Kinetic Study Of Phenolic Formaldehyde Resin Cure

Novalac resin can provide high adhesive strength,advanced mechanical strength and abrasion performance, is widely used as bingding agents in the manufacture of grinding wheel. At present, no reasonable curing process is existed for this kind resin in industry. The study of its cure kinetic can help to analysis and describe the cure behavior, which will provide theoretic evidences for the curing process in manufacture.Utilizing the non-isothermal Differential Scanning Calorimeter curve, the cure kinetic of phenol formaldehyde resin was studied through n-order model and autocatalytic model, respectively. In the analysis of both models, the kinetic parameters were determined and the kinetic model was built. Our results revealed that the cure of this resin fits well with the autocatalytic model at the prior and middle stage of the curing, while with the n-order model at the latter stage. According to these results, the cure behavior is discussed and predicted through piecewise fitting kinetic model. Moreover, it is observed interestingly that the Crane equation is not accurate for calculating the reaction order n in the n-order kinetic model analysis. Thus a innovative linear-fitting method was proposed to calculate the reaction order, which was then proved to be reliable through the fitting with the experiment data.The curing kinetic of modified phenol formaldehyde resin is then studied by model-free kinetic analysis. The dependences of reaction rates and activation energy on degree of conversion are calculated, through which the curing stages and curing behavior are researched. The result reveals that the reaction systems undergo gelation, crosslinking and diffusion, of these three stages the diffusion controlling is weak. Comparing the three different kinetic Friedman, Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose, we find that Friedman method is not exact while the results of the other two methods are approximate and reflect the curing process well and truly. The ability of predicting the isothermal curing behavior is studied, the results show that the model-free kinetic is proved to be accurate in predicting the isothermal curing behavior compared with the experiment dates, while model-fitting kinetic is insufficient.On the basis of the prior study, the uncured and cured structure of this resin is characterized through FTIR. It is found that the active group at the para position of the phenolic ring will react with precedence, which makes the methylene bridges of the cured resin are mainly in o-p'. Also, a small amount of azomethine exist, and no benzoxazine exist. At last, the cure process is studied and then through the analysis of the thermal stability,tests of mechanical and abrasion properties, we get to know that this resin perform well as a bingding agent using in the manufacture of grinding wheel.