Organic polymers are in general highly sensitive towards oxidative decay (degradation reactions include chain scission, loss of end groups, cross-linking). Thermal conditions during the initial polymerization (for synthetic organic polymers) and during the thermal processing and shaping (extrusion, injection molding) are particularly harmful and lead to thermo-oxidative decay. To circumvent this, polymers are generally stabilized for processing.

Additional treatment with antioxidants, UV absorbers, HALS etc. are used to prevent oxidative decay caused by external factors such temperature, light exposure, humidity etc. These treatments are crucial to ensure the requested service lifetime of polymers, in particular for long-term application and extreme conditions (outdoor applications, motors, isolation of cables). The technology of ACL Instruments allows a very precise characterization of the efficiency of such stabilizing treatments, especially since the application conditions can be very closely simulated to the application conditions. This permits optimization in regard to both the composition and quantity of stabilizing system used. The specific life expectancy of individual product formulations under given application conditions can be accurately predicted using isoconversional analysis of the oxidative kinetics.

leaflet polymers
Oxidation of polypropylene in air: evaluation of the temperature-dependent oxidation. The onset of the autocatalytic onset at ~168°C (melting temperature of PP) is very obvious. Using the CL-technology of ACL Instruments, two changes of the oxidations kinetic may be characterised in the solid state of the polymer (at ~85°C and ~122°C). The experimental conditions: 30 ml synthetic air per minute, non-isothermal temperature profile from 25-175°C during 72h.
Oxidation of new Plexiglas (PMMA 4k in pure oxygen): the peak at 125°C indicates the thermal decay of accumulated hydroperoxides (ROOH: verified by similar experiment in nitrogen); the increasing CL-emission after the peak results from the thermally induced oxidation of the polymer. Experimental condition: non-isothermal (dynamic) temperature profile from 25 to 180°C, heating rate = 0.43 Kmin-1, gas flow = 30 mlmin-1.
Oxidation of unstabilised natural rubber at different non-isothermal temperature profiles in air. With decreasing heating rate (dark curves), the oxidation reaction shifts toward lower temperature levels. Measurement conditions: non-isothermal (dynamic) temperature profiles from 25 to 180°C, heating rates from 0.005 to 0.072 Kmin-1, gasflow = 30 mlmin-1.
natural rubber
Oxidation of stabilised coating in air depending on the ageing with Xenon arc instrument (0, 12, 24 und 36h): the longer the ageing procedure, the earlier sets the oxidation of the sample. Measurement conditions: each in non-isothermal (dynamic) temperature profile from 25 to 200°C, heating rate = 0.12 Kmin-1, gasflow = 30 mlmin-1.
aged coating

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