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1. INTRODUCTION Natural rubber latex or commonly abbreviated

NRL is a compound which has pure content of 100% cis-1,4-polyisoprene. This compound are useful in improving the mechanical properties when it is strecthed. It is usually available as natural latex which is stabilized with ammonia [1]. In industrial usage, this NRL is usually filled by mineral or non-mineral fillers in order to enhance the properties of NRL products. One of mineral fillers which is commonly used is kaolin. Kaolin is used as a filler in many rubber goods. Kaolin offers strength, abrasion resistance, and rigidity to both natural and synthetic rubber products. The major reason that kaolin is used in rubber compounds is its whiteness and relatively low cost. Although kaolin costs less than most other rubber pigments, it has excellent functional properties [2]. Table 1 shows the mineral kaolin content as given by Murray [2]. Table 1. Composition of Mineral Clay Kaolin

Compounds Composition (%) Aluminum oxide 38,38 Silicon dioxide 45,30 Iron oxide 0,30 Titanium dioxide 1,44 Calcium oxide 0,05 Magnesium oxide 0,25 Sodium oxide 0,27 Potassium oxide 0,44 Ignition loss 13,97

Kaolin exhibited several properties as stated by

Murray (3) such as 1:1 layer, little substitution, minimal layer charge, low base exchange capacity, pseudo-hexagonal flakes, low surface area, very low

absorption capacity, and low viscosity. Kaolin is hydrophilic and can be dispersed in water and in various other systems. Because of the properties of its surface, kaolin can be chemically modified so that it will become hydrophobic or organophilic, or both. Generally, an ionic or a polar non-ionic surfactant is used as the surface-treating agent [2]. Several study about modifying the fillers has been done in NRL filled with mineral clay fillers such as silica, rectorite, kaolin [4-8]. From these studies, it is found that modified fillers were able to improve the mechanical properties from NRL products. In this study, the kaolin is modified with alkanolamide which is a compund derived from Refinery Bleaching Deodorant Product Stearin (RBDPS) and filled into NRL. Later, this study reports the effect of drying temperature on mechanical properties of NRL products filled with kaolin modified alkanolamide.

2. EXPERIMENTAL PROCEDURE

2.1 Kaolin Modified Alkanolamide Preparation The filler with 10 pphr (part per hundred rubber) is prepared by dispersing kaolin into a dispersion system which consists of water and alkanolamide. Table 2 gives the composition of the kaolin-alkanolamide dispersion system. Table 2. Dispersion System of Kaolin-Alkanolamide Ingredient Percentage (%) of 10 pphr

Kaolin 15 15 15 15 15 15 Alkanol-

amide 0 0,5 1 1,5 2 2,5

Water 85 84,5 84 83,5 83 82,5

ABSTRACT Kaolin is a clay mineral generally used as filler. Kaolin is white, with particle size of 300 mesh. It

can be used as natural rubber latex filler in a dispersion system. It consists of water, kaolin and alkanolamide. This dispersion system was mixed with natural rubber latex and curative agent with composition of 10 pphr (part per hundred rubber). This latex compound was pre-vulcanized at 68oC and dried at temperature of 100oC and 120oC for 30 minutes by dry dipping method. The mechanical properties of product were then investigated using Fourier transform infrared spectroscopy (FTIR) and analyzed by Scanning Electron Microscope (SEM).

KEY WORDS: Natural Rubber Latex / Kaolin / Alkanolamide / Dipping Method / Filler

PPaappeerr IIDD 5555

The Effect of Drying Temperature on Mechanical Properties of the Natural Rubber Latex Products Filled with Kaolin Modified

Alkanolamide Hamidah Harahap*, Indra Surya, Hanafi Ismail, Erick Kamil, Emelya Khoesoema,

Elmer Surya Department of Chemical Engineering, Universitas Sumatera Utara, Indonesia

Jalan Almamater, Kampus USU Medan 20155, North Sumatra, Indonesia *Authors to correspondence should be addressed via e-mail: hamidah_usu@yahoo.com

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2.2 Pre-vulcanization and Vulcanization Low commercial natural rubber latex with ammonia stabilized were used in this study. The NRL was mixed with the fillers with the composition showns at Table 3. Pre-vulcanized latex was mixed with 10 pphr filler dispersion system. The mixture was pre-vulcanized for 12 minutes at 68oC. After it has been pre-vulcanized, the mixture was opened up for 24 hours in order to release the bubblecap inside it. After the bubblecap has been released, the latex compound was vulcanized by dry dipping method at 100oC and 120oC for 30 minutes. Table 3. Formulation for NRL Compounds Ingredients

Ingredient Composition (Grams)

100% High Ammonia Latex

167

50% Sulphur 3 50% ZDEC 3 30% ZnO 0.83 50% Antioxidant 2 10% KOH 3 10% Fillers 16,7

2.3 Determination of Cross-Linking Density The NRL products were made into small piece of about 0,2 grams. The data to calculate the crosslink density is obtained from swelling data which is performed in accordance to ASTM D471. Then, the calculation for crosslink density is done using the calculation given by Flory-Rehner according to following equation [9]: 2.4 Mechanical Testing and Morphology Study The NRL products were tested in accordance to ASTM D412 using INSTRON 5565 with cross-head speed of 500 mm/min. The tensile strength, elongation at break, M100, and M300 were evaluated. Later, the morphological study in the fracture of the film is analyzed via Scanning Electron Microscope (SEM) JEOL-JSM 6360-LA. Then the film is characterized by Fourier Transform Infra-Red (FTIR) via Shimadzu IR-Prestige 21. 3. RESULTS AND DISCUSSION 3.1 Crosslinking Density Fig.1 shows an observation that NRL filled kaolin-alkanolamide (1,5 wt%) shows the highest crosslinking density meanwhile NRL filled kaolin-alkanolamide (0,5 wt%) shows the lowest crosslinking density. This condition shows that as the amount of alkanolamide increased, it has ability to enhance the interaction of NRL with kaolin produce strong physical cross-links [11]. This condition is later confirmed in Fig.6 where new groups is found in NRL filled kaolin-alkanolamide shows better interaction occurs. The other observation from Fig. 1 is the result of drying effect on NRL products at 100oC and 120oC. NRL filled kaolin- alkanolamide at

drying of 120oC shows relatively higher physical cross-linking density. This may be due to to the increase in diffusion of curatives into the NRL which results in the increase of cross-link formation in the films hence the cross-link network are formed more [12].

Fig. 1 The Effect of Drying Temperature on Physical Crosslinking Density of NRL Filled Kaolin Modified Alkanolamide 3.2 Tensile Strength

Fig. 2 The Effect of Drying Temperature on Tensile Strength of NRL Filled Kaolin Modified Alkanolamide From Fig.2, it can be seen that tensile strength of NRL products improved as the amount of alkanolamide increases for both drying temperature. It is found that the maximum tensile strength is at 2 % wt of alkanolamide loading. This shows alkanolamide has good role in increasing interaction between NRL and kaolin. However at 2,5 % wt loading, the tensile strength is significantly decrease. This may be due to occurence of fillers agglomeration leads to decrease in tensile strength. Fig.1 also supports the tensile strength of NRL products as it shows increasing physical crosslink density can also lead to higher tensile strength. It can be observed either that drying NRL products at 100oC gives relative higher tensile strength than drying at 120oC. It seems at more

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higher drying temperature, alkanolamide does not have proper function which resulting in lower tensile strength. 3.3 Elongation at Break

Fig. 3 The Effect of Drying Temperature on Elongation at Break of NRL Filled Kaolin Modified Alkanolamide Fig.3 shows that NRL products dried at 100oC and 120oC does not have any significant changes to its' elongation at break except for additional of 0,5 % wt of alkanolamide. It shows the elongation at break value of each products relative about the same to each other hence it can be concluded that drying temperature does not affect the elongation at break for NRL products. 3.4 M100 and M300

Fig. 4 The Effect of Drying Temperature on M100 of NRL Filled Kaolin Modified Alkanolamide Fig. 4 and Fig.5 shows effect of drying temperature to M100 and M300 for the dried products. In M100, it shows relatively equal result for 0-1 % wt loading of alkanolamide and both drying temperature meanwhile in M300, drying temperature at 100oC gives an increasing value while drying temperature at 120oC gives a fluctuated value. It then has significant increase in NRL filled kaolin modified by

alkanolamide for 1,5 % wt and 2 % wt. This shows that alkanolamide able to give stiffness in NRL products by increasing interaction between NRL and fillers. However it has dramatic drop for 2,5 % wt loading of alkanolamide. This may be due to disturbance in kaolin surface area as the alkanolamide works unproperly.

Fig. 5 The Effect of Drying Temperature on M300 of NRL Filled Kaolin Modified Alkanolamide 3.5 Characterization of Fourier Transform Infra-Red (FTIR) The NRL products which is NRL filled kaolin and NRL filled kaolin-alkanolamide then is characterized by FTIR analysis is shown in Fig. 6. From Fig.6, it can clearly be seen that alkanolamide has important role in modifying kaolin properties as new peak is shown at band 3657,0351 cm-1 which is free –OH groups from alcohols, band 1936,5313 and band 678,9432 cm-1 which are (=C-H) groups from aromatics [13]. This is happened due to intercalation of alkanolamide on kaolin surfaces occurs which results in decreasing the electrostatic attraction between the lamellae by causing an increase in the dielectric constant when the compound penetrate the layer [8].

Fig.6 FTIR Analysis of : (a) NRL Filled Kaolin; (b) NRL Filled Kaolin-Alkanolamide 3.6 Scanning Electron Microscope (SEM) The fracture of NRL products then is analyzed more via SEM which is shown by Fig. 7

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(a)

(b)

Fig. 7 SEM analysis of : (a) NRL Filled Kaolin-Alkanolamide (1 % wt) and (b) NRL Filled Kaolin-

Alkanolamide (2 % wt) with Magnificent 5000x Fig. 7 shows the SEM micrographs of NRL filled kaolin-alkanolamide (a) and (b) (1 % wt and 2 % wt) respectively. It is clearly seen that as amount of alkanolamide increased, the filler with its curatives are distributed more homogenously. Then as the amount of alkanolamide increase, the fillers can be easily agglomerated. This proves why the physical cross-link density increase due to larger specific area formed and smaller particle size of organokaolin which provide better rubber-filler interaction [8].

4. CONCLUSIONS It is observed that utilization of alkanolamide as modifying agent can modify kaolin properties. It is proved from its physical cross-linking density where alkanolamide has important role to form strong cross-link network hence increasing its mechanical properties. The physical cross-link density can also increase by increasing its drying temperature of NRL products.

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Kamaluddin, K. Mahmood (2013), An Assessment of Rice Husk Ash Modified, Marble Sludge Loaded Natural Rubber Hybrid Composites, J. Mater. Environ. Sci., 2013, Vol. 4, No. 2, pp. 205-216.

NRL molecules

Kaolins + Alkanolamide

NRL molecules Kaolins + Alkanolamide

Curatives

Curatives

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[12] H. Harahap, B. Azahari, M.R.H.M. Haris (2007), Effect of Drying Temperature on Tensile Properties of Natural Rubber Latex Films, Proceedings of International Conference On Chemical Sciences, 2007.

[13] D.L. Pavia, G.M. Lampman, G.S. Kriz (2001), Introduction to Spectroscopy : A Guide For Students of Organic Chemistry, 2001. Brooks/Cole Thomson Learning: Singapore, pg. 26.