NC State University Pulp & Paper Education Pack 1 Goals In this activity, students will conduct chemical pulping processes on a variety of plant raw materials. The raw materials, both wood-based and nonwoody, will be soaked or boiled in a solution of sodium hydroxide to remove the lignin holding the fibers together. The chemically-treated mass will then be subjected to mechanical action (blending) to separate the fibers. The resulting pulp will optionally be bleached with sodium hypochlorite or hydrogen peroxide. The pulp will then be refined to make the fibers ready for papermaking. Sample sheets of paper will then be made for evaluation of strength properties. Key Learning Concepts In conducting this activity, students should learn the theory and application of the following concepts: Χ Χ Χ Χ Χ Χ Χ The vascular and fibrous nature of plants The use of plant fibers for papermaking Chemical pulping/delignification Chemical reactions -- the effects of chemical concentration, reaction time, reaction temperature Bleaching Refining of fibers for papermaking Papermaking Basic Equipment Required * 125-ml glass Erlenmeyer flask * 1000-ml glass Erlenmeyer flask * laboratory hot plate * fine-mesh colander or strainer * kitchen blender with lid * Buchner filter funnel * suction flask * scale or balance * source of vacuum (water aspirator or vacuum pump)
NC State University Pulp & Paper Education Pack 2 Safety Equipment Required * heavy rubber gloves (chemical duty, with heat-resistant coating) * safety glasses Chemicals Required > sodium hydroxide [NaOH], solid * available from grocery and hardware stores as lye. Read the label to insure that only sodium hydroxide is listed. * do NOT use liquid drain cleaners, since the % sodium hydroxide by weight may not be listed and may vary from brand to brand. * do NOT use any liquid drain cleaner which lists sodium or calcium hypochlorite [NaOCL or Ca(OCL) 2 ]as an ingredient. > sodium [NaOCL] or calcium hypochlorite [Ca(OCL) 2 ] solution * available as household bleach. Look at the label to insure that the bleach is hypochlorite-based. > hydrogen peroxide [H 2 O 2 ] solution * available as common hydrogen peroxide solution from grocery and drug stores Background and Key Concepts PLANTS AND PULPING All paper is made from plant materials. More specifically, paper consists of a mat of fibers obtained from plant materials. These fibers are actually the conducting vessels (tracheids) which transport water from the roots of the plant into the leaves and distribute photosynthesis products throughout the plant. While it is possible to make paper from some plants by simply using mechanical action (beating, crushing, grinding) to pulverize the material into a fibrous mass, plants are generally not in a form ready for being made into paper. The fibers are made up mainly of cellulose, a polymer made up of the glucose generated during photosynthesis. Cellulose has good tensile strength, but it is soft and flexible in nature. If a tree or plant consisted only of cellulose, it would not have enough stiffness or strength to stand upright. So, as the cellulosic conducting fibers are being manufactured, the plant generates another polymer called lignin and encrusts it inside
NC State University Pulp & Paper Education Pack 3 of and in between the fibers. Lignin is much like an epoxy, with a huge molecular weight, random structure, and an enormous capacity to cross-link with other sites on the lignin molecule. The combination of cellulose and lignin makes wood a lightweight but extremely tough and durable material. For the papermaker, however, this structure presents a problem -- how to get rid of the lignin and liberate the cellulosic fibers. PULPING is the process of converting plant-based raw materials, such as wood or straw, into papermaking fibers. There are two basic methods of pulping: > Mechanical Pulping -- uses only mechanical force (and perhaps some heat energy) to pull the raw material apart into fibers. No lignin is removed. The resulting pulp is relatively crude, with a large content of damaged fibers. > Chemical Pulping -- uses heat and chemical energy to preferentially dissolve the lignin from the plant material, leaving only pure cellulosic fibers. The activities in this unit will focus on chemical pulping, since removal of lignin is required in order to produce the highest-quality bleached and unbleached pulps used for most common purposes. BLEACHING Bleaching is a process used to do two things to the material produced from the pulping process: > Remove the small amount of lignin remaining in the pulp > Chemically attack molecules the pulp which cause dark coloration In general, all of the lignin in a plant raw material cannot be removed by pulping. As the lignin content decreases, the pulping chemicals begin to attack the cellulose, since more of it is available by comparison. At some point, it is necessary to stop the pulping process and move on to the bleaching process. Bleaching chemicals tend to be more selective in their attack, preferring lignin to cellulose, even if more cellulose is available compared to lignin. However, bleaching chemicals also are more expensive than pulping chemicals, so the determination of when to stop pulping and start bleaching is critical.
NC State University Pulp & Paper Education Pack 4 It may seem strange, but after the pulping process, the pulp is often much darker in color than the original raw material. This darkening is usually due to the fact that the chemical attack on the lignin causes some of the molecules in the lignin remaining in the pulp to be modified in a way that it absorbs light in the wavelengths visible to the human eye. These chromophores must be chemically attacked by bleaching chemicals in order to convert them back into a colorless form. CHEMICAL REACTIONS Modern industrial processing is concerned with the conversion of raw materials into a finished product. The chemical processing industry uses thermal, chemical, and physical energy to make this conversion. Since the industry is always interested in producing products in the fastest and least expensive manner, the chemical reaction rate is always of importance. In general, a faster reaction will permit greater production in a given amount of time, thereby lowering overall costs and increasing productivity. Chemical reaction rates are governed by two main variables: > Concentration of chemical reactants > Temperature of the reaction The higher the concentration of chemical reactants, the more likely it is that key collisions will occur between the molecules of the reactant and the molecules of the raw material being attacked. A larger concentration of reactants thus produces a greater driving force for the reaction, thereby increasing the reaction rate. As the temperature of many chemical reactions is increased, the activity of the molecules is increased, thereby permitting more collisions between raw material and reactant molecules. It is a rule of thumb that increasing the reaction temperature by ten degrees Centigrade normally doubles the reaction rate. REFINING Even when liberated during pulping, plant fibers are not in a form most suitable for papermaking. The fibers still are hollow conducting tubes, which limits the surface area available for bonding to other fibers.
NC State University Pulp & Paper Education Pack 5 Try this test: take a common plastic drinking straw place it next to another. The point of contact is limited to a thin line between the two. Even when a number of straws are placed around the original straw, there is a significant amount of surface area on the straw which does not contact another straw. If the straw could be collapsed into a flat ribbon, with no open area in the middle, the entire periphery of the fiber would be available for bonding. Refining is an intense mechanical process carried out on pulp to cause the fibers to be ready for papermaking. Strong paper cannot be made without this treatment. Refining actually performs two key tasks to increase fiber-to-fiber bonding: > Collapses the fibers into flat ribbons > Shreds the outer layer of the fibers (called fibrillation), making it hairylooking and producing even more surface area for bonding In the paper industry, refining is carried out by passing the pulp between grooved plates rotating at high speed. In the laboratory, a very similar action can be achieved using a common household blender.
NC State University Pulp & Paper Education Pack 6 Pulping Experiment: Chemi-Mechanical Pulping with Sodium Hydroxide Wood is the raw material most widely used for making paper pulps. The dense nature of wood, combined with its relatively high lignin content, makes it necessary to use very intense conditions in the pulping process. For laboratory demonstrations, it is much easier to use nonwood materials, such as grass or straw. In this experiment, you will take common plant materials and convert them into pulp, using sodium hydroxide (also known as lye, caustic, or soda) as the attacking chemical. If sodium hydroxide is used at high temperatures and pressure, the process is called the soda pulping process. Since it is hazardous to use such conditions in common student laboratories, the sodium hydroxide will instead be used in a mild boil with the raw material. Unlike the soda process, the mildness of this treatment will not permit most of the lignin in the raw material to be removed. As a result, the raw material after pulping will be soft, but it will not be in fibrous form. To convert the boiled material into pulp fibers, some mechanical shearing action will be used on the pulp. Since both chemical and mechanical energy will be put into the raw material to pulp it, the process will be referred to as a chemi-mechanical soda process. The pulping will be followed by bleaching, then by refining to make a papermaking pulp. Sample sheets of handmade paper will be made and evaluated for appearance and strength. TASK 1: RAW MATERIAL PREPARATION Although papermaking started in 105 AD with the use of straw, bark, and other nonwoody materials, the bulk of papermaking pulp in developed countries today is made from wood (developing countries often have very little wood resources -- they have to use nonwoods). However, pulping wood requires higher temperatures and pressures than can normally be developed safely in student laboratories. For this reason, this experiment will use nonwood plants as starting materials.
NC State University Pulp & Paper Education Pack 7 Many common plants are poisonous and can cause skin irritation. Use caution when handling plants; stick with familiar varieties. The use of rubber gloves is advised. Avoid breathing the dust of any dried plant when Cutting it into pieces. Use of a dust mask is recommended. There are many common cultivated and wild (weed) plants available to the student which can be successfully converted into papermaking pulp. Here is a list of prospective raw materials: * grass clippings * hay * wheat or rice straw * dandelion * milkweed * dog fennel * ragweed * corn stalks * tobacco stalks * kudzu vines * bean stalks * sweet potato vines * cotton stalks * poke weed The key is that the plant should have stem that, when pulled apart, shows evidence of thread-like fibers at the pull-apart point. The plant stem is usually what is used for pulping. Avoid leaves, bark, and roots, since these materials contain little or no fiber and can consume all the chemicals used for pulping. Use the following procedure for raw material preparation: 1. Remove all roots, branches, flowers, and leaves from the material. Most nonwoods don t have bark, so removal should not be necessary. 2. Cut stalks into 1/2-inch long pieces or so. Grass clippings and more shredded types of raw materials can be used without cutting. 3. To minimize degradation of the raw materials and also to get them to a known
NC State University Pulp & Paper Education Pack 8 moisture content, spread the chopped materials out in a thin layer in a room or outside in the sun. Allow the materials to dry for several days, turning them once a day to insure even drying. After the materials are dry, place them in labeled plastic bags and tie closed. TASK 2: CHEMI-MECHANICAL SODA PULPING Soda pulping is a process using only sodium hydroxide as the chemical reactant. On wood chips, this process normally uses high temperatures (up to 160 C) and high pressures (up to 10 atmospheres) to dissolve lignin. However, some nonwoods can be adequately delignified using a boiling solution of sodium hydroxide, provided the pulping is followed by some mechanical action. In this activity, common nonwood plant materials will be converted into pulp using this type of caustic boil. Concept to Remember: The Moisture Content of Plant Materials All plant materials are hygroscopic, meaning that they absorb and desorb water in equilibrium with their environment. For proper dosing of chemicals, the actual content of moisture-free fiber in raw material must be determined. The term consistency is used in the paper industry to describe the dry solids content (by weight) of a fibrous material. The total weight of a sample of raw material, multiplied by the consistency, equals the moisture-free weight, also called the oven-dry weight. Most plant materials, if allowed to dry in open air for several days, will achieve a consistency of 90 % -- conversely, they achieve a moisture content of 10 %. The term air-dry weight is normally used to refer to the as-is weight of the material -- the
NC State University Pulp & Paper Education Pack 9 weight obtained when the dried material is placed on a balance. The following formula is used to convert from air-dry to oven-dry weight: Oven-dry weight, grams = (Air-dry weight, grams) x 0.9 Use the following procedure to conduct soda pulping on the raw material of your choice: 1. Using a balance, weigh out 50 air-dry (as-is) grams of raw material. The ovendry weight, using the formula above, will be 45 grams. 2. For a soda process, the following process specification will be used: Chemical concentration: NaOH, 18 % by weight in water Temperature: 100 C (boiling) Time: 30 minutes ALWAYS WEAR SAFETY GLASSES AT ALL TIMES WHEN CONDUCTING LABORATORY EXPERIMENTS! NO EXCEPTIONS! NO EXCUSES! CAUTION! Solid sodium hydroxide (lye) and sodium hydroxide solutions can cause severe burns if contacted with the skin! Always wear rubber gloves when measuring out solid sodium hydroxide or when handling sodium hydroxide solutions. When sodium hydroxide is dissolved in water, a fume is produced -- avoid breathing. 3. Prepare an 18 % sodium hydroxide solution by pouring 700 ml of water into the 1000-ml flask. Weigh out 154 grams of the lye/caustic soda powder and pour into the flask. Insert the 125-ml flask upside down into the top of the 1000-ml flask. Swirl gently until the white powder is dissolved. Note: the liquid will become warm due to the heat of solution, a term used to describe the release of energy when some solids are dissolved.
NC State University Pulp & Paper Education Pack 10 4. Place the weighed raw material into the 1000-ml flask along with the hydroxide solution. Replace the small flask cap and swirl to mix the dry material with the liquid. Some material may try to float; it will sink once the heating process starts. It may be necessary to take a glass or metal rod and push some pieces of material down off the sides of the flask. > NEVER leave a chemical process unattended at any time, especially if it is being heated. > When boiling liquids on the hot plate, avoid placing your hands or face directly over the boiling container, since material may shoot out unexpectedly. > Wear heavy rubber gloves at all times, to avoid forgetting and reaching to swirl the flask with bare hands. Flask is hot! > Always have a plan for what to do if the flask starts boiling over. Have a heat-resistant surface close by and ready for the flask if you need to move it quickly from the heat. Make sure the area around the hot plate is able to contain any boil-over of caustic material. 5. Place the capped flask on the hotplate and turn to the high setting. Monitor the flask at all times. Stir the flask occasionally (with a gloved hand) to promote uniform heating. When the flask starts to boil, reduce the heat to the medium setting. The goal is to establish a slow, uniform boil -- some trial and error may be necessary. When boiling, you should see evaporated liquid condensing on the small flask cap and then dripping back into the boiling liquid. The cap may jiggle a bit to release small amounts of pressure. 6. Once the boil is established, start timing the reaction. Permit the boil to continue for 30 minutes. 7. It is OK if a small amount of fiber sticks up out of the surface of the liquid. If some material is stuck on the wall of the flask and above the liquid surface, it
NC State University Pulp & Paper Education Pack 11 is permissible to gently remove the cap and use a glass or metal rod to push it back down into the liquid. NOTE: as the boil progresses, the liquid will turn dark brown or even black. This behavior is due to the dissolution of lignin and other components. The reason that the color is darker than the original raw material is that the sodium hydroxide causes some of the lignin molecules to change into a form that absorbs light in the visible spectrum. These molecules are called chromophores. 8. At the end of the boil, turn off the hot plate and remove the flask. Set the flask aside to cool for 15-30 minutes. 9. Using a pair of long tweezers or a glass rod, remove a small portion of the boiled material fiber and place it on a paper towel. Notice that, while made softer by the boil, the material is still not in the form of small fibers. It will be necessary to provide some mechanical action to the cooked material to fiberize it into pulp fibers. It is permissible to dispose of solutions of NaOH and dissolved raw material down the drain, if plenty of dilution used during and after the disposal. water is 10. The dark-colored liquid mixed in with the boiled material is known in the pulp and paper industry as black liquor. It must be separated from the solid material before fiberizing and washing. Turn on the cold tap water at the sink to a moderate level. Place the fine-mesh colander or strainer into the sink. Using a gloved hand, slowly pour the contents of the flask into the strainer, allowing the liquid to drain into the sink. It may be necessary to use a glass or metal rod to get all of the solid material out of the flask. Let the water run into the sink for several minutes after draining is complete to provide a good flush of the chemicals.
NC State University Pulp & Paper Education Pack 12 Processing chemical-containing material in a kitchen blender can be very hazardous. Before turning on the blender, do the following a) make sure that the spout of the blender container is turned away from you or anyone else; b) make sure the container lid is on securely; c) place a gloved hand on the lid to insure that it doesn t pop off during the initial surge of material. YOU MUST BE WEARING SAFETY GLASSES!!!!! 11. When the boiled material has finished draining, transfer it with a gloved hand into the blender container. Add 600 ml (600 grams) of cold tap water. Place the container cap on securely and hold down with your hand. Turn the blender on its lowest setting and permit to blend for 1 minute. NOTE: After fiberization, the material may now be called pulp. In its unbleached form, pulp is often referred to as brownstock. 12. Stop the blender. Wash the pulp by placing 1 paper towel in the Buchner filtering funnel (pre-wet the towel to make it conform to the shape of the funnel). Place the funnel into the filter flask, then connect the flask to the aspirator or other vacuum source. Turn on the vacuum. Slowly pour the contents of the blender container into the funnel. Liquid will start leaving the pulp immediately. When the liquid level in the filter flask reaches a point near the vacuum take-off, stop pouring into the funnel. Turn off the vacuum and remove the funnel, being careful not to dump out the contents. Turn on the sink tap water to a moderate level, then pour the flask contents into the sink. Replace the funnel, turn the vacuum back on, and resume pouring in material from the blender container. 13. When all the material has been poured from the blender container, allow all the liquid to be pulled from the pulp, forming a thick mat. Fill the blender container with hot tap water to the 1-liter mark. Pour this water on top of the pulp mat
NC State University Pulp & Paper Education Pack 13 in the funnel slowly, allowing the vacuum to pull it through. Turn off the vacuum and discard liquid as necessary. 14. Repeat step 13, using another liter of hot tap water. The pulp should now be thoroughly washed. NOTE: This type of washing, which uses a vacuum to pull a cleaner liquid through a pulp mat and displace the dirtier liquid, is called displacement washing. It is a very efficient method of washing and is used extensively in the industry. 15. Allow the pulp mat to drain until no liquid is noted coming out of the funnel. The mat will be slightly mushy to the touch. Turn off the vacuum and remove the funnel from the flask. Remove the paper towel from the funnel and lay flat. Separate the pulp mat from the paper towel, rolling the pulp ball across the towel to capture remaining fibers. 16. Take a small piece of the pulp mass -- about half the size of a pea -- and place it into the (clean) 1000-ml flask. Add 400-500 ml of water, cover with your hand, and shake vigorously to disperse the pulp. Hold the flask up to the light and you will see the liberated fibers suspended in water. You may also see bundles of poorly-separated fibers, known as shives. These bundles are normally separated from the fibers in a process called screening. They will hopefully be reduced to fibers during the bleaching step below. Place the wet pulp in a sealed plastic bag to keep it from drying out. Label the bag with the raw material name or type, the pulping process used (soda), the chemical charge (18 % NaOH). TASK 3: BLEACHING Bleaching is necessary for several reasons: > To remove residual lignin in the pulp, which not only gives the pulp a dark color, but it may also cause yellowing and degradation of the paper over time > To destroy color-causing chromophore molecules in the pulp, giving it a
NC State University Pulp & Paper Education Pack 14 lighter color more suitable for printing and writing > To attack shives and dirts in the pulp, improving its cleanliness Most chemicals used for bleaching pulp are strong oxidizers, meaning that they conduct their bleaching action on the pulp by stealing electrons from molecules in the pulp. Bleaching chemicals fall into two categories: Chlorine-Based * Chlorine * Hypochlorite * Chlorine Dioxide These chemicals were used exclusively by the industry for many years. However, due to restrictions on the discharge of chlorinated organic byproducts into the environment, only chlorine dioxide is used today. Oxygen-Based * Oxygen * Hydrogen Peroxide * Ozone These chemicals produce no chlorinated byproducts and have therefore been used in increasing amounts. Sodium or calcium hypochlorite solutions are more commonly known as household bleach. Even though it is not used much in the industry, it will be used for this activity because it works well under simple lab conditions. Avoid contacting hypochlorite solution with the skin. Always wear gloves when measuring out or using hypochlorite solution. Conduct bleaching in a well- ventilated area, and avoid breathing fumes. Never mix hypochlorite solutions with any other chemicals. Concept to Remember: Calculating Chemical Charge for a Process
NC State University Pulp & Paper Education Pack 15 The chemical charge is the amount of chemical measured out to react with the pulp. It is usually specified in terms of the weight % of reacting chemical based on the weight of the moisture-free (OD) fiber. If the reacting chemical is not diluted (for example, dry sodium hydroxide powder), then the calculation is straightforward: Chemical to Weigh Out, g = (OD grams of fiber) x % chemical desired on OD pulp 100 If, however, the chemical being used is in solution form, then the concentration of active chemical in that solution must be taken into account: Chemical to Weigh Out, g = (OD grams of fiber) x % chemical desired on OD pulp x 1 100 concentration where concentration = % active chemical by weight = g active chemical 100 g total solution 17. To make the proper bleaching chemical charge calculations, we can make the following assumptions: > the consistency (% dry fiber by weight) of the pulp after being vacuumdewatered in the suction funnel is about 7 % > the active hypochlorite content of common household liquid bleach may be assumed to be 5 % by weight. 18. For bleaching, the following process specification will be used: Hypochlorite charge : 8 % on OD fiber Temperature: 120-130 F (hot tap water temperature) Time: 30-60 minutes 19. Weigh out 143 grams of the pulp produced during the previous activity (after washing and dewatering in the filter funnel). Since we are assuming that the consistency of this pulp is 7 %, then OD grams of pulp for bleaching = 143 grams wet pulp x 7 OD grams pulp
NC State University Pulp & Paper Education Pack 16 100 grams wet pulp = 10 OD grams pulp 20. Using the chemical charge formula described above, the amount of bleach to weigh out is Bleach to weight out, g = 10 OD grams pulp x 8% hypochlorite on OD pulp 100 x 1 (5 % active chemical by weight/100) = 16 grams bleach 21. Put pulp into the blender container. Add 750 ml (750 grams) of tap water which has been allowed to run until hot. Place cover on container and energize blender motor at the lowest setting for 5 seconds to mix water and pulp. Processing chemical-containing material in a kitchen blender can be very hazardous. Before turning on the blender, do the following a) make sure that the spout of the blender container is turned away from you or anyone else; b) make sure the container lid is on securely; c) place a gloved hand on the lid to insure that it doesn t pop off during the initial surge of material. YOU MUST BE WEARING SAFETY GLASSES!!!!! 22. Stop the blender and open cover. Pour in the bleach solution. Replace cover
NC State University Pulp & Paper Education Pack 17 and energize the blender for 5 seconds. Allow the mixture to sit for 30-60 minutes, turning on the blender every 10 minutes or so for a few seconds to promote mixing. 23. Wash the pulp by placing 1 paper towel in the Buchner filtering funnel (pre-wet the towel to make it conform to the shape of the funnel). Place the funnel into the filter flask, then connect the flask to the aspirator or other vacuum source. Turn on the vacuum. Slowly pour the contents of the blender container into the funnel. Liquid will start leaving the pulp immediately. When the liquid level in the filter flask reaches a point near the vacuum take-off, stop pouring into the funnel. Turn off the vacuum and remove the funnel, being careful not to dump out the contents. Pour the flask contents into the sink. Replace the funnel, turn the vacuum back on, and resume pouring in material from the blender container. 24. When all the material has been poured from the blender container, allow all the liquid to be pulled from the pulp, forming a thick mat. Fill the blender container with hot tap water to the 1-liter mark. Pour this water on top of the pulp mat in the funnel slowly, allowing the vacuum to pull it through. Turn off the vacuum and discard liquid as necessary. 25. Repeat step 24, using another liter of hot tap water. The pulp should now be thoroughly washed. 26. Allow the pulp mat to drain until no liquid is noted coming out of the funnel. The mat will be slightly mushy to the touch. Turn off the vacuum and remove the funnel from the flask. Remove the paper towel from the funnel and lay flat. Separate the pulp mat from the paper towel, rolling the pulp ball across the towel to capture remaining fibers. 27. Place a sample of the bleached pulp next to a sample of the unbleached pulp to compare the brightness and color. 28. Place the wet pulp in a sealed plastic bag to keep it from drying out. Label with the raw material type, pulping process used, and bleaching chemical type and charge (8 % hypochlorite). TASK 3: REFINING Refining is an intense mechanical treatment performed on pulp fibers to make them
NC State University Pulp & Paper Education Pack 18 more suitable for papermaking. After pulping (and possibly bleaching), the fibers are hollow, tube-like structures (similar to drinking straws). To expose the most surface area for fiber-to-fiber bonding, these tubes must be collapsed into flat ribbons. Refining is the action which does this. Refining also makes the outer layer of the fibers hairy instead of smooth (scratches up the surface), which exposes even more bonding area. NOTE: Strong paper cannot be made without the use of refining. Without refining, sheets of paper feel like felt -- fluffy and weak. In the pulp and paper industry, refining is carried out by passing the pulp between grooved plates rotating at high speed less than 1 mm apart. Although refining causes some bad effects in the pulp water drains more slowly from it, and some of the fiber is damaged severely in the process papermakers need the strength of refining so much that they are willing to put up with these other effects. In the laboratory, refining can be carried out in a kitchen blender. The shearing action of the blender blade causes the collapse of the fibers into flat ribbons. The amount of refining required for optimum paper sheet strength is based on the nature of the fiber itself. For this activity, a standard refining time of 5 minutes will be used. 1. Place 114 grams of the bleached pulp from the bleaching activity into the blender container. Add 686 ml (686 g) cold tap water. Secure the lid and energize the blender for 5 minutes. 2. The pulp is now ready for sample sheet ( handsheet ) making. Refer to the Papermaking Lab Manual for instructions. Basic Applications for Student Science Projects
NC State University Pulp & Paper Education Pack 19 BASIC APPLICATION 1: COMPARING PLANTS FOR PAPERMAKING POTENTIAL It is interesting to most people that almost any common plant can be made into paper. The simplest and still very effective project for students is to pulp and bleach a variety of plant materials, refine the resulting pulps to some degree, make handsheets, and then display the results in a manner that shows the following for each raw material: > the raw material in dried, chopped form > a sample of unbleached pulp > a sample of bleached pulp > a handsheet from the bleached, refined pulp Pulp and handsheets from recycled pulps can be included for comparison. The student can include text and illustrations/photos in the exhibit which explain the pulping and bleaching process. BASIC APPLICATION 2: CHANGING PULPING INTENSITY ON A GIVEN RAW MATERIAL It would prove very interesting to see how the appearance and measured strength of sheets of paper made from a given raw material change as the intensity of the pulping process was increased or decreased. Theoretically, more intense pulping should improve the separation of fibers and their ability to bond with other fibers. However, at some point the harshness of the pulping process actually causes fiber damage, thereby reducing strength. Higher pulping intensity can also increase the need for bleaching. Under the terms of the activities described in this unit, pulping intensity may be changed three ways: 1. Changing the NaOH concentration in the boil (from as low as 5 % to as high as 30 %). 2. Pulping at lower temperatures 3. Increasing the blender speed or blending time during the fiberization step The student can set up a series of experiments to use one or more of these changes for the pulping of a single raw material. The brightness, cleanliness, and strength of the resulting sheets (see Strength Testing Lab Manual) could then be compared.
NC State University Pulp & Paper Education Pack 20 BASIC APPLICATION 3: DETERMINING THE BLEACHABILITY OF PULPS With only one stage of hypochlorite bleaching, chemi-mechanical soda pulps are usually light to dark yellow in color. The student can conduct multiple bleaching steps on the same batch of pulp, to see if the pulp color can be made white. The student can also study whether it is more efficient (uses less overall chemical) to bleach in one stage with more chemical or several stages with less chemical. Finally, the student can take several raw materials, pulp them in the exact same way, bleach them in the same way, then see if some of them respond to bleaching better than others. BASIC APPLICATION 4: COMPARING WOOD AND NONWOODS FOR PAPERMAKING People will undoubtedly ask why the paper industry does not use the nonwood raw materials used in the experiments, since they appear to make suitable pulp. The student can answer part of this question by comparing the strength of handsheets made from recycled wood pulp and from soda-boiled nonwoods. Refer to the lab manual for paper recycling for instructions on how to repulp wood-based paper. Refer to the lab manual for papermaking for instructions on how to make handsheets. Refer to the lab manual for strength testing for instructions on how to test the handsheets. The student can make handsheets from recycled newsprint, recycled copy paper, and from several caustic-boiled nonwoods. It is critical that the handsheets be of the same weight and made in the same way. Advanced Applications for Student Science Projects There is a wide variety of advanced experiments which can be set up to demonstrate more complex applications of pulping technology. Some examples are mentioned below. Only a brief description is shown; for setup of the actual experiment, the student may seek assistance from a teacher or from NCSU personnel.
NC State University Pulp & Paper Education Pack 21 1. Since there are three variables which can be changed in the caustic boil itself (NaOH concentration, temperature, and time), the questions arises as to which is more effective in improving the end results the brightness and strength of the paper. The student can set up a simple high-low experiment, which runs one trial at a low level of a given variable and one trial at a high level. The following levels might be used: Pulping Variable Low Level High Level NaOH concentration 10 % 20 % Temperature 60 C 100 C Time 20 min 60 min The first experiment would be run with all variables at the low level. Then, another trial would be run with one of the variables changed to the high level. This would be repeated until one trial had been run with each variable at the high level (repeats at each set of conditions are suggested to see how repeatable the process is). A standard fiberizing, bleaching, and papermaking sequence would be used on the pulps produced. The handsheets could be compared, so that the question could be provided to the question: which pulping variable, when raised to the high level, was most effective at improving paper brightness? Paper strength? 2. A classic study in the paper industry is to determine how the pulping process progresses with time. This is really a pulping rate study. Normally, this involves determining how much lignin is removed from the raw material as a function of time. Measuring lignin remaining in the pulp, however, is a very specific and complex process. The student can instead measure the loss of weight of the raw material as a function of pulping time. The following procedure would be used: a. Conduct pulping trials at a standard sample weight and NaOH concentration, using boil times of 5, 10, 20, 30, 40, 60, and 80 minutes. b. After each boil, drain the material in the fine-mesh colander or strainer. Wash thoroughly to remove as much black liquor as possible. c. Wrap the washed material in three thicknesses of cheesecloth, tying the ends up to totally enclose the material in a sack. Squeeze the sack to expel as much liquid as possible. d. Submerge the sack in a bucket of cold tap water, tying a weight onto the
NC State University Pulp & Paper Education Pack 22 end of the sack so that it is held under the surface of the water. Allow to sit for 8-12 hours (use the same number for all boils!). This step permits the dissolved lignin and NaOH inside the fibers to escape, so that they won t become part of the final weight. e. Remove the cheesecloth from the bucket and allow to drain in the strainer for several minutes. Squeeze by hand until no more liquid can be removed. f. The material must now be dried in a standard way. This can be done in a kitchen oven set at 225 F. Transfer the material from the cheesecloth after squeezing (be sure to get it all) into a small aluminum pie pan or similar small metal container. Place into the oven at 225 F for 6 hours. g. Oven-dried fiber will absorb water quickly from the environment. It is therefore important that the fiber samples, once removed from the oven, be weighed immediately. If it is not possible to have a balance near the oven, then each fiber sample should be removed from the oven and immediately placed into a plastic sandwich bag and twist-tied tightly closed. The bag and twist-tie should have been previously weighed on the balance, and this weight should be written, along with the sample identification, on the outside of the bag. In this way, the sample can be kept stable until weighing. The samples should still be weighed within 24 hours. Subtract the weight of the bag and tie from the measured weight to get the net oven-dry (OD) weight of the material. h. Be sure to do one oven sample on raw material which has not been boiled any time, to get the 0 minutes point. i. Repeat the process, using an NaOH concentration 3 % higher or lower than the one used for the first series of boils. j. Plot the data for each boil series on the same graph. It should look something like the one shown below. The slope of the linear portion of the plot can be called the pulping rate. In this way, the rate of pulping can be compared at several different NaOH concentrations, temperatures, times, etc.
NC State University Pulp & Paper Education Pack 23 Pulp Yield vs. Pulping Time OD Pulp Weight, gram 40 30 20 10 0 0 5 10 20 30 40 60 80 Pulping Time, minutes 18 % NaOH 21 %NaOH 3. Students can also plot sheet strength as a function of pulping time, using the technique described in Item 2. How does paper strength develop during the pulping process? 4. An important area of research in the paper industry involves pulping aids, chemicals which increase the rate of pulping (thereby improving mill production rate). Students can repeat the pulping rate trial described in Item 2, but comparing a basic caustic boil to one with the following additives in addition to the caustic: liquid hand soap, 0.2 % on OD raw material household white vinegar, 2 % on OD material household ammonia, 0.5 % on OD material (MUST be done under a hood or with good ventilation!!!!) household hydrogen peroxide, 2 % on OD raw material laundry borax, 1 % on OD raw material Note: NEVER add alcohol, oils, or solvents to a mixture which is to be boiled!!!! 5. The paper industry has moved away from the use of chlorine-based bleaching agents, due to concerns about the effects of chlorinated byproducts in the environment. One of the most promising non-chlorine-based bleaching agents is hydrogen peroxide. Students can set up an experiment to compare bleaching with both hypochlorite and peroxide on the same type of pulp. Each chemical
NC State University Pulp & Paper Education Pack 24 can be used at different dosages, in one or multiple stages. The resulting pulps can be refined and made into handsheets, which can be compared with respect to brightness and strength. The student can answer questions like: Which chemical requires more dosage to achieve the same level of brightness? Which one produces better strength? A typical bleaching condition for a single stage of hydrogen peroxide bleaching is *Hydrogen peroxide, 4 % on OD fiber (don t forget to factor in the concentration of the peroxide in the bottle!) *NaOH, 4 % on OD fiber (this gets the ph of the pulp to a point where the peroxide can react) *Epson salts (magnesium sulfate), 0.5 % on OD fiber (this stabilizes the peroxide and doesn t let it break down) *Use distilled water for bleaching when using peroxide! *Must heat the water for bleaching to 70 C in the microwave for both hypochlorite and peroxide bleaching for a fair comparison *React hypochlorite for one hour and peroxide for 2 hours *You will have to re-heat each bleaching batch in the microwave (in a separate container) every 30 minutes.