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Morphological Effects of Lignocellulosic Fibres on Poly(Lactic Acid) Biocomposites

Research output: Book/ReportDoctoral thesisCollection of Articles


Original languageEnglish
PublisherTampere University
Number of pages63
ISBN (Electronic)978-952-03-1363-0
ISBN (Print)978-952-03-1362-3
Publication statusPublished - 5 Dec 2019
Publication typeG5 Doctoral dissertation (article)

Publication series

NameTampere University Dissertations
ISSN (Print)2489-9860
ISSN (Electronic)2490-0028


Increasing environmental awareness and tightening EU legislations have gained
significant interest towards bio-based material solutions. Lignocellulosic fibre
reinforced biocomposites can provide a sustainable material alternative for several plastic products. In biocomposites, renewable raw material sources, such as wood fibres, replace typically fossil-based resources, often decreasing also the carbon footprint of the material. Utilisation of wood fibres also provide additional material improvements to plastics, such as increased mechanical performance and natural haptics. However, while biocomposite materials can be mechanically recycled, building up an economically viable municipal recycling system is challenging due to low material volumes and heterogeneous material streams. Thus, biocomposites based on biodegradable or compostable matrix materials can complement the circular economy by providing an alternative end-of-life solution for products that are not applicable for recycling, but on the other hand, not excluding recyclability.

This thesis concentrates on the effects of wood fibre morphologies on
biocomposite performance using compostable poly(lactic acid) (PLA) as the matrix material. The main objective was to increase knowledge of the factors influencing the material characteristics to enable their wider use in commercial applications. To reach this objective, the study focused especially to the effect of melt processing on fibre morphologies, as well as the effect of various fibre surface treatments and fibre selection on performance of injection moulded bicomposites. Particular attention was paid to fibre attrition, dispersion and their correlation to mechanical performance. In addition, new light-weight application areas were considered by evaluating the effect of fibre addition on PLA foamability in extrusion foaming process.

As a conclusion, it was observed that melt processing of wood fibres with PLA
has unpreventable effect on wood fibre morphology. All selected bleached wood
fibre types shortened to the same level independent of the initial fibre length while fibre diameters remained unchanged. Thus, aspect ratio depended on retaining fibre length and initial fibre width of the fibres. Industrial fibre bleaching was found to be one factor influencing the increased fibre attrition due to higher refinability of bleached fibres. However, due to differences in fibre dispersion, no straight conclusions could be made of the correlation between fibre aspect ratio after processing and the mechanical properties of the composites. On the other hand, fibre dispersion and fines content seemed to partly reflect the mechanical performance. Improved mechanical properties were obtained by utilisation of unbleached hardwood kraft pulp fibres with low fibre attrition during processing, thermomechanical pulp, fibre fractionation or addition of compatibiliser/dispersing agent to the system. The presence of lignin and epoxidated linseed oil also indicated improvement in fibre-matrix adhesion. The work also presented that recycled fibres, such as non-deinked newspapers and liquid packaging board scratch, have potential to be used as PLA reinforcement. In extrusion foaming process, addition of wood fibres to PLA still enabled the production of low-density foams with decreased cell size and increased cell density. As an overall conclusion, careful selection of fibre
type and treatments can provide significantly improved properties for wood fibre
reinforced PLA biocomposites.

Field of science, Statistics Finland