MONTE-CARLO SIMULATION OF PEROXIDE INITIATED DEGRADATION OF POLYPROPYLENE

Modification of the molecular weight distribution of commodity polypro pylene resins is frequently practised in industry in reactive extrusio n operations using peroxide initiated reactions in the melt. Thus, the processing characteristics can be modified in a controlled fashion by narrowing the molecular weight distribution (MWD) of the starting mat erial by means of random chain scissions. This process has attracted c onsiderable interest in recent years and several experimental and mode lling studies have been carried out. In this work, a systematic probab ilistic study is carried out for the peroxide initiated degradation of polypropylene, and a stochastic model is developed based on a Monte C arlo simulation algorithm. In this modelling framework, a polymer MWD is defined as an assembly of an entire population of reacting species and its state is characterized by the types of molecules and the numbe r of each type of molecules in the system. Chemical reactions are repr esented by the transitions of the system from one state to another and the temporal behaviour of the MWD takes the form of a Markovian rando m walk in the N-dimensional space of the molecular populations of the N species. Using this stochastic model, certain approximations previou sly used are relaxed and the evolution of the entire MWD is mapped out for different experimental conditions. Monte Carlo simulation results show very good agreement with experimental data as well as with predi ctions from a deterministic model.