Degradation phenomena are numerous and involve a number of variables often much greater than we can imagine and simulate. The study of these phenomena is related to the whole analysis of the materials. For this reason, before to approach experimentally a study on degradation, it is necessary to get an idea of what is the "state of the art" of the specific topic, by analyzing the literature. Sometimes the need is opposite, usually we work for avoiding "degradation", but, as example, in the case of biocompatibility degradation is a wanted phenomenon which has to be controlled.
INTERNATIONAL STANDARD AND REALITY
When there is the need to understand how a material or a product will react to specific environmental conditions and as a function of exposition time, there is the possibility to utilize different instrumental and testing approaches.
International standards are surely a good starting point for a complete study, but often they are not sufficient to solve the accelerated weathering needs: external variables are not reprodicible and 'vary' on a non predictive way.
In RDLAB137 we prefer sometime a material based approach, and, with a preventive analysis of its degradation behaviour, we can evaluate which are the best ways to accelerate and analyze the material.
HOW TO STUDY MATERIAL'S DEGRADATION
First point is to define clearly the target. Generally speaking :
- Evaulate the 'life' of a product, subjected to specific ambiental conditions
- Accelerate the natural degradation with appropriate techniques, which simulate as much as possible the external variables, and which allow an early evaluation of degradation phenomena
- To study the matierial's degradation mechanisms, in order to understand which are the most sensitive components of it
- Improve or set up of efficient stabilization systems (additivation)
- Compare market products
- Understand which are the by products of degradation (for example for 'bio' degradation)
We do not include here the big argument of 'Fire Resistance', but, strictly speaking, fire is one of the most important degradation promoter!
Here you can find a very brief description of laboratory studies, regarading the degradation study. We invite you to contact us directly for further deepening of specific themes.
DEGRADATION IN INERT ATMOSPHERE
If yout think on a degradation process of a polymer inside an extrusion machine, may be the oxygen is not so rilevant as outside, and degradation phenomena are of pure thermal origin. For this, and other, reason, it is imporant to study degradation mechanism without oxygen.
A vacuum oven and eventually inert gases
The first step is to focus on the temperatures of interest and work around these. For example, if you process at 230 °C, it is necessary to make tests at 210 °C, 230 °C, 250 °C and 270 °C. Same for degradation times. The analysis of mechanical and chemical changes on materials need the use of appropriate techniques: mechanical tests and infrared spectrocopy, in addition to the visual analysis, are the most useful tools
.THERMAL DEGRADATION IN OXIDATIVE ATMOSPHERE
After the understanding of the pure thermal degradation processes in inert atmosphere, we can try to understand the behavior with oxygen.
THERMAL DEGRADATION WITH PARTICULAR CONTAMINANTS
If the materials come into contact during processing or use, with particular substances (eg think of the cables carrying gasoline in the car), tests must be carried out taking this into account and artificial ageing tests will be specific depending on the different substances / atmospheres.
SPECIFIC DEGRADATION TESTS IN MACHINES
It is possible to verify what happens to a material if it remains long times in drying ovens, extruders, presses, etc. However, due to the large number of variables, these tests must be accompanied to the most serious and fundamental analysis. The results should be interpreted carefully.
ACCELERATED WEATHERING: LIGHT, WEATHER, NATURAL AGEING
The aging tests for outdoor exposure are intended to compare the behavior of different materials ONLY if these materials are exposed all together at the same time, in the same place and machine.
It seems trivial, but knowing how to prepare and properly expose the specimens to natural aging is not so simple and requires considerable attention and care. A small mistake risks to cost years of wrong tests.
Sometimeswe need only to observe the samples over time. Sometimes chemical or mechanical tests on degraded samples are needed. I always prefer the non-destructive tests, because the number of samples to be exposed to periodic destructive characterizations can be very high.
ACCELERATED TEST WITH XENON LAMPS
As for the so-called "accelerated test", it is true that accerelated conditions cannot reproduce the external conditions. However, even the outside conditions are never reproducible! Compared to degradation in outdoor they have the advantage, besides the higher speed, that, observing the CARE MAXIMUM in the instrument, it may also make comparisons between samples exposed at different times and in different machines. Preferred however, are comparisons between samples exposed simultaneously.
The Xenon irradiation found wide acceptance since their spectral emission should be the most similar to that of the sun. To get reliable test it is fundamental to monitor and maintain the equipment in perfect working order. It 'important not to skimp on spare parts and instrument control. Temperatures, water quality, irradiance, cycles, filters.....all this variables must be known in details and with precision.
The control is often visual. Of course you can use all the available analytical techniques to analyze the kinetics of degradation, but are preferred non-destructive testing, because you do not need high number of samples.
ACCELERATED TEST WITH UV LAMPS
The UV lamps (UV-a or UV-b) emit a lot of energy in the most degrading area of solar radiation and, for this reason, they accelerate the light degradation. In this case too, not always reproduce what can be done outside, but, if used to compare different materials, they can provide useful informations. UV machines are relatively cheap and the maintenance required is less than Xenotest.
As for other exhibitions, it is important to always check the type of lamps before making comparisons. Favorites is the continuous monitoring of radiation.
STUDY OF DEGRADATION PHENOMENA
The analysis of what's happening during degradation's tests could be very useful in order to evaluate in the early stage, the material's behaviour (saving time and money). It is impossible in some words to be exaustive, but here is a list of analytical techniques we can study in our laboratories:
- Infrared spectroscopy (bluk and surface)
- Raman spectroscopy
- Optical and Electronic microscopy
- Micronalysis EDX
- ICP with laser ablation
- Color, gloss, and optical characterization in reflexion and absorption at different wavelenghtsù
- Surface variables mesaurements: roughness, hardness, surface tension, electrical conducibility, etc.)
- Mechanical tests
Dr. Maurizio Veronelli - Specialist in Polymer Science
Last revision: 14 January 2019