Preparation And Properties Of High Carbon Residue Phenolic Resin Cured Without Ammonia

Traditionally,the resin matrix commonly used in phenolic molding compounds is mostly thermoplastic,which generally has the problem of free ammonia residues,which affects the accuracy and service life of the products,and even has potential safety hazards.Therefore,the demand for non-amino phenolic molding compounds has increased.However,domestic theoretical research and production technology are still insufficient to meet the increasing demand and performance requirements for resins,and most of the thermosetting resins currently available for phenolic molding compounds are liquid,so this aspect still needs to be further studied.This article aims to control a low-cost,simple process to prepare a solid state thermosetting phenolic resin that has excellent heat resistance and can be cured without ammonia.Optimize the formula and synthesis process,and further explore the reaction mechanism and curing behavior.First of all,by adjusting the synthesis process of phenolic resins,this article prepared multiple sets of solid thermosetting resins.The adjustment conditions involved the type and amount of catalyst,reaction temperature and phenolic ratio.Finally,an ammonia catalyzed solid resin with high residual carbon,high molecular weight,and excellent heat resistance and a magnesium catalyzed solid resin with high ortho position and high residual carbon characteristics are obtained.Focusing on comparing the effects of ammonia catalyzed and magnesium catalyzed catalysts and their amount on the basic performance and molecular structure of the resin,the gel time,solid content,moisture content,residual carbon rate,softening point and free phenol of each group of resins were measured.The molecular structure,molecular weight and distribution of the resin were characterized by GPC,FTIR and other means,and the influence of the two catalysts on the reaction mechanism was discussed.The results show that the solid thermosetting resin prepared by ammonia water and magnesium oxide catalysis has the characteristics of high residual carbon and good heat resistance.In addition,the degree of polycondensation of ammonia-catalyzed resin is higher,the molecular weight is higher,the ortho substitution is stronger than the para substitution,and ammonia water will participate in the reaction to generate nitrogen-containing compounds,there are carbon nitrogen triple bonds,and the polycondensation reaction has both etherification and hydrogen condensation.reaction.The magnesia catalyzed resin has the characteristics of high ortho position and high activity,the ratio of ortho to para position is as high as 4.08,and the polycondensation reaction is dominated by the hydrogenation reaction.In terms of performance,ammonia catalysis is easier to control,and there is a foaming phenomenon when the magnesium oxide catalyzed resin is cured,which is not conducive to the uniformity of the product surface,so ammonia catalysis is more suitable for solid thermosetting resins.In addition,adjust the amount of catalyst,reaction temperature and phenol-formaldehyde ratio,use performance testing as the basis for screening,and the characterization of molecular structure as theoretical support,and select resins with excellent performance.Finally,it is considered that NH3·H2O%=1.85 wt%,T=90?,P/F=0.82,the performance of the resin is balanced,the gel time is 64.43 s,the softening point is 62.25?,the solid content is 93.52%,and the moisture content is 1.89%,the residual carbon rate is 54.75%,and a solid thermosetting resin with good heat resistance and stability is obtained.Based on the above conclusions,this paper studies the curing behavior,curing kinetics and thermal degradation behavior of the resin through in-situ infrared characterization,DSC testing,and TG testing.The effect of the synthesis process on the curing behavior is also analyzed.The resin curing process mainly consumes methylol and phenolic hydroxyl groups,forming ether bonds and methylene bonds,and methylene bonds account for the majority.If the temperature is too high,it will further solidify and the carbonylation reaction of the ether bond will occur.The increase in the amount of catalyst and P/F facilitates the curing reaction of the resin,while the reaction temperature has a lower effect on it.Analysis of the DSC spectra at different heating rates showed that the approximate gel temperature of the resin sample was 361.6 K,the curing temperature was 435.2 K,and the post-treatment temperature was.527.7 K.In addition,by establishing a theoretical calculation model to simulate the curing kinetics of the prepared resin,the calculated Ea=73.24 kJ/mol,indicating that the resin has high activity characteristics.Finally,the thermal degradation behavior of the resin is discussed.At 800?,the weight loss rate of the resin is only 34.99%,indicating that the resin has excellent heat resistance and ablation resistance,and the use range of the resin can be extended to 400?or 500?.