Lecture

Photochemistry I: Photodegradation of Polymers

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In course

CH-442: Photochemistry

This course presents the theoretical bases of electronic spectroscopy and molecular photophysics. The principles of the reactivity of excited states of molecules and solids under irradiation are detailled. The main classes of industrial and natural photoc ...

Description

This lecture covers the photodegradation of polymers, focusing on the characteristics of various polymers, their absorptivity to the solar spectrum, and the primary and secondary photodegradation processes involved. It also discusses the photostabilization strategies used to prevent light absorption and deactivate excited states of chromophores, leading to the development of UV screeners, UV absorbers, excited state quenchers, and free radical scavengers. The lecture delves into the effects of stabilizers on the photostability of poly(propylene) and the mechanisms behind secondary photodegradation processes. Additionally, it explores reactions due to dyes and pigments, emphasizing singlet oxygen sensitization and photo-oxidation by semiconducting pigments.

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Related concepts (32)

Dyeing

Dyeing is the application of dyes or pigments on textile materials such as fibers, yarns, and fabrics with the goal of achieving color with desired color fastness. Dyeing is normally done in a special solution containing dyes and particular chemical material. Dye molecules are fixed to the fiber by absorption, diffusion, or bonding with temperature and time being key controlling factors. The bond between dye molecule and fiber may be strong or weak, depending on the dye used.

Dye

A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and may require a mordant to improve the fastness of the dye on the fiber. The majority of natural dyes are derived from non-animal sources: roots, berries, bark, leaves, wood, fungi and lichens.

Natural dye

Natural dyes are dyes or colorants derived from plants, invertebrates, or minerals. The majority of natural dyes are vegetable dyes from plant sources—roots, berries, bark, leaves, and wood—and other biological sources such as fungi. Archaeologists have found evidence of textile dyeing dating back to the Neolithic period. In China, dyeing with plants, barks and insects has been traced back more than 5,000 years. The essential process of dyeing changed little over time.

Photodegradation

Photodegradation is the alteration of materials by light. Commonly, the term is used loosely to refer to the combined action of sunlight and air, which cause oxidation and hydrolysis. Often photodegradation is intentionally avoided, since it destroys paintings and other artifacts. It is, however, partly responsible for remineralization of biomass and is used intentionally in some disinfection technologies. Photodegradation does not apply to how materials may be aged or degraded via infrared light or heat, but does include degradation in all of the ultraviolet light wavebands.

Tie-dye

Tie-dye is a term used to describe a number of resist dyeing techniques and the resulting dyed products of these processes. The process of tie-dye typically consists of folding, twisting, pleating, or crumpling fabric or a garment, before binding with string or rubber bands, followed by the application of dye or dyes. The manipulations of the fabric before the application of dye are called resists, as they partially or completely prevent ('resist') the applied dye from coloring the fabric.

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