1. INTRODUCTION:

Growing awareness about environment is promoting natural fiber reinforced polymer composites. Natural fibers, like jute, hemp, coconut, bamboo etc are being used to replace glass and other fibers in polymer composites. Considerable efforts are being directed to develop eco-composites and green composites based on natural fiber reinforced polymers. Natural fiber reinforced plastic composites are offering technological, environmental and economic advantages. Natural fiber polymer composites are finding applications in commodity materials and also in engineering and high tech materials. Processing, structure, properties and applications of natural fiber polymer composites, their life cycle assessment and the growing market for these materials have been regularly reviewed [1-3].

The main limitation of natural fiber polymer composite is the poor adhesion of natural fiber with polymers. Two methods have been used to improve this fiber / matrix interfacial adhesion. These are: chemical treatment of natural fibers and use of a compatibilizer. Chemical treatments given to various natural fibers to improve their

adhesion with the polymer matrix in the composite include, use of alkali, oxidizing agents, sodium hydroxide, silanes, maleic anhydride etc. These chemical treatments have been reviewed [4-7]. Natural fibers have also been physically modified to improve their adhesion with polymers in composites. Physical methods of fiber modification include, steam explosion, plasma, UV and g radiation treatments etc. These and other physical methods for modifications of natural fibers for improving their adhesion with polymers in composites have also been reviewed. [8-9].

Detailed studies on the use of compatibilizers for improvement on fiber / matrix interfacial adhesion indicate that several compatibilizers including, maleic anhydride modified polyolefins stearic acid and others used to improve fiber / matrix interfacial adhesion, have been extensively reviewed [10].

Our studies have been directed to extend the concept of natural fiber reinforced polymer composites to develop composite materials based on recycled polymers reinforced by recycled secondary fibers. Some efforts have been made to use either secondary fiber with a polymer or a natural fiber with a recycled polymer to develop composites. For example, waste paper based secondary fiber has been used as a reinforcer for engineering plastics [11, 12]. Waste paper fiber reinforced polypropylene composites have been developed and evaluated in terms of their mechanical properties and water uptake ability [13]. Newsprint fibers treated with sodium silicate and magnesium chloride have been used as reinforcers for natural rubber and acrylonitrile rubber [14, 15]. Recycled newspaper cellulose fiber (RNCF)- reinforced poly(lactic acid) (PLA) composites have also been developed. [16, 17]. Although several studies have been reported on use of secondary fiber as reinforcers for polymeric composites, no studies have been reported on development of composites based on secondary fibers and recycled polymers. In view of growing interest in use of secondary fibers as reinforcers for development of polymeric composites, this study aims to develop a composite based on a recycled polypropylene reinforced by secondary fiber.

2. MATERIALS:

2.1 Matrix for composite: Recycled Polypropylene

Recycled polypropylene was generated from waste polypropylene purchased from local market. Approximately 15Kg post consumer used household and commercial polypropylene items were obtained. A Pelletiser (Breaker-shredder) was used to disintegrate and break the polypropylene items into small particles or pellets. Polypropylene pellets were washed under running water to remove contaminants. Washed polypropylene pellets were passed through a dryer. The process was carried at the rate of around 40 kg/hr at 40^oC, where all the excess moisture was removed. The dried pellets were extruded to obtain recycled polypropylene.

2.2 Reinforcer for Composite: Secondary Fiber

Secondary fiber is the regenerated fiber from waste newspapers, magazines, journals, office waste, household waste etc. It is a product from paper mills. For this study newspaper based secondary fiber was obtained from Neral Paper Mill.

2.3 Compatibilizer:

Maleic anhydride modified polypropylene with 2% maleic anhydride was used as compatibilizer to improve the interfacial adhesion of secondary fiber with recycled polypropylene. Maleic anhydride modified polypropylene with 2% maleic anhydride was obtained from Pluss Polymer Pvt. Ltd., India in the form of their commercial product OPTIM P-425^®

3. COMPOUNDING AND PROCESSING OF COMPOSITES:

Secondary fibers were chopped to 5mm-10mm length and washed with distilled water. Secondary fibers, recycled polypropylene and maleic anhydride modified polypropylene were dried at 80^oC for 2 hours in hot air oven. Calculated quantities of reinforcing secondary fiber, recycled polypropylene matrix and maleic anhydride modified polypropylene (2% maleic anhydride) added as compatibilizer to improve interfacial adhesion of the secondary fiber with recycled polypropylene, were mixed manually. This feed was used for extrusion and compounding to process secondary fiber / recycled polypropylene composites of 10/90, 20/80 and 30/70 compositions. Compounding was performed on Haake Rheocord-9000 – a laboratory size extruder / mixer. The temperatures in various zones o the extruder varied from 125^oC to 185^oC. The raw materials feed, prepared as stated above, was fed from the hopper through the throat into the channel of the extruder screw. The temperatures during extrusion and compounding were kept relatively low to prevent degradation of secondary fiber. The extruded strands were cooled in water and cut into small pellets by a pelletizer. These pellets of 10/90, 20/80 and 30/70 secondary fiber / recycled polypropylene composites were used to prepare specimen for various testing and characterization by injection molding. Prior to injection molding, the composite granules were dried in an oven at 100^oC for 4 hours to remove moisture. Injection molding machine Model JAD series, JSW Ltd. Japan, was used to prepare the specimen following ASTM.

4. MECHANICAL PROPERTIES:

Tensile test were performed on a Universal Testing Machine, (Lloyds UTM-100K), with cross head speed of 5mm/min following the ASTM D638 standard. Results were recorded as an average of five samples of the matrix polymer and five samples of each composite tested. Flexural properties of composites were also evaluated by performing tests on a Universal Testing Machine, (Lloyds UTM-100K), with cross head speed of 5mm/min following the ASTM D790 standard.

4.1 Tensile Properties and Flexural Modulus

Table-1 records the tensile properties and flexural modulus of 10/90, 20/80 and 30/70 secondary fiber / recycled polypropylene composites. Tensile modulus, tensile strength and elongation at break of the recycled polypropylene (matrix) and 10/90, 20/80 and 30/70 secondary fiber / recycled polypropylene composites are recorded in Table-1.

4.1.1 Tensile Modulus

As evident from values recorded in the Table-1, the tensile modulus of recycled polypropylene matrix is 0.32 GPa. This value is considerably lower than the tensile modulus of new polypropylene, because the recycled polypropylene is post consumer used polypropylene that has undergone environmental, thermal and mechanical stresses. The tensile modulus of 10/90 secondary fiber / recycled polypropylene composite is 0.39 GPa. These values show that the tensile modulus of the recycled polypropylene increases as it is reinforced by secondary fiber. The higher tensile modulus of 10/90 composite as compared to the recycled polypropylene confirms the formation of 10/90 secondary fiber / recycled polypropylene composite. The tensile modulus of 20/80 secondary fiber / recycled polypropylene composite is 0.44 GPa. Thus the tensile modulus of 20/80 composite is higher than that of recycled polypropylene and is also higher than that of 10/90 composite. The higher tensile modulus of 20/80 composite as compared to that of 10/90 composite and also as compared to that of the recycled polypropylene confirms the formation of 20/80 secondary fiber / recycled polypropylene composite. These values show that the tensile modulus of the recycled polypropylene increases with increasing amounts of reinforcing secondary fiber in the composite. Further, the tensile modulus of 30/70 secondary fiber / recycled polypropylene composite is 0.49 GPa. Thus the tensile modulus of 30/70 composite is higher than that of recycled polypropylene and is also higher than that of 10/90 and also 20/80 composite. The higher tensile modulus of 30/70 composite as compared to that of recycled polypropylene and also as compared to that of 10/90 and 20/80 composite confirms the formation of 30/70 secondary fiber / recycled polypropylene composite. These values show that the tensile modulus of the recycled polypropylene increases with increasing amounts of reinforcing secondary fiber in the composite.

4.1.2 Tensile Strength

As evident from values recorded in the Table-1, the tensile strength of recycled polypropylene matrix is 17MPa. This value is considerably lower than the tensile strength of new polypropylene, because the recycled polypropylene is post consumer used polypropylene that has undergone environmental, thermal and mechanical stresses. The tensile strength of 10/90 secondary fiber / recycled polypropylene composite is 19.7MPa. These values show that the tensile strength of the recycled polypropylene increases as it is reinforced by secondary fiber. The higher tensile strength of 10/90 composite as compared to the recycled polypropylene confirms the formation of 10/90 secondary fiber / recycled polypropylene composite. The tensile strength of 20/80 secondary fiber / recycled polypropylene composite is 22.5MPa. Thus the tensile strength of 20/80 composite is higher than that of recycled polypropylene and is also higher than that of 10/90 composite. The higher tensile strength of 20/80 composite as compared to that of 10/90 composite and also as compared to that of the recycled polypropylene confirms the formation of 20/80 secondary fiber / recycled polypropylene composite. These values show that the tensile strength of the recycled polypropylene increases with increasing amounts of reinforcing secondary fiber in the composite. Further, the tensile strength of 30/70 secondary fiber / recycled polypropylene composite is 26.2 MPa. Thus the tensile strength of 30/70 composite is higher than that of recycled polypropylene and is also higher than that of 10/90 and also 20/80 composite. The higher tensile strength of 30/70 composite as compared to that of recycled polypropylene and also as compared to that of 10/90 and 20/80 composite confirms the formation of 30/70 secondary fiber / recycled polypropylene composite. These values show that the tensile strength of the recycled polypropylene increases with increasing amounts of reinforcing secondary fiber in the composite.

4.1.3 Elongation at Break

The values listed in Table-1 indicate that the elongation at break of recycled polypropylene is 76%. The elongation of the matrix polymer decreases as it is reinforced by secondary fiber. The fibers are rigid and do not elongate and further, the fibers also prevent the extension of the matrix. For this reason, the elongation at break of the materials decreases with the formation of the composite, and goes on decreasing with increasing amounts of reinforcing fibers in the composite. As evident from Table-1, the elongation at break of the 10/90 composite is 71%, that is lower than the elongation of recycled polypropylene. With the increasing amounts of fiber and formation of composites, the elongation at break further decreases. As recorded in Table-1, the elongation at break of 20/80 and 30/70 composites is 66% and 61% respectively, that is lower than that of 10/90 composite and also lower than that of recycled polypropylene. The decreasing elongation at break with increasing amounts of reinforcing fibers indicates good interfacial adhesion between the reinforcing secondary fiber and recycled polypropylene.

4.1.4 Flexural Modulus

As evident from values recorded in the Table-1, the flexural modulus of recycled polypropylene matrix is 0.17 GPa. This value is considerably lower than the modulus of new polypropylene, because the recycled polypropylene is post consumer used polypropylene that has undergone environmental, thermal and mechanical stresses. The flexural modulus of 10/90 secondary fiber / recycled polypropylene composite is 0.21 GPa. These values show that the flexural modulus of the recycled polypropylene increases as it is reinforced by secondary fiber. The higher flexural modulus of 10/90 composite as compared to the recycled polypropylene confirms the formation of 10/90 secondary fiber / recycled polypropylene composite. The flexural modulus of 20/80 secondary fiber / recycled polypropylene composite is 0.25 GPa. Thus the flexural modulus of 20/80 composite is higher than that of recycled polypropylene and is also higher than that of 10/90 composite. The higher flexural modulus of 20/80 composite as compared to that of 10/90 composite and also as compared to that of the recycled polypropylene confirms the formation of 20/80 secondary fiber / recycled polypropylene composite. These values show that the flexural modulus of the recycled polypropylene increases with increasing amounts of reinforcing secondary fiber in the composite. Further, the flexural modulus of 30/70 secondary fiber / recycled polypropylene composite is 0.28 GPa. Thus the flexural modulus of 30/70 composite is higher than that of recycled polypropylene and is also higher than that of 10/90 and also 20/80 composite. The higher flexural modulus of 30/70 composite as compared to that of recycled polypropylene and also as compared to that of 10/90 and 20/80 composite confirms the formation of 30/70 secondary fiber / recycled polypropylene composite. These values show that the flexural modulus of the recycled polypropylene increases with increasing amounts of reinforcing secondary fiber in the composite.

5. ENVIRONMENTAL ADVANTAGES:

The study demonstrates that engineering composites with good mechanical properties may be developed from recycled secondary fiber and recycled polypropylene. Polypropylene is used in very high volumes and has very high consumption as commodity plastic and also as an engineering plastic. Paper is also extensively used. High volume of waste paper is generated. Post consumer used polypropylene and secondary fiber generated from post consumer used paper is available in open market. This post consumer used polypropylene and secondary fiber from post consumer used paper may be used to develop polymeric composite based on recycled polypropylene reinforced by secondary fiber. The re-use of polypropylene and secondary fiber will be advantageous for the environment and reduce pollution problems.

6. CONCLUSIONS:

Secondary fiber reinforced recycled polypropylene composites have been successfully processed by extrusion and injection moulding. Maleic anhydride modified polypropylene with 2% maleic anhydride acts as an efficient compatibilizer and promotes interfacial adhesion between secondary fiber and recycled polypropylene. Secondary fiber reinforced recycled polypropylene composites demonstrate good tensile and flexural modulus and also good tensile strength. These mechanical properties make the secondary fiber reinforced recycled polypropylene composites potential materials for commodity applications. The re-use of polypropylene and secondary fiber will be advantageous for the environment and reduce pollution problems.

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Received on 21.05.2012 Modified on 25.05.2012

Asian J. Research Chem. 5(5): May 2012; Page 655-658