Coloration and branching of polypropylene by reactive processing

Abstract

Reactive melt processing is a known technique used to produce long-chain branched polypropylene. It involves polyfunctional substances that act as chain-linking agents (CA). In this work, polyfunctional amine dyes are used as CA in a novel method for simultaneously improving melt strength and fade resistance of polypropylene. Colored long-chain branched polymer is synthesized by reactive processing of maleic anhydride grafted polypropylene (PPg) in the molten state using glycerol, basic fuchsin and disperse blue 1. Selected CA concentrations avoid gel-like structures and impart good color intensity. FT-IR spectroscopy confirms the reaction between PPg and the CAs while rheological characterization supports the synthesis of long-chain branched structures. Covalent bonding of dye molecules to PPg is confirmed by both UV–visible spectroscopy and colorimetry. A maximum total color difference, ∆E*, of about 20 was measured after xylene purification. New materials show good color homogeneity and transparency with minimum bleeding after 48 hours exposure to water and ethanol.