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Wheat straw as raw material for manufacture of medium density fiberboard (MDF)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.ORCID iD: 0000-0003-3407-7973
2010 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 5, no 2, 1215-1231 p.Article in journal (Refereed) Published
Abstract [en]

Wheat straw was used to produce medium-density fiberboard (MDF). The chemical and physical characteristics of fractionated size-reduced wheat straw were investigated. The pH, pH-buffering capacity, ash, and silicon content increased as wheat straw particle size decreased. Ash of the finest straw, <0.2 mm, had high ash (15%) and silicon (18%) contents. The outer and inner parts of size-reduced straw were analyzed using scanning electron microscopy (SEM). The SEM micrographs revealed a complex ultrastructure containing a notable portion of thin-walled cells approximately 1 mu m thick. Pressurized defibration of size-reduced wheat straw produced lignocellulosic fibers nearly 1.0 mm long combined with approximately 24% of small particles and dust. The high water uptake of straw-based MDF was significantly reduced using melamine-modified urea-formaldehyde (UF) resin and removing wheat straw particles and dust by screening. UF resin was added at levels of 12.5%, 13.1%, and 14%. In terms of water resistance, 12-mm-thick straw MDF displayed thickness swelling below 10%, acceptable according to the EN 622-5 MDF standards. It was concluded that manufacturing wheat straw MDF entails straw size reduction (hammer-milling), removing small particles and dust, and adding melamine-modified UF resin to attain necessary MDF quality standards.

Place, publisher, year, edition, pages
2010. Vol. 5, no 2, 1215-1231 p.
Keyword [en]
Wheat straw; Medium-density fiberboard; Hammer-milling; Fiber length; Melamine urea-formaldehyde resin; MUF; Thickness swelling; Ash content; Silicon content; pH; pH buffering; EDX; SEM
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:miun:diva-11647ISI: 000278317900007Scopus ID: 2-s2.0-77956069041OAI: oai:DiVA.org:miun-11647DiVA: diva2:323556
Available from: 2010-06-11 Created: 2010-06-11 Last updated: 2016-09-22Bibliographically approved
In thesis
1. Manufacture of straw MDF and fibreboards
Open this publication in new window or tab >>Manufacture of straw MDF and fibreboards
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The purpose of this thesis was to develop an economical, sustainable, and environmentally friendly straw Medium Density Fibreboard (MDF) process, capable of full-scale manufacturing and to produce MDF of requested quality. The investigated straw was based on wheat (Triticum aestivum L.) and rice (Oryzae sativa L.). In this thesis three different methods were taken for manufacture of straw MDF; (A) wheat-straw fibre was blowline blended with melamine-modified urea-formaldehyde (MUF), (B) rice-straw fibre was mixed with methylene diphenyl diisocyanate (MDI) in a resin drum-blender, and (C) wheat-straw fibre was activated in the blowline by the addition of Fenton’s reagent (H2O2/Fe2+) for production of non-resin MDF panels.  The MUF/wheat straw MDF panels were approved according to the requirements of the EN standard for MDF (EN 622-5, 2006). The MDI/rice-straw MDF panels were approved according to requirements of the standard for MDF of the American National Standard Institute (ANSI A208.2-2002). The non-resin wheat-straw panels showed mediocre MDF panel properties and were not approved according to the requirements in the MDF standard. The dry process for wood-based MDF was modified for production of straw MDF. The straw MDF process was divided into seven main process steps.

  1. 1.       Size-reduction (hammer-milling) and screening of straw
  2. 2.       Wetting and heating of straw
  3. 3.       Defibration
  4. 4.       Resination of straw fibre
  5. 5.       Mat forming
  6. 6.       Pre-pressing
  7. 7.       Hot-pressing

 

 

 

The primary results were that the straw MDF process was capable of providing satisfactory straw MDF panels based on different types of straw species and adhesives. Moreover, the straw MDF process was performed in pilot-plant scale and demonstrated as a suitable method for producing straw MDF from straw bales to finished straw MDF panels. In the environmental perspective the agricultural straw-waste is a suitable source for producing MDF to avoid open field burning and to capture carbon dioxide (CO2), the biological sink for extended time into MDF panels, instead of converting straw directly into bio energy or applying straw fibre a few times as recycled paper. Additionally, the straw MDF panels can be recycled or converted to energy after utilization.

A relationship between water retention value (WRV) of resinated straw fibres, the thickness swelling of corresponding straw MDF panels, and the amount of applied adhesive was determined. WRV of the straw fibre increased and the TS of straw MDF declined as a function of the resin content. The empirical models developed were of acceptable significance and the R2 values were 0.69 (WRV) and 0.75 (TS), respectively. Reduced thickness swelling of MDF as the resin content is increased is well-known. The increase of WRV as a function of added polymers is not completely established within the science of fibre swelling. Fortunately, more fundamental research can be initiated and likely a simple method for prediction of thickness swelling of MDF by analysis of the dried and resinated MDF fibres is possible.

Abstract [sv]

Syftet med denna avhandling var att lägga grunden för en ekonomisk, hållbar och miljövänlig MDF process för halmråvara, kapabel för fullskalig produktion av MDF och goda skivegenskaper. Framställningen av MDF skivor utgick från halm av vete (Triticum aestivum L.) och ris (Oryzae sativa L.). Tre olika metoder användes för att producera MDF av halm; (A) fibrer av vetehalm belimmades i blåsledning med ett melaminmodifierat urea-formaldehydlim (MUF), (B) fibrer av rishalm belimmades i en limblandare med metylen difenyl diisocyanate (MDI), (C) Limfria MDF skivor av vetehalm framställdes med aktivering av fibrer genom tillsats av Fenton´s reagens (H2O2/Fe2+) i blåsledning utan någon tillsats av syntetiskt lim. Sammanfattningsvis kan det understrykas att framställda MDF-skivor av MUF/vetehalm var godkända enligt standard för MDF (EN 622-5, 2006). Dessutom var framställda MDF skivor av MDI/rishalm också godkända enligt krav i standard för MDF ”American National Standard Institute” (ANSI A2008.2-2002). Limfria vetehalmskivor visade på måttliga skivegenskaper och klarade inte kraven i MDF standard.

 

Fiberframställningsprocessen för MDF modifierades till en produktion utgående från halm. MDF processen för halm delades upp i sju primära processoperationer.

 

(1)            Storleksreducering och sållning av halm

(2)            Vätning och uppvärmning av halm

(3)            Defibrering

(4)            Belimning av halmfiber

(5)            Mattformning

(6)            Förpressning

(7)            Pressning

 

De viktigaste resultaten från denna studie är att MDF av halm kunde produceras utgående från olika typer av halmsorter och lim. Dessutom utfördes MDF-processen i pilotskala och visade på en lämplig metod för framställning av MDF-skivor från halmbalar till färdiga halmfiberskivor. Det miljömässiga perspektivet på att använda jordbruksavfall till framställning av halmskivor är att undvika förbränning av halm ute på fältet, men det är även möjligt att binda koldioxid (CO2) i halmskivor under längre tid än att omsätta halmråvaran omedelbart som bioenergi eller använda halmfiber som returpapper några få gånger. Dessutom kan MDF återanvändas eller bli omsatt till energi efter användning.

 

Ett förhållande mellan ”water retention value” (WRV), av belimmade halmfiber, tjocklekssvällning för motsvarande MDF av halmskivor och mängden av tillsatt lim vid olika nivåer har undersökts. Med ökande limhalt tilltog WRV fibersvällning, vidare minskade tjocklekssvällning för motsvarande MDF skivor. De framtagna empiriska modellerna var godtagbara och beräknade R2 värden var 0.69 (WRV) och 0.75 (TS). Minskad tjocklekssvällning med ökad limhalt är dokumenterad sen tidigare. Ökad fibersvällning WRV vid tillsats av polymerer (limmer) är inte fullständigt etablerad inom vetenskapen för fibersvällning. Lyckligtvis kan grundläggande forskning initieras och sannolikt föreligger en enkel metod för att prediktera tjocklekssvällning av MDF genom analyser av torkade och belimmad MDF fiber.

Place, publisher, year, edition, pages
Sundsvall: Kopieringen Mittuniversitetet, 2010. 82 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 92
Keyword
Rice, Wheat, Straw, MDF, HDF, UF, MUF, MDI, Non-resin, binderless MDF, Ash, Silicon, SEM, Hot-pressing, MOR, MOE, IB, Thickness swelling, MDF properties; fibre swelling, WRV, Refining, Defibration.
National Category
Natural Sciences Chemical Engineering Chemical Process Engineering
Identifiers
urn:nbn:se:miun:diva-11732 (URN)978-91-86073-86-2 (ISBN)
Public defence
2010-09-17, Sal 0111 Sunds Defibrator-salen, Mittuniversitetet, Sundsvall, 10:15 (English)
Opponent
Supervisors
Available from: 2010-06-21 Created: 2010-06-16 Last updated: 2011-01-17Bibliographically approved

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