Making Pulp
Describe the difference between the mechanical and kraft processes for making pulp and give examples of how and why the resulting paper and end uses differ
Chemical process depends on chemical treatment to liquefy the lignin glue and divide the lignin fibers, producing long fibers. Mechanical process relies on heat and mechanical action to tear the pulp apart, producing short fibers since lignin is not detached.
Which pulping process has the highest yield? Which pulping process results in the strongest paper?
Mechanical process has the highest yield while chemical process has the strongest paper.
Which wood and pulping process is used to make each of the following: corrugated linerboard, corrugated medium and glassine? How does the process affect the properties?
Corrugated fiberboard is made from softwood pulp through the kraft process. Corrugated medium is a product of hardwood since its short fibers allow easier corrugation. Glassine is a result of calendaring process from a hardwood and softwood blend that ensures an extremely smooth product.
What combination of wood type, pulping method and refining time produces the strongest pulp?
Chemical pulp from the chemical process, specifically the kraft process, produces the toughest pulp using the virgin fiber.
What is the sequence of operations involved in making pulp?
Cellulosic wood fibers are untied from chips by a break down process of intercellular lignin glue of the wood. Suspension in water slurry follows with bleaching and refining. The slurry may be employed in paper manufacturing or the pulp dried and further re-suspended in water. A well-controlled environment is important to avoid pulverizing into dust.
How does pulp beating/refining time affect the tensile, tearing and burst properties of paper? What kinds of paper are most highly refined?
Pulp heating, at high temperature (140-190ºC), at 2-3 hours, dissolves a great deal of lignin and frees the fibers, as opposed to the tear of wood mechanically. White paper is the most refined.
What are the benefits of recycling paper-based packaging? How does recycled fiber affect the properties of paper? How can packages be designed for recycling?
The recycled paper conserves trees, use lower costs and conserves land. Recycled fiber is weaker, has reduced folding strength, burst, tensile strength and density. A junker removes gross contaminants; a ragger produces a pull able content while a drum pulper tumbles paper into thread, washes then filters the fibers. Further screening and cleaning follows to remove tiny bits of contamination.
What is the purpose of adding the following additives to the pulp furnish: filler, binder, wet strength?
Wet strength allows the paper to regain strength after wetting. Fillers reduce gaps in fibers thus making the paper smoother and more printable. Binders are used to improve inter-fiber bonding by increasing folding strength, burst and tensile.
What is the purpose of sizing added to the pulp? From what is it made? What is the difference between hard sized and slack sized paper?
Sizing agents improve resistance of paper to liquids. High level of sizing paper results to hard sized paper, which is ink and water resistant while slack sized paper has little capability to resist liquid. The most common source of internal sizing is pine which produces rosin.
What are the most common filler and binder?
Most frequently used binder and filler are starch and white clay respectively.
Why is non-wood based pulp more commonly used in Asia than the U.S.?
This is because the production areas are those that have few forest resources; in this case, Asia has fewer forests as compared to U.S.
What are some of the non-wood materials used to make pulp?
The non-wood materials include sugar cane bagasse, wheat straw, kenaf, hemp, sisal, bamboo, jute, reeds, cotton linters and corn stalks.
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