Thermal oxidation polyethylene

Fourier transform NMR spectroscopy, polyethylene thermal oxidation, 695 Fourier transform-Raman spectroscopy hydroperoxides, 692 nitrile hydrolysis, 702 see also Raman spectroscopy Four-memhered peroxides, 164, 1212-13 FOX (Xylenol Orange-ferric complex) assay hydrogen peroxide determination, 628, 632, 657, 658... 

Although the general outlines of polyethylene thermal oxidation with molecular oxygen are understood generally, traditional investigative methods have left some questions unanswered. The exact nature of the oxidation products is not completely clear (10,11,12,13). This is caused by heavy reliance on ir spectroscopy. IR spectroscopy suffers from band overlap, particularly in the important carbonyl stretch region near 1725 cm"1, and from the necessity of establishing reliable extinction coefficients. 

Bocchini S, Frache A, Camino G, Claes M. Polyethylene thermal oxidative stabilisation in carbon nanotubes based nanocomposites. Eur Polym J 2007 43 3222-3235. 

E. Richaud. Kinetic modelling of phenols consumption during polyethylene thermal oxidation. European Polymer Journal 49(8), 2223-2232, August 2013. 

X. Colin, B. Fayolle, L. Audouin, J. Verdu. About a quasi-universal character of unstabilised polyethylene thermal oxidation kinetics. Polymer Degradation and Stability 80(1), 67-74, (2003). 

A study of the thermal oxidative breakdown of polyethylene under static conditions has revealed that polyamine disulfides are stabilizers, yet to varying degrees (Fig. 1). 

Figure 1 Thermal oxidative breakdown of polyethylene (temperature 200°C P02 = 350 Tor stabilizer concentration 0.5 mass percent). 1-without stabilizer 2-CaO-6 3-polydii-minodiphenylmethane disulfide 4-polydiiminodiphenylsul-fon disulfide 5-polyparaoxydiphenylamine disulfide 6-po-lydimethylaniline disulfide 7-polyaniline disulfide 8-polydiiminodiphenyloxide disulfide 9-polythiosemicarbaz-ide disulfide 10-polyamine disulfide 11-polycarbamide disulfide 12-poly thiocarbamide disulfide 13-polyethylenedi-amine disulfide.

Polythiosemicarbazide disulfide is the most efficient aliphatic polyamine disulfide for inhibiting the thermal oxidative breakdown of polypropylene, while polyimi-noaniline disulfide and polydiiminodiphenyloxide disulfide (Fig. 3) are the most efficient aromatic polyamine disulfides. In contrast to polyethylene, the thermal oxidative breakdown period increases as the concentration increases (Fig. 4), Depending on the concentration, the flow-melt index at 230°C increases at a lower rate than in the case of commercial stabilizer Santanox (Table 2)-... 

Fiber glass provides effective inhibition of polyethylene thermal destruction up to 400°C. The inhibitive efficiency increases with increased content of sodium oxide from 0.7-16% (Table 5). 

Thermal aging is another simple pretreatment process that can effectively improve adhesion properties of polymers. Polyethylene becomes wettable and bondable by exposing to a blast of hot ( 500°C) air [47]. Melt-extruded polyethylene gets oxidized and as a result, carbonyl, carboxyl, and hydroperoxide groups are introduced onto the surface [48]. 

As part of a multi-technique investigation (see also discussion under mid-infrared spectroscopy later), Corrales et al. [13] plotted the carbonyl index for films prepared from three grades of polyethylenes a high-density PE (HDPE), a linear low-density PE (LLDPE) and a metallocene PE (mPE) (see Figure 5). In this study, the data trend shown in Figure 5 correlated well with activation energies derived from the thermal analysis, which showed that the thermal-oxidative stability followed the order LLDPE > mPE > HDPE, whereas the trend... 

The products of thermal oxidation of polyethylene films can be characterized by C FTNMR furthermore, using the spin-lattice relaxation technique, quantitative estimates can be made of the oxidized functional groups. Observation of the development progress of the various functional groups leads to the postulation of hydroperoxides as the primary oxidation products, which undergo further transformations to the other derivatives in a complex scheme . 

A remarkable experiment was carried out by Blackadder et al. [62]. They annealed a linear polyethylene grade (Rigidex 50) by gradually heating it from 120 °C to 135.8 °C. The thermal treatment was conducted in vacuum to avoid thermal oxidation. The experiment took 2 years and the mass crystallinity and the melting point after subsequent cooling to room temperature... 

Han S, Kim C, Kwon D (1997) Thermal/oxidative degradation and stabilization of polyethylene glycol. Polymer 38(2) 317-323... 

Polyethylene (PEI. In an unpublished study, pouches were made from paper/foil/PE laminates, and headspace gas was taken from the bag after incubation at 60° C for 20 minutes and analyzed by a gas chromatograph. Three major components were identified as acetaldehyde, allyl alcohol and acrolein. When odorous bags were compared with non-odorous bags, there showed a direct correlation between odor, acetaldehyde and allyl alcohol levels. Those compounds were considered to be thermal oxidative decomposition products of polyethylene (Baxter, J. A., W. Grayson and Assoc., Ltd., unpublished data). 

S. A. Trifonov, E. A. Sosnov, and A. A. Malygin, Structure of the surface and thermal-oxidative breakdown of products that has obtained in reaction of polyethylene with vapor of PC13 and VOCl3, J. Appl. Chem. (in Russian) 77(11) 1872-1876 (2004). 

The rate of oxidation can be determined by measuring the oxygen uptake at a certain temperature. Such measurements have shown that the oxidation at 140 °C of low-density polyethylene increases exponentially after an induction period of 2 h. It can be concluded from this result that the thermal oxidation, like photo-oxidation, is caused by autoxidation, the difference merely being that the radical formation from the hydro peroxide is now activated by heat. 

In the following sections, particular attention is paid to polyethylene radio-thermal oxidation. 

A previously described kinetic model for polyethylene radical chain oxidation is tentatively extended to include the conditions relevant to embrittlement behavior in the case of thermal oxidation at 90°C. The important roles of chemi-crystallization and morphology as a follow-up to initial chemical changes are discussed. The philosophy of how chemical reactions will ultimately lead to physical polymer changes apparent in Mw and lamellar properties, and how these processes could be discussed in terms of advanced modeling strategies is briefly reviewed. 

It is well known that thermal oxidation in polyethylene (PE) in the presence of oxygen leads to sudden and deep embrittlement, in which oxidative chain scission plays a key, but perhaps indirect, role. We have developed a kinetic model, derived from a branched radical chain mechanistic scheme, able to predict accurately molecular structural changes (7). 

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