Effects of synthesis method, melamine content and GPC parameter on the molecular weight of melamine-urea-formaldehyde resins

This study was conducted to investigate the effects of the synthesis method, melamine content, and GPC parameters (such as flow rate, column-detector temperature, and sample injection temperature) on the molecular weight of melamine– urea–formaldehyde (MUF) resins. Two different synthesis methods were employed. In the first method, MUF-A resins were synthesized by simultaneously reacting urea, formaldehyde, and melamine (5%, 10%, and 20%) using the reaction of alkaline–acid–alkaline steps under controlled temperature and viscosity. In the second method, MUF-B resins were synthesized by first reacting melamine at the same levels with formaldehyde and then by adding urea. The highest weight average molecular weight (M_w) of MUF-A resins was found at 10% melamine content when the flow rate was 0.3 and 0.8 ml/min; M_w decreased slightly at 20% melamine content. The results showed that M_w increased with an increase in the melamine content when the flow rate was 0.5 and 1.0 ml/min. In addition, M_w was the highest when the flow rate, column-detector temperature, and injection temperature were 0.3 ml/min, 50°C, and 25°C, respectively. On the contrary, MUF-B resins had greater M_w and number average molecular weight (M_n) than MUF-A resins. Overall, M_w and M_n increased as the melamine content increased. The optimal GPC parameter for MUF resins was determined as follows: a flow rate of 0.5 ml/min, a column-detector temperature of 50°C, and a sample injection temperature of 50°C.