Study On The Structure And Properties Of FEP

Fluorinated ethylene propylene?FEP?is a copolymer via copolymerization of tetrafluoroethylene?TFE?with hexafluoropropylene?HFP?,which is widely used in various fields,such as electric wire,machine,chemical engineering,medical treatment and so on,and it has strategic significance.Compared with the similar one abroad,our extrusion grade FEP has the disadvantages of low thermal stabilities,easy to melt fracture,inferior thermal stress cracking performance,which caused by the differences of comonomer content,end group stabilizing treatment,molecular weight and its distribution,crystal structure.Therefore,establishing composition and methods for characterizing the end groups and investigating the rheological properties of related products and its crystalline structure at home and abroad have a great significance for the production of high-performance FEP products.This work chose China Luxi FEP-melt refers to 21.5 and Japan daikin FEP?NP 101?-melt refers to 22 as the research object,and the main contents and conclusions were as follows:We established a standard sample composition infrared analysis work curve using FTIR spectrometer.According to the absorption peaks of-CF3 at 980 cm^-1 and-CF₂ at2380 cm^-1,we analyzed the composition of FEP copolymer,and studied if there were unstable end groups by the qualitative approach.The experimental results showed that the quality percentage of HFP from Daikin FEP was 12.54%,less than 17.18% of Luxi FEP;we also discovered that there were no absorption peaks of-OH and C=O in the infrared spectra of both samples,indicating that the unstable end groups of-COOH have been stabilized.We measured the shear stress ? of FEP at a certain range of shear rate ? and apparent viscosity,calculated the viscous flow activation energy E?,non-Newtonian index n and shear sensitivity index I.We also discussed the relationship between the various rheological parameters and critical condition absence of melt fracture.It turned out that they all followed the law of shear-thinning behavior,but the ? of Luxi FEP sharply fellunder high ? with the crack of macromolecular;the drop rate of ? from Daikin FEP is slightly larger than that of Luxi FEP with the increase of temperature T,which were greatly influenced by temperature;the E? of both samples decreased with the increase of ?,but Daikin FEP still had good shear sensitivity under high ?;both I also declined with the temperature rising,but Daikin FEP had smaller shear sensitivity and bigger viscosity;both of them belonged to the typical pseudoplastic fluid,but the non-newtonian nature of Daikin FEP significantly was lower and the liquidity was better than the Luxi FEP.For the extrusion molding,the critical process conditions absence of melt fracture for Daikin FEP was follow: T?380 ??,??300 s-1?,which for Luxi FEP was T?385 ??,??200 s-1?,so the processing performance of Daikin FEP was better.We obtained the distribution of wafer in the FEP using DSC curve via differential scanning calorimetry,the equilibrium melting point of FEP was 567.6 K and the unit volume melting heat was 10.29 J·cm^-3;We also got the wafer thickness at different melting point by Thomson-Gibbs equation calculation.The relationship between wafer distribution content and the thermal stress cracking performance showed that our country's wafer thickness of FEP at similar melting point was similar to that of abroad,in the part of maximum and minimum,the thickness of wafer from Daikin FEP was thin than that of Luxi FEP;In the thickest part of the wafer thickness,the wafer percentage of Daikin FEP was less than 1/2 of Luxi FEP;There were more thin wafer in Daikin FEP,leading to tie molecule with certain chain length through more wafer,resulting in good thermal stress cracking performance.In this paper,compared the structure and performance of extrusion grade FEP at home and abroad,we provide guidance for the domestic production of FEP,in order to reach the international advanced level.