MONTMORILLONITE CLAY FILLED SKIM NATURAL RUBBER NANOCOMPOSITE AS A VALUE ADDED RAW RUBBER U.N Ratnayake 1 L.D.A.N Kumari 2 , A K W Prasad 1 W D R Wijesinghe 2 ( 1 Rubber Research Institute, Telawala Road, Ratmalana, Sri Lanka, 2 Department Chemistry, University Sri Jayewardenepura, Nugegoda, Sri Lanka. Correspondence: un_ratnayake@yahoo.co.uk ABSTRACT: Skim natural rubber (SNR), a by-product of centrifuged latex manufacturing process, contains a higher percentage of non-rubber substances, especially nitrogenous substances. SNR, known as a low quality grade of raw rubber, limits the industrial applications because of the inherited unfavourable curing characteristics and inconsistent raw rubber properties especially green strength and lower resistance to thermo-oxidative degradation. Montmorillonite (MMT) clay filled SNR was prepared by incorporating aqueous dispersion of MMT clay into skim natural rubber latex followed by a coagulation. The nanostructures of MMT clay in the skim rubber was evaluated with X-ray diffraction technique while process based characterization and un-cured tensile measurements were used to study the effect of the nanostructured of MMT clay on viscoelasticity and green strength respectively. Plasticity Retention Index (PRI), which measures the resistance to thermo-oxidative degradation, data have shown that montmorillonite clay loading has increased the thermo-oxidative stability of the skim rubber. Improved green strength of MMT clay filled SNR nanocomposite has revealed the presence of MMT nanostructures and its effect on strain-induced crystallization. However, processability, as measured with low shear strain rate viscoelastic behaviour, is affected by the added MMT clay. With this latex compounding methodology, a novel MMT clay filled SNR with improved physical properties, especially green strength and resistance to thermo-oxidative degradation has been developed as a value added raw rubber for different applications. Keywords: Skim natural rubber, montmorillonite clay, green strength, thermo-oxidative degradation, nanocomposite, Mooney Viscosity INTRODUCTION Skim natural rubber latex, a protein rich by-product of centrifugation process of natural rubber (NR) latex containing about 4-7 % dry rubber content and large quantities of non- rubber substances, converts into skim natural rubber (SNR), known as a lower grade of NR, with acid coagulation (Tillekeratne at al., 2003). As a result of less percentage of dry rubber and higher percentage of nitrogen rich non-rubber substances, characteristic features of natural rubber such as higher strength and resilient, resistance to thermo-oxidation and viscoelasticity/processability are not favourable for most of the applications in comparison to good quality raw rubbers like NR latex crepe and Ribbed Smoked Sheet (RSS). However, continuous attempts have been made to improve the quality of SNR and thereby make suitable for wide range of applications (Ismail and Veerasamy, 2011, Alex and Nah, 2006, Rattanaphan at el.,2011). In general most of the applications, NR requires reinforcement with particulate materials and recently, it was realized the potential of nano-scale materials (i.e. nanofillers) for reinforcement of NR as an alternative for conventional reinforcing material especially carbon black and silica (Arroyo at el., 2003, Aarasiri at el., 2013). Recent past, montmorillonite (MMT) clay, which belongs to 2:1 layered silicate has been identified as a potential reinforcing nanomaterial for preparing rubber nanocomposites because of a higher surface area to volume ratio of MMT clay platelets and its ability to surface modification through different methodologies (Galimberti, , 2012)