Hardness evaluation of cured urea-formaldehyde resins with different formaldehyde/urea mole ratios using nanoindentation method

Byung-Dae Park; Charles R. Frihart; Yan Yu; Adya P. Singh

doi:10.1016/j.eurpolymj.2013.06.013

Treesearch

Hardness evaluation of cured urea-formaldehyde resins with different formaldehyde/urea mole ratios using nanoindentation method

Formally Refereed

Authors:

Byung-Dae Park, Charles R. Frihart, Yan Yu, Adya P. Singh

Year:

2013

Type:

Scientific Journal

Station:

Forest Products Laboratory

DOI:

https://doi.org/10.1016/j.eurpolymj.2013.06.013

Source:

EUROPEAN POLYMER JOURNAL, Corrected proof. doi:10.1016/j.eurpolymj.2013.06.013 Park B-D et al. Hardness evaluation of cured urea–formaldehyde resins with different formaldehyde/urea mole ratios using nanoindentation method. Eur Polym J (2013), http://dx.doi.org/10.1016/j.eurpolymj.2013.06.013; 2013; 6 p.

Download (PDF 1.06 MB)

Download (PDF 1.06 MB): https://research.fs.usda.gov/download/treesearch/44269.pdf

Abstract

To understand the influence of formaldehyde/urea (F/U) mole ratio on the properties of urea–formaldehyde (UF) resins, this study investigated hardness of cured UF resins with different F/U mole ratios using a nanoindentation method. The traditional Brinell hardness (H_B) method was also used for comparison. The H_B of cured UF resin films with different F/U mole ratios was determined after exposing the films to different post-curing temperatures. The nanoindentation method was employed for these films to measure Meyer hardness (H_M) and reduced modulus (E_r) which have been used to calculate the elastic modulus (E_s) of cured UF resins. As the F/U mole ratio decreased, the H_B decreased continuously, indicating a less rigid network structure in low F/U mole ratio UF resins. The higher the post-curing temperature, the greater the value of H_B. The HM value also showed a similar trend as a function of F/U mole ratio. However, the E_r and E_s did not show a consistent trend as exhibited by H_M and H_B. Both H_M and E_r showed much greater variation in the coefficient of variation (COV) at lower F/U mole ratios 1.0 and 1.2, indicating a more heterogeneous composition of these resins. Linear relationships between H_M and E_r indicate that heterogeneity of the surface composition of samples contributes greatly to variations in the measured values. This variability is discussed in terms of crystal structures present in the cured UF resins of low F/U mole ratios.

Keywords

Urea–formaldehyde resin, Hardness, Modulus, Nanoindentation, Crystal structure

Citation

Park, Byung-Dae; Frihart, Charles R.; Yu, Yan; Singh, Adya P. 2013. Hardness evaluation of cured urea-formaldehyde resins with different formaldehyde/urea mole ratios using nanoindentation method. European Polymer Journal Volume 49, 2013; pp. 3089-3094.