Degradation, of plastics

The degradation of plastic materials, contained in items of everyday use, is a result of the sum of all the weathering effects 

A survey of plastics-containing objects in the British Museum and the National Museum of Denmark showed that 1% of objects were actively deteriorating and were in immediate need of conservation, while 12% exhibited deterioration and required cleaning, stabilising and repair. All the acute objects contained cellulose nitrate, cellulose acetate, plasticised PVC or polyurethane foam. Most objects (60%) were defined as being of low conservation priority, that is, they were in a stable condition but needed some treatment such as cleaning. Only just over one quarter required no conservation treatment. In general, deterioration of plastic objects in museums is visible within 5-25 years of collection. 

It should be remembered that most museum objects have been used or displayed before they are collected. They have an unknown past, usually, which contributes greatly to the rate and type of deterioration. Instability of the earliest plastics, cellulose nitrate and acetate is expected due to their poorly stabilised formulations and because they are the oldest man-made plastics in museums. However, PVC was first developed in 1926 and is still in use, so its deterioration is rather unexpected. 

Causes of deterioration of plastics may be broadly divided into physical and chemical. 

In addition to physical and chemical factors, all degradation reactions require energy in the form of heat, light or radiation. 

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Plastics and Synthetic Products. To prevent degradation of plastics at elevated processing temperatures, it is necessary to use suitable heat stabilizers. Eor example, flexible poly(vinyl chloride) (PVC) manifests uncontroUed color development in the absence of stabilizers. Accordingly, cadmium salts of organic acids are typically used in a synergistic combination with corresponding barium salts, in about a 1 3 cadmium barium ratio, to provide a cost-competitive heat stabilizer for flexible PVC. 

This comprehensive article supplies details of a new catalytic process for the degradation of municipal waste plastics in a glass reactor. The degradation of plastics was carried out at atmospheric pressure and 410 degrees C in batch and continuous feed operation. The waste plastics and simulated mixed plastics are composed of polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile butadiene styrene, and polyethylene terephthalate. In the study, the degradation rate and yield of fuel oil recovery promoted by the use of silica alumina catalysts are compared with the non-catalytic thermal degradation. 9 refs. lAPAN... 

Pinner, S. H., Ed. "Weathering and Degradation of Plastics", Gordon and Breach, London, 1966. 

This type of degradation can also be referred to as photodegradation or ultraviolet (UV) degradation. It includes photo-oxidation. It produces some of the more familiar signs of degradation of plastics embrittlement, discoloration and loss of transparency. 

Do degradable plastics disappear as soon as they are discarded What are the dangers of public confidence in the degradability of plastics ... 

Specifically the situation may involve a patent covering a method of reducing ultraviolet light degradation of plastic materials by... 

Radicals control the chemistry of the upper atmosphere, where they contribute to the formation and decomposition of ozone. Radicals also play a role in our daily lives, sometimes a destructive one. They are responsible for the rancidity of foods and the degradation of plastics in sunlight. Damage from radicals can be delayed by an additive called an antioxidant, which reacts rapidly with radicals before the radicals have a chance to do their damage. It is believed that human aging is partly due to the action of radicals, and antioxidants such as vitamins C and E may delay the process (see Box 2.1). 

K. Hodd, Weathering and degradation of plastics (summary of symposium), Anticor-... 

S. H. Pinner (ed.), Weathering and Degradation of Plastics , Columbine Press, Manchester, 1966. 

This method is the simplest of all the methods and is capable of detecting surface flaws such as corrosion, contamination, surface finish and surface discontinuities on joints.47 The discontinuities on joints such as welds, seals, solder connections and adhesive bonds can be detected. General corrosion, qualitative pitting corrosion, stress-corrosion cracking, weld-heat-affected zone attack, erosion corrosion and other type of degradation can be observed by visual examination aided by microscopes with sufficient magnification. Degradation of plastics can also be detected by visual examination. Visual examination is also used in conjunction with other techniques, such as powerful microscopes. 

The accessibility of the polymer to water-borne enzymes is vitally important because the first step in the degradation of plastics usually involves the actions of extracellular enzymes, which break down... 

Figure 8. Landfill Degradation of Plastic Films. Control samples on left, experimental samples on right, before (top) and after (bottom 10 months in a UK landfill at 2 meters depth.

Figure 3.10 Fractions of paraffins, olefins, naphthene and aromatic products from the catalytic degradation of plastics over spent FCC catalyst in a semi-batch reactor (400°C, P/C= 10, A/= 200 rpm) (a) HDPE (b) LDPE [70]. (Reproduced with permission from Elsevier)...

Figure 6.8). These results indicate that the proposed reactor system is useful for the continuous degradation of plastics. 

Catalytic Degradation of Plastic Waste to Fuel over Microporous Materials... 

An important aspect in a future catalytic process for degradation of plastic waste is the amount of catalyst used in such a process. In a batch system, which is the most broadly used so far to test the performance of various catalytic systems, the amount of catalyst is characterized by the polymer-to catalyst mass ratio. Results from initial experiments... 

The catalyst makes contact with melted MWP. Good contact between plastic particles and the catalyst is one of the key points for process development. Melted plastics can be degraded in a fluidized-bed reactor or a fixed-bed reactor. Since the usage of fixed beds leads to problems of blockage, scale-up to industrial size is not feasible. However the fluidized bed has a number of special advantages for catalytic degradation of plastics, because it is characterized by a good contact between catalyst and plastics as well as an excellent heat and mass transfer [4], In addition to selection of a snitable reactor, the catalyst used is very important in the process. 

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