Degradable polyethylene

Anaerobic microbes in the presence of water in the landfill will consume these natural products and produce methane, CO2 and humus. One study reported the average composition of 20 year old refuse to be 33 % paper, 22% ash and 12% wood [18]. Thirty core samples revealed a wide range of degradation and microbial activity that were directly attributed to sample moisture content. Recovered polyethylene degradation was evaluated and determined to be as high as 54 %. 

The most fundamental work on polyethylene degradation is being done by A. C. Albertsson in Sweden(27,28,29,30,31) using elegant science with labelled polymers to measure the rate and quantity of carbon dioxide evolution from buried high and low density polyethylene films. Degradation occurs at about... 

Polyethylene degradation rate enhancement has been claimed for blends with mercaptans,(32) ketones,(32) ethers,(32) and specifically by photodegradation in the presence of benzophenone,(33) and metal promoted oxidations.(34 )... 

Although rings made of polyethylene work very well, as we have already found, polyethylene degrades extremely slowly in the environment. A small amount of carbon monoxide (CO) can be polymerized with ethylene to produce a copolymer that degrades in sunlight (undergoes photodegradation) ... 

Olah (17a) has also reported the alkylation reactions (at -10 with 1 1 HS03F-SbF5) of n-butane with ethylene to yield 38 weight percent of hexanes and of n utane with propylene to yield 29 weight percent of heptanes. The former reaction has also been reported by Parker (31) at 60 , but the product in this case more nearly resembles polyethylene degradation products. In our work with 10 1 HF-TaF5 at 40 , in a flow system, ethylene (14.1 wt.%) reacted with rv-butane to form 3-methyl-pentane as the initial product of 94% selectivity (Scheme 6, path a). The alternative, i.e., the direct reaction of ethylene with a secondary-butyl cation (path b), can be ruled out since butane does not ionize under these conditions (vide supra). 

P. A. Jalil, Investigations on polyethylene degradation into fuel oil over tungstophos-phoric acid supported on MCM-41 mesoporous silica. Journal of Analytical and Applied Pyrolysis, 65, 185-195 (2002). 

A. M. CunUffe and P. T. Williams, Characterisation of products from the recycling of glass fibre reinforced polyester waste by pyrolysis. Fuel, 82, 2223-2230, (2003). J. H. Harker and J. R. Backhurst, Fuel and Energy, Academic Press London, 1981. A. C. Albertson and S. Karlsson, Polyethylene degradation products, In Agricultural and Synthetic Polymers, ACS Symposium Series 433, J. E. Glass and G. Swift (eds), American Chemical Society, Washington DC, 60-64, 1990. 

The content of aldehyde groups in the final product of polypropylene photodegradation is 7%. In the case of polyethylene degradation these groups are completely absent [6]. The relatively lower amount of aldehyde groups in the products of polyolefine photo-oxidation is due to the fact that they absorb radiation and subsequently react as above [278]. 

Sakata et al.20 have also studied polyethylene degradation over a mesoporous silica catalyst. The material used, called KFS-16, is closely related to MCM-41, although it is prepared by a different method starting from a layered silicate (kanemite). One of the most interesting observations in this work is the PE cracking activity exhibited by KFS-16 in spite of the absence of acid sites (it is a completely silica-based material). Figure 5.10 shows the cumulative volume of liquid products obtained in the thermal and catalytic cracking of PE in a batch... 

Apparently, this can explain an unusually steep temperature dependence of the OIT of polyethylene degradation, described in Application News T95 of Shimadzu DSC, entitled Measurement of Oxidizing Induction Time of PE by DSC. The authors have obtained the following data for the oxidation of polyethylene in the presence of an antioxidant ... 

Degradation, polyethylene Degradation, polymers, catalytic Dehydration, Cd-FAU Dehydration, clinoptilolite Dehydration, isopropanol Dehydration, K-LSX Dehydration, MOR Dehydrocyclodimerisation, butadiene Dehydrogenation, ethylbenzene Dehydrogenation, methanol Dehydroisomerisation, n-butane Dehydroxylation, phenol Delaminated zeolites De novo simulation DeNOx catalyst... 

Polylactone and poly(vinyl alcohol) films are readily degraded by soil microorganisms, whereas the addition of iron or calcium accelerated the breakdown of polyethylene. Degradable mulches should break down into small brittle pieces which pass through harvesting machinery without difficulty, and do not interfere with subsequent planting. Effective funaigant mulches require reduced-porosity films which reduce the escape of volatile chemicals, i.e. nematocides, insecticides, herbicides, etc., and therefore allow for lower application rates. 

Electrochemical tree growth, the electrical equivalent of environmental stress cracking (Chapter 10), occurs at lower electric stresses. The chemical species vary. Lead salts from petroleum entered a cable buried near a petrol station, whereas hydrogen sulphide from the decomposition of seaweed entered an undersea cable. The whole gamut of polyethylene degradation reactions occur on a micro-scale inside such trees. To avoid such failures, the cable can be fitted with an impervious outer layer, such as a lead sheath. 

The main commerdally useftil methods for aosslinking use agents whose sole purpose is to promote free-radical processes that essentially initiate polyethylene degradation. This ultimately aeates bonds direcdy between carbon atoms on adjacent polymer chains. Some crosslinking agents, such as silanes, integrate themselves between polymers to form intermediate "bridging" links that connect one chain to another. 

Sivan A, Szanto M, Pavlov V. Biofihn development of the polyethylene-degrading bacterium Rhodococcus ruber. Appl Microbiol Biotechnol 2006 72 346-352. 

Several interesting solutions have been proposed to make filled polyethylene degrade faster than previously observed. Incorporation of a chromophoric group, which increases the susceptibility of polyethylene towards photooxidation, is one choice. Metal salts are also useful and potent additives, and they give room for radical formation within the polymer chain and again increase the photo-oxidative behaviour of these materials. 

Adding oxidants can lead to photochemical reactions and thus to the formation of oligomeric polymer fragments that can be further metabolized by microbes. Primary degradation is caused here by radical oxidation. This process is observed when polyethylene degrades [906], [927]. 

The formation of the highly reactive superoxide radical ion (Oj") explains the exceptional photoactivating effect of iron dithiocarbamate in polyethylene degraded in air [124]. 

The thermal stability of high-density polyethylene and PE-HD/MDH composites is summarized in Table 4.4. High-density polyethylene degraded at a single step at temperature with maximal mass loss T ,=474.9 °C with remaining residue of about 0.1%. The thermal profile of PE-HD/MDFI composites was characterized by two main mass loss steps at temperature with maximal mass loss rate and... 

This present study attempted to establish the causes that led to the surface damage of polyethylene tibial insert from a knee prosthesis which was retrieved after 10 years in vivo. The patient was an elderly housewife who was a community ambulator, and was active and not overweight. Analysis on the worn surface polyethylene will provide information about the mechanism and process of the polyethylene degradation after 10 years implantation. 

Chiellini et al. [58] extracted thermally peroxidised polyethylene with acetone and measured the rate of mineralization of the solvent free extracts in forest soil. This is compared with cellulose and a number of low molar mass control hydrocarbons in Fig. 2. Surprisingly, the peroxidation products were converted to carbon dioxide and water more rapidly than cellulose. The extracted polyethylene degraded at a similar rate to the pure hydrocarbons and it is evident from this work that the rate controlling process in the overall sequence of degradation reactions is the initial peroxidation of the polymer. It has been demonstrated [19] that the exposure of peroxidised PE to an abiotic water-leaching environment did not remove the peroxidation products from the polymer, whereas bioassimilation began immediately (see Fig. 2)... 

Barabas K, Iring M, Kelen T, Tudos F. Smdy of the thermal oxidation of polyolefines volatile products in the thermal oxidation of polyethylene. Degradation and Stab cf Polyolefins, lUPAC Microsymp on Macromol, 15th 1977 57 65-71. 

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