Reversible Bonding of Aromatic Thermosetting Copolyesters for In‐Space Assembly

Abstract

usually divided into two main categories. One category is to use a micro-patterned surface that mimics the bio-structures and the other category is to solely apply nonpatterned adhesive polymers. The adhesion force between different surfaces is generated due to van der Waals forces, [7] capillary forces, [8] mechanical interlocking, [9] covalent bond, [10] and hydrogen bonding. [11] The patterned surfaces can have higher compliance and conformability to various substrate topographies, thus may exhibit better adhesion, compared to non-patterned counterparts. [12] Table 1 summarizes several studies reported in the literature that investigated reversible adhesion or reversible bonding mechanisms, including both patterned and non-patterned methods. The bonding parameters, measured bonding strength, and numbers of bond/debond cycles are listed in the table. Regardless of adhesive media and bonding conditions, the maximum pull-off strength (or bonding strength) is 10 MPa, corresponding to three cycles, and the maximum repeated cycle number is 60, corresponding to 0.53 MPa lap shear strength.The NASA 2015 technology roadmap TA12 [13] proposes lightweight joining concepts by eliminating bolted joints and the NASA 2017 SBIR solicitation [14] describes the ability to reversibly join structural truss units capable of sustaining loads of 100-500 N. In this work, we show a non-patterned reversible bonding solution which shows a combined bonding strength far over 10 MPa, and over 50 bond/debond cycles at both ambient and elevated temperatures, which is potentially of utility for applications such as in the automotive and aerospace industries. To be viable for in-space assembly, adhesive performance at elevated temperatures is a requirement for bonds exposed to the high temperatures that surfaces outside of Earth's atmosphere cyclically sustain when exposed to the Sun. Generally, the schemes described in Table 1 are characterized in terms of bonding strength at room temperature and use polymers that have glass transitions lower than typical values experienced in daylight in Earth orbit.Aromatic thermosetting copolyester (ATSP) is a cured product of cross-linkable aromatic polyester oligomers of various branch coefficients and molecular weight Aromatic Thermosetting CopolymersReversible bonding is an attractive option for assembly and disassembly of reconfigurable space structures due to the simplicity of the fastening concept. Interchain transesterifications reaction [ITR-a type of dynamic covalent exchange reactions afforded by aromatic thermosetting copolyesters (ATSP)] between two ATSP coatings can successfully be used as a reversible bonding concept, provided that the mode of debonding is completely cohesive (rather than adhesive or delaminatory from metal substrate). An optimization study is carried out on the ITR bonding for which ATSP coating is applied on 7075 aluminum substrates and bond/debond experiments are carried out using a custom-built tool kit. The toolkit enables precise control over bonding pressure, tempe...

Wide Area Reversible Adhesive for In‐Space Assembly

“…The results shown in this work demonstrates a substantial reduction in process time required to conduct the bonding operation relative to those presented previously by Meyer et al [22].…”

“…Figure 4(Bottom Left) is the debonding curve (force vs. time) for the bonded titanium coupons at room temperature, and it showed a maximum debond force of 2046 N -corresponding to a mixed tensile-shear strength of 26 MPa. This non-contact induction heating method is far more time-efficient compared with the clamshell radiant heating previously described [22] . The methods described here permit bonding of attachments across arbitrary surfaces of future space structures, permitting adaptable retasking of these assets with changing mission requirements.…”

“…Crosslinkable aromatic copolyester oligomers were synthesized in a batch melt polymerization in a 2L reactor at 270°C under an argon atmosphere with the acetic acid byproduct distilled out and measured during the process [20][21][22] . The reactions proceeded until acetic acid generation was complete.…”

“…This was using a CB2AB2-type coating bonded at 340℃ and debonded at 150℃ (to simulate lowest strength while under full sun of low earth orbit). Comparisons between the ATSP-based reversible adhesive scheme and other reversible adhesive systems was made with the ATSP-based process showing a higher strength (>14 MPa), at a higher debond temperature, and for a larger number of cycles as compared to other reversible adhesives found in literature [22].…”

Self-healing materials for space applications: overview of present development and major limitations

“…In these terms, a new class of polymers called vitrimers seems promising for improvement of spacecraft resistance to their synergic effects. These materials can simultaneously change their shape and be permanently cross-linked [43], and interest has grown towards the advantages of their self-healing capability for space applications, paving the way towards new perspectives on manufacturing on ground or even out of the Earth, thanks to their thermally triggered reversible bonding ability [44]. Vitrimers which can be processed and recycled multiple times and have high chemical resistance and dimensional stability can be obtained from existing plastics as poly(methyl methacrylate), polystyrene, and high-density polyethylene through mechanisms as the metathesis of dioxaborolanes [45].…”