Physico-mechanical properties of recycled polyethylene composites reinforced with chemically treated saw-dust

Abstract

Plastic wastes have been a major environmental concern not only in Bangladesh but also worldwide. In the present work, the wood waste and the rejected plastic were recycled to produce new useful product; Wood Plastic Composite (WPC), having characteristics similar or close to commercial wood. An innovative, clean, cheap, and effective yet simple technology with different procedures was introduced in this work to demonstrate the suitability of wood plastic composites' techniques for developing countries. Testing was done for some important mechanical properties; flexural strength and modulus, and physical properties; water absorption and thickness swelling, which has proven an acceptable final product and promising results; especially regarding the physical test. Wood plastic composites (WPCs) were made using matrices of recycled polyethylene (rPE) and sawdust or wood fiber as filler. Corresponding WPCs were also made using virgin plastics (HDPE and LDPE) for comparison with the recycled plastic based composites. WPCs were made through extrusion moulding and injection moulding machine with varying formulations based on the plastic type, plastic form (recycled and virgin), sawdust content. The chemical compositions of sawdust were determined in this experimental work. It was found that wood also have sufficient % of cellulose, hemicelluloses and lignin; so it can be defined as lignocellulosic materials. In this present work, sawdust is used as filler but before using it as filler several chemical treatment were conducted to prevent the water absorption properties because the water absorption is only one of the negative side which affect the mechanical properties of composites materials. As a chemical treatment, sawdust or wood fiber is treated by three categories of single and double pretreatment i.e. NaOH, NaOH+Benzoyl Chloride and NaOH+CTAB. FT-IR was conducted for observing the change in sawdust flour by chemical treatment. In this work the recycled PE is used after recycling the polyethylene bags successfully. Polyethylene shopping bags manufactured from both HDPE and LDPE these are collected as wastage from various sources then it was sorting, washing, drying, cutting, grinding and finally pelletizing. This pellet and saw dust were mixed with together in varying composition and composites were manufactured by using extruder and injection moulding machine. During the preparation of composites the raw and treated sawdust was taken 20%, 25%, 30% and 35% with recycled polyethylene. The prepared composite sample was then taken for various physical and mechanical tests for as example the mechanical tests are hardness test, tensile test, flexural test, impact test. The physical tests are SEM, Water absorption and FT-IR. The chemical treatments of the saw dust were conducted by surfactant and followed effect of chemical treatment on mechanical properties of WPCs. It was found from the experiment that the sawdust treated by NaOH+Surfactant showed better mechanical properties and better resistance to hydrophilic nature. The sample prepared from single pretreatment saw dust shows higher water absorption and low mechanical properties. In between the NaOH+Benzoyl chloride and NaOH+Surfactant treated sample the NaOH+Surfactant treated sample shows better mechanical properties and greater resistance to water absorption. On the other hand, FESEM result was also found very excellent for treated sample than raw sample. To justify the mechanical properties of recycled rPE composites with virgin PE both composites were prepared and it was also found that rPE have the excellent characteristics for engineering materials. So, recycled PE matrix based composites exhibited excellent durability and mechanical properties, which were comparable to those made from virgin plastics. The results from this work clearly show that rPE (rHDPE and rLDPE) can be successfully used to produce stable and strong WPCs, with properties and performances similar to or comparable to composites made of wood and virgin plastics. Therefore, WPCs based on recycled LDPE and HDPE matrix could have potential to use as engineering and construction materials.