Molecular interdiffusion is limited by crystallites, therefore it is more
difficult to achieve good adhesion on semi-crystalline compared to amorphous
thermoplastics. Adhesion on non-polar thermoplastics, e.g. polyolefins, will
improve considerably when the surface is pretreated using corona, UV, plasma
or flame treatments.
Poor bonding occurs when the adhesive layer does
not stick properly to the substrate. Pretreatment, e.g. cleaning, degreasing
and sanding, may be helpful.
Specific advantages of adhesives are:
- application on various
substrates like thermoplastics, thermosets, elastomers and metals
-
homogeneous distribution of mechanical loads
- differences in thermal
expansion of components can be compensated by using a thick adhesive layer
- Good aesthetics / no special requirements to hide the bond.
-
economic assembly
- low weight, no heavy screws, bolts and nuts
- heat sensitive constructions or materials, which welding would distort, can
be joined
- no thermal stresses introduced
- good sealing and
insulating properties.
Potential limitations are:
- long term behavior may not be very good
- stress cracking or crazing of the plastic may take place
-
dissimilar materials can only be joined if both are compatible with the
adhesive
- reproducibility/process control
- curing time can
be high dependent on the adhesive
- no disassembly possible
-
assembly hazards such as fire or toxicity
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