Photodegradable plastic films have also been known are known and more recently so-called biodegradable plastic films. The photodegradable plastic films are are obtained by introducing photoactive additives into a basic material which can be a polyolefin, for example. Generally, these additives are form by molecules containing oxygen and/or heavy metals the role of which is to initiate the formation of free radicals under the action of ultraviolet (UV) radiation; these radicals cause a rupture of the chains of the polymer and therefore make the polymer fragile, by making it weak and therefore mechanically degradable.
However, the use of certain additives which are strongly oxidizing causes the degradation to start immediately after the manufacture of the films, which has for consequence to reduce the storage capacity either of the master mixtures or of the films.
It should be noted that in agricultural uses of photodegradable films, portions of the films which are buried in the ground are protected from UV radiation and therefore not altered and not mechanically degradable, which has for its consequence to increase the scraps.
With respect to the biodegradable plastic films, they are obtained by the introduction of a so-called biodegradable organic filler such as starch which, consumed by the microorganisms, will make in turn the film fragile and therefore more easily degradable under the influence of the UV radiation.
The addition of starch as a consumable filler for microorganisms has consequences both concerning the fabrication of the film and in its mechanical properties; actually: starch is partially decomposed as soon as a temperature of 180.degree. C. is reached during the extrusion operation used in making the film; starch is not compatible with the polymers and therefore embrittles the films. Finally, the granulometry of the industrially available starch does not permit making films of small thickness. Yet, the thickness is an element of the cost price of the film, but also a parameter which governs the degradation speed of the film.