| 1. |
- Oksman, Kristiina, et al.
(author)
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Mechanical properties and morphology of sisal fiber-epoxy composites
- 2000
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In: Proceedings from the Third International Symposium on Natural Polymers and Composites and the Workshop on Progress in Production and Processing of Cellulosic Fibres and Natural Polymers. - São Carlos : Embrapa Instrumentacao Agropecuaria. - 8586463078
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Conference paper (peer-reviewed)
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| 2. |
- Oksman, Kristiina, et al.
(author)
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Morphology and mechanical properties of unidirectional sisal-epoxy composites
- 2002
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In: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 84:13, s. 2358-2365
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Journal article (peer-reviewed)abstract
- Plant fibers are of increasing interest for use in composite materials. They are renewable resources and waste management is easier than with glass fibers. In the present study, longitudinal stiffness and strength as well as morphology of unidirectional sisal-epoxy composites manufactured by resin transfer molding (RTM) were studied. Horseshoe-shaped sisal fiber bundles (technical fibers) were nonuniformly distributed in the matrix, In contrast to many wood composites, lumen was not filled by polymer matrix. Technical sisal fibers showed higher effective modulus when included in the composite material than in the technical fiber test (40 GPa as compared with 24 GPa). In contrast, the effective technical fiber strength in the composites was estimated to be around 400 MPa in comparison with a measured technical fiber tensile strength of 550 MPa. Reasons for these phenomena are discussed.
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| 3. |
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| 4. |
- Bengtsson, Peter, 1974-
(author)
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The release of Hydrocarbons from softwood drying : Measurement and modeling
- 2004
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In: MADERAS. - : SciELO Agencia Nacional de Investigacion y Desarrollo (ANID). - 0717-3644 .- 0718-221X. ; 6:2, s. 109-122
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Journal article (peer-reviewed)abstract
- The release of volatile organic compounds (VOC) during the drying of Norway spruce and Scots pine was experimentally studied. Heartwood and sapwood were separately dried at 60 ºC. The Flame Ion Detector (FID) was used to measure the total amount of hydrocarbons (THC) released during the drying process. A large difference of the emissions course between heartwood and sapwood were found. For heartwood, a release maximum of hydrocarbons followed by a typical negative exponential course was found. When drying sapwood, the released amount of hydrocarbons was evidently more fluctuating before reducing to zero. A model describing the release of hydrocarbons during the drying with only diffusion as transport mechanism was applied. The aim was to obtain a suitable explanation of the characteristic release behavior from sapwood and develop a model describing the process.
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| 5. |
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| 6. |
- Hagstrand, P.-O., et al.
(author)
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Mechanical properties and morphology of flax fiber reinforced melamine-formaldehyde composites
- 2001
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In: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 22:4, s. 568-578
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Journal article (peer-reviewed)abstract
- The mechanical performance of natural fiber reinforced polymers is often limited owing to a weak fiber-matrix interface. In contrast, melamine-formaldehyde (MF) resins are well known to have a strong adhesion to most cellulose containing materials. In this Paper, nonwoven flax fiber mat reinforced and particulate filled MF composites processed by compression molding are studied and compared to a similar MF composite reinforced with glass fibers. Using flax instead of glass fibers has a somewhat negative effect on tensile performance. However, the difference is relatively small, and if density and material cost are taken into account, flax fibers become competitive. Tensile damage is quantified from the stiffness reduction during cyclic straining. Compared to glass fibers, flax fibers generate a material with a considerably lower damage rate. From scanning electron microscopy (SEM), it is found that microcracking takes place mainly in the fiber cell walls and not at the fiber-matrix interface. This suggests that the fiber-matrix adhesion is high. The materials are also compared using dynamic mechanical thermal analysis (DMTA) and water absorption measurements
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| 7. |
- Mathew, Aji P., et al.
(author)
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Effect of initiating system, blend ratio and crosslink density on the mechanical properties and failure topography of nano-structured full-interpenetrating polymer networks from natural rubber and polystyrene
- 2001
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In: European Polymer Journal. - 0014-3057 .- 1873-1945. ; 37:9, s. 1921-1934
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Journal article (peer-reviewed)abstract
- The mechanical performance of full-interpenetrating polymer networks (IPNs) based on natural rubber/polystyrene (NR/PS) system has been studied in detail. The IPNs were prepared using different initiators viz., benzoyl peroxide (BPO), azo-bis-isobutyronitrile (AIBN), and dicumyl peroxide (DCP) and the effect of initiating systems on the properties was studied. It was observed that in all cases the IPNs initiated using DCP showed a superior property compared to BPO and AIBN initiated ones. The crosslink density of the IPN was varied by varying the percent of divinyl benzene (crosslinking agent of PS) and the effect of crosslink density on the properties has been studied. The stress-strain behaviour, tensile strength, Young's modulus, elongation at break, tear strength, tension set and tensile set were determined. The effects of strain rate on tensile properties were analysed. The studies on the morphology using scanning electron microscopy showed an increase in phase mixing on increasing the PS content and PS crosslinking. However, high level of PS content and PS crosslinking lead to a decrease in phase mixing. The morphology studies using TEM revealed the interesting fact that NR/PS IPN system was nano-structured. The fracture surfaces of tensile and tear specimens were studied using scanning electron microscopy, to get a clear picture of the mechanism of failure.
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| 8. |
- Mathew, Aji P., et al.
(author)
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Izod impact behavior of natural rubber/polystyrene interpenetrating polymer networks
- 2001
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In: Materials letters (General ed.). - 0167-577X .- 1873-4979. ; 50:2-3, s. 154-163
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Journal article (peer-reviewed)abstract
- The impact behavior of semi and full interpenetrating polymer networks based on natural rubber (NR) and polystyrene (PS) has been studied with special reference to blend ratio and cross-linking level of PS phase. As the PS cross-linker level increases up to 4% an increase in impact strength values was observed. This behavior was explained based on blend morphology and the fractography. It was also found that in moderately cross-linked IPNs, the blend composition with 70% PS showed maximum impact strength values. At higher cross-linking levels, samples with 60% PS showed maximum impact strength values. The fracture surface morphology satisfactorily explained the nature of failure and impact performance in all cases. Addition of NR to PS has changed the failure mechanism from crazing to shear yielding
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| 9. |
- Mathew, Aji P.
(author)
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Morphological investigation of nanocomposites from sorbitol plasticized starch and tunicin whiskers
- 2002
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 3:3, s. 609-617
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Journal article (peer-reviewed)abstract
- Nanocomposites were prepared from waxy maize starch plasticized with sorbitol as the matrix and a stable aqueous suspension of tunicin whiskers-an animal cellulose-as the reinforcing phase. The composites were conditioned at different relative humidity levels. The conditioned films were characterized using scanning electron microscopy, differential scanning calorimetry, water uptake experiments, and wide-angle X-ray scattering studies. Contrarily to our previous report concerning tunicin whisker filled glycerol plasticized starch nanocomposites (Macromolecules 2000, 33, 8344), the present system exhibited a single glass-rubber transition, and no evidence of transcrystallization of amylopectin on cellulose whisker surfaces and resultant antiplasticizing effects were observed. It was found that the glass-rubber transition temperature of the plasticized amylopectin matrix first increases up a whiskers content around 10-15 wt % and then decreases. A significant increase in crystallinity was observed in the composites by increasing either moisture content or whiskers content
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| 10. |
- Mathew, Aji P., et al.
(author)
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Plasticized waxy maize starch : effect of polyols and relative humidity on material properties
- 2002
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 3:5, s. 1101-1108
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Journal article (peer-reviewed)abstract
- The plasticizing effect of different polyols such as glycerol, xylitol, sorbitol, and maltitol on waxy maize starch was investigated. The concentration of plasticizer was fixed at 33 wt % (dry basis of starch). The structure and mechanical performance of resulting films conditioned at different relative humidity levels were studied in detail. The effect of the plasticizer on the glass-rubber transition temperature (Tg) and crystallinity was characterized using differential scanning calorimetry. It was found that Tg decreases with increasing moisture content and decreasing molecular weight of the plasticizer. The water resistance of starch increased steadily with the molecular weight of the plasticizer and was directly proportional to the ratio of the end to total hydroxyl groups. As the molecular weight of the plasticizer increased, the brittleness of the dry system increased. However, the use of high molecular plasticizer allowed good mechanical properties of the moist material to be obtained in terms of both stiffness and elongation at break.
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