**Polyurethane Hot Melt Adhesives** are a critical category in medical hot melt adhesives, combining flexibility and strong adaptability. Leveraging their unique molecular structure and performance advantages, they play an irreplaceable role in dynamic medical scenarios (e.g., joint movement, high-load fixation). Below is a detailed introduction from the perspectives of composition, performance, applications, and advantages:
### I. Core Composition and Structural Characteristics
Polyurethane hot melt adhesives are formulated with polyurethane prepolymers as the base material, supplemented with medical-grade plasticizers, cross-linking agents, antioxidants, and other additives. Their molecular backbone consists of repeating urethane groups, endowing the material with two core characteristics:
1. **Alternating Soft and Hard Segments**: Soft segments (e.g., polyester, polyether) provide flexibility and elasticity, while hard segments (e.g., diisocyanates) ensure bonding strength and chemical resistance. By adjusting the ratio of these segments, the hardness, elasticity, and tackiness of the adhesive layer can be precisely controlled.
2. **Compliance with Medical Safety Standards**: All components meet FDA and ISO 10993 biocompatibility certifications, are free of heavy metals, formaldehyde, and other harmful substances, and are non-irritating to the skin, making them suitable for prolonged contact with the human body.
### II. Key Performance and Advantages
1. **Exceptional Flexibility and Stretchability**
The cured adhesive layer is soft and elastic, with an elongation at break of 300%–500%. It can deform synchronously with joint movements (e.g., elbows, knees, fingers) without debonding or causing skin pressure. For instance, in orthopedic postoperative joint fixation dressings, the adhesive layer remains intact and bonded even during minor patient movements, preventing dressing displacement.
2. **Strong Bonding Strength for High-Load Scenarios**
The adhesive exhibits strong adhesion to metals, plastics, textiles, leather, and other medical materials (especially polar materials). Its stable cohesive strength after curing enables it to withstand certain levels of tension and friction. In applications such as orthopedic splint fixation and medical support assemblies (e.g., lumbar braces, wrist straps), it ensures tight bonding between material layers without delamination over long-term use.
3. **Outstanding Chemical and Aging Resistance**
The adhesive can withstand repeated wiping with common medical disinfectants like alcohol, iodine, and saline. It remains stable in humid environments (e.g., wound exudate, sweat) without easy hydrolysis. Additionally, it exhibits strong UV resistance, avoiding brittleness or failure under prolonged light exposure, making it suitable for long-term storage of medical supplies.
4. **Flexible Processing Compatibility**
With a wide melting temperature range (80–150°C), it is compatible with various coating processes such as spraying, roller coating, and dispensing. It also cures rapidly (10–30 seconds), meeting the efficiency requirements of automated production lines. Moreover, the adhesive layer thickness can be precisely controlled (5–50 μm), catering to both lightweight products (e.g., breathable dressings) and high-strength bonding scenarios requiring thicker layers.
### III. Typical Medical Applications
1. **Fixation and Protection of Dynamic Body Parts**
- **Orthopedic Dressings and Supports**: For example, rehabilitation braces after knee surgery use polyurethane hot melt adhesives to bond breathable non-woven fabric with supportive plastic sheets. The adhesive layer stretches synchronously with joint flexion, ensuring fixation without restricting movement.
- **Sports Medical Tapes**: Athletic tapes (e.g., kinesiology tapes) rely on the elasticity and adhesion of polyurethane hot melt adhesives to provide muscle support and fixation without skin tightness or detachment during exercise.
2. **Assembly of High-Durability Medical Products**
- **Medical Catheter Securement Devices**: Used to fix dialysis catheters, central venous catheters, etc., the adhesive layer withstands friction during catheter insertion/removal and adheres tightly to the skin to prevent bacterial invasion.
- **Durable Medical Kit Components**: Items like scissor straps and gauze storage bags in first-aid kits, bonded with polyurethane hot melt adhesives, remain secure even after repeated opening and closing, suitable for high-frequency use in emergencies.
3. **Medical Products for Special Environments**
- **Waterproof Medical Dressings**: Postoperative waterproof bandages with excellent water resistance prevent debonding during showering while maintaining breathability to avoid wound infection.
- **Disinfection-Resistant Medical Devices**: Reusable laryngoscope sheaths or ultrasound probe coupling patches retain adhesion after repeated alcohol wiping and multiple uses.
### IV. Advantages Compared to Other Medical Hot Melt Adhesives
Compared to acrylic and silicone rubber hot melt adhesives, polyurethane hot melt adhesives stand out due to:
1. **Balance of Rigidity and Flexibility**: Combining the flexibility of silicone rubber with the high bonding strength of acrylic adhesives, making them ideal for scenarios requiring both fixation and mobility.
2. **Broader Weather Resistance**: Stable performance in extreme temperatures (-40°C to 120°C) and humid environments, far exceeding the applicable range of acrylic adhesives.
3. **High Customizability**: By adjusting the soft/hard segment ratio, products ranging from "ultra-soft elastic" to "high-strength rigid" can be manufactured, meeting diverse needs from infant umbilical care patches to industrial medical equipment.
With their "strong dynamic adaptability, high durability, and flexible customization," polyurethane hot melt adhesives are an ideal choice for complex medical scenarios, particularly in products that require balancing fixation effectiveness with human movement needs, showcasing unique technological value.
