Peel-ply

Peel ply is a sacrificial layer of dry or resin-impregnated fabric that is placed on the bond surface during initial part fabrication. The peel ply is cured along... 

One surface preparation method that is unique for composites employs a peel or tear ply.77 Utilization of the peel ply is illustrated in Fig. 16.5. With this technique, a closely woven nylon or polyester cloth is incorporated as the outer layer of the composite during its production layup. This outer ply is then torn or peeled away just before bonding. The tearing or peeling process fractures the resin matrix coating and exposes a clean, fresh, roughened surface for the adhesive. This method is fast and eliminates the need for solvent cleaning and mechanical abrasion. 

Autoclave moulding is typically used in the aerospace industry for the production of high-value composites from prepregs. The laminate, which is covered on both sides by a fine polyester cloth peel-ply (for enhancing the surface effect), is built up on the mould surface. The top surface of the laminate is covered by a porous release film and bleeder cloth. The whole assembly is then covered with a non-porous membrane, which is sealed to the mould, and then placed inside an autoclave as shown in Figure 6.19. 

In order to understand the aim of surface treatments for composite bonding, we wiU concentrate on a real composite bonding problem for aeronautical purposes. Since classical surface treatments like peel ply can be limited by a cohesive failure occurring in the material, we wiU focus on a new kind of surface treatment (excimer laser) which can completely change surface parameters. The different aspects are presented in two steps the first consists in the surface characterization of the composite material and the second is related to results of destructive single lap shear tests of composite assemblies. Finally, both steps are Hnked in order to derive general mles on phenomena governing adhesion properties of polymer composites. 

Previous work performed on our composite materials [16] provided clear evidence of the influence of surface pollution prior to the use of any surface treatment on adhesion behavior. Several surface treatments can be performed to remove this surface pollution and increase single lap shear performances. As described in Section 20.1.2, peel ply treatment acts very specifically on composite materials. As several authors have already described [3, 5, 17] removing the peel ply before the application of the adhesive provides a rough (Fig. 20.2) and clean surface, free of pollution from the manufacturing process. 

In the case of adhesive X, the adhesive failure occurs principally for both untreated and peel ply treated surfaces. The corresponding improvement of lap... 

Different surface treatments such as peel ply make it possible to roughen and clean composite surfaces and consequently to improve adhesion performance. However, like many other treatments, it is limited by the cohesive failure that may occur in the material. As an alternative, laser ablation appears to be quite an interesting surface pretreatment for polymer composites since it fadhtates efficient control of the surfaces to be adhesively bonded. Furthermore, surface properties must be suitably defined by taking into account the nature of the composite material and the adhesive used. 

Strength reinforced plastic peel ply sandwich peel torque strength, puU. 

SCRIMP This process involves placing a peel-ply and distribution medium between the fibre preform and the vacuum bag (Figure 3.7). Advantages include speeding up the filling process, i.e. resin infusion. 

Adhesive strengths of bonds formed with a standard epoxy adhesive and a polyurethane adhesive were measured for the epoxy molded in PVOH-impregnated peel-ply molds and compared with epoxy molded against polyamide 6.6 and a silicon modified polyamide peel-ply machined to remove surface contamination. It was found that in all cases the PVOH modified epoxy had increased adhesion, and that the bonding with polyurethane was stronger than that with epoxy only. The lowest moleeirlar weight PVOH provided the greatest improvement... 

Peel Ply—The outside layer of laminate which is removed or sacrificed to achieve improved bonding of additional plies. 

The use of a peel ply on the bond surface during the component manufacture is recommended to prevent surface contamination. 

P(7) Bond surfaces having peel plies shall be prepared prior to bonding as follows ... 

The use of a peel ply is also beneficial because it provides a smooth surface as a base for further treatments. The coarse fibre pattern of certain mats and woven rovings can significantly lower the bondline quality. Removing the fibre pattern by machining or abrading is not recommended as it may seriously damage the fibres. If the use of peel ply is impractical, the reinforcement layers on the bond surfaces should be selected so that they provide a reasonably smooth surface for bonding. 

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