Chemical, morphological, mechanical and fracture characterization of natural weathered LDPE/EVA films used in agriculture

L. FASCE; D. FASCE; F. TILCARA; P. FRONTINI

Buenos Aires, Argentina

Congreso; Congreso Internacional de Plásticos para la Agricultura, CAPPA 2006; 2006

  Commercial LDPE/EVA films were outdoor exposed in La Puna, a place that  has been identified as one of the sites with higher UV radiation intensity in the world.  After natural weathering films exhibited significant variations in the mechanical and fracture properties. Also, parameters determined along the machine direction (MD) and along the transverse direction (TD) were dissimilar due to the stretching experienced in the blowing manufacturing process. Photo-oxidation products were detected by the broadening of the 1740cm-1 band associated with the carbonyl ester group in the EVA. Elastic modulus, yield stress, maximum strength, elongation at break, disc modulus, thickness related perforation energy, specific essential and non-essential work of fracture parameters were all improved after 3.5 months of outdoor exposure. These results correlate with changes in molecular structure and crystallinity. The stiffening effect observed is due to the crosslinking reactions that took place in the amorphous phase. After this time of natural weathering, films kept their mechanical integrity. Microscopy observations (not shown here) did not revealed the presence of microcracks, which has been indicated responsible for the abrupt decay in the mechanical performance of these type of films subjected to artificial photo-oxidative conditions. Hard work is being carried out by many researchers to simulate outdoor conditions in laboratory experiments in order to cause  film degradation in an accelerated way and with the aim of predicting service life of greenhouse covering materials.