Degradable plastic polymers

Krzan A, Hemjinda S, Miertus S, Corti A, Chiellini E. Standardization and certification in the area of environmentally degradable plastics. Polym Degrad Stab 2006 91 (12) 2819-2833. 

For more than 20 years, polymer scientists and plastics technologists have been working to develop plastics materials that would be more acceptable environmentally, and in the third edition of this book, published in 1975, the author devoted a section to photo- and biodegradation of polymers. In spite of such effort, an article in 1992 stated that Degradable plastics are still in the early... 

Since the last edition several new materials have been aimounced. Many of these are based on metallocene catalyst technology. Besides the more obvious materials such as metallocene-catalysed polyethylene and polypropylene these also include syndiotactic polystyrenes, ethylene-styrene copolymers and cycloolefin polymers. Developments also continue with condensation polymers with several new polyester-type materials of interest for bottle-blowing and/or degradable plastics. New phenolic-type resins have also been announced. As with previous editions I have tried to explain the properties of these new materials in terms of their structure and morphology involving the principles laid down in the earlier chapters. 

Polymers have inherently high hydrocarbon ratios, making liquefaction of waste plastics into liquid fuel feedstocks a potentially viable commercial process. The objective is to characterise the thermal degradation of polymers during hydrogenation. LDPE is studied due to its simple strueture. Isothermal and non-isothermal TGA were used to obtain degradation kinetics. Systems of homopolymer, polymer mixtures, and solvent-swollen polymer are studied. The significant variables for... 

PLASTIC/POLYMER DEGRADATION A ROUTE OF ECONOMIC UTILISATION AND RECOVERY OF CHEMICALS FROM POLYMER/PLASTIC WASTE... 

These are polymers that break down over time when exposed to environmental conditions, such as light and bacteria. The Chemistry Bulletin on the next page gives more information about degradable plastics. 

The ability of a degradable plastic to decay depends on the structure of its polymer chain. Biodegradable plastics are often manufactured from natural polymers, such as cornstarch and wheat gluten. Micro-organisms in the soil can break down these natural polymers. Ideally, a biodegradable plastic would break down completely into carbon dioxide, water, and biomass within six months, just like a natural material. 

When a degradable plastic decays, the starch or cellulose backbone may break down completely into carbon dioxide, water, and organic matter. What do you think happens to F, Cl, or other heteroatom groups on the polymer chain as the backbone decays Why might this be a problem ... 

As shown in Table I, the plastic component of MSW has increased dramatically. Past development of synthetic plastic formulations has focused on reducing the photo, chemical, and biological degradation of the plastic polymers. However, the persistence of plastics in the environment as litter, potential marine hazard, and with concern for global carbon cycling 1,6) has focused recent attention on the recycling of plastics or development of new biodegradable plastic formulations. 

The review is not meant to promote degradable plastics, but rather to highlight them as one possible route to a cleaner environment. In many applications, recycling of polymers or incineration of waste products may offer more protection to the environment. The final decision for any application requires careful deliberation and not emotional judgements. 

A frequently cited merit of biodegradable plastics is their lack of persistance in an intact state "environmentally friendly" is a widely used vernacular phrase, but there has also been speculation in the popular press that degradable plastics will release potentially harmful additives into the environment when the plastics degrade or disintegrate. An ideal biodegradable plastic will leave no undegraded polymeric residues, and for these materials, the persistance of additives as well as the polymers must be considered. In this case, the issue is not whether or not the additive... 

Secondary aromatic amines, such as phenyl beta-naphthylamine. have been used as antioxidants in elastomers, but the preferred antioxidants for plastics have been 2,6-disubstituted and 2,4,6-trisubstituted phenols. These hindered phenols serve as chain transfer agents with the macroradicals which are produced by the degradation of polymers. 

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