Physico-Mechanical Properties of LLDPE Composites Prepared From Natural Fiber

Transcription

1 Physico-Mechanical Properties of LLDPE Composites Prepared From Natural Fiber AliyuDanmusa Mohammed Department of Chemistry, Umaru Musa Yar adua University,PMB 2218,Katsina. Abstract Linear low density polyethylene ( LLDPE) composites were prepared using coconut fiber as reinforcing material. Varying-quantities of the coconut fiber were used to preparefive different samples of the composites. Compression moulding technique was used to prepare the LLDPEblends containing 0.0, 7.5, 15, 22.5 and 30% weight content offibers. Tensile properties and moisture uptake of the different composites were analysed. The physico-mechanical propertieswere observed to show some noticeable changes in the composites with the fiber content. The tensile strength increased up to 22.5% fiber addition and then levelled-off gradually with the fiber content, while the elongation at break decreased with increasingfiber contentin the composite. Keywords:Coconut fiber; Composites; LLDPE; Tensile properties Introduction Introduction of natural fiber as reinforcing material has become a common practice of great technological significance over the years. This is coupled with the fact that the composites are readily prepared using simple and cheapest techniques. Composite materials are those that are formed by the combination of two or more materials to achieve properties that are superior to those of their constituents [1]. Polymer composites consist of a polymer resin as the matrix with fibers as the reinforcement medium [2]. Considerable interest has been generated in the manufacture of thermoplastic composites due to their unique properties which include their good mechanical properties, thermal stability and a reduced product cost. Due to the combination of more than one material, the properties of the composites are influenced by many factors such as filler characteristics, filler content and interfacial adhesion [3]. This can cause the behaviour of the filled polymers to be more complex than the unfilled polymers. Like other natural fibers, coconut fibers are widely used as reinforcing agents in the production of thermoplastics. Natural fiber composite such as coir, jute, baggage, cotton, bamboo, hemp all comes from plant, which contains lingo cellulose in nature. Natural fibers are eco-friendly, light weight, strong, renewable, cheap which properties are influenced by that growing environment. Chemically modified natural fibers combinemost of the desirable properties of natural and synthetic fibers, hence, they serve as alternative to synthetic fibers.the composites are used indifferent industries which include textile, automobile and building industry. Natural fiber composites are attractive to industry because of their low density and ecological advantages over conventional composites. The height of the plant, strength of fibers and density are all affected by temperature, humidity and the composition of the soil. The harvesting and processing operations of the fibers also results in variation of their properties. Through modification, the interfacial bonding between the fiber surfaces can be enhanced through alkali treatment and treatment with coupling agents, which in turn will enhance the overall performance of the composites [4]. 1 AliyuDanmusa Mohammed

2 Natural fibers are abundantly available cheap and easy to handle and process and are environmentally friendly [5], but they also exhibit moisture absorption, hydrophilicity, poor reactivity and poor compatibility with polymeric matrices. Li et al.[6] however, reported that these problems can be overcome by chemical modifications to enhance interfacial between natural fibers and also to improve the physico-mechanical and thermal properties of the fibers. Eshitaet al., [7] reported the physiochemical properties of Jute fiber modified by sulphonation method, and it was observed that the lustre of sulphonated jute fiber increased with sulphonation. Guntiet al. [8] reported that chemical modifications are considered to optimize the interface of fibers or introduce new position that can effectively interlock with the fiber matrix. Apart from chemical modification of the natural fibers, incorporation of synthetic polymers with natural fibers has become a breakthrough in improving the physico-mechanical properties of the fiber composites. For instance, study on thesurface modification and adhesion mechanism of composites prepared from maleated polypropylene (MAPP), using natural fiber from wood and Kenaf as reinforcing material, shows an improved mechanical properties of the fiber/polypropylene composites [9-11]. This work, however, examines the study of composites from coconut fiber and LLDPE. The objective of the work is to fabricate different composite material, containing different fiber density, through compression moulding and to determine their performance through the measurement of physico-mechanical properties. 2. Experimental 2.1 Collection and separation of the fibers from their plants Coconut tree parts,from the fresh part of the tree, were cut into manageable size and kept under water to make them susceptible for microbial attack. The fibers were easily stripped off from other parts of the tree after 25 days. The collected fiber was washed with water and allowed to dry under the sun. 2.2 Raw materials The main raw materials used for the sample preparation are LLDPE and the coconut fiber. LLDPE technical grade was purchased from the manufacturer. The fibers were cut into small pieces and oven-dried at 100 C for another 24 h. 2.2 Light bleaching of the fibers The procedure of Choudhury [12] was used: Fibers were bleached by soaking them in water containing hydrogen peroxide 6%, NaOH 4%, sodium silicate 4%, soda ash 2% and soap 1% and then stored at room temperature for 24 h. The bleached fibers were washed with water and dried in an oven at 100 C for 24 h. 2.3 Preparation of composites (compression moulding techniques) The samples were prepared using compression moulding machine. The polymer material and the fiber were subjected to heat and pressure at a time using a hydraulic pressing device equipped with heated plates and Silicone(mould release agent), was used.in the moulding process, a force of 50 KN and a temperature of180 C were applied to get the desired shape and possible uniformity.after 25 min, the moulds were allowed to cool by running tap water through the outer surface of the heating plates. The composite samples were cut for analysis. 2.4 Mechanical testing of the composites The tensile testing of the composites was carried out according to ASTM D 638 [13], using a universal tensile testing machine (Capacity of 10 KN, Hounsfeld) at a crosshead speed of 1 mm/min. Each test was done until tensile failure occurred in the composites. Average values obtained from three specimens of each composition was considered and reported. The tensile strength was calculated using the following equation: Tensile strength, σ = P/A Where P is the breaking load (N) and A is the cross sectional area (mm).from the data obtained, stress versus strain curves are drawn. 2 AliyuDanmusa Mohammed

3 2.5 Water absorption test Water absorption tests of the composites were calculated according to ASTM D570-98[14]. Samples were dried in an oven at 105 C for about 2 h, cooled in a dessicator and immediately weighed to the variation of g. The dried weighed samples were then immersed in a boiling water for 2 h. Excess water on the surface of the samples was removed and the weights of the samples taken. Five specimens of each composition were weighed and average results reported. The percentage increase in weight after immersion in water was calculated as follow: Total moisture uptake, W t = W 2-W 1 x 100/W 1 Where W t is the total moisture uptake; W 1is the weight of the sample before immersion and W 2 is the weight of the sample after immersion in water. 3.0 Results and discussion The different polymer/fiber ratios in the composite samples are presented in Table 1. Different fiber/polymer proportions were prepared to study the effect of the natural fiber filler on the physico-mechanical properties of the composites. 3.1 Tensile properties of the composites The mechanical properties of LLDPE/fiber composites with different fiber loads are shown in Table 2. The fiber load in each composite affects the properties to some extent. The tensile properties increase with increase in the fiber content up to a level when the fiber and the LLDPE surface interconnections have become saturated. Table 1. LLDPE/coconut fiber samples LLDPE (%) Coconut fiber (%) That s why in the table, there is no significant change in the tensile strength of the blends containing 22.5% and 30% fiber content. Moreover, high fiber content leads to an increase in the stiffness of the composite which resultsin the decrease in elongation at break. Table 2. Tensile properties of the samples Blend Fiber (%) Force (40 N) Elongation at break Strain (NM -2 ) Stress (NM -2 ) Tensile strength (NM -2 ) AliyuDanmusa Mohammed

4 3.2 Moisture absorption of the samples The moisture uptake, on the other hand, goes proportional with the fiber load in the composite. Coconut fiber, like other natural fibers, has the ability to retain moisture in their structure due to the presence of structural spaces that could trap and store moisture in their formation. Once these fibers are blended with synthetic polymers, thehydrophilicity is enhanced in the overall property of the composite. The presence of some hydrophilic sites from the fiber surface in the blends allows more water absorption and retention within the composite. The more fiber content, the more hydrophilic sites, hence more water absorption. Table 3 shows the trend of moisture uptake stated above; it is clearly observed that the absorption increases with increase in the fiber addition. Moisture uptake in the LLDPE/coconut fiber composites is mainly due to the fiber material in the blends or those near the surface that absorb moisture faster than those in the interior. Table 3. Observed moisture uptake of the samples Blends Fiberwt (%) Weight before immersion W 1 Weight after immersion W 2 Moisture uptake (%) Conclusion Coconut fiber/lldpe composites prepared from different ratios shows different physico-mechanical properties. There is an increase in the tensile properties with the fiber content up to a certain level when the increase in the fiber content causes no further change in the property.likewise, the moisture uptake increases with more fiber content. The results, however, could help significantly in assessing the physical and structural properties of the fiber. Acknowledgement The authorsare grateful Umaru Musa Yar adua University Katsina, Nigeria for financial support. References [1] Wang Y., Yeh F.C., Lai S.M., Chan H.C. and Shen H.F. Effects of Functionalised Polyolefins as Compatibilizer for Polyethylene/Wood Flour Composites. Polymer Engineering and Science. 2003, 43, [2] Callister, W.D. Materials Science and Engineering: An Introduction, 3 rd Ed., USA, John Wiley & Sons. 2007, 47 [3]Liang J.Z. Effects of Particle Size on Melt Viscoelectric Properties During capillary extrusion of Glass Bead-Filled LLDPE Composites. Journal of Thermoplastic Composite Materials, 2006, 19, [4]Bachtiar, D., Sapuan S.M Hamadan M.M. The effect of Alkaline treatment on tensile properties of sugar palm fibre reinforced epoxy composite. Mater.Des. 2008, [5] Sahoo, P.K., Rana, P.K., Sarkar, D.B., Sahoo, A., Swain, S.K., Characterization and properties of chemically modified Corchoruscapsularis jute fibre via pulping and grafting: Journal of Applied Polymer. Science.Pt. A: Polym. Chem. 2003, 41, [6] Liu, X.Y., Dai, G.C., Surface modification and micromechanical properties of jute fibre mat reinforced polypropylene composites. Express Polym. Lett. 2007, 5, AliyuDanmusa Mohammed

5 [7] EshitaD., Rahman, S., Mohammad, M.H., (eds).,different Approaches to Modify the Properties of Jute Fiber: The International Journal Of Engineering And Science (IJES) Vol 5, [8] Gunti R., Atluri V. Ratina P., (eds).,tensile properties of successive Alkali Treated short jute fiber reinforced PLA composites. Procedia material science 2014, [9]Joseph S., Sreekala M.S., Oommen Z., Koshy P., Thomas S. A Comparison of the Mechanical Properties of Phenol Formldehyde Composite Reinforced with Banana Fibers and Glass Fibers. Composites Science and Technology. 2002, 62, [10] Pothan L.A., Oommen Z., and Thomas S. Dynamic Mechanical Analysis of banana Fiber Reinforced Polyester Composites. Composites Science and Technology. 2003, 63, [11] Sandeep K., and Mirsa R.K. Analysis of Banana Fibers Reinforced LLDPE/Poly(Caprolactones) Composites. Soft Materials 2007, 4, 1-13 [12] Choudhury A.K.R. Textile Preparation and Dyeing. Science Publishers Inc. Texas, 2006, 301 [13]ASTM Standard D Standard Test Methods for tensile Properties of Plastics. Annual Book of ASTM standard, 2002, 08 (01) : [14] ASTM Standard D Standard Test Methods for Water Absorption of Plastics. Annual Book of ASTM standard 2002, 08 (01): AliyuDanmusa Mohammed