ABSTRACT
LARC™-TPI is a linear aromatic polyimide that was developed at NASA Langley Research Center in the 1970’s and subsequently licensed to Mitsui Toatsu Chemicals, Inc., (MTC) in Japan. This company has made it easier to process for use in application as a structural adhesive or as a composite matrix resin. The present forms that exist are (1) high melt viscosity or Low Flow Grade (LFG); (2) medium melt viscosity or Medium Flow Grade (MFG); and (3) low melt viscosity or High Flow Grade (HFG). As expected, the low melt viscosity material is the easiest to process but has poor toughness; the high melt viscosity material is very tough but is more difficult to process. Because of these two extreme situations we have worked closely with MTC to develop an optimized system. This work has resulted in the medium melt viscosity material as well as two other modified or blended medium-flow variations.
These novel forms of LARC™-TPI have resulted in adhesives that can be melt processed at pressures as low as 0.01 MPa (15 psi) at temperatures between 343-371°C (650-700°F). Evaluation of adhesive performance has been accomplished using lap shear specimens and evaluating flow, wet out and shear strength. Initial strengths for these optimized materials range from 20.7-41.4 MPa (3000-6000 psi) at room temperature and 13.8-20.7 MPa (2000-3000 psi) at elevated test temperatures.
