Analysis of Aging Behavior of PP and Modified PP by RTIR Method

【Abstract】The FTIR infrared spectroscopy method was used to analyze the changes of the PP group and the modified PP at the time of aging （the most important is the infrared absorption peak of the carbonyl compound）.The change of the PP carbonyl index was also known.We can understand the process of light and oxygen aging and the mechanism of light stabilizer on PP.After accelerated aging，it was found that the carbonyl index of pure PP increased with the increasing of aging time.The carbonyl index of modified PP after adding HALS was relatively small，and the change range was small，and the anti-aging effect was obvious.

【Key words】PP；HALS；FTIR；Carbonyl Index

0 Introduction

In the process of the using PP products will produce such as peroxide，carbonyl compounds and unsaturated double bonds[1].These Compounds will make the PP occurring photo-oxygen aging reaction.It will make the PP products turn yellow，brittle，surface cracks and other phenomena[2].The more serious result are making the PP products in decreased of tensile strength，impact strength and other performance degradation，loss of using value.

HALS is a new type of high efficiency light stabilizer.It can through the purpose of capturing the active free radicals in polypropylene， quenching singlet hydrogen，and breaking down the hydrogen peroxide to achieve a unique light stabilization[3]，and the annual average demand growth rate was 20%-30% in the international.

FTIR technology is an important analytical method in the field of analysis，and plays an important role in many fields[4].

1 Experiment

1.1 Materials

The F401 of polypropylene is provided by the China Petrochemical Yangzi Petrochemical limited company；Hindered amine light stabilizer 783 is commercially available.

1.2 Sample Preparation

Sample selection group A：pure PP and group B：adding 0.4% HALS modified PP.Accurately weighed PP，HALS783 raw materials in turn add to the mixer，and running 20min；until the materials are fully melt mixed and removed，placed in hot press and pressed flat into a plate；and then the plate-like sample cut into strips Granulation on the pelletizer；the cut granular material is put into the drying oven for 4 hours， and then put into the injection molding machine，injection into a standard sample.

1.3 Performance Testing

1）Xenon lamp aging： put the standard sample into the xenon lamp accelerated aging test chamber，aging time 168h，336h，504h，672h，the experimental environment for the air atmosphere，temperature 55℃， humidity 43%，light source distance sample 10cm，Xenon lamp wavelength of 290nm-800nm，xenon lamp power 1800W，power density 1.10W/m2.

2）FTIR analysis

Infrared spectroscopy was used to carry out infrared test on the PP samples before and after aging.The detector was ID-1，the detection range was 4000cm-1-500cm-1，the scanning times were 16 times and the resolution was 4cm-1.

2 Results and discussion

2.1 Infrared spectroscopy analysis

The formula for the calculation of the carbonyl index is shown in Equation 1-1，which is the ratio of the relative area of the carbonyl absorption peak to the relative area of the internal standard peak[1].

In the above formula，CI is the carbonyl index；Ac=o is the peak area of the carbonyl absorption peak（1725cm-1）；Acon is a peak （internal standard peak） in which the polymer material does not change significantly during the photooxidation process Peak area，PP internal standard peak is usually selected 2720cm-1 at the peak.

Fig.1 Infrared spectra of pure pp after aging at different time

Fig.2 Infrared spectra of modified pp after aging at different times

It can be seen from Fig.1 that the width and height of the absorption peak of pure PP at 1650cm-1-1770cm-1 has increasing with the increase of aging time，which indicates that the concentration of carbonyl in the pure PP sample varies with the aging time extended and increased.It can be seen from Figure 2，after aging，the infrared spectroscopy with B samples at 1700cm-1-1780cm-1 also appeared in the absorption peak，but different aging time corresponding to the absorption（下轉第171页） （上接第209页）peak width and height change is not large，which shows After adding HALS，the anti-aging properties of modified PP were improved to some extent.

2.2 Carbonyl index

Tab.1 Samples after different aging time after ftir data

It can be seen from Table 1 that the Acon values of the A and B materials vary little with the increase of the aging time and fluctuate at 10.5，which is also in accordance with the above-mentioned standard of the internal standard.The AC=O value of pure PP increases with the aging time，and the CI value increases with the aging time.The modified PP AC=O value has changed，but no law，and its CI value decreases first and then increases with the increase of aging time.The reason for this phenomenon is that in the early stage of aging，the carbonyl group in HALS suppresses the formation of carbonyl groups in PP while decomposing.When the decomposition rate of carbonyl in HALS is greater than the rate of carbonyl formation in PP，the carbonyl index decreases.With the increase of aging time，the aging rate of PP sample increases，the carbonyl generation rate is higher than the decomposition rate of carbonyl group in HALS，then the carbonyl index increases.In addition，it can be seen from the table 1，through the same time after aging treatment，modified PP carbonyl index is less than pure PP carbonyl index，indicating that the addition of HALS to enhance the anti-aging properties of PP.

3 Conclusion

With the increase of aging time，the peak area of carbonyl absorption peak of pure PP gradually increased，and the carbonyl index increased gradually.The peak area of carbonyl absorption peak of modified PP after adding HALS did no significant changes，and the carbonyl index decreased first Big.For the two groups of samples with the same aging time，the carbonyl index of modified PP was less than that of pure PP，and the anti-aging effect was better.

【Reference】

[1]Leng L C，Zhang Y M，Han G T et al.Preparation and Properties of Additive Aging Polypropylene[J].2014.

[2]Wu M Y.Polymer photoaging，light stabilization mechanism and light stabilizer [J].Bulletin of Polymer Science，2006，4：76-83.

[3]Zhang H Z et al.Progress in Industrial Application of Light Stabilizer[J]. Refining & Chemical Industry，2012，23（1）：4-6.

[4]Wang D F；Su Y Q.Application of Fourier Transform Infrared Spectroscopy in Analytical Chemistry[J].2009，18（4）：82-86.

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