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Innovative Approaches for Converting a Wood Hydrolysate to High-Quality Barrier Coatings
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.ORCID iD: 0000-0002-1631-1781
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
2013 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, Vol. 5, no 16, 7748-7757 p.Article in journal (Refereed) Published
Abstract [en]

An advanced approach for the efficient and controllable production of softwood hydrolysate-based coatings with excellent oxygen-barrier performance is presented. An innovative conversion of the spray-drying technique into a coating applicator process allowed for a fast and efficient coating process requiring solely aqueous solutions of softwood hydrolysate, even without additives. Compared to analogous coatings prepared by manual application, the spray-drying produced coatings were more homogeneous and smooth, and they adhered more strongly to the substrate. The addition of glyoxal to the aqueous softwood hydrolysate solutions prior to coating formation allowed for hemicellulose cross-linking, which improved both the mechanical integrity and the oxygen-barrier performance of the coatings. A real-time scanning electron microscopy imaging assessment of the tensile deformation of the coatings allowed for a deeper understanding of the ability of the coating layer itself to withstand stress as well as the coating-to-substrate adhesion.

Place, publisher, year, edition, pages
2013. Vol. 5, no 16, 7748-7757 p.
Keyword [en]
wood hydrolysate, hemicellulose, lignin, spray drying, coatings, real-time SEM, oxygen permeability, food packaging.
National Category
Polymer Technologies
URN: urn:nbn:se:kth:diva-122166DOI: 10.1021/am401102hISI: 000323875800017ScopusID: 2-s2.0-84883267826OAI: diva2:621146
Vinnova, 2009-04311

QC 20131004. Updated from manuscript to article in journal.

Available from: 2013-05-13 Created: 2013-05-13 Last updated: 2013-10-04Bibliographically approved
In thesis
1. Wood hydrolysates- New concepts in renewable material design
Open this publication in new window or tab >>Wood hydrolysates- New concepts in renewable material design
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wood hydrolysates (WHs) are biomasses obtained in processes involving hydrothermal treatments of wood. WHs are rich in hemicelluloses and lignin. Instead of complicated extraction processes, such as precipitation, or extensive purification, this work utilizes the crude WHs. These WHs were successfully developed into oxygen-barrier films and coatings and a conceptual model was established to predict biomass matrix performance from molecular structures and interactions.

Free standing films and coatings from blends of WHs and either chitosan or carboxylmethyl cellulose (CMC) as a co-component, were produced. The films had an excellent oxygen-barrier performance which was even better than the corresponding films prepared from highly purified hemicelluloses. From a fundamental point of view, the Hansen solubility parameter (HSP) theory revealed the interactions between molecules in WHs, as well as in WH-based blends, which shed light on the great barrier performance of WH-based films. The hypothesis was that these strong interactions increased the mutual molecular affinity in the matrix, which led to a denser molecular packing and hence a good oxygen-barrier performance. The positron annihilation lifetime spectroscopy (PALS) measurements quantified the free volumes in the WH-based matrices. The HSP results, free volume size and distribution and thermal analyses supported the hypothesis well.

The HSP model was then used as a tool for designing oxygen-barrier coatings from WH-based blends. Using the HSP model, the interactions between different WHs and CMC were calculated and quantified. According to our hypothesis, the oxygen-barrier performance could thus be predicted. The free volume from PALS, oxygen permeability (OP) results were generally in consistence with the prediction from HSP model, which shows the potential of the HSP model for designing formulations of WHs for oxygen-barrier coatings for food packaging. 

To realize an industrially feasible and efficient process for WH-based barrier coating layers, some new approaches were attempted. Previously, coatings were prepared manually from WH-based blends. Now, a creative spray drying (SPD) coating technique was developed for a reproducible, efficient coating process of WHs with no additives or second components. Also, glyoxal crosslinking improved the ductility of the WH-based coatings which in turn improved the quality and oxygen-barrier performance of the coatings. Finally, scanning electron microscopy (SEM) integrated with a micro-tensile test device made it possible the real-time observation of coating surfaces during the deformation process. This can successfully analyze the mechanical performance of the coatings without being influenced by substrate.

In summary, the WHs present a viable and very promising resource for green barrier design.

Abstract [sv]

Hydrolysat är processvätskor från träindustrin. Istället för komplicerade utvinningsprocesser av ren hemicellulosa från processvätskor, används här det oförädlade hydrolysatet, som innehåller till största delen hemicellulosa och en del lignin. Den här avhandlingen beskriver hur vi framgångsrikt utvecklade detta hydrolysat till syrgasbarriärfilmer och bestrykningar som kan användas till matförpackningar samt hur modellering av strukturerna och interaktionerna mellan hydrolysatets komponenter kan förutsäga deras prestanda som barriärmaterial.

Fristående filmer och bestrykningar skapades från blandningar av vedhydrolysat och en samkomponent: antingen kitosan eller karboximetylcellulosa (CMC). Filmerna hade utmärkta syrgasbarriäregenskaper som till och med var bättre än filmer beredda av motsvarande renade hemicellulosa. Hansens löslighetsparametersteori (HSP) påvisade och kvantifierade interaktioner mellan molekylerna i både hydrolysat och hydrolysat-baserade blandningar vilket ger en förståelse för de goda barriäregenskaperna. Vår hypotes var att dessa starka interaktioner ökade affiniteten i matrisen vilket leder till tät molekylär packning och därmed bra syrgasbarriäregenskaper. Med Positron annihiliation lifetime spectroscopy (PALS) uppmättes de fria volymerna i de hydrolysat-baserade matriserna. HSP resultaten, storlek och fördelning av fri volym, samt termisk analys, verifierade hypotesen väl.

HSP-modellen användes sedan för att prediktera kompositionen hos syrgasbarriärbestrykningar från hydrolysat-baserade blandningar. Genom att använda HSP-modellen, kan interaktionerna mellan olika hydrolysat och CMC beräknas och interaktionerna i matrisen utvärderas. De fria volymerna uppmätta med PALS, syrepermeabilitet (OP)-resultaten var generellt överensstämmande med förutsägelserna från HSP-modellen, vilket visar potentialen för HSP- modellen som verktyg i formuleringen av barriärbestrykningarr för matförpackningar.

För att utveckla en industriellt realistisk och effektiv process för produktion av hydrolysat-baserade bestrykningar provades flera angreppssätt. Först gjordes bestrykningar manuellt från hydrolysat-baserade blandningar och dessa hade utmärkta syrebarriäregenskaper. Sedan utvecklades en spraytorkningsbeläggningsteknik (SPD) som en reproducerbar, effektiv bestrykningsprocess för hydrolysat utan tillsatser eller andra samkomponenter. Dessutom förbättrade töjbarheten hos bestrykningarna genom tvärbindning med glyoxal vilket i sin tur förbättrade kvalitet och syrgasbariäregenskaperna för bestrykningen. SEM integrerat med en dragprovutrustning gjorde det möjligt att i realtid observeraytan av bestrykningen under deformationsprocessen. Detta gjorde det möjligt att studera de mekaniska egenskaperna för beläggningarna utan inverkan av substratet.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 74 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2013:26
wood hydrolysate, oxygen barrier, coatings, films, hemicellulose, lignin, CMC, chitosan, HSP, PALS, spray drying, SEM with tensile test, glyoxal crosslinking., vedhydrolysat, syrebarriäregenskaper, ytbeläggningar, filmer, hemicellulosa, lignin, CMC, kitosan, HSP, PALS, spraytorkning, SEM med dragprovning, glyoxal tvärbindning.
National Category
Polymer Technologies
urn:nbn:se:kth:diva-122167 (URN)978-91-7501-743-3 (ISBN)
Public defence
2013-06-04, K2, Teknikringen 28, KTH, 100 44 Stockholm, 10:00 (English)
Formas, 243-2008-129Vinnova, 2009-04311

QC 20130515

Available from: 2013-05-15 Created: 2013-05-13 Last updated: 2013-05-15Bibliographically approved

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