Heat driven self-healing isocyanate-based crosslinked three-arm Star-shaped polyglycolide based on dynamic transesterification

Manipulating the Properties of Polymer Vitrimer Nanocomposites by Designing Dual Dynamic Covalent Bonds

Polymer vitrimer is a novel material that contains dynamic covalent bonds (DCBs) allowing it to combine the desirable characteristics of both thermoplastics and thermosets. Similar to the traditional polymer nanocomposites, introducing nanoparticles into polymer vitrimer is also an effective strategy to further enhance its properties. However, a comprehensive understanding of matrix and interfacial bond exchange reactions (BERs) to tailor the properties of polymer vitrimer nanocomposites (PVNs) is still lacking. Herein, we utilized coarse-grained molecular dynamics simulations to investigate model PVNs in which there are two different kinds of DCBs in the vitrimer matrix and at the interface. Our results show that the normalized bond autocorrelation function (Csw) confirms the independence of BERs in the vitrimer matrix and in the interface. By varying the bond swap energy barrier (Δ E sw ) in the matrix Δ E sw mat or in the interface Δ E sw int , or in both Δ E sw all , a maximum mechanical property is observed at the moderate value of Δ E sw mat , Δ E sw int , orΔ E sw all . Meanwhile, the effect of Δ E sw on the stress relaxation and the bond orientation as a function of the time under a fixed strain is well probed, which both decay more slowly at greater Δ E sw . We simulated the tension-recovery curve to examine the effect of Δ E sw on the hysteresis loss and permanent deformation of PVNs, finding an optimal value to achieve its minimum energy dissipation and maximum recovery ratio. Lastly, we investigated the efficiency of self-healing by building and removing walls from the system. Interestingly, a maximum self-healing efficiency of the stress-strain behavior is observed at moderate Δ E sw . Overall, this study provides valuable insights into the relationship between the structure and properties of PVNs, offering implications for the manipulation of their mechanical properties and enhancement of their self-healing capabilities.

Epoxy-Based Catalyst-Free Self-Healing Elastomers at Room Temperature Employing Aromatic Disulfide and Hydrogen Bonds

In this paper, catalyst-free room-temperature healing epoxy vitrimer-like materials (S-vitrimer) are introduced. The S-vitrimer can be healed at room temperature without any external stimuli such as solvent, pressure, heat, and catalyst through an aromatic disulfide exchange reaction and a hydrogen bond because the glass transition temperature of the S-vitrimer is lower than room temperature. Self-healing materials are attracting widespread attention nowadays with their potential to increase the durability of the materials. However, there is still elevating need for research, considering the limitations of various self-healing methods. To the best of our knowledge, epoxy-based catalyst-free room-temperature healing materials have not been investigated until now, yet they are promising to make self-healing easier. Moreover, the S-vitrimer showed higher healing efficiency when healed for a longer time and at a higher temperature. Especially when healed at room temperature for 96 h, the S-vitrimer presented an 80% healing efficiency. The S-vitrimer also showed an 80% healing efficiency when healed at 60 °C for 48 h. To investigate the factors affecting self-healing behavior, three control experiments were carried out. Control experiments showed that the S-vitrimer is healed mainly due to a disulfide exchange reaction, but hydrogen bonds also contribute to self-healing behavior. Also, it was found that tightly packed segments can hinder self-healing through control experiments.

Biodegradable Natural Rubber Based on Novel Double Dynamic Covalent Cross-Linking

In this paper, biodegradable epoxidized natural rubber containing cyclic carbonate groups (CNR) was prepared by the reaction between epoxidized natural rubber (ENR) and carbon dioxide. Dynamic disulfide bonds and a boronic ester structure were successfully constructed and then the cross-linking network was formed by the thermally initiated “click” reaction between thiol groups of the cross-linker and the residual epoxy groups of ENR. As a result of the exquisite double dynamic covalent structure, the material exhibits high self-healing efficiency. Moreover, by virtue of the cyclic carbonate structure of the CNR, the natural rubber was confirmed to be biodegradable according to the biodegradable measurement. To the best of our knowledge, natural rubber with biodegradable and self-healing characteristics was obtained for the first time.

Crude Glycerol as a Potential Feedstock for Future Energy via Thermochemical Conversion Processes: A Review

Biodiesel is an emerging substitute for petroleum-based products. It is considered an ecologically safe and sustainable fuel. The high cost of biodiesel production is linearly related to its feedstock. Crude glycerol, which is a by-product of the biodiesel industry, is also a major challenge that must be addressed. A large volume of crude glycerol needs to be disposed of, and this involves processing, dumping, and land requirements. This increases the cost of biodiesel production. One way to decrease the cost of biodiesel production is to utilize its by-product to make valuable products. Crude glycerol can be processed to produce a variety of chemicals and products. The present utilization of crude glycerol is not enough to bring down its surplus availability. Thermochemical conversion processes can utilize crude glycerol as a starting feedstock and convert it into solid, liquid, and gaseous fuels. The utilization of crude glycerol through integrated thermochemical conversion processes could lead to an integrated biorefinery. This review paper highlights the research scope for areas where crude glycerol could be utilized as a feedstock or co-feedstock in thermochemical conversion technology. Various thermochemical conversion processes, namely, gasification, pyrolysis, combustion, catalytic steam reforming, liquefaction, and supercritical water reforming, are discussed and shown to be highly suitable for the use of crude glycerol as an economical feedstock. It is found that the integration of crude glycerol with other thermochemical conversion processes for energy production is a promising option to overcome the challenges related to biodiesel production costs. Hence, this paper provides all the necessary information on the present utilization status of crude glycerol in thermochemical conversion processes, as well as identifying possible research gaps that could be filled by future research studies.

Biomass Shape Memory Elastomers with Rapid Self-Healing Properties and High Recyclability

Biomass bifunctional polyamide elastomers (BbPEs) were successfully prepared from dimer acid (DA), trimer acid (TA), and triethylenetetramine with shape memory and self-healing abilities. In the composition structure of BbPEs, vast hydrogen bonds formed among the amide bonds of different segments endowed the BbPEs with self-healing ability. At room temperature, the mechanical properties of BbPEs can be restored to 49% of the original condition after healing for 2 h. In addition, the physical and chemical cross-linking endowed the BbPE with preferable mechanical and shape memory properties. The tensile strength of the material is 4.4 ± 0.1 MPa, and the elongation at break reaches 1500 ± 2%. Under the recovery temperature of 60 °C, the shape memory recovery rate of 5 min can reach 95%. The recovery efficiency is 88.9%. This material can be utilized for many practical applications, such as intelligent electronic devices, bionic materials, and so on.