ADVANCED BIOFRIENDLY POLYMERS Mulching foils photochemical hydrolytical and

ADVANCED BIO-FRIENDLY POLYMERS Mulching foils – photochemical, hydrolytical and biodegradation Štefan Chmela

Plastic films for mulching of the soil are used to improve cultivation conditions and to modify the soil microenvironment under the covering by controlling soil humidity and temperature. Mulching films reduce water evaporation from the soil and the washout of nutrients into the ground water while the cultivation area is protected against erosion. The use of mulching film enables reduction of weeds and plant diseases coming from the soil, thus reducing the use of pesticides. Also plants are cleaner; the cultivation can start at lower soil temperatures; yield is higher with mulching films. Ø Foils thickness 12 – 80 µm Ø Width up to 3 m Ø Lifetime 2 -4 months Ø Colorless or pigmented (carbon black)

Current intensive and semi-intensive agricultural practices used throughout Europe require the use of large quantities of plastics. Recent data suggest that agriculture and horticulture is responsible for a consumption of some 1 500 000 t/year of all polymers in Europe. Concerning the category of thin films, more than 130 000 t/year mulching films are consumed per year in Europe and 2 600 000 t/year worldwide (2003– 2005). The corresponding consumption of direct cover and low tunnel films in Europe are 72 000 and 75 000 t/year, respectively.

The extensive and expanding use of plastics in agriculture results in increased accumulation of plastic waste in rural areas. Part of this plastic waste may be recycled, especially the greenhouse films, silage films and fertilizer sacks, pipes and other plastic products. Another part of the agricultural plastic waste is difficult to recycle for technical and/or financial reasons. A major agricultural plastic wastes category of low-recyclability (in general) are thin mulching films and in some cases, thin low tunnel and direct cover films. These films are too thin and usually heavily contaminated by soil and foreign materials.

The most common current disposal practices for the non-recyclable, but in many cases also for recyclable agricultural plastic wastes, is burying in the soil (mulching films), burning, or disposing them at the open fields or in landfills. These practices are illegal of course and have serious negative consequences for the environment Thus, for example polyethylene (PE) based mulching films do not break down in soil and should never be roto-tilled or incorporated into the soil However, the process of recovering and recycling them, following the end of the cultivation period, is difficult as approximately 80% of the weight of the recovered waste mulching film is foreign materials (e. g. soil, sand etc. ). Also the cost of removing from the soil and cleaning this material is prohibitively high. This is the main reason why the farmers usually incorporate them into the soil by roto-tilling, a practice which, apart from being illegal, also implies a serious risk for the environment due to the accumulated PE in the soil. An alternative option for disposing non-recyclable agricultural plastic waste is their use as alternative fuel for energy recovery (at a high cost).

Specifically for the case of agricultural plastic wastes that cannot be easily collected and recycled, a very attractive alternative is biodegradation. This refers to the replacement of conventional agricultural plastics, which cannot be recovered from the field for technical and/or financial reasons, with biodegradable mainly bio-based ones, which will biodegrade in the soil after the end of their useful lifetime without leaving toxic or polluting remains. The current use of biodegradable, mainly bio-based, plastics in agricultural applications in Europe is very limited (about 2 000 t/year in 2006). However, the use of biodegradable polymers for agricultural plastics is increasing for specific applications in the agricultural sector. Bio-based polymers are now moving into main-stream use for many applications (packaging being the dominant one), and the polymers based on renewable ‘‘feedstock’’ may soon be competing with commodity plastics, as a result of the sales growth of more than 20– 30% per year.

Plastic mulching foils PVOH PLA PTAB poly(butylene adipate-co-terephthalate) PCL PHAs Poly(butylenes succinate) PBS

Photodegradable polyethylene with pro-oxidants Several types of pro-oxidants (salts of iron manganese and cobalt, stearate) have been designed for polymers used in landfill, compost and soil disposal applications. As it is claimed from the technical guides and reports, these additives when compounded with conventional polymers at appropriate levels control the lifetimes of plastic films and articles. This degradation leads to the fragmentation of the plastic waste without need for collection and waste disposal. It is claimed that the oxidized molecular fragments are hydrophilic, have molar mass values reduced by a factor of 10 or more, and are biodegradable. However, from the various reports it is stated that materials with the above additives are fragmented into small parts, invisible to the eye, but it is not yet known if these parts are really biodegradable i. e. accessible by microflora (fungi, bacteria and the like) to convert and assimilate the carbon in any substrate and if yes, at which rate.

polyethylene with pro-oxidants Graph of fragmentation versus biodegradation The controversy over these materials is shown schematically in Fig. Degradation/Fragmentation are shown to represent the fist (preliminary) stage of the biodegradation process. Heat, moisture, sunlight and/or enzymes shorten weaken polymer chains in this stage, resulting in fragmentation residues and cross-linking to create more intractable persistent residues. Biodegradation is the second stage of this process and is considered to occur only if the fragmented residues are totally consumed by microorganisms as a food & energy source and if this happens in an acceptable rate. Biodegradation of the fragments of photodegradable (fragmentable) polymers based on polyethylene with pro-oxidants, remains however an open question as it has not been proven beyond any doubt while it failed to all biodegradable norms and standards

Europe is currently well placed in the markets for innovative bio-based products, building on established knowledge and a leading technological and industrial position. However, the bio-based polymers are not used widely as perceived uncertainty about product properties and weak market transparency hinder the fast take-up of these products. While some progress has been made with the expansion of the use of bio-based and biodegradable (compostable) packaging materials, the development, use and expansion of bio-based and biodegradable materials and products in the European Agriculture is very much limited. The two main reasons for this hysteresis are (a) the current cost of the bio-based and biodegradable plastics compared to the conventional ones in certain applications, and (b) the still open discussion with regard to testing agricultural biodegradable plastics for biodegradation in soil and under farm composting. The second one hinders the development of a relevant certification and labelling scheme which could be implemented, for example, in synergy with the recently developed labelling scheme for agricultural plastic wastes. For the same reason, confusion still exists in the marker about the performance of these materials under real soil conditions that hinders the wider expansion of their use in agriculturalapplications.

The rationale for the acceptance of biodegradable polymers in soil under ambient conditions may be summarised as follows: – Complete biodegradation (not simply disintegration): 90%; – Duration: depending on application – No harmful effect on soil quality and environment (heavy metals—ecotoxicity)

ASTM D 20. 96, Standards development protocol for degradable plastic products

General mechanism of plastic biodegradation under aerobic conditions

Ecoflex

Commercially available biodegradable mulches • AGROERG S (ERG Bieruń–Folie Sp. z o. o. , Poland), based on PE • Plastic Suppliers Inc. , Earth. First® PLA • • Rootplast International Inc. , Ohio, USA (http: //www. rootblast. cc/prodinfo. asp? number=ZWBR-8) • Waste not, Marchant Manufacturing Co. Ltd. , UK • BAYER AG „BAK“ (polyester amide family of biodegradable resins for agroculture applications, Germany) • Baoding Fengba Modern Agricultural Facility Co. , Ltd. , China (PE mulch and greenhouse film) • Shanghai Hi. Te. C Plastics, Shanghai, China LLDPE-PLA/starch blends • MATER Bi ® (Novamont, Italy) naturally biodegradable and compostable (PLA) ? ? ?

Materials PP – polypropylene, Tatren HPF, Slovnaft, Bratislava Ecoflex® F Blend C 1200 Biodegradable polyester for compostable film BASF statistical, aliphatic-aromatic copolyester based on the monomers 1, 4 butanediol, adipic acid and terephthalic acid in the polymer chain. Ecoflex® F Blend C 1200 will biodegrade to the basic monomers 1, 4 -butanediol, adipic acid and terephthalic acid and eventually to carbon dioxide, water and biomass when metabolized in the soil or compost under standard conditions. Ecoflex® F Blend C 1200 has properties similar to PE-LD Samples from STU, Faculty of food and chemical technology PLA-M 1 (Svit) PLA/PHB = 85/15 wt. + 10 % TAC

Preparation of film by pressing Photo-degradation Irradiation in two equipments 1. Merry-go-round apparatus, 250 W medium pressure mercury arc, laboratory temperature 2. Suntest CPS – Xenon arc, 40 o. C (minimal temperature) Analysis – FTIR spectroscopy, GPC

FTIR spectra of original films PLA-M 1 Ecoflex PP

Comparison of PP and Ecoflex photo-oxidation – carbonyl region Ecoflex Quantification for Ecoflex– almost impossible, huge carbonyl absorption, questionable subtraction, similar for PLA-M 1 (Svit) PLA/PHB = 85/15 wt. + 10 % TAC