Effect of Liquid Natural Rubber Addition to the Mechanical Properties of Elastomeric Thermoplastic / Polyethylene Polyblend

Addition of liquid natural rubber (LNR) to elastomeric thermoplastic (ETP)/polyethylene (PE) polyblend has been done. The aim of this research is to study the effect of LNR addition to the ETP /PE polyblend using blending process. The blending process was done by mixing of ETP and PE with composition of 30% and 70% by weight respectively. LNR was added to the ETP /PE with composition of 3%, 5%, and 7% by weight, to form composite materials, refer as PLB-3, PLB-5 and PLB-7. The density of the specimen was measure by picno-meter, the mechanical properties were tested by Stograph R-1, the thermal property was analyzed by Differential Thermal Analysis (DTA) and the microstructure was observed by Scanning Electron Microscope (SEM). The result shows that the melting point of ETP/PE poly-blend increased from near 140oC to near 160oC with addition of LNR, but decomposition temperature decreased. Likewise, the mechanical properties of ETP/PE poly-blend exhibit the improvement after being added LNR. The mechanical properties show a rigid structure with the highest tensile strength of 191 Kg.m-2, and referred as the most optimum composition ETP/PE poly-blend. This condition is reached with addition of 5% by weight LNR showing regular and homogenous microstructure. It can be concluded that the addition of LNR could improve miscibility of ETP/PE, so that a better quality was obtained.


INTRODUCTION
Elastomeric thermoplastic (ETP) represent one of plastic polymer type made from natural rubber and have excess compared to other polymer type, namely do not need crosslink agent, more simple process, nature of better physical and recycle-able (Dahlan, Khairul Zaman A and Ibrahim 2002;Ismail and Suryadiansyah 2002;Sudirman, et al. 2000). Indonesia is one of natural rubber producer, with production of about 1.4 million ton per year. The usage of ETP have especial upon which at car, weapon and plane industry, on that account production of ETP very according to be developed in Indonesia so that can improve natural rubber added (Olk, Pena and Ralf 2004;Deswita et al., 2002).
Currently, the common uses of materials based on ETP/PE reinforced rubber, glass or plastics have broad, propen applications include boats, automobiles, baths, hot tubs, water tanks, roofing, pipes, cladding, casts, external door skins, and sport equipments sectors (Fink 2010). Even more specifically are very attractive for aircraft and aerospace structural parts. However, much of the technology is new and not presented formally in secondary or undergraduate education, and the technology of advanced composites manufacture is continually evolving (Osha, 2010).
Usually ETP are less stable to high temperature and more flexible than other plastic materials and have very low mechanical properties, which are very soft and very brittle in the dry state, so as to be used in industry, such as for cars and aircraft industry accessories are not allowed. However, the ETP is very lightweight and easy to make in a variety of forms. For this purpose, the mechanical properties of the material must be high (Envis 2003;Halimatudahliana, Nasir and Ismail 2001).
One way to improve the mechanical properties and hardness of these materials is to form composite materials. By adding other polymer/copolymer such as polyethylene (PE) which may form a ETP/PE poly-blend they can be improved. In this research, ETP/PE polyblend was added with Liquid Natural Rubber (LNR) as a compatibilizer to form ETP/PE Polyblend-LNR composite materials. In point of view, compatibility among the phases is playing an important role which can be deceived by missing a material of compatibilizer to improve adhesion among the phases. The materials of compatibilizer can be expected to improved homogenity and nature of physics as well as mechanical properties, yielded a preeminent polyblend (Deswita et al. 2008;Mahsuri, Marini and Sudirman 2005;Mashuri et al. 2008;Deswita et al. 2008;Utama et al. 1995).
This research studied the influence of addition liquid natural rubber (LNR) as compatibilizer with variation composition to polyblend of natural rubber based ETP/PE. From this research a better ETP having nature of physical and mechanical properties is expected for materials industry.

Material
Material for this research are polyethylene (PE) and liquid natural rubber (LNR).

Method
ETP resulted from γ-irradiation process was mixed with polyethylene (PE) with comparison % of weight 70:30. The mixing than were added by LNR with composition of 0%, 3%, 5% and 7% by weight, later they called as PLB-0, PLB-3, PLB-5 and PLB-7 respectively (Deswita et al. 2008;Halimatudahliana, Nasir and Ismail 2001). Materials containing of TPE, PE and LNR were then inserted into a Haake (RHEOMIX 3000/3010) owning capacities 250 g processing at 130 o C for 10 minute, for each LNR variation composition (Mahsuri, Marini and Sudirman 2005). The process was confined by pressing use a hydraulic hot press at pressure of 150 Kg.cm -2 followed by hydraulic cold press at pressure of 16 ton. Examination of the specimen was conducted covers mechanical test using Stograph R-1 for tensile, yield strength and elongation at break. The microstructure of the specimen was observed by SEM (Scanning Electron Microscope), while the thermal property was measured by Differential Thermal Analysis (DTA). Synthesis and characterization of ETP/PE polyblend is mentioned schematically in Figure 1.

Thermal Properties
The thermal property of the materials was measured using Differential Thermal Analysis (DTA). The purpose of this measurement is to determine the transition temperature for the conversion of the precursor to ETP/PE polyblend phase which is demonstrated in Figure 2. Based on this Figure 2, it can be seen that there are two different endothermic peaks of each specimens.
The first endothermic peak is near 140 o C for origin specimen (PLB-0), near 161 o C for PLB-3, 163 o C for PLB-5, and 165 o C for PLB-7. These peaks give information about melting point of these materials. The second endothermic peak is near 526 o C for PLB-0, near 495 o C for PLB-3 and near 493 o C for PLB-5 and PLB-7, respectively. These endothermic peaks represent the decompositiontemperature of each of the specimens. It can be seen that the melting point of poly-blend materials increased with addition of LNR to 7% by weight. However, the decomposition temperature of polyblend with LNR content is lower than that of poly-blend origin.
This phenomenon indicates that the content of LNR in the ETP/PE polyblend influenced to changes in the thermal properties of both the melting point and decomposition temperature, see Figure 2. To know the mechanical properties, including yield, tensile and elongation break, the specimen were tested using Stograph R-1 apparatus.

Physical Properties
The result of density measurement is demonstrated at Table 1. It can be seen that the density of polyblend increases with increasing LNR addition. The origin sample (PLB-0) without content LNR, the density is very low only about 0.40 g.cm -3 , and then the density increased to about 0.75 g.cm -3 with increasing the content of 7% by weight LNR. The increasing of sample density can be assumed as increasing of molecular packing due to the missibility improvement.
To determine the effect of density on yield and tensile strength, all the specimens were tested the mechanical and physical properties using Stograph R-1 equipment. While the density of the specimen and variation of the LNR concentration was observed using SEM.

Mechanical Properties
The mechanical properties, including yield and tensile strength and also elongation break of the specimens were tested using Stograph R-1 equipment that avaliable at PTBIN-BATAN. The the mechanical test result was shown in Table  1 for specimen PLB-0, PLB-3, PLB-5 and PLB-7.
Based on the Table 1, it is seen that the mechanical properties of ETP/PE polyblend increase with increasing amount of LNR addition. The specimen with 5% weight of LNR addition (PLB-5) shows yield and tensile strength values of 106 Kg.cm -2 and 91 Kg.cm -2 respectively. This means that the PLB-5 specimen has most rigid specimen compared to the othes. It is shown that high tensile and yield strength values of the PLB-5 specimen represent the optimum variation composition of ETP/PE/LNR polyblend composite materials. To determine visually the surface shape of tested materials, further specimens were observed by SEM, as shown in Figure 3.
It can be concluded that mixing between ETP/PE polyblend and 5% weight of LNR as compatibilizer may form homogenous and high grain ordered composite materials having high mechanical properties.

CONCLUSION
Based on the result of this research, it can be concluded that the process of TPE/PE polyblend with mixture of LNR 0%, 3%, 5% and 7% by weight have succeeded to be conducted. The mixing materials may form TPE/PE polyblend-LNR composite materials. The density of TPE/PE polyblend-LNR composite materials shows higher density and melting point then the TPE/PE poly-blend origin materials, but the decomposition temperature decreased. The mechanical properties of TPE/PE polyblend origin materials increased with increasing filler LNR for all variation composition. The highest mechanical property is reached for 5% weight of LNR filler content. This condition represents the optimum composition of ETP/PE/LNR polyblend showing regular and homogenous microstructure.

ACKNOWLEDGEMENT
The author would like to thank to the Head of Center for Technology of Nuclear Industry materials. That way also thanks to Mrs. Anik S who assist for blending and mechanical test. This work has been supported by Blok Grant Research 2009. Sains Materi Indonesia, Vol.9 No.3 Juni 2008, ISSN 1411-1098, hal. 208-213. Olk, Olaf Pena, and Ralf H. 2004