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Polymers 2018, 10(6), 652; https://doi.org/10.3390/polym10060652

Revealing the Mechanical Properties of Emulsion Polymer Isocyanate Film in Humid Environments

1
Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072, China
2
Shanghai Key Laboratory of Mechanics in Energy Engineering, Shanghai 200072, China
*
Author to whom correspondence should be addressed.
Received: 6 May 2018 / Revised: 4 June 2018 / Accepted: 7 June 2018 / Published: 11 June 2018
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Abstract

Knowledge of the mechanical behaviors of polymer film in humid environments is of great significance for predicting the long-term performance of emulsion polymer isocyanate (EPI) as a high-performance wood adhesive. A tri-copolymer latex was cross-linked by the general polymeric methylene diisocyanate (p-MDI) and aqueous emulsified isocyanate (EMDI) at different loadings for preparing EPI. Furthermore, a series of uniaxial tension tests under different relative humidity (RH) were carried out on cured EPI samples before and after post-curing treatment, and the corresponding chemical structure, as well as the microstructure of polymers, was investigated in detail. In addition, a constitutive equation was formulated to calculate the viscoelastic characteristics of the adhesive layer. The results indicate that the EPI films reveal various kinds of intrinsic deformation as RH increases, and the tensile rupture stress and stiffness would obviously decrease, even at cross-linker weight ratios of up to 20%. Furthermore, the moisture resistance could be markedly improved by increasing the isocyanate content and post-cure. Importantly, EMDI-cross-linked film not only exhibits much better mechanical properties than that containing p-MDI at 0–80% RH, but is also more sensitive to post-cure. Finally, the derived viscoelastic model could efficiently track moisture-dependent stress-strain curves of EPI films, and the obtained relaxation time further reveals the influence mechanism of isocyanate and post-cure on the mechanical response of the cured polymer under moist conditions. View Full-Text
Keywords: emulsion polymer isocyanate; tensile properties; post-cure treatment; relative humidity; viscoelastic constitutive equation emulsion polymer isocyanate; tensile properties; post-cure treatment; relative humidity; viscoelastic constitutive equation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Guo, J.; Hu, H.; Zhang, K.; He, Y.; Guo, X. Revealing the Mechanical Properties of Emulsion Polymer Isocyanate Film in Humid Environments. Polymers 2018, 10, 652.

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