Chemical Pulp Bleaching The society always wishes for the best in everything, and to achieve that advancement, humanity have developed science as a form of solution. The simplest development that science have made in our daily lives is to make white paper. It might just be something that people take for granted, but to make a white paper, there’re profound scientific knowledge utilized into just making a paper white. White paper are bright, clean, low in pitch content and is better in reflecting light. These white papers are made from a process called the Chemical Bleaching of Pulp, involving chemicals like Chlorine Dioxide.
Pulp Bleaching mill, where pulp Lignin are removed to create a brighter pulp. (Fig.1)
Paper comes from a common raw material known as pulp. Pulp is a processed version of tree barks, hence its original colour is not naturally white. Pulp, like the colour of tree barks, are dark due to a natural glue that keeps wood fibers together, known as the Lignin ("Chemical Pulp Bleaching."). Lignin are what makes the natural pulp dark and not white as we want it. The process of Chemical Bleaching allows the removal of the Lignin by using chemicals such as Chlorine Dioxide, hence making the pulp brighter ("Chemical Pulp Bleaching."). When lignin is removed, the product will have a bright white colour for a period of time before later turning yellow.
The word Bleaching comes from the Anglo Saxon word blecan, which literally means to fade ("Chemical Pulp Bleaching."). The process of bleaching dates back to the ancient Gauls where bleaching was used to bleach grass by using Alkali solutions ("Chemical Pulp Bleaching."). Although it was later in the 1756 that a Scottish chemist, Francis Home created the first “white” paper from sorted white rags. Around 1790’s, English chemist Thomas Henry further developed the use of bleaching solution to paper ("Chemical Pulp Bleaching."). Development of bleaching continues until World War 2, where bleaching pulp was high in demand due to its explosive ability in a form of Nitrocellulose. The Nitrocellulose is a highly flammable material which can be turned into explosives if treated with concentrated Nitric Acid. Bleaching of Pulp was industrialized and in an industrial level, chemists used the chemical Chlorine Dioxide to bleach pulps. It Lignin acts like a glue to keep wood fibers together. has a molecular mass of 67.45, it has a boiling point (Fig. 2) of 11 degree centigrade and it is highly oxidant ("Chemical Pulp Bleaching."). Chlorine Dioxide is commonly used in conventional bleaching of pulp.
Post World War 2, Chlorine Dioxide are still used today for pulp bleaching. Although the usage have changed, it is primarily to create the clean white paper that we use today, not for Nitrocellulose explosives. The process of bleaching is mostly done in paper industries where there’re different stages for the pulp to reach the brightness intended. Each of the stages, the pulp will be washed and chemicals like Chlorine Dioxide is applied in order to remove the Lignin of the pulp so the pulp becomes brighter ("Bleaching of Wood Pulp."). Other than Lignin, Chlorine Dioxide is considerably the best in removing dirt and unwanted materials on the pulp ("Bleaching of Wood Pulp."). This makes the pulp even cleaner and brighter. The process of applying chemicals and washing it continuously will allow the pulp to gain brightness without decreasing its structure or strength. That is because the chemical used, Chlorine Dioxide is highly selective, meaning it does only little degradation to the processed pulp ("Bleaching of Wood Pulp."). Despite the fact that the chemicals like Chlorine Dioxide can remove Lignin to create a brighter pulp, it is also highly toxic and a high oxidant. Meaning, Chlorine Dioxide is dangerous to those around it and it may corrode metals if it comes in contact. Expensive materials like Titanium is needed for Chlorine Dioxide to be processed as Titanium is better in handling oxidation than most metals ("Chemical Pulp Bleaching."). Referring back to the history of Chlorine Dioxide and pulp bleaching used in explosives, factories of chemical pulp bleaching are highly explosives. Many of its material, if concentrated, may trigger an explosion. Those are just some of the danger within the industry of which chemical pulp bleaching is done.
Graph showing the human exposure to the toxic Dioxin in North America. (Fig. 4)
The Chlorine Dioxide Molecule (Fig. 3)
Environmentally, the toxic chemical from the chemical bleaching does affect the environment as its waste are affecting the waterways. Species and biological organisms living in the waterways may be affected as it toxic chemicals will cause impacts to the extreme, such as deaths. Its main impact are waterways or waterbodies because most paper mills are located near large water bodies as the process of washing the pulps require a huge amount of water. Hence an easy solution will be to use the water from large water bodies around the mill. Yet, this then caused organic waste to pollute the water bodies.
Socially in terms of health, conventional bleaching by using Chlorine Dioxide impacts on human health in the aspects of reproduction, development, immunity and hormones ("Dioxins and Dioxin-like Compounds."). This is due to the fact that Chlorine Dioxide produces other organic compounds such as chlorinated Dioxin. Dioxins are toxic chemical which are not intentionally produced and has no known uses. Even though the use of Chlorine Dioxide have been proven to reduce Dioxin production in pulp mills, Dioxin is still produced and are form of waste from the pulp industries. Dioxin is known to be carcinogenic, meaning it has the potential to cause cancer ("Dioxins and Dioxin-like Compounds."). Humans are 90% exposed to Dioxins as it may enter through food consumptions like fish, meat and dairy products ("Dioxins and Dioxin-like Compounds."). Due to chemical pulp bleaching’s environmental impacts and also its negative impacts on human health, science have been developing new technologies and methods to create the same or better pulp but with less negative impacts. One of the latest advancement pulp bleaching is the Total Chlorine Free Bleaching. It basically removed all Chlorine uses in the process of bleaching, hence removing the possible waste of chlorinated Dioxins that will pollute the environment ("Bleaching of Wood Pulp."). Total Chlorine Free Bleaching uses chemicals like Peroxide and Ozone ("Bleaching of Wood Pulp."). Ozone, like Chlorine Dioxide is a powerful oxidant and have been found to be very effective in removing Lignin from pulp. Ozone has the qualities that Chlorine Dioxide has, but with less environmental impacts. Although, an issue with Ozone is that it can not be stored, it has to be produced on-site. This requires sophisticated equipments which may be found costly to some paper companies. Environmentally and Socially, Total Chlorine Free bleaching is the least toxic method of all bleaching methods ("Bleaching of Wood Pulp."). Today, Total Chlorine Free bleaching is primarily practiced in the regions of Sweden and Finland. The European Union is diverting its pulp bleaching to Total Chlorine Free bleaching and is currently representing 25% of the European market ("Bleaching of Wood Pulp."). The busyness of our daily lives have perhaps left us without wonder on the conflicts, efforts and progress in creating simple things like white paper. Its history of starting off as an explosive material in the World War 2 have led its industrialization and today, it has been proven useful for many good purposes. Its progress have been directed from using chemicals like Chlorine Dioxide which harms both the environment and humanity through its effects of pollution, into process which uses chemicals like Ozone which has the same capability as Chlorine Dioxide but with less negative impacts. The advancement of Science have not only led us into creating a better product like the white paper, but also on how to create that better product by minimizing its negative impacts on other aspects of life.
Bibliography: "Chlorine Dioxide Bleaching." IPST. N.p., n.d. Web. 19 Nov. 2012. <http://www.ipst.gatech.edu/ faculty/ragauskas_art/technical_reviews/clo2.pdf>. "Chemical Pulp Bleaching." Chemical Pulp Bleaching. N.p., n.d. Web. 19 Nov. 2012. <http:// www.metso.com/corporation/info_eng.nsf/WebWID/WTB-060629-2256F-634BA>. "Bleaching of Wood Pulp." Wikipedia. Wikimedia Foundation, 16 Nov. 2012. Web. 19 Nov. 2012. <http://en.wikipedia.org/wiki/Bleaching_of_wood_pulp>. "Dioxins and Dioxin-like Compounds." Wikipedia. Wikimedia Foundation, 11 Dec. 2012. Web. 19 Nov. 2012. <http://en.wikipedia.org/wiki/Dioxins_and_dioxin-like_compounds>.
Images: "Pulp Mill." Aliimg. N.p., n.d. Web. 19 Nov. 2012. <http://i00.i.aliimg.com/img/pb/ 595/953/409/409953595_236.jpg>. (Fig.1)
"Chlorine Dioxide Structure." Getmms. N.p., n.d. Web. 19 Nov. 2012. <http:// www.getmms.org/media/chlorine_dioxide.jpg>. (Fig. 2)
"Lignin." Lignin. N.p., n.d. Web. 19 Nov. 2012. <http://www.ili-lignin.com/images/ content/crosssection.gif>. (Fig. 3)
"Dioxin Chart." Enjnet. N.p., n.d. Web. 19 Nov. 2012. <http://www.ejnet.org/dioxin/ dioxin_chart.gif>. (Fig. 4)