Improving the adhesion properties of polypropylene using a liquid-phase sulfonation treatment

• Published in: Journal of adhesion science and technology 2002-01, Vol.16 (12), p.1651-1668
• Main Authors: Cheikh, Ridha Ben, Askeland, Per A., Schalek, Richard L., Drzal, Lawrence T.
• Format: Article
• Language: English
• Subjects: adhesion; ammonium hydroxide; Applied sciences; Coating, metallization, dyeing; Exact sciences and technology; ftir; Machinery and processing; Plastics; polyethyleneimine pei; Polymer industry, paints, wood; polypropylene; sulfonation; surface treatment; Technology of polymers; xps
• ISSN: 0169-4243; 1568-5616
• DOI: 10.1163/15685610260255260

This work describes the effects of a stable, short-reaction time, liquid-phase sulfonation technique aimed at improving the adhesion properties of polypropylene. The relationships among SO 3 concentration (0.15, 0.2, and 0.3 N), treatment time, surface chemistry, and adhesion debond strength have been investigated for polypropylene (PP) sheets sulfonated with SO 3 dissolved in 1,1,2-trichloro 1,2,2-trifluoroethane and neutralized using ammonium hydroxide (NH 4 OH) or polyethyleneimine (PEI). It was confirmed that PEI neutralized specimens, compared to untreated PP, exhibited a larger increase in debond strength (~269% increase) than similarly treated specimens neutralized with NH 4 OH (~210% increase). ATR-FTIR spectroscopy indicates the formation of sulfonic acid, ethylenic, ketone and alcoholic hydroxyl groups. These results are supported by X-ray photoelectron spectroscopy (XPS) that show the O : C ratios increasing from 0.03 to 0.25 for both the NH 4 OH and PEI, and the S : C atomic ratios increasing from 0.0 to 0.05 and 0.06 for the NH 4 OH and PEI, respectively. Furthermore, XPS examination of PEI neutralized specimens revealed a nitrogenated surface (~6%), providing evidence that PEI had grafted onto the sulfonated surface. The observed increases in adhesion are attributed to formation of polar functionalities and increased wettability (as measured by water contact angle measurements). The neutralizing agent also affects degree of adhesion improvement: the PEI causes larger increases in adhesion compared to the NH 4 OH. The physical effects of sulfonation were examined using environmental scanning electron microscopy (ESEM), which showed crack formation after 2 min of treatment. Sulfonation times beyond 5 min degraded the polymer surface (severe microcracking and sloughing of the surface layer) decreasing the adhesion debond strength.