An overview of biodegradable films and spray coatings as sustainable alternative to oil-based mulching films

The use of plastic materials in agriculture causes the serious drawback of huge amount of wastes to be disposed of. In order to overcome this problem a new generation of biodegradable materials has been developed based on raw materials coming from renewable source. These materials retain their physical and mechanical properties during their lifetime and when they are integrated directly in the soil, the bacterial flora transforms them in carbon dioxide or methane, water and biomass. Biodegradable films can be made using natural polymers, such as starch, cellulose, chitosan, alginate and galactomannans. These materials can be obtained by means of thermoextrusion process, solvent casting and spraying technique. Mulch coatings can be realized directly in field by spraying water solutions based on natural polysaccharides, thus covering the cultivated soil with a protective thin geo-membrane. In this paper a focused overview on the formulation development, processing understanding, field performance and mechanical properties of these innovative materials for soil mulching is presented, in comparison to oil-based non renewable films. During their using time in field, the biodegradable mulches showed suitable mechanical properties if compared to the low density polyethylene films. At the end of their lifetime the biodegradable materials were shattered and buried into the soil together with plants. The film residues disposed of in the soil biodegraded in almost 1 month for the water borne coatings and in about 12 months for the biodegradable starch- based extruded films.