em 2004

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The nanosized calcium carbonate filler was added to the pre-vulcanized latex compound in different amounts. The effect of filler content on the modulus,.
13th Scientific Conference & 14th Annual General Meeting, Electron Microscopy Society of Malaysia 13-15 December 2004, The Palm Garden Hotel, Putrajaya

THE EFFECT OF CALCIUM CARBONATE ON THE MECHANICAL PROPERTIES AND MORPHOLOGY OF NATURAL RUBBER LATEX FILMS S. Manroshan * and A. Baharin School of Material and Mineral Resource Engineering, University Science of Malaysia, 14300 Penang, Malaysia.

The nanosized calcium carbonate filler was added to the pre-vulcanized latex compound in different amounts. The effect of filler content on the modulus, tensile strength, elongation at break (Eb), tear strength and morphology of the films was investigated. Results showed that modulus at 100 % elongation (M 100 ) and modulus at 300 % elongation (M 300 ) increased with filler loading. Tensile strength and Eb increased up to 10 phr of filler loading and then decreased again. The tear strength decreased up to 5 phr and the increased at 10 phr of filler loading before forming a plateau at 30 phr of filler loading. Micrographs showed aglomeration of the fillers as the filler content was increased.

INTRODUCTION The latex industry has been established for a long time. Latex is used to produce many products, such as gloves, adhesive tapes, elastic bandages rubber pads, condoms and ballons. Due to the global economic slow down, the natural rubber demand has been affected greatly [1], resulting in lowest ever market prices in the past 30 years. Recently, the developments in the natural rubber industry has resulted in an increase in the prices of bulk latex [2]. The result is the overall cost of manufacturing latex products has also increased. As an alternative, many manufacturers has opted to incorporate fillers into their products to reduce production cost. Lately, ultra – fine or nano – sized fillers are gaining popularity as additives in latex. One example is calcium carbonate. Cai et al [3] showed that ultrafine calcium carbonate could improve the tear strength, tensile strength and modulus values of NR latex films. Another study showed that the use of nano – sized calcium carbonate did not effect the extractable protein ( EP ) and the antigenic protein ( AP ) contents of the gloves [4]. In this study, the effect of addition of this nanosized calcium carbonate on the mechanical properties and morphology of pre-vulcanized natural rubber latex films was investigated.

EXPERIMENTAL Materials and Ingredients Nanosized calcium carbonate filler was provided by NanoMaterials Technology Pte. Ltd., Singapore while the natural rubber latex (HA) was purchased from Kilang Hevea Bukit Perak, Kedah, Malaysia. The specifications of the calcium carbonate are as shown in Table I below. Other ingredients viz sulphur, zink oxide, potassium hydroxide, zinc diethyldithiocarbamate (ZDEC) and Vulcanox BKF was supplied by Bayer (M) Ltd.

_______________ * Corresponding author : Tel. + 6 (019) 5676358 E-mail: [email protected] (S. Manroshan)

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13th Scientific Conference & 14th Annual General Meeting, Electron Microscopy Society of Malaysia 13-15 December 2004, The Palm Garden Hotel, Putrajaya

Table I

Specifications and contents of nanosized calcium carbonate. Specifications Contents Appearance White Dispersion Specific gravity, dry basis 2.5 – 2.6 Particle size (avg), nm 40 Surface area (BET), m2 /gm 40 Whiteness (%) = 90 Particle shape Cubic pH 8.5 – 9.5 Moisture content (wt), % 40 – 50 CaCO3 % (wt) dry basis (modified) = 97 MgO (wt), % = 0.6 Compounding and Preparation of Samples Preparation of pre-vulcanized natural rubber latex films Pre-vulcanized latex was compounded in in a reaction flask at 70 ± 1 º C using the ingredients shown in Table II. The degree of vulcanization of the compound was determined using the chloroform number test. Pre-vulcanization was stopped at chloroform number 3. The pre-vulcanized latex was next left to cool at room temperature for 3 days for maturation process to occur. Films were next prepared by casting the latex compound onto glass substrates. Drying was done at room temperature for 4 days. The natural rubber latex films were next removed from the glass substrates and further dried for another 4 days at room temperature. Table II Ingredients

Formulation for Pre-vulcanized Natural Rubber Latex Compound. Parts by mass Dry Wet 60 % HA Latex 100 166.7 10 % Potassium hydroxide 0.5 5 50 % Sulphur 1.5 3 50 % Zink diethyldithiocarbamate 1 2 25 % Zink oxide 2 8 50 % Vulcanox BKF 1 2 10 % Nanosized CaCO3 0, 2, 5, 10, 30 0, 20, 50, 100, 300 Measurement of Mechanical Properties A Tensometric Testing Machine was used to determine the tensile and tear properties of the films . The tensile properties were measured according to ASTM D412 - 92 method. The tear properties were determined according to ASTM D624 – 91 method with the tear pieces being cut using an unnicked 90 o angle spesimen cutter ( Die C ). Both test were conducted at room temperature (25 º C) using a crosshead speed of 500 mm/min. Scanning electron micrography Fractured test pieces were first coated with cromium using an EMITECH K575X sputter coater for 30 seconds. The coated surfaces were next scanned at a magnification of

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13th Scientific Conference & 14th Annual General Meeting, Electron Microscopy Society of Malaysia 13-15 December 2004, The Palm Garden Hotel, Putrajaya

10,000x using a Leo SUPRA 50VP ultra high field emission scanning electron microscope (FESEM ).

RESULTS & DISCUSSION Effect of filler on mechanical propeties Table III.

Mechanical properties of room temperature cured latex films filled with different loadings of nanosized calcium carbonate.

Filler loading ( phr ) Modulus at 100 % elongation ( M 100 ) Modulus at 300 % elongation ( M 300 ) Tensile strength ( MPa ) Elongation at break ( % ) Tear strength ( N/mm )

0

2

5

10

30

0.63

0.64

0.68

0.75

0.91

1.58 10.05 637.00 44.89

1.71 10.29 649.35 20.10

1.66 12.04 710.48 21.06

1.85 16.37 759.92 61.44

2.84 11.26 538.30 58.16

Table 3 shows the mechanical properties of room temperature cured latex films filled with different filler loadings. It is seen that the M100 values increases with filler loading. The same trend is also observed for M300 values which increased with increased filler loading. The increase in M100 and M300 with filler loading is due to the stiffening effect caused by the filler incorporated into the films. As stress is applied to the films, crystalization of the chains occurs [5] with the filler being embedded in between the rubber chains. The tensile strength increased with filler loading reaching a maximum value at 10 phr and then decreased. The improvements in tensile strength at 10 phr of the latex films suggests that there is possitive interaction between the rubber matrix and the filler particles thus giving additional reinforcements compared to the unfilled latex films. At 30 phr of filler loading, the tensile properties decreased due to an increase of filler to filler interaction compared to the filler to rubber interaction which is required to reinforce the rubber network. The elongation at break ( Eb ) as shown in Table 3 also shows a similar trend as the tensile strength with the Eb reaching a maximum at 10 phr of filler loading and then decreased with further filler incorporation. As shown in Table III, the tear strength decreased when the filler loading was increased to 2 and 5 phr. A rapid increase in tear strength was observed as the filer loading was increased up to 10 phr. Above 10 phr of filler loading, no increament in tear strength was observed. Furthermore, the tear pattern of the films changed from a straight tear pattern to a knotty tear pattern as more filler was incorporated. This could be due to the presence of agglomerates of the filler localizing in some areas as seen by Amir – Hashim et al [4] could be the cause of the knotty tears observed. More tear strength is required to tear the films at the agglomerating points in the films as the filler agglomerates appear to coalescence in between some rubber particles.

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13th Scientific Conference & 14th Annual General Meeting, Electron Microscopy Society of Malaysia 13-15 December 2004, The Palm Garden Hotel, Putrajaya

Effect of filler on morfology Fig. 1 shows the micrographs of fractured surfaces of test pieces with different filler loadings. As observed, the size of the filler particles increased with filler loading. This suggests that agglomeration of the fillers took place in the films.

( a ) 0 phr CaCO3

( b ) 2 phr CaCO3

( c ) 5 phr CaCO3

( d ) 10 phr CaCO3

( e ) 30 phr CaCO3

Fig. 1.

Morphology of fractured surface of test pieces filled with different ratios of filler loading.

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13th Scientific Conference & 14th Annual General Meeting, Electron Microscopy Society of Malaysia 13-15 December 2004, The Palm Garden Hotel, Putrajaya

Large agglomerates formed when filler content was increased up to 30 phr as shown in Figure 1 ( e ). This resulted in a drop in properties of films as shown in Table III. Improvements in tear properties were observed even tough minor agglomerations were seen in films with 10 phr of filler loading as the fillers were well distributed in them.

CONCLUSION The use of nano – sized calcium carbonate has a significant effect on the properties of latex films. Modulus at 100 % elongation (M 100) and modulus at 300 % elongation (M 300 ) increased with filler loading. Tensile strength and Eb increased up to 10 phr of filler loading and then decreased again. The tear strength decreased up to 5 phr and the increased at 10 phr of filler loading before forming a plateau at 30 phr of filler loading. Micrographs taken using FESEM showed aglomeration of the fillers as the filler content was increased. The results obtained shows that the reinforcing effect was found to be optimum at a content of 10 % calcium carbonate.

REFERENCES 1.

http://www.fao.org

2.

http://www.lgm.gov.my

3.

Cai H., Li S., Tian S., Wang H. and Wang J. (2003) Journal of Applied Polymer Science, 87, 982 – 985

4.

Amir – Hashim M.Y., Hasma H and Shamsul Bahri A.R., Nano – sized CaCO3 fillers in NR latex gloves. 2nd International Rubber Gloves Conference & Exhibition, Shangri – La Hotel, Petaling Jaya, 29th Jun – 1st July 2004.

5.

Treloar, L.R.G (1975). The Physics of Rubber Elasticity, 3rd edition (Oxford University Press) pp. 20

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