What are the connection methods of pre-oxidized fiber products? Which method can best ensure the connection strength?

Pre-oxidized fiber products (including fibers, fabrics, felts, and prepregs) are connected by methods tailored to their non-melting, thermoset properties and application scenarios (e.g., direct use as flame-retardant components or further processing into carbon fiber). The connection strength mainly depends on the bonding between interfaces and the retention of the fiber’s structural integrity. Below is a detailed breakdown of common connection methods and their strength characteristics, for industrial and military B2B application scenarios:

1. Common Connection Methods for Pre-oxidized Fiber Products

(1) Resin Adhesive Bonding – Most Widely Used for Structural Connections

This is the mainstream method for connecting pre-oxidized fiber fabrics/felts, relying on high-temperature resistant resins to form a strong adhesive layer between product interfaces.

• Operational process:

1. Select a resin compatible with pre-oxidized fiber (e.g., phenolic resin, epoxy resin, silicone resin) and apply it evenly to the connection surface (coating thickness: 0.1–0.3 mm).

2. Laminate the two components to be connected, apply a small amount of pressure (0.1–0.3 MPa), and cure at a temperature of 80–150°C (curing time: 1–3 hours, adjusted based on resin type).

Applicable scenarios: Connection of pre-oxidized fiber flame-retardant panels, thermal insulation linings for military equipment, and filter felt components.

Strength characteristics: The resin penetrates the fiber gaps to form a mechanical interlocking structure, and chemical bonding is formed between the resin and the oxygen-containing groups on the fiber surface. The shear strength of the joint can reach 5–12 MPa, which is suitable for load-bearing structural connections.

Advantages: Simple operation, good compatibility with pre-oxidized fiber, and adjustable curing parameters to adapt to different application environments.

Limitations: The connection strength is affected by resin type and curing process; low-quality resin or insufficient curing will cause interface debonding.

(2) Needle Punching Connection – Physical Interlocking for Non-woven Products

This is a physical connection method mainly used for pre-oxidized fiber felts and non-woven fabrics, relying on mechanical entanglement between fibers to form a stable structure.

• Operational process:

1. Overlap multiple layers of pre-oxidized fiber web or felt according to thickness requirements.

2. Use a needle punching machine with barbed needles to repeatedly puncture the overlapping layers; the barbs hook the fibers to interweave and entangle between layers, forming an integrated structure without additional adhesives.

Applicable scenarios: Manufacturing of thick pre-oxidized fiber thermal insulation felts, high-temperature filter materials, and fireproof blankets.

Strength characteristics: The connection relies on fiber-fiber friction and entanglement, with a shear strength of 2–5 MPa. It is not suitable for high-load structural connections, but has good integrity and high-temperature stability (can maintain connection strength at 200–300°C).

Advantages: No need for adhesives, environmentally friendly, and the product has good air permeability and flexibility.

Limitations: Low connection strength; excessive needle punching will damage the fiber and reduce the overall performance of the product.

(3) Sewing Connection – Mechanical Fixation for Fabric Products

This is a traditional physical connection method, using high-temperature resistant threads to stitch pre-oxidized fiber fabrics layer by layer.

• Operational process:

1. Select high-temperature resistant sewing threads matching pre-oxidized fiber (e.g., glass fiber thread, aramid fiber thread, or pre-oxidized fiber thread itself).

2. Use industrial sewing machines to stitch the overlapping fabric layers along the designed seam path (e.g., straight seam, zigzag seam) with a stitch density of 8–12 stitches per centimeter.

Applicable scenarios: Connection of pre-oxidized fiber fireproof clothing, tent fabrics, and aircraft cabin fireproof linings.

Strength characteristics: The connection strength depends on the sewing thread and stitch density; the tensile strength of the joint is 3–8 MPa. It has good detachability but poor resistance to high-temperature oxidation (the sewing thread may degrade first in high-temperature environments).

Advantages: Simple operation, low cost, and suitable for on-site rapid connection.

Limitations: The needle holes will cause local stress concentration, and the connection strength is lower than resin adhesive bonding.

(4) Hot Press Bonding – Semi-physical Semi-chemical Connection (Limited Application)

This method uses high temperature and pressure to soften the surface of pre-oxidized fiber slightly (without melting) and form a bonding interface, but it is less used due to the thermoset nature of pre-oxidized fiber.

• Operational process: Overlap the pre-oxidized fiber products, heat to 200–250°C (below the carbonization temperature) and apply pressure of 0.5–1.0 MPa for 10–30 minutes, relying on the slight softening of the fiber surface and the cross-linking reaction of functional groups to form a bond.

• Applicable scenarios: Connection of thin pre-oxidized fiber films or ultra-thin fabrics.

• Strength characteristics: The shear strength is 2–4 MPa, which is lower than resin adhesive bonding. Excessive temperature or pressure will cause fiber brittleness and reduce strength.

• Advantages: No need for adhesives, and the product has a flat connection surface.

• Limitations: Strict process parameter control; easy to damage the fiber structure, so it is only suitable for non-load-bearing connections.

2. Which Method Ensures the Best Connection Strength?

Resin adhesive bonding is the optimal method to ensure the highest connection strength for pre-oxidized fiber products, and the key to maximizing strength lies in resin selection and curing process optimization:

1. Resin matching principle: Choose phenolic resin or modified epoxy resin with high-temperature resistance and good compatibility with pre-oxidized fiber. These resins can react with the oxygen-containing groups (-COOH, -OH) on the fiber surface to form chemical bonds, while penetrating the fiber gaps to form mechanical interlocking—greatly improving the interface bonding force.

2. Curing process optimization: Control the heating rate at 2–5°C/min to avoid air bubbles in the adhesive layer; maintain the curing temperature and pressure stably to ensure complete resin cross-linking. After curing, a post-curing treatment (heating to 10–20°C higher than the curing temperature for 0.5–1 hour) can further improve the connection strength and high-temperature stability.

For special scenarios (e.g., high-temperature environments above 300°C or requirements for no adhesive residues), needle punching connection with high-density fiber entanglement is a better choice—it does not rely on resin and can maintain structural integrity in high-temperature environments, even though its strength is lower than adhesive bonding.

3. Key Precautions for Improving Connection Strength

• Surface treatment of pre-oxidized fiber: Before connection, clean the surface of the fiber product with anhydrous ethanol to remove dust and oil stains; plasma treatment can also be used to increase the number of surface functional groups and improve resin adhesion.

• Avoid fiber damage: During needle punching or sewing, control the process parameters to minimize fiber breakage at the connection interface—broken fibers will cause stress concentration and reduce strength.

• Environmental adaptation: For high-humidity or corrosive environments, select corrosion-resistant resins (e.g., silicone resin) or add anti-aging additives to the resin to extend the service life of the connection joint.