Oxidation in Polypropylene

Billingham N C (1989) Location of oxidation in polypropylene, Makromol Chem, Macromol Symp 28 ... 

With this in mind we applied uv microscopy to search for localisation of oxidation in polypropylene. 

The carbonyl absorption at around 280 nm can be used to see oxidation in polypropylene directly but this is only possible in heavily oxidised samples which are also too brittle to be sectioned for microscopy. It is possible in this way to look only at samples which have been directly crystallised from the melt as thin films. In order to work with samples with more normal oxidation levels we must stain the oxygen containing groups to make them uv absorbing. In principle it should be possible to separately stain carbonyl or peroxide groups but we have concentrated on 2,4-dinitrophenylhydrazine (I IPH) as a stain for carbonyl groups. Dansyl hydrazine was also tried as a fluorescent stain but was limited in its ability to penetrate the sample so that only the surface was stained. 

Eayolle B, Audouin L, Verdu J. A critical molar mass separating the ductile and brittle regimes as revealed by thermal oxidation in polypropylene. Polymer 2004 45 4323. 

Naugard HMll is a granular blend of hindered phenolic and diphenylamine antioxidants. This blend provides synergistic short and long term thermal protection against oxidation in polypropylene. 

Antioxidants may be assessed in a variety of ways. For screening and for fundamental studies the induction period and rate of oxidation of petroleum fractions with and without antioxidants present provide useful model systems. Since the effect of oxidation differs from polymer to polymer it is important to evaluate the efficacy of the antioxidant with respect to some property seriously affected by oxidation. Thus for polyethylene it is common to study changes in flow properties and in power factor in polypropylene, flow properties and tendency to embrittlement in natural rubber vulcanisates, changes in tensile strength and tear strength. 

In broad tonnage terms the injection moulding markets for high-density polyethylene and polypropylene are very similar. The main reasons for selecting polypropylene have been given above. In favour of HDPE is the inherently better oxidation and ultraviolet resistance. Whilst these properties may be greatly improved in polypropylene by the use of additives these may increase the cost of polypropylene compounds to beyond that which is considered economically attractive. It is for this reason that HDPE has retained a substantial part of the crate market. 

The term poloxamer is widely used to describe a series of ABA block coploymers of polyethylene oxide and polypropylene oxide, extensively used in industry as antifoams, emulsifiers, wetting agents, rinse aids, and in numerous other applications [1-5]. Poloxamers are amphiphilic in character, being comprised of a central polypropylene oxide (PO) block, which is hydrophobic, sandwiched between two hydrophilic polyethylene oxide (EO) blocks as shown below ... 

Color Urea, melamine, polycarbonate, polyphenylene oxide, polysulfone, polypropylene, diallyl phthalate, and phenolic are examples of what is needed in the temperature range above 200°F (94°C) for good color stability. Most TPs will be suitable below this range. 

The living nature of ethylene oxide polymerization was anticipated by Flory 3) who conceived its potential for preparation of polymers of uniform size. Unfortunately, this reaction was performed in those days in the presence of alcohols needed for solubilization of the initiators, and their presence led to proton-transfer that deprives this process of its living character. These shortcomings of oxirane polymerization were eliminated later when new soluble initiating systems were discovered. For example, a catalytic system developed by Inoue 4), allowed him to produce truly living poly-oxiranes of narrow molecular weight distribution and to prepare di- and tri-block polymers composed of uniform polyoxirane blocks (e.g. of polyethylene oxide and polypropylene oxide). 

In our study we have found that UV-light greatly accelerates the rate of ozone attack at the polypropylene surface. Presented results were undertaken to determine mechanism of the photo-oxidation of polypropylene surface upon UV-irradiation of polymer films in ozone. 

Figure 6 (A) Non-isothermal chemiluminescence runs for oxidation of polystyrene (PS), polyethylene terephthalate) (PETP) and polyfmethyl methacrylate) (PMMA), in oxygen, heating rate 2.5°C/min. (B) Non-isothermal chemiluminescence runs for oxidation of polypropylene (PP), polyamide 6 (PA 6), poly(vinyl pyrrolidone) (PVP), polyethylene (PE) and polyamide 66 (PA 66), in oxygen, heating rate 2.5°C/min.

Figure 19 Chemiluminescence from oxidation of polypropylene containing 0.5 % wt. of Irganox 1010 at 150°C in oxygen. Line 1 represents the original polymer film line 2 is the same sample after 7,890 s of annealing at 130°C.

Figure 20 An increase of induction time of oxidation of polypropylene stabilized by Irganox 1010 (points 1) due to prior sample annealing at 130°C (points 2) in oxygen. The induction time corresponds to the time of cross-section of the straight line passing the CL inflexion point and time axis. It was determined for an oxygen atmosphere and temperature 150°C.

G. George and M. Celina, Homogeneous and heterogeneous oxidation of polypropylene. In S. Halim Hamid and M. Dekker (Eds.), Handbook of Polymer Degradation, Second Ed., Inc., M. Dekker, New York, p. 277. 

Cullis and Hirschler (33) found that zinc acetylacetonate and cobalt acetyla-cetonate at 1% in polypropylene afforded self-extinguishing properties by the ASTM D635 test (Table TV). These additives appear to be catalytic pro-oxidants which enhanced the carbon yield. 

L. Bokobza, C. Pham-Van-Cang, C. Giordano, L. Monnerie, J. Vandendriessche, and F. C. De Schryver, Studies of the mobility of probes in polypropylene oxide) 2. Excimer fluoresence technique, Polymer 29, 251 (1988). 

The repeat unit (III) in polypropylene oxide) [IUPAC poly(oxy[l-methylethylene])], on the other hand, possesses stereocenters that are chirotopic since the two chain segements... 

The cross-linking rate of EPR by radiation comes close to that of polypropylene. EPDM terpolymers exhibit an enhanced cross-linking rate, and it increases with the diene content. However, not only the cross-linking rate, but also a greater yield of scissions results from the addition of the third monomer. Cross-linking of EPR can be promoted by the addition of a variety of additives, particularly by those that were found effective in polypropylene. Tetravinyl silane, chlorobenzene, nitrous oxide, allyl acrylate, neopentyl chloride, and N-phenyl maleimide were reported to promote the process. 

Cross-linking of EPR can be promoted by the addition of a variety of additives, particularly by those that were found effective in polypropylene. Tetravinyl silane, chlorobenzene, nitrous oxide, allyl acrylate and neopentyl chloride,191192 and biphenyl maleimide177 were reported to promote the process. 

Polyisobutylene and Polypropylene. In a similar way, the material balance of nitrous oxide in the case of polyisobutylene was measured as shown in Table IV. In this case, whereas the enclosed nitrous oxide is not completely consumed during irradiation, the consumption proceeds... 

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