Effect of Aging on Mechanical Properties of Natural Rubber Latex
Products Filled with Alkanolamide-Modified Cassava Peel Waste Powder
(CPWP)
Hamidah Harahap
1,a, Adrian Hartanto
1,b, Kelvin Hadinatan
1,c, Indra Surya
1,d,
Baharin Azahari
2,e1Department of Chemical Engineering, Universitas Sumatera Utara, Jalan Almamater, Kampus USU
Medan 20155, North Sumatra, Indonesia
2School of Industrial Technology, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia ahamidah_usu@yahoo.com, bjokernostalgic@yahoo.com
ckelvinhadinatan@rocketmail.com, dindradanas@yahoo.com, ebaharin@usm.my
Keywords: Aging, Alkanolamide, Cassava Peel Waste Powder, Natural Rubber Latex, Mechanical properties
Abstract. The effect of aging on mechanical properties of natural rubber latex (NRL) products filled with alkanolamide-modified cassava peel waste powder (CPWP) was studied. CPWP used as fillers was prepared by milling and sieving it until the size of 100 meshes. The powder then was dispersed in a suspension containing water and alkanolamide in order to modify the prepared powders. The dispersion system of 10 pphr (part per hundred of rubber) then was added into NRL matrix followed by pre-vulcanization at 70°C for 10 minutes. The NRL compounds were casted into films by coagulant dipping method and dried at 120°C for 10 minutes. Afterwards, the films were allowed to cool at room temperature for 24 hours before being aged in a circulation of hot air for 24 hours at 70°C. The properties such as tensile strength, tensile modulus, and elongation at break were evaluated between the aged samples and the unaged samples. From this study, it showed that the aged films have increasing value of tensile strength and tensile modulus while the value of elongation at break decreases. These data are supported by Scanning Electron Microscope (SEM) micrographs which indicate that the change of morphology in NRL films occurs before and after aging.
Introduction
Natural rubber latex (NRL) is one of polymers that are widely used daily life in household and industry application. The products such as gloves, rubber thread, balloons, catheters, bandage, condoms, inflatable stethoscope have unsaturated part of cis-1,4-polyisoprene with some good properties, such as high strength, outstanding resilience, and high elongation at break [1-2]. Generally, to improve the quality of NRL products, they are commonly incorporated with inorganic and organic fillers. However, the addition of fillers has its limitation since some of them are polar while the rubber matrix is nonpolar. Therefore, it is necessary to modify the filler. Several studies reported that modification of fillers succeeds in enhancing the quality of filled rubber [3-5].
During storage and service, NRL products will also encounter the occurrence of aging. According to Colclough et al. [6], a main-chain scission or crosslink scission occurs during the aging period, which lead to the cleavage of vulcanizates network structure and various changes of NRL properties can occur in an elastomer component as a result of aging [7].
In this work, the effect of aging on mechanical properties of NRL products filled with alkanolamide-modified cassava peel waste powder (CPWP) was investigated before and after aging for 24 hours at 70oC. The NRL was pre-vulcanized with CPWP as filler and different content of
alkanolamide as modifier and the products were then cast into film by dipping process. The objective of this study is to observe and compare the mechanical properties of unaged and aged films. The morphology of the films was also examined via Scanning Electron Microscope (SEM).
Experimental Procedure
Materials. High Ammonia Latex with 60% of dry rubber content was obtained from a local market in Medan, Indonesia. Cassava peel waste (CPW) was obtained from cassava cracker factory in Medan,
Indonesia and dried at 100 °C for 24 hours. The dried peel was milled and sieved until the size of 100 meshes was obtained. The supporting chemical substances such as potassium hydroxide (KOH), sodium hydroxide (NaOH), acetic acid (CH3COOH), calcium nitrate tetrahydrate (Ca(NO3)2.4H2O),
toluene (C6H5CH3), chloroform (CHCl3), diethanolamine ((C2H4OH)2NH), sodium chloride (NaCl),
diethyl eter ((C2H5)2O), methanol (CH3OH), sodium methoxide (CH3ONa), sodium sulphate
(Na2SO4) were used in this study. The materials were laboratory grade (MERCK) and were purchased
from CV. Multi Kreasi Bersama, Medan, Indonesia. The curatives for pre-vulcanization system of NRL consist of sulphur as crosslinking agent, zinc oxide (ZnO) as activator, zinc diethyldithiocarbamate (ZDEC) as accelerator, and antioxidant (AO). The curatives were obtained from Farten Technique (M) Sdn Bhd, Pulau Penang, Malaysia.
Methods. The preparation of alkanolamide followed the procedure described by Surya et al [8]. The fillers of 10 pphr (part per hundred of rubber) were prepared by dispersing CPWP inside the ball mill which consists of water and alkanolamide. The alkanolamide used was 0; 0.5; 1.0; 1.5; 2.0; 2.5 wt% (weight percent). Table 1 provides designated codes for NRL films.
Table 1. Designated Codes of NRL films Table 2. Formulation for NRL Compounds pre-vulcanized system was done at 70°C in order to achieve the curing of the system. During this period, with interval time of 3 minutes, 3 drops of mixing system were taken as a sample and tested by 5 drops of chloroform to observe whether the system has cured or overcured. The pre-vulcanization was stopped after the chloroform number has reached number 3.
The mixture then was left for 24 hours in order to release the bubbles into the surface. As the top layer of latex did not show any bubbles, a thin stainless steel plate former (125 mm x 125 mm x 0.5 mm) was dipped into latex system. The plates were washed by 10% potassium hydroxide solution and 10% acetic acid solution then continued by water to release the impurities on the plates. Then it was coagulated by dipping it in 10% calcium nitrate solution. The plates then were dried in the oven by hanging it. After it had dried, the plates were dipped in the latex system and the dwell time was set at 5 seconds. Finally, the film formers were hanged inside oven at 120°C for 10 minutes. Afterwards, the films were allowed to cool at room temperature for 24 hours before being aged in a circulation of hot air for 24 hours at 70°C.
The films were tested in accordance with ASTM D412 using GOTECH AL-7000M with cross-head speed of 500 mm/min. The tensile strength, elongation at break, tensile modulus such as modulus at 100% elongation (M100), and modulus at 300% elongation (M300) were evaluated. Later,
the morphological study in the fracture of the unaged and aged films was examined via Scanning Electron Microscope (SEM) JEOL-JSM 6360-LA.
Results and Discussion
Figure 1 shows that specimen C-0 and C-1 being aged, the tensile strength decreases due to the effect of heat that damages the molecular chain of unsaturated polymer and initiates the movement of the filler within the matrix, hence degradation occurs inside of the polymer matrix which lead to the breaking of the filler, filler-rubber, and rubber-rubber bonding [7,9]. Meanwhile, the additional of alkanolamide increases the value of tensile strength from specimen C-2 to C-6 as the alkanolamide success in modifying the interface layer of CPWP and result in improved interaction of matrix-filler.
Figure 5. SEM Micrograph of (a) Uanaged C-1; (b) Aged Sample C-1; (c) Unaged Sample C-2; (d) Aged Sample C-2; (e) Unaged Sample C-6; (f) Aged Sample C-6
It can clearly be seen also that aging improved the tensile properties from specimen C-2 to C-6. It should be noticed that alkanolamide is a chemical that behaves like surfactant properties. The alkanolamide will help the formation of few new crosslink in rubber matrix which is known as post-curing during the aging period [10]. Crosslink formation will hold on stress when tensile test was done into the natural rubber latex products. Figures 2 and 3 show that all specimens have the M100 and
Figure 1. Tensile Strength of Unaged
and Aged Vulcanizates Figure 2. MVulcanizates 100 of Unaged and Aged
Figure 3. M300 of Unaged and Aged
Vulcanizates Figure 4.and Aged Vulcanizates Elongation at Break of Unaged
Tear Lines
a b c
d e f
Tear
Lines Tear
Lines
Tear
Lines Tear
Lines
M300 value increase after aging. During aging, the tensile modulus increases as the main-chain
scission takes place and effect of cross-linking predominates [11]. While the specimens with alkanolamide have the tensile modulus increase due to the stiffening effect given by alkanolamide that modify the interface between NRL and CPWP. As the NRL becomes stiffer, the mobility of rubber chain will also be restricted and results in decreasing elongation at break which is shown in Fig. 4. Figure 5 displays the SEM of NRL fracture for specimens C-1, C-2 and C-6. It can be observed that the fracture surface tends to become smooth after aging. Also, the tear lines become more randomly after the samples were aged. This observation is similarly found on the fracture surface of ethylene-propylene-diene (EPDM) Rubber [12].
Conclusion
The result shows that aging of NRL films increases the tensile strength and tensile modulus while the elongation at break decreases with the additional of alkanolamide, which modified the interface layer of CPWP and enhance the matrix-filler interaction. There is also a barrier effect on the surface of NRL films due to the presence of alkanolamide.
References
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Effect of Aging on Mechanical Properties of Natural Rubber Latex Products Filled with Alkanolamide-Modified Cassava Peel Waste Powder (CPWP)
