Effect of Stabilizer States (Solid Vs Liquid) on Properties of Stabilized Natural Rubbers

Non-Covalent Interaction on the Self-Healing of Mechanical Properties in Supramolecular Polymers

Supramolecular polymers are widely utilized and applied in self-assembly or self-healing materials, which can be repaired when damaged. Normally, the healing process is classified into two types, including extrinsic and intrinsic self-healable materials. Therefore, the aim of this work is to review the intrinsic self-healing strategy based on supramolecular interaction or non-covalent interaction and molecular recognition to obtain the improvement of mechanical properties. In this review, we introduce the main background of non-covalent interaction, which consists of the metal–ligand coordination, hydrogen bonding, π–π interaction, electrostatic interaction, dipole–dipole interaction, and host–guest interactions, respectively. From the perspective of mechanical properties, these interactions act as transient crosslinking points to both prevent and repair the broken polymer chains. For material utilization in terms of self-healing products, this knowledge can be applied and developed to increase the lifetime of the products, causing rapid healing and reducing accidents and maintenance costs. Therefore, the self-healing materials using supramolecular polymers or non-covalent interaction provides a novel strategy to enhance the mechanical properties of materials causing the extended cycling lifetime of products before replacement with a new one.

Current challenges in thermodynamic aspects of rubber foam

Natural rubber (NR) foam can be prepared by the Dunlop method using concentrated natural latex with chemical agents. Most previous studies have focused on the thermodynamic parameters of solid rubber in extension. The main objective of this study is to investigate the effect of the NR matrix concentration on the static and dynamic properties of NR foams, especially the new approach of considering the thermodynamic aspects of NR foam in compression. We found that the density and compression strength of NR foams increased with increasing NR matrix concentration. The mechanical properties of NR foam were in agreement with computational modelling. Moreover, thermodynamic aspects showed that the ratio of internal energy force to the compression force, Fu/F, and the entropy, S, increased with increasing matrix concentration. The activation enthalpy, ∆Ha, also increased with increasing matrix concentration in the NR foam, indicating the greater relaxation time of the backbone of the rubber molecules. New scientific concepts of thermodynamic parameters of the crosslinked NR foam in compression mode are proposed and discussed. Our results will improve both the knowledge and the development of rubber foams based on the structure-properties relationship, especially the new scientific concept of the thermodynamical parameters under compression.

The Role of Non-Rubber Components on Molecular Network of Natural Rubber during Accelerated Storage

Though the non-rubber components have long been recognized to be a vital factor affecting the network of natural rubber (NR), the authentic role of non-rubber components on the network during accelerated storage has not been fully illuminated. This work attempts to clarify the impact of non-rubber components on the network for NR during accelerated storage. A natural network model for NR was proposed based on the gel content, crosslinking density, and the non-rubber components distribution for NR before and after centrifugation. Furthermore, the effect of non-rubber components on the network was investigated during accelerated storage. The results show that terminal crosslinking induced by non-rubber components and entanglements are primary factors affecting the network formation during accelerated storage. By applying the tube model to analyze the stress-strain curves of NR, we found that the contribution of the entanglements to the network formation is larger than that of terminal crosslinking during accelerated storage. The work highlights the role of non-rubber components on the network during accelerated storage, which is essential for understanding the storage hardening mechanism of NR.

Effect of Fillers on the Recovery of Rubber Foam: From Theory to Applications

Natural rubber foam (NRF) can be prepared from concentrated natural latex, providing specific characteristics such as density, compression strength, compression set, and so on, suitable for making shape-memory products. However, many customers require NRF products with a low compression set. This study aims to develop and prepare NRF to investigate its recoverability and other related characteristics by the addition of charcoal and silica fillers. The results showed that increasing filler loading increases physical and mechanical properties. The recoverability of NRF improves as silica increases, contrary to charcoal loading, due to the higher specific surface area of silica. Thermodynamic aspects showed that increasing filler loading increases the compression force (F) as well as the proportion of internal energy to the compression force (F_u/F). The entropy (S) also increases with increasing filler loading, which is favorable for thermodynamic systems. The activation enthalpy (∆H_a) of the NRF with silica is higher than the control NRF, which is due to rubber–filler interactions created within the NRF. A thermodynamic concept of crosslinked rubber foam with filler is proposed. From theory to application, in this study, the NRF has better recoverability with silica loading.

Performance of Nano- and Microcalcium Carbonate in Uncrosslinked Natural Rubber Composites: New Results of Structure-Properties Relationship

Calcium carbonate (CaCO₃) is one of the most important inorganic powders and is widely used as filler in order to reduce costs in the rubber industry. Nanocalcium carbonate reduces costs and acts as a semireinforcing filler that improves the mechanical properties of rubber composites. The objective of this study was to investigate the effect of nano-CaCO₃ (NCC) and micro-CaCO₃ (MCC) on the properties of natural rubber composites, in particular, new results of structure-properties relationship. The effects of NCC/MCC on the properties of rubber composites, such as Mooney viscosity, bound rubber, Mullins effect, and Payne effect, were investigated. The result of the Mullins effect of rubber composites filled with NCC was in good agreement with the results of Mooney viscosity and bound rubber, with higher Mooney viscosity and bound rubber leading to higher stress to pull the rubber composites. The Payne effect showed that the value of different storage moduli (ΔG') of rubber composites filled with 25 parts per hundred rubber (phr) NCC was the lowest due to weaker filler network, while the rubber supplemented with 100 phr NCC had more significant ΔG' values with increase in strain. The results of rubber composites filled with MCC showed the same tendency as those of rubber composites filled with NCC. However, the effect of specific surface area of NCC on the properties of rubber composites was more pronounced than those of rubber composites filled with MCC. Finite element analysis of the mechanical property of rubber composites was in good agreement with the result from the experiment. The master curves of time-temperature superposition presented lower free volume in the composites for higher loading of filler, which would require more relaxation time of rubber molecules. This type of nanocalcium carbonate material can be applied to tailor the properties and processability of rubber products.