The global agricultural film market consumed 3.6 million tonnes of plastic in 2007, with roughly 40% each on mulch and greenhouse film and 20% on silage film, according to Andrew Reynolds of AMI. Populations are growing and the same area under cultivation is expected to feed more people each year, so efficiency has to improve. Mr Reynolds was speaking at the AMI conference, Agricultural Film 2008 held in Barcelona.
Agricultural film is wide and production requires large extruders, special dies and good cooling systems; Davis-Standard lists standard sizes as:
- Silage wrap, 25-150 micron, 0.7-1.6m wide
- Mulch film, 30-90 micron, 1-1.2m wide
- Greenhouse film, 100-250 micron, 4-20m wide
- Fumigation film, 20-40 micron, 4-12m wide.
The masterbatch producer, Grafe, describes a standard greenhouse film as being 3-layered, 200 micron thick, comprised of PE and EVA, UV stabilisers (commonly hindered amine light stabiliser, HALS), an IR absorber (clay), a light diffuser (chalk), a UV absorber, and an antifog agent. Grafe has been carrying out research to reduce the loading using better additives with more transparency, and using the theory of light management. Coloured films are photoselective. XL Horticulture has a Smart Blue film which delays flowering for horticulture applications. The Smartlight luminescent additive gives a red film which helps to reduce rose petal blackening in the heat of South America.
Wageningen University in the Netherlands is a key focus of research on greenhouse coverings, analysing light transmission by different film types, temperature and crop growth. The active radiation for photosynthesis is 400-700 nm. If there is more blue light, plants have shorter stems, smaller thicker leaves and more side shoots, with less blue light, there is greater leaf area and faster growth. Different crops benefit from different wavelengths at different stages. For example, UV is needed for the colour in aubergines and lollo rosso, and also for bumble bees. Dark red roses, young plants and most leafy vegetables benefit from UV block films.
Repsol has worked on films for a variety of weather conditions. Cold climates require ultrathermic films with higher IR blocking effect and better antifog. In hot regions, degradation is a bigger problem: the best films have high NIR and UV blocking, good PAR transmittance and photostabilisation.
Total Petrochemicals has produced a metallocene polyethylene for greenhouse films with both stiffness and transparency, and it can be downgauged saving costs. It has been tested for pesticide and UV resistance. Rohm and Haas has developed a new film material for multispan greenhouses, which it claims will cost around 4% less than PE over a 15 year period. It has been tested in 150 micron gauge, against ETFE, PVC and PE. It offers excellent light transmission and durability.
Techmer has advanced IR reflector technology – the PM13548 product helps to control heat and maintain the radiation balance in the greenhouse, reducing the need for shading. Ciba’s main focus is light stabilisers and agriculture is the key application: Tinuvin NOR 371 has been used to extend cover life from 2 to 3 years in Sicily and outperforms methylated HALS + triazine.
Juergen Kloecking of BSK Plast Pack estimates global consumption of silage stretch film at 180,000 tonnes and production as 200,000 tonnes. The number of cows in Europe is declining and so is the silage film market. TEAGASC (Ireland) has carried out research on silage film – silage is pickled grass, fermented in anaerobic conditions. If the seal fails the grass goes mouldy. Damage to the film can occur on the roll, if bales are dropped or by cats, rats and birds. With bird attack, repellents are ineffective so methods such as painted images have been tested to some effect. Cabot has tested carbon black or a combination of titanium dioxide and HALS to protect silage film from degradation. Kronos also supplies titanium dioxide masterbatch for film applications: TiO2 is a strong UV absorber. The new grade disperses easily and helps to improve PE performance.
In Europe there are 400,000 hectares of mulched land. Mulch film needs to be opaque to prevent light reaching weeds around growing plants and impermeable to conserve water, but it can be difficult to recover after use hence degradable films are being trialled. Ciba has an additive to promote degradation in PE mulch film. An alternative is to use biodegradable mulches as tested by CTIFL in France: polyamide starch, starch-PCL (Mater-Bi), copolyesters, PE + prooxidants, and PLA-copolyester (BioFlex) were used in the study on both open field crops and sheltered crops. The mulch should last as long as the crop, if it breaks down too early then film sticks to the crop causing damage and fails to protect it from weeds. There are two key problems: the biodegradable mulch is 2-3 times more expensive and there are questions as to whether the material is totally broken down or whether residues accumulate in the soil. Professor Martin-Closas of the University of Lleida has studied the field performance of Mater-Bi mulch film compared with PE. He concluded that the spectroradiometric properties were similar, it was strong enough for conventional laying, crops were unaffected, that water vapour permeability of the new film needs improvement for Mediterranean use. FKUR is developing compostable PLA-blends (Bio-Flex) for film, which Oerlemans Plastics is using to develop biodegradable mulch film. Thus overall, biodegradable materials are showing good prospects for mulch use.
Waste agricultural film can be an problem as it is often dirty. Professor Briassoulis of Athens University is working on a European project (LABELAGRIWASTE) on recovery of plastic agricultural waste for recycling or energy recovery: labelling is a key part of this scheme.
Posted March 14th,2008