Difference between revisions of "Kraft process"

Latest revision as of 09:51, 12 November 2024

Unbleached softwood kraft fibers stained with Graff "C" Stain

Description

A chemical method of producing paper pulp from wood chips using Sodium hydroxide and Sodium sulfide in hot water. The kraft process has been used since 1890, but only gained popularity after an efficient system developed in 1930s to recover and reuse the inorganic pulping chemicals. Now, the kraft process is the most popular method for producing wood pulp in the US due to advantages over soda and sulfite pulping methods. Unlike the sulfite process, any wood species can be used. Additionally, cooking times are reduced, and the waste recovery is nearly a closed cycle process. Chemically, the kraft process breaks the bonds that link Lignin, Hemicellulose and Cellulose, then breaks down the lignin and hemicellulose into soluble fragments while leaving the cellulose fibers. In the final recovery process, Rosin soaps, Tall oil, and Turpentine are by-products as well as volatile sulfur emissions. The resultant Kraft paper is strong but brown due to approximately 5% residual lignin. Bleaching can be done to produce white paper, but this also decreases the strength of the fibers.

Synonyms and Related Terms

Sulfate pulp; kraft pulping; alkaline pulping; kraft pulp; softwood bleached kraft; softwood kraft; hardwood bleached kraft; hardwood kraft

Other Properties

Kraft pulp tends to be stronger than other types of pulp, but actual strength varies by species. Due to higher levels of chromophores, kraft pulps tend to be darker than sulfite pulps.

When stained with Graff "C" stain, kraft pulp can appear in a range of colors depending on the wood type (softwood or hardwood) and the amount of bleaching. Unbleached kraft pulps will appear yellow or blue/grey. With increased bleaching, pulps will appear lighter and tend more toward red when treated with stain, though this can be difficult to see with hardwood pulps. The stained color of kraft pulp tends to be darker than sulfite pulp.

Additional Images

Softwood kraft paper pulp stained with Graff "C" stain
Hardwood kraft paper pulp stained with Graff "C" stain
Hardwood kraft paper pulp stained with Graff "C" stain
Hardwood paper pulp stained with Graff "C" stain
Softwood kraft paper pulp stained with Graff "C" stain

Resources and Citations

J.R.G. Bryce.“Sulfite Pulping” and “Alkaline Pulping”. Pulp and Paper: Chemistry and Chemical Technology, Volume 1, Edition 3. John Wiley & Sons, 1980. James P. Casey Ed.
Christopher Biermann. Essentials of Pulping and Papermaking. Academic Press, 1993.
J. H. Graff "Color Atlas for Fiber Identification" The Institute of Paper Chemistry, Appleton, WI, 1940.
Walter Rantanen. 'Fiber ID Course.' Integrated Paper Services. June 2013. Lecture.
TAPPI Official Standard T401 om-08. Fiber analysis of paper and paperboard. 2008. http://www.tappi.org/Downloads/Test-Methods/UNTITLED-0104T401pdf.aspx
Wikipedia: Kraft process Accessed Nov. 2024

@@ Line 1: / Line 1: @@
+[[File:SUBK 10x2 label.jpg|thumb|Unbleached softwood kraft fibers stained with Graff "C" Stain]]
 == Description ==
-A chemical method of producing paper pulp from wood using [[sodium hydroxide]] and [[sodium sulfide]]. This process is an improvement on the [[soda process]], which is closely related. The process has been used since 1890, but only gained popularity after an efficient recovery system was developed in 1930. This method is the most popular method for producing wood pulp due to advantages over [[soda process|soda]] and [[sulfite process|sulfite]] pulping methods.
+A chemical method of producing paper pulp from wood chips using [[sodium hydroxide]] and [[sodium sulfide]] in hot water. The kraft process has been used since 1890, but only gained popularity after an efficient system developed in 1930s to recover and reuse the inorganic pulping chemicals. Now, the kraft process is the most popular method for producing wood pulp in the US due to advantages over [[soda process|soda]] and [[sulfite process|sulfite]] pulping methods. Unlike the sulfite process, any wood species can be used. Additionally, cooking times are reduced, and the waste recovery is nearly a closed cycle process.  Chemically, the kraft process breaks the bonds that link [[lignin]], [[hemicellulose]] and [[cellulose]], then breaks down the lignin and hemicellulose into soluble fragments while leaving the cellulose fibers.  In the final recovery process, [[rosin]] soaps, [[tall oil]], and [[Turpentine (oil)|Turpentine]] are by-products as well as volatile sulfur emissions.  The resultant [[kraft paper]] is strong but brown due to approximately 5% residual lignin.  Bleaching can be done to produce white paper, but this also decreases the strength of the fibers.
 == Synonyms and Related Terms ==
-Sulfate pulp; kraft pulp; softwood bleached kraft; softwood kraft; hardwood bleached kraft; hardwood kraft
+Sulfate pulp; kraft pulping; alkaline pulping; kraft pulp; softwood bleached kraft; softwood kraft; hardwood bleached kraft; hardwood kraft
 == Other Properties ==
-When stained with [[Graff's C-stain]], kraft pulp can appear in a range of colors depending on the wood type (softwood or hardwood) and the amount of bleaching. Unbleached kraft pulps will appear yellow or blue/grey. With increased bleaching, pulps will appear lighter and tend more toward blue when treated with stain. The stained color of kraft pulp tends to be darker than [[sulfite process|sulfite]] pulp.
+Kraft pulp tends to be stronger than other types of pulp, but actual strength varies by species. Due to higher levels of chromophores, kraft pulps tend to be darker than sulfite pulps.
-== Authority ==
+When stained with [[Graff "C" stain]], kraft pulp can appear in a range of colors depending on the wood type (softwood or hardwood) and the amount of bleaching. Unbleached kraft pulps will appear yellow or blue/grey. With increased bleaching, pulps will appear lighter and tend more toward red when treated with stain, though this can be difficult to see with hardwood pulps. The stained color of kraft pulp tends to be darker than [[sulfite process|sulfite]] pulp.
+== Additional Images ==
+<gallery>
+File:SUBK 40x label.jpg|Softwood kraft paper pulp stained with Graff "C" stain
+File:Redoak vessels 10x.jpg|Hardwood kraft paper pulp stained with Graff "C" stain
+Sycamore 10x2.jpg|Hardwood kraft paper pulp stained with Graff "C" stain
+Ash 10x.jpg|Hardwood paper pulp stained with Graff "C" stain
+UBK sugar pine 10x.jpg|Softwood kraft paper pulp stained with Graff "C" stain
+</gallery>
+==Resources and Citations==
 * J.R.G. Bryce.“Sulfite Pulping” and “Alkaline Pulping”. ''Pulp and Paper: Chemistry and Chemical Technology, Volume 1, Edition 3.'' John Wiley & Sons, 1980. James P. Casey Ed.
+* Christopher Biermann. ''Essentials of Pulping and Papermaking''. Academic Press, 1993.
+* J. H. Graff "Color Atlas for Fiber Identification" The Institute of Paper Chemistry, Appleton, WI, 1940.
+* Walter Rantanen. 'Fiber ID Course.' Integrated Paper Services. June 2013. Lecture.
+* TAPPI Official Standard T401 om-08. ''Fiber analysis of paper and paperboard''. 2008. http://www.tappi.org/Downloads/Test-Methods/UNTITLED-0104T401pdf.aspx
+* Wikipedia: [https://en.wikipedia.org/wiki/Kraft_process Kraft process] Accessed Nov. 2024
-* Christopher Biermann. ''Essentials of Pulping and Papermaking''. Academic Press, 1993.
+[[Category:Materials database]][[Category:MWG]][[Category:Sheet, Cellulose]]