Effect of montmorillonite activation method on formaldehyde content in urea-formaldehyde composites

In this paper, the synthesis of modified urea-formaldehyde (UF) composites with differently activated montmorillonite KSF (UF/KSF) was performed. Two types of montmorillonite (MMT) KSF were used: sample activated with sulfuric acid-KSF(H2SO4) and sample activated with acid and stirring-KSF(H2SO4+stirrer). In order to examine the effect of KSF activation mode on the thermal and hydrolytic stability of UF resins, thermogravimetric analysis (TGA) was performed, as well as A determination of the amount of liberated formaldehyde (FA) after acid hydrolysis. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis were used to characterize the samples of modified UF/KSF composites and differently activated KSF. Activation of KSF led to a decrease in its specific surface area (SSA) and to an increase in cation exchange capacity (CEC). SEM analysis showed that in the KSF(H2SO4+stirrer) sample, the layered microstructure was disrupted. Free formaldehyde was not detected in the sample of UF resin with KSF(H2SO4), and in the sample with KSF(H2SO4+stirrer) it was 0.06%. The UF/KSF(H2SO4) composite showed higher hydrolytic stability (3.9%) compared to UF/KSF(H2SO4+stirrer) (4.62%), but lower compared to the UF/KSF(inactive) (1.23%). TG analysis showed that the KSF(H2SO4) sample had better thermal stability than the KSF(H2SO4+stirrer) sample, but this did not contribute to the better thermal stability of UF/KSF(H2SO4) compared to UF/KSF(H2SO4+stirrer), both samples had a T5% value of 112 °C.