Study On Crosslinking Behavior Of Nylon 66 Anaerobic Thermal Degradation

Nylon 66(PA66)tends to undergo thermal degradation above melting point even in anaerobic conditions accompanied with a crosslinking reaction.The further occurrence of cross-linking reaction will cause the formation of gel.Gel will adversely affect the PA66 industrial pipeline transportation and following spinning,which caused economic losses to the enterprises.As the gel is produced by the side reaction of nylon 66 during the thermal degradation process,it is necessary to study the process and mechanism of the nylon 66 oxygen-free thermal degradation.There are many studies on the mechanism of anaerobic thermal degradation at home and abroad,but there are few studies on the inhibition of gel formation.This article firstly gauged and analyzed the PA66’s change of structure and thermal properties during thermal degradation.Then the effects of different hindered amine on the gel content,thermal properties and structural changes during the heat treatment to nylon 66 were studied.Finally,the PA66 and PA66 / PA6 T copolymer(PA6AT)were prepared by in situ polymerization.The structure of the prepared product was characterized.The change of gel content and the thermal properties with the heat treatment time were measured.The main content are shown as below:(1)With the increase of heat treatment time,the gel content initially increased slowly,after a certain time,the gel content increased rapidly,and finally the growth rate gradually slowed down.During the heat treatment,the amide bond concentration in the nylon 66 sample was reduced to form the terminal amino group and the cyclopentanone group-containing substance,and the terminal amino group was further reacted.The melting peak temperature and crystallization peak temperature of nylon 66 were gradually shifted to the low temperature with the prolongation of heat treatment time,which indicated that the stability of PA66 crystal decreased and the crystallization was difficult with the heat treatment time prolonged.(2)Mixture PA66/hindered amine A(PA66/HAA),PA66/hindered amine B(PA66/HAB),and PA66/hindered amine C(PA66/HAC)was prepared by melt blending.The gel content of PA66/HAA and PA66/HAB was lower than that of PA66 in the same heat treatment time,and the gel content of PA66/HAA was the lowest.While PA66/HAC had a higher gel content than PA66.The decrease of the melting peak temperature and the crystallization peak temperature of PA66/ HAA and PA66/HAB after 6 hours of heat treatment were less than that of PA66,while the decrease of PA66/HAC was more than PA66.(3)The PA6 T salt was prepared first,then PA66,PA66/HAA,PA66/HAB,and PA6 AT are prepared through polymerization.The structure of PA6 T salt was confirmed,and the PA6 AT was copolymerized by PA66 salt and PA6 T salt.The gel content of PA66/HAA and PA66/HAB was still lower than that of PA66 in the same heat treatment time,and PA66/HAA was the least.However,PA6 AT had a higher gel content than PA66 in the same heat treatment time.The melting point of PA66/HAA,PA66/HAB and PA6 AT without heated was inferior than PA66 by 0.1℃,1.1℃ and 2.9℃.After being heated for 6h,the decrease of the melting peak temperature and the crystallization peak temperature of PA66/HAA and PA66/HAB were still less than that of PA66,while the decrease of PA6 AT was more than PA66.