Influence of photoinitiator and temperature on photocross-linking kinetics of acrylated epoxidized soybean oil and properties of the resulting polymers

Abstract

Acrylated epoxidized soybean oil is a very attractive photocurable starting material for synthesis of high biorenewable content polymers with a wide range of applications, however its UV/VIS-curing kinetics studies is still lacking. A detailed investigation of photocross-linking kinetics of acrylated epoxidized soybean oil using four different photoinitiators was performed at various temperatures by real-time photorheometry for the first time. It was determined that the amount and type of photoinitiator did not affect the gel time, but influenced the final values of storage modulus (G’), which plateau values were in the range of (1.3–3.6)∙107 Pa. Photocross-linking at 50 °C resulted in the faster growth of the G’ values, though their plateau values were lower due to the increased oxygen inhibition by phosphine oxides. Obtained highly photocross-linked polymers exhibited high thermal stability with the thermal decomposition temperature at the weight loss of 10 % in the range of (337–352) °C and the glass transition temperature in the range of (41.1–50.9) °C. Higher amount of the used photoinitiators increased the values of elastic modulus and tensile strength of the resulting polymers, though the values of elongation at break were decreased. Phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide was the most efficient photoinititator in smaller amount forming a highly cross-linked polymer, though ethyl (2,4,6-thimethylbenzoyl) phenyl phosphinate, as the liquid photoinitiator, facilitated its incorporation into the resin. This work could help integrate modified soybean oil into UV/VIS curing systems using the most appropriate photoinitiator and temperature, thereby reducing their environmental impact.