| As a main adhesive used in wood industry, Urea formaldehyde resin ( UF resin) has many advantages such as low cost, available raw materials, excellent agglutinative intension and so on. However, it has some disadvantages: poor water-fast quality, brittle layer, quickly ageing, short shelf-time, especially high content of free formaldehyde which seriously hinders UF resin using range and its product quality. Therefore, it is of great academic and applied significance for us to determine the relationship between structure and quality of UF resin, seek a technique way to decrease the content of free formaldehyde in UF resin and to improve roundly the resin's quality.In the beginning of this paper, the actual state of industrial production and usage of UF resin were introduced respectively, then the study progress and situation of UF resin in domestic and abroad. In order to resolve problems mentioned above, the synthetic technique of UF resin and the relationship of the resin structure and its quality were generally researched on the basis of a large quantity of experiments. The experiments were done from the four main parts as follow:1.The study of optimum synthetic technique of UF resin. First, the results of the comparative study between two common technique routines show: the traditional synthetic technique of weak basic - weak acidic -weak basic has some advantages of good stability, excellent agglutinative intension and simple operation etc., but it is difficult to control the content of free formaldehyde in the resin. The products of the middle-low temperature technique based on strong acidity can provide with the quality of low content of free formaldehyde, but the shortcomings of the technique are too low content of methylic hydroxide, bad agglutinative intension and difficult operation in procedure. Secondly, the study results of the relation between main technical parameters and the quality of UF resin show: (1).With the decreasing of the mole-ratio of formaldehyde and urea(F/U) , the viscosity and solid-content increase, but the content of free formaldehyde decreases and the solidifying-time of products prolongs; (2) .The PH of reactive system, especially the PH in the phase of polycondensation works greatly on the quality of UF resin. The smaller the PH is, the higher the content of free formaldehyde and the viscosity of resin are. The fitting PH range in the phase of polycondensation is from 4 to 6; (3). The increase of reactive temperature could accelerate the synthetic reaction. At a suitable temperature, the viscosity and solid-content increase with the reactive time until they reach a stated value.2. The synthesis and modifying of UF resin with low-content of free formaldehyde. In this part, the relationship between the content of free formaldehyde and the mole-ratio of raw materials was determined with the experiments. The optimum mole-ratio occurs at 1.2 : 1. The mole-ratio in the phase of acidic reaction has a great influence on the agglutinative intension and stability of UF resin and it should be kept in the range of 2.0 ; 1 ~ 1.6 : 1. The low mole-ratio formulation was applied to the preparation of urea-formaldehyde resin in which an appropriate quantity of polyvinyl alcohol, phenol were used as modifiers. The results showed the free formaldehyde content in the products was steadily lower than 0.15%. The best quantity of PVA and phenol were respectively 0.5~~ 1.0% and 0.5% of the total weight of reactants. The small quantity of modifiers almost don't increase the cost of resin, but all-round properties of UF resin were remarkably improved.3. The relation of structure and quality of UF resin. Through the FTIR analysis of resin sample in different stage of a synthetic reaction, we qualitatively discuss the change of different radical content in the course of synthetic reaction. The ordinary chemical analysis and 13CNMR were employed in order to research primarily the relation of microstructure and macroscopical quality of UF resin. The results of study illuminate that the reactive pro... |
PDF Full Text Request