Visco-elastic properties of OMMT filled fractioned bleached crepe rubber
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Date
2015
Journal Title
Journal ISSN
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Publisher
Uva Wellassa University of Sri Lanka
Abstract
Natural Rubber (NR) latex tapped from Hevea brasiliensis converts into an important
engineering material for different applications. NR latex pale crepe, the purest form of NR
produced by Sri Lanka, is mainly used in pharmaceutical and surgical applications, infant toys,
food contact rubber articles and adhesives, (Senevirthne and Kumara, 2003). Natural Rubber has
a higher greenstrength as but it is soft and has lower dimension stability (Cohan and Spielman,
1948) which is one of the major draw backs in NR for engineering application.
Recently, Nanoclays such as montmorillonite clay are attracted as an alternative filler to achieve
the reinforcement of rubber compounds by replacing conventional fillers (Ratnayake and Peiris,
2010). Study the effect of Organo-montmorillonite (OMMT) on the visco elastic properties of
fractioned bleached crepe rubber will helpful for the advancement of the raw rubber industry as
value addition. In this study, OMMT dispersion in the rubber matrix has studied not only by
Mooney viscosity and stress relaxation properties but also by the physical properties of
vulcanizates. Therefore this study may help to have an advantage for the development of crepe
rubber industry and product manufacturing industry in Sri Lanka.
Material and Methods
NR field latex was obtained from NR processing factory at Rubber Research Institute,
Dartonfield, Agalawaththe. Montmorillonite clay modified with quaternary alkyl ammonium salt
(OMMT)was used as the nanofiller. Other general chemicals and laboratory equipment were
obtained from Rubber Research Institute, Rathmalana.
Initially, 5%(w/w) aqueous dispersion of OMMT was prepared using a surface active agent as a
dispersing agent. Latex mixing/intercalation method(Gatos and Kocsis, 2010) was carried out to
prepare OMMT filled fractioned bleached crepe rubber (OFBCR). Dry rubber content (DRC) of
fractionated bleached latex was diluted up to 10% and subsequently OMMT dispersion was
incorporated to latex samples at OMMTloading from 0 to 8 phr with an interval of 2 phr, with
simultaneous stirring.Standard latex crepe manufacturing procedure was adopted to prepare
OFBCR (Senevirthne and Kumara, 2003). Laces were dried in the drying tower at 34°C for three
days. Complete randomized design was applied to assign treatments, T 0(0 phr), T2 (2 phr), T4 (4
phr), T6 (6 phr) and T8 (8 phr).
The NR was characterized based on DRC and the OMMT was characterized by the ash content.
Money viscosity and stress relaxation of OFBCRs were measured according to the [ISO/R 289-
1963] by the Ektron Mooney viscometer. Then the OFBCR samples were compounded
according to the pre-determined formulation. Curing characteristics of the OFBCR samples were
measured by using MDR 2000 (moving die rheometer, M/S Alpha Technologies, USA) at
150°C according to the ISO 3417:2008 procedure. OFBCR samples were moulded by hydraulic
hot press at 150°C temperature and 20MPa pressure for optimum cure time derived from the
cure characteristics data.The tensile properties of OFBCR samples were determined by “Instron
3300 Series” material testing machine at a crosshead speed of 500 mm/min as per ISO 37:2011.
The hardness of the samples were determined using Elastocon bares digi hardness tester
according to the ISO 48:2010. Compression set at constant strain was measured according to
ISO 815-1:2008 test method andtear strength of OFBCR samples were determined by “Instron
3300 Series” material testing machine at a crosshead speed of 500 mm/min according to ISO 34-
1:2011. All tests were carried out at 27±2°C and each test was replicated at least 3 times. Data
were analyzed by using the Minitab 16 statistical software with the use of General Liner Model
(GLM) with Tukey’s all pair wise comparison tests at 95% confidence interval.
Results and Discussion
Field latex used for the preparation of nano crepe rubber showed the dry rubber content of 30%.
OMMT clay has modified with quaternary alkyl ammonium salts. The ignition weight loss of
OMMT is 43%–48%. Ash content of clay is 52%-58%. This ash content represents the amount
of silicates and other inorganic metal amount in the clay. Ignition weight loss is correlated to the
amount of quaternary ammonium alkyl modifier and adsorbed moisture amount in the clay.
Mooney viscometer is an instrument to measure the 'stiffness' of uncured compounds, the result
of that viscosity is called as Mooney viscosity at ML 1+4 (100°C). Mooney stress relaxation
coefficient is the slope of the power law model when it is in logarithmic scale (log M = a(log t)
+ log k) where M- torque units from the Mooney stress relaxation test, k- a constant equal to
torque 1 s after the rotor has stopped, ‘a’- an exponent that measures the rate of stress relaxation
and t- testing time. Also elasticity of rubber material is inversely proportionate to the
‘a’andlower elasticity improves the mixing of rubber and processing, especially extrusion and
calendaring. Malac J., (2009).
Clay loading level (phr) has significantly affected to the Mooney viscosity expressed as ML
(1+4) 100°C of OFBCR samples (p-0.000). Only T6 and T8 has not indicated a significant
difference (p-0.0569) between them with respect the Mooney viscosity but all other treatment
levels are significantly different among (p-0.000). Mooney viscosities for T0, T2, T4, T6 and T8
are presented in Figure 1. The reason for the reduction of Mooney viscosity is, when increasing
the OMMT loading, the plasticization of rubber material by OMMT and may possibly be the
chain slippage over the clay platelets (Kader et al., 2010).
As reported in Figure 2, the stress relaxation coefficient has increased up to 4 phr and there after
it reduces. The maximum stress relaxation coefficient has indicated at the 4 phr clay loading
level, therefore, it can be concluded that OFBCR with 4 phr OMMT clay loading has a better
processability than other samples. Long relaxation times and high amplitudes of stress relaxation
suggest the mechanism of structural relaxation involving large-scale displacements of isolated
clusters of nanoparticles within the rubber matrix and vice versa (Dick, 2010).
Description
Keywords
Agriculture, Export Agriculture, Crop Production, Rubber Technology, Rubber Production, Natural Rubber