A fluorescence labeling approach to assess the deterioration state of aged papers

Deterioration of historical papers is caused by several processes, such as acid hydrolysis or autoxidation due to the presence of metal ions contained in inks or pigments. Both processes can be studied by fluorescence labeling of carbonyl and carboxyl groups in combination with GPC-MALLS. This technique allows to determine not only the extent of hydrolysis, but also the concentration of oxidized functionalities within very low sample amounts.The thermally induced aging of rag papers with lines of copper pigment has been investigated, simulating green or blue copper pigments in historic wall papers. The cellulose parts with pigment coverage and adjacent pigment-free regions were analyzed separately and compared to paper parts not affected by metal ions. The cellulose underneath and close to the applied pigment strokes was severely affected. Although there was no difference in the molecular weight distribution, distinct differences in the carbonyl and carboxyl content were observed. Copper ion migration is suggested to be one possible explanation for this observation as a strong correlation between distribution of copper ions and carbonyl groups was found. For the first time, a detailed examination of cellulose damage in spatial proximity to metal-containing pigment lines is thus presented.     

Comparison of Aqueous and Non-Aqueous Treatments of Cellulose to Reduce Copper-Catalyzed Oxidation Processes

Summary. The present paper examines oxidative degradation of cellulose catalyzed by presence of Cu¹⁺and Cu²⁺ ions in the context of historic paper conservation treatments. Aqueous treatments of degraded papers further spread transition metal ions, such as copper, across the fibre matrix, and therefore augment the detrimental effect of these ions. In the paper industry, the inhibiting effects of magnesium ions on metal-catalyzed degradation of cellulose contaminated with metal impurities have been observed. Also, magnesium compounds dissolved in alcoholic or aqueous solutions are generally used in paper conservation as deacidification agents. Paper samples with artificially produced copper corrosion served as mock-ups for examination and comparison of different treatments which focused on the inhibiting effect of magnesium and antioxidants. Analytical examination of molecular weight distribution, carbonyl content, carboxyl content, and surface pH was performed. Results show an inhibiting effect of magnesium on copper-catalyzed cellulose degradation, although less pronounced than expected.     

Iron gall ink-induced corrosion of cellulose: aging,degradation and stabilization. Part 2: application on historic sample material

Degradation of cellulose in historic paper by iron gall ink is a synergistic process of both, acid hydrolysis caused by acidic ink ingredients and oxidation catalyzed by free iron and/or copper ions. The interplay of both reactions was studied according to the CCOA method on historic paper samples. Only minute amounts (few mg) of the samples were required to obtain profiles of naturally present and oxidatively introduced carbonyl groups, which was done by group-selective fluorescence labeling in combination with determination of the molecular weight distribution by GPC-MALLS. In the present study naturally occurring degradation pathways in historic sample papers have been investigated. Different extents of oxidatitive degradation were shown for paper with and without ink. A typical pattern of the molecular weight distribution in naturally aged papers was identified, the peculiar feature being a distinctive shoulder in the region of low molecular weight, roughly between 25,000 and 5,000 g/mol corresponding to a DP between 150 and 30. This pattern was a typical attribute of degraded natural samples: any artificial aging procedures aimed at modeling natural aging processes must thus attempt to reproduce this feature. Although the historic samples had been more severely oxidized than model papers, the inhibition of further oxidation and hydrolysis by the calcium phytate/hydrogen carbonate treatment was evident and could be proven for the first time on the molecular level. Also on plain paper without ink application the oxidation was suppressed and the molecular weight was stabilized on a high level.     

Controversial influence of aqueous treatments on historic textiles

Different historic textiles were subject to aqueous treatments with and without sodium borohydride as a reducing agent. As the action of borohydride generates an alkaline environment that is potentially harmful for oxidized cellulose in historic textiles, two less alkaline treatment options using buffer systems were additionally tested.In order to track the impact of the treatments on the samples, the development of oxidized cellulose functionalities and of the molecular weight was analyzed by selective labelling of carbonyl and carboxyl groups combined with gel permeation chromatography and multi-detector set-up. The crystallinity index of the samples was analyzed by CP-MAS NMR to elucidate the impact of age and treatment on the historic material.Already pure aqueous treatment changed the molecular weight distribution of historic textiles in some cases. These changes are discussed in the context of oxidized cellulose functionalities and crystallinity index. Furthermore the chosen historic samples reacted best towards a reduction treatment with sodium borohydride that had not been buffered, whereas the two buffered systems caused more damage and failed to reduce carbonyl groups along the cellulose chain.     

Iron gall ink-induced corrosion of cellulose: aging,degradation and stabilization. Part 1: model paper studies

Cellulose in historic paper documents is often damaged by the writing media used, especially iron gall ink or copper pigments. Degradation induced by iron gall ink is suggested to be a synergistic process comprising both hydrolytic and oxidative reactions. These processes were studied on very low sample amounts according to the CCOA and FDAM method, i.e. by fluorescence labeling of carbonyl and carboxyl groups in combination with GPC-MALLS, respectively. This study focused on preventive means to stop the deterioration induced by iron gall ink of cellulose and to prevent further damage, keeping in mind that a suitable conservation treatment has to hinder both, hydrolytic and oxidative processes, at the same time. A combination of the complexing agent calcium phytate and calcium hydrogencarbonate in aqueous solution was proved to give optimum results. To gain insight into long term stability, an aging step was performed after treatment and different ink modifications were tested. Recording the molecular weight distributions and the carbonyl group content over time GPC analysis verified for the first time the preventive effect of this treatment. This effect was not only seen for the ink-covered areas, but extended also to areas remote from the ink lines. Ink containing copper ions responded equally positively to the calcium phytate/hydrogencarbonate treatment as the iron gall ink papers did. Gelatine, sometimes used in a similar way due to an alleged cellulose-stabilizing effect did not have a beneficial influence on cellulose integrity when metal ions were present.     

Deterioration of ancient cellulose paper,Hanji: evaluation of paper permanence

Hanji paper, the paper material traditionally used in Korea, is in the focus of the present aging and mechanistic study. As raw materials and historic recipes for paper making are still available for Hanji today, specimen resembling historical material at the point of production can be prepared. While from that starting point, historical material had taken the path of natural aging, newly prepared samples—prepared according to both historic and current recipes—were artificially aged, and both aging modes can be compared. For the first time, an in-depth chemical and mathematical analysis of the aging processes for Hanji is presented. The aging of Hanji paper, resulting in hydrolysis and oxidation processes, was addressed by means of selective fluorescene labeling of oxidized groups in combination with gel permeation chromatography, providing profiles of carbonyl and carboxyl groups relative to the molar mass distribution. Starting Hanji showed the highest molecular weight (>1,400 kDa) ever reported for paper. We have defined two critical parameters for comparison of the paper samples: half-life DP (the time until every chain is split once on average) and life expectancy (the time until an average DP of failure is reached and no further mechanical stress can be tolerated). The two values were determined to be approximately 500 and 4,000 years, respectively, for the Hanji samples, provided there is no UV radiation. The rate of cellulose chain scission under accelerated aging (80 °C, RH 65 %), was about 600 times faster than under natural conditions. In addition, cellulose degradation of Hanji paper under accelerated aging condition was about 2–3 times slower than that of historical rag paper as those used in medieval Europe.     

Oxidation and structural changes in NMMO-regenerated cellulose films

Carbonyl and carboxyl groups introduced by oxidative processes during production and purification of celluloses determine intra- and intermolecular interactions and thus application-related bulk and surface properties of cellulosic materials. We report a comprehensive approach to the quantification of carboxyl and carbonyl groups in cellulose films upon reconstitution from NMMO solutions. Measurements of the excess conductivity were combined with the determination of the molecular weight distribution, quantification of the carboxyl and carbonyl group content, crystallinity and film swelling in aqueous solutions. TEMPO-oxidized, NMMO-regenerated cellulose films were additionally analysed as a reference system for extensive cellulose oxidation. Our reported data demonstrate that dissolution of cellulose in NMMO results in the formation of onic acids, chain degradation, increased ionization and film swelling, whereas TEMPO-oxidation introduced carbonyl groups as well as onic and uronic acids causing a significantly increased charging, ion accumulation and swelling even at higher crystallinity.     

Upgrading of paper grade pulps to dissolving pulps by nitren extraction: yields,molecular and supramolecular structures of nitren extracted pulps

Different paper grade pulps were extracted with nitren in order to produce dissolving pulps and polymeric xylan. The yield and molecular structure of the extracted pulps were investigated by carbohydrate analysis and HPSEC combined with fluorescence labelling in order to additionally monitor the carbonyl and carboxyl group profiles of the pulps. The supramolecular structure of selected pulps were further studied by solid state ¹³C-CP/MAS-NMR and wide-angle X-ray scattering (WAXS). These supramolecular data of nitren extracted pulps were compared to samples extracted with NaOH and a conventional dissolving pulp in order to classify the properties of nitren extracted pulps. Nitren extraction results in selective xylan removal without noticeable degradation or oxidation of the cellulose fraction. The resulting dissolving pulps have high molar masses, a narrow molar mass distribution and the typical contents of carbonyl and carboxyl groups. The supramolecular structure of cellulose is less affected by nitren compared to strong NaOH, and the resultant dissolving pulps still have the cellulose I structure. All laboratories are members of the European polysaccharide network of excellence EPNOE.     

13C nuclear magnetic resonance studies of cellulose acetate

¹³C-NMR spectra of ring carbons and O-acetyl carbonyl carbons of cellulose acetate (CA) in dimethyl sulfoxide-d₆ were analyzed. The CA samples with the degree of substitution (DS) ranging from 0.84 and 1.91 were prepared by homogeneous acetylation of cellulose with acetic anhydride in a 10% LiCl/dimethyl acetamide solvent. It was found that the use of these low DS samples permitted easier assignments not only of the ring carbon but also of the O-acetyl carbonyl carbon signals. The assignments were confirmed by comparing with the ¹H-NMR spectra of the samples obtained by complete acetylation of the corresponding CA samples with acetyl-d₃ chloride. Two methods for determining the distribution of O-acetyl groups of CA, i.e., the relative DS at the three different types of hydroxyl groups, were developed. One is based on the measurements of the relative intensities of the signals for the ring carbons and the other is based on the measurements of the relative intensities of the signals for the O-acetyl carbonyl carbons.     

Viscometric determination of dialdehyde content in periodate oxycellulose Part II. Topochemistry of oxidation

The kinetics of periodate oxidation of cellulose was followed through the alkaline degradation of the dialdehyde groups by measuring the viscometric degree of polymerisation and the alkali consumption. The obtained results show that a fast but limited attack of periodate occurs in the amorphous region of cellulose, causing the decrease of degree of polymerisation to its levelling-off value. The alkali consumption indicates at least two further slower reactions, that lead to the asymptotic complete oxidation of cellulose units. With the pseudo first-order approximation, the oxidation half-time of these three reactions can be calculated, corresponding to 1.2, 20 and 854 h respectively. In spite of the high oxidation of the analysed samples (up to about 46%), the residue after alkaline degradation shows a relatively high value of degree of polymerisation rather than the narrow molecular weight distribution of oligomers expected from a random oxidation, thus indicating that periodate oxidises cellulose in isolated domains. The sequence of analyses over the same sample utilised in this work (titrimetry, weight loss and viscometry), performed at room temperature in mild conditions, makes it possible to investigate the topochemistry of oxidation of paper and textiles of historic and artistic value with microdistructive techniques on a single, very small fragment of material.     

Determination of intrinsic viscosity-molecular weight relationship for cellulose in BmimAc/DMSO solutions

For simply and accurately determining molecular weight of cellulose, an ionic liquid mixed with a co-solvent, 1-butyl-3-methylimidazolium acetate/dimethyl sulfoxide (BmimAc/DMSO) (1:1, w/w) was used and dissolved cellulose well at ambient temperature. During the dissolution process no degradation of cellulose was observed, and all the resultant cellulose/BmimAc/DMSO solutions were transparent and stable. These advantages make it as an ideal solvent system to build a new characteristic method of cellulose’s molecular weight by the measurement of the intrinsic viscosity [η], which is significantly better than the currently used solvent systems. [η] of solutions of nine cellulose samples was measured by using rheometer with cylinder fixture and Ubbelohde viscometer, respectively. The [η] values obtained by these two methods were well consistent. The degree of polymerization (DP) of these cellulose samples was determined by Copper (II) ethylenediamine method. Then the molecular weight and its distribution of representative samples were cross-checked by gel permeation chromatography for soluble derivatives of cellulose. As a result, a relationship DP = 134 [η]^1.2 was built, suitable for DPs in the range of 220–1400. The uncertainty of this relationship was estimated to be 5 %. This work provided a simple, accurate and reliable method for determining [η] and the molecular weight of cellulose.     

Is cellulose degradation due to β-elimination processes a threat in mass deacidification of library books?

As papers become acidic and brittle over time, libraries apply mass deacidification processes to their collections in order to neutralize acids and deposit an alkaline reserve in the paper. Books commonly treated by mass deacidification have undergone natural aging of up to 150?years. The risk of alkali-induced degradation of cellulosic material upon mass deacidification remains uncertain. In the present study, the extent of β-elimination-type degradation reactions was investigated by comparing deacidified and non-deacidified counterparts, using deacidified library materials and identical issues of non-deacidified books from second-hand book shops. The study dealt with only naturally-aged papers focusing on investigation of immediate effects of mass deacidification rather than a long-term impact. Gel permeation chromatography coupled with carbonyl group labeling gave insight into cellulose chain cleavage as well as into the behavior of oxidized functionalities. Processes occurring under natural aging conditions were compared to those upon artificial oxidation of model pulps. Library books did not show a significant reduction in molecular weight after mass deacidification compared to the non-deacidified controls, which stands in contrast to oxidized model pulps. The models showed a more pronounced loss of molecular weight upon deacidification treatments. A decrease in carbonyl groups other than reducing ends was found to occur. Thus, oxidized functionalities were found to be reactive in mass-deacidification reactions; the different behavior was traced down to particular regions of oxidative damage along the cellulose chains. In general, β-elimination processes did not pose a large risk factor upon mass deacidification treatments of the naturally-aged library material tested.     

Characterization of cellulose by SEC-MALLS

Norway spruce (Picea abies) cellulose samplesdissolved in lithium chloride/N,N-dimethyl-acetamide(LiCl/DMAc) covering a wide range of average molecular weights were analyzed bysize exclusion chromatography (SEC) and multi-angle laser light detection(MALLS). The molecular weight distribution of the samples was compared to themolecular weight distribution of cotton linters cellulose samples. To obtaincomplete dissolution of high-molecular-weight wood cellulose, previouslypublished procedures for dissolving cellulose in LiCl/DMAc were modified. SECseparation was performed using macroporous monodisperse polymer particles ascolumn matrix. The refractive index increment (dn/dc) forcellulose in 0.5% LiCl/DMAc was found to be 0.104. The radius of gyration,R_G, of cellulose in 0.5% LiCl/DMAc depended on the molecular weight,M, according to the relation R_G M^0.55. Celluloseprepared from sprucewood by the sulfite cooking process had a broad molecularweight distribution compared to cotton linters cellulose.     

Grafting of model primary amine compounds to cellulose nanowhiskers through periodate oxidation

This study demonstrates regioselective oxidation of cellulose nanowhiskers using 2.80–10.02 mmols of sodium periodate per 5 g of whiskers followed by grafting with methyl and butyl amines through a Schiff base reaction to obtain their amine derivatives in 80–90 % yield. We found a corresponding increase in carbonyl content (0.06–0.14 mmols/g) of the dialdehyde cellulose nanowhiskers with the increase in oxidant as measured by titrimetric analysis and this was further evidenced by FT-IR spectroscopy. Grafting of amine compounds to the oxidized cellulose nanowhiskers resulted in their amine derivatives, which are found to be partially soluble in DMSO. Therefore, the reduction reaction between amines and carbonyl groups was confirmed through ¹³C NMR spectra, which was also supported by copper titration, XPS, and FT-IR spectroscopy. Morphological integrity and crystallinity of the nanowhiskers was maintained after the chemical modification as studied by AFM and solid-state ¹³C NMR, respectively.     

Effect of different coupling agents on the browning of cellulose-polypropylene composites during melt processing

The effects of two coupling agents on the discoloration of cellulose/polypropylene composites during melt processing have been investigated. Composites of polypropylene, coupling agent and bleached eucalyptus Kraft pulp were produced by compounding in a twin-screw extruder. The coupling agents were maleic anhydride-grafted polypropylene (MAPP) and polyethylenimine (PEI). The discoloration was measured using standard colorimetry and the discoloration was investigated using diffuse reflectance (FTIR and UV-Visible) spectroscopy. Both MAPP and PEI increase the browning, but the two mechanisms are clearly different. PEI reacts with carbonyl compounds produced in the cellulose degradation to form new chromophores; however, no specific discoloration processes were detected in composites made with MAPP. In this case, the detrimental effect on the discolouration was related to the increased frictional degradation.     

Radiation activation of cotton-cellulose prior to alkali treatment

The effect of alkali treatment on preirradiated cotton-cellulose was investigated using diffuse reflectance Fourier transformed infrared spectroscopy (DRIFT) and X-ray diffraction (XRD). The effect of two kinds of alkali solutions (NaOH and TMAH, tetramethyl ammonium hydroxide) on the crystalline structure of irradiated cotton-cellulose was compared. The transformation of cellulose I to cellulose II was observed applying DRIFT technique by the increase of the absorbance at 896 cm^-1 and XRD. The results obtained by the two methods were in good correlation. An increase in carbonyl content (as detected by FTIR by measuring the absorbance at 1740 cm^-1) was found in the samples due to oxidative degradation.     

Carbon Papers from Tall Goldenrod Cellulose Fibers and Carbon Nanotubes for Application as Electromagnetic Interference Shielding Materials

To transform tall goldenrods, which are invasive alien plant that destroy the ecosystem of South Korea, into useful materials, cellulose fibers isolated from tall goldenrods are applied as EMI shielding materials in this study. The obtained cellulose fibers were blended with CNTs, which were used as additives, to improve the electrical conductivity. TGCF/CNT papers prepared using a facile paper manufacturing process with various weight percent ratios and thickness were carbonized at high temperatures and investigated as EMI shielding materials. The increase in the carbonization temperature, thickness, and CNT content enhanced the electrical conductivity and EMI SE of TGCF/CNT carbon papers. TGCF/CNT-15 papers, with approximately 4.5 mm of thickness, carbonized at 1300 °C exhibited the highest electrical conductivity of 6.35 S cm⁻¹, indicating an EMI SE of approximately 62 dB at 1.6 GHz of the low frequency band. Additionally, the obtained TGCF/CNT carbon papers were flexible and could be bent and wound without breaking.     

On-line derivatization coupled to flow injection permanganate chemiluminescence detection of total carbonyl compounds in natural waters and drinking water

This work describes the development of a fast assay for the determination of low molecular weight carbonyl compounds based on the oxidative chemiluminescence of 2,4-dinitrophenylhydrazine with acidic permanganate, which is enhanced during conversion to the corresponding phenylhydrazone-carbonyl derivatives. By exploiting the common derivatization pathway and oxidation mechanism of phenylhydrazones under kinetically controlled conditions in a flow configuration, a common light emission is produced which corresponds to the total aqueous concentration of carbonyl compounds. The experimental conditions that afford the optimum analytical features were optimized for acetone, acetaldehyde and formaldehyde which constitute the most abundant carbonyl compounds in environmental samples. The method was successfully applied to the determination of total carbonyl content in natural waters and drinking water at the low μg L⁻¹ levels with satisfactory recoveries (94.0-99.5%) and very good reproducibility (RSD = 1.58-2.99%, n = 8, C = 2 μg L⁻¹). Validation of the results was performed with gas chromatography suggesting that the proposed method provides a fast alternative to the routine screening of low molecular weight carbonyl compounds in natural waters.     

Reducing end-group of cellulose as a reactive site for thermal discoloration

Thermal discoloration of cellulose (Avicel PH-101 and Whatman No. 42 filter paper) was studied in N₂ at 160-280 °C with glycerol-treated and NaBH₄-reduced samples, to understand the role of the reducing end. Thermal discoloration of glycerol-treated Avicel PH-101, in which some of the reducing ends were converted into glycosides (non-reducing ends), was suppressed compared with the original cellulose, and the level of suppression was directly related to the extent of glycosylation of the reducing ends. The stabilization efficiency of glycerol-treated Whatman No. 42 filter paper suggested that the reducing ends newly formed by reduction of the degree of polymerization (DP) (to about 200) during heat treatment contributed to the discoloration. The important role of the reducing ends in thermal discoloration was supported by the stabilization of Avicel PH-101 by reduction with NaBH₄ (giving a reducing end content that was 2% of that of the original cellulose). Thermally induced discoloration was also inhibited by heating cellulose in suspension in the polyether tetraethyleneglycol dimethylether, which has been reported to inhibit the thermal degradation of reducing sugars.     

The study of degradable polystyrene: Photolysis in solution and photo-oxidation in films

Radical copolymerization of styrene with benzalacetophenone or benzalacetone in bulk or in suspension yielded copolymers with as much as 10 wt% of carbonyl monomer. They were characterized by GPC, viscometry and spectroscopy. Photolysis of copolymers was investigated in benzene at 313 nm. Quantum yields for main chain scissions were about 0.005 and the life-time of the triplet state was 5 nsec. Photo-oxidation in films was followed by monitoring the decrease in molecular weight and by i.r. and emission spectra. Quantum yield for main chain scission in films was about 0.0002. During photooxidation in film, the molecular weight distribution widened. A new i.r.-band appeared at 3580 cm^?1 and the carbonyl band was spread between 1700 and 1800 cm^?1. In the emission spectra, the vibrational resolved emission (typical of the carbonyl chromophore) disappeared.