Kirsi Immonen

Effects of Surfactants on the Preparation of Nanocellulose-PLA Composites

Thermoplastic composite materials containing wood fibers are gaining increasing interest in the manufacturing industry. One approach is to use nano- or micro-size cellulosic fibrils as additives and to improve the mechanical properties obtainable with only small fibril loadings by exploiting the high aspect ratio and surface area of nanocellulose. In this study, we used four different wood cellulose-based materials in a thermoplastic polylactide (PLA) matrix: cellulose nanofibrils produced from softwood kraft pulp (CNF) and dissolving pulp (CNFSD), enzymatically prepared high-consistency nanocellulose (HefCel) and microcellulose (MC) together with long alkyl chain dispersion-improving agents. We observed increased impact strength with HefCel and MC addition of 5% and increased tensile strength with CNF addition of 3%. The addition of a reactive dispersion agent, epoxy-modified linseed oil, was found to be favorable in combination with HefCel and MC.

PP composites with Hybrid Nanofillers: NTC phenomenon

Electric conductive plastic composites have a wide potential for commercial applications, some examples are EMI shielding housings and components in automotive industry and in consumer electronics, equipments in health care sector and fuel cell components. A phenomenon in conductive composites, especially in composites with carbon based fillers, is change of thermal induced change in conductivity as a result of morphological transitions. Usually the observed changes are practically irreversible. The phenomenon may cause increasing resistivity, usually called as “positive temperature coefficient” (PTC) or decreasing resistivity, called “negative temperature coefficient (NTC), where the new morphology created by heat treatment is more favorable for electric conductivity compared to the original state. The existence of NTC is a sing of the lost potential in material design and processing. Therefore detailed information about the phenomenon gives us tools to develop high performance conductive materials. It t...

Potential of Hemp in Thermoplastic Biocomposites—The Effect of Fibre Structure

Hemp is one of the annual crops whose use has increased in recent years through different applications. This work compares the properties of PLA-based biocomposites, where different hemp structures resulting from a side stream from hemp production were used, such as hemp fibre, hemp pulp, shives and hemp dust. We have also produced hemp-based nanofibrils and compared their effect on the viscosity with the aim of finding novel applications for hemp. A wood-based cellulose was used as reference materials in both the biocomposite and nanofibril studies.

Coupling of PLA and bleached softwood kraft pulp (BSKP) for enhanced properties of biocomposites

The interest in totally bio-based materials is increasing due to their low carbon footprint and improved properties through intensive research. Polylactide (PLA)-based cellulose fibre compounds are finding their way into various injection-moulded applications. In addition to gain high-performance PLA–cellulose pulp fibre composites, there are also needed for additives such as plasticizers and coupling agents in the compounds. This research presents the use of a renewable material–based combined plasticizer-coupling agent as an additive in PLA bleached softwood kraft pulp (BSKP) composite. An epoxy-modified linseed oil showed capability for cross-linking PLA and cellulose fibre so enabling simultaneously improved strength tensile and impact properties for composite materials when added in amount of below 8% to fibre.

Predicting stiffness and strength of birch pulp – Polylactic acid composites

This paper studies failure of birch pulp–polylactic acid composites. Stiffness and strength are calculated using the theory of short fibre composites and the results are compared to experimental data. The results differed from the experimental values by 0–6%. With less aligned fibres the short fibre theory is not feasible. The performance of the 40 wt% birch pulp – polylactic acid composite is predicted with X-ray microtomography based finite element modelling, and the results are compared with experiments. Stiffness results differed from experiments by 1–17% . By adding into the models a third material phase representing the interface between the fibres and the matrix, the stress–strain curve of the composite was obtained with good accuracy. The work presents finite element modelling methodology of wood plastic composites and the critical further steps needed in order to assess the stress–strain behaviour, strength and stiffness. Tools for comparing different wood plastic composite microstructures are also presented.

Time-resolved X-ray microtomographic measurement of water transport in wood-fibre reinforced composite material

Natural fibre composites are prone to absorb moisture from the environment which may lead to dimensional changes, mold growth, degradation of mechanical properties or other adverse effects. In this work we develop a method for direct non-intrusive measurement of local moisture content inside a material sample. The method is based on X-ray microtomography, digital image correlation and image analysis. As a first application of the method we study axial transport of water in a cylindrical polylactic acid/birch pulp composite material sample with one end exposed to water. Based on the results, the method seems to give plausible estimates of water content profiles inside the cylindrical sample. The results may be used, e.g., in developing and validating models of moisture transport in biocomposites.