Light stabilization of polystyrene

Table I. Effect of Bisphenols on Light Stability of Polystyrene...

Certain phenolic antioxidants in combination with ultraviolet absorbers improve substantially the light stability of polystyrene. Combinations of this type can be used advantageously to prevent polymer discoloration in indoor fluorescent lamp fixture applications. However, studies of this type require further investigation, and an explanation must be sought for the striking differences in behavior of the various antioxidants tested. 

Savides C, Stretanski JA, Costello LR (1968). Light Stabilization of Polystyrene, in Gould... 

Among the types of ultraviolet absorbers that may be used as stabilizers are salicylates, o-hydroxybenzophenones, o-hydroxyarylbenzotri-azoles, and certain acrylonitriles. The stabilization of polystyrene by other additives has also been reported. Matheson and Boyer (10) found that certain aliphatic amines and amino alcohols improved the light stability of the polymer. 

Styrenic Polymers Stabilization of polystyrene and its copolymers is necessary for articles expected to be exposed to solar radiation or indoor fluorescent lighting. Because of the signiflcant role played by thermal oxidation products in the effect of these sources on the polymers, thermal stabilization at the processing stage is required to reduce their sensitivity to light. The use of a phenolic antioxidant was shown to increase the retention of mechanical properties and. 

With increasing concentration of DHB, the photoproduct forms more slowly, as evidenced by decreasing loss of fluorescence intensity (Table I, entries 1-3). Nevertheless, the concentration of photoproduct(s) and RET from the polymer to photoproduct(s) are expected to increase with time, and stabilization of the polymer will eventually depend upon the capability of the photoproduct(s) to dissipate excitation energy imparted in the RET process. The observed decrease in stabilization efficiency by DHB (based on film discoloration) with exposure time in an accelerometer indicates that DHB is more effective than the photoproduct(s) in dissipating the light energy. Similar spectroscopic studies on polystyrene have led to the same conclusion in this case, as well.6... 

Polystyrene light stabilization has been achieved with a variety of ulfravioler absorbers including the benzophenones, benzotriazoles. and salicylates. While yellowing of polystyrene occurs in many applications, it is particularly noticeable in diffusers used with fluorescent lights. This problem has been effectively solved by using ultraviolet light absorbers. In this instance, superior stabilization is achieved when the ultraviolet absorber is used in conjunction wirh specific antioxidants. 

It appears, therefore, that two accelerated devices may be needed an exposure unit, such as the Fade-ometer, for quick screening and relative performance studies of light-stabilized polystyrene samples, and a second unit, such as the high output fluorescent lamp, for predicting more accurately long term exposures. 

Further work will be necessary to determine the products formed on light exposure and thus elucidate more fully the mechanism of polystyrene photooxidation. Such investigations are quite useful for stabilization purposes, provided, however, that careful consideration is given to the irradiation conditions used. 

Polystyrene, its copolymers, and its alloys are used in a wide variety of applications where stability to both direct sunlight and filtered or artificial lighting is important. At wavelengths below 300 nm photolysis [12] of polystyrene can result in unacceptable color development (yellowing) along with reduction of physical prop-... 

Other Plastics Uses. The plasticizer range alcohols have a number of other uses in plastics liexanol and 2-ethylliexanol are used as part of the catalyst system in the polymerization of acrylates, ethylene, and propylene (55) the peroxydicarbonate of 2-ethylliexanol is utilized as a polymerization initiator for vinyl chloride various trialkyl phosphites find usage as heat and light stabilizers for plastics organotin derivatives are used as heat stabilizers for PVC octanol improves the compatibility of calcium carbonate filler in various plastics 2-ethylliexanol is used to make expanded polystyrene beads (56) and acrylate esters serve as pressure sensitive adhesives. 

In the current study, samples of impact polystyrene that contained a combination of light stabilizers LS I and LS II and samples that contained no light stabilizers were weathered outdoors in Florida and were monitored for changes in physical appearance and for changes in the chemical structure of the surface by use of a multiple internal reflectance IR spectrophotometer. Also, samples of a thermoplastic polyurethane that was stabilized with just LS I and samples that contained no light stabilizers were weathered and monitored in the same way as the impact polystyrene. We hope to establish at what point... 

Figure 2. SEM photomicrographs at 600x (left) and IR spectra (right) of impact polystyrene with no light stabilizers. The samples were exposed in Florida at a 45° angle...

After 9 months of outdoor exposure in Florida (Figure 5), and even after 12 months (Figure 6), the SEM photomicrographs of the IPS (impact polystyrene) show minimal surface deterioration for the samples that contain 0.5% LS I and 0.5% LS II, while the samples that contain no light stabilizers show extreme surface erosion and the presence of mildew. 

Figure 5. SEM photomicrographs of impact polystyrene exposed in Florida at a 45° angle facing south for 9 months. The light-stabilized samples contained 0.5% LS / (HALS) and 0.5% LS H enzotriazole UV absorber).

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