From paper durability to aging test
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Regarding the definition of paper durability (Permanence), although different research organizations can reach a consensus in concept, there are still some differences in the specific description. For ISO (The International Organization for Standardization) and ANSI (American National Standards Institute) as an example the two organizations. The former defines the term durability of the sheet of paper after a long period of time is still able to maintain its physical and chemical stability of the (The ability to remain chemically and physically stable over long periods of Time), while the latter has a more detailed and detailed description of paper durability. Her definition is that the paper will not appear in the normal use and storage environment of the library or file vault after at least several hundred years. significant deterioration (the ability of paper to last at least several hundred years without significant deterioration under normal use and storage conditions in libraries and archives). The deterioration of the paper mentioned above in the definition is generally understood as a change in the characteristics of the paper, and the more familiar is the strength of the paper and the brightness of the paper (Brightness - an indicator for measuring the yellowing of the paper).
The various physical and chemical properties of the paper change over time, mainly because of the continuous degradation of the cellulose (Cellulose) and hemicellulose (Hemicelluloses) molecules in the paper Degradation) reaction. The rate of degradation depends on the temperature, the water content of the paper (ie the relative humidity of the storage environment) and the pH of the paper. Studies have shown that pH plays an important role in the durability of paper. Most of the paper we use for printing is Acid Paper, which speeds up the aging of paper. The acidic components in the paper come from the bleaching agent in the papermaking process; the chemicals produced in the degradation of cellulose and hemicellulose (because of the acidity, this chemical will further catalyze the degradation of the fiber); the sizing on the paper Sizing Agent—Sugges the composition of the paper and improves the water absorption of the paper. Generally, it uses acidic Alum and Rosin. In addition to fibers, another material that makes up paper is mainly used to fill the space between fibers and fibers, and gives a certain weight to the paper; coating, etc. If we want the paper to have a certain durability, in the papermaking process, we can use a neutral or alkaline size, and at the same time use an alkaline filler such as calcium carbonate (Calcium Carbonate) to make a base. Alkaline Paper. Alkaline paper has the advantage of neutralizing the acidity of chemicals, printing inks, and other contaminants produced by fiber degradation. For these pH value (pH value - to reflect a pH indicator substance, the value 7 represents neutrality, values less than 7 are acidic, the less the value, the higher acid; contrary, value above 7 is alkaline, the value Large, alkaline is higher.) Alkaline paper higher than 7, also known as acid-free paper. ANSI also clearly states that the pH of durable paper should be defined between pH 7.5 and pH 10.
If we want to reduce the aging speed of paper, in addition to starting from the paper itself, the preservation environment needs to be strictly controlled. The temperature rises; the water mixes the oxygen in the air to oxidize the cellulose; the light, especially the natural light and the ultraviolet light; the air pollutants tend to decompose the cellulose to decompose the organic acid and accelerate the aging of the paper. Therefore, some important documents or books should be stored in the absence of light, clean air, proper and stable temperature and humidity.
Many research organizations, such as TAPPI (Technical Association of the Pulp & Paper), ASTM (American Society for Testing and Materials), ISO, etc., all hope to completely simulate the natural aging of paper by artificial aging. . In general, this is to artificially speed up the aging process of the paper. We are able to predict the durability of the paper and the changes in the composition and properties of the paper after a long period of time in a short period of time. Organizations have developed different test methods for everyone to follow. Take the TAPPI test method T544 as an example. It is to study the aging of the paper by placing the paper in a temperature of 50% relative humidity and a temperature of 90 °C for a long time. Due to the temperature and humidity of paper storage, long-term control is required at a stable level. Therefore, to carry out this type of test, it is generally necessary to have an Environmental Chamber that automatically monitors the temperature and humidity functions to meet the basic requirements of the test. In order to predict the impact of the paper aging process on the paper characteristics, our approach is to test the paper characteristics before and after the artificial aging process, and compare them. The choice of paper characteristics test depends on the actual needs of the user, and can be the mechanical properties of the paper such as Folding Endurance, Tensile Strength, Tearing Resistance; paper Optical properties such as Brightness, Opacity, and chemical properties such as pH. However, there is one point that readers should pay attention to. Up to now, the artificial aging test of paper has only accelerated the aging process of paper under controlled environment, and the results are not the same as the natural paper aging process. Therefore, different people There may be different understandings of the aging test. For example: Some people will define paper in a 100 ° C environment for 3 days, equivalent to 25 years in the natural environment, but some people understand 300 years. It can be seen that there are still many undetermined places left for research by using the artificial aging method to test the results. Therefore, in the current stage, the results of the artificial paper aging test are more suitable for research and reference purposes.