Abstract:
An improved phase transition analyzer ( 22 ) is provided which greatly facilitates analysis of composite mixtures such as protein and starch-containing extrudate mixtures to give valuable information about the mixture, e.g., glass transition and melt transition temperatures, T g  and T m . The analyzer ( 22 ) includes a body ( 74 ) having a chamber ( 192 ) adapted to receive a sample ( 196 ) of a material to be analyzed, together with a force-applying assembly ( 34-40, 68 ) operable to apply a compressive force to the sample  196  and a heating assembly ( 96, 138 ). In order to determine T g , the sample ( 196 ) is progressively heated under sustained exertion of compaction force with chamber ( 192 ) closed. The sample ( 196 ) is compacted and the volume of chamber ( 192 ) correspondingly decreases, this being sensed by movement of a portion ( 34, 36 ) of the force-applying assembly ( 34-40, 68 ) by a displacement transducer ( 44 ). To measure T m , the block ( 38 ) is moved to a second position providing a capillary escape opening ( 162 ) at the chamber ( 192 ). Continued progressive heating of the sample ( 196 ) under compressive force causes the sample ( 196 ) to melt and flow through opening ( 162 ). The consequent movement of the portion ( 34, 36 ) is again sensed by transducer ( 44 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     A CD-ROM containing a computer program listing appendix has been submitted. The CD-ROM contains 1 dick, containing a total of 218 files. 
     The present invention is broadly concerned with an improved material transition analyzer and method permitting analysis of non-uniform, composite materials in order to determine temperature-related phases of material, such as the glass transition temperature (T g ) and melt transition temperature (T m ). More particularly, the invention is concerned with such analyzer and method wherein the analyzer includes a body having a sample chamber, a sample heating assembly, and a force-applying assembly operable to apply a compressive force to the sample which decreases the chamber volume in response to sample phase changes; the change in volume is detected, preferably by monitoring corresponding shifting of a portion of the force-applying assembly. 
     2. Description of the Prior Art 
     Thermal processing techniques such as extrusion and pelleting generate complex chemical and physical changes in ingredients to produce final products with desired characteristics. Modern instruments and analytical tools can measure these often minute but critical changes. By correlating these changes to desired properties in finished products, it is possible to predict processing effects and to more accurately formulate diets and automated processing parameters. 
     A relatively new approach that is rapidly increasing in popularity is the application of polymer science to extrusion and similar technologies. Having roots in the plastic polymer industry, polymer science can be used to study the physical changes associated with glass transition and melt transition in biopolymers such as starches and proteins. In order to make use of the principles of polymer science, it is first important to recognize the difference between the crystalline physical state and the amorphous (noncrystalline state). In basic terms, if the polymers in a substance become very ordered, they interact with one another and form a crystalline structure. In amorphous materials, adjacent strands of the polymer do not interact with one another and, therefore, do not crystallize. It is important to understand that the principles of polymer science apply only to amorphous materials. 
     Both synthetic and food polymers often exist in an amorphous or partially amorphous state. These amorphous compounds undergo both glass transition and melting at characteristic temperatures T g  and T m , respectively. When the temperature of the compound is above T g  but below T m , it is easily deformed but is not so liquid-like that it flows, and the compound is considered “rubbery” or leathery. 
     An example of a rubbery material is a food product as it exits an extruder before cooling and drying. At this point in the process, the crystalline starch structure has been destroyed, and the mass is amorphous. When grasped by hand, the product can be easily deformed without fracturing the structure, yet it is sufficiently coherent that it will not flow through one&#39;s fingers. 
     When the temperature of a compound is below T g , it is considered “glassy”. An example of a glassy material is an extruded food product after it has been dried or, in some cases, only cooled. At this point, the structure is amorphous, and when deformed with one&#39;s fingers, the structure fractures. 
     When the temperature of a compound is above T m , its properties are fluid-like, and the compound is considered “melted.” An example of a melted material is extrudate that is heated and plasticized sufficiently to flow through the extruder die. 
     Important changes in the physical properties of polymers occur as they pass through their glass transition temperatures. The most notable changes occur in molecular mobility, viscosity, and elasticity. 
     In the rubbery state, molecular mobility, indicated by the material&#39;s viscosity, is much, much greater than in the glassy state. Therefore, in the rubbery state, viscosity is much, much lower than in the glassy state. For example, the viscosity of a glassy material may be in the range of 10 12  Pa while the corresponding viscosity of the same material in the rubbery state would be several orders of magnitude less. Similarly, several order-of-magnitude differences in viscosity can be seen between the rubbery state (T m &lt;T&lt;T g ) and the melted state (T&gt;T m ). See, Zhang et al., Factors Affecting Expansion of Corn Meals with Poor and Good Expansion Properties,  Cereal Chemistry , Vol. 75, No. 5, (1998); and Strahm, Fundamentals of Polymer Science as an Applied Extrusion Tool,  Cereal Foods World , Vol 43, No. 8, (1998). 
     Devices have been proposed in the past to measure the properties of grain products at or near the pressures and temperatures encountered in high-temperature short-time extrusion, Zhang et al., Capillary Rheometry of Corn Endosperm: Glass Transition, Flow Properties, and Melting of Starch,  Cereal Chemistry , Vol. 75, No. 6, (1998). The Zhang et al. device makes use of a capillary block with opposed, constant volume chambers on opposite sides of the block. Each chamber contained a piston which were moved together through sidebars ensuring that the volume of the chambers remained constant while preventing moisture loss through the atmosphere. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved phase transition analyzer comprising a body having a chamber presenting an open end and adapted to receive a material sample, together with a heating assembly for controllably heating a sample within the chamber and a force-applying assembly operable to apply a compressive force to the sample with the chamber during heating thereof. The force-applying assembly includes a block adjacent the open end of the body which at least substantially closes the chamber to inhibit flow of the sample therefrom. The force-applying assembly is operable to decrease the volume of the chamber in response to changes in the sample arising from heating and application of force thereto. A device is also provided to determine the decrease in volume of the chamber, which is used to denote a material phase change. In preferred forms, a portion of the force-applying assembly is shiftable in response to changes in the sample, and the device determines the shifting of the force-applying assembly portion. 
     In preferred forms, the analyzer body comprises an elongated, tubular member which receives an elongated stationary rod, and the block is coupled with a drive unit for urging the block in a direction to compress the sample between the block and the inner end of the rod. In this way, the material sample is subjected to heating and compaction forces so that, when a phase change occurs, the volume of the sample chamber is decreased and detected. 
     In order to most easily analyze for T g and T m , the block is preferably a shiftable member having a solid or blank portion and a spaced second portion provided with a capillary opening therethrough. In use, a sample is loaded into the chamber, with the latter closed in its first position, and a compressive force is exerted on the sample while the latter is heated at a predetermined rate; when the material reaches its T g , the sample contracts and the chamber volume correspondingly decreases, the latter being detected. Thereafter in order to measure T m , the block is shifted to its second position and the sample is again heated while being subjected to a compressive force. When the T m  is reached, a portion of the sample flows through the block capillary opening, again causing a detectable decrease in chamber volume. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a phase transition analyzer unit in accordance with the invention; 
     FIG. 2 is a perspective view of the analyzer assembly of the unit shown in FIG. 1; 
     FIG. 3 is a is a vertical sectional view of the analyzer shown in FIG. 2, prior to loading of the analyzer with a sample; 
     FIG. 4 is a vertical sectional view similar to that of FIG. 3, but depicting the apparatus at the conclusion of a glass transition temperature analysis; 
     FIG. 5 is a vertical sectional view of the apparatus shown in FIGS. 3 and 4, but depicting the apparatus in its opened, clean-out position; 
     FIG. 6 is a sectional view with parts broken away taken along lines  6 — 6  of FIG.  3 : 
     FIG. 7 is an enlarged, fragmentary sectional view illustrating the first position of the capillary block forming a part of the analyzer; 
     FIG. 8 is a fragmentary sectional view showing the location of one of the load cells of the analyzer; 
     FIG. 9 is an enlarged, fragmentary vertical sectional view illustrating the configuration of the analyzer with a material sample loaded therein and prior to initiation of an analysis cycle; 
     FIG. 10 is a view similar to that of FIG. 9 but showing the analyzer configuration at the time the material sample is heated to its glass transition temperature; 
     FIG. 11 is a view similar to that of FIG. 10, but showing the analyzer configuration during a melt transition analysis; 
     FIG. 12 is a schematic representation of the coolant circulation system used in the preferred phase transition analyzer; and 
     FIG. 13 is a typical displacement/temperature graph generated by the analyzer of the invention to establish the glass transition and melt transition temperatures for a sample. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, a preferred phase transition analyzer unit  20  is illustrated in FIG.  1 . The unit  20  broadly includes an analyzer  22 , cabinetry  24  supporting the latter and having an access door  26 ; the cabinetry  24  also supports a reservoir assembly  28  and a control circuitry housing  30 . The analyzer  22  generally includes a frame assembly  32 , upper and lower chambers  34 ,  36 , a shiftable capillary die block  38 , sample compaction cylinders  40 , chamber separation cylinders  42  and a displacement transducer  44 . 
     In more detail, and referring particularly to FIGS. 2 and 3, the frame assembly  32  includes a base  46  which rests within cabinetry  24 , a pair of upstanding tie rods  48  and  50  secured to the base  46 , as well as a central, upstanding, stationary guide rod  51 . The rod  51  has an upper sealing ring  51   a  and may be equipped with a load cell  51   b . Each of the rods  48 ,  50  has a threaded uppermost end and a stop collar  52 ,  54  below the upper threading. Assembly  32  also includes a top plate  56  having a pair of through bores  58 ,  60  permitting passage of the upper ends of the tie rods  48 ,  50  therethrough; each tie rod is equipped with an uppermost threaded knob  48   a ,  50   a  as shown. The plate  56  also has a threaded bore  62  at the central region thereof, which receives an elongated, threaded stop rod  64  provided with handle  66 . Although not forming a part of the frame assembly, it will be observed that the plate  56  supports an elongated, depending compaction rod  68  with a lower sealing ring  68   a , the rod  68  secured in place via an annular retainer ring  70  attached by screws to the underside of plate  56 . In addition, a load cell  72  is mounted within top plate  56  and has a lead  73  (FIG.  8 ), for purposes to be described. 
     The upper chamber  34  includes an elongated tubular sleeve  74  which receives the lower end of rod  68  and has a lower, transverse thermocouple-receiving opening  75  formed therethrough. The sleeve  74  is supported by a chamber body  76 , made up of bottom wall  78  having a central recess  79 , inner annular wall  80 , outer annular wall  82  and intermediate lateral wall  84 . The outer annular wall  82  is secured to an uppermost apertured crosspiece  86 . Note that the crosspiece  86  is provided with two openings  88 ,  90  therethrough, which are equipped with slide bearings  92 ,  94 ; the tie rods  48 ,  50  extend through the bearings  92 ,  94  so as to support crosspiece  86  and thus the remainder of chamber  34  for reciprocal up and down movement. 
     The upper chamber  34  is equipped with temperature maintenance and control apparatus in the form of an electrical resistance heater rope  96  wrapped about sleeve  74  between the latter and inner annular wall  80 . The lead  98  of the heater rope  96  passes through an opening  100  in wall  82  and is coupled with a conventional power source (not shown). Additional temperature control is provided by virtue of the annular passageway  102  defined between inner and outer annular walls  80 ,  82 . This passageway permits circulation of heating and/or cooling media, and for this purpose the wall  82  is provided with openings  104 ,  106  equipped with fluid inlet and outlet conduits  108 ,  110 . 
     A pair of connection ears  112 ,  114  are secured in opposed relationship to bottom wall  78  of chamber  34 . These ears in effect define lateral projections from the bottom wall  78  and are important for purposes to be described. Also, an elongated lateral bore  107  (FIG. 7) is provided through the bottom wall  78  and is in registry with sleeve opening  75 . 
     Lower chamber  36  is disposed directly below upper chamber  34  and essentially coaxial therewith. The lower chamber  36  has a tubular sleeve  116  which is slidably received on guide rod  51 . The sleeve  116  is coupled with a chamber body  118  made up of an upper wall  120  having a central recess  121 , inner and outer annular walls  122 ,  124 , and intermediate lateral wall  126 . The lower body chamber  36  is secured to a lower crosspiece  128  which is very similar to the crosspiece  86 . Specifically, crosspiece  128  has a pair of apertures  130 ,  132  therethrough with slide bearings  134 ,  136  seated therein. These bearings slidably receive the tie rods  48 ,  50 . 
     The lower chamber  36  has an electrical resistance heater rope  138  coiled about sleeve  116  between the latter and annular wall  122 . The heater rope  138  has a lead  140  which passes through opening  142  in wall  18  to afford a power connection. Additional temperature maintenance and control is provided by annular passageway  144  defined between inner and outer walls  122 ,  124 . As in the case of the passageway  102  of the upper chamber, appropriate inlet and outlet openings and conduits are provided to permit circulation of heating and/or cooling medium through the passageway  144 . 
     The capillary die block  38  (see FIG. 6) is in the form of an elongated, rectangular in cross-section block  146  having an outer manipulation handle  148 . The block  146  has a pair of spaced apart upper sealing rings  150 ,  150   a , as well as a lower sealing ring  151 , and is designed to fit between the upper and lower chambers  34 ,  36  within the mated recesses  79 ,  121  of the latter. In this orientation, the upper surface of the block  146  engages the butt end of upper sleeve  74 . Similarly, the lower face of block  146  directly engages the upper butt end of sleeve  116 . The side face of block  146  has a pair of spaced apart detent openings  152 ,  154  therein which mate with a spring loaded detent  156  provided in bottom wall  78  of upper chamber  34  (see FIG.  6 ). 
     The block  146  presents two operative segments which can be alternately positioned between the sleeves  74 ,  116  as will be described. The first segment  158  (FIG. 7) is a “blank” segment, meaning that it has no opening therethrough, with the sealing ring  150  surrounding this segment. The second segment  160  on the other hand is provided with a narrow capillary passage  162 , and has upper and lower sealing rings  150   a  and  151  disposed about this second segment. 
     The sample compaction cylinders  40  are in the form of conventional pneumatic pancake cylinders  164 ,  166  secured to the upper face of base  46 . Each of the cylinders  164 ,  166  includes an extensible piston rod  168 ,  170  connected to crosspiece  128 . 
     The chamber separation cylinders  42  are also pneumatically activated and include upright cylinders  172 ,  174  secured to crosspiece  128  on opposite sides of lower chamber  36  and having extensible rods  176 ,  178 . As illustrated in FIGS. 3 and 6, the rods  176 ,  178  are respectively secured to the ears  112 ,  114 . 
     The displacement transducer  44  comprises an elongated transducer body  180  having lead  180   a  and secured to tie rod  48  by way of couplers  181  and having a depending, shiftable probe  182 . The lower end of probe  182  has a radially enlarged engagement element  184  which rests atop crosspiece  128 . 
     In preferred operation, the analyzer  22  is provided with a fluid cooling medium which is circulated through the annular passageways  102  and  144 . To this end (FIG.  12 ), a supply of such coolant is located within reservoir or supply  28  and is connected via conventional valving  186  and conduit system  188  to the input and output conduits  108 ,  110  associated with the upper and lower chambers  34 ,  36 . An overflow reservoir  190  is also a part of the coolant circuit, together with return and overflow ports as shown. 
     FIG. 3 illustrates analyzer  22  where blank block segment  158  is positioned beneath sleeve  74 . In this orientation, it will be observed that a sample chamber  192  is defined by the annular sidewall of sleeve  74 , the lower surface of rod  68  and the upper surface of block  146 , specifically the surface of first segment  158 . This closed chamber  192  is sealed by virtue of the engagement of sealing ring  158  with the butt lower end of sleeve  74 . 
     The analyzer unit  20  is especially designed for measurement of glass transition and melt transition temperatures T g  and T m  of a selected composition such as an extrudable mixture. In setting up the analyzer unit, a personal computer loaded with the appropriate control software is operatively coupled with the conventional electronics located within circuitry housing  30 . Also, the analyzer  22  is opened to permit loading of a material sample  196  within the sleeve  74 . This is accomplished by first detaching the knobs  48   a ,  50   a  from the tie rods  48 ,  50  and removing top plate  56  from the analyzer. 
     The first segment  158  of block  38  is positioned within the recesses  79 ,  121  in blocking relationship to the open lower end of sleeve  74 . The sample  196  (e.g., 1.5 g) of the mixture to be analyzed is then placed within the sleeve  74  so that it rests atop the upper surface of the segment  158 . Next, the top plate  56  is reinstalled, by telescoping rod  68  into sleeve  74  and passing the tie rods  48 ,  50  through the top plate bores  58 ,  60 . Rod  64  is also adjusted to define the upper limit of travel of the chambers  34 ,  36 . FIG. 9 illustrates the apparatus in this initial state. The necessary sensors including load cell  72  and transducer  180 , and a thermocouple  194  (which is positioned within the bore  109  and opening  75  as best seen in FIG.  7 ), are coupled with the control electronics in housing  20 . 
     In order to measure the T g  of the sample, the pancake cylinders  164 ,  166  are actuated to extend the rods  168 ,  170  as shown in FIG.  4 . This serves to elevate crosspieces  128  and  86 , causing the upper and lower chambers  34 ,  36  to move upwardly relative to stationary rod  68 . As a consequence, a compressive force is exerted on the sample within chamber  192  by an assembly comprising cylinders  40 , crosspiece  128 , lower chamber  34 , upper chamber  36 , block  38  and rod  68 . Preferably, during the glass transition analysis the force exerted on the sample is at a predetermined constant level. During such application of force, the heating assembly including the resistance heaters  96 ,  138  is actuated to heat the sample at a controlled rate, for example 10° C. per minute. As the sample  196  softens and moves through its glass transition stage, it compacts to a smaller volume sample  196   a  depicted in FIG.  10 . This compaction and the resultant decrease in volume of the chamber  192  is sensed by the transducer  44 . In particular, as the volume of chamber  192  decreases as a consequence of the material moving through its glass transition stage, the crosspiece  128  moves upwardly, thereby shifting probe  182  upwardly. This movement of the transducer probe signals that the glass transition temperature has been reached. 
     If it is then desired to measure the melt transition temperature of the sample  196 , the following steps are followed. First, the resistant heating elements  96 ,  138  are shut down and coolant is circulated through the passageways  102 ,  144  in order to cool the sample. Also, the separation cylinders  42  are actuated to very slightly move upper chamber  34  relative to lower section  36 . This allows sliding movement of the block  38 , which is accomplished manually by grasping handle  148  and pushing the block  146  against the bias of detent  156 , until the bar is moved past detent opening  152  and seats within opening  154 . In this orientation, the second segment  160  is positioned between the sleeves  74  and  116  as illustrated in FIG.  11 . The cylinders  42  are then retracted to securely lock the bar  149  in place. At this point, circulation of cooling fluid is stopped and the heating elements are reactivated so as to increase the sample temperature at a controlled rate, again typically 10° C. per minute. This is continued until the sample  196   a  is sufficiently melted to permit flow of sample through the capillary opening  162  and into the open space below block  146 . Again, this results in a further decrease in the volume of sample chamber  192 , this being detected by upward movement of the crosspiece  128  by transducer  44 . 
     While this general procedure is followed to determine T g  and T m , it is subject to many variations. Thus, it may be desirable to initially compact the sample  196  within chamber  192  (e.g. to 100 bars) to a point where the first controlled heating step to determine T g  is initiated. The illustrative times and temperature rates given above can also be varied over a wide range, principally dependent upon the type of sample being measured. 
     FIG. 13 depicts a typical graph developed using the analyzer unit  20 . Displacement is tracked as the sample is heated, with glass transition indicated by sample compaction and resultant decrease in the volume of sample chamber  192 . The glass transition usually occurs over a temperature range as show, T g  initial and T g  end. The melt transition T m , occurring when the sample flows through capillary opening  162  (FIG. 11) is also tracked by the displacement transducer  180 . 
     The unit  20  is also capable of further analyses. If it is desired to measure sample viscosity, use can be made of optional lower load cell  51   b  below rod  51 . In such analyses, after passage through the capillary opening  162 , the material is collected within the lower secondary chamber between the upper end of rod  51  and the lower surface of block  146 . 
     FIG. 5 illustrates the configuration of the analyzer  22  in the fully opened, cleanup position. In this case, the knobs  48   a ,  50   a  are removed, and top plate  56  is slid off the tie rods  48 ,  50 . The cylinders  42  are then operated to extend rods  176 ,  178  to their maximum extent which fully separates the chambers  34  and  36 . This allows removal of block  38  and access to the components of the analyzer  22  for cleanup and repair. 
     The preferred control software resident on the personal computer (not shown) coupled with the unit  20  is presented in the source code appendix incorporated by reference herein. 
     All documents cited are incorporated by reference herein.