Low-density polyethylene waste/recycled wood composites
Introduction
The waste recycling covers several areas of interest such as environmental, engineering, economic and social and this is an important way to ensure sustainability in the world [1]. Due to the high consumption of polymers, especially in packaging, the polymeric waste have gained importance because the problems caused by their inappropriate depositional environment are becoming increasingly more significant. Nowadays, the consumption of polyethylene is the most representative in terms of international trade of commercial polymers. The global demand for LDPE in 2009 was about 18.4 million tons and the projected global demand is growing at an annual rate of 2% from 2009 to 2020 [2]. In addition, the recovery rate of plastic materials is the lowest of all commercial materials in countries like the United States, which is not more than 8.2% to the LDPE, considering the total consumption of virgin raw materials [3]. LDPE is mainly used to production of the polymeric films due both to their high elongation and flexibility [4].
On the other hand, the wood still is a material of expressive consumption for structural utilization for confection of furnishings, homes, building, among others. Packaging and pallets are also important products generated from timber industry. In Europe, around 20% of all sawnwood consumption is used for wooden pallets and packaging, while in Catalonia, northwest of Spain, 85% of the sawnwood is used to manufacture pallets [5]. Conifers species such as pine (Pinus elliottii) are the main raw material for manufacture of the pallets [5]. The use of the pine presents an import environmental advantage due to their source from reforestation [6].
The pine pallets are continuously submitted to high mechanical stress during use that of course lead to the usual break of the structural parts, disabling the entire pallet and generating pine waste wood (PWW).
Although the wood waste such as PWW can be used as fuel, only 15.2% of wood is reused [7]. Wood waste as well as others natural fibers have high potential for use as reinforcing in polymeric composites [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20]. Several authors show good results in relation to the data obtained from mechanical testing with composites using pine fibers as reinforcement for plastics [21], [22], [23], [24], [25]. PWW has been used to manufacture of particleboards, which is considered sustainable and aggregate value to final product, decreasing the use of natural wood and to extend the life of the landfills, besides to improve the biodegradation potential of the polymeric composite [26], [27], [28].
Besides, studies have demonstrated excellent results with the use of different types of polyethylene and natural fiber [29], [30], [31], [32], [33], [34], [35], [36]. Other authors show high potential for application using different recycled fibers (waste bananas, cotton and rice) with virgin LDPE arrays [37].
LDPE/wood fiber composites present higher rigidity and lower deformation than LDPE, allowing several applications. However, the adequate integration of the properties fiber/matrix in the polymeric composites depends of a strong interface interaction. Coupling agents such as grafted polymers with reactive chemical groups are used frequently to improve interface properties of polymer/wood composites [38], whose maleic anhydride grafted polyethylene (PE-g-MA) has been highlighted for composites with matrix of polyethylene [8], [39].
The development of materials obtained from the recycling will be important in the coming years, in order to reuse waste plastics and other materials. The purpose of this work concerns to the development of a composite from low-density polyethylene packaging and wood waste, for evaluating the behavior of the material in a mechanical, thermal and microscopic levels.
Section snippets
Materials
Post-industrial waste of low-density polyethylene (LDPEW) generated from extrusion processing to produce film for packaging and polyethylene-grafted with maleic anhydride (PE-g-MA) were both donated by TECNOVAL S.A, while pine wood waste (PWW) were obtained from milling of the pallets used for transporting and storage loads of large volume. Finally, the thermal stabilizer, SONGNOX 21B FF, was used to prevent thermal degradation during thermomechanical processing of the material, respectively.
Preparation and characterization of the composites
Mechanical properties
Table 2 and Fig. 1, Fig. 2, Fig. 3 show the results of the mechanical properties by tensile tests of the materials. The tensile strength results (Fig. 1) show that there was a little percentage of change in this property in the composites when comparing the values of the LDPEW isolated. The tensile strength of these materials remained between 10 and 12.5 MPa. It is observed that the presence of 1.5 wt% fiber promotes an increase in tensile strength of the material. However, the tensile strength
Conclusions
The LDPEW/PWW composites showed considerable changes in their properties, mainly mechanical properties, as a function of the fiber content incorporated to the material. Composites with low content of fiber (1.5–10%) have high elongation and less expressive Young’s modulus, while the behavior of composites with fiber content above 10% is opposite, i.e. the Young’s modulus increase, while the elongation decrease. These features are resulting of the adequate compatibility promoted by coupling
Acknowledgements
The authors would like to thank the TECNOVAL S.A for supplying the materials and CAPES and FAPESP (Proc. 2012/13715-5) for finance support.
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