Dismantlable adhesive

Recycling of industrially produced material is important from the environmental point of view. For the recycling of materials bonded with adhesives, dismantlement of the products is necessary to separate them, although that is quite difficult. Therefore, a novel technique by which adherends can be dismantled easily has to be established. A conventional way to solve the problem is the use of thermoplastic adhesives because they soften at high temperature and joints bonded with them can be separated by applying small forces. Recently, a new kind of adhesive including thermally expansive microcapsuies has been proposed as an alternative method [1]. A joint bonded with such an adhesive can be dismantled by heating, as shown in Fig. 34.1. 

Where bonding areas are large or there is a need for shape conformity between bonded parts Where the intention is to dismantle the bond later, the use of various labels, surgical and pressure-sensitive tapes, adhesives for positioning and locating parts, in lieu of jigs, prior to assembly by other means... 

Animal and starch glues, especially because of their low color and ease of application on complex joint surfaces, were the adhesives of choice in the furniture and cabinet industries from colonial days until the advent of synthetic emulsion adhesives after World War II. Service conditions were limited to dry interior applications, of course. Leaving a chair out in the rain meant dismantling and regluing. 

Difficulty in dismantling high-strength adhesive bonds, thus limiting recycling potential... 

Pneumatically powered devices fitted with a wide range of dosing needles are available for application of even the tiniest amounts of adhesive. Fig. 8. This means a high level of consistency in the adhesive amounts and surface areas - an important precondition for uniformly reproducible adhesive strength levels. Also, loss and waste of adhesive is minimized in such applications, so that very little waste disposal is required. Boiling in alkaline solutions completely depolymerizes and dissolves the adhesive. This facilitates reprocessing or dismantling of adhesively joined structural components. 

Since the dimethacrylate adhesives are thermoplastics, they soften as the temperature rises. This effect is made use of to dismantle screw compounds and seals, whose connections are insoluble at room temperature but soluble at higher temperatures. 

The concept of recycling is most readily implemented if different structural components can be made out of the same material (Al, plastics), i.e., in one-material systems. Recently, polyolefins have appeared to fit the bill particularly well in this respect, i.e., the many potential forms of polyolefins have made possible adaptations for a wide variety of structural requirements. As an adjunct to these developments, polyolefin melt adhesives have been developed for bonding polyolefin parts to one another. Where this is feasible, total dismantling is no longer necessary and the parts can be reprocessed without any essential loss of properties. 

Behavior of Dismantlable Adhesives Including Thermally Expansive Microcapsules... 

I 34 Behavior of Dismantlable Adhesives Inciuding ThermaHy Expansive Microcapsuies... 

As the filler of the dismantlable adhesive, thermally expansive microcapsules (Matsumoto Microsphere F-30 Matsumoto Yushi-Seiyaku Co. Ltd.) were used. They consisted of a poly(vinyl chloride) shell filled with liquid hydrocarbon (H-quefied isobutane) as shown in Fig. 34.2. The diameter of the microcapsule was 10-30 pm and the average was 20 pm. The shell thickness was 3—4 pm at room... 

Bisphenol A type epoxy resin (Epikote 828 Shell) cured with modified amine (Epomate B002 Shell) was used as the matrix of the dismantlable adhesive (re-sin/matrix=2 1 w/w). Fig. 34.3 shows their chemical structures. The bulk adhesive was cured at room temperature for 24 h before the experiments. Cured bulk resin mixed with the microcapsules was used for the specimens to measure the volume change. 

Dismantlability of Joints Bonded with the Dismantlable Adhesive... 

Fig. 34.5 Configurations and dimensions of joint specimens bonded with dismantlable adhesive.

Fig. 34.10 Specimens after heating (a) total dismantlement (b) adhesive protrusion ...

It has been mentioned previously that cohesive fracture occurred when a soft resin was used as the matrix of such dismantlable adhesives [5]. However, with... 

I 34 Behavior of Dismantlable Adhesives Inciuding Thermaiiy Expansive Microcapsuies Table 34.2 Results of dismantlement tests on specimens with a grit-blasted finish. ... 

Fig. 34.15 Variation of thermal volume expansion of dismantlable adhesive containing 50wt.% microcapsules, with pressure as a parameter, measured using the bellows vessel.

Even though the strength was lower than that of recent high-performance structural adhesives, we might say that the dismantlable adhesive has enough strength for semi-structural applications. 

The expansion behavior of the microcapsules observed using the syringe method seems to be quite similar to the situation inside the dismantlable adhesive, because the hydrocarbon gas cannot leak from the matrix resin so it accumulates. 

Using familiar products, the aim is to note component shapes, to see how they are assembled, and measure the variation in thickness. Recycling can also be considered the ease of dismantling depends on whether the product was intended to be repaired, or to be scrapped if faulty. Screws may be hidden under adhesive labels, and the location of snap-fit parts may be difficult to find. 

Environmental — Monocomposites are readily recyclable — No additional adhesives required — Dismantling more difficult with undetachable connections, so that different materials may not be separable... 

It must be realised that, among the many roles of adhesives, their being used to secure mechanical components is a special one. It is often necessary to dismantle mechanical assemblies for maintenance and this requires the use of the unique anaerobic adhesives. These are strong enough to hold parts together during use, but not so strong that they cannot be dismantled with conventional tools and techniques. 

---