A synthetic approach for the realisation of lifetime controlled biodegradable films is described starting from existing biodegradable polymers. Polyvinylalcohol (PVOH) chains are bridged through functionalised polycaprolactone (PCL) crosslinks directly during extrusion and film lamination. The resulting films are water resistant and their degradation may start only when buried in the soil due to microbial attack of the PCL bridges. The influence of blend composition on the mechanical properties and water sensitivity has been analysed. A thermal annealing is necessary after extrusion in order to complete the crosslinking of the obtained film. A mathematical model has been applied on the film to simulate their "greenhouse" effect. It was found that such films, when used as mulching film in agriculture, have a very interesting thermal response allowing temperatures inside the soil of 40-50degreesC, comparable to well known non biodegradable mulching films.