Sliding Plate Rheometers

A sliding plate rheometer (simple shear) can be used to study the response of polymeric Hquids to extension-like deformations involving larger strains and strain rates than can be employed in most uniaxial extensional measurements (56,200—204). The technique requires knowledge of both shear stress and the first normal stress difference, N- (7), but has considerable potential for characteri2ing extensional behavior under conditions closely related to those in industrial processes. 

Sliding angle (a), contact angle and drop size and, 22 113-114 Sliding plate rheometer, 22 738, 740 Slightly toxic substances, 23 113... 

Figure 22.9. Schematic diagram of a true shear sliding-plate rheometer. (Reproduced with permission from Gunasekaran and Ak, 2002.)...

The experimental device constructed to orient uniformly thick samples in simple shear is schematically represented in Fig. 3. It is basically a sliding-plate rheometer, the polymer sample being sheared between two temperature-controlled parallel plates. The upper plate is fixed whereas the lower plate can be displaced both horizontally and vertically with two pneumatic jacks. 

Specimens were sheared by using the above described sliding plate rheometer at two different shear stresses Oxyi 0.05 and 0.2 MPa. For axy=O.05 MPa, the behaviour of the melt was found to be nearly Newtonian. One sample was sheared at the highest shear stress up to a final shear strain of y=2.4. For the lowest shear stress, two samples with different shear strains were prepared y=2.8 and y=4. These samples are referenced in Table 7. 

As will be shown below, the experiment in the sliding plate rheometer does not allow one to determine Nl, since the normal force is in fact related to the second normal stress difference. For this reason, we studied the stress-optical law in shear by assuming that the principal directions of shear and refractive index are close to each other in the x-y plane. It is then straightforward to express the difference of principal stresses in the x-y plane... 

Fenijn J. and R.C. Krooshof. 1970. The sliding plate rheometer. A simple instrument for measuring the visco-elastic behaviour of bitumens and related substances in absolute units. Proceedings of the 9th Annual Conference CTAA, Vol. 15, p. 123. 

Hatzikiriakos SG, Dealy JM (1991) Wall slip of molten high density polyethylene. L Sliding plate rheometer studies. J Rheol 35 497-523... 

Schematic of sliding plate rheometer. The displacement Ax = vot (recall Examples 1.4.1 and 2.2.1).

Wall shear stress transducer mounted in a sliding plate rheometer. Shear between the sample and the wall causes die cantilever to deflect slighdy, which motion is detected by the capacitance probe. Adapted from Interlaken (1992). 

Currently, two general rotational rheometer types [29] are available commercially, that can be used for LAOS experiments controlled strain rheometers (also known as separated motor-transducer, SMT) and controlled stress (or combined motor-transducer, CMT) rheometers. Apart from the rotational rheometers, custom built instruments, such as the sliding plate rheometer by Giacomin et al. [13] are also suitable, but will not be discussed here, as they are not available commercially. 

Giacomin AJ, Samurkas T, Dealy JM (1989) A novel sliding plate rheometer for molten plastics. Polym Eng Sci 29 499-504... 

Methods for determining the first normal stress difference at higher shear rates than are accessible using a cone-plate rheometer include the Lodge Stressmeter rheometer [117-119] and the sliding plate rheometer [84]. The former makes use of the pressure measured at the bottom of a small side hole in flow through a slit. It has been demonstrated that these two instruments give comparable results for a polystyrene melt up to shear rates of 200 s" [85]. 

Many years of experience with sliding plate rheometers have revealed several phenomena that limit their utility under certain conditions. First, the normal stress differences create a pressure gradient in the sample that tends to pump melt in from the ends of the sample and out toward the edges. [ 147-149]. This flow can be prevented by the use of fluorocarbon side- rails. More serious limitations are imposed by slip, cavitation and rupture, which interrupt experiments at sufficiently high strains and strain rates. At the same time, however, sliding plate rheometers have been found to be useful tools for the study of melt slip [150]. Elastomers are particularly resistant to shearing deformations and even the use of deep grooves in the plates does not ensure their adherence [146]. 

Koran, E, Dealy, J. M. A high-pressure sliding plate rheometer for polymer melts. /. RheoL (1999) 43, pp. 1279-1290... 

Ortman, K. C., N. Agarwal, D. G. Baird, P. Wapperom, and A. J. Giacomin. 2011. Transient Shear How Behavior of Concentrated Long Glass Fiber Suspensions in a Sliding Plate Rheometer. J. Non-Newtonian Eluid Mech., 166 (11), 533-547. 

MEASUREMENT OF THE HIGH FREQUENCY VISCOELASTIC PROPERTIES OF POLYPROPYLENE USING A SLIDING PLATE RHEOMETER... 

The rheological behaviour of molten polymers is of prime importance as it relates to their microstructure and governs their processing characteristics [1]. Rotational rheometers, specifically cone-plate, parallel plate, and sliding plate rheometers are routinely used to characterize the linear viscoelastic properties of polymer melts. Small amplitude oscillatory shear experiments are employed to measure the storage (G ) and loss moduli (G"), which are related to the elastic and viscous character of the material, respectively, and the complex viscosity (77 ) as functions of angular frequency (a). 

A newly constmcted sliding plate rheometer was used to measure the high frequency viscoelastic properties of two PP resins. Measurements obtained using the SPR are in good agreement with extrapolated data obtained using the generalized Maxwell model and the Cross model. 

Figure 1. Schematic of the sliding plate rheometer fixture, where the filled black circles denote the location of the cartridge heaters and the filled grey circles denote the location of the K-type thermocouples. The numbers are ... 

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