Investigation on the use of coconut shell powder replacing carbon black as filler in natural rubber
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Date
2015
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Uva Wellassa University of Sri Lanka
Abstract
Natural rubber is an elastomer which mainly consists of cis-1, 4-polyisoprene. It is used in a wide
range of applications, mainly in tire manufacturing. Vulcanizates of natural rubber are reinforced by
incorporating fillers such as carbon black and silica.
There is a demand in replacing these fillers by fillers made of natural materials such as coconut shells,
since natural filler possesses environment friendly processing, with no wear of tooling and no skin
irritation (Bhaskar and singh, 2013). Coconut shell powder (CSP) is a natural lignocellulosic material
which has been used as reinforcing natural filler in a broad range of applications such as building
materials, marine cordage, fishing nets, furniture, and other household appliances (Sapuan and
Harimi, 2003). The presence of highly polarized hydroxyl groups on the surfaces of the
lignocellulosic fillers makes it difficult to achieve strong interfacial bonding with non-polar polymer
matrix. As a result, lignocellulosic fillers show poor mechanical properties in polymer composites.
However, the interfacial bonding can be improved by employing surface treatments methods
including alkaline treatment, esterification and silane treatment (Egwaikhide et al., 2007). In the
current research it was expected to improve the properties of natural rubber vulcanizates by
incorporating CSP and surface modified CSP replacing carbon black filler.
Methodology
Coconut shells were crushed into powder and it was dried in an oven at 80 ºC for 24 hours
(Tengkufaisal et al., 2010). The powder having the particle size range of 150 µm to 300 µm was
separated by sieving and used for this research (Koayseong chun et al., 2013).
Surface modification of coconut shell powder was achieved by acid treatment. The powder was
soaked in an aqueous acetic acid solution with powder to solution ratio of 1g/20 l and the mixture
was stirred for 1 hour. The treated powder was separated by filtering. It was washed with distilled
water and dried in an oven at 80 ºC for 24 hours. Two sets of natural rubber (RSS 1) compounds
were prepared according to the tire inner layer compound formulation by milling the ingredients. A
series of compounds were prepared by varying the relative amounts of carbon black (N330) and
untreated CSP. Another series of compounds were prepared by varying the relative amounts of
carbon black and treated CSP. The reference compound was prepared by adding carbon black.
Processing characteristics of prepared compounds were investigated by using a Rheometer.
Vulcanized samples were prepared using a hydraulic press maintaining the temperature at 150 C for
the relevant cure time determined from rheographs. Tensile properties of the samples were
determined following ASTM D412 using Intron machine model 2713. Abrasion test was performed
on the samples following DIN 53516 using Hampden machine model APH-40 and the hardness test
was performed following IRHD using Elastocon machine.
Result and Discussion
The effect of filler composition on tensile strength of the samples of natural rubber vulcanizates is
shown in Figure 01. In the sample designation, the letters C, U and T stand for the type of filler,
carbon black, untreated CSP and treated CSP, respectively. In addition, the amount of each type of
filler in phr is given by the number following each letter of designation. The sample with only carbon
black filler shows the highest tensile strength. As the relative amount of untreated and treated CSP
filler is increased the tensile strength decreases. This is due to the weak interfacial adhesion, low
wettability, and poor dispersion between hydrophilic CSP and hydrophobic rubber matrix with
compared to carbon black. The samples having treated CSP show a higher tensile strength than those
having untreated CSP except the sample C90U60. This behaviour attributed to the improved
interfacial adhesion and better dispersion between treated CSP and Rubber.
Description
Keywords
Science and Technology, Technology, Export Agriculture, Rubber Production, Rubber Technology