22 июля, 2015 
Malyar The surfaces of many plastics and rubbers have low surface energies (Table 3.1) such that wetting by an adhesive is inhibited unless special surface pretreatment processes have been employed. However, plastics which contain polar groups such as PVC, nylons and acrylics are bondable with a minimum of surface treatment.
Plastic composites such as glass — or carbon-fibre reinforced materials are often based on polar epoxy or polyester resins, and are therefore compatible with the common adhesives as well as being readily bondable. Surface treatment is required simply to remove contaminants such as oils, dirt, and especially fluorocarbon mould release agents. The two main techniques used to achieve this are:
(a) Solvent wiping, then gritblasting or sanding followed by degreasing.
(b) Provision of a tear-ply at the composite’s surface during manufacture, which is stripped off just prior to bonding.
In the former technique the degree of abrasion is known to affect subsequent bond strength and durability, heavy abrasion to expose surface fibres being recommended. Other technologists suggest that ‘wet’ sanding should be carried out below a ‘reactive primer’, such as a silane solution, which promotes chemical bonding with the adhesive and carries away the dust from abrasion.
Composite materials, like adhesives, are permeable to water. Moisture can therefore diffuse to the adherend/adhesive interface, which is a problem more in initial joint fabrication when a heat — cured adhesive is employed than when the joint is in service. Thus the moisture content of the composite at the time of joining should be low (say 1%) or else moisture may be drawn to the interface by heating the assembly during curing, so interfering with the adhesion and creating voids in the adhesive layer.
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