Photodegradation and Biodegradation Under Thermophile Conditions of Mulching Films Based on Poly(Butylene Adipate-co-Terephthalate) and Its Blend with Poly(Lactic Acid)

Two commercial mulching films based on aliphatic-aromatic copolyesters, poly(butylene adipate-co-terephthalate) (PBAT) and its blend with poly(lactic acid) (PBAT/PLA) were selected to study their photodegradation and their biodegradation under thermophile conditions. The films were buried in an agricultural field and bacteria were isolated from these. Bacterial strains were characterized with a combination of culture-dependent methods and sequencing of part of the 16S ribosomal RNA gene (rDNA). The most prevalent genus isolated was Bacillus and other related genera were found as well. Consortia of the isolated indigenous bacterial strains, IDN-EF and IDN-EC, and an additional consortia that had been previously isolated from exposed polyethylene, Bacillus-MIX, were prepared to perform the biodegradation assay at 45 degrees C on highly photodegraded films. Changes in the films were studied using chemiluminescence, ATR-FTIR, contact angle, SEM, GPC, DSC and TGA. A biodegradation assay was also performed on the four monomers that constitute the polymers using Bacillus subtilis and Bacillus licheniformis. Mineralization was evaluated by carbon dioxide measurements using an indirect impedance technique. This technique showed that overall there was a higher mineralization for the photodegraded materials. However, the biodegradation was most efficient when B. subtilis was present in the bacterial consortium and especially when the materials had been previously photodegraded.