2-44 Industrial Polymers, Specialty Polymers, and Their Applications
the object to be copied whereupon the illuminated areas of the photoconductive material become
conductive and dissipate their charge to the metal drum (earthed). The photoconductive material in the
dark areas is still charged and so is able to attract a positively charged black resin-coated toner powder
forming a latent image of the object. The latent image is then transferred to a piece of negatively charged
paper which is heated to fuse and fix the resin, thereby making the image permanent.
Early photoconductive materials were based on selenium compounds such as As2Se3. Such a material
is difficult to handle, because it needs to be applied by vacuum sublimation and it is rather brittle. Poly
(N-vinyl carbazole)-based materials are now replacing the selenium-based compounds.
Much work has been reported on the development of carbazole derivatives and also noncarbazole
photoconductive polymers. An example of the latter group is poly(bis(2-naphthoxy)phosphazene),
which is intrinsically an insulator with a very low photosensitivity toward both UV and visible radiation,
but when doped with trinitrofluorenone in a 1:1 molar ratio, it is a strong photoconductor.
2.4.4 Polymers in Fiber Optics
Polymeric optical fibers (POFs) combine the benefits of all optical fibers with additional amazing
simplicity in handling. This is mainly due to their relatively large diameter and acceptance angle (or
numerical aperture). In spite of the outer diameter being typically in the range of 1 mm, the fiber remains
flexible because of the polymer material used, mainly acrylics PMMA. These benefits make POF
attractive for a wide variety of under-water, indoor and outdoor lighting, data transmission, and sensor
application. The fiber optic cable or tube employs the phenomenon of total internal reflection (see Piped
Lighting Effect, Chapter 2 of Plastics Fundamentals, Properties, and Testing) to carry the light throughout
the length of the cable.
In construction, POF cable is made up of a light carrying solid polymer core with a thin protective
coating, or covering, called the cladding. The light entering the fiber optic tube is trapped within the core
and is continually reflected as it moves down the path, the interface between the core and the cladding of
the tube wall acting like a mirror. The light comes out of the other end or is diverted. A less common type
of fiber optic cable, called a side-emitting fiber, distributes the light along the entire length of the tubing
like neon lighting.
In its simplest form, a fiber optic lighting system consists of an illuminator or light source, and a
number of fiber optic cables or light guides that carry the concentrated beam of light produced by the
light source (Figure 2.28) [59]. The illuminator can use a filter to remove most of the lamp’s infrared and
ultraviolet energy that may damage and fade the colors in textiles, paintings and graphic art pieces.
Originally conceived as a means of lighting pools and fountains, the fiber optic technology has since
been embraced by lighting architects for several indoor uses due to its low heat production. As the fiber
optic lighting does not create electromagnetic fields, this lighting technology can be used in areas with
EMF-sensitive electronic equipment, such as magnetic resonance imaging (MRI) room.
As every other optical fiber, POF has a core-cladding structure as shown in Figure 2.29. In most cases,
the core material (diameter 980 mm) is highly purified PMMA with a typical refractive index, n1Z1.49,
coated with a cladding (thickness 10 mm) of fluorinated polymer with typical refractive index, n2Z1.42,
while the polymers used for sheath/jacket are PE, HDPE, PVC, and nylon. The numerical aperture (NA)
thus has a value of 0.50. With this high NA the bandwidth is limited to theoretical values of some
10 Mbit/s. Since the bandwidth is related to the fiber NA, the transmission capacity can be increased by
lowering the NA. However, lowering NA causes increased bending sensitivity. A trade-off has therefore to
be found for the optimum POF for a specific application.
As large core POFs suffer from sensitivity to bending, these losses can be reduced by using multiple
small cores [Figure 2.30(a)] instead of a single large one. The problem can also be overcome by using the
so-called double-step-index fibers [Figure 2.30(b)] as an intermediate step to multi-step-index fibers.
The best solution achieved so far for obtaining high bandwidth with large core diameter is using a
graded index profile [Figure 2.30(c)]. Since more than 15 years a lot of progress has been made in shaping
the profile by different methods. Until 1996, mainly PMMA has been used as the core material which had
the object to be copied whereupon the illuminated areas of the photoconductive material become
conductive and dissipate their charge to the metal drum (earthed). The photoconductive material in the
dark areas is still charged and so is able to attract a positively charged black resin-coated toner powder
forming a latent image of the object. The latent image is then transferred to a piece of negatively charged
paper which is heated to fuse and fix the resin, thereby making the image permanent.
Early photoconductive materials were based on selenium compounds such as As2Se3. Such a material
is difficult to handle, because it needs to be applied by vacuum sublimation and it is rather brittle. Poly
(N-vinyl carbazole)-based materials are now replacing the selenium-based compounds.
Much work has been reported on the development of carbazole derivatives and also noncarbazole
photoconductive polymers. An example of the latter group is poly(bis(2-naphthoxy)phosphazene),
which is intrinsically an insulator with a very low photosensitivity toward both UV and visible radiation,
but when doped with trinitrofluorenone in a 1:1 molar ratio, it is a strong photoconductor.
2.4.4 Polymers in Fiber Optics
Polymeric optical fibers (POFs) combine the benefits of all optical fibers with additional amazing
simplicity in handling. This is mainly due to their relatively large diameter and acceptance angle (or
numerical aperture). In spite of the outer diameter being typically in the range of 1 mm, the fiber remains
flexible because of the polymer material used, mainly acrylics PMMA. These benefits make POF
attractive for a wide variety of under-water, indoor and outdoor lighting, data transmission, and sensor
application. The fiber optic cable or tube employs the phenomenon of total internal reflection (see Piped
Lighting Effect, Chapter 2 of Plastics Fundamentals, Properties, and Testing) to carry the light throughout
the length of the cable.
In construction, POF cable is made up of a light carrying solid polymer core with a thin protective
coating, or covering, called the cladding. The light entering the fiber optic tube is trapped within the core
and is continually reflected as it moves down the path, the interface between the core and the cladding of
the tube wall acting like a mirror. The light comes out of the other end or is diverted. A less common type
of fiber optic cable, called a side-emitting fiber, distributes the light along the entire length of the tubing
like neon lighting.
In its simplest form, a fiber optic lighting system consists of an illuminator or light source, and a
number of fiber optic cables or light guides that carry the concentrated beam of light produced by the
light source (Figure 2.28) [59]. The illuminator can use a filter to remove most of the lamp’s infrared and
ultraviolet energy that may damage and fade the colors in textiles, paintings and graphic art pieces.
Originally conceived as a means of lighting pools and fountains, the fiber optic technology has since
been embraced by lighting architects for several indoor uses due to its low heat production. As the fiber
optic lighting does not create electromagnetic fields, this lighting technology can be used in areas with
EMF-sensitive electronic equipment, such as magnetic resonance imaging (MRI) room.
As every other optical fiber, POF has a core-cladding structure as shown in Figure 2.29. In most cases,
the core material (diameter 980 mm) is highly purified PMMA with a typical refractive index, n1Z1.49,
coated with a cladding (thickness 10 mm) of fluorinated polymer with typical refractive index, n2Z1.42,
while the polymers used for sheath/jacket are PE, HDPE, PVC, and nylon. The numerical aperture (NA)
thus has a value of 0.50. With this high NA the bandwidth is limited to theoretical values of some
10 Mbit/s. Since the bandwidth is related to the fiber NA, the transmission capacity can be increased by
lowering the NA. However, lowering NA causes increased bending sensitivity. A trade-off has therefore to
be found for the optimum POF for a specific application.
As large core POFs suffer from sensitivity to bending, these losses can be reduced by using multiple
small cores [Figure 2.30(a)] instead of a single large one. The problem can also be overcome by using the
so-called double-step-index fibers [Figure 2.30(b)] as an intermediate step to multi-step-index fibers.
The best solution achieved so far for obtaining high bandwidth with large core diameter is using a
graded index profile [Figure 2.30(c)]. Since more than 15 years a lot of progress has been made in shaping
the profile by different methods. Until 1996, mainly PMMA has been used as the core material which had
