Influence of Modified Cassava Peel Waste (CPW) Loading on Tensile Properties of Natural Rubber Latex (NRL) Products

Advanced Materials Research Vol. 1119 (2015) pp 342-346 © (2015) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.1119.342

Submitted: 2015-04-02 Accepted: 2015-04-02
Online: 2015-07-29

Influence of Modified Cassava Peel Waste (CPW) Loading on Tensile Properties of Natural Rubber Latex (NRL) Products
Hamidah Harahap1,a, Kelvin Hadinatan1,b, Adrian Hartanto1,c, Elmer Surya1,d, Indra Surya1,e, Hanafi Ismail2,f
1Department of Chemical Engineering, University of Sumatera Utara, Jalan Almamater, Kampus USU Medan 20155, North Sumatra, Indonesia
2School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia
ahamidah_usu@yahoo.com, bkelvinhadinatan@rocketmail.com, cjokernostalgic@yahoo.com
delmer.surya@gmail.com, eindradanas@yahoo.com, fhanafi@eng.usm.my
Keywords: Natural Rubber Latex, Cassava Peel Waste, Alkanolamide, Tensile Properties, Scanning Electron Microscope
Abstract. Cassava peel is one of agricultural waste that abundantly found in environment. One approach to manage this waste is to apply it as filler in natural rubber latex. In this work, the cassava peel waste (CPW) was powdered and dispersed in alkanolamide-water dispersion system to modify its surface. The amount of fillers used was 0, 5, 10, 15, 20 and 25 phr (part per hundred rubber) and loaded in natural rubber latex (NRL) formulation system. The products then were formed by dipping method after the NRL formulation was pre-vulcanized at 70oC. The observed parameter includes crosslink density, tensile strength, tensile modulus and elongation at break. Scanning Electron Microscope (SEM) was used to study the morphology of tensile fracture in NRL film. The results show that 10 phr loading of modified fillers increases the crosslink density, tensile strength, and tensile modulus but decreases the elongation at break. SEM study also reveals that higher filler loading above 10 phr will create the agglomeration in rubber matrix.
Introduction
There are several attempts to replace the utilization of conventional fillers such as carbon black, silica, and calcium carbonate in rubber products. One of alternative method that could be used is by employing agricultural waste as fillers. In Indonesia, one of agricultural products that has abundant waste is cassava. Many industries particularly utilize cassava as raw material to manufacture food based product. The unused peel from cassava is considered to be the waste from industrial processing. In reality, the cassava peel can be treated further as an ingredient in fertilizers, fodder, and snacks. However, it might be interesting if this peel could be used as fillers in rubber products because we can convert the waste into valued product to solve environmental issues. Several agricultural wastes such as rice husk, pineapple leaf, bamboo waste, and peanut shell has been used as fillers in rubber matrices as reported in previous studies [1]-[5].
In this work, cassava peel waste (CPW) was milled into powder with size of 100 mesh. In addition, modification of the surface properties of CPW powder is still required to enhance the rubber-filler interaction because the interfacial adhesion between rubber matrix and fillers plays an important role in enhancing the required mechanical properties [6]. Therefore, we introduced alkanolamide as the modifier for CPW surface for compounding with natural rubber latex (NRL) and curatives. Alkanolamide is a nonionic surfactant that commonly used as an ingredient in manufacturing of detergents. Each of latex films was filled with alkanolamide-modified CPW. The physical properties such as crosslink density and the tensile properties such as tensile strength, tensile modulus, and elongation at break were evaluated. The morphology of latex films were also observed by Scanning Electron Microscopy (SEM).

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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 mesh 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 modifier, alkanolamide followed the procedure described by Surya et al [7]. The

CPW was modified by dispersing 10 wt% of it in the ball mill which consists of water 89 wt% and

alkanolamide 1 wt% (wt% = weight percent of total dispersion system). The milling was operated for

24 hours in room temperature. From the dispersion system, the fillers were taken 0, 5, 10, 15, 20, and

25 pphr (part per hundred rubber) to be incorporated in latex. Table 1 shows the formulation of NRL

compounding.

Table 1. Formulation for NRL Compounds Ingredients


Ingredient

Composition (phr)

60% High Ammonia Latex 100

50% Sulphur

1.8

50% ZDEC

1.8

30% ZnO

0.5

50% Antioxidant


1.2

10% KOH

1.8

10% Fillers

0; 5; 10; 15; 20; 25

The pre-vulcanization took at 70oC. During pre-vulcanization, it should be carefully noticed the

interval time. For each 1 minute, 3 drops of mixing system were taken and tested by 5 drops of

chloroform to observe whether the system has reached chloroform number 3 (form of non-tacky

agglomerates). If it has reached the mentioned number, then the pre-vulcanization was terminated.

The mixture then was opened up for 24 hours to allow the bubbles escaped from the surface.


Meanwhile, the plate formers for dipping system (125 mm x 125 mm x 0.5 mm) were prepared by

washing it with sodium hydroxide and acetic acid, then coagulating it with calcium nitrate to release

the impurities of the plates. The plates then were dried in the oven. After it had dried, the plates were

dipped in the latex system and the dwell time was set at 5 seconds. The casted films were vulcanized at 120oC for 20 minutes.

The crosslink density of the films was evaluated using the equilibrium swelling in toluene method

in accordance to ASTM D-6814. The calculation was done using Flory-Rehner equation. The tensile

test of films were tested in accordance to ASTM D412 and carried out by GOTECH Al-7000M

Universal Testing Machine with crosshead speed of 500 mm/min. The fracture of vulcanizates was

examined by Scanning Electron Microscope JEOL- JSM- 6510LV.

Results and Discussion

Fig. 1 shows the influence of modified CPW on crosslink density of natural rubber latex products. The figure shows an increasing value of crosslink density with the increment of filler loading. It can

344 Key Engineering Materials V
be seen that NRL with 10 phr filler loading has the highest crosslink density. When the modified fillers were incorporated, the interaction of latex-CPW increases due to the contribution of alkanolamide that improved interfacial adhesion between rubber matrix and filler. Alkanolamide is a material based surfactant that has long carbon chain. This material might form a “bridge” that grasps matrix and filler together, hence the crosslink will be strengthened due to this contribution. The additional filler loading over 10 phr might lead to the deterioration of crosslink, thus the crosslink density value decreases.
Fig. 2 illustrates the similar trend with Fig. 1. When modified CPW succeed in strengthening crosslink network, the tensile strength will also improve as there is a good interfacial adhesion between NRL and modified CPW. This shows that modified CPW has reinforcing effect when it was incorporated in latex matrix. The filler addition over 10 phr will result in decreasing value of tensile strength. This might be due to the occurrence of agglomeration in the latex films as it will be explained further in SEM study.
Fig. 3 presents the tensile modulus of modified CPW filled NRL. From this figure, it can be seen that value of modulus at 100% elongation (M100) and modulus at 300% elongation (M300) increased with the increment of modified CPW loading. When the filler was introduced in the rubber matrix, the mobility of rubber particles will be restricted and rubber chain will lose its elasticity. This will result to more rigid latex films.
Fig. 4 shows the influence of modified CPW on elongation at break of natural rubber latex products. From this figure, it can be seen that there is decreasing trend of elongation at break with the addition of modified CPW. Although the CPW has been modified by alkanolamide, it might still have stiffening effect due to the presence of lignin in the CPW. Lignin is a chemical that cause the stiffness of organic materials [8]. This stiffness will lead to the limitation of extension and the decreasing value of elongation at break when more filler was loaded.

Fig. 1. Crosslink Density of Modified CPW-filled Natural Rubber Latex

Fig. 2. Tensile Strength of Modified CPW-filled Natural Rubber Latex

Fig. 3. Tensile Modulus of Modified CPW-filled Natural Rubber Latex

Fig. 4. Elongation at Break of Modified CPW-filled Natural Rubber Latex

Fig. 5 shows the morphology of SEM study. In Fig. 5(b), it can be seen that the filler distribution is not dispersed well in rubber matrix, hence it has small matrix tearing because several zone in matrix is

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not occupied by the fillers. When the fillers were loaded at 10 phr (Fig. 5(c)), it shows that the fillers are well distributed in matrix and gives a smooth surface. This is due to the promotion of alkanolamide that helps improving the interfacial adhesion between rubber-filler. In addition, it will also generate strong matrix tearing in rubber matrix that improves its resistance to the tensile failure. The similar results were also reported by Ooi et al [6] and Ismail et al [8-9]. Fig. 5(d) and (e) show the addition of 15 and 20 phr filler loading initiates the particle agglomeration in matrix. The surface will be coarser and reduce the matrix tearing. In Fig. 5(e), it can clearly be seen that addition of 25 phr filler loading will lead to the agglomeration of particles in massive extent, thus it will result in decreasing properties of NRL products.

(a)
Matrix Tearing

(b)

CPW Filler

CPW Filler
(c)
Agglomeration Matrix Tearing

(d)

Matrix Tearing

Matrix Tearing


CPW Filler

(e

CPW Filler

Agglomeration

CPW Filler
(f)
Matrix Tearing Agglomeration

Fig. 5. SEM Analysis of: (a) Cassava Peel Waste (CPW); (b) NRL/CPW 5 phr; (c) NRL/CPW 10 phr; (d) NRL/CPW 15 phr; (e) NRL/CPW 20 phr; (f) NRL/CPW 25 phr
Conclusion The utilization of cassava peel as one of agricultural waste could be carried out by applying this waste as fillers in natural rubber latex. If the filler was further modified by alkanolamide, then it would help

346 Key Engineering Materials V
improving the interfacial adhesion between rubber-filler. The amount 10 phr of filler loading is reported to be the optimum value for the increasing properties of latex products such as crosslink density, tensile strength and tensile modulus because it has the greatest matrix tearing. Higher filler loading will create the agglomeration of particles that result in decreasing properties of rubber products.
References
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[2] N. Lopattananon, K. Panawarangkul, K. Sahakaro, B. Ellis. Performance of Pineapple Leaf Fiber-Natural Rubber Composites: The Effect of Fiber Surface Treatments. J Appl Polym Sci, Vol.102, (2006), pg. 1974-1984.
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[7] I. Surya, H. Ismail, A.R. Azura. Alkanolamide as an accelerator, filler-dispersant and a plasticizer in silica-filled natural rubber compounds. Polym Test, Vol. 32, (2013), pg.1313-1321.
[8] H. Ismail, N.F. Omar, N. Othman. The Effect of Kenaf Fibre Loading On Curing Characteristics and Mechanical Properties of Waste Tyre Dust/ Kenaf Fibre Hybrid Filler Filled Natural Rubber Compounds. BioResources, Vol.6, No.4, (2011), pg.3742-3756.
[9] H. Ismail, K. Muniandy, N. Othman. Fatigue Life, Morphological Studies, And Thermal Aging of Rattan Powder-Filled Natural Rubber Composites as A Function of Filler Loading and A Silane Coupling Agent. BioResources, Vol.7, No.1, (2012), pg.841-858.

Key Engineering Materials V 10.4028/www.scientific.net/AMR.1119
Influence of Modified Cassava Peel Waste (CPW) Loading on Tensile Properties of Natural Rubber Latex (NRL) Products 10.4028/www.scientific.net/AMR.1119.342