Frozen, Cold, or Cool? Chemical Assessment of the Effectiveness of Storage Conditions for Celluloid 3D Objects.

Preserving celluloid artifacts is challenging for museums, as this plastic is highly prone to degradation. Frozen, cold, and cool storage solutions are typically recommended for inhibiting the chemical degradation of celluloid. However, they are rarely implemented for three-dimensional celluloid (3D-CN) objects because low temperatures might cause irreversible effects (e.g., microcracking). This work presents the effects of four different storage temperatures (+23 °C, +13 °C, +9 °C, -15 °C) on the preservation of artificially aged 3D-CN mock-ups, aiming at understanding their effectiveness by measuring molecular weight distribution, camphor, and nitrogen contents after storage. Gel permeation chromatography (GPC) results showed that the least loss of camphor content and fewer polymer chain scissions happened at -15 °C, hinting that this temperature was the best for preservation. However, the heterogeneous nature of celluloid alteration, i.e., the development of degradation gradients in thicker 3D-CN objects (>0.5 mm), made it necessary to apply a novel sampling technique, which selectively considers several depths for analyses from the surface to the core (depth profiling). This depth profiling made monitoring the degradation evolution dependent on the storage conditions in the thicker mock-ups possible. This approach was also used for the first time to quantify the polymer chain scission, camphor loss, and denitration of historical artifacts, indicating a dramatic difference in the degradation stage between surface and core. The effectiveness of frozen storage on the chemical stability of 3D-CN after seven months could support museums to consider reducing the storage temperatures to preserve precious artifacts.

Mock-Ups in Plastic Conservation Research: Processing and Aging of 3D Celluloid Specimens Simulating Historical Objects.

The preparation of mock-ups in heritage science studies represents a valid alternative for investigation purposes, avoiding extensive sampling of cultural heritage objects. This work presents for the first time the successful preparation of three dimensional (3D) mock-ups made of celluloid, considering a combination of historical industrial production strategies and small-scale lab facilities. Prefabricated transparent celluloid sheets were acquired and then shaped through compression molding for creating mock-ups with 3D geometries. These reflected common and representative shapes encountered in the collection of the Deutsches Museum. Visual inspection of the mock-ups allowed determining the best compression molding conditions. Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) confirmed the absence of molecular heterogeneity due to the processing method. Artificial aging of the mock-ups was conducted to reach degradation states comparable with naturally aged objects. ATR-FTIR investigation offered first insights into the induced artificial degradation. Ion chromatography (IC) and gel permeation chromatography (GPC) analyses allowed to assess the extent of the artificial aging of the celluloid mock-ups and confirmed the occurrence of loss of camphor, denitration, and main chain polymer scission, the latter being the predominant decay path. The comparison with historical objects highlighted that the mock-ups are representative of moderately aged artifacts. As such, this study paves the way for implementing moderately aged celluloid 3D mock-ups in heritage science research, enabling in-depth testing for the scope of conservation.

Characterization of poly(methyl methacrylate)-graft-poly(styrene)s using various chromatographic techniques.

Two graft copolymer samples of identical average composition were synthesized by grafting living polystyrene anions onto a broadly distributed PMMA backbone. Size exclusion chromatography (SEC) with only RI-detection, SEC with viscometry and light scattering detection, SEC with UV and RI dual detection, gradient chromatography and 2-dimensional chromatography were applied to compare the information that can be obtained by the different techniques. While only limited information was retrieved by conventional SEC or SEC with molar mass sensitive detection, SEC with UV and RI revealed different chemical heterogeneity of the samples. Using gradient chromatography and 2-dimensional chromatography it was possible to identify non-grafted side chains and unreacted parent PMMA besides the actual graft copolymer molecules. While in one sample a heavily grafted product was formed besides non-grafted PMMA, the second sample did not contain ungrafted PMMA but a graft product of lower grafting density. The different product distributions were explained by the different synthetic procedures.

On-line fractionated size exclusion chromatography-nuclear magnetic resonance of polymers with ¹H and ²H nuclear magnetic resonance detection.

A new approach for on-line SEC-NMR is introduced. The method combines time slicing, fractionation with adjusted loop collection and automatic stop-flow NMR analysis. It will be called on-line fractionated SEC-NMR. This technique allows the precise determination of molar mass distributions for any polymer which can be detected by NMR. It is a significant improvement of sensitivity and accuracy compared to onflow SEC-NMR and exhibits a much easier experimental setup than off-line SEC-NMR fractionation. The new method was applied to protonated and deuterated block copolymers by using ¹H NMR and for the first time also ²H NMR detection. In this case block copolymers can be correctly characterized according to their block length distributions. As the consequence very precise molar mass parameters M(n) and M(w) can be determined. The results of the on-line fractionated SEC-NMR are in very good agreement with the multi detector analysis. The new technique also proposes a method for separating the true copolymer and low molar mass fractions in the mixture, whose structures are confirmed by HPLC-FTIR and 2D chromatography.