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Compression molded wood pulp biocomposites: A study of hemicellulose influence on cellulose supramolecular structure and material properties
KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.ORCID iD: 0000-0001-9176-7116
Uppsala University.
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2012 (English)In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, no 3, 751-760 p.Article in journal (Refereed) Published
Abstract [en]

In this study, the importance of hemicellulose content and structure in chemical pulps on the property relationships in compression molded wood pulp biocomposites is examined. Three different softwood pulps are compared; an acid sulfite dissolving grade pulp with high cellulose purity, an acid sulfite paper grade pulp and a paper grade kraft pulp, the latter two both containing higher amounts of hemicelluloses. Biocomposites based the acid sulfite pulps exhibit twice as high Young's modulus as the composite based on paper grade kraft pulp, 11-12 and 6 GPa, respectively, and the explanation is most likely the difference in beating response of the pulps. Also the water retention value (WRV) is similarly low for the two molded sulfite pulps (0.5 g/g) as compared to the molded kraft pulp (0.9 g/g). The carbohydrate composition is determined by neutral sugar analysis and average molar masses by SEC. The cellulose supramolecular structure (cellulose fibril aggregation) is studied by solid state CP/MAS 13C-NMR and two forms of hemicellulose are assigned. During compression molding, cellulose fibril aggregation occurs to higher extent in the acid sulfite pulps as compared to the kraft pulp. In conclusion, the most important observation from this study is that the difference in hemicellulose content and structure seems to affect the aggregation behaviour and WRV of the investigated biocomposites.

Place, publisher, year, edition, pages
2012. Vol. 19, no 3, 751-760 p.
Keyword [en]
Chemical pulps, Composites, Compression molding, CP/MAS 13C-NMR, Fibril aggregation, Hemicelluloses, Mechanical properties, Aggregation behaviours, Average molar mass, Bio-composites, Content and structure, CP/MAS 13C-NMR, Material property, Neutral sugar analysis, Paper grade pulp, Softwood Pulps, Supramolecular structure, Water retention value, Wood pulp, Young's Modulus, Chemical pulp, Composite materials, Kraft process, Kraft pulp, Paper and pulp mills, Paper products, Pulp beating, Sugars, Sulfite pulp, Wood, Cellulose, Agglomeration, Sulfite Pulps
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-95695DOI: 10.1007/s10570-012-9688-2ISI: 000303459200017Scopus ID: 2-s2.0-84860387690OAI: oai:DiVA.org:kth-95695DiVA: diva2:529332
Note

QC 20150630

Available from: 2012-05-30 Created: 2012-05-29 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Structural changes during cellulose composite processing
Open this publication in new window or tab >>Structural changes during cellulose composite processing
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Two approaches for creating a new all-cellulose composite material have been studied: the biosynthesis of compartmentalised bacterial cellulose fibril aggregates and the compression moulding of commercial chemical wood pulps processed with only water. The objective was to study the structural changes during processing and the complexity of relating the mechanical properties of the final biocomposites to the nanoscale structure was highlighted.

Solid-state CP/MAS 13C NMR spectroscopy was utilised to determine both the fibril aggregate width and the content of the different crystalline cellulose forms, cellulose I and cellulose II. Using this method, the quantities of hemicellulose present inside the fibre wall and localised at the fibre surfaces could be determined.

The formation of cellulose fibrils was affected by the addition of hydroxyethylcellulose (HEC) to a culture medium of Acetobacter aceti, and the fibrils were coated with a thin layer of HEC, which resulted in loose bundles of fibril aggregates. The HEC coating, improved the fibril dispersion in the films and prevented fractures, resulting in a biocomposite with remarkable mechanical properties including improved strength (289 MPa), modulus (12.5 GPa) and toughness (6%).

The effect of press temperature was studied during compression moulding of sulphite dissolving-grade pulps at 45 MPa. A higher press temperature yielded increases in the fibril aggregation, water resistance (measured as the water retention value) and Young’s modulus (12 GPa) in the final biocomposite. The high pressure was important for fibril aggregation, possibly including cellulose-cellulose fusion bonds, i.e., fibril aggregation in the fibre-fibre bond region. The optimal press temperature was found to be 170°C because cellulose undergoes thermal degradation at higher temperatures.

The effect of hemicellulose was studied by comparing a softwood kraft paper-grade pulp with a softwood sulphite paper and a softwood sulphite dissolving-grade pulp. A significant fibril aggregation of the sulphite pulps suggested that the content and distribution of hemicellulose affected the fibril aggregation. In addition, the hemicellulose structure could influence the ability of the hemicellulose to co-aggregate with cellulose fibrils. Both sulphite pulp biocomposites exhibited Young’s moduli of approximately 12 GPa, whereas that of the kraft pulp was approximately half that value at 6 GPa. This result can be explained by a higher sensitivity to beating in the sulphite pulps.

The effect of mercerisation, which introduces disordered cellulose, on the softwood sulphite dissolving-grade pulp was also studied under compression moulding at 170°C and 45 MPa. The mechanisms causing an incomplete transformation of cellulose I to II in a 12 wt% NaOH solution were discussed. The lower modulus of cellulose II and/or the higher quantity of disordered cellulose likely account for the decrease in Young’s modulus in the mercerised biocomposites (6.0 versus 3.9 GPa).

Abstract [sv]

Två metoder för att skapa ett nytt kompositmaterial baserat på enbart cellulosa har studerats, biosyntes av fibrillaggregat bestående av bakteriecellulosa och varmpressning av kommersiella träfiberbaserade massor med vatten som den enda processkemikalien. Målet var att studera de strukturella förändringarna som sker under tillverkningsprocessen. Även komplexiteten i att relatera strukturen på nanonivå till de mekaniska egenskaperna hos de slutliga biokompositerna belystes.

Med fastfas CP/MAS 13C NMR-spektroskopi var det möjligt att bestämma både fibrillaggregattjockleken och mängden av cellulosakristallformerna; cellulosa I och cellulosa II. Det var också möjligt att bestämma mängden hemicellulosa dels närvarande inuti fiberväggen och dels mängden lokaliserad på fiberytor.

Tillsats av hydroxyetylcellulosa (HEC) i odlingsmediet för Acetobacter aceti påverkade bildandet av cellulosafibriller som blev belagda med ett tunt skikt av HEC, vilket också resulterade i löst bundna fibrillaggregat. HEC-beläggningen förbättrade fibrilldispersionen i filmerna och minskade sprickbildningen, vilket gav en biokomposit med mycket goda mekaniska egenskaper med kombinerad hög styrka (289 MPa), styvhet (12.5 GPa) och seghet (6%).

Effekten av presstemperatur vid varmpressning (45 MPa tryck) studerades på sulfit dissolvingmassor. Högre presstemperatur gav ökad fibrillaggregering, ökat vattenmotstånd (mätt som vattenretentionsvärde) och högre styvhet (12 GPa) för biokompositen. Det höga trycket var också viktigt för fibrillaggregeringen, som troligen omfattar cellulosa-cellulosa samkristallisation dvs. fibrillaggregering i fiber-fiber-bindningsregionen. Den optimala presstemperaturen föreslogs vara 170° C pga. termisk nedbrytning av cellulosa vid högre temperaturer.

Effekten av hemicellulosa studerades genom att jämföra sulfat pappersmassa med sulfit pappersmassa och sulfit dissolvingmassa. Mängden och fördelningen av hemicellulosa föreslogs ligga till grund för skillnaden i fibrillaggregering, som var mera uttalad i sulfitmassorna. Även hemicellulosans struktur kan påverka förmågan hos hemicellulosa att sam-aggregera med cellulosafibriller. Biokompositerna baserade på sulfitmassorna hade en styvhet på ca. 12 GPa, medan sulfatmassan bara hade hälften av den nivån ca. 6 GPa, vilket förklarades av sulfitmassornas högre känslighet för malning.

Även effekten av mercerisering av sulfit dissolvingmassa varmpressad vid 170° C och 45 MPa studerades. Mercerisering introducerar oordnad cellulosa och mekanismerna som endast ger en partiell omvandling av cellulosa I till II i en 12 vikt% NaOH-lösning diskuterades. Den sämre styvheten hos den merceriserade biokompositen (6.0 resp. 3.9 GPa) förklaras troligen genom cellulosa II kristallens lägre styvhet och/eller den högre mängden av oordnad cellulosa.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xi, 48 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:46
Keyword
CP/MAS 13C NMR, cellulose, fibril aggregation, biocomposite, compression moulding, supramolecular structure
National Category
Chemical Sciences Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-104568 (URN)978-91-7501-518-7 (ISBN)
Public defence
2012-11-30, K1, Teknikringen 56, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Wallenberg Wood Science CenterBiomime
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20121106

Available from: 2012-11-06 Created: 2012-11-06 Last updated: 2012-11-09Bibliographically approved
2. Compression-moulded and multifunctional cellulose network materials
Open this publication in new window or tab >>Compression-moulded and multifunctional cellulose network materials
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cellulose-based materials are widely used in a number of important applications (e.g. paper, wood, textiles). Additional developments are suggested by the growing interest for natural fibre-based composite and nanocomposite materials. The motivation is not only in the economic and ecological benefits, but is also related to advantageous properties and characteristics. The objective of this thesis is to provide a better understanding of process-structure-property relationships in some novel cellulose network materials with advanced functionalities, and showing potential large-scale processability. An important result is the favourable combination of mechanical properties observed for network-based cellulose materials.

Compression-moulding of cellulose pulp fibres under high pressure (45 MPa) and elevated temperature (120 – 180 oC) provides an environmentally friendly process for preparation of stiff and strong cellulose composite plates. The structure of these materials is characterized at multiple scales (molecular, supra-molecular and microscale). These observations are related to measured reduction in water retention ability and improvement in mechanical properties.

In a second part, cellulose nanofibrils (NFC) are functionalized with in-situ precipitated magnetic nanoparticles and formed into dense nanocomposite materials with high inorganic content. The precipitation conditions influence particle size distributions, which in turn affect the magnetic properties of the material. Besides, the decorated NFC network provides high stiffness, strength and toughness to materials with very high nanoparticle loading (up to 50 vol.%).

Subsequently, a method for impregnation of wet NFC network templates with a thermosetting epoxy resin is developed, enabling the preparation of well-dispersed epoxy-NFC nanocomposites with high ductility and moisture durable mechanical properties. Furthermore, cellulose fibrils interact positively with the epoxy during curing (covalent bond formation and accelerated curing). Potential large scale development of epoxy-NFC and magnetic nanocomposites is further demonstrated with the manufacturing of 3D shaped compression-moulded objects.

Finally, the wet impregnation route developed for epoxy is adapted to prepare UV-curable NFC nanocomposite films with a hyperbranched polymer matrix. Different chemical modifications are applied to the NFC in order to obtain moisture durable oxygen barrier properties.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 80 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:45
Keyword
compression-moulding, cellulose fibre, nanocomposite, magnetic nanoparticle, epoxy, UV curing, oxygen barrier
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-133564 (URN)978-91-7501-911-6 (ISBN)
Public defence
2013-11-29, K1, Teknikringen 56, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20131111

Available from: 2013-11-11 Created: 2013-11-06 Last updated: 2013-11-11Bibliographically approved

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Larsson, Per Tomas

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