Regarding the definition of paper durability, although different research organizations can reach a consensus in concept, there are still some differences in the specific description. Take the two organizations ISO (The International Organization for Standardization) and ANSI (American National Standards Institute) as examples. The former defines the term paper durability as the paper can maintain its physical and chemical stability over a long period of time (The ability to remain chemically and physically stable over long periods of time), while the latter is durable to paper There is a more detailed and specific description of sex. Her definition is that the paper is in the normal use and storage environment of the book library or document vault. After at least a few hundred years, the paper will not deteriorate significantly (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 in the definition above is generally understood as a change in the characteristics of the paper, and what is more recognized is the strength of the paper and the brightness of the paper (Brightness—a measure of the yellowing of paper).
The various physical and chemical properties of the paper will change with time, mainly because the cellulose (Cellulose) and hemicellulose (Hemicelluloses) molecules of the fiber composition in the paper continuously undergo hydrolytic degradation reactions. The rate of degradation depends on the temperature, the water content of the paper (that is, 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 will accelerate the aging of paper. The acid component of paper comes from the bleaching agent in the papermaking process; the chemical substances produced during the degradation of cellulose and hemicellulose (because it is acidic, so this chemical substance will further catalyze the degradation of fibers); Materials (Sizing Agent—think of the binder of the composition on the paper, and can improve the water absorption of the paper, generally use acidic alum (Alum), rosin (Rosin).); Filler on the paper (Filler-except In addition to fibers, another material that constitutes paper is mainly used to fill the space between fibers and fibers, and to give a certain weight to the paper); coating, etc. (Coating). If we want the paper to have a certain durability, in the papermaking process, we can use neutral or alkaline sizing materials, and at the same time use alkaline fillers such as calcium carbonate (Calcium Carbonate) and other materials to make alkali Alkaline Paper. The advantage of alkaline paper is that it can neutralize the acidity caused by the chemical substances, printing inks and other pollutants produced by the fiber degradation. For these pH values ​​(pH value-an indicator that reflects the acidity and alkalinity of the substance, the value 7 represents neutral, and the value below 7 is acidic, the lower the value, the higher the acidity; on the contrary, the value above 7 is alkaline, the more the value The larger, the higher the alkalinity.) Alkaline paper higher than 7 is also known as acid-free paper. ANSI also clearly states that the pH value of durable paper should be defined between pH 7.5 and pH 10.
If we want to reduce the aging rate of paper, in addition to starting from the paper itself, the preservation environment needs to be strictly controlled. Temperature rises; water mixes with oxygen in the air to oxidize cellulose; light, especially natural light and ultraviolet light; pollutants in the air will chew cellulose to decompose organic acidic substances and accelerate paper aging. Therefore, some important documents or books should be stored under the conditions of no 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., hope to completely simulate the natural aging of paper by artificial aging (Artificial Aging). . Generally speaking, this is to speed up the aging process of the paper by manual methods. We can predict the durability of the paper and the changes in the composition and characteristics of the paper after a long time. Each organization has developed different test methods for everyone to follow. Take TAPPI test method T544 as an example, it is to put the paper at 50% relative humidity; 90 ° C temperature environment for a long time to study the aging of paper. Because the temperature and humidity of paper storage need to be controlled at a stable level for a long time. Therefore, to carry out this type of test, it is generally necessary to equip the Environmental Chamber with automatic temperature and humidity monitoring functions to meet the basic requirements of the test. For predicting the impact of the paper aging process on paper characteristics, our approach is to test the paper characteristics before and after manual aging and compare the results. The choice of paper characteristics test depends on the actual needs of the user, it can be the mechanical characteristics of the paper such as folding endurance (Folding Endurance), tensile strength (Tensile Strength), tearing strength (Tearing Resistance); paper Optical property tests such as brightness and opacity; chemical property tests such as pH. But there is one thing that readers should pay attention to. At present, the artificial aging test of paper only accelerates the aging process of paper under a controlled environment, and the results obtained are not the same as the natural paper aging process. There may be different understandings of the aging test. For example: Some people will define that putting paper in an environment of 100 ° C for 3 days is equivalent to 25 years in a natural environment, but some people understand it as 300 years. It can be seen that there are still many undetermined areas to be studied by the results of the artificial aging test. So at the present stage, the results of the artificial paper aging test are more suitable for research and reference purposes.
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