Co-authors​ :

 Alessandro SORZE (ITALY), Francesco VALENTINI (ITALY), Andrea DORIGATO (ITALY), Alessandro PEGORETTI (ITALY) 

Topsoil covers (TSCs) are bio-based mulching films aimed to support reforestation and agriculture in arid conditions, by the inhibition of weed growth and the reduction of soil moisture losses after transplantation [1,2]. This study is focused on the development of bio-based composites as TSCs using Xanthan gum (XG) and wood fibers. Therefore, the idea behind this work was to find a viable, high-performance alternative to commercial plastic mulching films, which pose a serious threat to the environment [3]. By coupling biopolymers, characterized by high-water absorption capacity such as Xanthan gum, and other biomaterials, characterized by high-water retention capacity such as wood fibers, it would be possible to improve water management and reduce water consumption during irrigation. Different formulations of TSC were produced by first mixing XG and wood fibers in aqueous solution, and then by cross-linking the produced XG hydrogels with citric acid (CA), sodium trimetaphosphate (STMP) or tannic acid (TA) in different concentrations and under specific heat treatment conditions. The optimal cross-linking was achieved with a thermal treatment in an oven at 165 °C for 3 minutes and 30 seconds. TSCs cross-linked with CA exhibited the highest stability and exceptional water absorption capability (up to 1500 % increase over the original weight), retaining their shape even after multiple absorption and drying cycles. On the contrary, the use of STMP and TA as cross-linking agents, showed instability and leakage already after the second absorption cycle, due to a very high swelling of the samples and cracking. Additionally, TSCs with 50, 60, and 100 phr of CA displayed water vapor permeance values of 4.8·10−6 g/(Pa·s·m2), comparable to a commercial woven PP mulching film, as well as good dimensional stability and minimal volumetric shrinkage (14.6 %) after exposure to outdoor conditions. From tensile tests, it was found that the films showed poor tensile strength (less than 1 MPa) due to the presence of high porosity in the structure (also observed by scanning electron microscopy). However, the elongation at break was about 12 % for the CA cross-linked samples, which is comparable to that of bio-mulching films in the literature. Biodegradation assays were conducted in order to demonstrate the biodegradability of the produced TSCs. This research showed the potential of Xanthan-based composites as TSCs when cross-linked with citric acid, offering a simple, cost-effective, and scalable technology for forestry and agriculture applications with superior water-regulating properties.