Birefiingent materials

It was during the 19th century that Nageli developed a theory to deal with the birefiingent materials in plant cells and starch grains. This theory introduced the concept of crystalline micelles having submicroscopic dimensions. This, in turn, led to the proposal that crystalline micelles were separate, well-defined entities, stacked like bricks whose length coincided with the axis of the constituent cellulose molecules. In order to take account of the amorphous content of cellulose, the idea of... 

The birefiingence of a material is expressed by the anisotropic dielectric tensor at optical frequency, or the refractive index tensor which is the square root of i.e.. 

The fiber diameter distribution was studied by microscopy (optical microscope, Hitachi TM-1000 scanning electron microscope). Fiber orientation was studied by using birefiingence and polarization IR-spectroscopy (SPECORD M 80 IR-spectrometer). Crystalline phase of polymer was studied by differential scanning calorimetry (DSC) (differential scanning calorimeter). The packing density of fibrous materials was calculated as a function of airflow resistance variation with a special manometric pressure unit [8],... 

The plastic material is usually extended in the melt flow direction when it is injected in a mold. The molecular orientation and thermal stress freezes when the mold temperature goes below the matoial glass transition tenqrerature. The residual stress in the molded part is a critical issue causing part warp and birefiingence, which significantly reduces the yield rate for part production. 

The birefiingence is the decomposition of a ray of light into two rays, the ordinary and the extraordinary rays, when it passes through anisotropic plastic materials, depaiding on the polarization of the light. The birefiingence can be measured by measuring... 

ASTM D4093-95 (2005), Standard Test Method for Photoelasric Measurements of Birefiingence and Residual Strains in Transparent or Translucent Plastic Materials , ASTM International, (2005). 

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