Study On Microwave-assisted Synthesis Of Novolac Resins For The Shell Process

With the development of global economization, huge opportunities, but unprecedented challenges have been brought for the phenolic resin industry in china. In order to win the international market competition and meet the demand and development in the foundry industry, the technological innovation is required that sloving the problem, such as the high free phenol content, slow cure rate, low general performance and so on, based on the reduction of synthesis time, improvement of efficiency and economization of energy. Therefore, the microwave heating, which is high heating efficiency, rapid heating rate, low consumed energy and protected environment, has been introduced to the synthesis of novolac resins. The purpose of this subject is to develop novolac resins for shell process with excellent general performance, by means of the selection and optimization of the synthesis and chemical modification processes, and besides, investigate and analyze the mechanisms of the microwave-assisted synthesis and modification of the resins. In this paper, firstly, the conventional synthesis processes of novolac resins and the influences of the properties of physics-chemistry of the resins, e.g. softening point, cure rate and flow distance on the strength of the resin coated sands have studied. Secondly, in the laboratory, a microwave-assisted synthesis device, involved with refluxing, agitating and the measurement of the temperature, has been modified based on domestic microwave oven. Compared with conventional synthesis, the rules of the microwave-assisted polymerization and dehydration have been investigated and analysed comparatively in detail by means of the Infrared spectrum (IR), Gel permeation chromatography (GPC). The reasons of the improvement in the performances of novolac resins, e.g. flow distance, cure rate, caused by microwave heating have been disclosed. Furthermore, the existence of local potential 'hot spots'in course of microwave-assisted synthesis of novolac resins has been identified by the experiment and the results showed that the 'local hot'and overheating for the reaction system are the main reason for the notable reduction of synthesis time. Thirdly, a model of the Artificial Neural Networks (ANN) based on the experiments of the microwave-assisted synthesis of novolac resins has been built, and the further optimization of the synthesis process parameters was carried on, according to the ANN. On the basis of before-mentioned optimized processes, a series of modification experments, including to catalyst A, the hybrid catalyst of A and oxalic acid, bisphenol A and salicylic have been carried on, and the results showed that the modified novolac resins with high general performances could been obtained. According to the experiments and analyse of the synthesis mechanisms of the modified resins, some points of view have been put forward, as follows: The mechanisms of the 'high orth'novolac resins under the catalyst A should be concerned about the formation and breaking down of benzyl ethers etc. The mechanisms of bisphenol A introduced into the molecular structure of novolac resins could be attributed to the condensation reaction between prepolymer of bisphenol A and the base resins by means of 'embedment'or 'on end', and for salicylic modified resins, the reasons of improvement in the performance are considered as the introduction of carboxyl into the base of the resins. Finally, for examining the practical effectiveness of the modified resins, the further experiments were done, and the results showed that excellent effect is obtained, on the one hand, the free phenol content is obviously lower than the domesic novolac resins; on the other hand, the cure rate is rapid and the thermal stability is high on the basis of suitable softening point; what's more, the strength of resin coated sands is high.