The Universal Selection Source: Plastics & Elastomers

UV Stabilizers for Engineering Plastics

Engineering plastics like polyamides, polyesters, polycarbonates are majorly used for applications that demand long time U.V stabilization. This selection guide mainly deals with the query "which UV Stabilizer is ideal for which plastic"? This guide will familiarize you with various UV stabilizers used with these engineering plastics. You would be able to find out the functionalities of different UV stabilizers for different engineering plastics in demand. Also one can find the starting point formulations of polycarbonates, polyacetal polyoxymethylene, polyesters like PET & PBT and polyamides.

UV Stabilizers for Polycarbonate (PC)

  • Polycarbonate (PC) is one of the most versatile and widely used thermoplastic.
  • Polycarbonate show excellent mechanical properties and are thermally stable upto 135°C.
  • Polycarbonate is primarily used in applications where high impact resistance and transparency and UV resistance are required.
  • Typical examples are windows for transportation vehicles, globes for streetlights, extruded lighting canopy, etc.
  • Exposure of PC to UV light leads to surface degradation. This in turn affects various properties of the polymer, particularly impact strength and clarity (yellowing).
  • To reduce yellowing and loss of mechanical properties, in exterior applications, protection of polycarbonate/ stabilization of Polycarbonate becomes mandatory.

UV Stabilizers for Polycarbonate injection molded grades

  Light stability Discoloration Tensile elongation volatility Impact on formulation costs
1                
2                
3                

UV exposure of stabilized Polycarbonate leads first to a decrease in discoloration. The time to reach the original yellow shade again (yellowing induction time) is a function of the nature and the concentration of the additive.

HALS in PolycarbonateThe best performance is achieved with ultraviolet light absorbers (UV Absorber) of the hydroxyphenyl-benzotriazole class. Similar conclusions are reached if test elongation is the test criterion. Usually choosing the right benzotriazoles depends on the application. For extrusion of plates and profiles, low volatility is required to minimize deposits of the light stabilizer on chill rolls and gauging rolls. High molecular weight UV Absorbers of the hydroxyphenyl-benzotriazole class are therefore recommended.

It needs to be pointed out that hindered amine light stabilizers (HALS) are not recommended in Polycarbonate because these basic amine compounds accelerate Polycarbonate hydrolysis.

Injection molded Polycarbonate grade Starting point formulation

Applicable type: 2 mm injection molded grades

Applicable base polymer: polycarbonate

Applicable industrial sectors: globe lights fixtures

Ingredients
Parts by weight
Polycarbonate polymer
99.43%
Processing stabilizer PS
0.07%
High Mw UV Absorber of the hydroxyphenyl- benzotriazole class
0.5%

UV Stabilizers for Polycarbonate coextruded grade

Light stability
Discoloration
Prevention of cracks
Volatility
Impact on formulation costs
No stabilizers
-
-
(o)
+++++
High Mw UV Absorber of hydroxy phenyl-benzotriazole class
+++
++
++++
++
UV Absorber of hydroxyphenyl- triazine class
+++++
+++++
+++++
+

Weatherable polycarbonate sheet can be produced by coextruding a cap layer containing a UV absorber over a minimally stabilized bulk layer. Stabilization of thin Polycarbonate grades is difficult because protection by UV absorption is related to sample thickness and absorber concentration according to the Lambert-Beer law. Nevertheless, it is possible to achieve good UV protection by using hydroxyphenyl-triazine type UV absorbers which are significantly more efficient than benzotriazole type UV absorbers. The product provides superior long term weatherability because of its strong UV absorbance and its excellent photostability. It is also relatively nonvolatile and has only a minimal effect on melt viscosity. High concentrations of UV Absorbers are recommended in thin films formed on top of Polycarbonate by coextrusion.


Coextruded Polycarbonate twin wall grade / Starting point formulation

Applicable type: coextruded layer thickness 25 microns, Polycarbonate sheet 10mm sheet

Applicable base polymer: polycarbonate

Applicable industrial sectors: coextruded Polycarbonate twin wall sheet

Ingredients

Parts by weight

 Polycarbonate film

93 %

 UV Absorber of  hydroxyphenyl-triazine  class

7.0%

Resirene CET
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