- مبلغ: ۸۶,۰۰۰ تومان
- مبلغ: ۹۱,۰۰۰ تومان
The ability of films with an active layer of nanoporous–crystalline syndiotactic polystyrene (s-PS) to prolong shelf-life, not only of climacteric but also of non-climacteric fruits, is discussed. Studies on oxygen and carbon dioxide concentrations in the environment of packaged fruits as well as in s-PS active layers have been combined. Reported results indicate that prolonged shelf-life can be associated with large increases and decreases of carbon dioxide and oxygen concentrations inside the package, respectively. These data are consistent with a higher barrier offered to both gases by nanoporous–crystalline s-PS layers. This barrier phenomenon is due to reduction of gas diffusivity typical of nanoporous–crystalline polymer films, which is further enhanced by orientation, parallel to the film plane, of crystalline planes of closely packed s-PS helices.
Films with s-PS active layers, exhibiting a nanoporous–crystalline phase, are able to prolong shelf-life not only of climacteric but also of non-climacteric fruits. Studies inside packages of non-climacteric fruits (oranges and raspberries) show that for three-layer active film, exhibiting a nanoporous–crystalline s-PS layer, O2, and CO2 concentrations markedly decrease and increase, respectively, with packaging time. In the same conditions, for reference films (not activated three layer films or biaxially oriented commercial PP and PET films), smaller variations with packaging time of O2 and CO2 concentrations are observed. This behavior is due to a higher barrier to O2 and CO2 diffusion, offered by the activated (nanoporous–crystalline) d form of s-PS layer. These d form s-PS layers exhibit, for both gases, higher solubility and a much lower diffusivity in the crystalline regions, as compared to the amorphous ones. This reduction of gas diffusivity is enhanced by orientation, parallel to the film plane, of crystalline planes of closely packed s-PS helices. Increase of CO2 concentration inside fruit package has also a remarkable positive effect in slowing down the development of molds, due to well-known anti-microbial properties of carbon dioxide.