Sodium bicarbonate/azodiisobutyronitrile synergistic effect on low-density unsaturated polyester resin fabrication

The combination of sodium bicarbonate (NaHCO3) and azodiisobutyronitrile (AIBN) is an innovative idea for the fabrication of low-density unsaturated polyester resin (LDUPR). At 100 °C, acetic acid (HAc) was added to the polyester resin glue to facilitate the decomposition of NaHCO3 for the synergy between the gas releasing of NaHCO3 and that of AIBN in the foaming process. Regular and homogeneous cell distribution in LDUPR specimen was characterized by electron microscopy to clarify the foaming efficiency of NaHCO3 and AIBN combined. The LDUPR specimen containing AIBN/NaHCO3 and the LDUPR specimen containing AIBN/NaHCO3/HAc were demonstrated by X-ray diffractometry (XRD) to analyze the decomposition of NaHCO3. Heat balancing resulted from the combination of NaHCO3 and AIBN during the foaming process and it was realized through the endothermic heat of reaction of NaHCO3 and HAc, balanced by the exothermic heat of UPR curing process. This combination tempered the curing process of UPR, and was conducive to the foaming process of LDUPR. At 100 °C, the optimal contents of AIBN, NaHCO3 and HAc were all 1.5 phr, which were obtained from an orthogonal experiment, and the appropriate addition time of HAc was 18 min following the addition of AIBN/NaHCO3 mixture into the resin glue. The lowest apparent density of 0.34 ± 0.02 g−1 cm−3 and the highest specific compressive strength of 36.18 ± 1.02 MPa g−1 cm3 were obtained for LDUPR specimen.