Catalytic Degradation of Polystyrene: Modeling of Molecular Weight Distribution

Abstract

Two of the most abundant polymers in household waste streams, PS and PE, may be recycled by compatibilization through a Friedel‐Crafts alkylation. This reaction produces a graft copolymer PE‐g‐PS that improves the properties of the blend, but simultaneously degrades PS chains. Since the copolymer efficiency as a compatibilizer depends both on the molecular weight and MWD of its two blocks, the operating conditions for the copolymer synthesis must be carefully tuned. To aid in this task, we present a preliminary mathematical model that focuses on the effect of the catalyst and cocatalyst of the Friedel‐Crafts alkylation on the MWD of the PS chains. The model's predictions are shown to agree with experimental data.

Graft Copolymers for Blend Compatibilization: Mathematical Modeling of the Grafting Process

“…It is also assumed that shorter polymer molecules are more reactive toward grafting than longer ones, in qualitative agreement with reported data 3, 9. As discussed in previous works,15, 17, 21 PS chains contain several weak links that are easier to break than the remaining normal links. This difference in bond strength is also considered in the model.…”

“…Once reacted, the molecules of S or benzene are assumed to become part of the synthesized copolymer, where they are regarded as styrene monomeric units. The PS side reactions have already been described in another work,17 where we modeled the complete MWD during PS degradation using the pgf technique.…”

“…The method applied is similar to that applied in a previous work 17. First, mass balances were transformed to obtain pgf balances.…”

“…Both quantities agreed well with experimental data. On the other hand, the pgf technique in its univariate form was successfully applied to predict the complete PS MWD during its degradation process in the presence of AlCl 3 and S 17. First, the pgf transform was applied to the mass balances derived from the proposed kinetic mechanism, resulting in pgf balances for the MWD expressed in number fraction distribution, weight fraction distribution or differential‐log distribution.…”