Biodegradação do polipropileno pró-degradado com ácidos de Lewis

Abstract

Low-cost and short term polymers are essential to the environment. Controlled isotactic polypropylene (iPP) degradation via prooxidant additives is a way to lower the molar mass of the polymer. Usually these additives are peroxides and transition metal ions stearates (1-3) and the biodegradation of these modified polymers is also studied (3-6). Lewis acids are used as in-situ compatibilizants (7-9) and fillers for iPP (10). However, clarification is needed in terms of how some Lewis Acids degrade iPP in processing conditions and how the bacteria isolated from a specific topsoil act as biodegrading agents of the degraded polymer. In this work, it is aimed to understand the role of AlCl3, FeCl3 and AgNO3 as prodegradant agents of iPP by mixing them (separately) on the polymer in different concentrations in an internal mixer, and to understand the bahviour of the isolated topsoil bacteria in the presence of the degrade polymer as their only carbon source and in the presence of degraded polymer plus glucose as carbon sources. Results are obtained via parallel plate rheometry, DSC, FTIR, SEM and other techniques. Rheometry and DSC tests showed that AgNO3 is the Lewis acid that achieved the biggest degradation of iPP, reducing the polymer average molar mass the most in the concentration of 2.00 %w, from 221,473 g/mol to 114,270 g/mol, in the processing conditions. AlCl3 also reduced the molar mass of the polymer to 150.139 g/mol, while FeCl3 did not act as a prodegradant due to its melting point being higher than the processing conditions, thus reducing its reactivity with iPP. FTIR results showed us that double-bonds where formed on during degradation with AlCl3 and AgNO3 as prodegradants, in roughly the same amount, but only AgNO3 formed more aldehyde carbonyl than AlCl3, explaining why AgNO3 is more effective as a prodegradant agent than AlCL3 on iPP. In terms of biodegradation, SEM images shows us that in the conditions where glucose was part of the system, the bacteria were formed in a bigger quantity in the AlCl3 mixtures, a viscous material can indicate the formation of biofilm in the polymer surface, and the bacteria morphology did not show signs of cracks in the cellular wall. The test with AgNO3 shows a smaller population of bacteria and their cellular wall is affected by the silver in the system, modifying its morphology.