Biodegradability and Mechanical Properties of Low Density Polyethylene/Waste Maize Cob Flour Blends

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1 212 by the authors Licensee IJASER- Under Creative Commons License 3. Research article ISSN Biodegradability and Mechanical Properties of Low Density Polyethylene/Waste Maize Cob Flour Blends 1* H. C. Obasi, 2 G. C. Onuegbu 1,2 Department of Polymer and Textile Engineering, Federal University of Technology, Owerri, P.M.B 1526, Imo State, Nigeria. DOI: 1.688/ijaser.236 Abstract: The properties of blend of low density polyethylene and waste maize cob flour (/WMCF) and maleated polyethylene (MAPE) as compatibilizer were studied. /WMCF composites with different filler loadings, with and without the addition of MAPE were prepared using a laboratory injection moulding machine. Mechanical properties of the were found to be worse when it was blended with the filler, due to the poor compatibility between the two phases. The addition of MAPE led to a much better dispersion and homogeneity owing to the formation of ester linkage group and thus showed better properties. Water uptake of compatibilized /filler composite (/WMCF) was lower than that of uncompatibilized /filler composite (/WMCF). Both composite were buried in the soil to assess biodegradability. Weight loss of composites observed indicated that both were biodegradable, even at high of filler concentration. Keywords: Low density polyethylene, waste maize cob flour, maleated polyethylene, mechanical properties, water absorption, biodegradability, composites and weight loss. 1. INTRODUCTION The emergence of plastics for the past few decades as alternatives to other traditional material such as paper, metals and ceramics for packaging and other applications has led to the increase in the production of plastics. This has exposed the universe to environmental problems because most of these materials are non-degradable and have remained in the refuse dumps and landfills for years. Efforts have been made to get rid of these problems through re-use and recycling but not all plastics are recyclable; incineration process is often used but these results in heat generation and causes air pollution. These situations contribute to serious environmental problems (Hanafi et al, 211). Several researchers around the world now are engaged in synthesis of new polymeric materials and processes aimed at improving the environmental quality of a number of products (Singha et al, 28; Kaith et al, 28; Singha et al, 28). The use of biopolymers has been considered alternative in reducing environmental problems. The main advantage of using biofillers is that these materials are biodegradable and renewable and exhibit low cost, low density and high stiffness. Nevertheless, the incompatibility between them and polymer matrix, the low dispersion degree of the fillers as well as their poor moisture resistance, generally results in decreased toughness (Klason et al, 1984; Dalvag et al, 1985) and lead to low performance materials, thus limiting their use. Polyethylene (PE) is a stable polymer, and consists of long chains of ethylene monomers. Polyethylene cannot be easily degraded with microorganisms. "However, it was reported that lower molecular weight PE oligomers (of Mw=6-8) was partially degraded by Acinetobacter sp.351 upon dispersion, while high molecular weight PE could not be degraded. The biodegradability of synthetic polymers like polyethylene can be enhanced by the addition of biodegradable additives to the formulation of plastics (Huang et al., 199; Doi and Fukude, 1994, Potts, 1981). In plastics containing blends of PE with biofiller, microbes initially attack the filler resulting in an increase in the porosity and surface to volume ratio of the polymer blend and a consequent enhancement of its biodegradability. It has been shown that the increase in the filler content and decrease in the filler size enhance the biodegradability of the plastic blends (Lim et al, 1992, Peanasky et al., 1991, Zuchowska et al., 1998). Biopolymer, such as waste maize cob filler (WMCF) is a good example of degradable polymer that can be used to replace the hydrocarbon plastic material. The use of WMCF as reinforcing material for biodegradable composites can represent the conversion to industrially useful biomass energy. 233 *Corresponding author Received on May 213; Accepted on May 213; Published on June 213

2 Biodegradability and Mechanical Properties of Low Density Polyethylene/Waste Maize Cob Flour Blends The research purpose was to produce bio-composite of waste maize cob flour (WMCF) and low density polyethylene (). However, the incorporation of the bio-filler to polyolefin results in a reduction to the mechanical properties due to poor compatibility of the two dissimilar materials. These poor quality attributes can be improved through the addition of additives such as compatibilizers to enhance the compatibility between the two materials. In the present research, addition of maleated polyethylene (MAPE) has been considered to be a means of enhancing the mechanical properties and biodegradability of plastic material made from the blends. The effect of filler loading on the mechanical properties and biodegradability of the waste maize cob filler/ blend has been studied. 2. EXPERIMENTAL 2.1. Materials The low density polyethylene () with a density of.93g/cm 3 and melt flow index of 2g/1min used as a matrix material in the study was supplied by Ceeplast Industries Ltd, Aba, Nigeria. Maleated Polyethylene (MAPE) was used as obtained from Sigma-Aldrich Chemical Corporation. Waste maize cob flour (WMCF) used as bio-filler was obtain from a local market in Ehime Mbano, Imo State as woody core of maize ear and then processed to get waste maize cob flour Sample Preparation The filler prior to blending is first oven dried at 9 C for 24h to adjust its moisture contents. The and waste maize cob flour were blended in an injection machine having screw speed of 5 rpm and temperature range varied from 15 to 17 o C. WMCF loading were within the range of 4 to 6 wt (%) based on the weight of filler. After nixing for l minutes, the sample was ejected, allowed to cool down at ambient temperature and the sample was carefully removed from the mould Tensile Properties Tensile tests were carried out with a universal testing machine Instron 3366 according to ASTM D638. Dumbbell shape specimens of 3rnm thickness were cut from the moulded samples. The test was performed at a cross-head speed of 5mm/min. Five specimens were used to obtain average values for tensile strength, elongation-at-break and Young's modulus Soil Burial Test Biodegradability of the specimens sample were studied using weight loss of the composite with time in a soil environment. Sample of 2x2x3mm were weighed and then burial in boxes with tiny openings containing soil. Soil was maintained at about 2% moisture in weight and samples were buried at depth of 15cm. These samples were removed from the soil once a week, washed in distilled water dried and weighed to obtain a new weight before returning to the soil. The percentage weight loss was calculated using equation (1): Weight loss (%) = [(M - M d )/M ] x 1 (1) Where, M o is the initial mass and M d is the degradation mass at each designated week. The percentage weight loss was taken from the average of five samples Water Absorption Study The water absorption tests were carried out according ASTM D Water absorbed was calculated by immersing 15xl5x3mm composite sample in distilled water at room temperature for 7 days intervals. The weight gain measured periodically. The amount of waste absorbed by the sample at room temperature was determined according to equation (2): M t (%) = [(W t W o /W o ] x 1 (2) 234

3 Tensile Strength (MPa) Biodegradability and Mechanical Properties of Low Density Polyethylene/Waste Maize Cob Flour Blends Where, M t is the amount of water absorbed at time t, W t is the weight of the sample at time t and W is the initial weight of the composite sample. 3. RESULTS AND DISCUSSION 3.1. Mechanical Properties For all applications of bio-filled polymer composites, mechanical properties are of great importance. The effects of filler loading on the mechanical properties of WMCF and WMCF1 -filled composite are shown in Figures 1-3. It can be seen from Figure 1 that the tensile strength for the composite decreased with increase in filler loading. This result is similar to reports by Pina et al., (24) and Lee et al., (24). According to Salmah et al., (27), the decrease in tensile strength is due to the poor adhesion of the fillermatrix and the agglomeration of filler particles. Since the filler particles are very small a high interfacial surface exists between the polar filler and then non-polar matrix. As this area increases, the worsening bonding between them decreases the tensile strength. The poor interfacial bonding creates partially separated micro-spaces between the filler particles and the polymer matrix. The presence of voids obstructs propagation of stress when tensile stress is loaded and thus induced increased brittleness (Yang et al., 24). Figure 1 also shows the effects of filler loading on the tensile strength in the presence of the coupling agent. The addition of 2 wt (%) MAPE, based on the weight of filler showed that the tensile strength for WMCF1 is higher than for WMCF. This is probably because of a better interfacial adhesion between the filler and the matrix after the addition of coupling agent. The better adhesion can be attributed to the reaction of the hydrophilic -OH groups from the filler and the acid anhydride groups from MAPE, thus forming ester linkages /WMCF1 HDPE/WMCF Filler loading (% wt) Figure 1: Effect of filler loading on the tensile strength of WMCF-filled composites Incorporation of filler showed reduction in elongation - at- break of WMCF and WMCF1 - filled composites compared to the neat polymer (Figure 2). Increased filler loading resulted in the stiffening and hardening of the composite. This reduced its toughness with increase in brittleness, thus leading to lower elongation- at- break. The elongation-at-break for WMCF is higher than for WMCF1 from Figure 2. This is due to the presence of MAPE in the composite. However, the effect of' the coupling agent was not pronounced on this property. Young's modulus of the composite increased with the increase in filler loading (Figure 3). It was verified that stiffness increased from 129MPa to more than 15MPa. This is a common phenomenon when rigid fillers are incorporated into softer polymer matrices. Some authors have also related the increase in composite rigidity with the reduction of polymer chains mobility in the presence of the filler (Rana et al., 1998). The WMCF1 composite showed higher Young's modulus values compared with WMCF due to the enhancement of interfacial adhesion between the filler and matrix. 235

4 Young's Modulus (MPa) Elongation at break (%) Biodegradability and Mechanical Properties of Low Density Polyethylene/Waste Maize Cob Flour Blends /WMCF1 HDPE/WMCF Filler loading (% wt) Figure 2: Effect of filler loading on the elongation at break of WMCF-filled composites Filler loading (% wt) /WMCF1 HDPE/WMCF Figure 3: Effect of filler loading on the Young s modulus of WMCF-filled composites Soil Burial Test Figures 4 and 5 show changes in weight ratio (degraded sample/initial sample) with time for the WMCF and WMCF1- filled composite buried in soil. The weight loss of WMCF and WMCF1 which indicated the degree of biodegradation of the composite both increased as the filler content increased. The composites with a higher percentage of filler (6% filler content) degraded rapidly in the initial six weeks and a gradual decrease of weight occurred during the last three weeks. This suggested that micro organisms such as fungi and bacteria present in the soil environment consumed the maize filler and created pores in the polyethylene matrix. A comparison of the two composite WMCF and WMCF1 indicated that WMCF1 had a higher weight ratio difference of.579 and after the first week and the ninth week of study for the 6% filler content. The greater biodegradation of WMCF may be caused by the similar factors leading to its higher water absorption. 236

5 Weight Loss (%) Weight Loss (%) Biodegradability and Mechanical Properties of Low Density Polyethylene/Waste Maize Cob Flour Blends /4 WMCF1 /45 WMCF1 /5 WMCF1 /55 WMCF1 /6 WMCF Time (Weeks) Figure 4: Weight loss versus time of /WMCF 1 at different filler loadings /4 WMCF /45 WMCF /5 WMCF /55 WMCF /6 WMCF Time (Weeks) Figure 5: Weight loss versus time of /WMCF at different filler loadings. 3.3 Water Absorption Study The percentage of water absorption versus time for the WMCF and WMCF1 composites at different filler loading is shown in Figsures 6 and 7. WMCF1 composite exhibited moderately good water resistance and resistance was higher than that of WMCF at the same filler content. The weight gain difference for WMCF compared with WMCF1 was.289 and 6.87 at 6% filler content for the first and last week of the period of study. For both types of composite, the percentage water gain increased with filler content and it continued slowly over the 9-weeks test period. These phenomena were similar to the result of Bikiaris and Panayiotou (1998). They deduced by studying blend of starch and polyethylene that the marked increase in water absorption was probably caused by the increased difficulty in forming polymer chain arrangements as the starch prohibited the movement of the polymer segments. The hydrophilic character of maize filler 237

6 Water absorption (%) Water absorption (%) Biodegradability and Mechanical Properties of Low Density Polyethylene/Waste Maize Cob Flour Blends contributed to poor adhesion with the hydrophobic polyethylene. Lower water absorption of WMCF 1 compared to the WMCF was caused by the ester linkage group in the composite /4 WMCF1 /45 WMCF1 /5 WMCF1 /55 WMCF1 /6 WMCF Time (Weeks) Figure 6: Water absorption versus time of /WMCF 1 at different filler loadings /4 WMCF /45 WMCF /5 WMCF /55 WMCF /6 WMCF Time (Weeks) Figure 7: Water absorption versus time of /WMCF at different filler loadings 238

7 Biodegradability and Mechanical Properties of Low Density Polyethylene/Waste Maize Cob Flour Blends 4. CONCLUSION The influences of maleated polyethylene as a coupling agent on the mechanical properties, water absorption and biodegradability in WMCF/ composite were investigated. The addition of MAPE in the composite improved the compatibility and mechanical properties due to the formation of an ester linkage group between the filler and matrix. This group is responsible for many of the differences in mechanical properties of the two composite. Water absorption study shows that the addition of MAPE reduced the water uptake in WMCF/ composites and in a soil environment, the compatibilized composite (WMCF1) shows a lower biodegradation rate than the uncompatibilized (WMCF) one. REFERENCES 1. Bikiaris, D., and Panayiotou, C /Starch Blends Compatibilized with PE-g-MA Copolymers. Journal of Applied Polymer Science, 7, Dalvag, H., Klason, C., and Stromvall, H. E The efficiency of Aids and Coupling agents. International Journal of Polymer Materials, Doi, Y., and Fukuda, K Biodegradable Plastics and Polymers, Elsevier Science KV, Hanfi, I., Rohani, A. M., and Razaina, M. T Effect of Soil Burial on Properties of Linear Low Density Polyethylene/Thermoplastic Sago Starch Blends. Pertanika Journal of Science & Technology, 19(1): Huang, J.C., Shetty, A. S., and Wang, S. W Biodegradable Plastic: A review, Advances in Polymers Technology, 1, Kaith, B. S., Singha, A. S., Sanjeev, K., and Susheel, K. 28. Mercerization of Flax Fibre improves the Mechanical Properties of Fibre reinforced Composites. International Journal of Polymeric Materials, 57, Klason, C., Kubat, J., and Stromvall, H. E Polymers from Biobased Materials. International Journal of Polymeric Materials, 1, Lee, S. Y., Yang, U.S., Kim, H. J., Jeong, C. S., Lim, B. S., and Lee, J. W. 24. Creep Behavior and Manufacturing Parameters of Wood Flour Filled PP Composite. Composite Structure, 65(3-4): Lim, S., Jane, J., Rajagopalan, S., and Seib, P. A Effect of Starch Granule Size on Physical Properties of Starch-filled PE Film. Biotechnology Progress, 8, Peanasky, J. S., Long, J. M., and Wool, R. P., Percolation Effects in Degradable PE-starch Blends. Journal of Polymer Science, Part B: Physical 29: Piva, A. M., Steunder, S. H., and Wiebeck, H. 24. Physico- Mechanical Properties of Rice husk Powder filled PP Composites with Coupling agent Study. In: Proceedings of the Fifth International Symposium on Natural Polymer and Composites, Sao Pedro/Sp, Brazil. 12. Potts. J. E., Environmentally Degradable Plastics. In: Kirk-Othmer Encyclopedia of Chemical Technology, 3 rd ed. Suppli. Vol., John-Wiley, New York, Rana, A. K., Mandal, B. C., Mitra, K., Jacobson, R., Rowell, A., and Banerjee, N Short Jute Fibre reinforced PP Composites: Effect of Compatibilizer. Journal of Applied Polymer Science, 69 (2): Salmah, H., Ismail, A., and Barkar, A. 25. Dynamic Vulcanization of Paper Sludge Filled PP/EPDM. Malaysian Journal of Microscopy, 2,

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