Degradability of linear polyolefins under natural weathering |
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Authors: | Telmo Ojeda Ana FreitasKátia Birck Emilene DalmolinRodrigo Jacques Fátima BentoFlávio Camargo |
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Institution: | a Federal Institute of Education, Science and Technology (IFRS), 90035-007 Porto Alegre, RS, Brazil b Department of Soil Science, Federal University of Rio Grande do Sul (UFRGS), 91540-000 Porto Alegre, RS, Brazil c Department of Materials, UFRGS, 9500 Bento Gonçalves Ave, 15010-000 Porto Alegre, RS, Brazil d Department of Soil Science, Federal University of Santa Maria, 97105-900 Santa Maria, RS, Brazil e Department of Microbiology, UFRGS, 500 Sarmento Leite St, 90050-170 Porto Alegre, RS, Brazil |
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Abstract: | High density polyethylene (HDPE), linear low density polyethylene (LLDPE), and isotactic polypropylene (PP) containing antioxidant additives at low or zero levels were extruded and blown moulded as films. An HDPE/LLDPE commercial blend containing a pro-oxidant additive (i.e., an oxo-biodegradable blend) was taken from the market as supermarket bag. These four polyolefin samples were exposed to natural weathering for one year during which their structure and thermal and mechanical properties were monitored. This study shows that the real durability of olefin polymers may be much shorter than centuries, as in less than one year the mechanical properties of all samples decreased virtually to zero, as a consequence of severe oxidative degradation, that resulted in substantial reduction in molar mass accompanied by a significant increase in content of carbonyl groups. PP and the oxo-bio HDPE/LLDPE blend degraded very rapidly, whereas HDPE and LLDPE degraded more slowly, but significantly in a few months. The main factors influencing the degradability were the frequency of tertiary carbon atoms in the chain and the presence of a pro-oxidant additive. The primary (sterically hindered phenol) and secondary (phosphite) antioxidant additives added to PP slowed but did not prevent rapid photo-oxidative degradation, and in HDPE and LLDPE the secondary antioxidant additive had little influence on the rate of abiotic degradation at the concentrations used here. |
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Keywords: | HDPE LLDPE PP Polyolefin weathering and degradation Antioxidant and pro-oxidant additives |
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