Characterisation of historic plastics using terahertz time-domain spectroscopy and pulsed imaging
Centre for Sustainable Heritage, Bartlett School of Graduate Studies, University College London, London, UK. Analytical and Bioanalytical Chemistry
(Impact Factor: 3.44).
03/2012; 403(5):1405-14. DOI: 10.1007/s00216-012-5931-9
Terahertz (THz) time-domain spectroscopy and 3D THz pulsed imaging have been explored with regard to polymer materials, both commodity and historic polymers. A systematic spectroscopic study of a wide range of different polymer materials showed significant differences in their spectra. Polyolefins and polystyrenes generally exhibit lower absorption than other examined polymers, various cellulose derivates, poly(vinyl chloride), poly(methyl methacrylate), polyamide, hard rubber and phenol formaldehyde resin, the last of these exhibiting the most intense absorption over the entire range, 0.15-4.2 THz. It was also examined how the presence of plasticisers in poly(vinyl chloride), the presence of fillers in polypropylene, and the degree of branching in polyethylene and polystyrene affect the spectra; inorganic fillers in polypropylene affected the absorption most. With 3D THz pulsed imaging, features in polymer objects were explored, appearing either as integral parts of the material (coatings and pores in foams) or as a consequence of physical deterioration (cracks, delamination). All of these features of various complexities can be successfully imaged in 3D. Terahertz technology is thus shown to have significant potential for both chemical and structural characterisation of polymers, which will be of interest to heritage science, but also to the polymer industry and development of analytical technologies in general.
Available from: C.G Treviño-Palacios
- "Based on the accessible sources and detectors, THz has found some non-medical areas with successful introduction compared to other technologies: stand-off detection of hidden objects and weapons[14,37], non-contact material integrity imaging of coatings and composites, detection of cracks and defects in solar panels, and non-contact imaging for conservation of paintings, manuscripts and artefacts. Non-destructive rapid fault isolation in product lines has successfully been applied in some cases. "
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ABSTRACT: An overview of terahertz (THz) development is presented in view of possible medical applications, including details of the current technologies which could be effectively used. Although no clinical THz technologies are currently in use, its principal applicability has been already demonstrated in skin cancer detection and treatment, dental caries detection and pharmaceutical screening. Fundamental limitations of THz studies are highlighted which have to be overcome before clinical applications can be realized.
Available from: Gianluca Valentini
- "With respect to point-like analysis, imaging techniques can provide a rapid indication of the heterogeneous degradation and condition of plastic objects. More in detail, both spectroscopy imaging methods, including those based on the analysis of the NIR radiation reflected and absorbed by a surface  , and structural imaging methods, based on THz techniques , have proved to be effective tools for monitoring degradation. In turn, fluorescence imaging, based on the analysis of the spectral   and lifetime  properties of the emission, has been used for the assessment of the conditions of cultural heritage and specifically paintings and sculptures, but has not been applied to the analysis of plastics or historical objects. "
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ABSTRACT: Complementary use of fluorescence multispectral imaging and fluorescence lifetime imaging (FLIM) for the assessment of the degradation of a historical design object made in acrylonitrile–butadiene–styrene (ABS) is demonstrated. Model samples of ABS, exposed to UV irradiation to simulate photodegradation, have been analysed with fluorescence spectroscopy and fluorescence lifetime spectroscopy. Results demonstrate rapid modifications of the picosecond and nanosecond fluorescence lifetimes following short irradiation times, which are accompanied with significant modifications in fluorescence excitation-emission spectra. Changes in spectra and lifetimes in samples are ascribed to the accumulation of α,β unsaturated aldehydes and α,β diketones and the loss of volatile organic components (including acetophenone). Complementary analyses of samples with Fourier transform infrared spectroscopy suggest that modifications in fluorescence are correlated with photo-oxidative degradation of ABS. Fluorescence lifetime and fluorescence multispectral images of the Grillo telephone (1965) made in ABS were acquired. Analysis of images allowed the rapid mapping of differences in fluorescence which are attributed to heterogeneous degradation on the object surface. Implications for the assessment, monitoring and conservation of objects in ABS and other polymers are suggested.
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ABSTRACT: THz spectroscopy in the time domain was explored in combination with multivariate data analysis, for quantitative determination of chemical and mechanical properties of historic paper, such as lignin content, tensile strength, and ash content. Using partial least squares (PLS) regression, it was shown that quantitative prediction of the material properties is possible, which indicates the potential of THz spectroscopy for chemical characterisation of complex organic materials of natural origin. In addition, the results demonstrate that THz spectra and PLS loading weights for lignin content differ significantly, which leads to the conclusion that THz spectra of composite macromolecular materials do not represent sums of spectra of the individual components. This supports the premise that THz spectra reflect intermolecular interactions.
The study was carried out using 250 historical paper samples from the sixteenth century to present. Although the measurements were performed in vacuum to improve the quality of spectra, THz spectroscopy is in principle non-destructive. This research therefore reinforces the role of THz spectroscopy in characterisation of valuable historic materials, where invasive analysis is often not possible.
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