[Study on the Structure and Nanomechanical Properties of Organic Montmorillonite Reinforced Urea-Formaldehyde...

Montmorillonite (MMT) is a natural mineral that has great potential as reinforcing filler in wood adhesives. In order to study the reinforcing mechanism more clearly, organic MMT-reinforced urea-formaldehyde adhesive (UF-OMMT) was prepared to analyze its chemical properties and crystal structure with Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). The nanomechanical properties of UF, UF-MMT and PF-OMMT adhesives in the interphase of wood-based composite were analyzed by nanoindentation (NI) and the macro-bonding strength of composite were also tested. The results of FTIR and XRD indicated that in the spectra of MMT modified by cetyltrimethyl ammonium bromide (CTAB), the new peaks appeared at 2 929 and 2 853 cm-1corresponding to C—H stretching vibrations of the organic intercalation agent (CTAB). The (001) diffraction peak of MMT was shifted to a lower angle and the lamellar repeat distance increases from 1.51 nm to 2.71 nm after organic modification. The ion exchange of the cations in montmorillonite with organic ammonium ions and the separating and disorder crystalline improved the compatibility of the modified clay with the polymers and the dispersion of the layers into the matrix. The good physical filling of MMT particles and the elastomer formed during the reaction could transfer and distribute loads between components more homogenously, therebycontributing to the improved mechanical properties of adhesives. As compared to the untreated UF, the reduced elastic modulus and hardness of UF-OMMT in the interphase increased by about 66.9% and 24.2%, respectively. At the macroscale, the bonding strength of plywood bonded with UF-OMMT increased by about 97% as compared to that of unmodified UF resin. The positive effects of montmorillonite on water and heat resistance can be attributed to the better barrier properties of the interphase.