Paul M. Whitmore

Hydrolysis of the Amorphous Cellulose in Cotton-Based Paper

Hydrolysis of cellulose in Whatman no. 42 cotton-based paper was studied using gel permeation chromatography (GPC), electrospray ionization-mass spectrometry (ESI-MS), and uniaxial tensile testing to understand the course and kinetics of the reaction. GPC results suggested that scission reactions passed through three stages. Additionally, the evolution of soluble oligomers in the ESI-MS data and the steady course of strength loss showed that the hydrolysis reaction occurred at a constant rate. These findings are explained with a more detailed description of the cellulose hydrolysis, which includes multiple chain scissions on amorphous segments. The breaks occur with increasing frequency near the ends of amorphous segments, where chains protrude from crystalline domains. Oligomers unattached to crystalline domains are eventually created. Late-stage reactions near the ends of amorphous segments produce a kinetic behavior that falsely suggests that hydrolysis had ceased. Monte Carlo simulations of cellulose degradation corroborated the experimental findings.

The Effect of Oxidation on the Subsequent Oven Aging of Filter Paper

It has been observed that oxidation of cellulose can affect the rate at which thermal chain scissions subsequently occur, an effect thought to result from the weakening of the chain at the site of the oxidized groups formed along the chains during oxidation. This study examines the possibility that the number of such functional groups, in excess of the chain ends formed during oxidation, provides an estimate of the weak links created along the chain that will break rapidly during subsequent thermal aging. In these experiments, filter paper that had been chemically or photochemically oxidized was aged in a humid oven. Scission kinetics during the degradation of the oxidized papers were measured and compared with that of unoxidized papers. For all papers except the most heavily oxidized, the magnitude of the early weak link scissions in the oven is comparable to the measured excess carbonyls produced during the oxidized treatments. The oven aging of the oxidized sheets also demonstrated faster hydrolytic degradation even after the weak link period, which may be the result of increased acidity following oxidation of the cellulose. -- AATA

Minimally invasive monitoring of cellulose degradation by desorption electrospray ionization and laser ablation electrospray ionization mass spectrometry.

Minimally invasive desorption electrospray ionization-mass spectrometry (DESI-MS) and laser ablation electrospray ionization-MS (LAESI-MS) were used to look for soluble cellulose degradation products produced by accelerated aging in unsized cotton paper. Soluble extracts from papers aged 144 to 26,856 hours were first analyzed in solution using traditional electrospray ionization-MS (ESI-MS). Results were compared to those from direct analysis of condensed phase degradation products extracted from the absorbent paper substrate using DESI-MS and LAESI-MS. ESI-MS results showed evidence of oligosaccharide degradation products ranging from cellobiose to cellononaose; using DESI-MS and LAESI-MS, products from cellobiose to cellodecaose and glucose to cellooctaose, respectively, were observed. As degradation proceeded, increased quantities of both low and high molecular weight oligosaccharides were observed. The analytical approaches developed in the control study were applied for the detection of degradation products in two naturally-aged books dating from the 19th century, both made from cotton and linen. Oligosaccharides ranging from glucose to cellopentaose were observed.

Silver Nanoparticle Films as Sulfide Gas Sensors in Oddy Tests

The preparation and performance of a silver nanoparticle-based sensor for use in Oddy tests are reported. A suspension of spherical silver nanoparticles (Ag NPs) (mean diameter of 30 nm, absorption of surface plasmon resonance (SPR) at 428 nm) in methanol was synthesized and the Ag NPs were self-assembled into monolayer films on glass slides, using polyethylenimine as a linking agent. UV-vis spectrophotometry was employed to measure the SPR intensity of the Ag NP films in order to evaluate the extent of reaction. It was observed that the Ag NP films were quite stable under Oddy test conditions in a blank test, after a brief alteration of the spectrum due to particle dispersal, with no significant decrease in the SPR intensity after 1.5 months at 60°C and 100% RH. The sensitivity of Ag NP films to sulfide gases emitted from a test wool fabric in the Oddy test was investigated. UV-vis spectra taken after the Oddy tests showed the disappearance of the Ag NP SPR peak and the growth of the UV absorption due to Ag 2 S. Elemental analysis with energy dispersive x-ray spectroscopy confirmed that sulfur had been incorporated into the Ag NP film. Ag NP assemblies of lower NP density were created that indicated the presence of sulfide gases prior to significant tarnishing of a Ag foil. The results demonstrate that the Ag NP films can be used as sensitive, quantitative optical sensors to replace Ag foils in the Oddy test system.

Texture vision: a view from art conservation

The appreciation of many works of visual art derives from the observation and interpretation of the object surface. The visual perception of texture is key to interpreting those surfaces, for the texture provides cues about the nature of the material and the ways in which the artist has manipulated it to create the object. The quantification of texture can be undertaken in two ways: by recording the physical topography of the surface or by analyzing an image that accurately portrays the texture. For most art objects, this description of texture on a microscopic level is not very useful, since how those surface features are observed by viewers is not directly provided by the analysis. For this reason, image analysis seems a more promising approach, for in the images the surfaces will naturally tend to be rendered as they would when viewing the object. In this study, images of textured surfaces of prototype art objects are analyzed in order to identify the methods and the metrics that can accurately characterize slight changes in texture. Three main applications are illustrated: the effect of the conditions of illumination on perceived texture, the characterization of changes of object due to degradation, and the quantification of the efficiency of the restoration.