Weathering behaviour

From the foregoing sections it will be realised that the aging and weathering behaviour of a plastics material will be dependent on many factors. The following agencies may cause a change in the properties of a polymer ... 

In a commercial plastics material there are also normally a number of other ingredients present and these may also be affected by the above agencies. Furthermore they may interact with each other and with the polymer so that the effects of the above agencies may be more, or may be less, drastic. Since different polymers and additives respond in different ways to the influence of chemicals and radiant energy, weathering behaviour can be very specific. 

Cyanoacrylate adhesives are particularly valuable because of their speed of action, which allows the joining of intricate parts without the need for complex jigs and fixtures. Within very broad limits the more monomer that is used to make a joint the less will be the strength. These adhesives have in fact no gapfilling ability, nor can they be used on porous substrates. Whilst they have good heat and solvent resistance their weathering behaviour is limited and joints should not be in frequent contact with water. 

There is a frequent dememd for materials suitable for housings for computer, domestic, electrical and automotive equipment. In these applications toughness, excellent surface finish, surface durability, reasonable rigidity, dimensional stability, good weathering behaviour and low water absorption are common requirements. In these applications ABS is frequently considered first but its limited deflection temperature and heat aging resistance may lead to other... 

All of the factors involved in weathering, including both the amount of intensity of sunlight, vary both seasonally and geographically. To understand fully and predict the weathering behaviour of any polymer requires information about exactly how these factors vary and how they then contribute to the overall degradation process. 

Cox, G.A., Fleavens, O.S., Newton, R.G. and Pollard, A.M. (1979). A study of the weathering behaviour of Mediaeval glass from York Minster. Journal of Glass Studies 21, 54-75. 

In spite of its empirical nature, weathering behaviour can in some circumstances be predicted with a level of accuracy acceptable for design. Examples are given in Section 12.4. 

Fujimoto, H. (1992). Weathering behaviour of chemically modified wood with a maleic acid -glycerol (MG) mixture. In Pacific Rim Bio-Based Composites Symposium Chemical Modification of Lignocellulosics, Plackett, D.V. and Dunningham, E.A. (Eds.). FRI Bulletin 176, pp. 87-96. 

Because the composition of the clay was independent of glass substrate composition, Zevenbergen et al. (1994) proposed that local hydrochemical conditions (rather than ash composition) was the primary control on secondary mineral formation. This conclusion suggests that at least some weathering behaviours of CCB and MSWI wastes are analogous. 

Information on the natural weathering behaviour of joints is very useful. By combining this information with data from accelerated laboratory tests, some realistic predictions of service-lifetime may be made. Theoretical models of the pattern of bondline saturation of joints as a function of time of environmental exposure provide a useful appreciation of the possible extent of problems (e.g. Fig. 4.21). The process of joint failure, as observed in practice or in the laboratory, is frequently non-diagnostic i.e. it rarely reveals the true cause, or the series of stages, leading to deterioration or failure. 

All the physical and mechanical properties are altered at the same time when a filler is added, and the extent of the change depends on particle size and geometry. Chemical resistance may be affected (calcium carbonate is attacked by mineral acids) and weathering behaviour can alter. 

Tests on acrylic/styrene dispersions having varying minimum film forming temperatures demonstrate that when a suitable binder is used, solvent-free paints can be formulated, which exhibit weathering behaviour comparable to that of conventional solvent-based paints. Rutile titanium dioxide pigments are shown to have a greater influence on weathering resistance than the binder. 6 refs. 

Information is given on the frequency, level and formation of ground surface ozone concentrations in Central Europe, and a study is described of the weathering behaviour of various rubber materials (crack initiation and growth) under the effect of ozone. 20 refs. Articles from this journal can be requested for translation by subscribers to the Rapra produced International Polymer Science and Technology. 

---