Hydrolysis susceptibility and carbamate formation for a low moisture-absorbing, siloxane-modified cyanate ester resin matrix (TC410) material used for composite space applications

Abstract

Siloxane-modified cyanate ester resins are ideal matrix materials for next-generation, high-precision composites used for radomes and satellite structures. They provide extremely low moisture uptake, excellent microcracking resistance, and protection from atomic radiation. However, cyanate ester resins have been shown to be susceptible to hydrolysis during cure, which may significantly impact both mechanical and thermal performance. In this investigation, we evaluate the cure kinetics and hydrolysis susceptibility of a siloxane-modified prepreg system (TC410/M55J). DSC tests verified that the Ea of polymerization for the TC410 system is 65 KJ/mol. Samples were also exposed to moisture during cure at several temperatures, and FTIR was used to follow changes in the carbonyl peak absorption intensity to compare the rate kinetics and activation energy for hydrolysis leading to carbamate formation (52 KJ/mol). DMA tests of composites exhibited significantly reduced Tg’s with increasing moisture levels during cure. TGA of these cured samples exhibited both a significant decrease in the onset of the thermal decomposition temperature as well as an increase in the relative degree of volatiles generated at low temperature. Flatwise tension strength tests showed a linear reduction in strength with decreasing Tg, at an equivalent trend to previous work on an M55J/RS3C system indicating a similar mechanism. However, the added margin provided from the higher initial FWT strength in the TC410 system allows for larger decreases in Tg before significant degradation occurs. Laminates manufactured on composite mandrels resulted in parts with larger decreases in the tool-side Tg of the part when compared to the bag-side Tg, with the differential depending on the initial moisture content of the tool. AFM was shown to selectively identify these carbamate-affected regions by showing that the recession behavior of these less cross-linked areas was greater than in areas where the resin was properly cured. Composites with increased carbamate formation resulted in increasing warpage of the part with elevated temperature exposure due to variations in stress relaxation. This effect should be considered when manufacturing precision, high-dimensional stability composite hardware.

Degradation of high‐performance cyanate ester space composites by anodized aluminum

“…Topographical AFM measurements were performed on each composite following a method developed previously. 6 A Park NX20 Atomic Force Microscope was used to obtain topographic images of composite crosssections. A microfabricated silicon probe with 0.2 N/m force constant was used in contact mode to image over a 30 μm square area within a given ply.…”

“…As a result, curing produces a correspondingly less interconnected network and a more linear polymer with a reduced Tg. 6,14,17 However, challenges are present when characterizing such composites since the hydrolysis is typically located in the outer few plies (250 μm) adjacent to the water source. Therefore, when characterizing the thermomechanical response of a full thickness specimen, the DMA profile used to identify Tg becomes a convolution of both pristine and carbamate degraded material.…”

“…[3][4][5] Their lack of hydroxyl groups and their highly aromatic, non-polar structure contribute to many of these beneficial properties. Cyanate ester resins have become the primary material of choice for high precision space composite structures including optical benches, solar array substrates, reflectors, heat shield structural supports, replicated optics 6 and notably the optical telescope element (OTE) utilized for the James Webb telescope. 7 The polymerization behavior of cyanate ester resins and blends have been studied extensively over the last 30 years.…”

“…Zaldivar et al have also evaluated the effects of carbamate formation on both unmodified and modified, cyanate ester fiber reinforced composites. 6,14,17 Their work showed the moisture induced degradation is typically localized near the composite surface and is often misrepresented when performing standard full thickness quality inspection techniques that average over the full volume of the composite. Even though most of the composite may remain unaffected, the plies in proximity to the moisture source have been shown previously to decrease by as much as 50% in both matrix-dominated strength and Tg.…”

Preparation and Appraisal of High‐Modulus Resin‐Based Composites Reinforced by Silica‐Coated Multi‐Walled Carbon Nanotubes

“…[1] Among resin matrix composites, thermoset resin matrix embraces the characteristics of low viscosity and good processability before curing, while having excellent mechanical lightness, good high-temperature resistance and chemical stability after curing. [2,3] Hence it is widely used in aerospace structural materials, [4,5] high performance radomes, [6,7] high speed printed circuit boards and other fields. [8][9][10] Satellite structural materials are differentiated from other aerospace materials in requiring special properties such as high specific strength, high specific modulus, high dimensional stability, and low outgassing.…”