Preparation and characterization of porous epoxy micro-beads using single droplet in different oil systems

This study reported the production of porous epoxy micro-beads (PEMBs), which potentially serve as a filler. The PEMBs were produced to overcome the use of high filler content and enhance the composite properties. PEMBs were fabricated from a single epoxy mixture droplet containing epoxy, polyamide as hardener and blowing agent. In this study, the effect of oil system (i.e., corn oil and silicone oil), different types of blowing agents (i.e., ammonium bicarbonate, toluenesulfonylhydrazide and sodium bicarbonate), different processing temperatures (i.e., 80, 90 and 100 °C) and different ammonium bicarbonate contents (i.e., 0, 5, 10 and 15 phr) were investigated. Two different epoxy polyamide ratios of 10:6 and 10:10 were selected in this study. The 10:6 ratio was based on the stoichiometric ratio, while the 10:10 ratio was above stoichiometric ratio. A single epoxy mixture droplet was dropped into different oil systems (i.e., corn oil and silicone oil) at 100 °C. Because of the immiscibility of epoxy mixture and oil, the droplet was formed. After achieving the decomposition temperature of ammonium bicarbonate, the single epoxy mixture droplet burst into many smaller droplets and was cured as PEMBs in the corn oil system. The results showed that corn oil as oil system with epoxy polyamide ratio of 10:6 exhibited a smaller contact angle between the epoxy droplet and corn oil. This phenomenon induced the reduction in the interface tension between epoxy droplet and corn oil. Therefore, smaller particle sizes of PEMBs were obtained and resulted in lower porosity and higher bulk density. The use of ammonium bicarbonate as a blowing agent offered slower decomposition rate with lower total volume of gas generated between toluenesulfonylhydrazide and sodium bicarbonate. The decomposition of ammonium bicarbonate occurred after gel time in support of the rheological profile. This behaviour was caused by ammonium bicarbonate having open PEMBs pores with larger particle sizes as evidenced by morphological analysis. This resulted in higher porosity and consequently a reduction in bulk density. For the epoxy polyamide ratio, PEMBs with ratio of 10:6 obtained smaller particles size when using ammonium bicarbonate as blowing agent, resulting in the highest porosity and the lowest bulk density. As expected, the optimum processing temperature for ammonium bicarbonate in epoxy polyamide ratio of 10:6 was 100 °C to obtain many smaller PEMB particle with porosity up to 50% and lower bulk density of < 0.7. On the other hand, the effect of ammonium bicarbonate content on the properties was investigated. It was found that higher ammonium bicarbonate content of 10 phr exhibited slower decomposition rate and higher total volume of gas. This resulted in smaller particle sizes of PEMBs with epoxy polyamide ratio of 10:6 as supported by morphological analysis. Therefore, it offered higher porosity of around 61.84% with lower bulk density of 0.537. Through these findings, epoxy polyamide ratio of 10:6 dropped into corn oil at processing temperature of 100 °C produced many smaller micro-beads. Furthermore, PEMBs using 10 phr ammonium bicarbonate offered highest porosity and lowest bulk density.