Analysis Of Polyurethane Elastane In Blended Fibers By Pyrolysis Gas Chromatography/Mass Spectrometry

Polyurethane elastane is so far the best fiber with elongation and elastic recovery rate,mainly including poly(ether-urethane)elastane and poly(ester-urethane)elastane.A small amount of polyurethane elastane added into the blend fibers may have a great impact on the performance of textiles,such as improving the dimensional stability and conformity of the fabric,etc.Therefore,it is very important to determinate the polyurethane elastane accurately in the blended fibers.At present,the detection method of polyurethane elastane content is mainly based on the national standard GB/T 2910-2009 Quantitative Chemical Analysis of Textiles Part20: Mixtures of elastane and some other fibers(method of using dimethylacetamide).However,the whole process of the method is cumbersome and time consuming.Qualitative identification needs to be carried out in advance by other industry standard.In this paper,a method for qualitative identification and quantitative analysis of polyurethane elastane in blended fibers was established by pyrolysis gas chromatography/mass spectrometry(PyGC/MS).According to the characteristics of polyurethane elastane pyrolysis products quantitative analysis of polyurethane elastane in blended fibers,the characteristics of the pyrolysis products can be used for qualitative identification of polyurethane elastane in blended fibers.In this paper,the factors influencing pyrolysis temperature and pyrolysis time are studied,the standard working relationship curve is drawn,the test repeatability is investigated,and the actual sample is analyzed quantitatively.The thermal stability and pyrolysis mechanism of polyurethane elastic fibers were also studied.The results show that the main characteristic products of polyurethane elastane pyrolysis are tetrahydrofuran and diphenyl-methane-diisocyanate.And the polyurethane elastane can be identified by these two characteristic products.Chosen pyrolysis temperature is 550 ?,pyrolysis time is 30 s,and the pyrolysis characteristic product tetrahydrofuran as the quantitative characteristic peak.Choosing tetrahydrofuran as the quantitative characteristic peak.It's have also shown that when the pyrolysis temperature is low,the polyurethane elastane is incompletely pyrolysis,and the abundance of the characteristic pyrolysis peak tetrahydrofuran is not high.If the pyrolysis temperature is too high,the polyurethane elastane characteristic pyrolysis product diphenyl-methane-diisocyanate will be further pyrolysis,and the main component is not observed.At the pyrolysis temperature of 550 ?,the characteristic pyrolysis product is most obvious on the total ion chromatogram.The pyrolysis time is about 30 s,and the peak area of the characteristic cleavage products tetrahydrofuran and diphenyl-methane-diisocyanate reaches a maximum.The peak area of the characteristic pyrolysis product tetrahydrofuran has a good linear relationship with the concentration of the polyurethane elastane.The correlation coefficient was greater than 0.9990.After repeated tests,the repeatability of RSD < 5.0 % was calculated.At the same time,it can be concluded that the relative error of polyurethane elastane content in spinning samples measured by pyrolysis method and national standard method is between 4.0 %~ 8.0 %.In this paper,the thermal stability of polyurethane elastane was studied.The thermal decomposition activation energy of poly(ether-urethane)elastane was 45.48 kJ/mol,and the thermal decomposition activation energy of poly(esterurethane)elastane was 37.16 kJ/mol.Both have good thermal stability.In addition,the mechanism of thermal pyrolysis is also discussed,the bond between O-C in the main chain of polyurethane elastane is weaker than that of C-C.The bond with weak bond is prone to crotch breakage.After the diisocyanate chain is broken,diphenyl-methanediisocyanate monomer may be cleaved.The poly(ester-urethane)soft segment mainly cleaves pyrolysis products such as cyclopentanone and tetrahydrofuran,and the poly(ether-urethane)soft segment cleaves pyrolysis products such as tetrahydrofuran and 1,4-butanediol.