Composite pipelines are mainly divided into metal and non-metal reinforced pipeline. In metal reinforced composite pipelines, metal belt and wire can be used to reinforced layer, such as steel belt, steel wire or aluminium pipe, to produce steel mesh skeleton reinforced polyethylene composite pipeline, steel reinforced polyethylene spiral corrugated pipe, plastic lined steel pipe, aluminum-plastic PPR steady-state pipe, aluminum-plastic composite pipe etc. EVOH, PA and fiberglass are used in the production of non-metal reinforced composite pipelines.
Figure 4. Composite pipelines
Pipe hotemlt adhesive resin played a role to bond non-polar plastic layer with steel mesh or steel belt in production of composite pipelines. Firstly, adhesive resins can fuse with the non-polar pipeline material to form strong adhesive strength by molecular entanglement of hotmelt adhesive resin and material to be bonded. Then, the polar functional groups MAH in adhesive resin can form chemical bond with steel element. Oxygen lone pair in maleic anhydride molecule can coordinate with unoccupied molecular orbital of Fe atom in steel layer to form coordination bond (Figure 5). The value of its bond energy is 4×10~6×102 KJ·mol-1. Therefore, so strong chemical bond formed in the interface, is a key factor to improve adhesive strength of adhesive resin on steel surface.
Figure 5. molecular structure between adhesive resin and steel surfaces.
Besides aluminum atom, Al2O3 is another form existing in aluminum belt surface. The polar monomer in adhesive resin can react with Al2O3 to form stable chemical bond during processing, which leads to strong adhesive strength of adhesive resin to aluminum belt surface. On the other hand, acid group anion on adhesive resin molecular chain also can couple with Al3+ to form ionic bond (Figure 6), which will further improve the adhesive strength of adhesive resin.
Figure 6. molecular structure between adhesive resin and aluminum belt surface.
Similarly, for non-metal reinforced composite pipelines, non-metal functional materials (EVOH, PA, etc) used for reinforced layer, contain many kinds of functional groups on the surfaces such as hydroxy (-OH), amino (-NH2). So these groups can easily react with maleic anhydride of adhesive resin to form stable chemical bond during processing, once adhesive resin came into contact with the reinforced layer. Moreover, because of existence of -OH and -NH2, hydrogen bond can formed with carboxyl (-COOH), which will offer more adhesive strength for hotmelt adhesive resin.