Normally Torque increases when when high MW fraction added to HDPE upto certain extent but decreases further when concentration increases further
When low quantities of UHMWPE are added to HDPE melt, the long chain molecules of UHMWPE remain as separate entities and get dispersed and distributed within the matrix of the HDPE molecules that have relatively shorter chains than those of the UHMWPE. When the concentration is increased beyond 30%, the long chain molecules of UHMWPE get easily entangled within themselves and form large aggregated species. These larger sized species have a tendency to move away from the shearing surface much more easily than when they are in un-aggregated form. This leaves the shearing surface devoid of the higher concentration of the UHMWPE species, and the blended system behaves as though the concentration of the UHMWPE is lower, thereby showing a lower torque.
This phenomenon is similar to what happens when performing rheological tests on filled polymer systems in the higher shear rate ranges, and is often considered as slip. Better clarification can be got by reading more about this in the following book, if one is available for reference.
Aroon V. Shenoy, Rheology of Filled Polymer Systems, Kluwer Academic Publishers, Netherlands (1999).
Some discussion on the rheology of polymer blends is available in the following book that might also be useful.
A. V. Shenoy and D. R. Saini, Thermoplastic Melt Rheology and Processing, Marcel Dekker Inc., New York (1996).
A number of polymer blends are discussed in the above mentioned book though not specifically UHMWPE with HDPE. The only available discussion on UHMWPE in the book is on compression molding of UHMWPE, in case that is of interest.
Thanks for your answer. I still need to clarify whether HDPE and UHMWPE get homogenized at molecular level or they will still exist as separate phases at higher concentration
One indirect way to assure that there is some level of molecular dispersion and distribution of one species with the other in a polymer blend is by ensuring that the compounding is done under optimum or as near to optimum conditions as possible. The methodology for achieving this is discussed in the following paper:
A. V. Shenoy, Estimation of Compounding Conditions and Grade Selections in the Preparation of Thermoplastic Melt Blends, Polymer-Plastics Technology and Engineering, 24:1, 27-41(1985)
and on pages 284-298 of
A. V. Shenoy and D. R. Saini, Thermoplastic Melt Rheology and Processing, Marcel Dekker Inc., New York (1996).
In the case of UHMWPE / HDPE blend, determinations of the optimum compounding conditions may be more difficult than for other blends since the viscosity or Melt Flow Index values of the two components could have too large a difference at the temperature and shear rate of convenience during compounding. Hence, as a compromise it would be okay to select conditions as close to optimum as possible. In order to then evaluate the goodness of blending, atom force microscopy may be used to assess the level of blending and to clarify whether HDPE and UHMWPE get homogenized at molecular level or they will still exist as separate phases at higher concentration.
Goodness of mixing, mixing mechanism, compounding techniques and compounding/mixing variables, at least for polymer melts in which fillers are added, have been discussed
on pages 175- 242 of
Aroon V. Shenoy, Rheology of Filled Polymer Systems, Kluwer Academic Publishers, Netherlands (1999).
Some of the ideas borrowed from filled polymer systems may be useful for the polymer blend under discussion.
- Badges
- Science topic
- Similar topics
- Force