Introduction and intention

Elastomer materials are mandatory for temperature- and media-resistant components which are under dynamical load. Their service life is significantly influenced by external factors such as the effects of ozone, oxygen and temperature, as well as the load spectrum. These influences lead to function-limiting material changes that are irreversible and, in the worst case, can lead to the failure of a component. Due to their microstructure, the influence of ozone is a main problem especially for diene rubbers such as NR, BR, NBR and SBR. Ozone attack on the rubber can only be prevented by adding antiozonants or saturated polymers (if sufficiently compatible). The damage mechanism is an electrophilic addition of ozone to the double bonds, e.g. of the polymer backbone, with subsequent degradation reactions. In recent decades, p-phenylenediamines such as "6PPD" have proven their worth due to their excellent combinatorial protective effect against ozone and oxygen, but nowadays 6PPD is under discussion because of ecological and toxicological concerns (REACH). At this point, there will be a need in the future to find efficient substitutes and to know their effect mechanisms.

Objective

The project has arisen from the need to find suitable alternatives to 6PPD, which is expected to be regulated by REACH in the future. From this situation the aim results to investigate possibilities in ozone protection (additives, polymeric blend systems) for polydienes, which are already available and known from literature concerning their efficiency (effect per unit of concentration). This also includes aspects such as chemical compatibility or solubility of antiozonants in different rubber matrices in order to detect problems as for example phase separation and blooming, as well as to find out the optimum ratio between concentration and effect in technically relevant compounds. With regard to the long-term effect of ozone-protecting additives, it is also a goal to gain knowledge about the kinetics of consumption as well as their diffusion properties. One special aspect that has been repeatedly observed in practice and needs to be investigated is stress that may be induced in the material by unfavourable process parameters for molding and vulcanization, which significantly increases damage by ozone despite the presence of antiozonants.

Approach and methods

In addition to unfilled model systems, selected technically used compounds based on rubbers with different double bond concentration in the main chain with different antiozonants (available on the market, literature) are to be considered in the investigation program. Furthermore 6PPD will be used as a reference. After detailed coordination with the project partners the following steps are to be pursued for the approach:
 

1. Determination/definition of the systems (polymer matrices, ozone protection). The selection is made according to representative chemical structures and ex-pected effect mechanisms

2. Compounding and vulcanization with comprehensive basic chemical and physical characterization (e.g. double bond concentration on the surface)

3. Characterization of the consumption (kinetics) of the antiozonants at different stretching of the material (short-term ozone tests at elevated ozone concentra-tion, time-dependent quantitative analyses of the content of the antiozonant)

4. Chemical analyses of the reaction products and description of damage mech-anisms depending on different antiozonants

5. Systematic determination of the optimal concentrations of investigated anti-ozonants

6. Compatibility, diffusion and solubility studies of blends (saturated polymers used as ozone inhibitors) and internal antiozonants in selected rubber matrices

Methods: Ozone tests, time lag-method (diffusion coefficient), (ATR)-FT-IR spectroscopy, extraction, LC-MS, GC-MS, DSC, compounding (laboratory internal mixer), vulcanization (press), microscopy, physical tests according to DIN/ISO.

Scientific and economic benefits

With the knowledge of the mechanism of action, efficiency and compatibility of antiozonants, the economic benefit of this project results in particular in findings of alternative antiozonant with regard to the future regulation of the use of 6PPD. Improved ozone protection also pro-vides financial savings in the absence of complaints. Knowledge of the optimal efficiency and effect of antiozonants result in saving of raw materials and the associated costs.

Conditions

•  Funding of the project by industrial partners (consortium)
• Duration: 2.5 years
• Costs: 90,000 EUR/year, apportionment between partners, max. 20,000 EUR (plus VAT) per partner and year

If you are interested and for details please contact us until the 28th of February 2021