15 “Polymer–Oxide” Micro-/Nanocomposites: Background and Promises
253
15.3.1 Optical Properties of the “Pure” Cellulose Materials
Cellulose is a biopolymer built on D-glucose units linked to unbranched chains by
ß-1,4-glycosidic bonds. The microcrystalline cellulose (MCC) is a pure partially
depolymerized cellulose. The linear cellulose chains are connected as microfibrils
spiraled together in the walls of plant cell. Each microfibril shows a high level of
three-dimensional internal bonding resulting in the crystalline phase of cellulose.
Some part of the microfibrils form amorphous phase of the last one [35–38], APP.
Cellulose fibers—both those obtained from vegetable raw materials and the
man-made—are widespread materials available in many areas of life. The ongoing
development of the methods of modifications of cellulose fiber properties and giving
specific functionalities allow finding new uses in many, however not so obvious,
applications such as substrate for electronic component, military industry (e.g.,
paper patching jacketed bullets, filters), aircraft, and cosmic space industry [49, 52].
Manifestations of the various cellulose materials’ photoluminescence (PL) are
known and described long ago [45–47, 53–55]. It is intensive observable luminescence. Up to now, there are no reliable conclusions about origins of the
cellulose-based materials’ luminescence, but undoubtedly, there are several of them.
Regarding electronic structure of the basic elements of cellulose composition, β(1,4)-glycosidic-linked glucose unit, it is hard to think that it was capable to
emit luminescence light. At the same time, these constituents can be involved in
absorption of incident light which exits photoluminescence.
The PL emission of various types of cellulose materials revealed quite similar
luminescence characteristic. So, three different PL bands with peak positions lying
near 370, 430–470, and 505–510 nm were found and then ascribed to three different
luminescence centers in the work [56]. The PL bands with maxima near 420–460 nm
and 495 nm were also described [57, 58]. Above-noted statement concerns the
luminescence of the various cellulose materials, and those are made from different
sources such as bleached craft and sulfite pulps, Whatman filter paper, biomedical
cellulose [58, 59], etc.
We have seen that the physical properties as well as the degree of crystallinity
and chain order of cellulose-based materials depend highly on conditions of the
manufacturing and treatment procedure. Thus, we have performed experiments on
luminescence spectroscopy for our cellulose samples. There were four types of
cellulose samples used for the study. Sample labeled SC or CT was the starting tablet
of chemically pure microcrystalline cellulose (MCC) manufactured at ANCYRB, Ukraine. The next samples, CD, were prepared from the CT samples by their
dispersion using mechanical milling of the cellulose tablet followed by ultrasonic
treatment (f = 4:2 kHz). Then, the powder was pressed into a disc using light
pressure.
All, made by us, cellulose samples are characterized with intensive PL. The
widely composed emission band located in the 325–750 nm range is observed in
the PL spectra of cellulose samples SC and CD under excitation in a wide range of
excitation wavelengths, λ ex = 300–532 nm.
253
15.3.1 Optical Properties of the “Pure” Cellulose Materials
Cellulose is a biopolymer built on D-glucose units linked to unbranched chains by
ß-1,4-glycosidic bonds. The microcrystalline cellulose (MCC) is a pure partially
depolymerized cellulose. The linear cellulose chains are connected as microfibrils
spiraled together in the walls of plant cell. Each microfibril shows a high level of
three-dimensional internal bonding resulting in the crystalline phase of cellulose.
Some part of the microfibrils form amorphous phase of the last one [35–38], APP.
Cellulose fibers—both those obtained from vegetable raw materials and the
man-made—are widespread materials available in many areas of life. The ongoing
development of the methods of modifications of cellulose fiber properties and giving
specific functionalities allow finding new uses in many, however not so obvious,
applications such as substrate for electronic component, military industry (e.g.,
paper patching jacketed bullets, filters), aircraft, and cosmic space industry [49, 52].
Manifestations of the various cellulose materials’ photoluminescence (PL) are
known and described long ago [45–47, 53–55]. It is intensive observable luminescence. Up to now, there are no reliable conclusions about origins of the
cellulose-based materials’ luminescence, but undoubtedly, there are several of them.
Regarding electronic structure of the basic elements of cellulose composition, β(1,4)-glycosidic-linked glucose unit, it is hard to think that it was capable to
emit luminescence light. At the same time, these constituents can be involved in
absorption of incident light which exits photoluminescence.
The PL emission of various types of cellulose materials revealed quite similar
luminescence characteristic. So, three different PL bands with peak positions lying
near 370, 430–470, and 505–510 nm were found and then ascribed to three different
luminescence centers in the work [56]. The PL bands with maxima near 420–460 nm
and 495 nm were also described [57, 58]. Above-noted statement concerns the
luminescence of the various cellulose materials, and those are made from different
sources such as bleached craft and sulfite pulps, Whatman filter paper, biomedical
cellulose [58, 59], etc.
We have seen that the physical properties as well as the degree of crystallinity
and chain order of cellulose-based materials depend highly on conditions of the
manufacturing and treatment procedure. Thus, we have performed experiments on
luminescence spectroscopy for our cellulose samples. There were four types of
cellulose samples used for the study. Sample labeled SC or CT was the starting tablet
of chemically pure microcrystalline cellulose (MCC) manufactured at ANCYRB, Ukraine. The next samples, CD, were prepared from the CT samples by their
dispersion using mechanical milling of the cellulose tablet followed by ultrasonic
treatment (f = 4:2 kHz). Then, the powder was pressed into a disc using light
pressure.
All, made by us, cellulose samples are characterized with intensive PL. The
widely composed emission band located in the 325–750 nm range is observed in
the PL spectra of cellulose samples SC and CD under excitation in a wide range of
excitation wavelengths, λ ex = 300–532 nm.