Solvay LTS90B/G sealant tape is supplied as a calendered thermosetting epoxy-based sealant film on a release liner. The LTS prefix identifies a low-temperature sealant chemistry; the numeric suffix 90 is conventionally associated with a nominal thickness of 0.090 in (2.29 mm); the B/G suffix denotes the black/grey liner or surface variant. These identifiers are manufacturer-specific and must be verified against the Solvay technical datasheet. The product is used in aerospace structural assembly to fill faying-surface gaps, exclude moisture, and reduce galvanic corrosion between carbon/epoxy skins and metallic substructure. Its principal difference from non-curing PTFE thread-seal tapes is that LTS90B/G undergoes irreversible cure, eliminating cold flow; its principal difference from one-part moisture-curing polysulfide sealants is that cure is thermally driven rather than atmospheric-moisture dependent. Qualification of the sealant tape normally references ASTM D1002, ASTM D1876, and ASTM D3539; however, because Solvay technical bulletins are revision-controlled, published data for this specific configuration is limited and should be confirmed against the current datasheet.

How Does Autoclave Cure of LTS90B/G Differ from Non-Curing Sealant Tapes?

In autoclave-processed assemblies, the tape is debulked under vacuum at 0.8–0.9 bar (80–90 kPa) for 10–15 min at ambient temperature before positive pressure is applied. Production-scale autoclaves with internal working envelopes of 3.0 m × 1.5 m and pressurization to 6.2 bar typically use heat-up rates of 1.5–2.0 °C/min to avoid premature gelation of the tape edges before the core reaches set point. Unlike non-curing PTFE tapes, which rely on cold-flow deformation and are not designed for structural load transfer, LTS90B/G develops crosslink density during cure; therefore, the sealant must be placed before cure and cannot be reworked by re-compression after cure. Degree of conversion can be tracked by differential scanning calorimetry per ASTM E1356; residual exotherm less than 5 J/g is often used as a shop-floor cure indicator, but the acceptance value must be taken from the Solvay datasheet. Premature application of autoclave pressure before the minimum viscosity window can cause resin-starved faying surfaces and low fillet coverage.

For composite wing spar chordwise seam sealing, the tape is hand-applied at 18–25 °C after plasma or gritblast surface preparation. On CNC-cut CFRP laminates, surface energy of at least 40 mN/m is verified by dyne pens before tape laydown; the release liner is removed only after alignment to avoid particle entrapment. In fastener-row faying surfaces, a continuous strip is pressed with a roller at 0.2–0.3 MPa nip pressure to ensure wet-out into the 120–180 µm ablation profile left by 180-grit abrasion. Because LTS90B/G is thermosetting, overlaps and splices should be limited to ≤6 mm and staggered between plies to avoid local thickness spikes that produce hard points under clamp-up.

When the Tape Is Substituted for Polysulfide Fuel-Tank Sealants

Where LTS90B/G is considered as a replacement for polysulfide or polythioether sealant tapes in integral fuel-tank faying seams, the substitution must account for cure-temperature mismatch and post-cure flexibility. Polysulfide sealants classified under AMS 3265 typically remain flexible from -55 °C to 121 °C and are resistant to Jet A and JP-8; an epoxy-based sealant tape may exhibit lower ultimate elongation and higher modulus after cure, which can reduce strain accommodation at skin-to-spar joints under cyclic pressurization. The LTS90B/G material should not be qualified solely by lap shear; fluid-immersion testing per ASTM D471 or ISO 1817 and peel after immersion per ASTM D1876 are required. In production-scale fuel-tank sealing, air-atomized polysulfide sealant beads are applied with 2–4 mm fillet radii; LTS90B/G tape does not form a fillet by gun application, so edge-seal details must be redesigned to provide continuous tape contact. Published comparative data for this specific configuration is limited; therefore, a full redesign qualification under 14 CFR Part 25 or equivalent airworthiness requirements is necessary.

Cold-bond repair applications place the sealant tape between a pre-cured patch and an abraded parent structure before vacuum-bag-only cure at 80–90 °C when heat-sensitive backing plies are present. The low-temperature cure response of LTS90B/G reduces thermal stress at the bonding interface; however, service temperature after low-temperature cure is generally lower than after a 177 °C post-cure. The repair shop should verify through ASTM D1002 lap shear on coupons cured with the same heat-blanket control zone as the aircraft part. Thermal surveys on actual production heat blankets with ±5 °C zone control are required because uncured epoxy sealant tapes exhibit a steep viscosity drop during heat-up, and uneven heating can cause resin to flow away from the faying surface before gelation.

Shelf-Life, Out-Time, and Preconditioning Control

Solvay LTS90B/G sealant tape is a latent-cure thermosetting material; the as-received storage condition is normally frozen at -18 °C or below, with a shelf life commonly limited to 12 months from date of manufacture when the roll is sealed in moisture-barrier packaging. Out-time at 24±2 °C and 50% RH should be tracked cumulatively; once the manufacturer's out-time is exceeded, the material must be discarded, as latent hardener activation and moisture uptake can cause false cure and surface tack loss. Thawing before use should be conducted inside the closed bag until the roll surface reaches 18–25 °C to prevent condensation-induced porosity. If the sealant tape is exposed to relative humidity above 60%, pre-drying is generally required; the specific drying schedule must be taken from the Solvay technical bulletin. Production experience on high-humidity assembly lines shows that condensation on cold rolls is a primary cause of bondline microvoiding.

Compression and gap-fill data for LTS90B/G are typically generated from stepped-shim wedge panels with gaps from 0.25 mm to 2.0 mm; void content is evaluated by ultrasonic C-scan per ASTM E2580. On actual wing assembly fixtures with clamp forces of 22 kN per meter, tape thickness is specified to accommodate the maximum faying-surface mismatch; a stack of two layers may be used only if the datasheet permits, because the second layer introduces an additional release-liner interface and can trap air.

Compared with silicone sealant tapes, LTS90B/G does not release acetic acid cure products and is preferred in closed-cavity aluminum structures where corrosion inhibition is critical. Compared with butyl sealant tapes, LTS90B/G offers higher temperature resistance after cure but requires frozen storage, which is not necessary for non-curing butyl. Compared with hot-melt sealant tapes, LTS90B/G has a thermoset cure and will not remelt after processing. These differences are material-class generalizations; the selection decision must be supported by the current Solvay datasheet and application-specific test panels.

If Low-Temperature Cure Is Selected, What Verification Protocol Applies?

A low-temperature cure at 121±3 °C for 60–90 min is typically used for composite-to-metal assemblies with close-tolerance tooling. The verification protocol begins with a cure-cycle temperature survey using tool-attached thermocouples at ≤1 m spacing; the coldest and hottest locations must be recorded. Lap shear specimens cured on production tooling are tested per ASTM D1002, and the minimum acceptable failure mode is cohesive within the sealant tape. When a 177±3 °C post-cure is used, the heat-up rate from 121 °C to 177 °C should not exceed 2 °C/min to prevent modulus-driven microcracking at the tape edges. Published data for this specific configuration is limited, so the verification protocol should be qualified on a component-representative panel before production runs.

Adhesive bondline thickness is controlled by the tape thickness, not by conventional liquid adhesives; therefore, surface mismatch beyond 0.5 mm should be corrected by shimming before tape application. On an autoclave-cured fuselage panel, actual tape thickness under clamp-up can decrease by 15–25% depending on pressure and temperature; this flow must be characterized by cross-sectioning and optical microscopy rather than assumed. Process capability studies on twin-panel tools with vacuum integrity below 10 mbar have shown that leaks at the tape overlap are the dominant cause of porosity; leak checks before cure are mandatory.

Regulatory documentation for LTS90B/G should be requested for each batch; aerospace qualification often references flammability requirements under FAR 25.853 and gas toxicity under BSS 7239. Because epoxy resin constituents may be subject to REACH Candidate List substances, a full material declaration is necessary prior to production release. The product should not be used in potable water or implantable medical applications unless explicitly cleared under applicable regulations.

On twin-screw compounding and extrusion lines, this tape is not extrusion-compounded; it is a calendered film product and must be processed by ply layup, not melt compounding. Do not combine with amine-based liquid shim materials unless the Solvay datasheet explicitly permits, because free amine can alter the latent cure reaction and produce undercured sealant edges. Mixing with polysulfide or silicone residues on tools must be avoided; silicone contamination reduces adhesion and produces fisheyes on the tape surface. All release liners must be removed before cure; entrapment of polyethylene liner fragments in the bondline is a documented cause of local disbond.