DETERMINATION OF THE RADIOMETRIC PROPERTIES OF PLASTICS USED AS GREENHOUSE COVER

• the LD - PE are enriched by ± important quantities of U-V stabilizers which ensure the films a life of some months to 2–3 years;
• the E V A are PE containing different doses of Vinyl-Acetate: the higher the quantity of V A used, the better the absorption for long I-R (5–35 μm); nevertheless, the mechanical properties may be not quite satisfactory;
• the thermic I-R (or "modified P E") are produced from compounds enriched with special "charges" which absorb other parts of the long I-R radiation than VA do;
• the thermic P E contain low quantities of V A and simultaneously some thermic charges; they possess the advantages of the EVA and of the thermic P E but do not present their disadvantages;
• the "linear P E" seems to present some advantages interesting in Agriculture.

Then the authors explain how their Laboratories understand the problem of the radiometric measurments done on the plastic films : they find logical to propose a method which makes it possible to determine :

• the hemispherical angular monochromatic transmittance and reflectance of the materials, within the limits of the sun radiation;
• the biangular monochromatic transmittance and reflectance fo the long infrared.

Finally, the authors propose an agronomical interpretation of the spectral data obtained as showed higher, by generating a number of calculations to integrate the results of measurements on the spectrum of the sun and of those of the sky (clear or overcast).

Download Adobe Acrobat Reader (free software to read PDF files)