The effects of pigments on the photostability of polyethylene

Abstract

The affect of carbon black and various colourizing pigments on the ultraviolet (UV) stability of high and low density polyethylene (HDPE and LDPE) was determined using a novel method for the analysis of oxygen uptake profiles. Samples were exposed to 0.27 W m -2 (measured at 340nm) UV irradiation at 25.0 4-0.1° C in air at 1.0atm. The usefulness of this method of assessment of UV stability is demonstrated. The method also enables the rapid collection of data that enable the comparison of the relative photostabilities of experimental and commercial formulations containing pigments and stabilizing additives. The results show that carbon black is an effective UV screening agent for HDPE when added at levels as low as 0.05% (wt/wt) and that increased photoprotection is achieved with increasing concentration of carbon black, up to 5% (wt/wt), above which there is no further significant increase in photostability. LDPE containing ultramarine blue pigment (Na7AI6SiaO24S3) exhibits relatively poor photostability, whereas ferric oxide (Fe203) and chrome orange (PbCrO4. PbO) pigments are better photostabilizers for this material. Cadmium sulphide (CdS) was found to photosensitize LDPE. A compound containing 0.10% (wt/wt) carbon black, 0.12% (wt/wt) titanium dioxide (TiO2) and 1.78% (wt/wt) phthalocyanine green (C33H2N8CI14Cu) is an effective formulation for the stabilization of LDPE. Formulations of LDPE containing ultramarine blue-TiO2 or ferric oxidecarbon black combinations absorb heat on exposure and this may affect their photostability.

Degradation and stabilization of polyurethane elastomers

“…Adding CB above this level will not significantly improve UV resistance. CB contents of 2 to 3 wt.% are generally sufficient for most polymer systems [255,256].…”

Effects of a titanate coupling agent on the mechanical and thermo‐physical properties of talc‐reinforced polyethylene compounds

“…Many fillers of different types and shapes can be blended with polymers, such as metals, carbon, glass fiber, and ceramics, each of which can contribute different qualities and properties. For example, carbon black has been used as an economical and highly effective additive in many thermoplastics and also in thermoset compounds for outdoor stabilization . In the literature on composites, it has been shown that compounding polymers with fillers and particles can improve mechanical properties, electrical conductivity, and thermal behavior as well as protect against ultraviolet radiation .…”

Mechanical and thermo‐physical properties of high‐density polyethylene modified with talc

“…Carbon black (CB) has been used as an economical additive in many thermoplastics and thermosets compounds; it is also a very effective additive for improvement of the outdoor stability of plastics. It has been shown that for high density polyethylene‐CB (HDPE) composites, even at a level of 0.05 wt % of CB, the composite has very good UV‐screening strength and this can be enhanced further by adding up to 5 wt % of CB 6, 7. The drawback is, however, that CB can reduce the mechanical properties of HDPE at higher loadings 8.…”