BIODEGRADABILITY OF CELLULOSE AND CHITOSAN BASED MULCHING FILMS ENRICHED WITH MONOAMMONIUM PHOSPHATE

Abstract

Plastic pollution has emerged as a significant environmental concern, particularly in the agricultural sector, where plastic mulching films are commonly used to enhance crop productivity and control weeds. However, the extensive use of conventional plastic films has led to serious environmental issues, including soil contamination and accumulation of non-biodegradable waste. Therefore, there is a growing need to develop sustainable alternatives that can provide similar benefits without causing long-term harm to the environment. Within the Mulching+ project, funded by the Italian Ministry of University and Research, innovative mulching films based on cellulose and chitosan, as well enriched with ammonium phosphate (NH4H2PO4), have been developed. However, if such innovative films are biodegradable or not, it is under investigation. The aim of this study was to assess the chemical characterization and biodegradability of these innovative mulch films. For the study, 4 types of mulch films were used. The films were prepared using a 1:1 or 17:3 mass ratio of chitosan to cellulose, both with and without the addition of 90% NH4H2PO4. First, an elemental analyzer-isotope ratio mass spectrometer (EA-IRMS) coupled system was used to evaluate C and N concentrations of these films and their isotopic signatures (i.e., δ13C and δ15N). Moreover, the films were analyzed by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) in order to characterize their chemical structure according to the different components. Furthermore, by means of Py-GC-MS a fingerprint is obtained which is useful both for highlighting any structural changes due to biodegradation and for determining its presence in soil matrices. To test the biodegradability, the films were cut into pieces less than 5 mm in size and added to the soil at a ratio of 1.5% (w/w). During a 120-day monitoring period, CO2 emission was measured. According to ISO 17556, a plastic material is considered biodegradable if the difference in CO2-C between the soil with the film and without (control soil) is 90% or more of the carbon added as film. The obtained results indicated that the CO2-C difference between the 1:1 mass ratio film-modified soil and the control soil was greater than 90% of C added as film, suggesting that the 1:1 films are completely biodegraded within 120 days. In contrast, films with a 17:3 mass ratio did not achieve complete biodegradation within 120 days. In conclusion, this study showed that mulch films made with 1:1 ratio exhibit good biodegradability in soil. These results offer promising prospects for the use of these innovative films as a sustainable alternative to plastic in agricultural mulching practice. Further research will be needed to optimize film formulations and evaluate their effectiveness in the field.