Characterisation of historic plastics using terahertz time-domain spectroscopy and pulsed imaging

Abstract

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.

Terahertz and Cultural Heritage Science: Examination of Art and Archaeology

“…THz spectroscopy has been tested on art made with plastics [97] since it is sensitive to their plasticizers and fillers, while THz 3D imaging can distinguish coatings and layers of degradation in historical plastics. There is interest into using THz imaging to obtain stratigraphic information regarding corrosion and encrustations layers of archaeological metals [98] and for historical stone objects conservation [43].…”

Raman Spectroscopy of cultural heritage Materials: Overview of Applications and New Frontiers in Instrumentation, Sampling Modalities, and Data Processing

“…In the field of art and design, the potential of Raman spectroscopy is still somehow under-utilised [102,231,232,272], but some comprehensive review of Raman applications for the identification of postconsumer plastics for recycling purposes using PCA [7], and other industrial applications are available [135,139].…”

Non-destructive evaluation by terahertz spectroscopy for penetration of acid solutions into epoxy resin

“…The main advantages of THz-TDS for NDT studies are the high penetration of THz electromagnetic waves into polymers [13][14][15][16][17][18], high sensitivity to the inter/intra molecular vibrations (especially for water) [18][19][20][21][22][23][24][25][26], and ability to estimate the materials dielectric properties without direct contact [27][28][29]. The THz spectra of various thermoplastics [13][14][15] and thermosets [16,17] measured by THz-TDS were reported.…”

“…The THz spectra of various thermoplastics [13][14][15] and thermosets [16,17] measured by THz-TDS were reported. In contrast with FT-IR spectra, the THz spectra shows a few clear features to distinguish polymer molecular structures.…”

“…However, THz spectroscopy can be useful for monitoring the glass transition of the polymer because the polymer chain motion above and below the glass transition temperature affects the THz refractive index [14]. In addition, owing to the significant difference of dielectric properties between polymers and other materials, spectral features of inclusions such as inorganic fillers [15] and carbon nanotubes [17] in polymer materials were also recognized in the THz spectra. The dielectric properties of liquid water, aqueous solutions, and water in materials were also studied with to understand hydrogen bonding state i.e.…”