Surface treatments of wood by chemically modified shellac

Abstract

Shellac is an animal resin, which has been widely used as a decorative lacquer for wooden handicrafts in the last centuries. It still finds application as wood sealer and finisher because of its peculiar properties. However, there are also some limitations, such as sensitivity to alcoholic solvents and to pH variations and considerable tendency to chromatic variations upon ageing. The aim of this work is to improve some features of shellac by inducing a cross-linking in its structure. Two new materials were obtained by addition of a polyamine and a polyaziridine to shellac, and their performance were studied by different experiments. The varnish obtained by addition of polyaziridine shows a considerably improved performance when compared to plain shellac. In particular, it preserves almost unaltered the chromatic properties of shellac varnish and it shows an increased resistance to alcohols, to basic agents and to artificial ageing caused by a long lasting UV irradiation.

Esterification Process Induced by UV Irradiation of Shellac thin Films Deposited by Matrix Assisted Pulsed Laser Evaporation

“…Bending vibrations of CH 2 can be seen at 1462 cm -1 . As stated also by M. Licchelli et al in [14] and by Derrick et al in [15], the 1715 and 1733 cm -1 peaks are ascribed to C=O stretching vibration in acids and esters (fresh shellac), respectively. The C-O stretching vibration for esters, acids and alcohols can be identified at 1247, 1195 and 1051 cm -1 [16,17].…”

Shellac Thin Films Obtained by Matrix-Assisted Pulsed Laser Evaporation (MAPLE)

“…The weak signal at 1412 cm −1 was associated to the CH2 group attached to the ester chain as reported in Zumbühl et al in [32]. The absorption bands at 1175 and 1050 cm −1 may be due to stretching vibrations of C-O and C-C bonds [31]. Weak signals can be seen at 944 and 882 cm −1 for pristine shellac, dropcast, and the low fluence used of 0.6 J/cm −2 .…”

“…The other two strong vibrations peaked at 1712 cm −1 and 1733 cm −1 are attributed to the C=O stretching vibration of esters [23] and acids, respectively [28,29]. The other medium bands of the characteristic fingerprint are: 1636 cm −1 corresponding to the C=C stretching vibration of vinyl [30]; and 1463 cm −1 and 1376 cm −1 are attributed to CH 3 asymmetric and symmetric bending, respectively [31]. The weak signal at 1412 cm −1 was associated to the CH 2 group attached to the ester chain as reported in Zumbühl et al in [32].…”

Improving Wood Resistance to Decay by Nanostructured ZnO-Based Treatments

“…Shellac is a resinous material of animal origin obtained from the secretions of Lac insects (e.g., Kerria lacca, Laccifer lacca), hosted as parasites by some trees growing in eastern Asia [41,42]. Shellac has been widely used since the 17 th century to varnish and protect the surface of fine wood artifacts due to some peculiar properties such as low toxicity, good film-forming ability, high adhesion to the wood surface, and excellent aesthetical appearance [15,42]. It is still considered as one of the most elegant finishes for furniture, and it is one of the most used varnishes for string musical instruments.…”