Unilateral NMR and Micro DSC Study of Artificially Aged Parchments

Abstract

New and artificially aged parchments were studied by unilateral NMR and micro DSC. Samples were obtained by exposing new parchments to 80 °C and alternate 40 and 80% relative humidity for increasing times up to 32 days. The impact of accelerated ageing was assessed by measuring both the proton transverse relaxation times (T 2eff ) and thermodynamic parameters associated with thermal denaturation of fibrillar collagen. Depending on the ageing time, significant structural changes correlated with thermal stability and collagen heterogeneity were observed, in good agreement with changes in phase composition and relaxation times. The results suggest two ageing regimes depending on the balance between the two main processes which drive the behavior of parchments during thermal ageing, i.e. thermally induced cross linking and thermal destabilization and denaturation.

The effect of halloysite nanotubes dispersions on vegetable-tanned leather thermal stability

“…This quantitative parameter is the energy required to disrupt the interactions stabilizing the secondary and tertiary structures of the triple helix. It was shown to be very useful in quantifying the effects of damaging factors on chemically unmodified collagen in parchment [36,37,42]. Recently, Carșote et al [25,35] have shown that micro DSC offers both qualitative and quantitative information to also characterize chemically modified collagen in historical leather.…”

“…Effective 1 H spin-spin relaxation T 2eff measurements have been measured using the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence with an echo-time (TE) of about 25 µs. The experimental CPMG curves were best analyzed by a combination of double exponential functions [37,38].…”

“…This could be attributed to an increase in the bulk water content [57] since deterioration of the collagen native structure causes increased mobility of water and consequentially increased water content within the collagen matrix. In fact, in the unfolded collagen structure more polar groups are exposed to water, and can therefore bind to significantly more water molecule that the native collagen [37]. The decrease of T 2eff_long value after both HNT-PEG and HNT-BNUTO treatments could therefore indicate a reduction in the "pools" of bulk water in treated leathers through substitution with PEG or urea.…”

13C solid‐state NMR complemented by ATR‐FTIR and micro‐DSC to study modern collagen‐based material and historical leather

“…[47,48] On the other hand, shrinkage behaviour is related to collagen hydrothermal destabilisation and conversion to gelatin, [18,49] while at glass transition temperature, collagen changes from the glassy (crystalline) to the rubbery (amorphous) state. [19,46,50]…”

“…Although NMR has already gained a great deal of importance in the study of heritage materials, [12,13] only a few studies have been conducted to characterise historical and archaeological parchment and leather. NMR spectroscopy was used with particular attention to the degradation processes triggered by the presence of water and thermal conditions, [14][15][16][17][18][19][20] as well as for characterising commercial vegetable tannins extracts [21,22] and modern tanned leathers. [23] In literature, only two studies were focused on the identification of tannins in historical leather by NMR spectroscopy.…”