filler content (phr). From Figure 1, it shows tipical trend for these three types of fillers. The t90 of the compounds was sharply decrease at 2phr filler content then followed by a gradual decrease upon further addition of the filler. This is caused by the amine functionalities in the filler after the modification process or ion exchange process.(3) The amine containing compounds will facilitate the curing reaction of natural rubber stocks. Mechanical Properties Figure 2 and 3 illustrates the influence of the different type nanoclays on the tensile properties of NR/organoclay compounds.

FIG 2: Tensile strength of compound 1,2,3,4,5,and 6. FIG 3: Elongation at break of compound

1,2,3,4,5, and 6. 1 - SMR L/ ENR25 (5phr) 2 - SMR L/ ENR25 (5phr)/ CB (50phr) 3 - SMR L/ ENR25 (5phr)/ Silica (30phr) 4 - SMR L/ ENR25 (5phr)/ 1.30TC (4 phr) 5 - SMR L/ ENR25 (5phr)/ 1.30P (4phr) 6 - SMR L/ ENR25 (5phr)/ 1.28E (4phr) Filler content of 4 phr have been choosen for the comparison because the compound shows the highest tensile properties at this level of filler loading. The organoclay nanocomposites shows higher tensile strength than carbon black (CB) and silica filled compounds(Fig 2). The silicate surface area in organoclay contributes a better dispersion of the organoclay in natural rubber(3).

CONCLUSION

The t90 of the compounds was influenced by the filler content. The organoclay could enhance the performance of natural rubber. It could compete with the carbon black and silica.

REFERENCES

1. Yen T.V., James E.M., et al. (2001). J. Appl. Polym. Sci., 82, 1391-1403.

2. Gloaguen J.M. & Lefebvre J.M. (2001). Polymer, 42, 5841-5847.

3. A.Mousa & J. Karger-Kocsis (2001). Macromol .Mater. Eng, 286, 260-266. 0

5

10

15

20

25

30

35

1 2 3 4 5 6Rubber Blends

Ten

sile

Str

eng

th (

MP

a)

23

45

67

89

0 2 4 6 8 10Filler content (phr)

t 90 (

min

)

1.30P 1.30TC 1.28E

0

200400600

80010001200

14001600

1 2 3 4 5 6Rubber Blends

Elo

ng

atio

n a

t B

reak

(%

)

Post Graduate Research Papers 2001/2002 School of Materials & Mineral Resources Engineering, USM

3

3