| 1. |
- Chinga-Carrasco, Gary, et al.
(författare)
-
A method for estimating the fibre length in fibre-PLA composites
- 2013
-
Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720 .- 1365-2818. ; 250:1, s. 15-20
-
Tidskriftsartikel (refereegranskat)abstract
- Wood pulp fibres are an important component of environmentally sound and renewable fibre-reinforced composite materials. The high aspect ratio of pulp fibres is an essential property with respect to the mechanical properties a given composite material can achieve. The length of pulp fibres is affected by composite processing operations. This thus emphasizes the importance of assessing the pulp fibre length and how this may be affected by a given process for manufacturing composites. In this work a new method for measuring the length distribution of fibres and fibre fragments has been developed. The method is based on; (i) dissolving the composites, (ii) preparing the fibres for image acquisition and (iii) image analysis of the resulting fibre structures. The image analysis part is relatively simple to implement and is based on images acquired with a desktop scanner and a new ImageJ plugin. The quantification of fibre length has demonstrated the fibre shortening effect because of an extrusion process and subsequent injection moulding. Fibres with original lengths of >1 mm where shortened to fibre fragments with length of <200 μm. The shortening seems to be affected by the number of times the fibres have passed through the extruder, the amount of chain extender and the fraction of fibres in the polymer matrix.
|
|
| 2. |
- Kaombe, Divina D., et al.
(författare)
-
Turbiscan as a tool for studying the phase separation tendency of pyrolysis oil
- 2013
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 27:3, s. 1446-1452
-
Tidskriftsartikel (refereegranskat)abstract
- One of the main obstacles in using pyrolysis oils in heat and power applications is their instability upon storage, which leads to unacceptable quality, from the end user's point of view. Because of the opaque nature of pyrolysis oils, there are presently many challenges associated with determining their stability. Thus, techniques are needed for the characterization of the phase separation of pyrolysis oils, as well as determining the underlying mechanisms of their instability. Here, we present the application of the Turbiscan technique for the evaluation of phase separation tendency of pyrolysis oils over a period of 24 h at various temperatures, compared to the Karl Fischer method. A well-stored pyrolysis oil from poplar wood and fresh pyrolysis oil from forest residue were used for the investigation. For each of the oils, one batch was diluted with water in order to force phase separation, and a second batch was used without dilution. The study reveals that the Turbiscan technique makes it possible to study several aspects of phase separation in a single experiment; such as sedimentation, clarification, migration velocity and phase fraction. The advantages and potential limitation of the Turbiscan technique are discussed.
|
|
| 3. |
- Lenes, Marianne, et al.
(författare)
-
Performance properties and micro-structural quantification of cellulose fibre-polypropylene composites
- 2012
-
Ingår i: Fiber-reinforced composites. - : Nova Science Publishers, Inc.. - 9781614703037 ; , s. 143-157
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This study focuses on the effects of cellulose content and cellulose morphology on the structural and mechanical properties of PP/cellulose fibre composites. A detailed structural characterisation was performed, including SEM-BEI analysis of fibre spatial distribution and X-μCT analysis of fibre orientation. The results indicated that the fibres were well-dispersed and oriented mostly along the main direction of the PP/cellulose test specimen. Based on light microscopy it was found that the cellulose fibres acted as nucleators in the PP matrix. By use of DSC it was shown that addition of cellulose fibres increased both the crystallinity and Tc. The increased crystallinity is mainly a result of the transcrystallinity formation. The tensile properties of the composites were affected by the fibre dimensions and the fibre concentration. The long fibres yielded the highest increase of Young's modulus. Elongation at break was mostly affected by the fibre concentration. The results thus indicate that there is a major potential for improving the mechanical properties of fibre-reinforced composites, provided an adequate concentration of fibres is applied.
|
|
| 4. |
- Rodionova, Galina, et al.
(författare)
-
Gas-phase esterification of microfibrillated cellulose (MFC) films
- 2013
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 20:3, s. 1167-1174
-
Tidskriftsartikel (refereegranskat)abstract
- The barrier properties of microfibrillated cellulose (MFC) films were improved by heterogeneous gas-phase esterification using various combinations of trifluoroacetic acid anhydride, acetic acid and acetic anhydride. The temperature, reagent ratio and reaction time were varied in the experimental design. The effects of two different purification procedures on the barrier properties of esterified MFC films were investigated. Washing with water did not affect the barrier properties compared to those of the films that were not washed, while the use of diethyl ether led to improved barrier properties as measured by the contact angle (CA) of water. The chemical composition of the modified films was studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Alterations in hydrophobicity and oxygen permeability were evaluated using dynamic CA and oxygen transmission rate measurements, respectively.
|
|
| 5. |
- Rodionova, Galina, et al.
(författare)
-
Mechanical and oxygen barrier properties of films prepared from fibrillated dispersions of TEMPO-oxidized Norway spruce and Eucalyptus pulps
- 2012
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 19
-
Tidskriftsartikel (refereegranskat)abstract
- TEMPO-oxidized cellulose nanofibers (TOCN) were obtained from commercial Norway spruce and mixed Eucalyptus cellulose pulps using TEMPO/sodium bromide (NaBr)/sodium hypochlorite (NaClO) system at pH 10 and 22 °C. After reaction, the fibrillated TEMPO-oxidized celluloses were used for preparation of self-standing films and casting of laminate films on 50 μm thick polyethylene terephthalate. Significant differences between N. spruce and Eucalyptus TOCN were registered. The tensile strength of the films showed a maximum value for spruce samples oxidized with addition of 10 mmol g -1 of NaClO. Oxygen permeability decreased with increasing oxidation levels, being lower for N. spruce TOCN compared to Eucalyptus.
|
|
| 6. |
- Rodionova, Galina, et al.
(författare)
-
TEMPO-mediated oxidation of Norway Spruce and Eucalyptus Pulps : Preparation and Characterization of Nanofibres and Nanofiber Dispersions
- 2013
-
Ingår i: Journal of Polymers and the Environment. - : Springer Science and Business Media LLC. - 1566-2543 .- 1572-8919 .- 1572-8900. ; 21:1, s. 207-214
-
Tidskriftsartikel (refereegranskat)abstract
- This study deals with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of cellulose. Softwood and hardwood pulp fibers were suspended in water and oxidized to various extents at pH 10 and 22 °C using sodium hypochlorite in the presence of TEMPO radical and sodium bromide. This reaction system is known to be the most efficient one for the introduction of both surface carboxyl and aldehyde groups. Important relationships between formation of these functional groups and the fibrillation yield, light transmittance of the water dispersions and degree of polymerization of the oxidized softwood and hardwood pulps were established in the present study. A birefringence test confirmed the presence of nanofibers which according to atomic force microscopy analyses had diameters in the 1. 6-3. 8 nm range.
|
|
