The Effect of Side Chain Functionalization and Formulation of Cashew Nutshell Liquid (CNSL) on the Properties of Thermoset Networks

• Main Author: Kinaci, Emre
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2018
• Subjects: Materials science; Polymer chemistry
• ISBN: 0438540832; 9780438540835

Cardanol which is the main component of the thermally treated cashew nutshell liquid (CNSL) is a versatile molecule with a C15 aliphatic side chain connected to a phenyl ring at the -meta position. The dual structure of cardanol which combines a rigid aromatic ring with a flexible and hydrophobic side chain with different degrees of unsaturation makes this molecule a suitable and sustainable candidate to utilize in top coat and primer formulations to improve corrosion performance. However, cardanol lacks reactive polymerizable functional groups on its structure and cardanol-derived networks possesses long dangling chains on their backbone which decrease the network performance regardless of their benefits. Thus, in this dissertation, the effect of cardanol’s side chain functionalization on network properties and corrosion performance was explored. The unsaturation sites of the side chain of the mono-epoxy cardanol molecule, cardanol glycidyl ether (CGE), were epoxidized via peroxyacids to achieve secondary epoxies on the side chain and to connect the C15 chain of the cardanol into the polymer network. This side chain epoxidized CGE (SCECGE) epoxy resin was cross-linked with a range of amine curing agents. The lower reactivity of the secondary epoxies towards amines was demonstrated via a number of direct and indirect curing studies and a systematic methodology was developed to assess the extent of cure of secondary epoxies by using cardanol-derived model secondary epoxy. Structural characterization of SCECGE monomer also revealed the reduced reactivity of the terminal double bonds of the aliphatic chain towards epoxidation with respect to inner ones because of their reduced electronegativity. Thus, a useful methodology was developed to effectively epoxide the terminal double bonds of the SCECGE and to make a correlation between the degree of side chain functionalization and the network performance. SCECGE monomer was mixed with a bis-phenol A derived di-epoxy monomer (DGEBA, EPON 828) with changing weight rations and thermally cross-linked with a cycloaliphatic amine (PACM) to demonstrate the effect of side chain cross-linking on the water barrier and corrosion performance. Network properties and the coating performance of the DGEBA/SCECGE blends were evaluated and the results showed that; upon proper functionalization and careful formulation with DGEBA, cardanol based building blocks can meet significant requirements ofthermoset coatings while keeping satisfactory thermal and mechanical resistance for corrosion coating applications. The reactivity issue of the secondary epoxies was addressed via further reacting the epoxy moieties with methacrylic acid to fully react the side chain into the polymer network thus to improve the polymer performance and network properties. Due to the stearic limitations of the secondary epoxies; they are not able to fully react with amine hardeners. Replacing these secondary epoxies with methacrylate units and using the free radical polymerization mechanizm resulted in almost full cross-linking of the side chain in vinyl ester formulations. Finally, a useful hybrid molecule synthesized via the combination of cardanol and fatty acid based building blocks was incorporated with DGEBA-PACM system. This hybrid molecule demonstrated similar toughening effect to epoxidized soybean oil based tougheners while keeping the modulus significantly higher owing to its aromatic content.