Polymer Processing Lab 8: Fiber Spinning

Objective: To make fibers and investigate the processing parameters in this polymer processing operation.

Background: Web notes and

Middleman:
Chapter 9
Chapter 3 Elongational Flows p. 42-48
Chapter 3 Viscoelastic Flow p. 54
Chapter 14 Elastic Flows
Chapter 15 Flow Stability
Chapter 13 Heat and Mass Transfer

Tadmor and Gogos:
Chapter 1 pp. 6 - 8
Chapter 13 section 13.3 pp. 542-545
Chapter 15 section 15.1 pp. 632-637
Figure 17.2 pp. 686 Elongational Flows Chapter 6 pp. 184-190
Orientation of processed polymers, Chapter 3 pp. 65-84 (and other parts of Chapter 3).

Terms You Should Know: Sizing, Draw Ratio, Pull Rolls, Rate of Haul-Off (like Draw Ratio), Denier, Melt Spinning, Trouton Viscosity, Orientation Function, Uniaxial Orientation, Feedback Gauge Control, Cold Drawing, Melt Stretching, Dry Spinning, Wet Spinning, Spinnerette, Spinablility, Point of Solidification, Melt Draw Down Region, Takeup Rolls, Draw Resonance, Stanton Number.

Material: Polypropylene (or HDPE or LDPE).

Procedure: We will first find a usable barrel and die temperature, die diameter (1/4, 1/8 inch), cooling bath temperature combination where fibers can be drawn reproducibly. We will then draw a number of polypropylene fibers under different processing conditions varying:

-The extrusion rate, FAST or SLOW, for fixed barrel and die temperatures.

-The takeup rate, Fast, Medium, Slow.

(You will need to measure:

  1. the rotation rate for the extruder and
  2. rotational takeup rate of the takeup roll, as well as
  3. the mass velocity of the extrudate.)

This results in 6 runs on which we will measure:
  1. The fiber diameter as a function of "z", distance down the fiber, using a ruler and a caliper gauge.
  2. The frost line position, Zf.
  3. The Die Exit diameter, d0.
  4. Fibers from each of the 6 processing conditions and from various positions in "z" will also be examined between crossed polars to estimate the crystalline orientation visually. You should sketch what you observe and include copies of these sketches in the report.
  5. XRD 2-d patterns will be collected for the fibers produced. You will need to provide a bundle of about 40 fibers all oriented in the same direction making a 1 cm square sample. These can be taped together with one layer of scotch tape. (A volunteer will be needed for this part).
  6. Instron measurement of the modulus, yield point strain and yield point stress as well as ultimate elongation and stress at failure of the spun fibers (web data available).
  7. Observe the melt speed (and acceleration!) in the web by placing a small piece of paper on the extrudate during fiber spinning.
  8. At the end of the lab cool the die and observe the change in the melt strength as the die temperature drops.

Control Parameters: Take-up rate (Fast, Medium, Slow), Extruder rate (Fast: Slow), Barrel Temperature, Die Temperature, Cooling Bath Temperature, Die Diameter.

Measurable Parameters: Die Diameter, Die exit area, A0 in figure 13.19, Frost line position, Zf., Fiber Diameter, XRD on Films use Phillips and Polaroid Film, Orientation by Polarizers.

Your Results Should Include:

  1. A plot of Fiber diameter as a function of z for all conditions with calculations based on Middleman Chapter 9 (figure 9-4) or Tadmor chapter 15 (figure 15.1). The plot should clearly mark where the frost line forms.
  2. A calculation (plot) of the linear velocity of the fiber as a function of z assuming axially isotropic fibers (second normal stress difference is 0). You should discuss the appropriateness of this assumption based on your fibers. Graphically compare Middleman equation 9-26, 9-31 and 9.51 with your velocity. You will need to obtain power-law parameters from the polymer handbook or a suitable source.
  3. Descriptions of differences in the fibers under crossed polars.
  4. Discussion and copies of the XRD patterns from the fibers.
  5. A description of the melt velocity and acceleration along the z-direction.
  6. A description of the change in melt strength (spinnability) as the die temperature drops.
  7. Instron Results from the spun fibers.

Problems:
  1. Define each term in the "Terms You Should Know" list above.
  2. Middleman Problem 3.22
  3. Middleman Problem 9.4
  4. Middleman Problem 9.14
  5. Given the velocity and acceleration of the melt web from the extrudate to the take-up roll, do you think the melt spinning operation is very well described by simple elongational flow? Explain your answer.
  6. What is the limiting factor for a fiber spinning operation? Discuss.
    (Note that heat transfer is generally the limiting factor in polymer processing operations.)
  7. Can the change in melt strength with die temperature be explained by changes in the Trouton viscosity? (i.e. What is the Trouton viscosity and how do you think it changes with die temperature?)
  8. How do the mechanical test results correlate with the XRD orientation and processing conditions?