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FTIR-Deconvolution Spectra of Paper Documents"
No full textInfrared spectra of paper samples often show many overlapped hands in the most significant region of 1400-1900 cm(-1). The digital deconvolution reveals the underlying information, as shown by some examples of both authentic items and reference samples, appositely prepared.
The IR absorbance of oxidized groups (both unconjugated and conjugated) in cellulose, as well as gelatine, rosin and lignin can be detected with the deconvolution technique even in the presence of the broad band at similar to 1630 cm(-1) due to adsorbed water. The deconvolution technique allows a rough identification of the mechanism of degradation which leads to yellowing and browning of the paper samples
Degradation Action of Iron and Copper on Paper: a FTIR-Deconvolution Analysis
No full textSamples of FeCl3 and CuCl2 treated cellulose paper were analysed by FTIR before and after accelerated ageing at 90±10°C (sealed tube technique). The main mechanism of Fe(III) degradation appeared to be a strong hydrolysis and dehydration of cellulose chains, with formation of a C4-C5 double bond, and C6 oxidation. Cu(II) oxidized the C2- and C3-OH groups to aldehydes and carboxyls, thus opening the pyranose ring, and hydrolyses and oxidized the C4-OR group with the formation of a C4-C6 β-ketoaldehyde or β-ketoacid. Among the FTIR-deconvolution bands in the 1250–1850 cm-1 region, the ~1660 cm-1 signal is attributed to the unsaturated C=C-CO, and the 1612–1622 cm-1 signal to CO-C-CO group (chelate form of the enol tautomer). These bands, which can only be detected by the deconvolution technique, appear more significant than those of unconjugated CO groups above 1700 cm-1
On the Rate of Paper Degradation: Lessons From the Past
No full textThe kinetics of paper degradation has been reviewed briefly and updated in order to emphasise
the key factors that have been (and still are) largely neglected in the interpretation of experimental
results.
A simple re-elaboration of the literature data reveals many questionable statements in the field
of paper conservation science. In particular, it is shown that accelerated ageing techniques do not
allow any prediction of the life expectancy of paper, owing to the exponential structure of the
Arrhenius relationship. Moreover, some results obtained from viscometric analyses appear misinterpreted,
since the experimental planning does not differentiate the actual (hydrolytic) from
the potential (oxidative) degradation of cellulose. Finally, the widely utilised pseudo zero-order
kinetics of degradation leads to questionable statements, since most of the mechanisms of paper
degradation do not follow such a simple pathway, so that the results of the research in the field of
paper conservation science should be in part revised
Surface and bulk reactions of cellulose oxidation by periodate. A simple kinetic model
No full textThe kinetics of periodate oxidation of cellulose was followed by exploiting the beta-alkoxy degradation of oxidised units in alkaline medium, that brings about a decrease of viscometric degree of polymerisation. The parallel strong weight loss after NaOH treatment indicates a non-random mechanism of oxidation. The obtained results are interpreted on the basis of an appositely derived kinetic model that can be applied to other mechanisms of bulk and surface degradation
Autocatalytic Degradation of Cellulose Paper in Sealed Vessels
No full textAn autocatalytic model for the degradation in sealed vessels has been developed in order to investigate the key factors that influence the degradation of paper in an enclosed environment or arranged in stacks. Owing to the non-linearity of the model an analytical solution cannot be easily found, but a computer simulation shows in a qualitative way that the initial acidity of paper plays a role on the shape of the kinetic plots, while an increase in the rate of development of volatile acidic compounds (VOCs) causes an increase in the rate of degradation. Our results indicate that the initial acidity and the chemical mechanism of oxidation, other than the degree of polymerisation, should be taken into account in the studies of both accelerated and natural ageing of paper in non-ventilated environments
On the kinetics of cellulose degradation: looking beyond the pseudo-zero order rate equation
No full textThe kinetics of cellulose degradation was analysed by means of a two-stage model, characterised by an autoretardant and autocatalytic regime, later tempered by the consumption of glycosidic bonds in the amorphous regions. The proposed model explains the effects on the kinetic equations of different modes of ageing (acid hydrolysis, ageing in ventilated oven or sealed vessels), initial oxidation of cellulose and experimental procedures (with or without reduction of oxidised groups). The autoretardant branch can be analysed in a quantitative way, while the integration of the non-linear autocatalytic branch is allowed in some cases, characterised by the decrease of pH and/or emission of acid volatile organic compounds (VOCs). Most of the controversial results of the literature can be easily explained, but the proposed model offers also a guide for further studies on the kinetics of cellulose degradation
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