Polypropylene/polypropylene-grafted acrylic acid blends for multilayer films: Preparation and characterization

Abstract

Polypropylene (PP) was functionalized with acrylic acid (AA) and styrene (st) as a comonomer by means of a radical-initiated melt-grafting reaction. FTIR, ESCA, and 1H-NMR spectroscopies were used to characterize the formation of polypropylene grafted with acrylic acid (PP-g-AA) and polypropylene grafted with acrylic acid and styrene (PP-g-AAst). The content of AA grafted onto PP was determined by using volumetric titration. Blends of PP with 0–100 wt % of PP-g-AA were prepared by melt mixing. The effect of the modified polymer content on the surfaces of cast films was characterized through FTIR–ATR and ESCA analysis as well as contact-angle, wetting-tension, and ink-adhesion measurements. The influence of the content of AA on the melting and crystallization temperature of PP was investigated by DSC. The contact angles of water on cast-film surfaces of PP/PP-g-AA blends decreases with increasing modified polymer content and decreasing PP-g-AA molecular weight. A notorious improvement on wetting tension was observed with increasing modified polymer content and decreasing PP-g-AA molecular weight. From FTIR–ATR and ESCA spectra of the blends, a calculation was made of the carbonyl index on the films' surfaces. It was found that the higher the carbonyl index, the lower the contact-angle value for the polypropylene blends. An increase in crystallization temperature of PP was observed when AA monomers were grafted into PP and with increasing PP-g-AA content in the blend, probably caused by a nucleation effect of AA monomers that would improve the crystallization capability of PP. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1497–1505, 2001