Discoloration Resistant Polyolefin Films

Abstract

The preservation of physical properties and aesthetics are two important aspects of the film industry. As such, forethought and care need to be taken in terms of the type of polymer and stabilization systems that are used to derive robust and attractive film products. For most applications, a combination of a phenolic antioxidant and a phosphite melt processing stabilizer can provide the base stabilization that is necessary to provide the retention of physical properties, good processability, long term thermal stability without compromising the overall aesthetic appearance of the film product. However, in selected end-use applications, it is very desirable to have film products that do not discolor during initial processing or while the product is kept in storage. Under a selected set of circumstances, certain types of phenolics have been shown to be susceptible to discoloration, either due to inadequate stabilizer concentrations, harsh processing conditions, ionizing radiation, prolonged storage of the films in an environment containing oxides of nitrogen (pollution), or a combination of these factors. Approaches to eliminate discoloration, by using “phenol” and “phenol-free” stabilization systems will be discussed. “Phenol-free” stabilization systems are recommended for color critical polyolefin film applications.

Keywords

antioxidants heat stabilizers stabilization melt processing stabilizers phenolic phosphite HDPE LLDPE PP blown film cast film TiO2 oven aging gas fade aging oxidative induction time color retention yellowness index hydroxylamines polyolefins lactones hindered amines NOx molecular weight molecular weight distribution free radicals arylbenzofuranones UV stabilization

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References

1. King III, R.E. (2000). Low Color Stabilization Systems for Polyolefins, SPE Color and Appearance RETEC, Washington DC.

2. King III, R.E. (August 1998). “Phenol” and “Phenol-free” Stabilization of High Density Polyethylene, TAPPI Polymers, Laminations and Coatings Conference Proceedings, San Francisco, pp. 1201-1218.

3. Horsey, D. (February 1996). Additives `96, Houston.

4. King III, R.E. (August 1999). Stabilization of Gamma Irradiated High Density Polyethylene, TAPPI Polymers, Laminations and Coatings Conference Proceedings, Atlanta, pp. 1047-1063.

5. King III, R.E. (2001). Recent Advances in the Phenol-free Stabilization of Polypropylene Fiber, Proceedings SPE Polyolefins RETEC 2001, Houston, pp. 501-520.

6. Solera, P. (2000). Recent Advances in the Stabilization of Polymers for Automotive and Construction Applications, 4th International Symposium on Weatherability, Japan.

7. King, R.E. (February 1999). Stabilization of a Clarified Gamma Irradiated Controlled Rheology Polypropylene Random Copolymer, Proceedings SPE Polyolefins RETEC Conference, Houston, pp. 479-504.

8. In regard to the unexpected discoloration with binary blends of hindered amine and hydroxylamine, we were initially tempted to associate the color with the generation of N-O• (from the oxidation of the hindered amine during melt processing). However, it was difficult to come up with a definitive set of experiments that would allow for confirmation of this hypothesis. Our initial ESR work was not definitive, and we learned that whatever the color body is, it seems to be something that cannot be easily characterized by traditional wet method analytical techniques. We are currently working with an improved ESR instrument/software to see if we can characterize some type of free radical that may be associated with color. We have been successful in generating characterizable N-O• functional group during long term oven aging experiments[2]. We are still struggling with the lower concentrations that are generated during short term melt processing experiments.

9. Pauquet, J.R. , Todesco, R.V. and Drake, W.O. (November 1993). Limitations and Applications of Oxidative Induction Time (OIT) to Quality Control of Polyolefins, 42nd International Wire & Cable Symposium.

10.

10. Samuels, S.B. , Steele, T.P. and Wagner, A.H. (1995). Gas Fading, on Paper and in Practice, SPE Polyolefins RETEC 1995 Proceedings, Houston, pp. 671-686.

11.

11. Gugumus, F. (1990). Plastic Additives, Chapter 1; 3rd edn.,Hanser Publisher, New York,

12.

12. Moss, S. , Pauquet, J-R. and Zweifel, H. (1991). Degradation and Stabilization of Polyolefins During Melt Processing, Patsis, A. (ed.), International Conference on Advances in the Stabilization & Degradation of Polymers, Lucerne 1991.

13.

13. Zweifel, H. and Moss, S. (1989). Degradation and Stabilization of High Density Polyethylene during Multiple Extrusion, Polymer Degradation and Stability, 25: 217-245.

14.

14. Drake, W.O. and Cooper, K.D. (February 1993). Recent Advances in Processing Stabilization of Polyolefins, SPE Polyolefins VIII International Conf., Houston.

15.

15. Cooper, K.D. (1995). A New Melt Processing Stabilizer for Polyolefins”, SPE Polyolefins RETEC 1995 Proceedings, Houston, pp. 653-669.

16.

16. Smith, P.A. and Gloyer, S.E. (1975). J. Org. Chem., 40: 2508-2512.

17.

17. DeLaMare, H.E. and Coppinger, G.M. (1963). J. Org. Chem., 28: 1068-1070.

18.

18. Nesvadba, P. and Kröhnke, C. (February 1997). A New Class of Highly Active Phosphorus Free Processing Stabilizers for Polymers, Additives 97, 6th International Conference, New Orleans.

19.

19. Kröhnke, C. (February 1997). A Major Breakthrough in Polymer Stabilization, Polyolefins X Conference, Houston.

20.

20. Pauquet, J.R. and Zingg, J. (December 1995). Improving Polyethylene Processing Stability with Novel Synergistic Blends, Specialty Plastics 95, 11th Annual World Congress, Zürich.

21.

21. Pauquet, J.R. , King, R. and Kröhnke, C. (May 1997). Revolutionary Stabilizer Systems for Polyethylene, Polyethylene `97 Maack Conference, Milan.