Degradable mulch films

Figure 5.6 Automated laying of degradable mulching film...

Two different levels of degradable plastic highly oxidized degradable mulching film was buried in the ground in such a quantity as to simulate 25 years and 50 years of continuous use and... 

Depending on the crop and the specific enviromnental requirements of the region (e.g., EU compared to Asia), different compounds have to be developed to achieve these requirements. For example, in Europe more than 8 weeks of intact performance of the mulch film is required. Limited UV-stability, different degradation speeds and the different mechanical properties of the individual polymers have to be considered in the formulation development. 

Gilead D (1995) The disposal of mulching films after use. In Scott G, Gilead D (eds) Degradable polymers principles and applications. Chapman Hall, London, chap 10... 

Ecoflex is also found in agricultural films such as cover sheeting and mulch film. The film can be ploughed into the field and is degraded in the soil after use. 

Several years ago, Princeton Polymer Labs. contracted with a client to develop a degradable agricultural mulch film. A first generation additive system was developed and some 12,000 sq. ft. of polyethylene film containing the additive was tried out in 14 states in the U.S.A. Both black and clear films... 

A second generation, and far more effective photo-degrading additive system was later developed and extensive indoor and outdoor testing was done. With such an effective system it was obvious that its use could go much further than just agricultural mulch films. 

Realistic uses for Degradable Plastics include those applications where materials are used outdoors for a limited time only and it is not economically desirable to collect the residual materials after use. Examples are agricultural mulch, films and cordage, twine, etc. Another application is that of packaging which is stored and used indoors and discarded outdoors, in other words litter for which manual collection is not practicable. 

A good example of a class of materials with specific stability and degradability criteria are mulch films for corn production as seen in Fig. 1. They should protect the crops at the beginning of the season but be brittle enough... 

At the time of writing, the applications of biodegradable polymers are confined mostly to the field of agriculture, where they are used in products with limited lifetimes, such as mulch films and pellets for the controlled release of herbicides. The synthetic polyesters used in medical applications, principally polylactide and poly(lactide-co-glycolide), while claimed to be biodegradable, are degraded in the body mainly, if not entirely, by chemical hydrolysis. There is little evidence that the hydrolysis of these polyesters of a-hydroxyacids can be catalyzed by hydrolase or depolymerase enzymes. 

Polylactone and poly(vinyl alcohol) films are readily degraded by soil microorganisms, whereas the addition of iron or calcium accelerated the breakdown of polyethylene. Degradable mulches should break down into small brittle pieces which pass through harvesting machinery without difficulty, and do not interfere with subsequent planting. Effective funaigant mulches require reduced-porosity films which reduce the escape of volatile chemicals, i.e. nematocides, insecticides, herbicides, etc., and therefore allow for lower application rates. 

Estimating the rate of (bio)degradation of mulching films (protocol by simulation in humid chamber) (non-normative methodology)... 

Figure 14.5. Each strip offilm is half buried in damp soil and half remains on the surface. The following are examined over time the samples buried in soil, the samples on the surface and the soil-air interfaces (testing the degradation of mulching films was developed by SERAIL, September 2002)...

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