Storage Aging Of Carbon Fiber/Phenolic Resin Prepreg And Its Composite Forming Process

Prepreg is a combination that continuous fibers or fabric impregnated by resin matrix under controlled conditions.As an intermediate material for the manufacture of composite,many properties of the prepreg can be brought into the composite directly.The composite has the excellent performance of raw materials,the commonly used carbon fiber reinforced resin composite has light weight,high strength and excellent acid and alkali resistance,and it is widely used in various fields such as automobile industry,aerospace,rail transportation,and military industry.The use of prepregs to produce composite materials is one of the most important methods for the production of many composite materials.The use of prepregs to prepare composite materials can often reduce labor intensity and production difficulty,and also facilitate the production of composite materials of different shapes,so it is important to study the prepregs in preparing composite materials.The quality of prepreg is related to the composite.There is often a period of storage for the prepreg from preparation to use.During this period,the properties of the prepreg will decrease with the resin aging,consequently,the performance of the composite will decrease either.In order to investigate the storage aging behavior of phenolic resin prepreg,this paper prepares carbon fiber/phenolic resin prepreg by solution method and stores it under two storage conditions,one is 20±2°C,and the other is-18°C..Then,the effects of storage time on the properties of prepreg under different storage conditions were investigated and the following conclusions were drawn: the prepreg stored at 20±2 oC had good quality on the 2nd to 20 th day of storage.The prepreg has good viscosity and low volatile content,and is suitable for the preparation of composite materials as a whole;while the total volatile content and insoluble content of the prepreg stored at-18 ° C are small,but It is more viscous within30 days before storage,and it is not suitable for layering,but it is beneficial for long-term storage.Combined with the curing principle of phenolic resin at room temperature,it can be found that the low temperature inhibits the curing of the phenolic resin,resulting in less decrease of the volatile content of the prepreg and slower increase of the insoluble content.The decrease of the methylol index indicates storage.As time increases,the reaction inside the phenolic resin consumes a methylol group,which causes the methylol index to decrease.In order to prepare a composite with excellent performance,it is advantageous to select a suitable curing process by studying the curing kinetics of the phenolic resin.Thus,the curing kinetics of the phenolic resin was investigated and analized by both model fitting method and non-model fitting method.In the study of the model fitting method,the activation energy of the resin system and the mathematical model followed by the reaction were obtained.Theanalysis indicates that the reaction is promoted by the autocatalytic effect in the early stage of the curing process.The first-order effect plays a major role in the middle and late stages of the reaction.In the study of non-model fitting method,the FR method,FWO method,and KAS method were used.The relationship between different degrees of cure and activation energy is obtained,and then the curing history of phenolic resin was analyzed as folllows: the methylol group is consumed to form a methylene bond or a dibenzyl ether and the molecular chain grows in the gel period.Then the dibenzyl ether reacts and formaldehyde produces and escapes in the curing stage.Finally,the phenolic resin generates and a three-dimensional network structure forms in the post-cure stage.In addition,the conditions suitable for isothermal curing were calculated according to the non-model fitting method.The carbon fiber/phenolic resin composite was prepared with prepreg through the different curing process obtained by calculation.And then a curing process suitable for the phenolic resin prepreg system was selected combining the extrapolation method.The composites prepared by the optimized curing process have much better mechanical properties than those prepared before.This indicates that the determination of the curing process is more successful.