Reactive molecular dynamics simulation for analysis of thermal decomposition of oligomeric polyacrylicester model nanocomposite and its experimental verification

Investigation of Polymer Aging Mechanisms Using Molecular Simulations: A Review

Aging has a serious impact on the properties of functional polymers. Therefore, it is necessary to study the aging mechanism to prolong the service and storage life of polymer-based devices and materials. Due to the limitations of traditional experimental methods, more and more studies have adopted molecular simulations to analyze the intrinsic mechanisms of aging. In this paper, recent advances in molecular simulations of the aging of polymers and their composites are reviewed. The characteristics and applications of commonly used simulation methods in the study of the aging mechanisms (traditional molecular dynamics simulation, quantum mechanics, and reactive molecular dynamics simulation) are outlined. The current simulation research progress of physical aging, aging under mechanical stress, thermal aging, hydrothermal aging, thermo-oxidative aging, electric aging, aging under high-energy particle impact, and radiation aging is introduced in detail. Finally, the current research status of the aging simulations of polymers and their composites is summarized, and the future development trend has been prospected.

ReaxFF molecular dynamics simulation of the thermal decomposition reaction of bio-based polyester materials

Bio-based polyester elastomers have been widely studied by researchers in recent years because of their comprehensive sources of monomers and environmentally friendly characteristics. However, compared with traditional petroleum-based elastomers, the thermal decomposition temperature of bio-based polyester elastomers is generally low, limiting the application of bio-based elastomers. An effective strategy to increase the intrinsic thermal decomposition temperature (T_d) of bio-based elastomers is to increase the length of the monomer carbon chain in the bio-based elastomers. In this work, the content of dodecanedioic acid (DDA) in a bio-based polyester elastomer composed of butanediol (BDO) and succinic acid (SUA) was increased to improve the T_d of the bio-based polyester elastomer through the reaction force-field molecular dynamics (ReaxFF-MD) simulations. And the thermal decomposition mechanism of the bio-based polyester was analyzed in detail. By calculating the change rate of the molecular chain mean square displacement (MSD), it was determined that when the content of DDA was 50%, the T_d of the bio-based elastomer was up to 718 K. By calculating the activation energy of thermal decomposition and further analyzing the thermal decomposition process, it is found that the thermal decomposition of the bio-based polyester elastomer is mainly through breaking the C-O bond in the backbone. This work is expected to provide theoretical guidance for designing and fabricating highly heat-resistant bio-based elastomers by systematically exploring the thermal decomposition mechanism of bio-based polyester elastomers.

INFLUENCE OF FLUOROACRYLATE CURE SITE MONOMER ON THE THERMAL AND MECHANICAL PROPERTIES OF THE POLYACRYLIC ESTER ELASTOMER

The rubber industry is facing strong challenges in recent times because of imposed stringent standards on the performance of a product under adverse thermal and chemical applications. The choice of proper elastomer plays a significant role in imparting useful product performance. A new type of acrylic rubber with a fluoroacrylate cure site monomer was developed. Structural characterization, such as Fourier-transform infrared spectroscopy and nuclear magnetic resonance (NMR), suggested the presence of four different monomer units. Two-dimensional NMR spectroscopy analysis was also performed to support the assessment of the resonance peaks of coupled nuclei spins in the terpolymer. The newly developed acrylic rubber exhibited superior thermal and mechanical properties. Hexamethylenediamine carbamate in combination with zinc oxide (ZnO) was used as the curing package for the new elastomer. ZnO acts as an acid scavenger to avoid the micro-void formation. The new elastomer with a higher number of cross-link junctions resulted in superior mechanical and thermal properties as well as swelling resistance of the vulcanizate both with and without carbon black.

INFLUENCE OF DIANILINE CROSS-LINKING SYSTEMS ON THE STRUCTURE, CURING MECHANISM, AND PROPERTIES OF POLYACRYLICESTER ELASTOMER

To develop high-performance polyacrylicester (ACM) elastomeric components with higher scorch safety and superior thermal and mechanical properties, we replaced aliphatic diamine curatives with aromatic dianiline curatives. The influence of dianiline curatives 4,4′-(4,4′-isopropylidenediphenyl-1,1′-diyldioxy)dianiline, 4,4′-(hexafluoroisopropylidene)bis(p-phenyleneoxy)dianiline, and 4,4′-(1,1′-biphenyl-4,4′-diyldioxy)dianiline on the network structures and thermal, dynamic mechanical, and mechanical properties of ACM vulcanizates was investigated. The kinetics of vulcanization was analyzed for different dianiline curatives, with the use of rheometer curves. To understand the electronic properties and study the relation between chemical structure and reactivity, density functional theory was used. The time–temperature superposition principal was used to evaluate the activation energy for degradation of cross-linked samples. Finally, the curing mechanism of ACM in the presence of dianiline curative was studied with X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. These spectroscopic analyses suggested that the reaction mechanism took place via two steps: the first step was formation of the amide linkage and the second step was formation of imide linkages.

INFLUENCE OF NANOFILLER ON THERMAL DEGRADATION RESISTANCE OF HYDROGENATED NITRILE BUTADIENE RUBBER

Studies on the degradation of elastomers and their prevention have become increasingly important in recent years because of stringent environmental conditions in many industrial applications. The reactive atomistic simulation was executed on a hydrogenated acrylonitrile-butadiene rubber (HNBR40) model compound composed of 40 monomer units. The reactive simulation was used to study the decomposition behavior of HNBR40, to visualize different pyrolysis products, and also to analyze the degradation mechanism of HNBR40. Ethylene, propylene, and acrylonitrile were observed as dominant products at lower temperature, and 1-butene was found at higher temperature. Pyrolysis–gas chromatography–mass spectrometry was used to verify the decomposition products obtained from the prediction of atomistic simulation. In this study, nanofillers, especially nanoclays and nanosilicas, were used to prevent degradation significantly. Restricted degradation by the nanofiller-reinforced rubber prolonged the durability. Furthermore, the reactive simulation was performed to understand thermal decomposition characteristics of the model compound in the presence of the nanofiller. The initial decomposition temperature, the final degradation temperature, and the rate of degradation improved to a great extent on the addition of the model nanosilica compound as obtained from the simulation studies. Moreover, the lifetime of nanoclay- and nanosilica-reinforced hydrogenated acrylonitrile–butadiene rubber was calculated by using thermogravimetric analysis, and its useful lifetime was compared with that of the pristine polymer in the application temperature range of 150 °C.