Assessing the Impact and Suitability of Dense Carbon Dioxide as a Green Solvent for the Treatment of PMMA of Historical Value.

Surface cleaning of plastic materials of historical value can be challenging due to the high risk of inducing detrimental effects and visual alterations. As a result, recent studies have focused on researching new approaches that might reduce the associated hazards and, at the same time, minimize the environmental impact by employing biodegradable and green materials. In this context, the present work investigates the effects and potential suitability of dense carbon dioxide (CO2) as an alternative and green solvent for cleaning plastic materials of historical value. The results of extensive trials with CO2 in different phases (supercritical, liquid, and vapor) and under various conditions (pressure, temperature, exposure, and depressurization time) are reported for new, transparent, thick poly(methyl methacrylate) (PMMA) samples. The impact of CO2 on the weight, the appearance of the samples (dimensions, color, gloss, and surface texture), and modifications to their physicochemical and mechanical properties were monitored via a multi-analytical approach that included optical microscopy, Raman and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopies, and micro-indentation (Vickers hardness). Results showed that CO2 induced undesirable and irreversible changes in PMMA samples (i.e., formation of fractures and stress-induced cracking, drastic decrease in the surface hardness of the samples), independent of the conditions used (i.e., temperature, pressure, CO2 phase, and exposure time).

Analytical methods for determination of anthraquinone dyes in historical textiles: A review.

Historical and archaeological textiles are among the most crucial and vulnerable records of our social and cultural history. Analysis of organic colorants found in these materials is unquestionably one of the most powerful tools to understand historical developments, cultural exchanges, and progress in science and technology. Natural anthraquinones represent the most commonly used natural colorants for textile dyeing until the late 19th century. The identification of anthraquinones in cultural heritage objects is a challenging task due to the small size of historical samples, diversity of potential dye sources, variable extraction procedures and dyeing methods, complex chemical constitution, structurally analogous chromophores, and possible presence of degradation products and contaminants. Developments in dye analysis of historical interest have originated and expanded along with the general advances in analytical science. In the last few decades, a close cooperation between science and cultural heritage disciplines contributed enormously to this field. The topic of historical dyes and their analysis in textiles, artworks, archaeological objects and cultural heritage materials has been reviewed several times in the last fifteen years. However, no review has been published to-date exclusively on the analysis of anthraquinone colorants in historical and archaeological textiles. Overall, liquid chromatography (LC)-based techniques have been the most widely used method for anthraquinone dye analysis. Owing to increasing demand of minimally invasive/non-invasive techniques, recent developments of novel techniques have resulted in the availability of many alternative/complementary methods to LC-based analysis. This review begins with a short overview of sources, chemistry and importance of natural anthraquinone dyes found in historical textiles before turning to a detailed discussion on developments involving established and emerging analytical techniques of anthraquinone dye analysis for textile cultural heritage materials. To illustrate the state-of-the-art, representative examples of analytical techniques highlighting their advantages, limitations and applicability are also presented.

Characterisation of oil and aluminium complex on replica and historical 19th c. Turkey red textiles by non-destructive diffuse reflectance FTIR spectroscopy.

This work investigates historical and replica Turkey red textiles with diffuse reflectance infrared (DRIFT) spectroscopy to study the coordination complex between cellulose, fatty acids, and the aluminium ions that form the basis of the colour lake. Turkey red was produced in Scotland for around 150 years, and is held in many museum and archive collections. The textile was renowned for its brilliant red hue, and for its fastness to light, washing, rubbing, and bleaching. This was attributed to its unusual preparatory process, the chemistry of which was never fully understood, that involved imbuing cotton with a solution of aqueous fatty acids and then aluminium in the following step. Here we show, for the first time, a characterisation of the Turkey red complex on replica and historical textiles. The development of techniques for non-destructive and in situ analysis of historical textiles is valuable for improving understanding of their chemistry, hopefully contributing to better conservation and display practices. The results show the fatty acids condense onto the cellulose polymer via hydrogen bonding between the CO and OH of the respective compounds, then the aluminium forms a bridging complex with the fatty acid carboxyl. This contributes to an improved understanding of Turkey red textiles, and shows the useful application of handheld diffuse FTIR instruments for heritage textile research.

Characterisation of chemical components for identifying historical Chinese textile dyes by ultra high performance liquid chromatography - photodiode array - electrospray ionisation mass spectrometer.

This research makes the first attempt to apply Ultra High Performance Liquid Chromatography (UHPLC) coupled to both Photodiode Array detection (PDA) and Electrospray Ionisation Mass Spectrometer (ESI-MS) to the chemical characterisation of common textile dyes in ancient China. Three different extraction methods, respectively involving dimethyl sulfoxide (DMSO)-oxalic acid, DMSO and hydrochloric acid, are unprecedentedly applied together to achieve an in-depth understanding of the chemical composition of these dyes. The first LC-PDA-MS database of the chemical composition of common dyes in ancient China has been established. The phenomena of esterification and isomerisation of the dye constituents of gallnut, gardenia and saffron, and the dye composition of acorn cup dyed silk are clarified for the first time. 6-Hydroxyrubiadin and its glycosides are first reported on a dyed sample with Rubia cordifolia from China. UHPLC-PDA-ESI-MS with a C18 BEH shield column shows significant advantages in the separation and identification of similar dye constituents, particularly in the cases of analysing pagoda bud and turmeric dyed sample extracts.

Liquid chromatography determination of natural dyes in extracts from historical Scottish textiles excavated from peat bogs.

Textiles excavated from Scottish sites belonging now to the collections of the National Museums of Scotland, including seventeenth century textiles from peat bogs in the Scottish Highlands and Islands, were selected for analysis by high performance liquid chromatography with photodiode array detection (PDA HPLC) to detect whether any dyes remained and, if so, to identify their biological sources. Dye components were identified in 36 of the 81 samples analysed. Although it was not possible to identify the exact sources of the dyestuffs because of the wide-spread occurrence of these natural dyes components, the study has shown that textiles previously not thought to have been coloured had detectable traces of dye. Before the historical textiles were analyzed, an improved extraction procedure that combined the routine acid hydrolysis method with one using dimethylformamide (DMF) was applied. The DMF method enabled increased recovery of major flavonoid and anthraquinoid compounds, and very high efficiency of recovery of indigotin even in textiles with no colour visible, thereby complementing the acid hydrolysis method already in use. Extracts from historical thread samples were analysed by PDA HPLC using a reversed-phase gradient system comprising of a C18 column (150 mm x 4.6 mm i.d., 25 +/- 1 degrees C) with water, methanol and o-phosphoric acid at an eluent flow rate of 1.2 ml/min. A preliminary investigation to improve the detection limits further for a selection of natural dyes was made by comparing results from the 4.6mm internal diameter (i.d.) column with a narrow bore C18 column (2.1 mm i.d.). An increase in the detector response was observed for narrow-bore column proving its possibility of enhancement of sensitivity.

Negative ion electrospray mass spectrometry of neoflavonoids.

The electrospray ionisation mass spectra of the neoflavanoids brazilin and hematoxylin are reported in both their reduced (1 and 2, respectively) and their oxidised forms (3 and 4, respectively). In the reduced forms, breakdown pathways under collision induced decomposition (CID) conditions produce fragments characteristic of rings A and C; in their oxidised forms, the fragments are characteristic of rings B and D. The structural assignments of the fragments are substantiated by recording the spectra after deuterium exchange at the hydroxyl groups.

The natural constituents of historical textile dyes.

The sources and structures of dyes used to colour Western historical textiles are described in this tutorial review. Most blue and purple colours were derived from indigo--obtained either from woad or from the indigo plant--though some other sources (e.g. shellfish and lichens) were used. Reds were often anthraquinone derivatives obtained from plants or insects. Yellows were almost always flavonoid derivatives obtained from a variety of plant species. Most other colours were produced by over-dyeing--e.g. greens were obtained by over-dyeing a blue with a yellow dye. Direct analysis of dyes isolated from artefacts allows comparison with the historical record.

Characterisation of "bog butter" using a combination of molecular and isotopic techniques.

The chemical analyses of "bog butters" recovered from peat bogs of Scotland were performed with the aim of determining their origins. Detailed compositional information was obtained from "bog butter" lipids using high temperature gas chromatography (HTGC) and GC-mass spectrometry (GC-MS). The results indicate the degree to which "bog butters" have undergone diagenetic alterations during burial to form an adipocere like substance, consisting predominantly of hexadecanoic (palmitic) and octadecanoic (stearic) acids. GC-combustion-isotope ratio MS (GC-C-IRMS) was used to determine delta13C values for the dominant fatty acids present, revealing for the first time that "bog butters" were derived from both ruminant dairy fats and adipose fats. The results are compared and contrasted with modern reference fats and adipoceres produced in vitro.