Sustainable composites for mulch films preparation: Evaluation of starch, chitosan and alginate-based formulations

MERINO, D.; COLMAN, S.; SALCEDO, M.F.; ALVAREZ, V.A.; MANSILLA, A.Y.; CASALONGUÉ, C.A.

Sorocaba, San Pablo

Workshop; III Workshop in Environmental Nanotechnolgy; 2018

University of Sorocaba

In order to improve yields and crop traits, polymeric materials are commonly used to cover soils as agricultural mulchfilms. Their use provides important benefits to farmers and the environment: they maintain humidity, temperature andprevent the growth of weeds. However, the most widely used mulches are mainly made of low density polyethylene(LDPE). The use of polyethylene films or other non-biodegradable polymers presents great environmental and economicdisadvantages for responsible farmers, which have to remove them before the next crop period. In this context, thedevelopment of biodegradable or short lifespan films is highly attractive. The objective of this work was to developdifferent sustainable formulations of mulch films and evaluates their ability as active agricultural mulch films. Starchnanocomposites with chitosan-modified bentonite as filler, starch-chitosan composites with natural algae (UndariaPinnatifida) and the novel alginate composites with the same algae applied by spray were prepared. Compositespreparation. Starch nanocomposite films were prepared from native and oxidized corn starch using 30% (w/w) of glycerolas plasticizer and 4% (w/w) of filler (Bent or Bent-CS). Nanocomposite films were prepared by extrusion in an ExtrualexDoble Argentina twin screw 25% Starch- 75% chitosan composites with 30% glycerol as plasticizer with and without0.5% of algae powder as filler were prepared by solution casting. Films were dried in an oven during 48 h at 45 °C. Similarprocedure was followed for alginate-algae solution preparation but they were not obtained as films since they weredirectly applied by spray onto soil. Water vapor permeability (WVP) was measured according to the desiccant methodproposed in ASTM E96-00e1. Transparency was determined by UV−vis spectrophotometry. Tensile tests were performedin a universal testing machine INSTRON 3396. The antibacterial activity was evaluated against phytopathogenicbacterium Pseudomonas syringae pv tomato DC3000 (Psy) using agar disc diffusion technique or counting colony formingunits (CFU) after the treatments. For in planta assays, pots with commercial soil mixture were covered with different filmsto be tested as agricultural mulch. As a control, polyethylene (PE) was used. Tomato seeds (Solanum lycopersicum var.Platense) were soaked for 4 hours and 12 seeds were planted per pot. Seeds were incubated at 25 ° C with a photoperiodof 16 hours light/ 8 hours dark (120 μmol photons m-2 s-1) and controlled humidity. Soil temperature and water contentwere recorded in each pot. Results indicated no significant differences in the WVP of the different starch matrices andtheir nanocomposites. With regard TPS-CS composites the addition of algae produced an increase in WVP. Oxidation ofthe TPS matrix to give TPS-Ox produced a statistically significant increase in Young?s modulus and tensile strength with adecrease in elongation at break. In TPS, the plasticizing effect promotes the decrease of these parameters and the increaseof elongation at break. Then, the addition of the Bent and Bent-CS nanoclays to both matrices did not produce changes orproduced a decrease in the mechanical properties of the nanocomposites. Results the lower transparency or greateropacity was obtained for the TPS-Ox film. In general, the addition of Bent and Bent-CS produced a decrease in the opacityof the films, but this was more significant for the TPSOx matrix. The incorporation of CS or Bent-CS to starch films confersthem antibacterial activity. Addition of different amounts of algae to the films did not produce significant variations in thisactivity. Soil microorganisms play an important role; they participate in nutrient mineralization, soil structure formation,and the capture and transport of nutrients to crops. We reported the preparation and properties of different sustainableagricultural mulch films formulations based on thermoplastic corn starch: nanocomposites with chitosan-modifiedbentonite as filler by extrusion, starch-chitosan composites with natural algae (Undaria Pinnatifida) by casting andalginate composites with algae applied by spray. Results suggest that the materials proposed presented interesting light,barrier and antibacterial properties but still is needed to improve mechanical ones and reduce their interaction withwater.