Measuring and testing – Testing of material
Reexamination Certificate
1999-03-12
2001-03-13
Raevis, Robert (Department: 2856)
Measuring and testing
Testing of material
Reexamination Certificate
active
06199437
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to studying the effects of flow fields imposed on a material during processing.
The engineering properties of a material are determined by the meso-, micro-, and nano-structure of the material. These features, in turn, are extremely sensitive to the processing history of the material, including the temperatures and flow fields to which the material was exposed during processing. For example, in typical commercial polymer processing operations such as extrusion molding, film blowing, or fiber spinning, a polymer melt is subjected to intense flow fields (shear, elongational, or a combination thereof), thereby distorting the melt. In the case of semi-crystalline polymers, imposing flow fields on the melt accelerates the rate of crystallization, and can result in the formation of crystallites oriented in the flow direction, both of which affect the morphology and properties of the resulting material. In the case of amorphous polymers, imposing flow fields can result in a “frozen-in” orientation that modifies the mechanical and optical properties of the material. Similarly, flow fields imposed during processing can alter the microstructure of polymer blends, filled polymers, and other materials.
Optimizing the engineering properties of materials requires an understanding of the effects of flow fields imposed during processing to permit a rational choice of suitable materials and processing conditions for a particular application. The work of Janeschitz-Kriegl et al., reported in Int. Polym. Process, 8, 236 (1993); Int. Polym. Process, 10, 243 (1995); Rheol. Acta 35, 127 (1996); and Int. Polym. Process, 12, 72 (1997), represents one approach towards understanding the underlying physics of polymer melt crystallization. Janeschitz-Kriegl subjected a subcooled polymer melt to brief, intense shearing at shear rates similar to those experienced in typical polymer processing operations by driving the polymer through a slit under high pressure generated by an extruder, after which the polymer was allowed to crystallize. The progress of crystallization was tracked using a rotating polarizer setup that monitored birefringence. The resulting data provided information regarding the relationship between crystallization time and both wall shear rate and shearing time.
The apparatus used in the Janeschitz-Kriegl studies suffers from two disadvantages that limit its commercial utility. First, using an extruder requires the use of large amounts of polymer samples, thereby limiting the number and type of polymers that can be studied. In addition, the rotating polarizer set-up limits the time resolution of the data, making it difficult to monitor the deformation of the melt during short shearing times.
Capillary rheometers have also been used to study the flow properties of polymeric materials. The rheometer is operated by forcing polymer through capillaries of varying lengths using pneumatic or hydraulic pressure, a screw feed, or a dead weight.
Capillary rheometers are typically used to study isothermal, steady state, stress-strain relationships. However, they are not well-suited for generating well-defined transient deformations and recording structure development in real time while the polymer is under the influence of the flow field.
SUMMARY OF THE INVENTION
The invention provides an improved apparatus for studying the effects of flow fields imposed during processing on the structure and properties of a material. Unlike capillary rheometers, the apparatus is well-suited for studying the effects of both steady and transient flow fields. Unlike the extruder-based device used in the Janeschitz-Kriegl studies, which required kilogram-sized samples, this apparatus is capable of establishing flow fields on the order of those encountered during typical processing operations using only small quantities of sample. For example, the apparatus is operable using samples of about 0.5 cm
3
. Accordingly, it is well-suited for studying experimental materials that are available only in small quantities.
Another useful feature of this apparatus is that it is designed to accommodate a wide variety of real-time, in-situ probes for studying structure such as infrared, optical, and x-ray-based probes, and to facilitate subsequent ex-situ characterization by, e.g., optical or electron microscopy. For example, it is possible to use the apparatus with synchrotron x-ray sources for in-situ x-ray scattering studies of the evolution of nanostructure. Data can be acquired rapidly during the pressure pulse. For example, in some cases, data can be acquired at around 5 millisecond time resolution.
The apparatus can be used to study many different materials. It is particularly useful for studying polymer samples, including, for example, semi-crystalline polymers, amorphous polymers, engineering plastics, elastomers, thermoplastic elastomers, polymer melts, polymer blends, polymer solutions, polymer suspensions, composite structures, foams, and gels. Ceramic samples, e.g., in the form of sol-gels, can also be studied.
The apparatus includes a flow chamber through which a sample can flow. The flow chamber can be designed to accommodate various flow geometries, thereby making it possible to study a large number of different flow conditions, including uniform and non-uniform shear flow; uniaxial, biaxial, and intermediate extensional flow; and flows having both shear and extensional components. For example, the flow chamber may be provided in the form of a channel having a cross-section that remains constant along the length of the channel, or which varies along the length of the channel. In the case of channels in which the cross-section varies, the channel may be tapered or it may include abrupt contractions and/or expansions. Specific examples of suitable flow geometries include a simple rectangular channel that acts as a capillary for studying shear flow, and a channel having a tapered region for studying a mixture of shear and extensional flow. It is also possible to design the flow chamber, e.g., by incorporating obstructions in the flow chamber, in order to study flow around corners or flow around an obstacle leading to a weld line.
The flow chamber includes one or more ports arranged to accommodate one or more analytical probes for measuring the properties of the sample as it moves through the flow chamber. These ports enable data relating to the behavior of the sample to be gathered while the sample is subject to a flow field, as well as after cessation of flow.
Suitable ports include windows that are transmissive to a certain range of radiation wavelengths. One window, for example, is positioned to receive a signal from a radiation source and the other window is positioned to transmit the signal to a detector after it has passed through sample in the flow chamber. Quartz windows are useful for visible radiation, while beryllium windows are useful for x-ray radiation. Examples of other suitable windows include silicon, which is useful for infrared radiation; calcium fluoride, which is useful for visible and infrared radiation; and polyimides such as Kapton® which are useful for x-ray radiation.
The flow chamber is housed within a thermal reservoir. To facilitate ex-situ characterization of the sample after exposure to a given set of flow and thermal conditions, the flow chamber may be provided in the form, e.g., of a cartridge that can be removed from the thermal reservoir.
Because structure development (e.g., crystallization kinetics in the case of semi-crystalline polymers) can be very sensitive to temperature, the thermal reservoir is temperature-controlled, preferably to within about ±0.1° C., to ensure proper control and temperature stability. Preferably, the thermal reservoir is designed to perform transient temperature control. According to one embodiment, this objective is achieved by equipping the thermal reservoir with a pair of cartridge heaters, a thermocouple, a feedback temperature controller, and a plurality of channels extending the length of the th
Kornfield Julia A.
Kumaraswamy Guruswamy
Verma Ravi K.
California Institute of Technology
Fish & Richardson P.C.
Raevis Robert
LandOfFree
Apparatus for studying the effects of flow fields imposed on... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for studying the effects of flow fields imposed on..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for studying the effects of flow fields imposed on... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2478934