Hot melt adhesives are solvent-free chemical compounds that are used to join materials. They can be repeatedly softened by heat and hardened or set by cooling, allowing parts to be removed or repositioned during assembly. Most hot melt adhesives solidify at temperatures below 180° F and become low viscosity fluids at temperatures above 180° F. They form strong bonds, set rapidly upon cooling, and are relatively easy to handle. In general, hot melt adhesives are more resistant to water, moisture, and humidity than thermoplastic polymers. Some products contain acetals, acrylics, elastomers, natural or synthetic rubbers, epoxy resins, water-based resins, wax-based binders, styrene compounds, or vinyl systems. Others contain bituminous substances, ethylene copolymers, styrene copolymers, glues and gums, polyamides, thermoplastic polyesters, vinyl esters, or polyethylene (PE). Commonly used chemical systems also include polypropylene (PP), polysulphone, polyurethane (PUR), polyetherimide, and polyolefin. Filled or reinforced compounds consist of resins with additional modifiers such as fillers, pigments, or chopped fibers.

Hot melt adhesives vary in terms of material compatibility and features. Some products adhere to substrates made of ceramics, glass, concrete, masonry, metal, paper, paperboard, or plastic. Others are compatible with substrates made from composite materials, textiles, fabrics, wood, rubber, elastomers, or porous surfaces. Products that can bond dissimilar substrates such as metal to rubber are also available. In terms of features, hot melt adhesives that are designed for electrical and electronics applications often provide protection against electrostatic discharge (ESD), electromagnetic interference (EMI), and radio frequency interference (RFI). Materials that are electrically conductive, resistive, insulating, or suitable for high voltage applications are also available. Flame retardant materials reduce the spread of flames or resist ignition when exposed to high temperatures. Dampening materials are used to form layers that can bend or flex without cracking or delaminating. Thermal compounds and thermal interface materials absorb heat from electronic devices or electrical components. Threadlocking adhesives bind threads that are subject to transverse and axial loads against vibrational loosening.

Hot melt adhesives are solvent-free chemical compounds that are used to join materials. They can be repeatedly softened by heat and hardened or set by cooling, allowing parts to be removed or repositioned during assembly. Most hot melt adhesives solidify at temperatures below 180° F and become low viscosity fluids at temperatures above 180° F. They form strong bonds, set rapidly upon cooling, and are relatively easy to handle. In general, hot melt adhesives are more resistant to water, moisture, and humidity than thermoplastic polymers. Some products contain acetals, acrylics, elastomers, natural or synthetic rubbers, epoxy resins, water-based resins, wax-based binders, styrene compounds, or vinyl systems. Others contain bituminous substances, ethylene copolymers, styrene copolymers, glues and gums, polyamides, thermoplastic polyesters, vinyl esters, or polyethylene (PE). Commonly used chemical systems also include polypropylene (PP), polysulphone, polyurethane (PUR), polyetherimide, and polyolefin. Filled or reinforced compounds consist of resins with additional modifiers such as fillers, pigments, or chopped fibers.

Hot melt adhesives vary in terms of material compatibility and features. Some products adhere to substrates made of ceramics, glass, concrete, masonry, metal, paper, paperboard, or plastic. Others are compatible with substrates made from composite materials, textiles, fabrics, wood, rubber, elastomers, or porous surfaces. Products that can bond dissimilar substrates such as metal to rubber are also available. In terms of features, hot melt adhesives that are designed for electrical and electronics applications often provide protection against electrostatic discharge (ESD), electromagnetic interference (EMI), and radio frequency interference (RFI). Materials that are electrically conductive, resistive, insulating, or suitable for high voltage applications are also available. Flame retardant materials reduce the spread of flames or resist ignition when exposed to high temperatures. Dampening materials are used to form layers that can bend or flex without cracking or delaminating. Thermal compounds and thermal interface materials absorb heat from electronic devices or electrical components. Threadlocking adhesives bind threads that are subject to transverse and axial loads against vibrational loosening.

Selecting hot melt adhesives requires an analysis of mechanical, thermal, electrical and optical properties. Mechanical properties include tensile strength (break), tensile modulus, and elongation. Thermal properties include use temperature, thermal conductivity, and coefficient of thermal expansion (CTE). Thermal conductivity is the linear heat transfer per unit area for a specific temperature. CTE is the amount of linear expansion or shrinkage that occurs in a material with a change in temperature. Resistivity, dielectric strength, and dielectric constant are important electrical properties for hot melt adhesives. Optical properties include index of refraction, a measure of the speed of light in a material.  

Hot melt adhesives are used in many industries and applications. For example, some products are used in aerospace, automotive, marine, military, photonics, optical, or tooling applications. Others are designed for use with electronic devices, electrical power products, high voltage applications, semiconductors, or integrated circuit (IC) packaging. Materials that are suitable for medical, pharmaceutical and food processing applications meet requirements established by the Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA). Original equipment manufacturers (OEMs) and repair, maintenance and overhaul (MRO) organizations also use hot melt adhesives.