삼보과학

[Rheometer] Correlating Melt Rheology of PET to IV
작성자 : 삼보과학 작성일 : 2011-04-05 조회수 : 5434
파일첨부 :
Dynisco사의 J.F. Reilly와 A.P.Limbach가 발표한 논문 'Correlating Melt Rheology of PET to Solution Intrinsic Viscosity'을 소개합니다. 본 논문에서는 PET resin의 IV를 결정하는 방법에 대한 이론적인 설명과 실험데이터. 그리고 수분이 PET의 IV에 미치는 영향에 대하여 소개하고 있습니다. 아래에 일부 내용을 발췌하여 올립니다. 논문자료 전체를 원하시는 분은 전화나 이메일로 연락주시기 바랍니다. ------- 발췌 내용 -------- >> Correlating Melt Rheology of PET to Solution Intrinsic Viscosity<< by J.F. Reilly and A.P. Limbach 1. INTRODUCTION This work continues our study of the rheology of PET resins. Specifically this paper covers efforts made at improving capillary test methods and algorithms for estimating Intrinsic Viscosity(IV) from viscosity measurement in the melt. Polymers have the unique ability to dramatically increase the viscosity of a liquid they are dissolved in, even at very low concentrations. Intrinsic Viscosity is a quantitative assessment of this ability. IV is not, however, directly related to molecular mass(molecular weight). A polymer chain with a branched structure will have a different IV than a linear chain with the exact same molecular mass. This is because the increase in viscosity is related more directly to the volumetric size of coiled polymer in the solvent. It is necessary therefore to develop empirical correlations between IV and molecular mass(obtained by some absolute method like light scattering, end group analysis etc.) for IV to predict molecular mass with accuracy. IV is used commercially to differentiate grades of resins along with other properties. Most applications for polymers do not involve dissolution into solvent. More typically they are extruded, injection molded, calendered etc., all processed in the meeting the application's specifications or production cost requirements. It makes sense therefore to test the material as close as possible to its final form since removal of thiese key components are critical to the final behavior of the material. Measuring solution viscosity, of course, necessitates the removal of these components whereas testing in th molten state does not. The first step in using melt rheology is to correlate neat(no additives) polymer IV to melt rheology. Correlations between IV and melt rheology for neat polymer exist for Plypropylene and PET though they have not received wide spread use. The two rheological parameters typically used for the correlation are th Zero Shear Viscosity and Intrinsic Melt Viscosity(IMV). Zero Shear Viscosity is used to describe a viscositywhich has been obtained by extrapolating viscosity vs. shear rate data to zero rate. Like IV the Zero Shear Viscosity can be related empirically to molecular mass. IMV is typically obtained from a constant shear rate test(or constant stress) where viscosity versus time is obtained for a degrading polymer and the data is extrapolated to obtain the viscosity at zero time (described in detail in the appendix of ASTM D3835). Previously we had shown a very clear correlation of IV to Zero Shear Viscosity, IMV and Melt Flow Rate for one particular vendor of PET using virgin materials. We wil reiterate some of of that work and append it with results from an additional vendor along with some recent model development work for obtaining a limiting viscosity at zero time. - 중략 - CONCLUSIONS When correlating melt rheology to IV a multitude of potential problems can be remedied by "calibrating a system" with a known IV sample. The known IV ample adjusts the vertical offset value on the log-log plot to account for 1)systematic variations in the IV measurement (use of different IV test temperatures between vendors etc.) 2)systematic change in the polydispersity of a group of samples and 3)minor inaccuracies in the test device. That is, since the slope of the Zero Shear Viscosity curve versus IV semms fairly robust, the known sample fixes the vertical position of a trace. For a single supplier of virgin material results within +/- 0.01 dl/g are typically produced. Assumptions include, that moisture level does alter the power dependence (slope of the line) significantly or that deviations are not overwhelming especially if the correlation is used over a limited window, near the reference point, as in inspection of incoming/outgoing material. Drying must be consistent. Melt flow index can also be used though care must be taken to assure proper drying has occurred and an empirical rather than theroretical power dependence should be used. A reference sample of known IV is needed for each IV generated from different labs (vendors) unless consistent IV test methods are used. - THE END -

이전글	[제지/오염도] Papermill의 오일 오염도 측정
다음글	[ViscoSensor] IV from Melt Viscosity

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