Polyolefins degradation

These environmentally degradable polyolefins, because of their cost/ performance profiles are very competitive for the growing markets for such plastics. They will be strong competition for the polyester types such as poly(lactic acid) and polyhydroxyalkanoates so frequently publicized as the innovative solution to plastic waste management. 

The history of the development of environmentally degradable polyolefins reveals some interesting technologies and innovation. Unfortunately most were without much commercial success. A few of these are shown below ... 

Are a commercially viable approach to developing environmentally degradable polyolefins. 

Fig. 10 Strain at break Vs. UV exposure time for polypropylene copolymer bars made from (a) virgin polymer (V) (b) virgin polymer + undegraded recyclate (U) (c) virgin polymer + photodegraded recyclate (P). Results for blends with recyclate contents of 10% and 25% are shown. (More details in Craig, I.H. White, J.R. Mechanical properties of photo-degraded recycled photo-degraded polyolefins. J. Mater. Sci. 2006, in press.)...

Keywords Block copolymers, Interface reactive injection moulding, Polyamide degradation, Polyolefine polyamide graft copolymers, PTFE polyamide materials... 

On the contrary, Contat-Rodrigo et al." proposed USE as a better method in terms of reproducibility and extraction efficiency. They studied the extraction of degradation products from degradable polyolefin blends aged in soil. Higher amounts of certain products (e.g., carboxylic acids) were extracted by USE than by MAE. 

Contat-Rodrigo, L., Haider, N., Ribes-Greus, A., and Karlsson, S., Ultrasonication and microwave-assisted extraction of degradation products from degradable polyolefin blends aged in soil, J. Appl. Polym. Set, 79, 1101-1112, 2000. 

D 3826] Practice for determining degradation end point in degradable polyolefins using... 

Zuchowska, D., Streller, R., Meissner, W., 1998. Structure and properties of degradable polyolefin-starch blends. Polymer Degradation and Stability 60, 471—480. 

UV absorption of a polymer influences the response to photolytic degradation. Polyolefins, which are relatively transparent in the UV, receive essentially constant radiation throughout the sample and thus yield photolysis products as a function of total sample weight. Highly UV absorbing polymers, such as PS, strongly attenuate the incident radiation. Measurements of the photolysis yield of benzene from PS films showed that photolysis is surface area controlled and products are formed within a thin surface layer. 

Thermoplastic starch alone can be moulded as traditional thermoplastic materials its sensitivity to humidity, however, makes it unsuitable for most applications. Starch-filled degradable polyolefins show good disintegration properties. There is no evidence, however, of a significant biodegradation of the fragments produced by disintegration. 

One of the most successful applications of degradable polyolefins is in plasti-culture. Non-degradable polyethylene has been used in crop protection since... 

A major concern has been the contamination of the soil by transition metal ions ( heavy metals ) that may leach out of degrading polyolefins after repeated use of the same formulation on the same soil. This is to a large extent a function of the low molecular weight additives used in the polymer. However, agricultural soils already vary enormously in transition metal content. Nickel has been studied in some detail because it is used in a number of plastics products and concern has been expressed about its environmental toxicity and possible accumulation in growing plants. Table 3 shows the concentrations of Ni in different types of soils. It is clear that some common soils, notably limestone, contain very considerable concentrations of nickel but no health hazards have been reported in... 

Degradable polymers destined for composting should, therefore, be modelled on the behaviour of lignin as far as possible [12]. Oxo-biodegradable polyolefins, particularly the polyolefins and polystyrene, have been shown to be particularly suitable for this application. They cannot, because of their chemical structures, ultimately produce any products other than carbon dioxide and water. The practical applications of these materials are the main focus of this Chapter and composting standards for degradable polyolefins will be discussed in Section 9. 

The evaluations indicated in the side-branches of Fig. 5 have a different purpose. They are intended to show from a scientific standpoint that the oxidation products formed from degradable polyolefins in the natural environment are bioassimilated by soil microorganisms. It would be ideal to take samples of plastics from compost at intervals to carry out biometric (carbon dioxide formation) tests and to measure mass-loss due to bioerosion of the plastic. However, this is a difficult procedure since CO2 formation is concomitant with mass loss during composting and it is difficult to achieve even an approximate mass balance. 

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