Photodegradable films

As far as the cultivation is concerned, mulching plays a decisive role. This technique consists of covering the soil with a very thin transparent or opaque plastic film, at the time of sowing or transplanting. The conditions which are controlled by this technique are the soil and weather characteristics and the plant environment. These relate to factors such as thermal imbalance, prevention of evaporation and particularly the elimination of negative effects of cold wind and excessive heat. These will manifest themselves in an increase in the quantity and the quality of the yield, in water saving and in earlier maturity. 

The use of plastic mulch, however, causes serious problems due to the need to dispose of the plastic debris after the harvest. At the end of the cultivation cycle the plastic film must be in good condition so that it can be picked up without too much difficulty by manual or mechanical operations. That is, provided the type and nature of the crops allows such a removal. The costs of the removal are not only in the actual time and labour spent, but also in the need to impart sufficient mechanical strength to the film by using high-quality raw materials and thickness gauges of at least 30 pm. This last requirement translates into the use of 250-400 kg of plastic film per hectare, depending on the type of crops. Once the cultivation cycle is finished and the films have been removed from the field there still remains the final disposal of the collected plastic. This can be handled in different ways. 

By far the best solution to the disposal problem is the use of photo-biodegradable self-destruct film which are time controllable in order to be adaptable to the requirements of the specific crops and their cultivation procedures. 

Great progress has been made in this field, by setting up formulations and processing techniques for the manufacture of products to meet the requirements of the grower. These products leave a very small residue on the ground which disappears within a short time. 

No problems have been experienced from the plastics residue during harvesting and any subsequent cultivating operation such as tilling, sowing or transplanting. Research has been going on in order to reduce the quantity of plastic used per unit area and thus reduce still further the transient residues. 

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Hancock M, Marsh J E, Lee R L, Mineral Catalyzed Photodegradable Films, ECC International. 

FIGURE 16.2 Rate of reduction in molecular weight as function of change in carbonyl absorption during UV exposure (SEPAP12-24) of different LDPE photodegradable films. (Reproduced with permission from Ref. 29 Published by Marcel Dekker, Inc., 1995.)... 

Several specialized types of polyethylene film are also available. These include heat-resistant film, heat-retaining film, water-absorbing antistatic film, and photodegradable film. 

Gilead, D. 1990. Photodegradable films for agriculture. Polym. Degrad. Stab., 29, 1, 65. 

Figure 10.1 Mid-trench cultivation of peppers with photodegradable film.

Mechanical strength is a function of the film thickness. Over the years down-gauging of the films has become possible by the introduction of improved raw materials and more sophisticated production methods. As the price of the films is based on their weight per unit area it becomes obvious that adequate mechanical strength becomes the governing property. Photodegradable films must not impair mechanical properties as compared to normal films. The Scott-Gilead methods have been shown to maintain the full mechanical... 

It can be seen from Table 10.8 that there is good cause for the grower to use plastic mulch. The extra cost involved in the use of photodegradable film, even... 

In 1991 the experiment was completed, laying the foundation for practical conclusions on the use of photodegradable films in commercial agricultural practice. 

Mulched cultivation with two types of photodegradable film, natural transparent and opaque, both of a thickness of 12 pm. 

CasaUccio G H, Bertoluzzo A and Fabbri A (1990) Photodegradable film research -Initial research into the possible toxic effect of photodegradabihty inductors on sweet com and melons Plasticulture 86 (2), 21-28. 

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