Combined impact of ultraviolet and chemical fluids on high-density polyethylene packaging material
(2012)
To investigate the ageing behaviour of filled plastic containers outdoors, square cuts of the wall of two high-density polyethylene (HDPE) types were exposed to ultraviolet (UV) radiation at their front side and to specific liquid chemicals (de-ionized water, surfactant or White Spirit) at their back. The UV radiant exposure at the front side was 80 MJ/m².
To compare the actions of the different exposures, separate dark backside fluid exposures were performed, in parallel. Besides, UV weathering was carried out until a UV radiant exposure of 325 MJ/m², being roughly comparable to outdoor exposure of one year in Northern Australia.
An unpigmented HDPE included in the investigation gave no sufficient protection for the White Spirit. In addition, it showed clear degradation after several of these exposures. In combination with the White Spirit, an increase of carbonyl bonds was measured, presumably assignable to degradation products of the White Spirit.
For a pigmented HDPE material, with the implemented combined exposures, no relevant damage was observed, within applied the exposure period.
Jerrycans made from three different types of high-density polyethylene (HDPE) were exposed outdoors, for one Berlin summer season. They were filled with a 55 percent nitric acid solution (HN03), pure water, or air, and half of them were protected from sunlight by an UV absorbing canvas. Thus, the separate effects of UV radiation and nitric acid could be compared to the combined impact. Combined impact was mainly affected by decomposition of nitric acid, resulting in presence of reactive nitrogen oxides, increased oxygen partial pressure, and UV radiation energy, simultaneously in vapour phase.
To investigate the degradation effects after the outdoor exposure, jerrycans were exposed to a so called hydraulic internal pressure test, similar to an approval test for dangerous goods packaging. After combined impact of UV radiation and nitric acid, internal pressure tests showed very fast failures, whereas after separate impacts no remarkable deteriorations were observed, compared to unaged jerrycans.
A new irradiation device for the exposure of plastic products is presented. Developed in the BAM division 3.1 "Dangerous Goods Packaging" it can be used for artificial UV irradiation of plastic Containers filled with hazardous liquids.
Present regulations and tests only investigate the exposure effects of UV and of media separately, but as the damaging effect is expected to be synergistic for at least some media, a combined test was looked for.
A chamber of 60 cm by 60 cm base area and 1 m height gives space for up to 40 cm wide objects. Two fluorescent UV lamp arrays are arranged on opposite walls, separated from the chamber by quartz glass panes. By continuously rotating the exposure object by means of a rotary disc that the object is placed on, spatial irradiation homogeneity is achieved over the exposure duration. The spectral irradiance of the chosen UVA 340 nm lamps gives the best match of global solar radiation in the short wavelength ränge. The close arrangement of the UVA lamps (15 each side) results in 60 W m'2 UV irradiance.
Constant temperature is adjusted to typically 40 °C by the control of the fan speed. This temperature is chosen, as it is the required temperature for three week storage of filled polyethylene Containers, for proving Chemical compatibility in the field of dangerous goods. To ensure homogeneity, an interiorfan provides for air circulation.