which is measured by means of a transducer. The polymer sample is placed in the space between the cone and plate and the torque experienced by the stationary cone is measured for different rotational speeds of the plate. Relating the shear stress at the cone surface to the measured torque and the shear rate to the angular velocity of the plate, the expression for the viscosity (h) is obtained as h Z 3Kq sin a 2pR 3 p u ð3:114Þ where K is the torsional constant and q is the deflection of the spring; R p is the radius and u is the angular velocity of the plate; and a is the angle of the cone. While q and u are experimentally determined quantities, K and a are obtained by calibration on other materials. The cone and plate viscometer gives reliable experimental data over an extensive range of shear rates (10 –4 –10 4 sec K1 ). Not only can it be used to measure viscosities in simple shear, but it can also be used to determine the dynamic properties of viscoelastic materials. The unit is also set up to measure the normal stresses exhibited by viscoelastics, i.e., those perpendicular to the plane of shear. 3.2.17.2 Capillary Rheometers These rheometers are widely used to study the rheological behavior of molten polymers. As shown in Figure 3.35 the fluid is forced from a reservoir into and through a fine-bore tube, or capillary, by either mechanical or pneumatic means. The fluid is maintained at isothermal conditions by electrical temperature control methods. Either the extrusion pressure or volumetric flow rate can be controlled as the independent variable with the other being the measured dependent variable. Under steady flow and isothermal conditions for an incompressible fluid (assuming only axial flow and no slip at the wall), the viscous force resisting the motion of a column of fluid in the capillary is equal to the applied force tending to move the column in the direction of flow. Thus, t Z RDP 2L ð3:115Þ where R and L are the radius and length of the column and DP is the pressure drop across the capillary. The shear stress t is therefore zero at the center of the capillary and increases to a maximum value at the capillary wall. This maximum value is the one generally used for the shear stress in capillary flow. Air bearing Transducer Transducer Amplifiers Recorders Torsional spring Constant speed motor Gear assembly Bearing FIGURE 3.34 Scheme of a Weissenberg Rheogoniometer. 3-44 Plastics Technology Handbook q 2006 by Taylor & Francis Group, LLC which is measured by means of a transducer. The polymer sample is placed in the space between the cone and plate and the torque experienced by the stationary cone is measured for different rotational speeds of the plate. Relating the shear stress at the cone surface to the measured torque and the shear rate to the angular velocity of the plate, the expression for the viscosity (h) is obtained as h Z 3Kq sin a 2pR 3 p u ð3:114Þ where K is the torsional constant and q is the deflection of the spring; R p is the radius and u is the angular velocity of the plate; and a is the angle of the cone. While q and u are experimentally determined quantities, K and a are obtained by calibration on other materials. The cone and plate viscometer gives reliable experimental data over an extensive range of shear rates (10 –4 –10 4 sec K1 ). Not only can it be used to measure viscosities in simple shear, but it can also be used to determine the dynamic properties of viscoelastic materials. The unit is also set up to measure the normal stresses exhibited by viscoelastics, i.e., those perpendicular to the plane of shear. 3.2.17.2 Capillary Rheometers These rheometers are widely used to study the rheological behavior of molten polymers. As shown in Figure 3.35 the fluid is forced from a reservoir into and through a fine-bore tube, or capillary, by either mechanical or pneumatic means. The fluid is maintained at isothermal conditions by electrical temperature control methods. Either the extrusion pressure or volumetric flow rate can be controlled as the independent variable with the other being the measured dependent variable. Under steady flow and isothermal conditions for an incompressible fluid (assuming only axial flow and no slip at the wall), the viscous force resisting the motion of a column of fluid in the capillary is equal to the applied force tending to move the column in the direction of flow. Thus, t Z RDP 2L ð3:115Þ where R and L are the radius and length of the column and DP is the pressure drop across the capillary. The shear stress t is therefore zero at the center of the capillary and increases to a maximum value at the capillary wall. This maximum value is the one generally used for the shear stress in capillary flow. Air bearing Transducer Transducer Amplifiers Recorders Torsional spring Constant speed motor Gear assembly Bearing FIGURE 3.34 Scheme of a Weissenberg Rheogoniometer. 3-44 Plastics Technology Handbook q 2006 by Taylor & Francis Group, LLC Wide-angle light scatter Light source Light source Light trap Light trap absorbs all light scattered by film less than 2½° After T 1 is determined the sphere is rotated to measure T 2 Photocell collecting all transmitted light reflected Photocell collecting all wide- angle transmitted light scattered by film more than 2½° (T 2 ) (T 1 ) Film sample Film sample Reflecting sphere Reflecting sphere Film Object FIGURE 3.86 Test for haze of transparent plastics. Haze, %Z100!T 2 /T 1 . A low haze value is important for good short distance vision. Standard test method: ASTM D1003. Narrow-angle light scatter Film Object Light source Light stop Annular photocell collecting light greater than that at ½° to normal = T 1 Less than ½° to normal = T 2 ½° FIGURE 3.87 Measurement of narrow-angle light-scattering property of plastic film. Clarity, %Z100!T 1 /(T 1 CT 2 ). 3-94 Plastics Technology Handbook q 2006 by Taylor & Francis Group, LLC TABLE 3.8 Heating Tests of Some Common Polymers Polymer Color of Flame Odor of Vapor Other Notable Points The material burns but self-extinguishes on removal from flame Poly(vinyl chloride) Yellow–orange, green bordered Resembles hydrochloric acid and plasticizer (usually ester like) Strongly acidic fumes (HCl), black residue Poly(vinylidene chloride) As above Resembles hydrochloric acid As above Polychloroprene Yellow, smoky As above As above Phenol-formaldehyde resin Yellow, smoky Phenol, formaldehyde Very difficult to ignite, vapor reaction neutral Melamine- formaldehyde resin Pale yellow, light Ammonia, amines (typically fish like), formaldehyde Very difficult to ignite, vapor reaction alkaline Urea-formaldehyde resin As above As above As above Nylons Yellow–orange, blue edge Resembling burnt hair Melts sharply to clear, flowing liquid; melt can be drawn into a fiber; vapor reaction alkaline Polycarbonate Luminous, sooty Phenolic Melts and chars Chlorinated rubber Yellow, green bordered Acrid Strongly acidic fumes, liberation of HCl; swollen, black residue The material burns and continues burning on removal from flame Polybutadiene (BR) Yellow, blue base, smoky Disagreeable, sweet Chars readily; vapor reaction neutral Polyisoprene (NR, gutta percha, synthetic) Yellow, sooty Pungent, disagreeable, like burnt rubber As above Styrene-butadiene rubber (SBR) Yellow, sooty Pungent, fruity smell of styrene As above Nitrile rubber (NBR) Yellow, sooty Like burnt rubber/ burnt hair As above Butyl rubber (IIR) Practically smoke free candle like Slightly like burnt paper Melt does not char readily Polysulfide rubber (polymer itself emits unpleasant, mercaptan like odor) Smoke-free, bluish Pungent; smell of H 2 S Yellow, acidic (SO2) fumes Cellulose (cotton, cellophane, viscose rayon, etc.) Yellow Burnt paper Chars, burns without melting Cellulose acetate Yellow–green, sparks Acetic acid, burnt paper Melts, drips, burns rapidly, chars, acidic fumes Cellulose acetate butyrate Dark yellow (edges slightly blue), somewhat sooty, sparks Acetic acid/butyric acid, burnt paper Melts and forms drops which continue burning Cellulose nitrate (plasticized with camphor) Yellow Camphor Burns very fast, often with explosion Methyl cellulose Yellow, luminous Burnt paper Melts and chars Ehtyl cellulose Pale yellow with blue–green base Slightly sweet, burnt paper Melts and chars Polyacrylonitrile Yellow Resembling burnt hair Dark residue; vapor reaction alkaline Poly(vinyl acetate) Yellow, luminous, sooty Acetic acid Sticky residue, acidic vapor Poly(vinyl alcohol) Luminous, limited smoky Unpleasant, charry smell Burns in flame, self extinguishing slowly on removal; black residue (continued) 3-98 Plastics Technology Handbook q 2006 by Taylor & Francis Group, LLC . 3 .87 Measurement of narrow-angle light-scattering property of plastic film. Clarity, %Z100!T 1 /(T 1 CT 2 ). 3-94 Plastics Technology Handbook q 2006 by Taylor & Francis Group, LLC TABLE 3 .8. smell Burns in flame, self extinguishing slowly on removal; black residue (continued) 3- 98 Plastics Technology Handbook q 2006 by Taylor & Francis Group, LLC . flow. Air bearing Transducer Transducer Amplifiers Recorders Torsional spring Constant speed motor Gear assembly Bearing FIGURE 3.34 Scheme of a Weissenberg Rheogoniometer. 3-44 Plastics Technology Handbook q 2006 by Taylor & Francis Group, LLC which is measured by means of a transducer.