Effect of chain length of cardanol based phenalkamines on mechanical properties of air-dried and heat-cured epoxies

摘要

Four cardanol-based phenalkamines (named PK1, PK2, PK3 and PK4, respectively) with different polyethylenepolyamine chain lengths were synthesized using ethylenediamine, diethylenetriamine, triethylenetetramine and pentaethylenehexamine, respectively, and then air-dried and heat-cured epoxies were prepared using these four phenalkamines as curing agents. The effects of the polyethylenepolyamine chain length on the mechanical and thermal properties of these epoxies were investigated. The adhesion and hardness of air-cured coatings, and the thermogravimetric analysis, dynamic mechanical properties, swelling degree and mechanical properties of heat-cured epoxies were investigated. The results show that the crosslinking density of cured epoxies calculated based on the dynamic mechanical results and rubber elasticity theory follows the order of DGEBA/PK1 < DGEBA/PK3 < DGEBA/PK2 < DGEBA/PK4, which can be affected by many factors such as chain length, viscosity and phenalkamine dosage. The chain length of polyethylenepolyamines follows the order of PK1 < PK2 < PK3 < PK4. A longer chain length contains more secondary amines, which can react with more epoxy groups and therefore form more tertiary amino groups. As a consequence, the curing reaction can be catalyzed during the epoxy-secondary amine reactions, resulting in a higher curing degree. A similar trend is observed in thermogravimetric analysis and mechanical properties, but an opposite trend is observed in swelling degree of epoxies. Thus, the epoxies cured by phenalkamines with a longer polyethylenepolyamine chain generally have better balanced mechanical and thermal properties.