The Use of Agricultural Wastes in Modifying Thermo-Mechanical Properties of Recycled Low Density Polyethylene (LDPE)

       Low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) are widely used in plastic film industries causing a large quantity of waste with unpredictable mechanical and thermal properties. Olive solid waste and almond shell, abundant materials usually thrown into land causing harms to environment were mixed with recycled plastic films and used as modifying fillers.

The blends were prepared once by a home-made single screw extruder, operating at constant screw speed and zone temperatures, and once by film stacking using a home-made Thermo press Apparatus operating at constant air pressure and cooling and heating rates. Three olive solid waste and almond shell particle sizes range (less than 150 µm, 150-250 µm and larger than 250 µm) were used. The effect of both olive solid waste and almond shell contents from 0 to 25 %wt on mechanical and thermal properties were tested to find that for extruded blends up to 10%wt olive solid waste and 10%wt almond shell of less than 150 µm resulted in a noticeable improvement of elastic modulus and ultimate tensile strength. While for other particle sizes 150-250 and larger than 250 µm the optimum value of both ultimate tensile strength and elastic modulus were found at 2.5%wt olive solid waste content and at  5%wt  almond shell content.

For the film sticking composites, it was found that blends up to 15%wt olive solid waste and 5% wt almond shell of less than 150 µm resulted in a noticeable improvement of elastic modulus and ultimate tensile strength. While for other particle sizes 150-250 and larger than 250 µm the optimum value of both ultimate tensile strength and elastic modulus were found at 10 wt% olive solid waste content and at 5%wt almond shell content.

Besides that it was found that an addition of olive solid waste particles enhances crystallinty of the blend and improve compatibility between both polymers used to manufacture plastic films (LDPE and LLDPE) and also biodegradability of plastic films may be increased due to the addition of olive solid waste.

Different processing temperatures (140-260 °C) were used for preparing a 5%wt content of both types of waste at the medium particle size (150-250 µm). It was found that up to 220°C the mechanical properties were improved significantly, and then began to decay due to clear decrease in polymeric melt viscosity or to some extent to begin of polymeric degradation.