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Self-Healing Technology
Published in Ghasan Fahim Huseien, Iman Faridmehr, Mohammad Hajmohammadian Baghban, Self-Healing Cementitious Materials, 2022
Ghasan Fahim Huseien, Iman Faridmehr, Mohammad Hajmohammadian Baghban
Cross-linking of polymeric materials, which is an irreversible process, is performed to achieve superior mechanical properties, such as high modulus, solvent resistance, and high fracture strength. However, it adversely affects the refabrication ability of polymers. Moreover, highly cross-linked materials have the disadvantage of brittleness and have the tendency to crack. One approach to bring process ability to cross-linked polymers is the introduction of reversible cross-links in polymeric systems. In addition to refabrication and recyclability, reversible cross-links also exhibit self-healing properties. However, reversible cross-linked systems do not show self-repairing ability on their own. An external trigger such as thermal, photo, or chemical activation is needed to achieve reversibility, and thereby the self-healing ability. Thus, these systems show non-autonomic healing phenomenon. Later in this book, different approaches that are considered to bring reversibility in cross-linked polymeric materials are discussed [35].
Polymer Technologies
Published in Ghenadii Korotcenkov, Handbook of Humidity Measurement, 2020
We also need to take into account that in some humidity-sensor applications, where the swelling effect plays the main role, the using of cross-linkers can be limited. Cross-linking increases the strength of the cross-linked material but decreases its flexibility and increases its brittleness. Most chemical cross-linking is not easily reversible.
Polymerization of Natural Oils for a Quartz Crystal Microbalance-Based Gas Sensor Application
Published in Chin Hua Chia, Chin Han Chan, Sabu Thomas, Functional Polymeric Composites, 2017
Rashmi.T.A. Das, Panchan.A.N. Pramanik, Raj.I.B. Bandyopadhyay
Although the biggest usable area of this polymerized oil is in coating industry, in the last few decades, triglyceride oil-based polymers have been used for many different applications. Linseed, sunflower, rapeseed oils, and soybean oil-based resins are commonly used in the printing industry. Polyesters, polyurethanes (urethane oils), polyamides, acrylic resins, epoxy resins, and polyester amides are prepared from triglyceride oils. The cross-linked polymers have high modulus, high fracture strength, and solvent resistance. It is also found that highly cross-linked polymers are used for synthesis of composites, foamed structures, structural adhesives, insulators for electronic packaging, and other applications.23 Without using any activator, soybean oil can be oxidized by permanganate oxidation with sub/supercritical CO2. The oxidized oil is used as semi-drying oil in paint industries.24
Tannic acid-crosslinked chitosan matrices enhance osteogenic differentiation and modulate epigenetic status of cultured cells over glutaraldehyde crosslinking
Published in Soft Materials, 2022
Veena Acharya, Aritri Ghosh, Amit Roy Chowdhury, Pallab Datta
Amongst several cross-linking systems, chemical crosslinking was one of the earliest developed methods, which crosslink polymers through covalent bonding. Dialdehydes like glutaraldehyde (GA) is one of the most commonly used cross-linking agent for chitosan. The crosslinking mechanism for chitosan and GA is not very clear. Many studies have been made to understand the mechanism and three propositions have been made to understand the crosslinking mechanism: (a) one Schiff base forms with one aldehyde group and the other aldehyde group remains free for subsequent reaction; (b) two Schiff bases are formed with both aldehyde groups of the GA and two chitosan unities; (c) a number of GA molecules polymerize to form a greater crosslinking chain.[4] The chemical crosslinking between chitosan and GA is shown in Figure 1a. However, the most important drawback of GA is its toxicity, which limits its application in tissue regeneration. Several studies concerning biocompatibility of GA-crosslinked constructs have showed the cytotoxic effect of GA on attachment and proliferation of osteoblast cells while induction of apoptosis by GA is also known for a long time.[7] Leaching, immunogenicity of GA-crosslinked scaffolds has also been observed in long-term in vivo studies .[8]
Fabrication and characterization of jute cotton blended fabrics reinforced UPR based composite: effect of gamma radiation and reactive dye
Published in Radiation Effects and Defects in Solids, 2021
Md. Tarik Hossain, Md. Sahadat Hossain, Samina Ahmed, Ruhul A. Khan, A.M. Sarwaruddin Chowdhury
Ionizing radiation is the radiation that carries sufficient energy to liberate electrons from atoms or molecules and hence ionize them. On the other hand, non-ionizing radiations do not carry sufficient energy to liberate electrons completely from the atoms or molecules. Ionizing radiation is made up of energetic subatomic particles, ions, and atoms moving at high speeds. Gamma radiation is well known for its ionizing ability with high penetrating capacity. It is widely used in polymer-based composites for the cross-linking of the polymer. Gamma radiation produces free radicals in the polymer chain and thus helps to cross-link inside the polymer. Gamma irradiated composites ultimately augment the physic-mechanical properties of natural fiber-reinforced composites (11, 16, 20–22).
Post-processing treatments to enhance additively manufactured polymeric parts: a review
Published in Virtual and Physical Prototyping, 2021
F. Tamburrino, S. Barone, A. Paoli, A. V. Razionale
Another approach relies on the use of ionising radiation on polymers blended with specific radiation sensitisers, such as trimethylolpropane triacrylate (TMPTA) and triallyisocyanurate (TAIC). In this case, ionising radiation creates crosslinks between polymer chains of the blended polymer. The effect is an improvement in mechanical properties such as toughness, ductility, and ultimate tensile strength. In (Shaffer et al. 2014), for example, sensitised PLA-FDM parts were treated with gamma rays to improve interlayer adhesion and reduce anisotropy. The results showed a significant enhancement of toughness, ductility, and ultimate tensile strength of PLA samples blended with TAIC and exposed to ionising radiation at 60 °C. However, worse results were obtained at 20 °C, highlighting that temperatures below the glass transition hinder chain mobility, thus preventing a high degree of crosslinking.