Abstract
Abstract The use of polymer blends and composites based on fossil-based and bio-based polymers has become an important environmentally protective alternative for common use and disposable plastics applications such as packaging, bottles and trays. The disposal of these more degradable products, however, may also harm the environment and, therefore, recycling these systems becomes relevant. Recycling involves reprocessing which can significantly change the morphology and properties of polymeric products. Therefore, this study deals with the effects of reprocessing cycles on the properties and morphology of blends and nanocomposites based on fossil and bio-based polymers. The systems investigated were: a) neat polypropylene (PP), b) a polypropylene/poly(3-hydroxybutyrate) (PP/PHB) blend and c) PP/PHB/organoclay nanocomposite compatibilized with polypropylene-g-maleic anhydride (PP-g-MA) and erucamide. These materials were submitted to up to seven extrusion cycles in a single screw extruder operating at 60 rpm. Samples were taken after the first, third, fifth and seventh extrusion cycles and their tensile properties and morphology were determined. Scanning electron microscopy indicated that two phases were observed in the blend which showed spherical PHB domains. The addition of clay, PP-g-MA and erucamide improved the adhesion between the nanocomposites components. X-ray diffraction analysis showed that crystallinity tended to increase with the number of reprocessing cycles for all systems investigated up to the fifth cycle and then tended to decrease. A 10% crystallinity increase was observed for neat PP in the fifth cycle. In general, the tensile properties of all systems decreased with reprocessing and the highest losses were observed for the PP/PHB blend after seven processing cycles with 50% and 37% decreases in stress at break and elastic modulus, respectively. Impact strength of the PP matrix and of the PP/PHB blend tended to decrease with reprocessing, except for the nanocomposite which showed a slight increase especially after the seventh processing cycle in which an 18% increase in impact strength was observed.
Highlights
Polymer consumption increases annually due to properties such as low density, easy processing and a wide range of applications
Our results indicate that all systems investigated degraded with the reprocessing cycles, which is more evident for each material after the seventh cycles
A PP/PHB blend and a nanocomposite based on this blend were extruded for up to 7 times and the effect of reprocessing on their morphology and mechanical performance was investigated
Summary
Polymer consumption increases annually due to properties such as low density, easy processing and a wide range of applications. Materials Research with the synthesis and development of new monomers has steered scientist to develop new materials with good performance and viable costs for industrial applications. This has led to systems based on polymer blends[7]. Considering environmental concerns, blends that include the partial or total replacement of traditional polymers by biodegradable ones are on the rise as they increase their application range and improve the resulting materials biodegradability[9]. The literature on blends that associate polymers from fossil sources with those of natural origin is vast, integrating the search for alternatives capable of combining biodegradation and recycling
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