CHARACTERISTICS of CR39

The CR39 plastic is made by polymerization of the dietilenglycol bis allylcarbonate (ADC). The monomer is an allyl resin containing the following functional group [1]:

                      [ CH2 = CH - CH2 - ].

The monomer itself contains two of these functional groups and has the following structure:

                               O
                               ||
               CH2 - CH2 - O - C - O - CH2 - CH = CH2
              /    
             O                 O
              \                ||
               CH2 - CH2 - O - C - O - CH2 - CH = CH2.

Because of the presence of the two allyl functional groups, the monomer can not only polymerize but also cross-link which results in a thermoset plastic characterized by being hard, infusible and insoluble in all solvents. In addition, CR39 homopolymer is a high-grade optical plastic whose index of refraction is just slightly less than that of crown glass.

The monomer is polymerized by adding a few percent of the catalyst diisopropyl peroxydicarbonate (IPP) to the monomer, and then heating.

CR39 is a transparent, thermosetting resin which combines an exceptional range of qualities which are not available in other plastic transparent material.

The CR39 plastic sheets :

• are colorless and completely transparent to the visible light and almost completely opaque in infrared and ultraviolet region of the spectrum. For these reasons, it is largely used for the production of sun glass lenses. They can be coloured by surface dyeing or bulk tinting;
• have high abrasion resistance and high-quality optical properties;
• weigh about half as much as glass;
• keep their excellent optical properties despite long-term exposure to chemicals like solvents, highly oxidizing acids, and strong basis;
• resist to heat distortion up to 100 ° C and are resistant to small hot flying particles such as welding sparks.

These qualities combined with the exceptional optical characteristics, make CR39 the best choise for applications where severe conditions of use exclude all other optical materials.

The following table summarizes the main properties of INTERCAST ADC sheets compared to the most popular transparent materials.

PROPERTIES                       GLASS  PC¹   PMMA²   CR39
  __________________________________________________________________________

Superior optical quality         YES     NO    NO     YES
Lightness and strength           NO      YES   YES    YES
Scratch resistant                YES     NO    NO     YES
Stress cracking resistant        NO      NO    NO     YES
Solvents and chemical resistant  YES     NO    NO     YES
Welding sparks resistant         NO      YES   NO     YES
Plasticizer migration resistant  YES     NO    NO     YES
Ageing resistant                 YES     NO    NO     YES
Gamma radiation resistant        YES     NO    NO     YES
Wide range of colour             NO      YES   YES    YES
Wide range of U. V. absorbtion   NO      YES   NO     YES
  __________________________________________________________________________
¹PC: Aromatic Polycarbonate
²PMMA: Polymethyl methacrylate

   The main properties of polymerized ADC are listed as follows:

SPECIFIC WEIGHT  at 25° C        :    1,32 g/cm³
REFRACTIVE INDEX at 20° C        :    1,501 
TRANSMITTANCE (thickness mm 6,3) :    89-92 %
ROCKWELL HARDNESS                :    M95-M100
ABRASION RESISTANCE (grinding)
   Taber test                   (Methyl metacrylate)  30-40
   Modified test (falling sand) (Methyl metacrylate)   9-12

FLEXURAL MODULUS kg/mm2
        at 50° C: 112-140
        at 25° C: 185-235
        at 10° C: 305-325
        at 57° C: 390

TRACTION RESISTANCE kg/mm2       :    3,5-4,2
        Tensile Modulus          :      210

COMPRESSION RESISTANCE kg/mm2    :      15,8
        Compressive Modulus      :      210

        IMPACT RESISTANCE
        IZOD test (ft. lb/in2)
        notched                  :    0,2-0,4
        unnotched                :     2-3

MAXIMUM TEMPERATURE RECOMMENDED ( no-load operating )
        continuous service           :  100° C
        one time, one hour duration  :  130° C

SPECIFIC HEAT cal./g.° C         :   0,55

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REFERENCES
[1] R. M. Cassou et al., Properties and applications of CR39 polymeric nuclear track detector, Nucl. Track Detection 2 (1978) 173.

For information : intercast@relay1.it.net

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