Atomistic simulations of the processes underlying agro-industrial waste valorization as biofillers in plastics

Introduction

The valorization of agro-industrial waste as biofillers in plastics addresses critical needs in waste management and sustainable materials development. However, the industrial adoption of this process is often hindered by heat sensitivity of the biofiller during mixing with polymer in the melt phase (where heat can lead to biofiller degradation and generate poisonous gases) and/or poor biofiller-polymer compatibility (segregation can degrade mechanical properties of the composite). Using High-Performance Computing (HPC) atomistic simulations, we investigated two processes addressing these limitations: the reaction mechanisms governing thermal degradation of aminoacids (key contributors to emissions of nitrogenous species during pyrolysis), and the role of compatibilizers in stabilizing polymer-biofiller composites.

Methods

Our strategy utilizes stochastic sampling, including (Reactive) Global Optimization, alongside Molecular Dynamics simulations, coupled with QM-based force-fields to compute energy and forces.

Results

We derived a comprehensive reaction network for the thermal decomposition of glycine, the simplest aminoacid [1]. We found that, unlike water evolution, pyrolytic ammonia evolution can only proceed via many-body mechanisms involving ionic-pair proton-exchange polymerization pathways. Properly accounting for these mechanisms reconciles theoretical predictions with TGA experiments.

We investigated composite models of host-polymers/biofillers [2], i.e., we modeled polypropylene (grafted or not with a few percent of maleic anhydride as compatibilizers) mixed with cellulose and hemicellulose (Hemi-A, and Hemi-B). We found that grafting promotes interfacial mixing by systematically suppressing self-contacts and stabilizing biofiller-polymer inner interfaces, with particularly glucuronic acid hemicellulose exhibiting markedly higher compatibility with grafted polypropylene than cellulose.

Conclusions

We present a predictive computational framework to elucidate atomistic degradation pathways and polymer-filler-compatibilizer interactions. The information thus drawn can be exploited to design heat-stabilization and biofiller-functionalization protocols, to overcome thermal and mechanical limitations of biocomposites and paving the way for their industrial use.

References

[1] Lupi, et al. J. Am. Chem. Soc. 2025, 147, 28259−28267.

[2] Lupi, et al. (in preparation).