The present study includes compounding of Low density poly ethylene (LDPE), Recycled Low density Polyethylene(R-LDPE) with Sugarcane Bagasse Fibre (SBF) and evaluation of the composite properties. The LDPE-R.LDPE(50:50%) / Bagasse composites have been prepared in a co-rotating Twin Screw Extruder. 4 formulations were taken as (0 %, 5%, 10% and 15%) of Bagasse with LDPE - R.LDPE in the ratio of 50:50 and one R.LDPE 100%- without Bagasse. The extruded strands has been cut into pellets and injection moulded to make test specimens. The assessment of interaction between polymer matrix and fibres has been studied by Mechanical (Tensile Strength, Elongation at break, Tensile modulus, Impact strength, Hardness), Thermal (Melt flow index) and Physical (Density) properties of the composite were evaluated and reported. The mechanical properties such as Tensile strength, Elongation at break, Impact strength are decreased and Tensile modulus, Hardness are increased by the addition of LDPE-RLDPE with bagasse. Melt Flow Index is also decreased. The properties were uniformly changed and hence the Glycerol compatibilizes the LDPE/RLDPE and bagasse materials.
Key words: LDPE/Recycled LDPE, Bagasse, Twin Screw Compounding, Mechanical/ Thermal properties
RECYCLING of plastics in India is not organized in a well planned manner. PE is the largest consuming plastics materials which should be effectively recycled, and unless properly not recycled, there will be large environmental pollution and more difficulty for the solid waste management and its disposal during land-filling. Since these polymers are not inherently photo degraded or bio-degradable and it will take millions of years to degrade into small fragments. Hence, incorporation of bio-degradable polymeric additives are more important which accelerate their disintegration and degradation of the plastics materials with a short period of time.
The use of composite materials dates from centuries ago and it all started with natural fibres. During the sixties, the rise of composite materials began when glass fibres in combination with tough rigid resins could be produced on large scale. During the last decade there has been a renewed interest in the natural fibre as a substitute for glass, motivated by potential advantages of weight saving, lower raw material price and 'thermal recycling' or the ecological advantages of using resources which are renewable. On the other hand natural fibres have their shortcomings and these have to be solved in order to be competitive with glass. Natural fibres have lower durability and lower strength than glass fibres. However, recently developed fibre treatments have improved these properties considerably. To understand how fibres should be treated, a closer look into the fibre is required.
India, endowed with an abundant availability of natural fibres such as Jute, Coir, Sisal, Pineapple, Ramie, Bamboo, Bagasse, Banana etc. has focused on the development of natural fibre composites primarily to explore value-added application avenues. Such natural fibre composites are well suited as wood substitutes in the housing and construction sector. The development of natural fibre composites in India is based on two pronged strategy of preventing depletion of forest resources as well as ensuring good economic returns for the cultivation of natural fibres.
The use of natural fibre for the reinforcement of the composites has received increasing attention both by the academic sector and the industry. Natural fibres have many significant advantages over synthetic fibres. Currently, many types of natural fibres have been investigated for use in plastics including flax, hemp, jute, straw, wood, rice husk, wheat, barley, oats, rye, sugarcane and bamboo, grass, reeds, kenaf, ramie, oil palm empty fruit bunch, sisal, coir, hyacinth, pennywort, kapok, paper mulberry, raphia, banana fibre, pineapple leaf fibre and papyrus. Thermoplastics reinforced with special wood fillers are enjoying rapid growth due to their many advantages; lightweight, reasonable strength and stiffness.
Due to the light weight, high strength to weight ratio, corrosion resistance and other advantages, natural fibre-based composites are becoming important composite materials in building and civil engineering fields. In case of synthetic fibre based composites, despite the usefulness in service, these are difficult to be recycled after designed service life. However, natural fibre based composites are environment friendly to a large extent.
The developments in composite material after meeting the challenges of aerospace sector have cascaded down for catering to domestic and industrial applications. Composites, the wonder material with light-weight, high strength-to-weight ratio and stiffness properties have come a long way in replacing the conventional materials like metals, wood etc. The material scientists all over the world focused their attention on natural composites reinforced with Jute, Sisal, Core, Pineapple, etc. primarily to cut down the cost of raw materials.
Sugarcane Bagasse, an abundant agricultural lingocellulosic by product is a fibrous residue of canes stalks left over after crushing and extraction process of the juice from sugarcane. About 54 million dry tons of bagasse is produced annually throughout the world. Among the agro-industrial residue diverse, sugarcane bagasse is detached to be a residue widely generated in high proportions and contains cellulose ( 46 %), hemi-cellulose ( 24.5%), lignin (19.5%), fat and waxes (3.5%), ash (2.4%), silica (2%) and other elements (1.7%). Thus the utilization of cellulosic materials in production of polymeric composites is attractive particularly because of low cost and one method of production of value added products (1-7).
The combination of LDPE-RLDPE with Sugarcane Bagasse Fibre is selected in order to evaluate the properties to be used in engineering application with cost reduction.
Materials and methods
Commercially available injection moulding grade LDPE has been procured from Indian Oil Corporation Limited and the properties of which are given in the Table 1(8).The RLDPE is also collected from local vendors and their properties are given in Table 2. Sugarcane Bagasse fibres are collected from External sources and the reported properties are given in Table 3. Commercially available glycerol is procured from Diucon laboratory, Chennai. Its molecular weight is 92.09 & its weight per ml is 1.255-1.260.
Twin screw compounding, testing and product development
The LDPE material was blended with sugarcane Bagasse fibre in five formulations such as (0 %, 5%, 10% and 15%) of Bagasse with LDPE and R.LDPE in the ratio of 50:50 and R.LDPE 100% without Bagasse. The temperature of 160 to 195oC was used for melt blending. The extrudate was cut in the cutter and granules were made. These granules were injection moulded into tensile, flexural and impact specimen and test were conducted and evaluated as per ASTM Standards (9,10). Mechanical (Tensile Strength, Elongation at break, Tensile modulus, Impact strength, Hardness) Thermal (Melt flow index) and Physical (Density) properties of the composite were evaluated. Tool Trays were developed by using Injection molding technique using similar Temp range 150-190 oC with a Tool tray mold. Injection pressure and other parameters are like LDPE processing.
Result and discussion
The physical properties like density and surface hardness for LDPE-RLDPE composites at different reinforcement loadings are depicted in Table 1. In case of density (Table 4.). There is only a marginal increase in density from 0.918 to 0.996 gm/cc with addition of Bagasse. Figure 1 depicts surface hardness of LDPE-RLDPE and three formulations. The marginal increase in the density may be due to the bulky nature of Bagasse, which does not affect the material applications. The surface hardness of LDPE-RLDPE matrix increased with increase in the Bagasse content. However, increase is only marginal even at higher percentage of Bagasse used.
Tensile properties (ASTM D 638)
The tensile strength and elongation test results of LDPE –RLDPE (50:50%)/ Bagasse composites at different filler loadings are given in Table 5. Tensile strength decreased from 14.83 to 11.89 MPa and elongation from 258.94 to 88.65 as the loading of Bagasse increases from 0.0 to 15 %. The reduction in tensile strength and tensile elongation may be due to the poor interaction between the hydrophilic filler and the polymer matrix. This is because, as the filler loading increased, the interfacial area increased, worsening the interfacial bonding between filler and the matrix polymer, which decreased the tensile strength.
Because of the Bagasse fillers, the strength of the composite decreases because of the inability of the filler to support the stress transferred from the polymer matrix. Poor interfacial bonding causes partially separated micro spaces between filler and matrix polymer, which obstructs stress propagation, when tensile stress is loaded, and induces brittleness. The addition of Bagasse filler in LDPE- RLDPE matrix follows the general trend of filler effects on polymer properties where the tensile strength and elongation decrease as the Bagasse addition increases. It was found that there is a marginal increase in tensile modulus with the increase in Bagasse loading. This may be due to the fact that the polar –OH groups and hygroscopic nature of filler may contribute formation of hydrogen bond with Hydrogen atoms of PE material. Also, the hardness was increased (fig 1) & strain was decreased and hence the modulus was increased. Figure 2-4 depicts tensile strength, tensile modulus and elongation of LDPE- RLDPE with bagasse content.
Impact properties (ASTM D 256)
The impact strength test results of LDPE -RLDPE/Bagasse composites at different filler loadings are given in Figure 5. As per the data, it was found that impact strength of LDPE-RLDPE/Bagasse composites decreased as the loading of Bagasse increased. This may be due to variation in interaction between filler and matrix due to change in nature and chemical composition of filler. Since Hardness and Tensile modulus increases, the flexibility decreases and hence, the impact strength decreases as the bagasse concentration increases.
Melt flow index (ASTM D 1238)
In case of MFI, the addition of Bagasse decrease MFI from 17.89 to 14.32 g/10 min. The decrease in melt flow is due to the high viscous nature of Bagasse. Table 6 depicts the values of melt flow index properties of LDPE-RLDPE/Bagasse composites at different filler loadings. Melt Flow Index of LDPE-RLDPE and Bagasse formulations. For 50:50% LDPE-RLDPE, the MFI is higher since Recycled LDPE has lower mol.wt than Virgin LDPE. But the bagasse natural polymer is having very high mol.wt, (in millions), so the MFI decreases as the Bagasse concentration increases.
LDPE-RLDPE/Bagasse composites were prepared at various weight % of Bagasse. LDPE - RLDPE and Bagasse was optimized to 5 and 15 weight % respectively due to bulky and voluminious nature of bagasse fibers and feeding in the hopper of the twin screw compounding extrusion will be very difficult for higher percentage of bagasse short fibres. The mechanical properties such as Tensile strength, Elongation at break, Impact strength are decreased and Tensile modulus, Hardness are increased by the addition of LDPE-RLDPE with bagasse. Melt Flow Index is also decreased. The properties had uniformly changed and hence the Glycerol compatibilizes the LDPE/RLDPE and bagasse materials.
The tool box was made by injection molding technique from all compositions. The product cost will be lowered due to Recycled LDPE (50%) and Bagasse 15%. The compounding cost will be 10-15% Per Kg. The overall cost may be reduced by 50% per Kg due to Recycled LDPE and Bagasse, The bio-degradability can be imparted and after biodegradation the LDPE-RLDPE will be as powder matrix and will not litter in the environment. Value added products can be made from recycled LDPE and bagasse like Tool Boxes, Dust bins etc.
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K. Balaji, M. Praveenkumar, S. Sanalkumar, V.K. Suriya and S.Soundararajan
Dept of Plastics Technology Central Institute of Plastics Engineering and Technology-IPT (Institute of Plastics Technology) Guindy, Chennai-600032, India