Polietileno pre-tratado para adesão : caracterização das superficies tratadas e obtenção de juntas adesivas




Low-density polyethylene (LDPE) exposure to aqueous KMnO4 solution has two major consequences: polymer coating with MnO2 and (slower) its corrosion. MnO2- coated LDPE can be used to prepare adhesive joints with a peel strenght >1,6 kNm (LDPE-MnO2 undergoes cohesive fracture). MnO2 is found by scanning electron microscopy to have a porous gel structure. The LDPE surfaces obtained by fracture of adhesive joints and pre-treated LDPE were investigated by infrared of reflectance (MIR-IR) and transmission spectroscopy. The funcional groups formed by oxidation of the LDPE fi1ms and detected by MIR-IR spectroscopy react with amoniurn hidroxide, sodium borohydride, potassiurn hidroxide, n-butylamine and with the components of the epoxi adhesive, taken separately. These reactions show the presence of carbonyl (keto and/or aldehyde) and carboxyl groups at the oxidized surfaces. Surface concentration of carboxyl groups in the oxidized PE surface is 1,6 10 cm, as determined by H - K ion exchange. Water contact angles were also measured: they are lower, in the oxidized polymer than in untreated PE. The experimental resuts are discussed, leading to the following conclusions: i) oxidation improves, adhesive spreading over LDPE surface, due to the reactivity of carboxyl groups with epoxy resin components and to the presence of surface polar groups.lmproved spreading leads to enchanced van der Walls interaction forces; ii) adhesion is algo enchanced by mechanial oclusion of epoxy in MnO2 pores and/or in corrosion pits generated by oxidation, at the LDPE surface; iii) surface, weakly-bonding layers are removed from PE surface during oxidation, leading again to stronger adhesion.


adesão polietileno

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