Articles
PLASTIC FILMS AND THEIR APPLICATION IN AGRICULTURE
Less than 10 years ago, the average life of a polyethylene film 150 to 200 μthick was not most often inferior to 12 months.
Since 1966–1967 great strides have been made and non-rigid films have proved to be interesting even in the most exacting cultural techniques.
A better understanding of the needs and of the preoccupations of the growers has led to a great number of technical improvements and to the creation of different qualities meeting the requirements of each particular use.
Times when plastics were supposed to be useful for any purpose but actually answered no particular purpose have gone.
In 1967, for the first time in Europe, the La Cellophane company, a branch of the Rhône-Poulenc Group put on the market a long-lived polyethylene which was to resist more than 24 months as greenhouse cover, under the most difficult insolation conditions.
Today our films live up to 33 months and present experiments give us all reasons to believe that they will shortly be made to stand four years.
In most agricultural applications films have to bear mechanical stress not to be neglected.
Therefore, the first works aiming at qualitative improvement of the films have been centred upon their dynamometric value as a whole.
Films for the mulching of perennial plants such as vine, and for the semi-forcing and forcing under large shelters must absolutely be made from resins the melt index of which ranges from .7 to .2 if they are to meet the exigencies of the users.
The second stage of the research was obviously devoted to the study of the ageing of polyethylene.
We manage to combat the great enemies of plastic by the addition of antioxidants and ultraviolet radiation inhibitors, without bringing about the slightest change in its physico-chemical properties and in getting a product which is sure to resist for a rather long time.
At the same time we took care that the optic properties of the material suffer no reduction due to the green shade of the resulting film.
As far as black-shaded films are concerned – protected by carbonblack
- two conditions have to be fulfilled: the percentage of carbonblack and its distribution.
For the PF brand the following values are to be respected: - percentage of carbon-black: 2.5% ± 2%;
- distribution of carbon-black: equal or superior to the reference mark 1.5 The lower the note, the lesser the agglomerates of carbon-black,