Agriculture/Horticulture a) b) Figure 1.a) The film obtained by low-pressure spray technique onto a glass surface and then detached is flawless, flexible, and resistant to tearing; b) Mulching coating via the spray technique at the experimental field. How to eliminate agricultural plastic waste using bioplastics a) Figure 2: a) The setting up of the mulching coating at the beginning of the experimental field;b) Mulching coating and c) the control (un-mulched) after 90 days. b) c) By: Evelia Schettini Giuliano Vox University of Bari Bari, Italy Figure 3: Scanning electron microscopy image of a mulching film section obtained after cryogenic fracture after six month’s exposition to soil (left) and sunlight (right). Luciana Sartore University of Brescia Brescia, Italy Figure 4. The containers for seedling transplanting based on biodegradable polymeric materials. a) b) Figure 5. The biodegradable containers at the transplanting (a) and after 16 days in the substrate. 26 bioplastics MAGAZINE [<strong>02</strong>/17] Vol. 12
Agriculture/Horticulture Petroleum based plastics are largely used in agriculture as plastic films for crop protection and soil mulching, pipes, containers for seedlings transplanting and pots. After the cultivation period is complete, however, agricultural plastic waste is coated with soil, organic matter, and agrochemicals and must therefore undergo the correct collection, disposal, and recycling processes. One sustainable solution to the serious problem of the environmental pollution is the employment of biodegradable polymeric materials in agriculture; such materials are able to be integrated directly in the soil, at the end of their lifetime, where the bacterial flora transforms them in water, biomass, carbon dioxide or methane. Many of the possibly suitable biodegradable polymers, however, show unsuitable mechanical performance or processability and may be not cost effective if compared to petroleum based plastics. Due to increasing environmental awareness, researchers continue to seek new materials that can be used as ecologically friendly alternatives to agricultural materials based on synthetic petrochemical polymers. The research teams around the authors have developed biodegradable polymeric materials—for spray mulching coatings and plant pots—by using protein hydrolysates that are derived from waste products of the leather industry and functional poly(ethylene glycol) as a crosslinking agent [1, 2] Protein-based waste materials are especially suited for this purpose because they have an intrinsic agronomic values for soil fertilization due to their high nitrogen content. Several experimental tests were carried out to prove the feasibility to generate in situ mulching films and coatings showing good mechanical performances and environmental durability (Figure 1a and Figure 1b). Their functionality as well as their mechanical and physical behaviors was investigated in standard and controlled experimental conditions [1, 2]. To assess whether or not water suspensions would be capable of achieving a consistent coating when sprayed directly onto soil, poly(ethylene glycol) diglycidyl ether (PEGDGE) and protein hydrolysates were chosen as starting materials. The scientists prepared the novel derivatives in water solutions following a synthetic procedure based on the reaction between protein hydrolysate amino groups and functional end groups of PEGDGE. They also added wood-cellulose microfibers (up to a final 18wt %) to enhance the mechanical properties of the composite, and carbon black to obtain black films (and thus prevent photo-oxidation and weed photosynthesis). The bioplastic solutions were then distributed with an airbrush using a spray machine. In this way, it was possible to completely cover the growing substrate around the plants with a thick mulching coating that dried to a hard consistency (Figure 2a). The biodegradable coatings maintained their mulching effect for a period ranging from one to nine months achieving weed suppression (Figure 2b and Figure 2c). The lifespan of the coating depends on its thickness as well as the temperature and moisture content of the soil, but is mainly dependant on the structure and morphology of the material. Morphological analysis performed on a sample that was directly sprayed onto the soil and exposed for six months—see Figure 3—shows a different pattern depending on its exposure. The side exposed to solar radiation does not differ significantly from the original film, and there is no indication of degradation. The surface facing the soil, however—see Figure 3—consists almost exclusively of fibers, thus indicating that degradation begins in the polymeric component of the material. These results show that the biodegradation process occurs more rapidly where there is direct contact between the film and micro-organism and the remaining fibers act as a barrier, modulating the environmental duration of the blend thus promoting slow release of fertilizers. More recently tests were carried out using novel biodegradable containers for seedlings. The objectives of this research are to develop new biodegradable materials starting from renewable biobased raw products, and to engineer the properties of these materials so that they can be used to produce biodegradable plant pots that guarantee no damage to roots, no transplant shock, an enhancement to plant growth, and the slow release of fertilizing protein-based compounds during their degradation. The preparation of these novel biodegradable polymeric materials began from an aqueous solution of protein hydrolysate (derived from waste products of the leather industry), PEGDGE, and natural fillers (i.e., sawdust or wood flour). Compounding was then performed in a Brabender mixer at 60°C and subsequently the pots were prepared by compression molding the biocomposites (which were the consistency of a paste) and drying them at 70°C: see Figure 4. It was found that the biodegradable containers for seedlings showed good resistance during the first stage of use (i.e., when the seedlings were grown from seed, before transplanting): see Figure 5(a). After the transplant, the containers (which were buried in soil) degraded in roughly two weeks, allowing the roots to pass through the container walls and thus enabling the overall growth of the plants: see Figure 5(b). As a result of the slow release of proteinaceous material, the containers showed a soil-positive fertilizing effect. To test the efficacy of this approach, the researchers implemented them in the cultivation of pepper plants. At harvest, the mean height of the pepper plants grown inside the biodegradable pots was 0.94m. In contrast, the control plants (grown in non-biodegradable containers) were characterized by a mean height of 0.67m [3]. In summary, the newly developed biodegradable sprayable mulches and plant pots (for transplanting seedlings) could promote valid ecologically sustainable cultivations, enhance the protection of the landscape against pollution in rural areas, and increase the use of renewable non-oil raw materials. The teams are currently experimenting with these approaches by applying them to different cultivations. They hope to prove the feasibility of their novel biodegradable materials by investigating their functionality as well as their physicochemical and mechanical behavior in standard and controlled experimental field conditions, and by following their biodegradation process during plant cultivation. References [1] L. Sartore, G. Vox, E. Schettini, 2013. Preparation and Performance of Novel Biodegradable Polymeric Materials Based on Hydrolyzed Proteins for Agricultural Application J. Polym. Environ. 21 (3), pp718-725. doi: 10.1007/ s10924-013-0574-2 [2] E. Schettini, L. Sartore, M. Barbaglio and G. Vox, Hydrolyzed protein based materials for biodegradable spray mulching coatings. Acta Horticulturae (ISHS) 952, pp.359-366, 2012. [3] L. Sartore, E. Schettini, F. Bignotti, S. Pandini, and G. Vox, Biodegradable plant nursery containers from leather industry wastes, Polym. Composite. 2016. doi:10.10<strong>02</strong>/pc.24265. www.uniba.it | www.brescia.edu bioplastics MAGAZINE [<strong>02</strong>/17] Vol. 12 27
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