Lifetimes of plastics

Strictly, the useful life of a product can only be measured directly by service trials or tests on the complete product. Most assessments of lifetime of plastics are made by considering some measure of performance and specifying some limit or threshold value for the property, which is taken as the end point corresponding to where the material is no longer usable. 

Weathering, oxidation, hydrolysis and other forms of chemical attack are complex mechanisms, which depend on environmental conditions such as temperature and humidity as well as on the intensity of radiation, the availability of oxygen or chemical concentration. In recent years these mechanisms have been studied and better understood, the principal success of which has been the development of stabiliser systems which greatly prolong the lifetime of plastics and which have extended their use to a much wider range of applications. 

INTRODUCTION. LIFETIME OF PLASTICS AND PLASTIC-BASED COMPOSITES EXAMPLES... 

All plastics, as well as all organic materials, retain their functional properties during only a certain period of time. There are multiple events that shorten the lifetime of plastics—some of them are accidental, such as mechanical failure as a result of reaching an ultimate load, that is, a break load for a given profile, or a critical impact resistance, or a case of fire, and some of them are cumulative, spreading over a long time period, such as wear and tear, or thermo- and photooxidation. 

That is why commercial plastics commonly contain added antioxidants, typically in amonnts between 0.05 and 0.15% by weight, and 0.2-0.5% for stabilization of regrinds. This significantly extends the lifetime of plastics compared to unprotected ones, thongh a good portion of these antioxidants is consumed during the subsequent processing of plastics into shapes. 

Metals in metal stearates quite significantly effect the lifetime of plastics and composite materials. Table 15.18 illustrates these effects. 

These recycling techniques aside, it is also possible to extend the lifetime of plastics dnring their nsage. It has been shown by certain studies that wood flour/poly(ethyIene) composites used to build public benches could have a more favorable balance than wood itself, which is because of the non-biodegradabihty of PE [HOL 04]. Other authors have observed that the introduction of a certain quantity of wood flour into poly(propylene) helped increase its durabihty and improve its mechanical properties [LAM 08]. 

Private collectors wish to preserve the artistic, historical and financial values of their olgects and artworks. With the dramatic increase in monetary value of modem art since 2000, art insurance companies are also concerned with the short useful lifetime of plastics and the limited options for their conservation today. In January 2003 AXA Art Insurance funded a research laboratory and research into the conservation and restoration of modem plastic furniture at the Vitra Design Museum in Germany (Albus et al., 2007). Artists are also stakeholders in the conservation of their own and their feUow professionals works. The durability of an artwork, as well as providing a guarantee for the collector, affects the artist s reputation and immortality (Hummelen, 1999). Durability is affected by artists selection of appropriate materials and techniques. The artist David Hockney is credited with saying Love will decide what is kept, and science will decide how it is kept (Corzo, 1999). 

Egypt s pyramids, the largest and the oldest stone structures, were built about 4500years ago. Lifetimes of plastics outdoors or in the ocean, sometimes published in the popular literature, are speculative and not reliable. 

The technical advances in degradation and stabilization techniques which impact the lifetimes of plastics and wood products routinely exposed to solar UV radiation and the protection to humans offered by materials against solar UV radiation were recently assessed [1]. 

The main aim has to be that this test can predict lifetime of plastic products under complex conditions (e.g. heat, oxidation, chemicals and mechanical loading) within a short test time in the laboratory. We agree with the discusser that such a test wll be a more economical and quicker method than the current method. 

The modulus of elasticity can also influence the adhesion lifetime. Some sealants may harden with age as a result of plasticizer loss or continued cross-linking. As a sealant hardens, the modulus increases and more stress is placed on the substrate—sealant adhesive bond. If modulus forces become too high, the bond may faH adhesively or the substrate may faH cohesively, such as in concrete or asphalt. In either case the result is a faHed joint that wHl leak. 

Photochromism Based on Triplet Formation. Upon absorption of light, many polycycHc aromatic hydrocarbons and their heterocycHc analogues undergo transitions to their triplet state which has an absorption spectmm different from that of the ground state (24). In rigid glasses and some plastics, the triplet state, which may absorb in the visible, has a lifetime of up to 20 seconds. 

Compared with tar, which has a relatively short lifetime in the marine environment, the residence times of plastic, glass and non-corrodible metallic debris are indefinite. Most plastic articles are fabricated from polyethylene, polystyrene or polyvinyl chloride. With molecular weights ranging to over 500,000, the only chemical reactivity of these polymers is derived from any residual unsaturation and, therefore, they are essentially inert chemically and photochemically. Further, since indigenous microflora lack the enzyme systems necessary to degrade most of these polymers, articles manufactured from them are highly resistant or virtually immune to biodegradation. That is, the properties that render plastics so durable... 

It is instructive to consider the sources of plastics waste. Table 11.1 shows the types of plastics and their use in packaging, whilst Table 11.2 shows the proportion of waste classified by end use. This shows how significant packaging is in generating waste, and causing environmental problems. Applications such as furniture and electrical appliances show more acceptable use of polymers, because discard rates are low and lifetimes of the products are generally long. 

This paper considers plastics and their positive role during the lifetime of a car, the case of end-of-life vehicles, energy recovery from shredding refuse by means of co-... 

This paper explores the use of plastics in cars to make them more environmentally friendly. It lists major environmental issues. It then discusses in detail the positive role of plastics during the lifetime of a car (more plastics means less fuel consumption), the fact that automotive plastic parts are user-friendly and safe, the current and future uses of plastics in cars, recovery options for plastics in end-of-life vehicles, mechanical recycling (which is the best recovery option for many large automotive parts), energy recovery (the solution for small plastic parts), and feedstock (or chemical) recycling. Lastly, the way forward is considered. 

In Fig. 3.5A a comparison between time-gated detection and TCSPC is shown. The time-gated detection system was based on four 2 ns wide gates. The first gate opened about 0.5 ns after the peak of the excitation pulse from a pulsed diode laser. The TCSPC trace was recorded using 1024 channels of 34.5 ps width. The specimen consisted of a piece of fluorescent plastic with a lifetime of about 3.8 ns. In order to compare the results, approximately 1700-1800 counts were recorded in both experiments. The lifetimes obtained with TG and TCSPC amounted to 3.85 0.2 ns and 3.80 0.2 ns respectively, see Fig. 3.5B. Both techniques yield comparable lifetime estimations and statistical errors. 

Data are available for plasticizers and ionophores, and indicate the operational stability (the higher the log P value, the higher the lipophilicity). The minimal lipophilicity log P required for membrane components with a lifetime of 30 x 24 h upon exposure to aqueous solution is estimated to be around 10 whereas it has to be as high as 25 for direct measurement in blood, serum and plasma. 

In exterior exposure, PS yellows somewhat, due to UV radiation. In order to shield the plastic from degradation in UV light, it is also supplied in combination with UV absorbents. This prolongs the lifetime of the products by a factor of three to five. Grades which contain UV absorbents are slightly yellowish, a fault which may be corrected by adding transparent blue colorants such as soluble dyes or Ultramarine Blue [36]. 

Definition of the plastic is fundamental to the prediction of the lifetime of a plastic component. 

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