Self-Healing Coating Materials

  Metallic materials are widely used across numerous applications in industry. Recent research shows that industrialized countries spend 2-5% of their annual budgets on metal protection. The long-term durability and protection of the fundamental properties of metals is critically important. Harsh environmental conditions affect materials and the formation of micro-cracks can easily begin. For this reason, protecting metal surfaces with polymeric coatings and extending the service life of coating materials is an important factor. The presence of localized defects or micro-cracks in polymeric coatings causes fatal damage to metals when corrosion begins. Several approaches related to self-healing mechanisms have been proposed to make polymeric coatings more durable. These approaches can be divided into two major categories: intrinsic and extrinsic self-healing mechanisms. In the extrinsic (autonomous) mechanism, smart, self-healing microcapsules are incorporated into the protective polymeric matrix. When a crack occurs, it ruptures and healing agents are released from the microcapsules. In the intrinsic (non-autonomous) self-healing mechanism, dynamic reversible ionic and/or covalent bonds act as binders in the polymeric network after a crack forms. Functional groups in polymeric coatings require physical stimuli such as heating, mechanical force, ultraviolet (UV) radiation or pH adjustment to initiate self-healing capability. [1-3]

Figure 1. Differences between autonomous and non-autonomous self-repair processes

Paints and varnish coatings used particularly in the protection of metals in bridges, pipelines, aircraft fuselages, automobiles and similar applications attract considerable attention due to the economic benefits they provide by preventing metal corrosion and imparting durability to metals. Epoxy-amine curing systems with self-healing properties are of particular interest to researchers due to their various design flexibilities when compared to silicones, thermoset polymers, elastomers and hydrogels. They are commonly used as corrosion-preventive coating materials in the maritime industry. [4-6]

Figure 2. (a) Ester bond of alkyd and epoxide group and (b) Possible curing reactions of alkyd and amine hardener to form formamide bonds

Self-healing mixtures can be obtained by adding chemicals with functional groups, particularly alkyd, to epoxy-amine curing systems. By heating the crack area, carboxylic acid groups of alkyds react with unopened epoxy groups and also with hydroxyl groups. Additionally, acid groups react with amine groups to form formamide bonds. Possible reaction mechanisms have been proposed by researchers (Figure 2). [6] İzel Kimya is conducting research on the production of new bio-based materials with self-healing properties to protect metals from corrosion. Various oil derivatives, in particular, are good candidates that can be modified to demonstrate self-healing properties. Dr. Cemil Dızman - Head of Research and Development - İzel Kimya Merve Boy - Research Manager - İzel Kimya

References 1) Mphahlele, Keletso&Sinha Ray, Suprakas&Kolesnikov, Andrei. (2017). Self-Healing Polymeric Composite Material Design, Failure Analysis and Future Outlook: A Review. Polymers. 2) Wang, Rongguo&Hu, Honglin&Liu, Wenbo&Guo, Qiong. (2011). Preparation and Characterization of Selfhealing Polymeric Materials with Microencapsulated Epoxy and Imidazoline Derivatives Curing Agent. Polymers and Polymer Composites. 3) Yu, Kunhao&Xin, An&Du, Haixu&Li, Ying&Wang, Qiming. (2019). Additive manufacturing of self-healing elastomers. NPG Asia Materials. 4) Post, W. (2017). Self-Healing Polymer Composites. 5) Madara, Sahith Reddy et al. "Review of research and developments in self healing composite materials." (2018). 6) Shahabudin, N., Yahya, R., Gan, S. N&Sonsudin, F. (2018). Curing of epoxy/alkyd blends in self-healing coating. High Performance Polymers, 30(8), 1009–1015.