Ultraviolet reflective and mechanical properties of polyethylene mulching films

In order to assign the insect-repelling property to the mulching films for horticultural applications, low density polyethylene (LDPE) films were prep ared by incorporating ultraviolet (UV) reflective additive (Tismo-D) in a m elt-extruder, Not only their reflective characteristics but also their mech anical properties were investigated as a function of additive content. The comparison of optical properties between single and two layer films was als o made. Single layer films containing Tismo-D showed a distinctive reflective behav ior over a range of a wavelength from 300 to 800 nm compared with pure LDPE film. With the additive content: UV reflectance increased and showed a max imum peak neat the wavelength of 430 film. Film of 5% Tismo-D content had t he highest characteristic ratio, which was defined as a ratio of peak refle ctance at UV region to reflectance at 500 nm. The characteristic ratio of t wo layer film in which a carbon black-filled film was laminated was larger than that of single layer film. It was above the critical value which is 1. 4 and has been accepted as a criterion to have insect-repelling effect. How ever, any changes in reflectance spectra due to polymer crystallization wer e not found, indicating that UV reflectance might not be dependent on the p olymer properties. On the other hand, the tenacity and elongation-to-break of single layer films decreased with the additive content, but tensile modu lus increased due to stiffening effect of the additive. Consequently, it wa s proposed that two layer film with 5% Tismo-D content was the most effecti ve for the purpose of insect-repelling action. (C) 2001 Elsevier Science Lt d. All rights reserved.