INFLUÊNCIA DA ENERGIA SUPERFICIAL NA ADESÃO PRÁTICA DE JUNÇÕES ADESIVAS DE POLIPROPILENO
Polypropylene (PP) is known for its mechanical properties, high crystallinity, chemical stability among other characteristics, but also for its inert nature and consequent low adhesion capacity. This work seeks to improve the adhesion of PP through the addition of the natural polymer lignin. For this, pure Kraft lignin, as well as chemically modified lignin with maleic anhydride and acetic anhydride in three different weight concentrations, 2%, 5% and 10%, were added separately to the PP matrices. In addition, in a specific condition, the compatibilizer PP-gMA (polypropylene graphitized with maleic anhydride) was included in 2% of the weight of the lignin’s. Spectroscopy in the infrared region by Fourier transform in attenuated total reflectance mode (FTIR-ATR) showed significant alterations in the chemical groups of lignin, in relation to Kraft lignin, mainly in the modification with acetic anhydride. In both cases, the modifications were confirmed with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) thermal analyses. The surface energies of composites and PP were measured using the technique of contact angle of materials, and showed an increase in this energy, in any condition of addition of lignin in relation to pure PP. In the modified lignins, a significant increase in this energy was observed, in the composites PP-AKL g 10%, PP-MKL 5%, PP-AKL 5% and PP-MKL g 2.5%, with gains of 81.44%, 52.5%, 50.84% and 40.04% respectively. The composites were also thermally characterized by DSC, so that an increase in crystallinity of more than 6 percentage points (%) was verified in the PP-MKL g 2.5% condition compared to pure PP. The mechanical behavior of the substrates was characterized by shear tests by simple overlapping of plates and impact. These results point to an increase in the practical adhesion of PP by incorporating lignin, contributing to the solution of the usual problem of low adhesion of this material.