Analysis of the mechanical and degradation performances of optimised agricultural biodegradable films

The introduction and the expanding use of biodegradable materials represent a really promising alternative for enhancing sustainable and environmentally friendly agricultural activities in mulching and low-tunnel cultivation. The main challenges for the development of agricultural films biodegradable in the soil concern primarily the effects of ageing and degradation during the useful lifetime, which may cause premature losses in their mechanical performance. A set of Mater-Bi based biodegradable films was developed and tested, following the selective optimisation of some processing parameters of the film manufacturing along with the optimisation of the structural low-tunnel system design. The behaviour experienced during the experiments suggests that the so optimised biodegradable films perform in a way comparable to the corresponding LDPE films, within the period of their useful lifetime. Experimental investigation indicates that water and high temperatures do not affect the mechanical behaviour of the biodegradable films significantly, as it is experienced during the first period of their exposure to real field conditions. A high dose of UV radiation has detrimental effects, however, on the elongation at break of both mulching and low-tunnel films. These films are shown to be readily degraded within 4-6 months under irrigated agricultural soil conditions, indicating a high biodegradability rate.     

Monitoring abiotic degradation of branched polyethylenes formulated with pro-oxidants through different mechanical tests

The mechanical properties of two linear low density and low density polyethylenes containing a pro-oxidant additive were monitored during accelerated aging (60 °C in a convection oven) and weather exposure. Tearing tests (trouser) were performed for the first time in polyethylenes subjected to oxo-degradation revealing a transition from an extensible to a non-extensible material, at exposure times when standard tensile tests were not able to detect any changes in the materials. The essential work of fracture (EWF) technique was also applied and the results were in agreement with those of trouser tests. The specific essential work of fracture first increased with exposure time until the sample experienced a transition to a less ductile state where EWF was no longer applicable. EWF and trouser tear tests were more sensitive detecting the onset of degradation probably because they employ notched specimens that impose more critical stress concentration conditions than conventional tensile tests.     

Study of the degradation mechanisms of polyethylene during reprocessing

The present work aims at evaluating the behaviour of various grades of high and low density polyethylene subjected to continuous injection moulding operations. It is based on a wide range of experimental techniques that allowed the establishment of relationships between the observed property changes and the structural modifications developed in the polymers. The study confirmed the coexistence of two distinct degradation mechanisms, crosslinking and chain scission, that occur due to thermo-oxidative reactions arising during the different injection moulding stages. The relative importance of these two mechanisms depends on the material structure and on the processing conditions used. It was also possible to confirm that the polyethylenes with lower molecular mass show low sensitivity to degradation during reprocessing. Furthermore, the more branched polymers (as is the case of LDPE) also proved to be less sensitive to thermo-degradation phenomena. Overall, it was concluded that the primary recycling of polyethylene, if performed under well controlled conditions, will lead to only minor material property losses.     

Liquid-phase catalytic degradation of polyethylene wax over MFI zeolites with different particle sizes

The liquid-phase catalytic degradation of polyethylene wax into fuel oil was studied over MFI catalysts with different particle sizes (0.2 to 4.0 μm). Although structures and acidities of these catalysts were almost the same, the degradation activity varied greatly according to their particle size. The small particle catalyst showed higher activity due to its larger external surface, due to the low restriction on the mass transfer of large polymer molecules. Product distribution was also dependent on the particle size, producing higher hydrocarbons in the liquid product on the catalyst of small particles. The particle size effect of MFI zeolite on its activity and product composition in the liquid-phase degradation was discussed.