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 prepared by incorporating ultraviolet (UV) reflective additive (Tismo-D) in a melt-extruder. Not only their reflective characteristics but also their mechanical properties were investigated as a function of additive content. The comparison of optical properties between single and two layer films was also made. Single layer films containing Tismo-D showed a distinctive reflective behavior 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 maximum peak near the wavelength of 430 nm. Film of 5% Tismo-D content had the highest characteristic ratio, which was defined as a ratio of peak reflectance at UV region to reflectance at 500 nm. The characteristic ratio of two 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. However, any changes in reflectance spectra due to polymer crystallization were not found, indicating that UV reflectance might not be dependent on the polymer properties. On the other hand, the tenacity and elongation-to-break of single layer films decreased with the additive content, but tensile modulus increased due to stiffening effect of the additive. Consequently, it was proposed that two layer film with 5% Tismo-D content was the most effective for the purpose of insect-repelling action.