Hindered amine light stabilizers in pigmented coatings

It is common practice to combine hindered amine light stabilizers (HALS) with UV absorbers (UVA) for optimal protection of coatings and plastics. The ratio of UVA and HALS strongly depends on the concentration of pigments (acting as UVA) used in the paint; that is, a clearcoatings require higher amounts of UVA, whereas opaque pigmented coatings require higher amounts of HALS. Here, especially basic HALS types can interfere with paint components like, for example, pigments due to acid/base interactions. In this article, we want to discuss the influence of HALS basicity on long-term performance in opaque white pigmented solventborne (SB) and waterborne (WB) coatings for industrial applications in correlation to the quality of the used TiO₂.     

Interactions between light stabilizers and pigment particles in polymeric coatings

Adsorption experiments have been carried out to understand the interactions responsible for UV light stabilizer adsorption on pigments in coatings. Light stabilizer adsorption on various pigments was studied in xylene solutions to eliminate potential interference from the cure process. Adsorption isotherms were determined for UV absorbers and hindered amine light stabilizers (HALS) compounds. Infrared spectral analysis revealed that chemical interactions at the pigment surface are responsible for the observed effects. In some cases the chemical surface interactions are likely to prevent the adsorbed molecules from functioning as light stabilizers.     

Synergistic effect of hindered amine light stabilizers/ultraviolet absorbers on the plasticized PVC during photo-irradiation

Two kinds of piperidine derivatives including a low-molecular weight (Wt. 481, T770) and a high-molecular weight (Wt. 2000–3100, C944) hindered amine light stabilizers (HALS) are added singly or with ultraviolet absorbers (UVA) in combination to plasticized poly(vinyl chloride) (PVC) samples. Digital photos, color changes, attenuated total refection-Fourier transform infrared spectra (ATR-FTIR), and mechanical properties are obtained to investigate the photostable effect of the light stabilizers on the plasticized PVC after artificial aging. PVC samples with HALS perform well at the first 400 h of irradiation in color change, FTIR, and mechanical properties, but at the last 400 h the photostability decreases. Besides, C944 performs better than T770, because C944 is a high-molecular weight UV stabilizer and has good extraction resistance. Plasticized PVC samples with UVA resist discoloring and photooxidation from the photo-irradiation. Excellent synergism is observed between the combination of HALS and UVA. PVC with HALS/UVA performs better than PVC with HALS and PVC with UVA in color differences, FTIR, and mechanical properties. The synergism is due to the different stages of functions between HALS and UVA. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Studies on the interaction of photoreactive light stabilizers and UV-absorbers

Coatings, like all organic substances, are submitted to photoageing during their life time. Ultraviolet light absorbing additives (UVAs) and hindered amine light stabilizers (HALS) often are added to improve their performance. These additives can be lost by migration to the surface, where they are exposed to physical depletion, as well as through photodegradation of the molecule itself. Modifying hindered amine light stabilizers by introducing a photoreactive site gives the possibility to fix the stabilizing molecule onto the polymer matrix. The influence of the presence and the type of UV absorbers onto the photografting reaction will be discussed.     

Effect of penta- and tetramethyl HALS on the radiation resistance of polypropylene

2,2,6,6-Tetramethyl-4-piperidinyl methacrylate (TMPM), a new pentamethyl HALS 1,2,2,6,6-pentamethyl-4-piperidinyl methacrylate (PMPM), their homopolymers (PTMPM and PPMPM), and their copolymers, [i.e., TMPM or PMPM copolymerized with monomers methyl methacrylate (MMA), methacrylic acid (MAA), acrylic acid (AA), and styrene (St) separately] were synthesized. PMPM shows an extremely excellent stabilizing effectiveness on improving the radiation resistance of polypropylene (PP) in comparison with other low molecular weight (LMW) HALS or polymeric HALS. Polymeric HALS shows a much higher thermal stability and better extraction resistance than that of LMW HALS. It is found that the Eb values of the PP-added pentamethyl HALS series are higher than those of PP with the corresponding tetramethyl HALS series at a given irradiation dose. A conclusion can be drawn that the pentamethyl HALS series has a higher stabilizing effectiveness than that of the tetramethyl HALS series. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2649–2656, 1998     

Modifications of carbon for polymer composites and nanocomposites

The various forms of carbon used in composite preparation include mainly carbon-black, carbon nanotubes and nanofibers, graphite and fullerenes. This review presents a detailed literature survey on the various modifications of the carbon nanostructures for nanocomposite preparation focusing upon the works published in the last decade. The modifications of each form of carbon are considered, with a compilation of structure-property relationships of carbon-based polymer nanocomposites. Modifications in both bulk and surface modifications have been reviewed, with comparison of their mechanical, thermal, electrical and barrier properties. A synopsis of the applications of these advanced materials is presented, pointing out gaps to motivate potential research in this field.