Thermoplastic adhesives components

At the same time, natural adhesives such as casein glues, animal glue and polysaccharide gums have gradually been replaced by synthetic adhesives vinyl thermoplastic adhesives [poly(vinyl acetate)], adhesives obtained by reticulation in situ of two components (as epoxy resins), represent very important materials in this field. 

Polyurethane adhesives are ideal for repairing thermoplastic cabin components. 

The water-based component is the main adhesive component in EPI adhesives. Generally, it consists of water, poly(vinyl alcohol) (PVA), one or more water-based emulsions, filler(s) and a number of additives such as defoamers, dispersing agents and biocides [1, 4, 5, 8, 9]. As with traditional thermosetting and thermoplastic wood adhesives, properties such as viscosity and solids content vary with the intended application. In the European market the typical viscosities are 2000-8000 mPa s at 25°C and the solids content is normally 50% or more. The adhesives are normally neutral with a pH in the range of 6-8 [3]. The storage stability of the EPI adhesive component is typically half a year when stored at a temperature between 10 and 30°C. 

Most of the glued components produced in Europe for non-structural purposes such as joinery use urea-formaldehyde (UF), poly (vinyl acetate) (PVAc) or polyurethane (PUR) adhesives. These adhesives must meet the performance requirements specified in EN 204 (2002) [15] for thermoplastic adhesives or EN 12765 (2002) [16] for thermosetting adhesives when tested in accordance with the following test methods ... 

For glued components for non-structural applications, the same tendency can be seen and one must consider EN 204 (2002) [15] for thermoplastic adhesives and EN 12765 (2002) [16] for thermosetting adhesives. 

There are three general classes of adhesives. These are hot melt adhesives (HMA), pressure sensitive adhesives (PSA), and hot melt pressure sensitive adhesives (HMPSA). A HMA is a 100 % solids, thermoplastic composition which is compounded and applied molten at elevated temperatures and whose strength is obtained solely by the removal of heat. A PSA is a viscoelastic material which is permanently tacky at room temperature, such that a low force contact to a surface will cause the material to adhere instantaneously. A HMPSA is a viscoelastic material which is permanently tacky at room temperature and which is applied as a 100 % solids, thermoplastic composition in the molten state. Solvent based systems are the oldest technology. Water based systems have the advantage that they avoid flammability and generally do not give off obnoxious odors. Basic adhesive components within each of the three classes are ... 

Thermoplastic adhesives do not cross-link during cure, so they can be resoftened with heat. They are single-component systems that harden upon cooling from a melt or by evaporation of a solvent or water vehicle. Hot-melt adhesives commonly used in packaging are examples of a solid thermoplastic material that is applied in a molten state, and adhesion develops as the melt solidifies during cooling. Wood glues are thermoplastic emulsions that are a common household item. They harden by evaporation of water from the emulsion. 

Components that are attaehed with thermoplastic adhesives are easiest to remove Parts to be removed are simply heated with a hot solder iron... 

Polymers may form an important part of the component s packaging as is the case with butt bonded thermocouples where the free filament is supported on a temporary polyimide film carrier which can be peeled off, or partly cut away, prior to attachment to the surface whose temperature is being monitored. The carrier is tough, dimensionally stable and able to withstand a continuous operating temperature of 260 °C. The frame is coated with a thermoplastic adhesive film to facilitate surface attachment. 

Thermoplastic materials have curing temperatures that are lower and time durations that are shorter than thermosetting materials. Some compositions will cure at room temperature, making them suitable for temperature-sensitive components or when thermal expansion mismatch, residual stresses are of concern. Another advantage of thermoplastic adhesives is that because they readily soften at elevated temperatures, they can be easily removed to allow for the rework of components. 

Thermoplastic adhesives soften and melt when heated (provided that they do not decompose). In other words, they do not cross-link during cure. These adhesives are single-component and harden upon cooling by evaporation of a solvent or water vehicle. They have poor creep resistance, fair peel strength, and are used mostly in unstressed joints and designs with caps, overlaps, and stiffeners. The most common application is to bond nonmetallic materials such as wood, leather, cork, and paper.In general, thermoplastic adhesives are not used for structural applications or at temperatures above 66°C (150°F). Thermoplastic adhesives includeit t ... 

Materials that can be used as main components of thermoplastic adhesives are vinyl acetate, polyvinyl alcohol, polyvinyl acetal, ethylene-vinyl acetate copolymer (EVA), vinyl chloride, acrylic resin, polyamide, cellulose, alfa-olefin resin, and waterborne isocyanate resin. 

---