“Material Degradomics: On the Smell of Old Books”, 2009-09-17 (; similar):
We successfully transferred and applied ✱-omics concepts to the study of material degradation, in particular historic paper.
The main volatile degradation products of paper, constituting the particular “smell of old books”, were determined using headspace analysis after a 24 h predegradation procedure.
Using supervised and unsupervised methods of multivariate data analysis, we were able to quantitatively correlate volatile degradation products with properties important for the preservation of historic paper: rosin, lignin and carbonyl group content, degree of polymerization of cellulose, and paper acidity. On the basis of volatile degradic footprinting, we identified degradation markers for rosin and lignin in paper and investigated their effect on degradation. Apart from the known volatile paper degradation products acetic acid and furfural, we also put forward a number of other compounds of potential interest, most notably lipid peroxidation products.
The nondestructive approach can be used for rapid identification of degraded historic objects on the basis of the volatile degradation products emitted by degrading paper.
[Keywords: degradation, organic polymers, biopolymers, materials, volatile organic compounds]
[Analytical Chemistry: …“Ordinarily, traditional analytical methods like [LC] are used to test paper samples that have been ripped out”, Strlič says. “The advantage of our method is that it’s nondestructive.”
Strlič calls the method “material degradomics”. Like other ✱-omic methods in research, he explains, material degradomics correlates phenotype—ie. a book’s condition—to metabolic byproducts: in this case, VOC emissions from degrading paper.
The team analyzed 72 well-characterized historical papers from the 19th and 20th centuries. These documents included papers made with rosin (a pine tar resin), bleached pulp, groundweed, and rag fiber. VOCs from these papers were measured using GC/MS. The 15 most abundant VOCs were then related statistically to key constituents in paper, including lignin, reducing carbonyl content, rosin, ash, pH, degree of polymerization, and protein content. The scientists used partial least squares (PLS) multivariate regression models to relate VOC peaks to their underlying chemical sources in paper, Strlič says. The team took this approach because different chemical constituents can emit the same VOCs, he explains. PLS is better suited to co-correlated data than classical regression models, which resolve more independent data sets.
From a degradation standpoint, the 2 most problematic constituents in paper are lignin and rosin, Strlič explains. Lignin—a natural component in wood fiber, which replaced the more durable rag paper made before 1850—yellows with age. And rosin, which is a hydrophobic compound added to paper to make it suitable for writing, eventually breaks down into corrosive, acidic byproducts. As these 2 constituents degrade, they emit characteristic patterns of VOC emissions at predictive levels, Strlič and his colleagues found. Lignin releases acetic acid, hexanol, and furfural, whereas rosin gives off various aldehydes and ketones, in addition to 2-ethylhexanol. Some constituents—notably ash and protein content—could not be correlated with any VOC emissions.
Strlič hopes material degradomics methods will one day be used to evaluate culturally-significant, historical papers. Ideally, a hand-held analytical device could “sniff” valuable holdings on a book-by-book basis, he says. Gerrit de Bruin, head of conservation at the National Archives in the Hague (The Netherlands), agrees. “We need more nondestructive tools for cultural forensics”, he says. “As an end-user of this technology, I find the concept promising.”
De Bruin and other specialists in the field worry especially about books, newspapers, and other documents made 1850–140199034ya. Paper products made during this period were “sized”, or saturated, with rosin precipitated into fiber. The acidic byproducts released by rosin cause paper to degrade nearly 10× faster than earlier papers, which were sized with gelatin, a more neutral additive, Strlič explains. In the US and elsewhere, rosin sizing was phased out for environmental reasons (rosin-containing pulp and paper effluents are toxic) and because the U.S. Permanent Paper Law, passed in 1990, gave paper mills incentives to convert to more alkaline processes. Meanwhile, papers made from 1850–140199034ya could degrade within one to 2 centuries after their production, posing a crisis for archives around the world.]