Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The extractive materials in wood often cause pitch problems in pulp mills. During pulping and
bleaching extractives are released from the wood and pulp and later stick to ceramic and metal
parts, forming pitch deposits. Pitch deposits impair both product quality and production rates. It
decreases the efficiency of pulp washing, screening, centrifugal cleaning, and refining, and can
disrupt many paper machine operations. The deposits also break loose from equipment and
cause spots in the final product. There are a few triggering mechanisms that induce pitch
deposition. Hydrodynamic or mechanical shear can destabilise the colloidal pitch emulsion,
causing pitch to agglomerate and deposits to form. Similarly, sudden temperature drops and/or
pH shocks and/or the introduction of water hardness ions from fresh water inlets or showers can
also cause pitch deposits by destabilising the colloidal pitch emulsion. Inorganic salts, such as
calcium carbonate, can catalyse pitch deposition by acting as the building blocks for the sticky
pitch. Calcium ions in the white water can react with fatty acids, forming insoluble, sticky
calcium soaps. Triglycerides have also been shown to be a major contributor to pitch deposition
in kraft pulping and bleaching mills. It forms a sticky deposit to which less sticky particles
attach.
To attain an improved understanding of pitch problems associated with the kraft pulping and
bleaching of Eucalyptus spp., various analyses were done on wood- and pulp extractives and
pitch from a South African kraft pulp mill. High molecular weight compounds (involatile)
constituted a large portion of the extracts and pitch. Approximately 40% of volatile Eucalyptus
grandis extract was f3-sitosterol, with fatty acids (22.8%) and triglycerides (15.5%) also making
a substantial contribution. Fatty acid amides were a prominent fraction of pulp extracts from the
latter stages of bleaching. The amides constituted 38.3% and triglycerides 10.1% to total volatile
pitch deposits.
Lipases hydrolyse triglycerides and could therefore help to reduce pitch problems. Consequently
381 filamentous fungi isolated from indigenous and commercial forests in South Africa were
screened for lipase activity on tributyrin and Tween 80. Eight strains were selected and the
tributyrin and Tween 80 assays were repeated by monitoring lipase activity over a seven-day period. The selected strains were also assayed for their activity toward p-nitrophenyl palmitate.
Ophiostoma piliferum Cartapip 58™ and Phanerochaete chrysosporium BKM-F-1767, two
strains known for respectively their biodepitching and biopulping ability, were' used as controls.
A few of the strains compared well and even outperformed the control strains, indicating their
potential for use in pitch control.
The effect of pretreatment with the eight selected fungal strains on E. grandis wood- and pulp
extractives was determined. Cartapip 58™ and P. chrysosporium BKM-F-1767 were used as
control strains. Several of the strains compared well to the control strains in their ability to
reduce the triglyceride content of wood extract. The South African isolate, white-rot fungus
Phanerochaete psuedomagnoliae nom. prov., reduced triglyceride content significantly.
Consequently it can act as an agent for both biopulping and biodepitching. The treated wood
samples had a lower triglyceride content than the sterile controls. Consequently more
triglycerides would be released into process waters by the sterile controls than the treated
samples. The effect of commerciallipases on deposited brown stock pulp extract was also
evaluated. The lipases did not reduce the triglyceride content of the deposited extract. The
addition of lipases in pulping and bleaching processes would therefore not affect already
deposited pitch. / AFRIKAANSE OPSOMMING: Die ekstrakstowwe van hout veroorsaak dikwels 'n neerslag tydens verpulping. Gedurende
verpulping en bleiking kom ekstrakstowwe van die hout enpulp vry en kleef aan keramiek- en
metaalonderdele. Gevolglik benadeel dié neerslag produkkwaliteit en produksietempo. Dit
verlaag die effektiwiteit van pulpwas, sifting, sentrifugale skoonmaakprosesse en suiwering, en
kan die werkverrigting van papiermasjiene ontwrig. Die neerslag kan ook later los breek en
kolletjies op die finale produk veroorsaak. Verskeie meganismes kan die neerslag veroorsaak.
Hidrodinamiese of meganiese wrywing kan die kolloïdale ekstrakstofemulsie destabiliseer en
sodoende die ekstrakstof laat konglomereer en neerslaan. Op soortgelyke wyse veroorsaak
skielike temperatuurverlaging en/of pH-skokke en/of die toevoeging van ione in varswater om
waterhardheid te beheer ook die neerslag deur die kolloïdale ekstrakstofemulsie te destabiliseer.
Anorganiese sout soos kalsiumkarbonaat kan neerslagvorming kataliseer omdat dit optree as
bousteen vir die klewerige, sementagtige ekstrakstowwe. Kalsiumione in die proseswater kan
ook reageer met vetsure om onoplosbare, klewerige kalsiumsepe te vorm. Dit is bewys dat
trigliseriede een van die hoofoorsake is in die vorming van die neerslag tydens kraft verpulpingen
bleikingprosesse.
Om die neerslagreaksie wat met die kraft verpulping en bleiking van Eucalyptus spp. geassosieer
word, beter te verstaan, is verskeie analises op hout- en pulpekstrakte asook die neerslag van 'n
Suid-Afrikaanse kraft verpulpingsaanleg uitgevoer. Hoë molekulêre massa (nie-vlugtige)
stowwe het 'n groot gedeelte van die ekstrakte en neerslag uitgemaak. Ongeveer 40% van die
vlugtige Eucalyptus grand is ekstrak bestaan uit ~-sitosterol met vet sure (22.8%) en trigliseriede
(15.5%) wat ook aansienlike bydraes lewer. Vetsuuramiede verteenwoordig 'n beduidende
komponent van pulpekstrak by die laaste stadiums van bleiking. Die amiede het 38.3% en
trigliseriede 10.1%tot die vlugtige fraksie van die neerslag bygedra.
Lipases hidroliseer trigliseriede en kan dus help om neerslagprobleme te voorkom. Gevolglik is
381 filamentagtige fungi geïsoleer uit inheemse en kommersiële woude van Suid-Afrika en hul
lipase-aktiwiteit op tributyrin en Tween 80 geëvalueer. Agt rasse is geselekteer en die tributyrin
en Tween 80 toetse is herhaal deur lipase-aktiwiteit oor 'n sewe-dag periode te monitor. Die
geselekteerde rasse is ook getoets vir lipase-aktiwiteit met p-nitrofenielpalmitaat. Ophiostoma piliferum Cartapip 58™ en Phanerochaete chrysosporium BKM-F-1767, twee rasse wat
daarvoor bekend staan vir onderskeidelik hul vermoë om houtekstrakstowwe te verminder en te
bioverpulp, is as kontroles gebruik. 'n Paar van die geselekteerde rasse het goed vergelyk en
selfs beter presteer as die kontrolerasse; 'n aanduiding van hul potensiaal om neerslagreaksies te
beheer.
Die effek van voorafbehandeling met die agt geselekteerde fungi rasse op E. grandis hout- en
pulpekstrak is vasgestel. Cartapip 58™ en P. chrysosporium BKM-F-1767 is gebruik as
kontrolerasse. Verskeie rasse het goed vergelyk met die kontrolerasse in hul vermoë om die
trigliseriedinhoud van die houtekstrak te verlaag. Die Suid-Afrikaanse isolaat,
witverrottingswam Phanerochaete pseudomagnoliae nom. prov., het ook die trigliseried inhoud
beduidend verminder. Gevolglik sou dit as 'n middel kon dien vir beide neerslagvoorkoming en
bioverpulping. Die trigliseriedinhoud van die behandelde monsters was laer as dié van steriele
kontroles. Gevolglik sal meer trigliseriede in proseswater vrygestel word deur die steriele
kontroles as die behandelde monsters. Die effek van kommersiële lipases op ongebleikte kraft
pulpekstrakneerslag is ook geëvalueer. Omdat lipases nie die trigliseriedinhoud van die neerslag
kon verlaag nie sal die gebruik van lipases dus nie die ekstrakstofneerslag in verpulpings- en
bleikingsprosesse beïnvloed nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51745 |
| Date | 03 1900 |
| Creators | Scheepers, Gerhardus C. (Gerhardus Coenraad) |
| Contributors | Janse, B. J. H., Rypstra, T., Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 108 p. : ill. |
| Rights | Stellenbosch University |
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