Crazed Celluloid


Antonios Zavaliangos
Professor
Dept. Materials Science and Engineering Drexel University

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Some of us enjoy studying and understanding failures.
One of the most interesting problems in plastics is the problem of crazing. Usually observed in transparent (amorphous) plastics as a network of tiny cracks, it can also occur in translucent or opaque plastics (in the latter it is difficult to observe until the end).

 


An example of a crazed transparent section is shown in the photo below.

      
       
  A craze starts as a microscopic crack that appears when the material is under tension due to residual stresses from processing, assembly or stresses from usage. In plastics it is often helped by the action of the environment (ESC=environmental stress cracking) - a solvant is wicked into the surface and facilitates/accelates crazing cracks.      
         
         
  The photo below shows a high resolution microscopy photograph of a crazing crack (1 micron is about 50 times smaller than a hair diameter). The crack surfaces are connected with fibrils - i.e. groups of polymer chains that run across the crack and have not yet been broken.      
 
     
         
         
  The photo below shows a image of the plastic surface after the crack have linked up and have gone through the material.