Additive Blends in Polymers

Quantitative polymer/additive analysis is particularly troublesome in case of additive blends. For production control of Irganox B220 (a nominally 3 1 blend of Irgafos 168 and Irganox 1010) in PE in 1993 a series of samples in the concentration range of 

500-2500 ppm were prepared for calibration purposes using XRF (P analysis), cfr. Table 6.9. The results were subsequently corroborated with independent ICP measurements on different samples (Table 6.10 = 0.9983 for ICP/XRF relationship). 

A PE/Irganox B220 control sample was also measured daily for Statistical Process Control (SPC) over a 4 year period with a variation coefficient 

Three major error sources may be indicated the inaccuracy in the determination of the P content, the variability in the blend composition (at macro or micro level) and the stability of the standards. Irganox B220/B225 blend analysis based merely on P analysis (with XRF) translates a 5 ppm uncertainty 

As an alternative tool for production control, various spectroscopic methods for blend analysis have been evaluated. Determination of Irganox B220 in PE by means of IR lacks sensitivity and NIRS is rather inaccurate at low additive levels. As shown in Chp. 6.4.1, UV spectrophotometry is the most promising method as Xmax for Irganox 1010, Irgafos 168 and the main degradation products are rather similar. 

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