Paper deacidification and UV protection using ZnO atomic layer deposition

Abstract

Acid degradation of cellulosic paper in archival books, periodicals, and historic documents is a serious and widespread problem. Using acidic page samples from ∼40 year old books, we demonstrate that atomic layer deposition (ALD) ZnO can adjust and controllably neutralize the paper acid content. The paper samples were collected and analyzed in accordance with recognized Technical Association of the Pulp and Paper Industry (TAPPI) test standards. The average pH of the starting paper was 3.7 ± 0.4 and 4.4 ± 0.1 as determined using the TAPPI surface probe and cold water extraction methods, respectively. After 50 ALD ZnO cycles, the same tests on the coated paper produced an average pH of 7.39 ± 0.08 and 7.3 ± 0.4, respectively. Scanning electron microscopy confirmed that the cellulose structure remained intact during ALD. Additional tests of recently printed newspaper samples coated with ALD ZnO also show that ALD can effectively prevent paper discoloration and embrittlement caused by UV sunlight photoexposure. While there are many known methods for paper preservation, including others using diethyl zinc, the control afforded by ALD provides attractive advantages over other known approaches for preservation of archival paper and other natural fibrous materials.