Manufacture of all-cellulose film from paper by using ionic liquids

Paper material consists of fibres bound primarily with hydrogen bonds. Thus water can disrupt those bonds, making paper to be non-water-resistant, if no any wet strength agent is used. In this study, we investigated the "chemical welding" of kraft-pulp-paper with the ionic liquid, 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc). The process was in two steps. Firstly, ionic liquid was transported into the paper structure. In the second phase, the dissolution and subsequent embedding of the fibre surfaces were achieved by the heat activation (80–95ºC). The IL treated paper was purified with water from IL and dried under compression. Precipitation of the dissolved cellulose resulted in a fusion of the fibres of paper into a solid, uniform material, whose properties are similar to thermoset plastics. Such obtained "chemically welded" paper structure elevated both dry and wet strength. The treatment conditions can be adjusted (i.e. dosage of ionic liquid, activation temperature, time) to produce both paper-like materials and films. The most severe treatment conditions produce films, which are fully transparent and whose oxygen and grease barrier properties are excellent. This study demonstrates conversion of ordinary paper into novel materials. As an all-cellulose material, the "chemically welded" paper is fully biodegradable and is a potential alternative to fossil fuel-based plastics.