High retreatability and dimensional stability of polymer grafted waterlogged archaeological wood achieved by ARGET ATRP

Yihang Zhou,Kai Wang,Dongbo Hu

doi:10.1038/s41598-019-46366-7

Abstract

To explore new methods to maintain the dimensional stability of waterlogged archaeological wood after drying and keep the natural cell lumens unaltered for future retreatments, activator regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) is employed to consolidate archaeological wood. To prepare the ATRP process, the waterlogged archaeological wood samples (Pinus massoniana with maximum moisture content of around 529%) were first modified by 2-bromoisobutyryl bromide in CH2Cl2 to acquire C-Br bonds as initiators. Then, butyl methacrylate or styrene was polymerized to the remaining cell walls with catalyst (CuBr2), reductant (ascorbic acid) and ligand (PMDETA) in ethanol. After the treatment, the samples were washed and naturally dried. The results characterized by microscopy showed that the polymerization only took place within the remaining cell walls, showing no sign of collapse or distortion after air drying, and all natural cell lumens could be retained for future retreatments. Also, anti-shrinkage efficiencies as high as 87.8% for the wood sample grafted with polystyrene and 98.5% for the wood sample grafted with polybutylmethacrylate were obtained from the treatment described in this paper, indicating modification of grafting polymer through ARGET ATRP can help maintain the dimensional stability of water archaeological wood effectively.

Highlights

Scientists and conservators have put tremendous efforts into methods aimed at maintaining the dimensional stability of waterlogged archaeological wood, preventing them from shrinkage, cracking and deformation
Recent research has proven in situ polymerization of isoeugenol is a green and promising method for waterlogged archaeological wood with potential retreatability[7], while many oligomers were generated in solution, reducing the efficiency
The most appropriate approach is called atom transfer radical polymerization (ATRP)[16]. This approach was revised and improved in 2006 to initiators for continuous activator regeneration (ICAR) ATRP and activator regenerated by electron transfer (ARGET) ATRP17

Summary

Introduction

Scientists and conservators have put tremendous efforts into methods aimed at maintaining the dimensional stability of waterlogged archaeological wood, preventing them from shrinkage, cracking and deformation. Recent research has proven in situ polymerization of isoeugenol is a green and promising method for waterlogged archaeological wood with potential retreatability[7], while many oligomers were generated in solution, reducing the efficiency. The application of wood-polymer composites (WPC) in art conservation was proposed in the 1970s, as a method that can greatly reduce the effect of wood defects due to changes in moisture content, such as decay, shrinking and swelling[15]. We are aiming to reinforce secondary cell walls of archaeological wood through graft polymerization using the ARGET ATRP approach (Fig. 1.) after immobilization of the initiator on wood substrate. Thereafter, it is of necessity to conduct a morphological and chemical study of the archaeological wood modified by grafting polymer through ARGET ATRP to show the integration between cell walls and polymers, and voids ready for future retreatments

Methods

Results

Conclusion