ANSI T 702 OM-2014 Rheological measurements for characterization of polyolefins low-density polyethylene (LDPE) for extrusion coating.pdf

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1、TAPPI/ANSI T 702 om-14 ISSUED 2006 REVISED AND UPGRADED TO OFFICIAL METHOD 2010 REVISED 2006 2014 TAPPI The information and data contained in this document were prepared by a technical committee of the Association. The committee and the Association assume no liability or responsibility in connection

2、 with the use of such information or data, including but not limited to any liability under patent, copyright, or trade secret laws. The user is responsible for determining that this document is the most recent edition published. Approved by the Standard Specific Interest Group for this Test Method

3、TAPPI CAUTION: This Test Method may include safety precautions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the method to safety issues related to such use. The user is responsible for determining that the safety precautio

4、ns are complete and are appropriate to their use of the method, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use, disposal, or both, of chemicals which may present serious health hazards to humans. Procedures for the ha

5、ndling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of potentially hazardous chemicals. Prior to the use of this method, the user must determine whether

6、 any of the chemicals to be used or disposed of are potentially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal authorities for safe use and disposal of these chemicals. Rheological measurements for characterization o

7、f polyolefins: low-density polyethylene (LDPE) for extrusion coating 1. Introduction 1.1 In extrusion coating a thin molten polymer film is coated on some kind of substrate. At high extrusion coating speed, even a minor disturbance on the melt web causes major quality problems, which very rapidly le

8、ad to large quantities of waste. Therefore, higher coating speeds require polymers with high and even quality in order to avoid waste due to polymer edge instability and web break. 1.2 The rheology-related phenomena that may cause problems in extrusion coating are neck-in (NI) and draw-down (DD). Th

9、e neck-in is the reduction of the film width and may cause uncoated areas on the substrate. The neck-in is less if the melt elasticity is high. The draw-down is the ability of the melt to be drawn to thin films without breaking. Draw-down is favored by a melt that is more viscous than elastic. 1.3 C

10、hanges in the molecular structure have a great impact on the rheological and processing properties of a polymer. Storage modulus and zero shear viscosity have been found to be useful parameters to predict the extrusion coating performance of LDPE. Storage modulus quantifies a materials ability to st

11、ore energy elastically and so to deform under stress. As the storage modulus increases, the ability of the material to deform decreases. Zero shear viscosity is related to molecular weight; a small change in molecular weight results in a big change of zero shear viscosity. Knowing this, there is a r

12、elation between storage modulus, zero shear viscosity, draw down and neck-in. As storage modulus and zero shear viscosity increase, neck-in decreases and so does the draw down capacity, meaning a lower line speed at which the polymer can be drawn down to a desired thickness. 2. Scope In optimizing t

13、he extrusion coating processing performance it is of utmost importance to balance the rheology of the polymer. This method describes how rheological measurements can be used to characterize LDPE. The T 702 om-14 Rheological measurements for characterization / of polyolefins: low-density polyethylene

14、 (LDPE) for extrusion coating 2storage modulus and zero shear viscosity have been found to be useful parameters to predict the extrusion coating performance of LDPE. 3. Significance LDPE from high-pressure autoclave reactors for extrusion coating with a Melt Flow Index (MFI) range from 4 to 15 g/10

15、min., and with a density of 915-924 kg/m3has for a long time been considered as a uniform commodity. However, as evolution goes towards faster coating lines, differences in processing performance between various LDPE grades have been observed. Various LDPE grades behave differently in the coating pr

16、ocess due to different rheological properties. 4. Definitions 4.1 The storage modulus and zero shear viscosity are determined from linear viscoelastic data. 4.2 Storage modulus: The storage modulus at a loss modulus of 500 Pa measured at 170C expressed in Pa. 4.3 Zero shear viscosity: The constant p

17、lateau value of the complex viscosity at low frequency measured at 170C expressed in Pas. The zero shear viscosity defined in this method is a fitting parameter of the Cross model. This zero shear viscosity could be different from the zero shear viscosity determined at long creep tests. 5. Apparatus

18、 5.1 Laboratory hot press. 5.2 Controlled-stress rheometer or controlled-strain rheometer with parallel plates ( = 25 mm) geometry operated in the oscillatory mode. In using the controlled-stress mode a sinusoidal torque of constant amplitude is applied and the resultant sinusoidal displacement func

19、tion and the phase shift between the torque and displacement functions are determined. 5.3 In using the controlled-strain mode a sinusoidal displacement of constant amplitude and the resultant sinusoidal torque function and the phase shift between the torque and displacement functions are determined

20、. 5.4 Measurements of the oscillatory rheological properties of specimens in accordance with this standard are restricted to the linear viscoelastic region of behavior. Measurements are done under nitrogen atmosphere to prevent degradation/crosslinking of the sample. 6. Test specimens 6.1 Compress m

21、old pellets of sample at 150C with a preheating for 60 s, a linear increase of pressure up to 50 bar during 50 s. Keep the pressure at 50 bar for 40 s. Cool for 30 s with cooling cassette (cold water circulation). 6.2 Stamp discs with a diameter of 25 mm and a thickness of 1.21.5 mm from the pressed

22、 specimen. Make five test specimens. 7. Conditioning Condition the sample at 170C for 4 min in the rheometer before starting measurements. The gap should be preferably 0.81.2 mm. After 2 min of the conditioning time, open the oven and carefully trim the edges. 8. Procedure Perform a frequency sweep

23、between 200.01 Hz (1250.06 rad/s) divided logarithmically into 18 steps at 170C in the linear viscoelastic region. The linear viscoelastic region is determined by a stress or strain sweep 3 / Rheological measurements for characterization T 702 om-14 of polyolefins: low-density polyethylene (LDPE) fo

24、r extrusion coating measurement at 20 Hz. The strain or stress sweep will determine the maximum allowable strain to be used for the frequency sweep. Take three measurements with three test specimens. If any values appear to be outliers, see TAPPI 1205 “Dealing with Suspect (Outlying) Test Determinat

25、ions” (use one or more of the extra test specimens specified in the section on test specimens to replace outliers). 9. Calculations 9.1 Plot the loss modulus versus the storage modulus (log-log plot) in the range of 200700 Pa of the loss modulus. A linear relation is obtained and the storage modulus

26、 can be determined at a loss modulus of 500 Pa: Storage modulus = ml500log10 where l = intercept of the linear regression line m = slope of the linear regression line 9.2 Define zero shear viscosity by extrapolating the three parameters Cross equation: n1*0where * = complex viscosity, Pas Pas 0 = ze

27、ro shear viscosity, Pas Pas = characteristic relaxation time, s = frequency, rad/s n = power law index 9.3 The curve fit calculation is preferably done with the Microsoft Excel Solver but any other software giving comparable data could be used. 10. Report 10.1 Report the following information: 10.1.

28、1 Complete sample identification and date. 10.1.2 Type of rheometer used. 10.1.3 Average value of storage modulus in Pa. 10.1.4 Average value of zero shear viscosity in Pas Pas. 10.1.5 Software used for the curve fit calculation of the zero shear viscosity. 11. Precision 11.1 Storage modulus. For th

29、e maximum expected difference between two results, each of which is the average of three (3) test determinations: Repeatability (within a laboratory) = 2% of mean. Reproducibility (between laboratories) = 11 % of mean T 702 om-14 Rheological measurements for characterization / of polyolefins: low-de

30、nsity polyethylene (LDPE) for extrusion coating 411.2 Zero shear viscosity. For the maximum expected difference between two results, each of which is the average of three (3) test determinations: Repeatability (within a laboratory) = 4% of mean. Reproducibility (between laboratories) for MFI 4-6 = 2

31、2 % of mean. Reproducibility (between laboratories) for MFI 7-15 = 15 % of mean. In accordance with the definitions of these terms in TAPPI T 1200 “Interlaboratory Evaluation of Standards to determine TAPPI Repeatability and Reproducibility.” 12. Keywords Rheology, Extrusion coating, Low-density pol

32、yethylene (LDPE) 13. Additional information 13.1 Effective date of issue: November 4, 2014. 13.2 The major change in the 2014 version was the additional of Section 1.3 to describe the impact that changes in the molecular structure have on the rheological and processing properties of a polymer. Refer

33、ence Per-Ake Clevenhag, Claes Oveby; TetraPak Carton Ambient AB, “Rheological Indicators to predict the Extrusion Coating Performance of LDPE,” Tappi PLACE conference 2004 (document PLA 0407) Your comments and suggestions on this procedure are earnestly requested and should be sent to the TAPPI Standards Department.