Sumitomo Chemical has developed two new grades of epoxy resin for use in prepreg production. Versus the standard aerospace grade — Sumi-Epoxy ELM 434 with a viscosity of 11,900 mPa-s — the new -434L grade has a viscosity of 8,200 mPa-s and the new 434VL grade has a viscosity of 5,100 mPa-s. Sumitomo also offers two higher-temperature grades (Sumi-Epoxy ELM-100 and 100H), which both have a Tg of 260°C vs. the standard 230°C of ELM-434.
The company also has expanded its offering of SumikaExcel PES micron-powder tougheners for epoxy composites. In addition to its standard grade of SumikaExcel 5003P, a new lower molecular weight 2603P grade has been introduced. The standard 5003P grade has a viscosity of 0.52 dl/g vs. a reduced viscosity of 0.26 for the new 2603P grade (both measured as 1% PES in N,N-dimethylformamide (DMF) solution @ 25°C). The molecular weight (Mw) of 5003P is 42,000 vs. 16,000 for the 2603P grade. Additionally, the Tg of 5003P is 227°C vs. 220°C for 2603P as measured with a differential scanning calorimeter. The new 2603P grade also features more terminal -OH groups vs. the standard grade (4.5 vs. 1.1 per 100 units).
SumikaExcel 2603P, a lower-viscosity PES additive, benefits aerospace composites where the viscosity of the combined epoxy/PES matrix is highly dependent on the molecular weight of the PES even at low letdown ratios. While the original SumikaExcel 5003P additive is effective at improving fracture toughness in epoxy composites, it was not always easy for formulators to add as much additive as desired due to the high viscosity of the combined resin system — especially during prepreg production.
By opting to use the lower-viscosity 2603P grade, formulators can now increase the ratio of PES to epoxy to further improve toughness of the final composite. Or, formulators can add additional polymers and additives to further modify functional properties of the composite. Yet another option is that formulators can choose one of the new lower-viscosity Sumi-Epoxy grades rather than use a lower molecular weight PES in order to drive down the viscosity of the combined polymer matrix.
