Center for Molecular Modeling - J. Vekeman

Evaluation of Green Biobased Plasticizers in Poly(vinyl chloride): Sustainability, Thermal Behavior, Mechanical Properties and Durability

jvekeman — Fri, 07 Jun 2024 08:07:02 +0000

A. De Bruyne, K. Cérdan, G. O'Rourke, W. Stuyck, J. Leinders, M. Denayer, J. Vekeman, F. De Proft, P. Van Puyvelde, D.E. De Vos

ACS Applied Polymer Materials

6, 11, 6831-6842

2024

Abstract

We report the use of biobased plasticizers prepared from citric acid in poly(vinyl chloride) (PVC). The use of citric ester plasticizers is well known for PVC. However, these are known to leach out of the plastic material over time. Currently, this problem is resolved by the acetylation of the tertiary hydroxyl group of citric acid through environmentally polluting processes. An alternative strategy consists of the reductive removal of the tertiary hydroxyl group, resulting in propane-1,2,3-tricarboxylic acid. Esters of this compound lead to plasticizers that have not been tested in PVC yet. In this work, the syntheses of citrate esters, acetylated citrate esters, and esters of propane-1,2,3-tricarboxylic acid are evaluated based on their sustainability using the CHEM21 metric toolkit and lab-scale data. Next, the different esters of propane-1,2,3-tricarboxylic acid were blended in PVC. Their influence on the thermal, i.e., glass-transition temperature (T_g), and mechanical (Young’s modulus, stress, and strain) properties of PVC along with their migration out of the PVC material were compared to that of commercially available citric acid-based plasticizers. Our results show that similar or better results were obtained with these green plasticizers, while their synthesis showed a high degree of sustainability.

DOI

http://dx.doi.org/10.1021/acsapm.4c00809

Simple Molecular Model for Hydrate Silicate Ionic Liquids, a Realistic Zeolite Precursor

jvekeman — Wed, 10 Apr 2024 07:22:36 +0000

J. Vekeman, D. Vandenabeele, N. Doppelhammer, E. Vandeurzen, E. Breynaert, C.E.A. Kirschhock, T. Verstraelen

Chemistry of Materials

36, 8, 3886-3897

2024

Abstract

Despite the widespread use of zeolites in the chemical industry, their formation process is not fully understood due to the complex and heterogeneous structure of traditional synthesis media. Hydrated silicate ionic liquids (HSILs) have been proposed as an alternative. They are truly homogeneous and transparent mixtures with a low viscosity, facilitating experimental characterization. Interestingly, their homogeneous nature and simple speciation bring realistic molecular models of a zeolite growth liquid within reach for the first time. In this work, a simple molecular model is developed that gives insight into the crucial role of the alkali cations (sodium, potassium, rubidium, and cesium). Thereby, molecular dynamics simulations are combined with experimental measurements to demonstrate that the HSIL liquid structure strongly depends on the charge density and concentration of the alkali cation. As the water content increases, it transitions from a glassy network with fast ion exchange to an aqueous solution containing long-lasting solvated ion pairs. Furthermore, simulations reveal that the cation is capable of bringing several silicate monomers together in a glassy network, displaying perfect orientations for condensation reactions that underlie zeolite formation. This work is an important step toward the development of molecular models that can fully describe the early nucleation process of zeolites in combination with experiments.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1021/acs.chemmater.4c00285

Private attachment

2404.14170.pdf

New Tricarboxylate Plasticizers for Use in Polylactic Acid: Synthesis, Thermal Behavior, Mechanical Properties and Durability

jvekeman — Mon, 08 Apr 2024 09:20:34 +0000

A. De Bruyne, K.C. Gómez, G. O'Rourke, M. Denayer, J. Vekeman, F. De Proft, W. Stuyck, J. Leinders, P. Van Puyvelde, D. De Vos

Journal of Polymers and the Environment

32, 4483-4495

2024

Abstract

We report the use of novel biobased plasticizers prepared starting from citric acid (CA) in polylactic acid (PLA). Citric acid based plasticizers are well-known softeners for PLA, with citrate esters as the most commonly used class. However, citrate esters are known to leach out of the plastic material over time. This problem is currently addressed by acetylating the tertiary hydroxyl group of citric acid via complex and environmentally polluting processes. An alternative strategy consists in the reductive removal of the tertiary hydroxyl group, resulting in propane-1,2,3-tricarboxylic acid. Derivatizing this compound leads to novel plasticizers which have not been tested in PLA yet. Here, different esters of propane-1,2,3-tricarboxylic acid were synthesized and blended in PLA. Their influence on the thermal (T_g and T_m) and the mechanical properties (Young’s modulus, stress and strain) of PLA along with their migration out of the material were compared to those of commercially available citric acid based plasticizers. Our results show that similar or better results were obtained with these new PLA plasticizers.

DOI

http://dx.doi.org/10.1007/s10924-024-03254-0

Total Revalorization of High Impact Polystyrene (HIPS): Enhancing Styrene Recovery and Upcycling of the Rubber Phase

jvekeman — Fri, 01 Dec 2023 08:13:34 +0000

N.S. Giakoumis, C. Vos, K. Janssens, J. Vekeman, M. Denayer, F. De Proft, C. Marquez, D.E. De Vos

Green Chemistry

26, 340-352

2024

Abstract

High impact polystyrene (HIPS) is a two-phase polymeric material that consists of a free polystyrene (PS) matrix and rubber particles. HIPS occupies a substantial portion of the plastic wastes. Even though HIPS waste could potentially be employed as an efficient feedstock for the recovery of the styrene monomer via pyrolysis, several challenges must be overcome first, like the low styrene yield (< 50%) and the generation of char due to the presence of rubber. To tackle these challenges, a green fractionation process using ethyl acetate (EtOAc) as an efficient solvent to separate rubber from the free PS matrix in HIPS is envisioned, which is carried out under mild conditions. The subsequent pyrolysis of the fractionated sample at 300 °C led to a 20% increase in styrene selectivity compared to the pyrolysis of untreated HIPS. Moreover, the revalorization of the rubber particles was accomplished by ethenolysis metathesis, in which after 4 h at 100 °C, polybutadiene was split to produce 1,5-hexadiene as a major product (60% yield) and isolated PS, which was further thermally degraded, achieving a styrene selectivity of 70%.

DOI

http://dx.doi.org/

Elucidating the Impact of Chemical Variability on the Nano-Structure of Fe-Rich Slags

jvekeman — Mon, 07 Aug 2023 08:12:36 +0000

C. Siakati, J. Vekeman, F. Tielens, D. Seveno, Y. Pontikes

Journal of Non-Crystalline Solids

618, 122541

2023

Abstract

Fe-rich silicate slags are promising resources in the production of alternative cementitious materials. In this investigation, molecular dynamics simulations have been employed to provide a comprehensive structural description of a range of binary FeO-SiO₂ and ternary CaO-FeO-SiO₂ glasses, which are the basis of the slag systems that are observed in the non-ferrous metallurgy. The impact of the chemical variations on the structure of the glasses is assessed. Fe atoms have a slightly more profound role as network modifiers, and Ca as charge compensators for lower SiO₂ content. There is a preference of Fe atoms to be associated with free oxygens, as compared to Ca atoms, forming small scale clusters. The obtained results enrich our understanding of the relationship between the composition, the structure and the reactivity of such complex glasses.

DOI

http://dx.doi.org/10.1016/j.jnoncrysol.2023.122541

A Molecular Understanding of Citrate Adsorption on Calcium Oxalate Polyhydrates

jvekeman — Wed, 19 Apr 2023 14:38:54 +0000

Y. Su, J. Vekeman, F. Siro Brigiano, E. P. Hessou, Y. Zhao, D. Sorgeloos, M. Raes, T. Hauffman, K. Li, F. Tielens

Physical Chemistry Chemical Physics (PCCP)

25, 12148-12156

2023

Abstract

Calcium oxalate precipitation is a common pathological calcification in the human body, whereby crystallite morphology is influenced by the chelating properties of biological ions such as citrate. It has been suggested that citrate could steer oxalate formation towards its dihydrated form and away from the monohydrated form, which was identified as a major cause for disease. To assess the influence of the citrate ion on the resulting calcium oxalate, surface energies were calculated at the dispersion-corrected density functional level of theory for both monohydrated and dihydrated calcium oxalate. Different adsorption geometries were considered by varying the attacking angle of citrate as well as by considering the citrate ion on top of an adsorbed water layer or penetrating the water layer. The obtained results were compared to ab initio molecular dynamics simulations and experimental scanning electron microscope images. A strong preference for citrate adsorption on calcium oxalate dihydrate was observed, suggesting medical applications for the treatment of such pathological calcifications.

DOI

http://dx.doi.org/

Development of Accurate Potentials for the Physisorption of Water on Graphene

jvekeman — Fri, 06 Jan 2023 13:10:43 +0000

J. Vekeman, I. García Cuesta, N. Faginas-Lago, J. Sánchez-Marín, A. Sánchez de Merás

The Journal of Chemical Physics

158, 024104

2023

Abstract

From CCSD(T) calculations on the water dimer and B97D/CC on the water-circumcoronene complex at a large number of randomly generated conformations, interaction potentials for the physisorption of water on graphene are built, accomplishing almost sub-chemical accuracy. The force fields were constructed by decomposing the interaction in electrostatic and van der Waals contributions, the latter represented through Improved Lennard-Jones potentials. Besides, a CHARMM-like term was included in the water-water potential to improve the description of hydrogen bonds, and an induction term was added to model the polarization effects in the interaction between water and PAH's or graphene. Two schemes with 3 and 6 point-charges were considered for the interactions water-water and water‑PAH, as Coulomb contributions are zero for the water-graphene system. The proposed fitted potentials reproduce the ab initio data used to build them in the whole range of distances and conformations and provide results for selected points very close to CCSD(T) benchmarks. When applied to the water-graphene system, the obtained results are in excellent agreement with p-CCSD(T), revised DFT/SAPPT and DMC reference values. Furthermore, the stability of the various conformers water-PAH and water-graphene, as well as the different trends observed between these systems, is rationalized in terms of the modifications of the electrostatic contribution.

DOI

http://dx.doi.org/10.1063/5.0131626

A Sustainable Way of Recycling Polyamides: Dissolution and Ammonolysis of Polyamides to Diamines and Diamides Using Ammonia and Biosourced Glycerol

jvekeman — Wed, 24 Aug 2022 12:05:37 +0000

W. Stuyck, K. Janssens, M. Denayer, F. De Schouwer, R. Coeck, K.V. Bernaerts, J. Vekeman, F. De Proft

Green Chemistry

24, 6923-6930

2022

Abstract

In order to make recycling a viable strategy for post-consumer plastics, economically feasible revalorization processes must be developed. The ammonolysis of polyamides can be such a cutting-edge recycling technology; however, due to the rigid structure of these polyamide plastics, operating conditions of current ammonolysis processes are harsh, including high temperatures (>300 °C) and high NH₃ pressures. Here, we report a very green and elegant ammonolysis process of the widely abundant polyamide 66 by using a hard Lewis acid catalyst and 1 bar of NH₃ in a simple glycol solvent at 200 °C. Computational studies revealed that especially the vicinal diol moiety of these glycol solvents plays a key role in activation of the ammonia nucleophile, with glycerol being the most effective solvent, reaching the depolymerization equilibrium after 20 h even without a catalyst. To our delight, a biosourced glycerol (obtained from the saponification of triglycerides) could also directly serve as a suitable solvent, even outperforming the ammonolysis process in highly purified glycerol.

DOI

http://dx.doi.org/

Synergistic Effects in the Activity of Nano-Transition-Metal clusters Pt12M (M = Ir, Ru or Rh) for NO dissociation

jvekeman — Tue, 14 Jun 2022 14:24:32 +0000

J. Vekeman, Q. Wang, X. Deraet, D. Bazin, F. De Proft, H. Guesmi, F. Tielens

ChemPhysChem

23, 21, e202200740

2022

Abstract

The dissociation of environmentally hazardous NO through dissociative adsorption on metallic clusters supported by oxides, is receiving growing attention. Building on previous research on monometallic M 13 clusters [J. Phys. Chem. C, 2019, 123(33), 20314-20318], this work considers bimetallic Pt 12 M (M = Rh, Ru or Ir) clusters. The adsorption energy and activation energy of NO dissociation on the clusters have been calculated in vacuum using Koh,-Sham DFT, while their trends were rationalized using reactivity indices such as molecular electrostatic potential and global Fermi softness. The results shown that doping of the Pt clusters lowered the adsorption energy as well as the activation energy for NO dissociation. Furthermore, reactivity indices were calculated as a first estimate of the performance of the clusters in realistic amorphous silica pores (MCM-41) through ab initio molecular dynamics simulations.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1002/cphc.202200740

Rules All PIs Should Follow

jvekeman — Fri, 15 Apr 2022 07:54:31 +0000

J.S. Chen, C.Y. Huang, S. Lanke, M.S. Fernandopulle, Y. Ji, Y. Zhi, S.G. Rodríguez, A.Y. Frommel, M. Lukacisin, Y. Zhang, C.N. Zdenek, X.-Y. Wu, S. Seenuvasaragavan, Y. Zhuang, C. Bergh, J. Coulbois, S. Salloum-Asfar, B. Cao, K. Davis, F. Oda, N. Konstantinides, L. Zhang, D. Agarwal, J.N. Rainaldi, J. Kadlec, J. Vekeman, V.A. Kanicherla, K. Oi, K.J. Isaacson, R. Ganji, E. Dawson-Glass

Science

376, 6588, 24-26

2022

Abstract

We asked young scientists to write a rule that all principal investigators (PIs) should be required to follow to improve the experience of young scientists in their lab. Read a selection of their suggestions below. Follow NextGen Voices on Twitter with hashtag #NextGenSci.

DOI

http://dx.doi.org/