scholarly journals Dynamic Crosslinking: An Efficient Approach to Fabricate Epoxy Vitrimer

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 919
Author(s):  
Yin Ran ◽  
Ling-Ji Zheng ◽  
Jian-Bing Zeng
Keyword(s):  
Stress Relaxation ◽  
Production Efficiency ◽  
Specific Property ◽  
Sebacic Acid ◽  
Compression Molding ◽  
Diglycidyl Ether ◽  
Self Healing ◽  
Gel Fraction ◽  
A New Technique ◽  
Transesterification Catalyst

Epoxy vitrimers with reprocessability, recyclability, and a self-healing performance have attracted increasingly attention, but are usually fabricated through static curing procedures with a low production efficiency. Herein, we report a new approach to fabricate an epoxy vitrimer by dynamic crosslinking in a torque rheometer, using diglycidyl ether of bisphenol A and sebacic acid as the epoxy resin and curing agent, respectively, in the presence of zinc acetylacetonate as the transesterification catalyst. The optimal condition for fabricating the epoxy vitrimer (EVD) was dynamic crosslinking at 180 °C for ~11 min. A control epoxy vitrimer (EVS) was prepared by static curing at 180 °C for ~11 min. The structure, properties, and stress relaxation of the EVD and EVS were comparatively investigated in detail. The EVS did not cure completely during static curing, as evidenced by the continuously increasing gel fraction when subjected to compression molding. The gel fraction of the EVD did not change with compression molding at the same condition. The physical, mechanical, and stress relaxation properties of the EVD prepared by dynamic crosslinking were comparable to those of the EVS fabricated by static curing, despite small differences in the specific property parameters. This study demonstrated that dynamic crosslinking provides a new technique to efficiently fabricate an epoxy vitrimer.

scholarly journals Influence of Network Topology on the Viscoelastic Properties of Dynamically Crosslinked Hydrogels

2020 ◽  
Author(s):  
Emilia M. Grad ◽  
Isabell Tunn ◽  
Dion Voerman ◽  
Alberto S. de Léon ◽  
Roel Hammink ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Stress Relaxation ◽  
Network Topology ◽  
Viscoelastic Properties ◽  
Polymeric Materials ◽  
Direct Result ◽  
Reference Network ◽  
Self Healing ◽  
Combine Stress ◽  
Synthetic Cell

Biological materials combine stress relaxation and self-healing with non-linear stress-strain responses. These characteristic features are a direct result of hierarchical self-assembly, which often results in fiber-like architectures. Even though structural knowledge is rapidly increasing, it has remained a challenge to establish relationships between microscopic and macroscopic structure and function. Here, we focus on understanding how network topology determines the viscoelastic properties, i.e. stress relaxation, of biomimetic hydrogels. We have dynamically crosslinked two different synthetic polymers with one and the same crosslink. The first polymer, a polyisocyanopeptide (PIC), self-assembles into semi-flexible, fiber-like bundles and thus displays stress-stiffening, similar to many biopolymer networks. The second polymer, 4-arm poly(ethylene glycol) (starPEG), serves as a reference network with well-characterized structural and viscoelastic properties. Using one and the same coiled coil crosslink allows us to decouple the effects of crosslink kinetics and network topology on the stress relaxation behavior of the resulting hydrogel networks. We show that the fiber-containing PIC network displays a relaxation time approximately two orders of magnitude slower than the starPEG network. This reveals that crosslink kinetics is not the only determinant for stress relaxation. Instead, we propose that the different network topologies determine the ability of elastically active network chains to relax stress. In the starPEG network, each elastically active chain contains exactly one crosslink. In the absence of entanglements, crosslink dissociation thus relaxes the entire chain. In contrast, each polymer is crosslinked to the fiber bundle in multiple positions in the PIC hydrogel. The dissociation of a single crosslink is thus not sufficient for chain relaxation. This suggests that tuning the number of crosslinks per elastically active chain in combination with crosslink kinetics is a powerful design principle for tuning stress relaxation in polymeric materials. The presence of a higher number of crosslinks per elastically active chain thus yields materials with a slow macroscopic relaxation time but fast dynamics at the microscopic level. Using this principle for the design of synthetic cell culture matrices will yield materials with excellent long-term stability combined with the ability to locally reorganize, thus facilitating cell motility, spreading and growth.

scholarly journals Swap-Driven Self-Adhesion and Healing of Vitrimers

Coatings ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 114 ◽  
Author(s):  
Simone Ciarella ◽  
Wouter Ellenbroek
Keyword(s):  
Molecular Dynamics ◽  
Relaxation Time ◽  
Stress Relaxation ◽  
Healing Process ◽  
Star Polymers ◽  
Coarse Grained ◽  
Self Healing ◽  
Central Question ◽  
Trade Off ◽  
Dynamics Simulations

Vitrimers are covalent network materials, comparable in structure to classical thermosets. Unlike normal thermosets, they possess a chemical bond swap mechanism that makes their structure dynamic and suitable for activated welding and even autonomous self-healing. The central question in designing such materials is the trade-off between autonomy and material stability: the swap mechanism facilitates the healing, but it also facilitates creep, which makes the perfectly stable self-healing solid a hard goal to reach. Here, we address this question for the case of self-healing vitrimers made from star polymers. Using coarse-grained molecular dynamics simulations, we studied the adhesion of two vitrimer samples and found that they bond together on timescales that are much shorter than the stress relaxation time. We showed that the swap mechanism allows the star polymers to diffuse through the material through coordinated swap events, but the healing process is much faster and does not depend on this mobility.

SYNTHESIS AND CHARACTERIZATION OF SELF-HEALING MORTAR WITH MODIFIED STRENGTH

2015 ◽  
Vol 76 (1) ◽  
Author(s):  
Gassan Fahim Huseien ◽  
Jahangir Mirza ◽  
Nur Farhayu Ariffin ◽  
Mohd Warid Hussin
Keyword(s):  
Early Stage ◽  
Polymeric Materials ◽  
Building Blocks ◽  
Ultrasonic Pulse Velocity ◽  
Cementitious Materials ◽  
Ultrasonic Pulse ◽  
Pulse Velocity ◽  
Diglycidyl Ether ◽  
Self Healing ◽  
Research Initiative

Cementitious materials being the most prospective building blocks achieving their absolute strength to avoid the deterioration in the early stage of service life is ever-demanding. Minimizing the labor and capital-intensive maintenance and repair cost is a critical challenge. Thus, self-healing mortars with modified strength are proposed. Lately, self-healing of micro-cracks by introducing bacteria during the formation of mortar or concrete became attractive. Self-healing with polymeric admixtures is considered to be relatively more durable and faster process. Certainly, the self-healing of synthetic polymeric materials is inspired by biological systems, where the damage triggers an autonomic healing response. This emerging and fascinating research initiative may significantly improve the durability and the safety limit of the polymeric components potential for assorted applications. In this work, using epoxy resin (diglycidyl ether of bisphenol A) without any hardener as admixture polymeric-cementitious materials is prepared. These epoxy-modified mortars are synthesized with various polymer-cement ratios subjected to initial wet/dry curing (WDC) together with long term dry curing (DC). Their self-healing function and hardening effects are evaluated via preloading and drying of the specimens, chemical analysis, and ultrasonic pulse velocity testing. It is demonstrated that 10% of polymer is the best proportion for polymer-cement ratio. Furthermore, the wet/dry curing is established to be superior process for healing hairline cracks present in the mortar. The excellent features of the results suggest that our novel method may constitute a basis for improving the compressive strength and self-healing features of mortars.    

Preferential Control of Forward Reaction Kinetics in Hydrogels Crosslinked with Reversible Conjugate Additions

2020 ◽  
Author(s):  
Thomas FitzSimons ◽  
Felicia Oentoro ◽  
Tej V. Shanbhag ◽  
Eric Anslyn ◽  
Adrianne Rosales
Keyword(s):  
Stress Relaxation ◽  
Rate Constant ◽  
Rate Constants ◽  
Forward Rate ◽  
Self Healing ◽  
Strong Electron ◽  
Kinetic Rate ◽  
Plateau Modulus ◽  
Kinetic Rate Constants ◽  
Reverse Rate Constant

<p>Molecular substitutions were used to demonstrate preferential control over the kinetic rate constants in a poly(ethylene glycol)-based hydrogel with two different reversible thia-conjugate addition reactions. A strong electron withdrawing nitrile group on the conjugate acceptor showed a 20-fold increase in the forward rate constant over a neutral withdrawing group, while the reverse rate constant only increased 6-fold. Rheometry experiments demonstrated that the hydrogel plateau modulus was primarily dictated by reaction equilibrium, while the stress relaxation characteristics of the hydrogel were dominated by the reverse rate constant. Furthermore, the dynamic crosslinking allowed the hydrogel to rapidly and spontaneously self-heal. These results indicate that decoupling the kinetic rate constants of bond exchange allow systematic control over dynamic covalent hydrogel bulk properties, such as their adaptability, stress relaxation ability, and self-healing properties.</p>

scholarly journals Robust synthesis of epoxy resin-filled microcapsules for application to self-healing materials

2016 ◽  
Vol 374 (2061) ◽  
pp. 20150083 ◽  
Author(s):  
Patryk A. Bolimowski ◽  
Ian P. Bond ◽  
Duncan F. Wass
Keyword(s):  
Epoxy Resin ◽  
Size Distribution ◽  
Fibre Composite ◽  
Diglycidyl Ether ◽  
High Yield ◽  
Self Healing ◽  
Carbon Fibre Composite ◽  
Scanning Calorimetry ◽  
Water Emulsion ◽  
Oil In Water Emulsion

Mechanically and thermally robust microcapsules containing diglycidyl ether bisphenol A-based epoxy resin and a high-boiling-point organic solvent were synthesized in high yield using in situ polymerization of urea and formaldehyde in an oil-in-water emulsion. Microcapsules were characterized in terms of their size and size distribution, shell surface morphology and thermal resistance to the curing cycles of commercially used epoxy polymers. The size distribution of the capsules and characteristics such as shell thickness can be controlled by the specific parameters of microencapsulation, including concentrations of reagents, stirrer speed and sonication. Selected microcapsules, and separated core and shell materials, were analysed using thermogravimetric analysis and differential scanning calorimetry. It is demonstrated that capsules lose minimal 2.5 wt% at temperatures no higher than 120°C. These microcapsules can be applied to self-healing carbon fibre composite structural materials, with preliminary results showing promising performance.

scholarly journals Stress Relaxation and Refractive Index Change of As2S3in Compression Molding

2016 ◽  
Vol 8 (3) ◽  
pp. 255-265 ◽  
Author(s):  
Jian Zhou ◽  
Jianfeng Yu ◽  
L. James Lee ◽  
Lianguan Shen ◽  
Allen Yi
Keyword(s):  
Refractive Index ◽  
Stress Relaxation ◽  
Refractive Index Change ◽  
Compression Molding ◽  
Index Change

scholarly journals Application of Infrared Heating for Roasting Nuts

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Hadi Bagheri
Keyword(s):  
Energy Consumption ◽  
Production Efficiency ◽  
High Energy ◽  
Quality Characteristics ◽  
Infrared Heating ◽  
Ir Radiation ◽  
Thermal Methods ◽  
Hot Air ◽  
A New Technique ◽  
Time And Energy

Roasting is a key process in production of nuts. Improving the flavor and crispiness of texture in nuts is considered as a purpose of roasting, which increases the overall acceptance of the product. This review aims to introduce the infrared method as a new technique of roasting and evaluate the quality characteristics of some nuts after infrared roasting. Usually, the traditional roasting methods are time-consuming with high energy consumption and low production efficiency. One of the best ways to decrease roasting time and energy consumption is to provide heat by infrared (IR) radiation. However, the low penetration power of infrared radiation is one of the limitations of this method. The combination of infrared with other thermal methods can overcome this limitation. Studies have been done on roasting of nuts and other foods by different IR roasting methods such as IR, IR-hot air, and IR-microwave roasting methods. This paper reviews the effect of different IR roasting methods on the quality characteristics of roasted pistachio, peanut, hazelnut, almond, sunflower, soybean, and other food products. IR heating has been applied successfully to the roasting of some nuts. The use of infrared roasting has several advantages in comparison with traditional convective roasting methods. According to the results of most of these studies, the combination of infrared with other thermal methods to roast nuts has distinctly improved the potential of the technology as compared to the IR roasting alone.

scholarly journals Design Strategy for Self-Healing Epoxy Coatings

Coatings ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 50 ◽  
Author(s):  
Dian Yuan ◽  
Vahab Solouki Bonab ◽  
Ammar Patel ◽  
Talha Yilmaz ◽  
Richard A. Gross ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Phase Separation ◽  
Thermoplastic Polyurethane ◽  
Polymeric Materials ◽  
Secondary Phase ◽  
Diglycidyl Ether ◽  
Self Healing ◽  
Structure Property ◽  
Chain Entanglement ◽  
Epoxy Network

Self-healing strategies including intrinsic and extrinsic self-healing are commonly used for polymeric materials to restore their appearance and properties upon damage. Unlike intrinsic self-healing tactics where recovery is based on reversible chemical or physical bonds, extrinsic self-healing approaches rely on a secondary phase to acquire the self-healing functionality. Understanding the impacts of the secondary phase on both healing performance and matrix properties is important for rational system design. In this work, self-healing coating systems were prepared by blending a bio-based epoxy from diglycidyl ether of diphenolate esters (DGEDP) with thermoplastic polyurethane (TPU) prepolymers. Such systems exhibit polymerization induced phase separation morphology that controls coating mechanical and healing properties. Structure–property analysis indicates that the degree of phase separation is controlled by tuning the TPU prepolymer molecular weight. Increasing the TPU prepolymer molecular weight results in a highly phase separated morphology that is preferable for mechanical performances but undesirable for healing functionality. In this case, diffusion of TPU prepolymers during healing is restricted by the epoxy network rigidity and chain entanglement. Low molecular weight TPU prepolymers tend to phase mix with the epoxy matrix during curing, resulting in the formation of a flexible epoxy network that benefits TPU flow while decreasing Tg and mechanical properties. This work describes a rational strategy to develop self-healing coatings with controlled morphology to extend their functions and tailor their properties for specific applications.

scholarly journals Alleviating Molecular-Scale Damages in Silica-Reinforced Natural Rubber Compounds by a Self-Healing Modifier

Polymers ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 39
Author(s):  
Bashir Algaily ◽  
Wisut Kaewsakul ◽  
Siti Salina Sarkawi ◽  
Ekwipoo Kalkornsurapranee
Keyword(s):  
Natural Rubber ◽  
Zinc Acetate Dihydrate ◽  
Crosslinking Agent ◽  
Annealing Treatment ◽  
Self Healing ◽  
Rubber Compounds ◽  
Healing Efficiency ◽  
Molecular Scale ◽  
Transesterification Catalyst ◽  
Natural Rubber Vulcanizates

The property retentions of silica-reinforced natural rubber vulcanizates with various contents of a self-healing modifier called EMZ, which is based on epoxidized natural rubber (ENR) modified with hydrolyzed maleic anhydride (HMA) as an ester crosslinking agent plus zinc acetate dihydrate (ZAD) as a transesterification catalyst, were investigated. To validate its self-healing efficiency, the molecular-scale damages were introduced to vulcanizates using a tensile stress–strain cyclic test following the Mullins effect concept. The processing characteristics, reinforcing indicators, and physicomechanical and viscoelastic properties of the compounds were evaluated to identify the influences of plausible interactions in the system. Overall results demonstrate that the property retentions are significantly enhanced with increasing EMZ content at elevated treatment temperatures, because the EMZ modifier potentially contributes to reversible linkages leading to the intermolecular reparation of rubber network. Furthermore, a thermally annealing treatment of the damaged vulcanizates at a high temperature, e.g., 120 °C, substantially enhances the property recovery degree, most likely due to an impact of the transesterification reaction of the ester crosslinks adjacent to the molecular damages. This reaction can enable bond interchanges of the ester crosslinks, resulting in the feasibly exchanged positions of the ester crosslinks between the broken rubber molecules and, thus, achievable self-reparation of the damages.

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