Plastics have been used to increase food production and conserve water for 50 years in horticulture and agriculture: the demand in this market was 2.8 mln tons in 2009, according to Andrew Reynolds, Research Director at Applied Market Information (AMI). Film applications include greenhouse (31%), mulch (45%) and silage (24%). Asia is by far the largest market, followed by Europe. Reynolds was speaking at the AMI conference on Agricultural Films. As food security becomes a global issue, plastics can be used in developing sustainable, high levels of production. The International Federation of Agricultural Producers (IFAP) has reported that farm output needs to double by 2050.
The 2008 UN Population Report outlined trends worldwide from 2009 to 2050, including an increase in North and South America, Africa and Asia, with a fall in Europe, and predicted that overall the global population will rise from 6829 mln in 2009 to 9149 mln in 2050. BSK Plast Pack & Agrarservice und Trade has studied this report in relation to plastics demand: Europe, Japan, and the Anzac nations are relatively mature markets, whereas Brazil, Mexico, China, India and Russia are rapidly growing and want to increase productivity in agriculture. In Europe there is expected to be competition for crops grown for energy (principally bioethanol) and for food. EU Directive 2003/30 states that by 2020, 10% of fossil fuels must be replaced by biofuels. This will change demand for plastics, for example, packaging silage for animal fodder versus packaging for fuel conversion. A large amount of crop will have to be packed, stored and transported for the new industry and the plastics processors will need to adapt to requirements.
Professor Pietro Picuno of the University of Basilicata has reviewed environmental aspects of the use of plastics in agriculture: the major uses are for protection from wind, hail, snow and heavy rainfall in fruit and ornamental plant production, and to create a better microclimate for production. In Southern Italy there is increasing use as protection for crops like vines and kiwi fruit grown in the traditional structures. There is a need to develop covers with lower visual impact in tourist regions where large areas are under cultivation. Plastics waste is another issue as film covers degrade over time, so the LabelAgriWaste project was set up to encourage labelling and recycling of used plastics. As productivity increases alongside environmental awareness, there has been a move towards sulfur based pesticides according to BASF. Sulfur is commonly used as a fungicide for grapes, strawberries and vegetables, and is the primary agrochemical for organic production. A BASF study of agricultural films collected from different regions showed that plasticulture countries like Spain and Morocco have a major percentage of films exposed to sulfur levels in excess of 1500ppm. This has led to a need for new light stabilizers to protect the plastic such as Tinuvin XT 200, which is registered for REACH and has undergone extensive field trials, including treatment of films with a wide range of current pesticides such as permethrin and methyl bromide. Test films were set up at sites across the world including Zhejiang, Sicily and Guadalajara, and amounting to over 5000 hectares since 2006. In the BASF portfolio, Tinuvin NOR 371 and Tinuvin ST 200 light stabilisers show the best resistance to agrochemicals.
Kafrit Industries has examined the effect of UV absorbers on film resistance to pesticides. Studies showed that raising sulfur levels from around 1000ppm to 2000ppm reduced the life of greenhouse films by 20-25%. UV absorbers act by absorbing radiation and dissipating it as heat, for example by proton transfer in phenolic based chemicals. Under artificial weathering testing BZT type absorbers degraded fastest, then TRZ type I and II, whereas TRZ III showed little change. Hindered amine light stabilizers (HALS) were added to different UV absorbers and compounded into PE/EVA films then exposed to sulfur in field trials. HALS I with BZP failed at 16 months and the best performance came from HALS II plus TRZ III, which showed the least reduction in absorbance and lasted around 30 months. Kafrit is seeing new market demand for films resistant to 3,000ppm sulfur.
EVOH (brand name Soarnol) from Nippon Gohsei is used in stretch silage films in agriculture. The material is a copolymer of ethylene for extrudability and vinyl alcohol for barrier properties. The University of Torino has shown that the oxygen barrier properties of standard PE do not preserve the quality of forage in long-term storage, because it allows yeast and fungi to grow, aerobic degradation and a rise in temperature. There are significant improvements with a thinner silage film with an EVOH layer.
Another use of EVOH in agriculture is for fumigation films, to prevent contamination of the surrounding area. EVAL Europe (part of the Kuraray Group) is a supplier of EVOH in the totally impermeable film (TIF) market; this has use in applications such as broadcast fumigation, as a fumigant barrier in mulch, as an oxygen and odour barrier in silage, and to extend the lifespan of fumigant impregnated greenhouse film. A TIF film is multilayer comprising typically, outer layers of PE, adhesive layers and a middle EVOH layer. Nylon can also be used as the barrier layer, but it is not as effective (VIF film).
Polimeri Europa supplies ethylene-vinyl acetate copolymer (EVA) used in coextruded EVA-PE films to the agricultural market and lists the benefits of the material in greenhouse and tunnel use: improved thermicity, toughness, elasticity, transparency, good creep resistance, longer lifespan and photoselectivity beneficial to crops. Use in this market is expected to increase. A standard greenhouse film incorporating EVA includes UV absorbers, HALS and antifog, and a high thermal film combining 19% EVA with LLDPE, also includes mineral fillers. The coextruded greenhouse films were shown to improve crop yields of tomatoes, eggplant and cucumbers.
Biodegradable plastics are increasingly being used in mulch films. The Telles grade Mirel A5004 can be used in cast and blown mulch films with thickness from 8 to 125 microns. In field trials it improved the yield of red and green fruit compared to PE film and it has been tested at sites worldwide. Camp Tecnico of Japan has produced high performance biodegradable film, by blending higher and lower melting point bioplastics. The resulting film has higher strength than conventional LDPE film. Biodegradation speed can be controlled to fit the crop, e.g. 5 months for a rice paddy dyke and 15 months for Chinese chives.
Clariant produces masterbatch for biodegradable plastics and other agricultural films, including IR absorbers, anti-fog and photoselective. Light stabilizers used for polyesters, such as benzotriazoles, can be used for PLA as well, although PLA often does not require additional light stabilization. Fatty acids, talc and silica can be used as anti-blocking agents for bioplastics, and talc and calcium carbonate can be used as nucleating agents during foaming. Clariant has “OK Compost” certification for its bioplastics masterbatches, some of which were developed with Novamont and are pigmented. Kuhne has tested and adapted machinery for biodegradable film production. Paul & Co. supplies paper cores for winding agricultural films, and these have been tested for weathering. They are made with 100% recycled paper and glue made from naturally occurring materials, and can be included in paper recycling or composted, according to the manufacturer.
In South Africa, GREENCULT has developed netted mulch for use with cucurbit crops like melons and butternut squash. Wind stress causes a lot of problems with these crops, tearing leaves, exposing fruit to excess sunlight and twisting the stems. Conventional mulch films are too smooth and don’t provide anywhere for the vine tendrils to hold on, so nets over the mulch can provide more stability for the plants and also reduce tearing of the films. The system is patented and was tested on a farm in Worcester, where melon yield was raised around 15-20% by using netted mulch compared to conventional material.
Plastic mulch decreases the amount of water required in irrigation. Different films can also improve crop yield, for example, Naksan has presented data showing that yield of water melon using clear plastic was around 30 tons per hectare, and with silver-black mulch this rose to 90 tons per hectare. The reflected light from the coloured mulch enhanced photosynthesis and deterred pests.