Ultraviolet light stabilization mechanism

This study was therefore undertaken to prepare and evaluate acrylonitrile—butadiene-styrene (ABS) and methyl methacrylate-butadiene-styrene (MBS) polymers under similar conditions to determine whether replacement of acrylonitrile by methyl methacrylate could improve color stability during ultraviolet light aging, without detracting seriously from the good mechanical and thermal-mechanical properties of conventional ABS plastics. For purposes of control, the study also included briefer evaluation of commercial ABS, MBS, and acrylonitrile-butyl acrylate-styrene plastics. 

The stabilizers chosen for evaluation include different types of heat and light stabilizers selected to represent different mechanisms of action as well as chemical compositions (ArJi). Types of stabilizers evaluated include benzotriazole and benzophenone light stabilizers [ultraviolet (UV) light absorbers], hindered amine light stabilizers (HALS, catalytic radical scavengers), hindered phenol heat stabilizers (antioxidant radical scavengers), and thioester heat stabilizers (antioxidant hydroperoxide decomposers). 

The chemical stability of PE is comparable to paraffin. It is not affected by mineral acids and alkalis. Nitric acid oxidizes PE and halogens react with it by substitution mechanisms. By chlorination in the presence of sulfur dioxide, chlorine groups and sulfonyl chloride are incorporated and an elastomer is formed. Oxidation of polyethylene which leads to structural changes can occur to a measurable extent at temperatures as low as 50 °C. Under the influence of ultraviolet light the reaction can occur at room temperature. 

Obtained effect of stabilization by hexaazocyclanes appeared to be effective and at simultaneous action of mechanical load and ultraviolet light. As dependence of durability of initial and dyed samples of CDA on the value of the load (Figure 2.13) at photomechanical destruction shows, the durability of stabilized sample is higher than initial one by 1,3 times. 

This results in deterioration of the mechanical and electrical properties of the polymer resistance to photooxidation by ultraviolet light varies. The following groups of plastics show decreasing light stability in the order of low-density polyethylene > high-density polyethylene > polypropylene > polystyrene. 

Besides the need for high mechanical strength, low shrinkage, dimensional stability, and ease of processing, the final formulations must also be resistant to the elements such as water and ultraviolet light (105). For automotive use, the materials also must be paintable. Thus the SMC technology involves not... 

Cyanoacrylate monomers are highly reactive compounds and will polymerize via anionic and/or free radical mechanisms. The anionic reaction route is by far predominant and can be initiated by even small amounts of a weak base such as water. Exposure to extended high temperatures, ultraviolet light, or heat in the presence of peroxides can cause free radical polymerization to be initiated. The extreme anionic reactivity of these monomers was unobserved by early workers, probably due to crude preparatory methods which resulted in very impure, overstabilized product. Early attempts to polymerize the monomers nearly always involved thermal methods. It was not until the early 1950s that Coover and Shearer of Eastman Kodak, using purer material stabilized with SO2 gas, discovered the unique polymerization and bonding characteristics of the cyanoacrylate monomers. 

---