Environmental ageing

Environmental Aging. AH ceUular polymers are subject to a deterioration of properties under the combined effects of light or heat and oxygen. The response of ceUular materials to the action of light and oxygen is governed almost entirely by the composition and state of the polymer phase (22). Expansion of a polymer into a ceUular state increases the surface area reactions of the foam with vapors and Hquids are correspondingly faster than those of soHd polymer. 

Antioxidants. Antioxidants are rarely needed because of the highly saturated nature of the polymer chains. If protection against severe environmental ageing conditions is needed, typical antioxidants (Ethanox 702, Irganox 1010) can be added. In some cases, zinc dibutyldithiocarbamate (0.05-0.2 wt%) or butylated hydroxytoluene (BHT) can be used as stabilizers. 

Apicella, A., Nicolais, L., Carfagna, C., de Notaristefani, C., Voto, C. 27th National SAMPE Meet., San Diego, 1982, The Effect of the Prepolymer Composition on The Environmental Ageing of Epoxy Based Resins ... 

For many applications it is not possible to put a component into service to test its durability. Similarly, in product testing one cannot always simulate full service conditions in one test or things become too complicated - for example, time-dependent loading plus abrasion plus environmental ageing. Car tyres have a complicated pattern of cornering, sports surfaces are subject to the actions of different sports and pipes in the North Sea have almost unpredictable wave motions superimposed. No simulation test will reproduce service conditions perfectly, therefore, in accordance with Section 4.13, the test has to be restricted to the critical agents of degradation. 

Oilfields in the North Sea provide some of the harshest environments for polymers, coupled with a requirement for reliability. Many environmental tests have therefore been performed to demonstrate the fitness-for-purpose of the materials and the products before they are put into service. Of recent examples [33-35], a complete test rig has been set up to test 250-300 mm diameter pipes, made of steel with a polypropylene jacket for thermal insulation and corrosion protection, with a design temperature of 140 °C, internal pressures of up to 50 MPa (500 bar) and a water depth of 350 m (external pressure 3.5 MPa or 35 bar). In the test rig the oil filled pipes are maintained at 140 °C in constantly renewed sea water at a pressure of 30 bar. Tests last for 3 years and after 2 years there have been no significant changes in melt flow index or mechanical properties. A separate programme was established for the selection of materials for the internal sheath of pipelines, whose purpose is to contain the oil and protect the main steel armour windings. Environmental ageing was performed first (immersion in oil, sea water and acid) and followed by mechanical tests as well as specialised tests (rapid gas decompression, methane permeability) related to the application. Creep was measured separately. 

Keizers, H.L.J. (1995) Accelerated ageing of AP/HTPB propellants and the influence of various environmental ageing conditions. Proc. Inti. Symp. on Energetic Materials Technology, American Defense Preparedness Association, Phoenix, Arizona, USA, Sept. 24-27, 1995, p. 199. 

The sections below describe the characteristics of various metal substrates with regard to epoxy adhesives. Only the more common substrates and those that are most reactive (to either the adhesive or the environment) are discussed. Metal substrates not covered are generally easy to bond with epoxy adhesives, and there is little change in properties with environmental aging. 

Environmental aging is usually less severe in service (laboratory tests tend to accelerate aging so that the testing can be completed in a reasonable time). However, the effects of the actual service environment are generally more complex. For example, there may be simultaneous exposure to cyclic stress, cyclic temperature, and humid environments. 

Adhesives may experience many different and exotic environments. Environmental aging of adhesives is accomplished by exposing a stressed or unstressed joint to simulated operating conditions. Exposure is typically to elevated temperature, water, salt spray, or various chemical solutions that simulate the service conditions. A number of standard chemicals that are used to soak bonded specimens for 7 days at room temperature are... 

Altstadt V, Keiter S, Renner M, Schlarb A (2000) Accelerated evaluation of environmental ageing monitored by fatigue crack growth experiments. In Cardon AH, Fuduka H, Reifsnider KL, Verchery G (eds) Recent developments in durability analysis of composite systems. Balkema, Rotterdam, pp 195-209... 

Materials with minimal mechanical degradation and environmental aging... 

Proper design of biomaterials, especially for long-term applications, should consider mechanical degradation and environmental aging problems. Thermal degradation is of lesser importance in biomaterials, due to the relatively small fluctuations of the temperature in most biomedical applications. 

H Parvatareddy, J Z Wang, D A Dillard and T C Ward, Environmental aging of... 

EFFECT OF ACCELERATED AND ENVIRONMENTAL AGING ON RIGID POLYURETHANE FOAM. 

In addition, newer aspects, such as the effects of sustainable materials based on starch on the macro or nanostructure and subsequent processing, thermomechanical properties and performance properties of plasticized starch pol5mciers have been examined (10). Specific structures and the resulting properties are controlled by many specific factors, such as filler shape, size and surface chemistry, processing conditions and environmental aging. In case of nanosized biocomposites, the interfadal interactions are extremely important to the final nanostructures and performance of these materials. 

Zadorecki P, Flodin P (1986) Surface modification of cellulose fibers III. Diuability of cellulose-polyester composites under environmental aging. J Appl Polym Sci 31 1699-1707... 

M.M. Thwe, and K. Liao, Effects of environmental aging on the mechanical properties of bamboo-glass fiber reinforced polymer matrix hybrid composites. Compos. A Appl. Sci. Manuf 33, 43-52 (2002). 

Optimum properties Very excellent ageing resistance and medium strength Good environmental ageing resistance, some oil resistance, self-... 

Table XVI. Environmental Aging of Aluminum-to-Aluminum Bonds"...

Table XVII. Environmental Aging of Polystyrene and Chloroprene Overlap Shear bonds"...

Two aspects of the effects of environmental aging deserve mention here. The first concerns the locus of joint failure, i.e., the path followed by the fracture surface during the breaking of the joint. If structural adhesive joints are prepared correctly, then failure invariably occurs by cohesive fracture through the adhesive layer. However, it is commonly found that after environmental exposure the locus of failure is at, or very close to, the adhesive/adherend interface.As pointed out by Kinloch, this change in... 

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