Chemistry, polymer dynamics and mechanical properties of a two-part polyurethane elastomer during and after crosslinking. Part I: dry conditions. (21st April 2017)

• Record Type: Journal Article
• Authors: Zimmer, Bettina; Nies, Christophe; Schmitt, Christian; Possart, Wulff
• Is Part Of: Polymer. Volume 115(2017)
• Page Start: 77
• Page End: 95
• Publication Date: 2017-04-21
• Subjects: Polyurethane -- Crosslinking -- Maturation -- Aging -- FTIR-ATR spectroscopy -- Dielectric spectroscopy -- Tensile test; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2017.03.020
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: Due to their chemical and morphological versatility, polyurethanes may be susceptible to fabrication conditions (curing procedure, moisture). Industry reports 'maturation' phenomena, i.e. unstable mechanical properties of PU elastomers and PU based adhesive joints right after fabrication. This paper elucidates the impact of fabrication conditions and possible causes of maturation. Chemical and physical bulk properties of a crosslinking two-part PU are monitored during and after cure in dry atmosphere (at room temperature followed by a post-cure). The influence of curing procedure is revealed by processes characteristic of the post-cure, i.e. chemical side reactions (allophanate, carbodiimide) and a new dielectric relaxation. Tensile tests demonstrate the practical relevance of the findings (mechanical modulus). Properties of the fully crosslinked, dryly stored PU are stable during a three-week observation, indicating that maturation is preventable by complete cure and dry conditions. In contrast, chemical crosslinking after an insufficient cure likely causes maturation phenomena. Graphical abstract: Highlights: Unexpected chemical reactions occur during post-cure at elevated temperature. Properties of a 2-part PU are stable after complete crosslinking in dry conditions. Incomplete crosslinking is a likely cause for maturation reported in industry.