Preventing the whitening of injection molded poly (propylene-co-ethylene) parts

Author(s)

Denison Ricardo Justino Maia

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2006-09-06

Examining board members

Marco Aurelio De Paoli; José Augusto Marcondes Agnelli; Ricardo Baumhardt Neto; Ines Joekes; Maria do Carmo Gonçalves

• Advisor: Marco Aurelio De Paoli

Abstract

In this work we studied an alternative to minimize degradation and whitening of injected parts made of TiO2 containing poly(propylene-co-ethylene). The catalytic effect of the white pigment TiO2 (anatase and rutile) in the polymer photooxidation has been assigned to the reaction of an excited electron in the conduction band of TiO2 with atmospheric O2. For long periods of ambient exposition it was observed that tension generated by flexion does not affect degradation, and it was assigned to polymeric chain relaxation processes. To minimize catalytic action of TiO2 we used the black pigment conducting carbon black (CCB) in substitution to the non conducting grade (CB), and it has been verified less degradation in these samples. The effect was not observed for samples without TiO2, hence the process is related to the interaction between CCB and TiO2. We propose that the improvement of stability is associated to deactivation of the excited electron in the conduction band of TiO2. Tests of nine commercial stabilizer mixtures have selected NDB Anox¿ as the most effective in the formulation stabilization, combining high stability and greater homogeneity of samples degradation characteristics. In addition synergistic or antagonistic interaction was not observed between NDB Anox¿ and CCB, showing that the high stability provided by the stabilizer system is the major variable in the material stabilization. We also present an alternative application for self-organizing maps (SOM), used in this work for FTIR reflectance spectra treatment and classification, providing an useful tool in the characterization of comparative degradation of polymeric samples. (AU)